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Competition between exit channels leading to the same residual nucleus in heavy-ion reactions
Volume 90B, number 3
PHYSICSLETTERS
25 February 1980
COMPETITION BETWEEN EXIT CHANNELS LEADING TO THE SAME RESIDUAL NUCLEUS IN HEAVY-ION REACTIONS A.C. XENOULIS, E.N. GAZIS, P. KAKANIS and D. BUCURESCU 1 Tandem Accelerator Laboratory, NRC Demokritos, Athens, Greece
and A.D. PANAGIOTOU Nuclear Physics Laboratory, University of A thens, Greece
Received 26 November 1979
Competition between pn and d as well as between p2n, dn and t emission in the production of individual residual states has been observed in nuclear reactions induced by 160 on 12C and 13C targets. The experimental relative yields for the production of the 417 keV state in 26A1by pn and d emission, measured as a function of bombarding energy in the reaction 12C(16O, pn/d)26AI, are successfullydescribed by Hauser-Feshbach calculations.
Much effort has been devoted in recent years to cross-section measurements in heavy-ion nuclear reactions and comparison with theoretical predictions. An aspect, however, the significance of which has not been fully investigated is the possibility that in a nuclear reaction the same residual nucleus may be produced by different exit channels. For instance, in the bombardment of 13C with 160 the 26A1 nucleus may be formed by p2n, dn and/or t emission. In such cases, although the entrance channel is the same, the exit channels competing for the production of the same residual nucleus are distinctly different reaction modes, demanding appropriate treatment for either their theoretical description or their experimental identification. The presence and effect, however, of such exit channels cannot be distinguished by the usual methods of cross-section measurements, such as detection of single 3' rays or recoiling heavy ions. These, instead, provide the sum of the cross sections of all the channels participating in the production of a specific residual nucleus. Evidence about the predominance of pn over d emission in the production of 24Mg has been previously ob1 Permanent address: Institute for Physics and Nuclear Engineering, Bucharest, Rumania. 224
tained by Olmer et al. [1 ] by comparing deuteron yields with the intensities of 7-ray transitions in 24Mg observed in the bombardment of 12C by 14N. We are not aware of previous results concerning competition between p2n, dn and t emission. In the present study light charged particle-gamma coincidence techniques were utilized in order to directly observe competition between exit channels producing an individual residual state. The discrete coincident 3' rays were used to identify the heavy residual nucleus. Thin, 50/~g/cm 2, targets of 12C and 13C,deposited on Au backing sufficiently thick to stop the heavy-ion beam, were bombarded with 24 MeV to 38 MeV 160 beams supplied by the NRC Demokritos Tandem Accelerator. For particle detection a A E - E counter telescope of silicon detectors of various thicknesses was used in a semicircular scattering chamber. The 3' rays were observed with an 18% Ge(Li) detector with the axis in the reaction plane at 90 ° with respect to the beam, at a distance of 2 cm from the target. Particle identification with pile-up rejection, and fast-coincidence circuitry for particle-3' coincidence were employed. The raw data were stored event by event on magnetic tape by an on-line PDP-11/15 computer. We first present the results of 12C(160,pn/d)26Al*(3')
Volume 90B, number 3
PHYSICS LETTERS
coincidence measurements with the help of which we shall discuss the essential features o f the technique. The mass spectrum of particles in coincidence with all "y rays, as well as the lower energy part of ~/-ray spectra in coincidence with protons or deuterons, are shown in fig. 1. The main discrete 3'-ray transitions observed, 417 keV and 440 keV, are associated with the 26A1 + pn (or d) and 23Na + p e exit channels, respectively. The 417 keV transition appears in coincidence with both proton and deuteron groups, indicating that the corresponding 417 keV state in 26A1 is in fact produced by pn and d emission. Considering these data quantitatively we note that, due to the simultaneous detection, under the same
160 2C. EtA¢ 35 MeV PROTONS
i
i
1~
i
ALPHAS I
UTEIIONS
10
":~:2-"
Z % 2OO
U
it
loo
L
'
2;o
3oo
proton -y
100
J/5 lJl
.-?
deuteron - y
25 February 1980
geometry, of protons and deuterons in coincidence with a specific 3' ray, the detection efficiency for P - 7 1 and d - 7 1 coincidence is identical. Furthermore, since neutrons are not detected, the p - 7 coincidences correspond to pn events integrated over all angles o f neutron emission. Taking these into account and also assuming that particle- 7 angular correlation effects are negligible, it can be shown that the ratio of the intensity o f a discrete 3' ray in coincidence with protons over the intensity of the same "), ray in coincidence with deuterons equals the relative differential yields or the ratio o f differential cross sections for producing the corresponding residual state by pn and d emission, for a given angle of particle detection• Particle-7-ray angular correlation effects should have been washed out in the present measurements due to the large solid angle o f the 7-ray detector. Furthermore, the technique takes into account all reaction events populating by side feeding or prompt "),-ray cascade the residual state. This cascade further reduces any particle-7 correlation effects, especially when a low-lying state is studied. In order to obtain a ratio o f angle-integrated cross sections, the angular distribution of the ratio (dopn/ dl2)/(dod/dI2 ) was measured as a function of the charged particle angle. The particle telescope subtended a total solid angle o f 35 msr. It was found that, although the individual relative differential cross sections for pn and d emission were forward peaked, their ratio remained approximately constant throughout the measured angular range o f 5 0 - 6 0 ° . Relevant data associated with the production o f the 417 keV state in 26A1 are shown in fig. 2. According to the above, the competition ratio measured at any angle of particle emission represents the ratio o f integrated cross sections for pn and d exit channels. The excitation function o f the ratio Opn/Od for the production of the 417 keV state is shown in fig. 3,
~
2O
G[ J-
I
10
• 0
i
0
[
....
I. . . .
100
0L
:-;-i:.:-:-: *. . . . .
.
....
; ....
1"-
0° - -
....
200 300 C H A N N E L B
Fig. 1. Particle-gamma coincidence spectra obtained in the bombardment of 12C with 160.
~2C(160, pn/d ) 2eAI . , ~ ~ . E~,,.= 30 H e Y ....
I °
10
t
20.
I
30*
I
40o
l
I
50*
60*
~LAB Fig. 2. Differential relative yield for the population of the 417 keV state in 26A1by pn and d exit channels as a function of the angle of charged particle emission. 225
Volume 90B, number 3
PHYSICS LETTERS
,60'(r+C,pn/cl)26A' t
'
~.-""
'
'
+(b'L J
(a)
I""
_
-
rr
o I
25 February 1980
Table 1 Results of Hauser-Feshbach calculation for the reaction 12C(160, pn/d)26A1 at Elab = 28 MeV. ofus State (mb) (keY)
Opn Onp od (rob) (rob) (rob)
R = O(pn+np)/O d
g.s. 228 584 417 1058 26Al(total)
35.30 65.67 16.37 3.34 1.53 5.34 9.30 6 . 5 9 7.78 1.29 0.68 3.58 38.64 67.20 21.71
6.17 0.91 2.04 0.55 4.88
I
Elab (MeV)
Fig. 3. Experimental relative yield for the population of the 417 keV state in 26A1 by pn and d exit channels as a function of bombarding energy, compared with Hauser-Feshbach predictions (full line). The broken fines demonstrate the energy dependence of the ratio of cross sections for the total production of 26A1 by pn and d emission as calculated by the HauserFeshbach code STAPRE (a) and the statistical code ALICE (b).
where a dependence of the competition on the bombarding energy is demonstrated. The error bars represent the statistical uncertainties introduced by the analysis of the coincidence photopeaks. In order to obtain a theoretical estimate of competition in the reaction 12C (16 O, pn/d)26A1, the cross sections for (pn +np) and d emissions were calculated, as a function of bombarding energy, in the framework of the Hauser-Feshbach theory, using the code STAPRE [2]. In these calculations the contribution from the emission of light particles (p, n, d and a) and 3' rays has been taken into account for each sequence of the reaction in populating specific residual states. Previously known [3] excited states were explicitly considered in the calculations. For the density of the rest of the level the back-shifted Fermi gas model [4] was used with level density parameters adopted from refs. [5-7]. The optical model parameters were taken from refs. [8] and [9]. Theoretical results for some individual states as well as the total production of 26A1 at 28.0 MeV laboratory bombarding energy are sampled in table 1. The cross section for the total population of 26A1 equals the sum of the cross sections for the production of the ground (5 +) and the 228 keV (0 +) isomeric states. The fusion cross sections obtained in the present calculations agree reasonably well with reported experimental values [10]. It should be noted that the theoretical results suggest that the pn/d competition de226
pends on the nature of the residual state (see table 1). The theoretical Opn/Od ratio for the production of the 417 keV state is compared with the experimental values in fig. 3, where it can be seen that a satisfactory agreement is obtained. In the same figure, although not corresponding to the experimental quantities, we considered it interesting to demonstrate the theoretical pn over d competition in the total production of 26 A1 as obtained by STAPRE and the statistical model code ALICE [11 ]. As ALICE does not distinguish between pn and d emission, the d channel was estimated by subtracting the cross sections calculated with and without d emission. As seen in fig. 3, ALICE strongly underestimates the relative d contribution in comparison with the HauserFeshbach results. Competition between exit channels leading to the same nucleus was also observed in the nuclear reactions induced by 160 and 13C in the energy range between 24.5 and 32.0 MeV. Coincidence spectra at 27.0 MeV bombardment energy are shown in fig. 4. These data demonstrate that at 27.0 MeV the 417 keV state in 26A1 is exclusively produced by t emission. At 32.0 MeV, however, it was found that the p2n, dn and t exit channels significantly participate in the production of this state, with relative yields 29 -+4, 32 + 4 and 39 + 5%, respectively. The 1058 keV state of the same residual nucleus is also almost exclusively produced by t emission, as evidenced by the behaviour of the corresponding 830 keV deexciting 3' ray. In these spectra it can also be observed that both pn and d exit channels contribute to the production of the 1014 keV state in 27 A1, with pn/d yield ratio values varying between 7.6 + 1.1 and 8.4+ 1.2 at 24.5 and 32.0 MeV bombardment, respectively. Finally, it is observed that the 844 keV state in 27A1 is predominantly produced by pn emission.
Volume 90B, number 3
PHYSICS LETTERS
"C,
'60 + r
I
I
A. C O.
g 20(
proton-
the total counts of the energy spectra of particles in coincidence with a specific 3' ray. This process was used in order to assess the effect of low-energy detector cut-offs. Specifically, the pn/d relative yields were obtained from the integrated counts of the p and d coincident energy spectra after the particle spectra were extrapolated to zero energy. The extrapolation can be applied primarily to the p spectra, which show a continuous energy distribution due to the sharing of energy between the two particles of pn exit channel. The effect of low-energy cut-offs was also investigated by using AE detectors of various thicknesses, between 25 #m and 150/am. The corresponding cross-section ratio values, obtained under various conditions of measurement or analysis, were overlapping within the experimental error for bombarding energies higher by a few MeV than the thresholds for the competing channels considered. The experimental results presented here, as well as additional preliminary ones, related to a series of other nuclear reactions, suggest that competition between exit channels leading to the same residual nucleus bears a significant role in heavy-ion reactions. The double and triple competition was found to depend on the bombarding energy and the target-projectile combination. In fact, the pn/d cross-section ratio was observed to progressively increase with increasing neutron numbers of target or projectile. The data, furthermore, do not overrule the possibility that this competition may be related to structural characteristics. It is finally concluded that the explicit consideration of d and t emission in cross-section calculations should be important for a proper comparison with experimental results.
=27MeV I
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15C
10C
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deuteron - "f
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2C . . . . . . .
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25 February 1980
,
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.
.
~-.'. . ..!!.-I ..-_- - i n - -~" :.~-'-.:':.:-.:. [" .....
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; ---'l----'r-
300
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This work was supported in part by a grant from the National Research Foundation of Greece. The assistance o f Dr. V. Agrigeanu with the calculations and a critical reading o f the manuscript by Dr. A. Katsanos are gratefully acknowledged.
--"
500
C H A N N E L S
Fig. 4. Particle-gamma coincidence spectra obtained in the bombardment of 13C with 160.
It should be pointed out that the competition studied here, instead of using the coincidence intensities o f a discrete ~,-ray, can be equivalently extracted by using
References
[1] C. Olmer et al., Phys. Rev. C10 (1974) 1722. [2] M. Uhl, Acta Phys. Austriaea 31 (1970) 245. [3] P.M. Endt and C. Van tier Leun, Nucl. Phys. A310 (1978) 1. [4] H. Vonach and M. Hille, Nucl. Phys. A127 (1969) 289. [5] R.A. Dayvas, R.G. Stokstad, Z.E. Switkowski and R.U. Wieland, Nucl. Phys. A261 (1976) 478. 227
Volume 90B, number 3
PHYSICS LETTERS
[6] Z.E. Switkowski, R.G. Stokstad and R.M. Wieland, Nucl. Phys. A274 (1976) 202. [7] H.C. Cheung, M.D. High and B. Cujec, Nucl. Phys. A296 (1978) 333. [8] Y.D. Chan et al., Nucl. Phys. A303 (1978) 500. v
228
25 February 1980
[9] C.M. Perey and F.G. Perey, Nucl. Data Tables 13 (1974) 293. [101 Y. Eyal, M. Beckerman, R. Checkik, Z. Fraenkel and H. Stocker, Phys. Rev. C13 (1976) 1527. [11] M. Blann and F. Plasil, Phys. Rev. C l l (1975) 508.
PHYSICSLETTERS
25 February 1980
COMPETITION BETWEEN EXIT CHANNELS LEADING TO THE SAME RESIDUAL NUCLEUS IN HEAVY-ION REACTIONS A.C. XENOULIS, E.N. GAZIS, P. KAKANIS and D. BUCURESCU 1 Tandem Accelerator Laboratory, NRC Demokritos, Athens, Greece
and A.D. PANAGIOTOU Nuclear Physics Laboratory, University of A thens, Greece
Received 26 November 1979
Competition between pn and d as well as between p2n, dn and t emission in the production of individual residual states has been observed in nuclear reactions induced by 160 on 12C and 13C targets. The experimental relative yields for the production of the 417 keV state in 26A1by pn and d emission, measured as a function of bombarding energy in the reaction 12C(16O, pn/d)26AI, are successfullydescribed by Hauser-Feshbach calculations.
Much effort has been devoted in recent years to cross-section measurements in heavy-ion nuclear reactions and comparison with theoretical predictions. An aspect, however, the significance of which has not been fully investigated is the possibility that in a nuclear reaction the same residual nucleus may be produced by different exit channels. For instance, in the bombardment of 13C with 160 the 26A1 nucleus may be formed by p2n, dn and/or t emission. In such cases, although the entrance channel is the same, the exit channels competing for the production of the same residual nucleus are distinctly different reaction modes, demanding appropriate treatment for either their theoretical description or their experimental identification. The presence and effect, however, of such exit channels cannot be distinguished by the usual methods of cross-section measurements, such as detection of single 3' rays or recoiling heavy ions. These, instead, provide the sum of the cross sections of all the channels participating in the production of a specific residual nucleus. Evidence about the predominance of pn over d emission in the production of 24Mg has been previously ob1 Permanent address: Institute for Physics and Nuclear Engineering, Bucharest, Rumania. 224
tained by Olmer et al. [1 ] by comparing deuteron yields with the intensities of 7-ray transitions in 24Mg observed in the bombardment of 12C by 14N. We are not aware of previous results concerning competition between p2n, dn and t emission. In the present study light charged particle-gamma coincidence techniques were utilized in order to directly observe competition between exit channels producing an individual residual state. The discrete coincident 3' rays were used to identify the heavy residual nucleus. Thin, 50/~g/cm 2, targets of 12C and 13C,deposited on Au backing sufficiently thick to stop the heavy-ion beam, were bombarded with 24 MeV to 38 MeV 160 beams supplied by the NRC Demokritos Tandem Accelerator. For particle detection a A E - E counter telescope of silicon detectors of various thicknesses was used in a semicircular scattering chamber. The 3' rays were observed with an 18% Ge(Li) detector with the axis in the reaction plane at 90 ° with respect to the beam, at a distance of 2 cm from the target. Particle identification with pile-up rejection, and fast-coincidence circuitry for particle-3' coincidence were employed. The raw data were stored event by event on magnetic tape by an on-line PDP-11/15 computer. We first present the results of 12C(160,pn/d)26Al*(3')
Volume 90B, number 3
PHYSICS LETTERS
coincidence measurements with the help of which we shall discuss the essential features o f the technique. The mass spectrum of particles in coincidence with all "y rays, as well as the lower energy part of ~/-ray spectra in coincidence with protons or deuterons, are shown in fig. 1. The main discrete 3'-ray transitions observed, 417 keV and 440 keV, are associated with the 26A1 + pn (or d) and 23Na + p e exit channels, respectively. The 417 keV transition appears in coincidence with both proton and deuteron groups, indicating that the corresponding 417 keV state in 26A1 is in fact produced by pn and d emission. Considering these data quantitatively we note that, due to the simultaneous detection, under the same
160 2C. EtA¢ 35 MeV PROTONS
i
i
1~
i
ALPHAS I
UTEIIONS
10
":~:2-"
Z % 2OO
U
it
loo
L
'
2;o
3oo
proton -y
100
J/5 lJl
.-?
deuteron - y
25 February 1980
geometry, of protons and deuterons in coincidence with a specific 3' ray, the detection efficiency for P - 7 1 and d - 7 1 coincidence is identical. Furthermore, since neutrons are not detected, the p - 7 coincidences correspond to pn events integrated over all angles o f neutron emission. Taking these into account and also assuming that particle- 7 angular correlation effects are negligible, it can be shown that the ratio of the intensity o f a discrete 3' ray in coincidence with protons over the intensity of the same "), ray in coincidence with deuterons equals the relative differential yields or the ratio o f differential cross sections for producing the corresponding residual state by pn and d emission, for a given angle of particle detection• Particle-7-ray angular correlation effects should have been washed out in the present measurements due to the large solid angle o f the 7-ray detector. Furthermore, the technique takes into account all reaction events populating by side feeding or prompt "),-ray cascade the residual state. This cascade further reduces any particle-7 correlation effects, especially when a low-lying state is studied. In order to obtain a ratio o f angle-integrated cross sections, the angular distribution of the ratio (dopn/ dl2)/(dod/dI2 ) was measured as a function of the charged particle angle. The particle telescope subtended a total solid angle o f 35 msr. It was found that, although the individual relative differential cross sections for pn and d emission were forward peaked, their ratio remained approximately constant throughout the measured angular range o f 5 0 - 6 0 ° . Relevant data associated with the production o f the 417 keV state in 26A1 are shown in fig. 2. According to the above, the competition ratio measured at any angle of particle emission represents the ratio o f integrated cross sections for pn and d exit channels. The excitation function o f the ratio Opn/Od for the production of the 417 keV state is shown in fig. 3,
~
2O
G[ J-
I
10
• 0
i
0
[
....
I. . . .
100
0L
:-;-i:.:-:-: *. . . . .
.
....
; ....
1"-
0° - -
....
200 300 C H A N N E L B
Fig. 1. Particle-gamma coincidence spectra obtained in the bombardment of 12C with 160.
~2C(160, pn/d ) 2eAI . , ~ ~ . E~,,.= 30 H e Y ....
I °
10
t
20.
I
30*
I
40o
l
I
50*
60*
~LAB Fig. 2. Differential relative yield for the population of the 417 keV state in 26A1by pn and d exit channels as a function of the angle of charged particle emission. 225
Volume 90B, number 3
PHYSICS LETTERS
,60'(r+C,pn/cl)26A' t
'
~.-""
'
'
+(b'L J
(a)
I""
_
-
rr
o I
25 February 1980
Table 1 Results of Hauser-Feshbach calculation for the reaction 12C(160, pn/d)26A1 at Elab = 28 MeV. ofus State (mb) (keY)
Opn Onp od (rob) (rob) (rob)
R = O(pn+np)/O d
g.s. 228 584 417 1058 26Al(total)
35.30 65.67 16.37 3.34 1.53 5.34 9.30 6 . 5 9 7.78 1.29 0.68 3.58 38.64 67.20 21.71
6.17 0.91 2.04 0.55 4.88
I
Elab (MeV)
Fig. 3. Experimental relative yield for the population of the 417 keV state in 26A1 by pn and d exit channels as a function of bombarding energy, compared with Hauser-Feshbach predictions (full line). The broken fines demonstrate the energy dependence of the ratio of cross sections for the total production of 26A1 by pn and d emission as calculated by the HauserFeshbach code STAPRE (a) and the statistical code ALICE (b).
where a dependence of the competition on the bombarding energy is demonstrated. The error bars represent the statistical uncertainties introduced by the analysis of the coincidence photopeaks. In order to obtain a theoretical estimate of competition in the reaction 12C (16 O, pn/d)26A1, the cross sections for (pn +np) and d emissions were calculated, as a function of bombarding energy, in the framework of the Hauser-Feshbach theory, using the code STAPRE [2]. In these calculations the contribution from the emission of light particles (p, n, d and a) and 3' rays has been taken into account for each sequence of the reaction in populating specific residual states. Previously known [3] excited states were explicitly considered in the calculations. For the density of the rest of the level the back-shifted Fermi gas model [4] was used with level density parameters adopted from refs. [5-7]. The optical model parameters were taken from refs. [8] and [9]. Theoretical results for some individual states as well as the total production of 26A1 at 28.0 MeV laboratory bombarding energy are sampled in table 1. The cross section for the total population of 26A1 equals the sum of the cross sections for the production of the ground (5 +) and the 228 keV (0 +) isomeric states. The fusion cross sections obtained in the present calculations agree reasonably well with reported experimental values [10]. It should be noted that the theoretical results suggest that the pn/d competition de226
pends on the nature of the residual state (see table 1). The theoretical Opn/Od ratio for the production of the 417 keV state is compared with the experimental values in fig. 3, where it can be seen that a satisfactory agreement is obtained. In the same figure, although not corresponding to the experimental quantities, we considered it interesting to demonstrate the theoretical pn over d competition in the total production of 26 A1 as obtained by STAPRE and the statistical model code ALICE [11 ]. As ALICE does not distinguish between pn and d emission, the d channel was estimated by subtracting the cross sections calculated with and without d emission. As seen in fig. 3, ALICE strongly underestimates the relative d contribution in comparison with the HauserFeshbach results. Competition between exit channels leading to the same nucleus was also observed in the nuclear reactions induced by 160 and 13C in the energy range between 24.5 and 32.0 MeV. Coincidence spectra at 27.0 MeV bombardment energy are shown in fig. 4. These data demonstrate that at 27.0 MeV the 417 keV state in 26A1 is exclusively produced by t emission. At 32.0 MeV, however, it was found that the p2n, dn and t exit channels significantly participate in the production of this state, with relative yields 29 -+4, 32 + 4 and 39 + 5%, respectively. The 1058 keV state of the same residual nucleus is also almost exclusively produced by t emission, as evidenced by the behaviour of the corresponding 830 keV deexciting 3' ray. In these spectra it can also be observed that both pn and d exit channels contribute to the production of the 1014 keV state in 27 A1, with pn/d yield ratio values varying between 7.6 + 1.1 and 8.4+ 1.2 at 24.5 and 32.0 MeV bombardment, respectively. Finally, it is observed that the 844 keV state in 27A1 is predominantly produced by pn emission.
Volume 90B, number 3
PHYSICS LETTERS
"C,
'60 + r
I
I
A. C O.
g 20(
proton-
the total counts of the energy spectra of particles in coincidence with a specific 3' ray. This process was used in order to assess the effect of low-energy detector cut-offs. Specifically, the pn/d relative yields were obtained from the integrated counts of the p and d coincident energy spectra after the particle spectra were extrapolated to zero energy. The extrapolation can be applied primarily to the p spectra, which show a continuous energy distribution due to the sharing of energy between the two particles of pn exit channel. The effect of low-energy cut-offs was also investigated by using AE detectors of various thicknesses, between 25 #m and 150/am. The corresponding cross-section ratio values, obtained under various conditions of measurement or analysis, were overlapping within the experimental error for bombarding energies higher by a few MeV than the thresholds for the competing channels considered. The experimental results presented here, as well as additional preliminary ones, related to a series of other nuclear reactions, suggest that competition between exit channels leading to the same residual nucleus bears a significant role in heavy-ion reactions. The double and triple competition was found to depend on the bombarding energy and the target-projectile combination. In fact, the pn/d cross-section ratio was observed to progressively increase with increasing neutron numbers of target or projectile. The data, furthermore, do not overrule the possibility that this competition may be related to structural characteristics. It is finally concluded that the explicit consideration of d and t emission in cross-section calculations should be important for a proper comparison with experimental results.
=27MeV I
"f II a, O
15C
10C
.... :. .'2""
"
U)
I- e Z~ :)
deuteron - "f
~n
0 (J
4.
3C v
2C . . . . . . .
.
.
q. ql" m
.
17 /: :-: -I - : : : ( :
....
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . "...
x
e=
i"..
"--':"
:-"
•
'
i
-I
? '
"::'" I
["
"~--i: I
25 February 1980
,
triton- T
2(
1C r
" "-, ....
.
.
~-.'. . ..!!.-I ..-_- - i n - -~" :.~-'-.:':.:-.:. [" .....
100
, ......
I ....
;"-'1"---'"
; ---'l----'r-
300
.-
.;
This work was supported in part by a grant from the National Research Foundation of Greece. The assistance o f Dr. V. Agrigeanu with the calculations and a critical reading o f the manuscript by Dr. A. Katsanos are gratefully acknowledged.
--"
500
C H A N N E L S
Fig. 4. Particle-gamma coincidence spectra obtained in the bombardment of 13C with 160.
It should be pointed out that the competition studied here, instead of using the coincidence intensities o f a discrete ~,-ray, can be equivalently extracted by using
References
[1] C. Olmer et al., Phys. Rev. C10 (1974) 1722. [2] M. Uhl, Acta Phys. Austriaea 31 (1970) 245. [3] P.M. Endt and C. Van tier Leun, Nucl. Phys. A310 (1978) 1. [4] H. Vonach and M. Hille, Nucl. Phys. A127 (1969) 289. [5] R.A. Dayvas, R.G. Stokstad, Z.E. Switkowski and R.U. Wieland, Nucl. Phys. A261 (1976) 478. 227
Volume 90B, number 3
PHYSICS LETTERS
[6] Z.E. Switkowski, R.G. Stokstad and R.M. Wieland, Nucl. Phys. A274 (1976) 202. [7] H.C. Cheung, M.D. High and B. Cujec, Nucl. Phys. A296 (1978) 333. [8] Y.D. Chan et al., Nucl. Phys. A303 (1978) 500. v
228
25 February 1980
[9] C.M. Perey and F.G. Perey, Nucl. Data Tables 13 (1974) 293. [101 Y. Eyal, M. Beckerman, R. Checkik, Z. Fraenkel and H. Stocker, Phys. Rev. C13 (1976) 1527. [11] M. Blann and F. Plasil, Phys. Rev. C l l (1975) 508.