Московский экономический журнал 2/2017

KINEMATICAL CHARACTERISTICS OF α PARTICLES IN DIFFERENT TOOPOLOGICAL CHANNELS OF BREAKUP OF OXYGEN NUCLEI IN INTERACTIONS WITH PROTONS AT 3.25 A GeV/c

 S. Yuldashev, S. L. Lutpullaev, K. Olimov, T.M.Myminov , E. Kh. Bоzоrov,

Sh. D. Tojimamatov,C.R.Palvonov, SH.Kh. Khyshmyradov

Physico-Technical Institute of the «Physics-Sun» NGO of the Academy of Sciences of the Republic of Uzbekistan, Tashkent

КИНЕМАТИЧЕСКИЕ ХАРАКТЕРИСТИКИ α-ЧАСТИЦ В РАЗЛИЧНЫХ ТОПОЛОГИЧЕСКИХ КАНАЛАХ РАЗВАЛА ЯДЕР КИСЛОРОДА ВО ВЗАИМОДЕЙСТВИЯХ С ПРОТОНАМИ ПРИ 3.25 А ГэВ/с

Б.С. Юлдашев, C.Л.Лутпуллаев,  К. Олимов, Т.М.Муминов ,Э.Х. Бозоров,

Ш. Д.Тожимаматов, С.Р.Палвонов, Ш.Х.Хушмуродов .

Аннотация

Представлены экспериментальные результаты изучения различных кинематических характеристик α-частиц в зависимости от топологии событий в ¹⁶Ор-соударениях при 3.25 А ГэВ/с. Обнаружено, что средние значения полного и поперечного импульсов, а также углов вылета α-частиц являются максимальными в топологическом канале (2). Основной вклад в сечение образования α-частиц дают топологии с образованием различного числа двухзарядных фрагментов – (2), (22), (222) и (2222).

Ключевые слова: α-частиц, кислород, ядра, ⁵Li, ⁵He, ⁸Be ,⁹B, ¹⁶Ор-соударениях, дейтрон, ядер гелия-3, α-кластерная структура, топологии, сечение, фрагмент.

Abstract

Experimental results of investigation of different kinematical characteristics of α particles depending on event topology in ¹⁶Op collisions at 3.25 A GeV/c are presented. It is found that the average values of the total and transverse momenta and of emission angle of α particles attains its maximum in topology (2). The main contribution to cross section of formation of α particles is due to topologies with the different number of doubly charged fragments – (2), (22), (222) и (2222). 

Keywords: α-particles, oxygen, nuclei, ⁵Li, ⁵He, ⁸Be ,⁹B, ¹⁶Ор -collisions, deuteron, helium-3 nuclei, α-cluster structure, topology, cross section, fragment

The study of the formation of α particles in various topological channels of the breakdown of oxygen nuclei makes it possible to obtain information both on the initial structure of the fragmenting nucleus and on the mechanisms of the formation of ⁴He nuclei. In [1-5], we showed that in the ¹⁶Op collisions at 3.25 A GeV / c, the main part of the α particles is formed from the decay of the unstable nuclei ⁵Li, ⁵He, ⁸Be and ⁹B, and also of the excited ⁶Li *, ⁷Li * nuclei, ¹⁰B* and ¹²C*. In [6], various characteristics of the mirror channels (with the formation of the ³He or ³H nuclei) of the decomposition of oxygen nuclei into light fragments with mass numbers A ≤ 4 depending on the number of α particles were studied in [6] in ¹⁶Op collisions at 3.25 A GeV / c. That the mechanisms of the formation of deuterons, helium-3 and tritium nuclei do not depend on the mechanism of production of α particles. Not long ago [7] we also studied the behavior of the kinematic characteristics of α particles at different excitation levels of the oxygen nucleus in interactions with protons at 3.25 A GeV / c and found their strong dependence on the excitation degree of the fragmenting nucleus. It was also shown that for a small excitation of the oxygen nucleus, its α-cluster structure is preserved to a greater degree.

The present work is devoted to the study of the kinematic characteristics of α particles in various topological channels for the breakdown of oxygen nuclei in interactions with protons at 3.25 A GeV / c. The experimental material was obtained with the aid of 1 m of the hydrogen bubble chamber of the LHE of JINR irradiated with oxygen nuclei with a momentum of 3.25 A GeV / c at the Dubna synchrophasotron and consists of 8712 fully-measured inelastic ¹⁶Op events. For more reliable identification of fragments by mass, events were considered in which the length of tracks of doubly-charged fragments in the working volume of the chamber was not less than 30 cm, which ensures high accuracy of pulse measurements. Double-charged fragments with p> 10.75 GeV / c were related to α-particles. With such a selection, the admixture of ³He nuclei among the α particles does not exceed 3.4%.

Let us consider the dependences of the mean values of the total (in the rest system of the oxygen nucleus), transverse momenta, and the angles of emission of α particles from the topology of the event in ¹⁶Op collisions at 3.25 A GeV / c. In the α-particle formation experiment, 11 possible topological channels are observed in the following 10 channels: (2), (22), (222), (2222), (23), (24), (25), (26) , (223), (224) (here the figure in brackets indicates the charge of the fragment, and their number is the number of fragments in the event). The topological channel (233) is not observed in the experiment, the absence of which is related both to the high excitation energy of the nucleus for the realization of this topology in comparison with the experimentally observed channels and the rearrangement of the initial (-cluster) structure of the oxygen nucleus [8].

In Table. 1 shows the mean values of the total (in the rest system of the oxygen nucleus) and transverse momenta, as well as the emission angles of the α particles in the topologies of the decomposition of oxygen nuclei in the ¹⁶Op collisions under consideration at 3.25 A GeV / c

Table1. The average values of the total (in the rest system of the oxygen nucleus) and transverse momenta, as well as the emission angles of the α particles, depending on the topology of the decay of the oxygen nuclei in ¹⁶Op collisions at 3.25 A GeV / c

As can be seen from Table. 1 that the mean values of the total, transverse momenta, as well as the emission angles of the α particles, have their maximum value in the topology (2); In channels with the formation of one α-particle. The remaining part of the experimental data on the average values of the kinematic characteristics of α particles by topology are divided into two groups: the I group — is the topology (22), (23), (24) and (26), corresponding, basically, to knocking out one of the α-clusters Core; II group — (25), (222), (223), (224) and (2222) corresponding to the peripheral decay of the fragmenting nucleus. Although the topology (26) has a lower threshold realization energy than the channels (22), (23), (24), nevertheless in these topologies the average values of the total and transverse momenta, as well as the emission angles of the α particles within the experimental errors Are the same. An analysis of the peripheral channel of the decomposition of oxygen nuclei into two- and six-charge fragments (topology (26)) [9] has shown that an appreciable part of the events of this topology is realized by knocking out one of the α-clusters of the oxygen nucleus by the proton target. Due to this process, the average values of the kinematic characteristics of the α particles from the topology (26) become 15-20% larger than in the topologies (25), (222), (223), (224), and (2222).

Now, for completeness of the information on the mechanism of the formation of α particles, we consider the inclusive cross sections for their formation, depending on the topology of the events. For this purpose, we will use the results of work on the cross sections for the yield of various topological channels involving doubly-charged fragments [10], as well as the proportions of α particles among the doubly-charged fragments in the topological channels under consideration [11], the decay of oxygen nuclei in interactions with protons at 3.25 A GeV / c . The inclusive cross sections for the production of α particles in various topological channels for the decay of oxygen nuclei were determined as follows:

σ_incl(top) = σ(tоp)*n*p_α(top),

Where σ (tоp) is the exit cross section of a given topological channel, n is the number of doubly charged fragments in a given topology, and pα (top) is the fraction of α particles among the doubly-charged fragments in a given topology. It is seen from this formula that the inclusive cross section for the formation of α particles in the topology is determined, mainly by the cross section for the yield of a given topological channel and the number of doubly-charged fragments in it (the fraction of α particles (pα (top)) among the doubly-charged fragments varies very little, only From 0.6 to 0.84) [11].

In Table. Figure 2 shows the inclusive cross sections for the production of α particles in the topological channels of the decay of oxygen nuclei in interactions with protons at 3.25 A GeV / c.

Table 2. Inclusive cross sections for the production of α particles in various topological channels for the decay of oxygen nuclei in ¹⁶Op collisions at 3.25 A GeV /c

As can be seen from Table. 2, the maximum cross section for the production of α particles is observed in the topological channel (222), and the minimum cross section in the topology (224). The latter circumstance is connected with the small value of the exit cross section of the topology itself (224). In the topologies (24), (25) and (223), the inclusive cross sections for the production of α particles within the statistical errors coincide. The total inclusive cross section for the production of α particles in the topological channels under consideration turned out to be equal to 166.9 ± 2.1 mb, which within the limits of statistical errors coincides with the inclusive cross section for the production of α particles (164.0 ± 1.9 mb) in the ¹⁶Op reaction at 3.25 A GeV / c [12] .

Analysis of the isotope composition in topologies with the yield of beryllium (224) and carbon (26) nuclei shows that in the first case only 7Be nuclei are observed, and in the second case 70% consists of ¹²C nuclei, about 25% —  ¹¹C and about 5% —  ¹⁰C.

In the topological channel (25), the contribution of the ¹⁰B and ¹¹B isotopes within the experimental error is the same and does not depend on which isotope of helium is formed in the final state.

This, it can be concluded that the maximum average values of the kinematic characteristics of the α particles are observed in the topological channel (2) corresponding to the largest excitation of the oxygen nucleus, and the minimal ones in the topological channels (25), (222), (223), (224) And (2222). The main contribution (82 ± 1.4%) to the cross section for the production of α particles comes from the topological channels (2), (22), (222), and (2222). The contribution of other topologies in which the formation of α particles is accompanied by another multiply charged fragment — (23), (24), (25), (26), (223) and (224) is only (18 ± 0.3)%.

BIBLIOGRAPHY

1. Gulamov KG, Lutpullaev S.L. And others. Uzbek. Phys. Jour. № 5, 35 (2000).
2. Bazarov E.H. And others. JF 67, 170 (2004).
3.  Bazarov E.H. And others. JF 67, 2207 (2004).
4. Bazarov E.H. And others. JF 67, 2297 (2004).
5. Kh. K. Olimov et al. Intern. Journ. Of Modern Physics E Physics E Vol. 22, 1350057 (2013).
6. Yuldashev B.S. And others. Uzbek. Phys. Jour. (Accepted for publication in 2017).
7.  Kosim Olimov et al. Intern. Journ. Of Modern Physics E Physics E Vol. 23, 1450086 (2014)
8. Belov M.Ai et al. DAN RUz No. 3, 16 (2002).
9.  Kosim Olimov et al. Intern. Journ. Of Modern Physics E Physics E Vol. 25, 1650060 (2016)
10. Abdullaeva K.N. And others. DAN RUz No. 5, 21 (1996).
11. Glagolev V.V. Et al. Europ.Phys. Journ. Vol 11A, 285 (2001).
12. Bazarov E.Kh., JETP Lett. Vol. 81, No. 4, 140 (2005).