ЭЛЕМЕНТАРНЫЕ ЧАСТИЦЫ И ПОЛЯ
RECOIL STUDIES IN THE REACTION OF 12C IONS WITH THE ENRICHED ISOTOPE 118Sn
© 2010 A. R. Balabekyan1)*, A. S. Danagulyan1), J. R. Drnoyan1)-2), N. A. Demekhina2)'3), G. H. Hovhannisyan1), J. Adam2)-4), V. G. Kalinnikov2), M. I. Krivopustov2), V. S. Pronskikh2), V. I. Stegailov2), A. A. Solnyshkin2), V. M. Tsoupko-Sitnikov2), S. G. Mashnik5), K. K. Gudima6)
Received July 24, 2009; in final form, October 29, 2009
The recoil properties of the product nuclei from the interaction of 2.2 GeV/nucleon12 C ions from Nuclotron of the Laboratory of High Energies, Joint Institute for Nuclear Research at Dubna with a 118Sn target have been studied via catcher foils method. The experimental data were analyzed using the mathematical formalism of the standard two-step vector model. The results for 12C ions are compared with those for deuterons and protons. Three different Los Alamos versions of the Quark—Gluon String Model were used for comparison with our experimental data.
1. INTRODUCTION
Studies of the interactions of high-energy projectiles with complex nuclear targets lead to an overall picture of great complexity. The violent processes associated with a high multiplicity of emitted particles that lead to products of hundred or more masses removed from the target are not well understood.
On the other hand, if one investigates less violent encounters, which can be classified under the generic term of target fragmentation, some simplifications will be obtained. Many observations of the target or projectile fragmentation appear to be consistent with the two hypotheses originally associated with peripheral hadron—hadron interactions at high energies [1]. The first hypothesis predicts that both cross sections and kinematical characteristics of fragments will become independent of bombarding energy at high energies ("limiting fragmentation"). The second asserts that these fragment properties can be written as a product of target and projectile factors ("factorization"). That means the possibility to observe the scaling behavior in the cross sections of different interaction channels and in kinematical characteristics of the reaction products.
!)Yerevan State University, Armenia.
2)JINR, Dubna, Russia.
3)Yerevan Physics Institute, Armenia.
4)INF AS, Rez, Czech Republic.
5)Los Alamos National Laboratory, USA.
6)Institute of Applied Physics, Academy of Sciences of Moldova, Chig ina u.
E-mail: balabekyan@ysu.am
The investigation of target fragmentation could be made both in the exclusive [2—5], and inclusive measurements [6, 7] in on-line and off-line experiments. The results received on known facilities FAZA, ALADIN [2—5] concern exclusive investigations of multifragmentation processes connected with multiple formations of intermediate mass fragments (IMF) 3 < Z < 20. One possible mechanism for such a process would be a simultaneous clustering of nucleons into fragments near the liquid-gas critical point [8]. The formation of heavy fragments on the above-mentioned facilities was not measured.
The on-line experiment can provide a more comprehensive picture of the processes, but the cross sections of the formation of residual nuclei and their kinematical properties obtained by induced-activity methods in off-line experiments can give an additional information about the interaction mechanism.
The kinematical properties of residual nuclei are determined often via "thick-target—thick-catcher" experiment. The quantities measured are the fractions F and B of the product nuclei that recoil out of the target foil into the forward and backward directions (relative to the beam direction), respectively.
The results of the experiment are usually proceeded by the standard two-step vector representation [9—11]. The following assumptions are made in this model:
(1) In the first step, the incident particle interacts with the target nucleus to form an excited nucleus with velocity v\\, momentum Pn, and excitation energy E*.
Kinematic characteristics of product nuclei on 12C-ion-induced reactions
Product F/B V 2 W(F + B) Tkin, MeV vn, (MeV/a.m.u.)1/2
24Na 1.40 0.084 4.82 ± 1.02 20.24 ± 4.29 0.1089
28Mg 1.54 0.107 4.41 ±0.94 19.18 ±4.07 0.1255
43 K 1.55 0.108 2.86 ±0.61 15.11 ±3.20 0.0909
44Sc 2.32 0.207 2.49 ±0.53 12.21 ±2.59 0.1543
52Mn 1.88 0.157 3.27 ± 0.69 21.51 ±4.56 0.1426
67 Ga 1.02 0.005 1.55 ±0.33 7.17 ± 1.52 0.0024
71As 2.48 0.223 1.50 ±0.32 7.12 ± 1.51 0.1001
73Se 3.33 0.292 1.51 ±0.32 7.33 ± 1.55 0.1309
86my 3.38 0.296 1.05 ±0.22 4.37 ±0.93 0.0943
77Br 2.35 0.210 1.35 ±0.29 6.11 ± 1.29 0.0837
89 Zr 2.87 0.258 0.73 ±0.15 2.45 ±0.52 0.0605
90Mo 2.32 0.207 1.28 ±0.27 6.35 ± 1.35 0.0778
90Nb 3.49 0.303 1.01 ±0.21 4.08 ±0.86 0.0912
93 mMo 4.33 0.351 0.92 ±0.19 3.69 ± 0.78 0.0988
93 Tc 1.63 0.121 1.26 ±0.27 6.23 ± 1.32 0.0445
94 Tc 3.14 0.278 0.98 ±0.21 4.21 ±0.89 0.0833
95 Tc 3.64 0.312 0.61 ±0.13 1.97 ±0.42 0.0635
97 Ru 4.02 0.334 0.59 ±0.13 1.93 ±0.41 0.0667
"mRh 3.16 0.280 0.50 ±0.11 1.48 ±0.31 0.0484
109 In 4.47 0.358 0.17 ±0.03 0.28 ± 0.06 0.0256
110Sn 2.52 0.227 0.23 ±0.05 0.48 ± 0.08 0.0213
mIn 3.34 0.293 0.13 ±0.03 0.19 ±0.04 0.0169
117mSn 1.08 0.020 0.17 ±0.03 0.27 ±0.06 0.0014
(2) In the second step, the excited nucleus loses mass and excitation energy to form the final recoiling nucleus with an additional velocity V.
The results of the recoil experiments depend on the range—energy relation of the recoiling nuclei. It is convenient to express this relation as [10]:
R = kVn, (1)
where parameters k and n are obtained by fitting the range dependence on energy of accelerated ions [12]. It is possible to calculate n = v\\/V and the longitudinal velocity vn in frame of two-step vector model [10], knowing the F/B ratio of the experiment.
In the present paper the investigation of the kinematical characteristics of residuals produced in reactions of12C ions with enriched tin isotope 118 Sn
was made with the purpose of studying the spatial, velocity and energy distributions of mediummass and heavy fragments. Comparison of the recoil properties of the residual nuclei obtained in precent experiment with the results of our previous measurements (including deuteron- and proton-induced reactions [13]) and some data from other experiment at high energies [14, 15] was made for the verification of the hypothesis mentioned above.
2. EXPERIMENTAL DETAILS AND RESULTS
Target foils of enriched tin isotope 118Sn (98.7%) were irradiated at the Nuclotron of the LHE, JINR by 12C ion beams with energies of 2.2 GeV/nucleon during 10 h. The reaction 27Al(12C,X)24Na with cross sections of 19.0 ± 1.5 mb [16] for beam monitoring was used.
F/B 6 г
AA/At
Fig. 1. F/B versus the fractional mass losses AA/At: dots are the results of present experiment; solid curve shows the calculation by LAQGSM.01, dashed curve shows the calculation by LAQGSM.S1, dotted curve shows the calculation by LAQGSM.G1.
4
2
0
(F/B)i2c/(F/B)p 2
Experimental data Avrage value
* h* h m
U
01-L.
J_I_I_L-
(F/B)i2C/(F/B)rf 2
J— 0
20 40 60 80 100 120 20 40 60 80 100 120
At At
Fig. 2. Product mass dependence of ratios of F/B from26.4-GeV C ion and 3.65-GeV proton bombardment of 8 Sn, C ions and 7.3-GeV deuterons.
1
1
The target consisted of 11 high-purity target metal foils of size 20 x 20 mm sandwiched by one pair of Mylar foils of the same size, which collected the nucleus recoil in the forward or backward directions with respect to the beam. The thickness of each target foil was 66.7 mg/cm2. The whole stack, together with an Al beam-monitor foil was mounted on a target holder and irradiated.
After irradiation the target foils and all of the forward and backward catcher foils were collected separately, and assayed for radioactivities with Hp(Ge) detectors at LNP, JINR for one year. Detectors energy and efficiency calibration were made regularly using standard gamma-sources. The radioactive nuclei were identified by characteristic y lines and by their half-lives [17]. The spectra were evaluated with the code package DEIMOS32 [18].
The main results of this experiment are the fraction of total activity of the given isotope collected in forward and backward catcher foils F, B and mean range 2W(F + B), where W is the target thickness [the mean range of the recoils is somewhat smaller
than 2W(F + B), but it is conventional to refer to the latter quantity as range]. The kinematical characteristics of twenty product nuclei were obtained. The relative quantities of the forward- and backward-emitted nuclei (relative to the beam direction) were calculated from relations:
F = Nf/(Nt + Nf + NB ), (2)
B = Nb/(Nt + Nf + Nb ),
where NF, NB, Nt are the numbers of nuclei emitted in the forward and backward catchers and formed in target foils, respectively.
The measurement results are summarized in the table. We note that uncertainties concerning definite quantities within 15—20% are not listed in our table to keep it concise.
The F/B quantity defines the preferred recoil direction of the fragment and regards to the transfer momentum in initial interaction. As shown in Fig. 1 and the table, the ratios F/B via AA/At (AA = = At — A res, where At is the mass number of target and Ares is the mass number of product nuclei) for
2W(F + B)
5 -
3 -
20 40 60 80 100 120 At
Fig. 3. Mean ranges of fragments emitted in the interaction of12C ions with target via product mass. Dots are the results of present experiment. Solid curve shows the trend in the data. Dashed and dotted curves show the trends in similar data for the interaction of118Sn with 3.65-GeV protons and 7.3-GeV deuterons, respectively.
At
Fig. 4. Mean ranges of fragments emitted in the interaction of12C ions with targets of mass At. Basic data for 18.5-GeV 12C ions were taken from [15]. Our data are for At = 118. The curves show the trends in the data.
12C-ion-induced reactions are of the order of ^3—4 for heavy product nuclei and decrease to about ~1.5
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