ETUDE DU MECHANISME DE REACTION
PAR LA DESINTEGRATION DES NOVAUX
COMPOSÉS 66GB*, 68Ga* et 91 Zr*
A L'AIDE DES PROJECTILES
FAIBLEMENT LIÉS d et 3He
THESE PRESENTÉE
Pour l'obtention du titre
de Docteur d'ETAT
de
l'Universitê de
BONN
soutenue par
KABA MAMADV
BONN 1978
-_.......

---

-2-
equilibrium isospin formalism and is best reproduced by
initial particle exciton numbers n
= n
= 1.5 for d and
op
on
n
= 2.5, n
= 1 . 5 for 3He projectiles, indicating conservation
op
on
of charge asymmetry in the entrance channel.
Isomeric ratios have been measured for 89 Y (d,2n)89 zr and
93Nb(3He,xn)96-xTC
(x= 1,2,3). Calculations with a full
statistical model fail to reproduce a /0
as weIl as a
and a
g
m
g
m
for reasonable values of the spin cut off parameter. Inclusion
of a preequilibrium decay mode improves the fit,
in particular
if the angular momentum depletion of the composite system due
to preequilibrium decay is increased over that of the equilibrium
decay at the same channel energy.
NUCLEAR REACTIONS 64, 66 zn , 89 y (d, xnypzex.), E = 9-26 MeV,
d
63 65
93
3
,
Cu,
Nb( He,xnypza), E3He= 10-44 MeV, x::s4, y::s1,
z::s2; measured o(E) by activation, enriched targets.
Statistical model analysis including preequilibr!um
decay, deduced reaction mechanism, charge asymmetry
conservation, spin depletion.

---

-3-
1.
Introduction
In recent years,
the study of proton and alpha induced
reactions was the main source of information for preequili-
brium
(PE)
phenomena in nuclear reactions. For their inter-
pretation a variety of reaction models has been developed
111
which weIl account for the hard component of the continuous
energy spectra of nucleon and complex particle emission,
the
strongly forward peaked angular distributions and the high
energy tails of excitation functions for nucleon emission.
The validity of these models for reactions induced by loosely
bound projectiles like the d- and 3He-particle has been less
intensively investigated since for these projectiles transfer
and break-up reactions have to be considered,
too.
In a first independent and later on joint effort,
the
present authors at the Bonn and Hamburg cyclotrons aimed for
a closing of this gap by studying excitation functions for
d- and 3He-induced reactions on sorne medium weight nuclei
between A - 60 and 90 12-4 1. The experimental procedure is
described in section 2.
Essentially three lines were followed
in the analysis of the data:
(1)
General behaviour of the measured excitation functions:
We study in section 3 how far the simple Weisskopf-Ewing
(WE)
and a more detailed Hauser-Feshbach
(HF) model do
describe the data for the reactions 63,65cu , 93 Nb +3He
and 89 Y+d without and with the inclusion of PE nucleon
ernission.
(2)
Entrance channel phenomena:
Inspired by the historical
experirnent of Ghoshal
15]
investigating the decay of the

---

-4-
composite system 64
*
Zn formed through the entrance
63
channels
Cu + p and 60Ni + ex, we looked for a similar
system for d-and 3He-induced reactions:
its decay
should yield radioactive daughter nuclides following
the emission of a single proton or neutron.
The
rather unique composite system fulfilling this condition
is 66Ga *. It can be formed by the entrance channels
64
63
3
Zn+d (Sd= 10.85 MeV) and
Cu+
He
(S3He= 13.07 MeV).
66
.'.
We observed the decay of
Ga" between 2') and 36 MeV
excitation energy where the emission of a single nucleon
is dominated by noncompound processes.
In section 4 we
investigate in how far the relative branching of the
total reaction cross section to the final evaporation
residues does depend on the entrance channel, and how
much proton emission is enhanced over neutron emission
in the 3He-induced reaction and whether or not this is
related to the different charge asymmetries in the 3He
and d projectiles.
(3)
Isomerie cross section ratios:
The neighbourhood of the
(1g /
TT)
and
(2P1/2TT)
states near A= 90 leads to long-
9 2
lived isomers in many of the residual nuclei which were
reached by the 89 y + d and 93 Nb + 3He reactions. The study
of isomeric ratios with a Hauser-Feshbach model extended
to include a PE decay mode should reveal information on
the spin distribution in the residual system due to the
nonequilibrium
processes involved (section 5).
Nonequilibrium contributions to the excitation functions under
consideration are not necessarily due to PE decay, although PE
decay models may include direct interaction contributions 11,6;;

---

-5-
therefore a short section
(chapter 6)
is devGted to the
question of further competing reaction mechanisms. The
conclusions drawn from this work are presented in section 7.
2.
Experimental Procedure
The excitation functions listed in table 1 were measured
with activation techniques.
The irradiations were per-
formed at the Bonn
(BN)
and the Hamburg (HH)
isochronous
cyclotrons, respectively. Self-supporting metallic foils
of high purity and isotopie enrichment
(see table 2) were
activated in most cases in combination with energy degrading
foils
(of aluminium, and of yttrium for 89 y + d ) as foil
stacks.
Projectile energies and the maximum energy degrada-
tion ~E within a stack were calculated from the tables of
Williamson et al.
171. The uncertainty in energy after
degradation of 3He from 25 MeV to 10 MeV, for example, was
calculated
Isi to be about ±0.95 MeV (fwhm). Single foil
activation was applied to reactions leading to residual
nuclei with short half-lives
(T1/2~ 40 min) either by tuning
the cyclotron to the projectile energy under consideration
or with a fixed projectile energy and the target being
placed behind an energy degrader.
These irradiations were
performed with currents in the order of 200 nA extending
over -5 min, whereas the longer living components were
activated for 2-10 hours.
In both experiments the irradiations were performed in
. reaction chambers designed to allow the direct determination

---

-6-
of beam current by integration of the charge collected
in a Faraday cup.
In cases where the total irradiation
time was comparable with the half-life of a nuclide under
investigation,
the variation of the current in time was
accounted for by a technique developed for neutron acti-
vation
191.
After irradiation the samples were placed in front of
3
3
a coaxial Ge(Li) detector of 77 cm
(69 cm ) active volume
and a resolution of 2.43 keV (2.3 keV) at E
= 1332 keV.
y
SignaIs were handled with conventional electronics and
accurnulated into 4k multichannel analyzer arrays. The pulse
height spectra were stored on mag tape mostly 3-4 times per
half-life and sample. A reference pulser was fed into the
signal line for accurate dead-time correction.
The peak integrals were obtained from the pulse height
spectra with multiple line fit prograrns including linear
background and exponential tailing corrections
J2-4J.
Additional corrections for recoiling residual nuclei that
leave or enter the target foil were not applied, because
their ranges are in the order of 300 ~g/cm and less ]10), i.e.
small compared with the thickness of the target foils.
The
half-lives and y-energies used for identification as weIl as
the branching ratios l a r e given in table 1 and are collected
y
from
j 11-1 3 j •
.
The efficiencies of the detectors were determined by
58
GO
88
152
182
means of calibrated "y-sources
(BN:
Co,
Co,
Y,
Eu,
Tai
HH
22 N
54 M
57
GOc
13 7C )
. h l ' b '
. t
:
a,
n,
Co,
0 ,
s
. T e ca 1
ratl0n poln s
were used to interpolate best fitting efficiency curves ~(Ey)

---

-7-
from a 10gli
vs.
log E
presentation (BN), and from Monte
y
Carlo calculations performed on the basis of the geometrical
data of the x-rayed and y-scanned detector
(HH).
In fig.
1 the resulting excitation functions for the
65cu + 3He reaction are compared with previous measurements
by Bryant et al.
114j
and Golchert et al.
1 1 51. Within the
experimental errors the data are in agreement except for the
case of 65Cu (3He ,2n) where we find a yield twice as large.
A similar discrepancy is observed for the case of the
93 Nb (3He ,xn)93,94m,gTC reaction with respect to the data of
Flach 1101 which remains unexplained since the same spectro-
scopie data were used
(fig.
2). The other excitation functions
will be presented in the next section.
Their absolute values
show errors of ±8-10%
(BN) and ±10-20%
(HH).
These quotations
include uncertainties due to counting statistics, photo peak
integration, target thickness, current integration, recoiling
residual nuclei and detector efficiency, but not those of
the y spectroscopie data given in table 1. Al: excitation
functions are available in tabular form on request.
3.
Analysis in Terms of Equilibrium and Preequilibrium Models
3.1.
Equilibrium Emission Models
Before discussing the effects of preequilibrium particle
emission i t is interesting to compare part of the data with
existing equilibriurn model predictions. The WE approach
16
1
1
is incorporated in the widely used code OVERLAID ALICE
117 1.
It allows computation of the e~issian of up ta 20 nucleons in a

---

-8-
deexcitation cascade. The following input parameters were
used:
(i)
The particle separation energies were taken
from the tables of Wapstra and Gove 1181:
(ii)
reaction
cross sections and inverse cross sections were calculated
from optical model
(DM)
transmission coefficients. For p, n
and 3He particles the DM parameters of Becchetti and
Greenlees
119,201 were used,
for a particles those of
McFadden and Satchler 1211:
(iii)
the level density expression
-2
1/2
p(U) = const. U
exp(2(aU)
) with a = (ATarget + ~rojectile)/
1
8 MeV-
was applied to aIl nuclei in the decay cascade. No
pairing corrections were introduced.
In fig.
3 the WE calculations are compared with the
experimental data for 63 cu + 3He . For the 2n emission and the
sum of the 3n and p2n emissions the rising parts of the
excitation functions as weIl as the height of the maxima are
quite weIl described. Aiso shown are curves computed with
the separation energies of Myers and Swiatecki
/22\\
which are calculated from the liquid drop model including
shell corrections without pairing. Since the reaction thresholds
are generally less weIl reproduced,
this option was abandoned
furtheron. Aiso shown in fig.
3 as weIl as in figs.
5 and 6
are the predictions of the more sophisticated statistical
code of Uhl
]231
taking full account of angular momenturn
effects and y-ray competition.
In addition to the input data
(i)
and (ii)
this code applies a back-shifteè Fermi-gas level
density (for details see section 5). Generally,
these calcu-
lations reproduce reactian thresholds weIl and predict a
somewhat flatter decrease of the yield to higher energies.
However, the absolute height of the excitation functions is

---

-9-
reproduced with about the same
degree of accuracy as
with the simpler WE model.
Both approaches cannot explain
the fIat high energy tails. Here, a mechanism for a fast
cooling of the primary composite system is needed: the
emission of more energetic preequilibriurn particles.
3.2.
Preequilibrium Emission
For the investigation of PE phenomena the hybrid model
1241 was used. It has been successfully applied to a
variety of light particle induced r~actions and should
serve as a good approximation of an overall estimate of
nonequilibrium processes
(see section 7). Differences existing
to other approaches e.g.
the exciton model of Gadioli et al.
are noted in ref.
125 1 and are explici tely discussed in ref.
126,271. AIl calculations were performed with OVERLAID ALICE
code )17]. In addition to the input parameters specified in
section 3.1
the following quantities enter into the PE part
of the program:
(iv)
the nucleon-nucleon collision rate was
calculated from the mean free path of nucleons in nuclear
matter;
(v)
the density of particles per MeV in an n-exciton
state containing p particles and h holes was calculated from
the expressions of Ericson
\\281, however, modified for a
limited potential depth of 40 MeV ]1,171. Starting with an
ini tial exci ton nurnber n
= p + h
the exci ton nurnber is
0 0 0
increased by 2 in each step of the deexcitation cascade.
The depletion due to PE emission of previous stages is taken
into account. Any charge asymmetry of the projectile may be
reflected in different initial particle nurnbers Pop and Pon
for protons and neutrons, respectively.
Their value is

---

-10-
increased in each step of the relaxation process by 0.5.
Hence the only free set of fit parameters are the initial
In figs.
4-7 the experimental excitation functions for
63 65
93
3
89
,
Cu,
Nb +
He and
Y + d are compared wi th the theore-
tical predictions for the indicated sets of n
(p
p
).
o
on, op
In fig.
4 th;e curves for 63Cu + 3He clearly demonstrate the
improvement obtained by the inclusion of PE ernission. In
particular,
the flatter fall-off of the high energy tails
for n and 2n ernissions are better reproduced than by the
equilibrium code
(cf.
fig.
3). At the high energy end the
n
= 5 curves tend to decrease steeper than do the experimental
o
data. Yet i t is apparent that only the excitation functions
for one or two nucleon emission are sensitive enough to the
choice of no while for more nucleons
an
extended projectile
energy range is needed.
From the 63,65cu data alone, no
definite conclusion on the best initial proton to neutron
ratio can be drawn,
though the single neutron ernission seerns
3
to be most sensitive (see section 4). For
He particles the
generally adopted set is 4(1.5,2.5}. Corresponding curves
for the case of 93Nb + 3He are displayed in fig.
6;
i t also
contains the results of a geornetry dependent hybrid model
(GDH) calculation \\1,17]
where the average nuclear density
along classical projectile trajectories is taken into account.
In individual calculations for each partial wave, this ~-
dèpendent density enters into the single particle state
density,
the Fermi energy and the nuclear collision rate.
In
further
analysis we stick to the simpler hybrid model,
since in the present cases the GDH calculations do not improve
the fit to the experimental data.

---

-11-
The strong discrepancy of aIl theoretical curves for the
93Nb(3He,4n)92Tc react;on
. .
t
f
th
l
f
•
or~g~na es
rom
e neg ect 0
pairing and shell effects in the level densitl calculation.
Since the separation energy of the fourth neutron from the
closed shell
(N=50)
nucleus 93 Tc is especially high
(12.8 MeV)
while the proton separation energy is rather small (4.1 MeV),
the
population of the doubly odd nucleus 92 Tc is considerably
affected by this neglect of pairing effects.
The inclusion of pairing corrected separation energies
for the emission of a fourth particle removes this dis cre-
pancy (see fig.
6). However,
taken as a general recipe,
this
procedure leads to unphysical shifts of subsequent reaction
thresholds.
Similar observations can be made for the d-induced
reactions on 89 y
(fig.
7). The experimental results are
compared with hybrid model calculations using the initial
exciton numbers 3(1.5,1.5). At the evaporation peak the
(d,2n)
curve is overestimated by the theory by nearly a
factor of 2,
the (d,3n)
curve by about a factor 3 while the
(p,2n) reaction is much stronger than predicted. Also here
t h e popu l
·
at~on 0 f
t h e d oubl y even nuc l eus 88 zr
·~s over-
.
d '
h
d ubl
dd
l
88y
A
.
est~mate
~n contrast to t
e
0
y 0
nuc eus
.
ga~n,
the exciton number dependence of PE decay shows up strongly
only in the theoretical curves for single nucleon emission
i. e.
for the 89 y (d, p) 90y excitation functions wi th no = 2 and
3 in fig.
7. At higher energies the data for populating the
7+ isomer in 90y are reproduced quite weIl by the curve with
n
= 3. At our bombarding energies the high spin isomer should
o

---

-12-
be populated much more than the 2
g.s •• However, as found
by Riley et al.
;291 the g.s. of 90y is fed about one
order of magnitude more than is the isomer, a fact which is
explained by the dominance of stripping reactions to mainly
low spin states (see sect.
5).
The low spin isomer of
87m
-
Sr(1/2 ) is less strongly populated and shows a fIat
high energy tail while the theoretical curve falls aff
steeply due ta the neglect of preequilibrium a-emission in
the OVERLAID ALICE code.
4.
Entrance Channel Phenomena
The composite system 66 Ga* was formed through the
entrance channels 64 zn + d and 63 Cu + 3He (see Table 1) at
excitation energies where the preequilibrium emission
dominates the emission of the first particle out. The (2n)
decay of 68Ga* formed in the reactions 66 Zn + d and 6 5Cu + 3He
(see table 1) was studied in a similar way. For a better
comparison, the experimental and theoretical evaporatian
residue yields were normalized to the optical model reaction
cross section;
thus the influence of the Coulomb barriers
of the respective entrance channels is removed,
and entrance
channel effects show up more clearly.
66 68
4. 1
Decay of
'
Ga*
The normalized excitation functions as a function of the
.
t .
.
th
.
t
66 , 68G *
exc1ta 10n energy 1n
e composlte sys ems
a
are
displayed in figs.
8-11.
If isospin effects and srnall

---

-13-
differences in the angular momentum distribution in the
entrance channel are neglected, both kinds of projectiles
should lead to the same normalized yields,
assuming a pure
compound nucleus reaction.
In preequilibrium processes
the influence of different initial exciton numbers for d-
and 3H~-induced reactions should show up.
For single nucleon emission yields this feature is
clearly observed
(fig.
8).
The n and
(n +p)
curves follow
quite weIl the hybrid model predictions with n
(d) = 3 and
o
3
no ( He) = 4. The remaining deviations. are attributed to the
simplifying assumptions entering the hybrid model code as
already discussed in section 3.
It is to be noted that,
different from input (ii)
in sect.
3.1.,
the inverse cross
sections were computed from a subroutine provided with the
OVERLAID ALICE code 1171.
For single nucleon emission,
improved fits are obtained
while the theoretical yields for multi-nucleon emission
are hardly changed (cf.
figs.
4,8,9 and figs.
5,10). For
64 Zn + d
the theoretical curves for n and
(n + p)
emission
deviate from the experimental on es by a constant factor while
f
l
. .
h
.
l
63 c
3H
.
or
ow excltatlons t
e experlmenta
u +
e curves rlse
less steeply than the OM calculated branchings. One reason
for this may be the too large reaction cross sections at low
66
bombarding energies
(20 MeV excitation in
Ga* corresponds
to 7.5 MeV) while the uncertainties of OM predictions do not
enter in the theoretical curves.
The optimal splitting of
the initial particle exciton number Po into initial proton
and neutron numbers p
and p
cannot be deduced from the
op
on

---

-14-
quality of individual fits alone since curves for different
ratios p
/p
are almost parallel
(see figs.
4 and 5). A
op
on
more sensitive procedure is developed in the next subsection
4.2.
The optimal initial exciton numbers are indicated in
f igs.
8-11. Both curves for n-emission and
(n + p) einission
differ from the hybrid model predictions by about the same
factor in each case. While n-emission is overestimated, p-
emission is clearly underestimated.
For two-particle emission (e.g.
(2n)
in figs.
9 and 10,
and
(an)
in fig.
11)
the influence of the initial exciton
number is already rather weak. Hence,
the reduced yields for
d- and 3He-induced reactions nearly coincide and cross at
about the same excitation energies as the theoretical curves.
The initial exciton number dependence shows up only at the
high energy tails; e.g.
in figs.
9 and 10 the
(3 He ,2n) data
rather follow the curves for n
= 4 than those for n
= 3.
o
0
From the systematics of binding energies anl Coulomb
barrieis
i t
is deduced that for the population of 61 cu by
the (a,n)
process,
first a preequilibrium neutron ia emitted
followed by an equilibrium a-particle. Only at the hiqher
bombarding energies might first chance preequilibrium a-
emission play a more important role. This seems to be indicatcd
in fig.
11 by an eX!1crimcntal fall-off which i5 flatter than
shown by the thearetical
(un) curves, which do not imply
preequilibrium ~-emissian. As deduced from Q-value arguments.
the reaction leading to S8 co is only viable by the (2a)
emission. As shawn in fig.
11,
the two experiments differ
more strangly from cach ot.her than the theoretical curves fCl

---

-15-
pure equilibrium a-emission,
indicating a stronger
nonequilibrium process for d- than for 3He-induced reactions.
Finally,
the emission of three nucleons is observed as
the sum
of the
(3n)
and
(2pn)
reactions leading to 63 Zn
(fig.
9). At the high excitation energies the data actually
coincide with the model predictions, but below 30 MeV
excitation the theory underestimates the experiments by
more than an order of magnitude. Apparently, reactions
having lower Q-values
(e.g.
inelastic processes like (d,dn),
break-up reactions like
(3He ,dn) and transfer and charge
exchange reactions like
(d,t)
and
(3He ,t)) do contribute
(cf.
sect.
6).
4.2.
Conservation of Projectile Charge Asymmetry
4.2.1.
General considerations
As shown in section 3.2.,
the excitation functions for
single nucleon emission are the most sensitive probes for
determining not only the initial exciton number no' but
also the initial number of protons Pop and neutrons pon·
The ambiguities in fitting these data are minimized by
comparing not single excitation functions,
but the calcu-
lated double ratio
3
3
R(E
)
= o( He,p)/o( He,n) : o(d,p)/o(d,n)
(1)
exc
with the corresponding experimental value
3
3
= o( He,p+n)-o( He,n)
o(d,p+n)-o(d,n)
R (E
( 66 Ga* ) )
( 2)
exc
o(3 He ,n)
c(d,n)

---

-16-
Naively, one would expect that the ratio a(3He ,p)/a(3He ,n)
is much larger than the corresponding ratio a(d,p)/a(d,n),
since the initial
(active)
exciton particles stem from the
projectile, and the proton to neutron ratio is two for the
3H
. . 1
b t
1
f
h
d
h
e prO)ect1 e
u
on y one
or t e
euteron. T e symmetry
of the deuteron and the charge symmetry of the nuclear
force demand synunetric particle numbers
(p
/p
= 1)
in the
op
on
deexcitation cascade. For 3He this ratio is less well fixed
a priori. Assuming a charge independent nuclear interaction
in the first collision of a 3He nucleon with the target, one
would expect n
= 4,
o
Pop
=
2. 5 and p
= 1 .5, i. e. the excited
on
additional nucleon is equally likely to be a proton or a neutron
Assuming charge symmetry only with a(np):
a(nn):
a(pp) = 3:1:1
one would get almost the same result, p
=29/12=2.42 and
op
p
= 19/12 = 1.58. On the other hand, one could argue that a
on
quasi equilibrium holds in each stage of the relaxation
process i. e.
ini tially all possible n
= 4 exci ton states are
o
excited and p
= p
•
op
on
Hence, within the framework of current PE models
11,26,271
one may try to answer this question by investigating which
initial exciton numbers fit the data best (method A).
Another,
less empirical approach would be to check if the
well developed theory of isospin conservation in compound
nucleus reactions
]30! may be extended to PE reactions.
Suggestions and calculations along this line have been proposed
by Chevarier et al.
131 1
and Kalbach-Cline et al.
] 321.
In
the next subsection we shortly review this approach
(method B).
Finally,
i t is worth mentioning that a more thorough treatment
of isospin in PE reactions has recently been published by

---

-17-
Feinstein
38);however, at present this theory does not
1
allow computation of residual nucleus yields.
4.2.2.
Model caldulations of R(E
)
exc
Method A
(charge dependent initial exciton nurnbers): In
R(E
) theoretical uncertainties in the optical model reaction
exc
cross section cancel and uncertainties in level densities due
to pairing and shell effects should be diminished, leaving
only a dependence on the exciton nurnbers. With the weIl
established choice of n (d) = 3 and n (3He ) = 4, R(E
) in
.
0
0
exc
eq.
(1) strongly depends on the charge asyrnrnetry of the
initial exciton nurnbers p
and p
for 3He-induced reactions.
on
op
From arguments of charge synunetry we put Pon = Pon = 1 .5 in
the deuteron. Hence -
in short notation - we get
= 0p(4,pon'pop) a (3,1.5,1.5)
RPE(E
)
n
( 3)
A
exc
°n(4,pon'pop) a
(3,1.5,1.5)
P
Method B
(Isospin formalism wi th p
= P
): The basic
on
op
ideas of the compound nucleus isospin forrnalism are illustrated
in fig.
12. The excitationenergies t.ET>for the T> g.s. were
taken from ref.
1341. Assuming strict isospin conservation
in d-induced reactions, one may only form T< states in 66 Ga*
2
due to the isospin Clebsch-Gordon coefficients C (d,<) = 1 and
C2 (d, » = O. For the 3He projectile, the corresponding coef-
2
ficients are C (3He , <) = 5/6 and c 2 (3He , » = 1/6. The isospin
Clebsch-Gordon coefficients for p, n and a particle ernissions
from the T< and T> states in 66 Ga*are indicated in fig. 12.
For a pure PE reaction populating only T< states in the

---

-18-
residual nuclei 65 Zn and 65 Ga
(see fig.
12) we get, with
T
being the g.s.
isospin of the residual nucleus
o
66
65
Ga -p =
Zn:
Here,
the op>«op«)
indicate PE transition yields from
initial T>
(T<)
states to the final T< isospin states in
2
the residual nuclei for the 3He-indUCed reaction with C = 1,
starting with equal probability for exciting protons or
neutrons in the initial exciton state (p
= p
= 2). The
on
op
term in curly brackets gives the enhancement of the 3He-
induced reaction due to isospin conservation. In PE emission
to the low lying states under consideration,
the first stage
contributes most,
and any difference in depleting proton or
neutron states due to isospin effects may be neglected. Hence,
the ratio 0p></Op«
-(1-ET>/Eexc)-no+1 with n
=4 does not
o
depend very much on the excitation energy, and the enhancement
-2
will be strongly damped
by
the
(2T)
dependence.
o
The double ra tio ~N (E
) for a pure compound nucleus
-"B
eXC
reaction with ~trict isospin conservation is derived to be
~N(E
)
<
>
N (E
c)/N (E
c-~ET».
( 5)
-"B
exc
ex
ex
Here,
the quantities N< and N> are defined as the sums
2
N< = L C2 «,f)T
and N> = L C (>,f)T
of the transmission
f
f
f
f
coefficients for all decay channels
fi
they may be calculated
from isospin dependent compound nucleus decay codes
130,32].

---

-19-
It may be interesting to note
for codes not containing
,
'>
isospin conservation,
that the ratio N'IN
can be
expressed as
-1
> >
<
<
1+ (2T +1)
(a N IN -a
)/a
o
n 0
0
p
R
( 6)
-1
>
-1
>
< <
>
1- 2(2T +3)
a laR
-
(2T +1)
(a -a N IN )/a
o
p
0
n
p o o
R
where aIl terms on the right hand side of eq.
(6) can be
calcula ted by
scttoing C2 :: 1
and
separately treating the
decay of both isospin systems to T< or T> levels of the corre-
<
>
<
sponding residual systems.
The quantities a ,
a , ap' and
n
n
>
a
are the resulting total cross sections for p- and n-
p
emission, and a
= a + an +
R
aa.
The ratio N~/N~ can be approxi-
p
mated by the ratio of level densities for n-emission from
both isospin systems,
respectively, using the expression (iii)
given in sect.
3.1.; i t is found that t~e result does not
depend strongly on this ratio since the relation
N</N>~(2To+1)aRla~-1 holds in the limit N~/N~»1.
4.2.3.
Comparison of theory and experiment
The experimental double ratio R(E
(66 Ga*»
was determined
exc
according to eq.
(2).
It is fairly insensitive to potential
systematic errors
(resulting e.g.
from target thickness,
charge collection,
y detector efficiency, branching ratios).
The targets were separately irradiated in short (65 Ga ) and
65
long (
Zn)
periods.
In sorne cases different excitation
energies were reached.
Hence for calculating R(Eexc),neigh-
bouring data points were linearly interpolated. Experimental

---

-20-
error bars were derived from a maximum uncertainty of 9%
in each data point.
Experimental results and theoretical
curves are plotted in fig.
13.
The dotted curve represents the results for a pure
compound nucleus mechanism conserving isospin
(eqs.
(5,6)).
3
At 10 MeV
He energy i t is R ~1.4 and it decreases with
increasing energy.
For E 3He>14 MeV the equilibrium contri-
butions to op and on are smaller than 20% and the PE model
predictio~s have to account for the large double ratio
observed. The thin full curve gives the results of the isospin
conserving PE model
(eq. (4)) with no = 4 (2,2).
I t is only
slightly larger than the corresponding dash-dotted curve for
the isospin nonconserving calculation according to eq.
(3),
and does not reproduce the high experimental value of
<R(26-36 MeV»
= 1.92 ± 0.19.
This strong enhancement is only
matched by PE calculations with asymmetric initial exciton
numbers for protons and neutrons. The shaded areas at low
excitation energies give the uncertainty due to the influence
of the compound nucleus reaction. The lower boundaries for
the curves with n
= 4(1.5,2.5)
and 4(1.75,2.25)
and the
o
upper boundary for n
= 4 (2,2)
resul t
from combined PE + CN calcula-
o
tions without isospin conservation. The calculations to someextent
depend on the effective Coulomb barrier for p-emission from
65 Ga (cf. fig.
12). Increasing i t from 2 to 3 MeV would lower
the curve for n
= 4(1.5,2.5)
from R= 2.36 to 2.06 at 34 MeV
o
excitation in 66Ga~ With this theoretical uncertainty in
mind,
the experiment justifies the usual choice 131,351
p
= 1.5 and p
= 2.5 for
3He-induced reactions,
thus confirming
on
op
the conservation of charge asymmetry in preequilibrium processes.

---

Entrance and Exit Channel Phenomena in
d- and 3He-Induced Preequilibrium Decay+
H.H. Bissem, R.
Georgi and W. Scobel
I.
Institut für Experimentalphysik
Univ.
Hamburg, Hamburg, Fed.
Rep.
of Germany
and
J. Ernst, M. Kaba, J.
Rama Rao and H. Strohe
Institut für Strahlen- und Kernphysik
der Univ. Bonn, Bonn, Fed. Rep. of Germany
Abstract
Activation techniques were used to measure more than 30
excitation functions for single and multiple nucleon and/or
64
a particle emission for d+
,66 Zn , 89 y with E
= 9-26 MeV and
d
3He + 63,65Cu , 93Nb with E(3 He ) = 10-44 MeV. The excitation
functions are generally in agreement with the results of a
combined equilibrium and preequilibrium hybrid model calcu-
lation applying initial exciton numbers n
= 3 for d and
o
n
= 4 for 3He reactions. The composite system 66 Ga has been
o
64
produced via d+
Zn and 3He +63 Cu at excitation energies
between 22 and 36 MeV. An entrance channel dependence shows
up in the yields for single p- and n-emission when compared
,
-
3
in the double ratio R=(a(3He,p)/a( He,n)/(a(d,p)/a(d,n».
It
approaches a value of about 2,indicating enhanced p-emission
for the 3He-induced reaction.
This value disagrees with the
+Work supported by the Bundesministerium für Forschung und
Technologie

---

-21-
5.
Isomerie Cross Section Ratios
For the systems
(table 3)
and projectile energies
under investigation,
the population of the residual nuclei
at low excitation energies is significantly determined by
PE decay modes.
Therefore,
the determination of the ratio
a /a
of cross sections for the population of ground and
g
m
isomeric state, respectively, with a method similar to that
of Huizenga and Vandenbosch 136/, needs sorne modification J 371,
because a /a
now also reflects the spin distribution follow-
g
m
ing an initial PE emission mode. The·model applied here will
be presented next,
followed by a comparison of its results
with our experimental data.
5.1.
The Model
The statistical model formulation applied to calculate the
influence of the initial and intermediate angular momenturn
distribution on isomer yields is that of Uhl
1381. The
initial distribution is assumed to be that of the compound
s ys tem , i . e .
SP+ST
I+S
21 + 1
P(I) = TI~2
L
L
Tt(E )
(7 )
s=jSp-ST]
t=II-Sj (2S p+1) (2S +1)
p
T
with the de Broglie wave length ~, the projectile (target)
spin Sp(ST)'
the projectile energy Ep and the transmission
coefficient T~(Ep) for the orbital angular momenturn t in
the entrance channel.
The sequential decay of this system is described by fully
taking into account conservation of parity,
angular momentum

---

-22-
and energy.
The competing exi t
channels are those of n, p, d, 'j
and y cascade emission. Equilibrium (EQ)
transitions to the
states of the corresponding residual nue lei are treated
individually at low excitation energies
(typically for the
first 10-12 discrete levels, with the spectroscopie informa-
tion taken from 139 l, whereas for the continuum region the
level density formula of the back-shifted Fermi gas model
has been used:
1
U(1+1»
p(U,1)
p (U) 0
(21+1)
exp(-
=
"2""(j2
20 2
(8)
1
1
exp2(a(U-t.»~
peU) = - - 0
j.,.
s
12/2
oa"
(U-t.+t) ~
Here,
t
is the thermodynamic temperature given by
U -
~ = at 2 - t ;
( 9 )
a and t. are level density parameter and fictive ground
state position, respectively and were taken from
1401. The
spin eut off parameter ° related to the momentum of inertia
via
(10)
is referred to as oR'
if the rigid body value is taken for
19
El
(wi th r 0 = 1.25 fm).
Particle decay widths are calculated with optical model
transmission coefficients
119-21,41 l, decay widths for E1
radiation from y absorption cross sections by using the
Brink-Axel parameterization of the E1 giant dipole resonance
:421,
those of radiation with higher multipolarity
(L$3)
from

---

-23-
the WeiBkopf model normalized to the E1 value.
PE emission
precedes the first step of the sequential EQ evaporation
and depletes the compound nucleus formation.
None of the PE
decay models presently used conserves angular momentum. We
assume that
(i)
the spin and parity population do(ETI,U)/dU
at excitation energy U of the residual nucleus is that of
the EQ population, doEQ(ITI,U)/dU and that (ii)
the fractional
PE depletion is the same for each partial wave in the entrance
channel
143,441. This leads to
1381
( 11 )
dO(ITI,U)
dU
E
l', TI '
In eq.
(11), doPE
(U)/dU denotes the energy distribution
x
after PE emission of particles x.
The fraction of interactions
leading to nucleon PE emissîon of type x is
U~ax _d_O-=-~=E_(_U_) dU
l
x = n,p
( 12)
dU
o
with 0R(E p ) being the optical model reaction cross section.
Complex particle PE emission will be neglected so that
fpE(E p ) = f~E(Ep)+ffE(Ep). The PE component has been calculated
in the framework of the hybrid model
1241 with the parameters
given in section 3.
5.2.
Comparison with Experiment
The experim~ntal results obtained for the reactions
89 Y(d,2n)89m,gzr, 93 Nb (3He ,n)95m,gTc, 93 Nb (3He ,2n)94m,gTc

---

-24-
and 93 Nb (3He ,3n)93m,gTc are shown in figs.
14 and 15. AlI
three reactions have in cornrnon that the ground state is
the high spin state (cf.
Table 3). Therefore,
the ratio
a /0
is expected to increase with projectile energy if eq.
(7)
9
m
fully applies.
The experimental data however, approach a
constant value already at fairly low projectile energies,
indicating only a moderate preference of high spin state
population.
This can be traced back to the PE contribution.
At low projectile energies the spin population of the
initial compound system is almost centered ar0und the target
spin
(fig.
16a).
The spins of ground state
(7+)
and isomeric
state (2+)
of the residual nucleus differ by the sarne amount
from the target spin 9/2+ and we therefore expect an isomeric
ratio close to 1 at these energies.
The ratio will corne out
closer to 1 the narrower the initial spin distribution,
i.e.
the smaller the spin cut off parameter a,
is. The calculations
shown in fig.
14.confirm these considerations. For projectile
energies up to 20 MeV the PE contribution is small
(fpE $ 0.2);
best agreement is obtained with 0= 0.7 oR'
• A similar reduc-
.1g
tion has been deduced from 93 Nb (n,2n)92m,gNb 145 J and from
the 93 Nb (n,a)90y angular distribution 146 j.
At higher projectile energies, however,
the pure EQ
mechanism with 0~0.5 0Rigoverestimates the isomeric ratio,
although the radius parameter r
has been given a fairly low
o
value.
On the other hand c is expected to approach oR'
,
19
because at high excitation energies,
effects due to pairing
correlations vanish.
This discrepancy is reduced by introducing

---

-25-
the PE decay mode. A considerable fraction of the nucleons
emitted
Cf
~
pE
0.5 for E3He ~ 40 MeV) then populates 95Tc at
low excitation;
the emission of high energy neutrons removing
several units of angular momentum Ccompare figs.
16a and 16b)
is enhanced and so is the relative yield for the low spin
isomer. A similar shift is obtained by a substantial reduction
ofaCcf.
fig.
16c).
The ground state spin value for 93 Tc is identical with
.
+
that of the target
C9/2 ) and exceeds that of the isomeric
state by four units of~. Therefore, the isomeric ratio for
3
3
C He,3n) will generally be higher than that for theC He,2n)
reaction. At projecti le energies E 3He < 20 MeV the ratio is
essentially determined by the individual discrete level
sequence in the residual system, because the reaction threshold
is at 13.3 MeV and the first excited state populating the
isomeric state is at 1.4 MeV.
These features are weIl repro-
duced by the model calculation applying cr = 0.7 cr
and PE
Rig
competition.
3
3
For
C He,n)
the spin situation is the same as for
C He,3n),
cf.
taole 3. One might therefore expect weIl above the
reaction threshold a similar energy dependence
of the
isomeric ratios.
Figure 14, however, shows that the ratios
differ by more than a factor 2.
In addition,
the EQ calculations
3
for
C He,n)
fail to reproduce the ratio and exceed the experi-
mental result considerably.
Inclusion of the PE decay mode
improves the calculation in shape, but not in 1bsolute values.

---

-26-
Due to lack of spectroscopie information on 93 Nb (3He ,n)
to low lying states in 95Tc , no explanation can be offered
for the increasing discrepancy below E3He = 10 MeV, where
the PE fraction f pE is weIl below 0.1, except a possible
contribution of the (3He ,n) stripping reaction to low spin
states (see section 6).
Here the initial population of the compound system, due to
the low target spin value of 1/2 and ,the light projectile,
is concentrated at low spin values for very low projectile
energies E ,
favouring the transition to 89mzr in the (d,2n)
d
reaction. With increasing E
the spin distribution extends to
d
higher spins and the isomeric ratio therefore increases too.
At highest projectile energies the introduction of PE deexci-
tation again improves the model calculation, but still fails to
reproduce the shape of the isomeric ratio at high energies,
cf.
fig.
15.
In contrast to the isomer ratios discussed so far,
the
.
89
90m g
react10n
Y(d,p)
, Y shows a strong preference for the
low spin state. The production cross section for the 7+ isomer
remains almost constant up to E
= 25 MeV (fig.
15). Therefore,
d
the isomer ratio is not expected to change in this energy
range by more than one order of magnitude, which is-necessary
to make experiment and calculation (fig.
15)
comparable.
This observation was interpreted by Riley et al.
]29] with
a dominant stripping mechanism.
Indeed, Lins et al.
1471
have shown that in 89 Y (d,p)90y the neutron predominantly is
transferred to low spin states (sl/2
,d /
,d /
) that populate
3 2
5 2

---

-27-
the 2
ground state by y-deexcitation.
5.2.4.
Spin distribution after PE decay
What is the origin of the discrepancies remaining at
high projectile energies,
in particular for the isomeric
ratios for the
(3He ,n),
(3He ,2n) and
(d,2n)
reaction? If,
for the moment,
the angular momenta of the second and third
neutron evaporation may be neglected, i t must rest on a
difference in the dominant reaction mechanism for the emission
of the first neutron.
The insert in. fig.
14 emphasizes that
the isomeric ratio for
(3He ,n)
almost exclusively reflects
the spin distribution after direct and PE neutron emission.
3
In agreement with the tendency observed for
( He,2n)
and
(3 He ,3n), we must conclude that the PE (and direct, if present)
decay modes favor low spin states even more th an assumed in
eq.
(11). What then could replace assumption
(i) of sect.
5.1.
leading to this equation?
Here we suggest ]501 implementing
one feature of nucleon
PE emission, namely its forward peaked angular distribution,
-+
-+
-+
-+
-+
-+
to give an estimate of the spin l = Sp+ ST+ R- p - Sn - R-
remaining
n
-+
in the residual system. Forward peaking means that R- p is
-+
parallel to R-
, so that approxirnately l = R-
,
if the spins
n
p - R- n
of the particles involved are neglected. Herein R-
is c'alcu-
n
lated from
R.p and the linear momenta of projectile/pp,and
neutron p , assuming a fixed impact parameter: R-p.~/pp =
J
n
.
R- ·-h/P
or Zn = R-p·Pn/pp· The spectral distribution of P
n
n
n
calculated from daPE(U)/dU determines the spectral distribution
n
of Z • Assumption
(1i)
of sect.
5.1.
remains unmod1fied.
n

---

-28-
The resulting isomeric ratios and excitation functions
are shown in figs.
14 and 15, too. Considerable improvement
is obtained in the regions where PE decay plays an important
role.
This indicates that the assumption of a spin distribu-
tion for PE emission identical with that of an evaporation
process may be wrong due to restrictions on the accessible
residual states and therefore in favour of too much angular
momenturn remaining in the system that cannot be carried away
by subsequent particle evaporation.
6.
Competing Reaction Mechanisms
The analysis of excitation functions for loosely bound
projectiles 50 far has been performed in terms of equilibrium
and preequilibrium processes. Hawever,
the analysis is not
unique due to the presence of other direct or nonequilibrium
mechanisms like inelastic scattering of the projectile,
particle transfer reactions,
etc., sorne of which show up in
"sub-threshold" cross sections of
(particle, xnyp)
reactions
i.e.
in the emission of complex particles having lower Q-
values
(see e.g.
fig.
9).
The observed high energy tails in
excitation functions for a-emission
(fig.
7 and 11)
al 50
clearly show the importance of preequilibriurn emission
of complex particles -
yet codes accounting for i t in multi-
particle decay cascades are still lacking. However, complex
particle emission should play a minor role above
the threshold
for the corresponding multi-nucleon emission processes.
Another mode of multi-nucleon emission reaction must also
be discussed -
the inelastic break-up of the projectile.

---

-29-·
Hereby, one of the break-up partners
(e.g. a neutron)
is
absorbed by the target nucleus.
The excited secondary
composite system may furtheron decay by neutron or proton
emission and thus contribute to the
(particle, xn)
as
weIl as
(~article, pxn) excitation functions. Hence, the
inelastic break-up bumps observed in particle spectra do
contribute to excitation functions in a smooth way while the
elastic part reduces the flux into other nonelastic channels.
In recent investigations of d- and 3He-induced break-up
reactions
]48, 49 1 i t was found that this inelastic break-up
mode normally dominates over the elastic one. In the d-
induced break-up this mode is about 15% of the total reaction
cross section at A = 60-90.
Competitive reactions to single nucleon preequilibrium
emission are transfer reactions to bound states.
In particular,
neutron transfer reactions occur already below the coulomb
barrier of the projectile, 50 that for lower bombarding
.
h'
d
d '
t
A l i
th
89 Y (d,p)90m,gy
energ1es t
15 mo e may
om1na e.
n examp e
5
e
reaction as discussed in sections 3 and 5. For the 63 cu + 3He
and 6 4 "
Zn d
+
.
react10ns t h e Cou10rob b '
arr 1ers are l ower and
preequilibrium emission of charged particles (i.e. protons)
should be considerably enhanced as compared with the A = 90
mass region. Since direct transfer reactions do conserve iso-
spin, they cannot give ri se to the observed relative enhance-
ment of a(3He,p)/~3He,n) as compared with the ratio
a(d,p)/a(d,n) .
The extracted numbers of the initial degrees of freedom
(see sections 3 and 4)
are consistent with the results of
analyses of continuous nucleon spectra in d- and 3He-induced
•

---

-30-
reactions near A = 60
131,351. Yet i t
is obvious that these
analyses of initial exciton numbers take care of sorne of the
direct reaction modes mentioned in an averaging way and
hence should not be taken too literally.
7.
Conclusion
The present work contains a systematic survey on reactions
induced by the loosely bound d and 3He projectiles for targets
in the A = 60-90 mass region. From the "analysis of the measured
excitation functions by equilibrium and preequilibrium
models the following general conclusions can be drawn:
(1)
In comparison to the simple Weisskopf-Ewing model,
the inclusion of y-ray competition and angular momentum
conservation only slightly improves the agreement with
the data.
Using experimental separation energies, both
approaches weIl describe thresholds and maxima, but the
high energy tails for few particle emission processes
are only explained by preequilibrium decay.
66
3
(2)
The study of the decay of
Ga* formed by d- and
He-
induced reactions similarly shows that typical entrance
channel effects are smeared out the more particles are
emitted.
The charge distributions of the initial exciton
particles in both entrance channels can only be determined
from the comparison of single proton and neutron emission
yields.
From the hybrid model analysis of aIl data,
the
initial set of exciton numbers n
(P
,p
) were found ta
a
on
op
be 3(1.5,1.5)
for d-,
and 4(1.5,2.5)
for 3He-induced
reactions.

---

-31-
(3)
Near A=90 for both types of projectiles,
the pure
Hauser-Feshbach calculation only accounts for the
observed isomeric ratios where emission from an equili-
brated system domina tes.
The inclusion of PE emission -
assuming the same spin distribution as calculated for
equilibrium emission -
considerably improves the overall
fit.
The remaining discrepancy indicates that PE particles
carry away more angular momentum than equilibrium particles.
This feature cou Id be accounted for in a simple and
qualitative approach and should be taken care of in
more
refined
models of PE emission.
(4)
Improved codes should also contain pairing and shell
effects in level density calculations. This neglect of
the present preequilibrium codes may explain the observed
over- and underestimation of yields for even-even and
doubly odd residual nuclei,
respectively.
(5)
At present, i t seems
difficult to include competing
direct reaction modes in the analysis of excitation
functions
(cf.
however
\\511). With respect to processes
involving complex particle emission,
they are dominant
below and near thresholds for respective multi-nucleon
emission.
Hence,
in the analysis of initial exciton
numbers from excitation functions as weIl as from particle
spectra,
i t is not possible to clearly distinguish
preequilibrium processes from other direct reactions.
On the whole one might say that also for loosely bound
projectiles at bombarding energies up to 45 MeV,
the simple
Weisskopf-Ewing approach to equilibrium and preequilibrium

---

-32-
nucleon emission - as represented by the OVERLAID ALICE code -
yields reasonable fits to a large variety of excitation
functions with rather few input parameters.
Acknowledgement:
The authors of the University of Bonn are grateful to
Prof.Dr. T. Mayer-Kuckuk for his continuous interest and
support. One of the authors (J.R.R.) wishes to acknowledge
the receipt of a fellowship from the Heinrich-Hertz-Stiftung
Another author (M.K.) is indebted to the Otto-Benecke-Stiftung
for a grant.

---

-33-
P.eferenees
1) M. Blann, Ann. Rev. Nuel. Sei. ~,123(1975) and further
referenees therein.
2) H.R. Georgi,
PhD thesis,
University of Hamburg (1977)
3) H. Strohe, Staatsexamensarbeit, University of Bonn (1978)
4) M. Kaba,
PhD thesis, University of Bonn (1978)
5) S.N. Ghoshal,
Phys.
Rev. 80,939(1950)
6) C. Kalbaeh,
Z. Physik A283,401(1977)
7) C.F. Williamson, J.P. Boujot and J. Picard,
Report CEA-R3042
(1966)
8) C. Tsehalar, Nuel. Instr. and Meth. ~(1968)141
9) M. Bormann, H.-K. Feddersen, H.-H. Holseher, W. Seobel
and H. Wagener,
Z. Physik A277,203(1976)
10) S. Flaeh, PhD thesis and Report KFK 2279, Karlsruhe (1976)
11) G.
Erdtmann and W. Soyka,
"Die Y-Linien der Radionuklide",
Beriehte der KFA Jülieh,
2nd Ed. Jül-1003-AC (1974)
12) Nuelear Data Sheets,
(Nuel. Data Projeet ORNL, eds.),
Academie Press, New York (1978)
13) A.A.C. Klaasse and P.F.A. Goudsmit,
Z. Physik 266,75(1974)
14) E.A. Bryant, D;R.F. Coehran and J.P. Knight,
Phys. Rev.
130,1512(1963)
15) N.W. Golehert, J. Sedlet and D.G. Gardner,
Nuel.
Phys. A152,419(1970)
16) V.F. Weisskopf and D.H. Ewing, Phys.
Rev.
57,472(1940)
17) M. Blann, OVERLAID ALICE, US ERDA Report No. COO-3494-29,
1976
(unpublished)
18) A.H. Wapstra and N.B. Gove, Nuel. Data Tables ~,267(1971)

---

-34-
19) F. Becchetti and G. Greenlees,
Phys.
Rev.
182,1190(1969)
20)
F.D. Becchetti and G.W. Greenlees,
in: Polarization
Phenomena in Nuclear Reactions
(H.H.
Barshall, W. Haeberli,
eds.)
p.
682, The University of Wisconsin Press, Madison,
Wise
(1971)
21) L. McFadden and G.R. Satchler, Nucl.
Phys. ~,177(1966)
22) W.D. Myers and W.J. Swiatecki, Nucl. Phys. ~,1(1966)
23) M.
Uhl, Acta Phys. Austr. 11,245(1970);
M.
Uhl, Nucl. Phys. A184,253(1972)
24) M. Blann, Phys. Rev. Lett. 22,337(1~71) and 1550;
28,757(1972)
25) J. Ernst and J.
Rama Rao,
Z. Physik A281,129(1977)
26) M. Blann, Phys. Rev. C17,187"1(1978) and further references
given therein
27) E. Gadioli, E. Gadioli Erba and G. Tagliaferri,
Phys. Rev. C17,2238(1978) and further references given
therein
28) T. Ericson, Adv.
in Phys. ~,425(1960)
29) C. Riley and B. Linder, Phys. Rev.
134,B559(1964)
30) H.L. Harney, H.A. Weidenmüller and A.
Richter,
Phys. Rev. C16,1774(1977)
31) A. Chevarier, N. Chevarier, A.
Demeyer, G. Hollinger,
P. Pertosa, A. Alevra,
R.
Dumitrescu, 1.R. Lukas, M.T. Magda
and M.E.
Nistor, Nucl. Phys. A231,64(1974)
32) C. Kalbach-Cline,
J.R. Huizenga and H.K. Vonach,
Nuel. Phys. A222,405(1974);
C. Kalbach, S.M.
Grimes and C. Wong,
Z. Physik A275,175(1975)
33)
R.L. Feinstein, Ann.
Phys.
107,222(1977)
34) W.J. Courtney and J.D.
Fox, At. Data. Nuel. Data Tables,
.12,141 (1975)

---

-35-
35) J. Bisplinghoff, J. Ernst,
R.
Lohr, T. Mayer-Kuekuk
and P .. Meyer, Nuel.
Phys. A269,147(1976)
36) R. Vandenboseh and J.R.
Huizenga, Phys. Rev.
120,1313(1960)
37) C.L. Branquinho, S.M.A. Hoffmann, G.W. Newton, V.J. Robinson,
H.Y. Wang and I.S. Grant,
J. Inorg. Chem. !l,617(1979)
38) M. Uhl, Proe.
"Consultants Meeting on the Use of Nuelear
Theory in Neutron Data Evaluation", lAEA-190, p.361,
Vienna 1976
39) Table of Isotopes,
eds. C.M. Lederer and V.S. Shirley,
7th edition (New York,
1978)
40) W. Dilg, W. Sehantl, H. Vonaeh and M. Uhl,
Nuel. Phys. A217,269(1973)
41)
D. Wilmore and P.E. Hodgson, Nuel. Phys.
55,673(1"964)
42) P. Axel, Phys. Rev.
126,671(1962)
43) J. Gilat, A. Fleury, H.
Delagrange and J.11.
~lexander,
Phys. Rev. C16,694(1977)
44) H. Sakai, H. Ejiri, T. Shibata, Y. Nagai and K. Okada,
Phys.
Rev. C20,464(1979)
45) M. Bormann, H.H. Bissem, E. Magiera and R. Warnemünde,
Nuel. Phys. A157,481(1970)
46) M. Bormann, W. Schmidt, V. Sehrëder, W. Seobel and U. Seebeck,
Nuel. Phys. A186,65(1972)
47) W. Lins, J, Ernst, N.
Takahashi, E. Grosse and D. Proetel,
Nuel. Phys. A179,16(1972)
48) J.
Pampu~, J. Bisplinghoff, J. Ernst, T. Mayer-Kuekuk,
J. Rama Rao, G. Baur, F. Rosel and D. Trautmann,
Nuel. Phys. A311,141 (1978)
49) J. Bisplinghoff, J. Ernst, J. Kleinfeller,
T. Mayer-Kuekuk,
G. Baur and R. Shyam, Contributions to the International
Symposium on "Continuum Speetra on Heavy Ion Reactions",
San Antonio, Texas,
Dee.
3-5,
1979

---

-36-
50)
H.H. Bissem, M.D.A.
Rahman and W. Scobel,
to be published
51)
H. Feshbach,A.K. Kerman and S. Koonin,
preprint
(1979)

---

-37-
Table Captions
Table 1
Reactions under investigation and y-lines used
for identification. The laboratory (BN or HH),
number N of data points of the excitation
function, maximum projectile energy E and
maximum energy degradat~on 6E are given in the
last colurnns.
Table 2
Target specifications
Table 3
Spins and parities of nuclei involved
J12 J

---

Reaction
T~
EyCkeV}
l
Lab.
N
E(MeV)
6E(MeV)
Y
63CuC3He,n)65Ga
15.2m
11 5; 1 53; 752
0.532;0.087;0.08
BN
5
24.8
1 1
HH
14
31.7
0
63
3
65
CuC He,n+p)
Zn
243.8d
1116
0.498
BN
5
24.8
1 1
63cuC3He~2n)64Ga
2.6m
809; 992
0.14;0.46
HH
15
35.0
0
63
3
63
CuC He,3n+p2n)
Zn
38.8m
670; 962
0.0883;0.0695
BN
5
24.8
1 1
HH
17
42.5
0
63
3
61
CuC He,an)
Cu
3.41h
283;656
o. 13; 0.096
BN
5
24.8
11
63CuC3He,2a)58Co
71 .3d
811
0.994
BN
5
24.8
11
-----------------------------------------------------------------------------------------------i
.
,
65CuC3He,n)67Ga
78.0h
93.3
0.70
HH
16
43.8
9
!
1
w
65CuC3He,2n)66Ga
1
9.4h
834; 1039
0.059;0.373
HH
23
43.8
9
co
1
1
65cuC3He,3n)65Ga
15.2m
115;153
0.532;0.087
HH
20
41.4
0
65cuC3He,4n)64Ga
2.6m
992;1387
0.46;0.14
HH
4
41.7
0
1
-------------------------------------------------------------~----------------------------______I
64znCd,n)65Ga
15.2m
115;153;752
0.532;0.087;0.08
BN
8
26.7
15
64
65
ZnCd,n+p)
Zn
243.8d
1 1 16
0.498
BN
7
26.7
16
64ZnCd,2n)64Ga
2.6m
809; 992
0.14;0.46
BN
6
23.9
14
64
63
38.4m
670;962
0.883;0.0695
BN
7
25.8
~ 4
ZnCd,3n+p2n)
Zn
64
61
ZnCd,an)
Cu
3.41h
283;656
0.13; o. 09 6
BN
6
23.9
14
64ZnCd,2a)58Co
71.3d
811
0.994
BN
6
25.8
15
66
66
ZnCd,2n)
Ga
9.4h
834;1039
0.059;0.373
BN
5
25.8
5
66ZnCd,3n)65Gaa)
15.2m
115;153;752
0.532;0.087;0.08
BN
3
25.8
3
66
65
a)
ZnCd,3n+p2n)
Zn
243.8d
1 1 1 6
0.498
BN
3
25.8
5
------------------------------------------------------------------------------------------------
3)Used to correct for the
6~Zn impurity in the 64 Zn target Csee table 2)

---

Reaction
T~
Ey(keV)
I y
Lab.
N
E(MeV)
6E(MeV)
---------------------------------------------------------------------------------------------
89 Y(d,p)m90y
3.19h
203;483
0.965;0.90
BN
8
25.9
15
89 Y(d,2n)g89 zr
78.4h
909
0.99
BN
10
25.9
20
89 Y(d,2n)m89 zr
4.18m
588
0.93
BN
8
25.9
15
89 Y (d,3n)88 zr
85d
393
0.97
BN
5
25.9
6
89 Y(d,p2n)88 y
107d
1836
0.994
BN
4
25.9
6
1
89 y (d, p3n) m87 y
14h
381
0.74
BN
3
25.9
2
89 Y (d,rx)m87 sr
2.8h
388
0.83
BN
8
25.9
15
-----------------------------------------------------------------------------------------------:
93Nb(3He,n)m95TC
61d
204
0.803
BN
1 1
30
21
93Nb(3He,n)g95Tc
20h
766
0.94
BN
10
30
21
1
w
HH
12
42.8
9
,
\\.0
,
1
93Nb(3He,2n)m94TC
52m
871
0.94
HH
15
42.8
9
93Nb(3He,2n)g94Tc
293m
703;850;871
0.998;0.977; 1.0
HH
15
42.8
9
93Nb(3He,3n)m93TC
43.0m
390
0.63
HH
16
42.8
9
93Nb(3He,3n)g93Tc
2.75h
1363;1521
0.67;0.25
HH
13
42.8
9
93Nb(3He,4n)92TC
4.4m
148
0.55
HH
7
42.8
0
Table 1

---

-40-
Target
Thickness
Enrichment
Major Impurities
(mg/cm2 )
(%)
(%)
63Cu
4.95 -
10.37
99.9
65Cu (0.1 )
65Cu
5.41 -
11.14
99.8
63Cu (0.2)
64
66
68
zn
9.54 -
1 1 .18
98.6
Zn(o.8),
Zn(0.5)
66
6 4 ·
68
zn
9.64 - 10.47
96.9
Zn(1.5),
Zn(0.9)
89 y
11 . 10 and 47.14
100
93 Nb
4.62,11.0 and 22.4
>99.9
Ta(0.05), Fe (0.01)
Table 2

---

-41-
Reaction
l(Target)
19 (Res .Nuel.)
lm (Res .Nuel.)
89
-
-
Y (d,P)90y
1/2
2
7+
89
-
-
Y (d,2n)89 zr
1/2
9/2+
1/2
93 Nb (T,n)95Te
9/2+
9/2+
1/2-
93 Nb (T,2n)94 Te
9/2+
7+
(2+)
93
-
Nb (T,3n)93Te
9/2+
9/2+
1/2
Table 3

---

-42-
Figure Captions
Fig. 1
Experimental excitation functions for the 65Cu (3He ,xn)
reactions
(X = 1-4)
and comparison to those of the
literature 114,15\\.
Fig. 2
Measured excitation function for the 93 Nb (3He ,xn)96-x,m,gTI
reactions (x = 2,3) and compar ison wi th the work of
Flach 1101.
Fig. 3
Measured excitation functions for the 63 Cu + 3He
reactions and comparison with the full statistical
model of Uhl 1231 and two Weisskopf-Ewing calculations
/16J using the code OVERLAID ALICE 117J with binding
energies of Myers and Swiatecki /221 and those of
Wapstra and Gove 118]
(see text).
Fig. 4
Comparison of the experimental excitation functions
63Cu + 3He wi th the hybrid model j 24 1 using the code
OVERLAID ALICE 117\\ for the initial exciton numbers
n (p
,p
) indicated.
o
on
op
Fig. 5
Same as fig. 4 for 65Cu + 3He •
Fig. '6
Same as fig.
4 for 93 Nb + 3He . In addition, the predictions
of the geometry dependent hybrid model ~GDH) are shown
as weIl as those of the full statistical model of Uhl J23]
The GDH calculation with pairing for the (3He ,4n) reaction
is explained in 'the texte

---

-43-
Fig.
7
Same as fig.
4 for 89 y + d .
Fig.
8
Comparison of experimental and calculated normalized
yields for n and
(p+n)
emission from the composite
system 66Gl formed in the reactions 64 Zn+d and
63 Cu+3 He .
Fig. 9
Same as fig.
8 for the 2n and (3n+p2n) emissions from
66Ga*. For the 2n process also the prediction of the
Weisskopf-Ewing (WE) model is displayed.
Fig.
10: Same as fig.
8 for the 2n emission from the composite
68
system
Ga*.
Fig.
11: Same as fig.
8 for the
(an)
and
(2a)
emissions from 66 Ga*
For the (an)
process the prediction of the Weisskopf-
Ewing model is given,
too.
Fig.
12: Decay modes of the T<
(thick arrows)
and T>
(thin arrows)
states in 66 Ga* at 30 MeV excitation energy. The
respective isospins of the nuclei involved as well as
the squares of the Clebsch-Gordon coupling coefficients
are indicated. The shaded areas in 65Ga and 65 Zn
correspond to the region of excitation where further
particle decay is prohibited.
Fig.
13: Comparison of the different theoretical predictions for
the double ratio R(E
) = o(3 He ,p)/o(3He ,n): o(d,p)/o(d,l
exc
with the experimental values
(error bars).
The dotted

---

-44-
curve represents the prediction of the compound
nucleus theory with full isospin consecvation. The
thin full curve corresponds to the isospin conserving
PE reaction with symmetric initial exciton numbers
4(2,2)
for the 3He-induced reaction.
The dash-dot,
dash-dash and the thick full curves give the results
of the usual PE model with 3He initial exciton numbers
equal to 4 ( 2,2) ,4 ( 1 . 75, 2. 25)
an;d 4 ( 1 . 5,2.5) ,
respectively.
For the d-induced reaction the initial
configuration 3(1.5,1.5) was kept fixed.
Fig.
14:
Isomer ratios tor 93g,mTc , 94g'ffiTc and 95g'ffiTc produc~ion
in reactions of 3He with 93 Nb . Experimental results:
this work. Calculations: pure EQ mechanism with
a/ aR'
= 1.0 (thin solid line), 0.7 (thick sol id line),
1.g
0.5
(dash-dotted)~ PE competition included with
a/aR'
= 1.0 and the spin distribution of eq. (11)
1.g
(dashed line), or enhanced angular momentum depletion
(dotted).
In the insert,
the corresponding excitation
functions for a
t = a + a
are sho\\'ln,
too.
t o
g
m
Fig.
15:
Same as fig.
11 for 90g,90my and 89g,89mzr production
.
89
89
in reactions of deuterons w1.th
Y. Data for
Y(d,p)
are from
1 291·
Fig .. 16:
Normalized populations of
a)
positive parity states of the initial compound system
3He + 93 Nb for different projectile energies (cf. eq. (7
b)
the same system (for E1ie =43 MeV) after emission of
one neutron with the spin distribution given by eq.
(1

---

-45-
c)
the residual system 94 Tc* after sequential neutron
(and gamma)
emission at E* = 7.5 MeV, i.e. below
the neutron emission threshold
(Sn = 8.6 MeV).

---

-
c
c
("1")
eu
l
. ("1")
+
:J
U
Ln
CD
o
('W')
LI')
: 1
N
o
•
o
N
, .
1
1
.. .
tr
, ,
o
.-
--
,
---. ' .........
.--...-- "............---.............
,...,
N
l!).c
0
o
E
-
-
-'
-

---

,,
1
1
,o
o
Flach
..
• this work
•
10
15
20
25
30

---

63
G
·
CU+ 3He
(3 He,p2n+3n)
[mbJ -
ft 2Experiment
~-+-2.~
- -
Statistical Model
_
( l J
)
_ "
-----AlICE IVJyers
/::::-- _
-......... .... "
102 -' - ALlCE(Wapstra)
,,?
"" ""
'" "
/
" - ' , "
">..;;;
,
~
" ' -
i / / '
l"
"
"
jpJj' !I/'~\\
(3He.2nl
\\~
'.
1,
'\\~
\\
"'-
10 1
I~
.
1Il
'\\~\\.
f'I
"
~-~. ,.
"
l
\\
/
1, '/
il:
\\\\.
3
\\
/,
r-.
~
"\\'\\.
(He,3n)
\\
1/ //1 /. ~:
'~""
/ 1/ i!1 \\'~,l}He.nl
1\\\\, "-
'1
\\
" "
/
' " ' '
ri
.~'
'- !..
..", ." ."'-.
5
10
15
20
2S
30
35
40
Ji
~'
E3
[MeV]
;,J
He

---

tDÊ
......
--,
tD M
M
U
J:
::J
CV
+
-
.N
M
:::r:
M
~
Q)
C
+
a.
N
"
v
.- 0
M
:::r:
N
cv
C -
"
.- 0 -
rt--------.-J
/
/
./
.-
/
/
/
/
/
1
LI)
.- 0
.- LI)
N
o
N
Ln
M
o
M
LI)

---

G
65
3
(mbl
(3 He.3n)
Cu+ He
.--..........
102
'""
101
/
--~~
1
',.'-...
/ ,,#--
Hybri1
""-
~. """1"" "j
-r-
(3 He,4n)
.
.~._
4(2.5.1.5) - -
Experiment
:)1
40.5.2.5) - - --
"
Statistical Madel -
-
5(3.2)
_ . -
v'
u\\
5
la
15
20
25
30
35
40
45
E
[MeVl
3He

---

G f 93
3
[mbl
Nb. He
10'
-
~
1
---
/
" " /
~(3He,n)
-i-i
L.--: ,
" .'\\/ 1 Experimen-t
!\\
- - - Statistical Model
cs--
5
10
15
20
25
30
35
40
45
E
[MeVl
3He

---

Y1d
89
,xnypzal
Id,2nl
_
1000
--r-~
--..rA"..
/~
.-_1..-
~~I--,
1
Exp.
5)-
H brid 3(1.5,1.
y
20.1)----
0.1
15
20
25
Ed (Lab)(MeV)

---

0.1

---

0.01
Hybrid 3(1.5,1.5) --=-
4(1.5,2.5) -
W.E. -----
0.00120
30

---

U)
U) N c :g~..c N -C
.....
..
1
U)
U')
WI
~I
U
:r::
N
::J
cu
C-- ---
to01
.
1
..
~
.0.
:E:
.- "'0
("f)
LnU")
~N Ln _-
,
~
,
'tOt
,
. ..
...:1
Ln
. ..
---_.'
--
~~
..
-
-
-
.--.--
_.-
V
---
---
/
-------------
/
/ / 1 / 1 / / 1

---

- - - ......
-:;..;. -
-.........
;t'/
-.....
....
"
..........
.....
,,/
0.1
"
.....
//
~,
/ /
'
/
:'\\.. '
,Ir.
- L _ '"",
~
B......--I~-:::.2~
"
.~
"t:::-i,
/11
"
) 6 4 Zn(d an)
i
§.".
63Cu (3He,an) ~
5~~
Weisskopf-Ewing ------
Hybrid 3( 1.5 J1.5)
0.01
4(1.5 2.5) - - -
J
. 64 Zn(d,la)
t
Ex.
63Cu(3He,2 a)
~ ;~~:.:.~..
r~:-~7'1~
/
/
/
--
/
0.001
f
// ~
/
~/
1
20
30 .66
Eexc\\- Ga)(MeV)

---

('1')
0
1
~~~"":::::"""------r----------'
i....-____
~ ~
N~
N
0
1
Ln
<D
~I
~
1
1
1
~ + c:
cuL>
tg
~
-
~I
1
1
1
- 0 -CD (J ~ + ~ + c:
1
CD N U ~ + tS
0
~
CD CDC!J
cs

---

---

W.Q
~ l
· Il 1· Il 1. Il
1
1
1
f 1 1
5.9
, i 1 ; 1 ~ 1
~I
.........-;
-."--1
1
OqDJ
g o o
JawosI
H1:-i \\
~
(qwl
1
, ,
i !
\\'.
'1
1 1
u.v.
1
1
:
•
.
i
1
m (")
C"'!-
0'
(")
zzZ
•
I~
.0.0.0
•
:
0
0
0
If
...
-î~::I: MNC -C ~
1I~
0
i
0
'9!,
/~
0
0
..
/
..
/~
mm,... M
t",L
m
:
--3
/
...g..
-0'
•
c-
~r
" . .
..
M
t",L
LI')
!?}
og
Q)~
u
ô
o
M o
~>-
- .Do
lJJ
QI
QI
C
QI "- al
.., X 4J

---

1000
-.D
E
20
~~
'-
~
.......
.
t::
.. ~... . ;t-~~~
±
.
•.4r...
·:··I······..11.
.'
.'
..' .' /
o
, ....····:V·
89
/ '/'~..
.'
0
~.,
y (d p)90
J
y
t -:(';:::::::".
• 89y (d, 2n 189Zr
L-
2
<1J
E
o
tIl
.........
(d. P )
l
~
10
15
20
25
.
Projectl ,e en erg y
E ' ab (M eV)
d

---

1
1
1
1
1
f
1
015
•
E l :
13 MeV
....
o
31 MeV
•
t.3 MeV
010
0.05
-
a 0
-
5
10
15
25·
Spin l of compound nucleus
Q..
- 0.10
-
/~
Q..
~~.
/
\\
c
".
o
-o
/'
005
/
\\\\
:J
.
0-
o
0-
! ..
".
/
~ "'.
C
:/
~.
0-
1/)
00
5
lO
15
20
25
Q)
Spin l of residual nucleus 95Tc·(U=14 MeV)
>
-oQ)
0::

---