Recoil ranges of products from reactions copper 65 with 11-35 MeV helium 3 ion

Porile, N. T.

Saha, G. B.

English

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G. B. Saba t and I. T. Por i le  
Department of Chemistry, Furdue University, h f a y e t t c ,  LadLaoa 
Abstract 
' i \ ' j  ' ' 
J 
Atrpnge p~9joct.d tango8 bvc been dctcrmiacd far the (flCS,n), 
(ea), and (&=,a) reactions of cue5 over th energy range of 11-33 L ~ V .  
T& r e s u l t s  have been compared w i t h  calculat ions based on the assuaptioa 
of compound nucleus formation. 
(€k3,2n) react ion a t  a l l  energies and for  t h e  (kg,n) react ion up to  
17 &v. 
a t  a l l  energies indicat ing that t h e  (&',a) react ion involves a d i r e c t  
interaction. 
Excellent agreesent is obtained f o r  the 
The ranges of CU- are D N C ~  smaller than the  theo re t i ca l  values -.c 
https://ntrs.nasa.gov/search.jsp?R=19660022084 2020-03-16T20:40:07+00:00Z
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I. Introduction 
In a recent  report' w e  presented the  r e s u l t s  of a r e c o i l  study of 
severa l  react ions of Cues w i t h  medium-energy He4 ions. 
of a 'detenninat ion of t he  average projected ranges of the  product nuclei. 
The recoil ranges are d i r e c t l y  re la ted to the momentum t ransferred to 
the ~triit's; iiiicle-us by the incidenr particle. 
in turn,  a sens i t i ve  probe of the reac t ion  mechanism, 
compound nuclear process the p ro jec t i l e  thus t r ans fe r s  its e n t i r e  momentum 
to the compound nucleus. 
symmetric about 90" in the center-of-mass system and has a relatively 
minor e f f e c t  on the recoil range. 
ac t ion  the momentum brought in by the  p r o j e c t i l e  is t o  a la rge  extent 
immediately removed by the  p r e d d n a n t l y  forward emission of particles. 
The recoil range of the product w i l l  therefore  be considerably smaller 
than in the case of compound nucleus formation. 
This study consisted 
The momentum t r ans fe r  is, 
In the case of a 
The subaequent evaporation of particles is 
On the o ther  hand, i n  a d i r e c t  i n t e r -  
1 In our earlier work w e  found that the ranges of the (a,n), (a,&), 
and (a,3n) reac t ion  products indicated the  predominant occurrence of 
compound nucleus formation a t  a l l  energies studied, i.e. up t o  43 MeV. 
On the  other  hand, the ranges of Cum indicated a s izeable  contr ibut ion 
of a d i r e c t  process t o  the (a,ah) reac t ion  above 30 HCV. 
The present work concerns a s imilar  study of the react ions of Cues 
with  He3 ions. 
the  r e l a t i v e  importance of d i r e c t  and compound nuclear mechanisms €or 
these two projec t i les .  We report  r e s u l t s  for the (iie3,n), (Iie3,2n), 
and (&',a) reac t ions  f o r  incident energies of 11-33 MeV. 
Comparison with the Be4 r e c o i l  studies should ind ica te  
The excitation 
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functions of some of these reactions have previously been determined by 
Bryant e t  al. 
s t a t i s t i c a l  model calculations.  Recoil measurements a r e  more sens i t i ve  
t o  d i r e c t  interact ion admixtures anJ t h e  present work shows a s ign i f i can t  
contribution of t h i s  process to some of the above reactions. 
2 These authors obtained qua l i t a t ive  agreement w i t h  
XI. FJltperimental Procedure and Results 
The experimental procedures a re  s i m i l a r  t o  those given in our previous 
report '  and only a b r i e f  suannary w i l l  be given here, The t a rge ts  consisted 
in most cases of self-supporting f o i l s  of highly enriched copper-@ 3 , 
4-6 dcm2 in thickness, 
composition (1.8 mg/cm2 thick) were a l s o  employed, 
f o i l s  consisted of 0.001 inch thick alumiaum f o i l s  of high pu r i ty  (99.m). 
It was previously established that the  contribution t o  the observed 
a c t i v i t y  of impurit ies i n  the aluminum was negligible.  
usua l ly  consisted of 5 t o  10 target  and catcher f o i l s  together with 
appropriate degrader fo i l s .  
Bicheel e t  a1 for protons w a s  used t o  determine the  bombarding energy 
a t  any given posi t ion in the stack. 
I n  some instances f o i l s  of natura l  i so topic  
The forward catcher 
The target stacks 
A range energy r e l a t ion  based on that of 
4 
I r r ad ia t ions  were performed with the &"-ion beam of the  &-inch 
The i r r ad ia t ion  conditions 
1 
cyclotron a t  Argome National Laboratory. 
were similar t o  those described previously. 
and gallium were radiochemically separated from the various samples. 
a c t i v i t y  measurements were performed w i t h  s c i n t i l l a t i o n  and y-y coincidence 
spectrometers. 
After bombardment copper 
The 
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. !  
c 
The present type of experiment permits  the determination of the 
project ion a1oni-j the bean direct ion of the  average range of the product 
i n  t h e  t a rge t  material. This quantity is given a s  
R p = W  (1) 
w h e r e  F is the f rac t ion  of t h e  t o t a l  a c t i v i t y  of t he  product found i n  
the  forward catcher f o i l  and W i s  the t a rge t  thickness. 
that a l l  of the recoi l ing products are emitted a t  a n  angle of less than 
90" with respect  t o  the beam direction. 
react ions i n  most cases insure that this condition is met .  
asstums tha t  the formation cross sect ion fo r  t h e  nuclide of i n t e r e s t  is 
constant throughout the target.  
having s teep  exc i t a t ion  functions and corrections f o r  t h i s  e f f e c t  were 
f i r s t  considered by Porile. 516 I n  the present study t h i s  correct ion amounted 
t o  l e s s  than 3 percent and was neglected. 
It is here assumed 
The kinetmatics of low-energy 
Eq. (1) a l s o  
This is of ten  not the case f o r  react ions 
Average projected ranges for  the (Eie3,n), (Ik3,2n), and (&",a) 
react ions have been measured over t h e  energy range of 11-33 MeV. 
r e s u l t s  a r e  summarized i n  Table I and plot ted as a function of bombarding 
energy i n  Figure 1. 
includes t h e  uncer ta in t ies  in the  d is in tegra t ion  r a t e  and chemical yield 
determinations a s  w e l l  as the  e f f ec t  of non-uniformity i n  the t a rge t  
thickness. 
t h i s  estimate. 
The 
The estimated experimental e r r o r  of 15-20 percent 
The scatter of the experimental points  is consis tent  with 
The ranges of the various reaction products a r e  seen t o  exhib i t  
d i f f e r ing  trends w i t h  bombarding energy. 
react ion t h e  ranges increase monotonically w i t h  energy indicat ing an 
I n  the case of the (€k3,2n) 
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increasing momentum t r ans fe r  to t h e  s t ruck  nucleus. The ranges of Ga67, 
formed i n  the  (He3,n) reaction, approach a constant value a t  an  incident  
energy of about 17 MeV. 
reac t ion  a t  the higher energies. 
Evidently a d i r e c t  process contr ibutes  to the 
The ranges of Cu- have a rather complicated energy dependence. I n  
crder to obtain fur ther  information about t h i s  reac t ion  its exc i t a t ion  
function w a s  measured. The r e su l t s  are shown i n  Figure 2. 
cko 
from d i f f e r e n t  reac t ion  paths. 
react ion,  whose Q-value is positive, to  be t h e  pr inc ipa l  contributor t o  the  
formation of Cum. T b  Q-values of the (He3,Ee3n) and (He3,2p2n) reac t ions  
are -9.9 and -17.6 MeV respectively. One o r  both of these reac t ions  appear 
The breadth of 
and the possible occ~rence of a minimum suggest a contribution 
A t  low energies  w e  expect t he  (&',CY) 
t o  make a s ign i f i can t  contribution t o  the Cue4 formation cross sec t ion  a t  
t h e  higher energies. 
111. Discussion 
The measured r e c o i l  ranges may be compared with a ca lcu la t ion  based 
on the  assumption of compound nucleus formation. 
used i n  our previous work.' 
We follow the  approach 
The momentum of the  compound nucleus is modified 
by the  evaporation of particles, This e f f e c t  is  determined by an  adaptation 7Y8 
of the  Monte Carlo evaporation code by Dostrovsky et al .9 At t he  end of 
t he  evaporation chain the  product nucleus has a ce r t a in  k i n e t i c  energy and 
is moving i n  a pa r t i cu la r  d i rec t ion  with respect t o  t h e  beem. 
the range-energy r e l a t i o n  of Lindhard et at" permits t he  conversion of 
The use of 
k i n e t i c  energy t o  r e c o i l  range and pro jec t ion  of t h e  lat ter along the b e a m  
a x i s  gives  the  value of %. 
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. 
One thousand I t e ra t ions  were performed a t  a given bombarding energy 
and the  r e su l t i ng  Rp values for each product were averaged fo r  comparison 
with experiment. 
w a s  chosen as 5 = A/20 and the  nucldar rad ius  parameter as  ro = 1.5f. 
As i n  our previous calculat ion,  the level dens i ty  parameter 
The results of the calculat ion are given by the so l id  l i n e s  i n  
Figure 1. 
produced by the  (He3+) reaction. 
peaks a t  a bombarding energy of about 16 MeV. 
process remains the dominant mechanism fo r  t h i s  reac t ion  a t  least 16 MeV 
beyond the  peak energy. 
Blann" i n  the  case of the  Fefs(lQe3,2n) reaction. 
Excellent agreement with experiment is obtained f o r  Gam, 
2 The exc i t a t ion  function f o r  t h i s  reac t ion  
Evidently, a compound nuclear 
A similar conclusion was reached by Haean and 
The calculated ranges fo r  Ga67 are i n  very good agreement with the 
experimental values up t o  a bombarding energy of 17 MeV but are s ign i f i can t ly  
la rger  than t h e  latter above t h i s  energy. A look a t  the exc i t a t ion  function 
f o r  t h e  (&=,XI) reaction' indicates  t h a t  t h i s  discrepancy sets i n  only 
4 MeV beyond the  peak energy. 
Cues(a,n) reaction' remain i n  agreement with t h e  campound nucleus ca lcu la t ion  
fo r  a t  l e a s t  18 MeV beyond the corresponding peak energy. 
between the two p r o j e c t i l e s  is suggestive of a s t r ipp ing  mechanism f o r  the  
(He9,n) reac t ion  a t  the higher energies. 
p a r t i c l e  is obviously much less susceptible t o  s t r ipping.  The experimental 
r e s u l t s  above 17 MeV are consis tent  with an average neutron emission angle 
of approximately 55 degrees on the  assumption that t h e  r e s idua l  nucleus is 
le f t  i n  a law-lying s t a t e .  
By contrast ,  the  r e c o i l  ranges for  the  
This difference 
The mre t i g h t l y  bound alpha 
This value appears t o  be s o m e w h a t  l a rge r  than 
expected f o r  a pure s t r ipp ing  process and may indica te  an admixture of a 
compound nuclear mechanism even a t  the  higher energies. 
c -7- 
The theore t ica l  range curve for Cue* predicts  much larger  values than 
a re  obtained experimentally. 
a t  about 23 MeV is due t o  the change from a (Ee3,a) t o  8 (&e3,2p2n) 
reaction. 
function shows two branches ascribable t o  the above reactions. 
i n  mechanism leads to a decrease in the predicted range both because of 
the  inherently larger  r e c o i l  associated w i t h  the emission of a single heavy 
p a r t i c l e  as opposed t o  four l i g h t  pa r t i c l e s  and of the  sudden decrease 
in t h e  k ine t i c  energy of the evaporated par t ic les .  
The decrease i n  the  calculated ranges observed 
This is c lear ly  seen in Figure 2 where the calculated exc i ta t ion  
This cbange 
The decrease i n  the experimental ranges from values that approach the 
calculated ones a t  low energies reveals an increasing contribution of a 
d i r e c t  process, presunnrbly pickup, to the  (&',a) reaction. 
of the range expected according t o  t h i s  mechanism reveals, i n  fac t ,  that  
r e c o i l  should occur i n  the backward direct ion.  
d i s t r ibu t ion  measurements of t h e  Cue* r eco i l s  a r e  current ly  i n  progress. 
The increase in the measured r eco i l  ranges observed above approximately 26 MeV 
implies an increasing momentum t ransfer  t o  the s t ruckpucleus.  
reasonable t o  a t t r i b u t e  t h i s  increase t o  the  (Ee3,2p2n) reaction, a s  is 
a l s o  suggested by the measured exc i ta t ion  function. 
ranges remain much smaller t h a n  tbe values expected for compound nucleus 
formation probably ind ica tes  t h a t  t he re  is s t i l l  a s igni f icant  contribution 
f ran  the (Ee3,a) react ion a t  the  highest energies studied. 
A calculat ion 
Confirmatory angular 
12 
It is 
The f a c t  that  t h e  
The cooperation of Mr. M. O s e l k a  and the crew of the Argonne &-inch 
cyclotron is appreciated. 
1 '  
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Table I 
Experimental Average Projected Ranges 
Bombarding q m g / c m z )  
Gam Ga- Cue4 
Energy (MeV) 
32.6 
30.8 
28.5 
rj. 5 
25.3 
22.3 
20.0 
18.2 
17.3 
16.2 
14.5 
14.0 
11.3 
.150* 
196 
.149* 
.13W 
.168 
.142* 
.I42 
.14W 
.151* 
.118* 
. l30 
.11g* 
.046 
237* 
253 
.227* 
.a* 
.250 
-191~ 
. la3 
.174* 
.145* 
.123* 
.121 
.123* 
029 
* Enriched Cues target. 
I 
? 
t . 
*9- 
Figures 
Figure 1 - Energy dependence of the average projected ranges. 
The so l id  curves are  the result of a calculation 
assuming compound nucleus formation. 
Figure 2 - Excitation function of the (Hes,a) reaction. 
The s o l i d  curve is  drawn through the experimental 
points. The dashed curve i s  the resu l t  of a 
sta t i s t i c a  1 theory calculation. 
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References 
1. G. 3. Saha and N. T. Pori le ,  submitted to Phys. Rev. 
2. 
3* 
4. 
5. 
6. 
7. 
a. 
E. A. Bryant, D.R.F. Cochran, and J. D. Knight, Phys. Rev. z, 
1512 (1963). 
Obtained from Oak Ridge National Laboratory. 
8. Bichsel, R. F. Mozley, and W. A. Aron, Phys. Rev, x, 1788 (1957). 
H. T. Pori le ,  Phys. Rev. - 127, 224 (1962). 
N. T. Por i le ,  Phys. Rev. w, A l l 1 5  (1964). 
N, T. Por i le  and S. Tanaka, Phys. Rev. m, B122 (1964). 
N. T. Pori le ,  Phys. Rev. 134, B371 (1964). 
9. I. Dostravsky, Z. Fraenkel, and G. Friedlander, Phys. Rev. s, 
683 (1959)- 
10. J. Listdbard, M, Scharff, and E. E. Schiot t ,  Kgl .  Danske Videnskab. 
Selskab, Hat,  Fys. Hedd., E, No. 14 (1963)- 
J. P. fleean and M. BlaM, Phys. Rev. x, B1202 (1965). 
I. Fujiuara and N. T. P o r i l e  ( t o  be published). 
11. 
12. 


Recoil Ranges of Products from Reactions of Cu65 with 11-33 Mev He3 Ions

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