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Багш ажилтан
A systematical analysis of experimental (n, 2n) cross sections has been carried out by many authors for long time. However, a substantiated theoretical approach to explain the observed systematical regularity of the experimental (n, 2n) cross sections has not been available until now. In this work, in the framework of the statistical model, a general expression for (n, 2n) reaction cross sections is obtained using the compound mechanism and evaporation model. This expression is then used to deduce the nonstatistical share of the (n, 2n) cross section. It is shown for the first time that the nonstatistical theoretical formula adequately describes the experimental (n, 2n) cross section data for 14–15 MeV neutrons taken from the EXFOR library
Investigation of few body cluster systems is very important in nuclear physics. Problems appearing in few body systems can in principle be divided into two classes: bound state problems and scattering problems. The bound state problems are usually related to the spectroscopy of such systems while scattering problems describe their reactions. The main focus in the work is the scattering problem for systems consisting of two cluster systems. The single channel two body scattering problem is considered in the framework of different spin parity states for lithium isotopes. Scattering phase shifts on negative and positive parity states of 5Li, 6Li and 7Li nuclei are calculated applying two-body 𝛼𝛼𝛼𝛼 + 𝑝𝑝𝑝𝑝, 𝛼𝛼𝛼𝛼 + 𝑑𝑑𝑑𝑑 and 𝛼𝛼𝛼𝛼 + 𝑡𝑡𝑡𝑡 systems and the complex scaling method. 6Li and 7Li are stable nuclei and their ground and low-lying excited states are considered in this work. In this study, we calculated scattering phase shifts of the negative parity 𝐽𝐽𝐽𝐽𝜋𝜋𝜋𝜋 = 3/2− and 𝐽𝐽𝐽𝐽𝜋𝜋𝜋𝜋 = 1/2− states for 𝑝𝑝𝑝𝑝 −wave of 5Li, 𝐽𝐽𝐽𝐽𝜋𝜋𝜋𝜋 = 7/2−, 5/2−, 3/2− and 1/2− states for 𝑝𝑝𝑝𝑝 − and 𝑓𝑓𝑓𝑓 −waves of 7Li and the positive parity 𝐽𝐽𝐽𝐽𝜋𝜋𝜋𝜋 = 1+, 2+, 3+ states for 𝑠𝑠𝑠𝑠 − and 𝑑𝑑𝑑𝑑 − waves of 6Li.
We apply the complex scaling method to the calculation of scattering phase shifts andextract the contributions of resonances in a phase shift. The decomposition of the phase shiftis shown to be useful in understanding the roles of resonant and non-resonant continuumstates. We apply this method to the two-body alpha nucleon systems. We discuss the explicitrelation between the scattering phase shifts and complex-energy eigenvalues in the complexscaling method via the continuum level density. The results provide us with deeperunderstanding of the role of resonant states characterized by the widths described as animaginary part of the eigen-energy
Цөмийн физикийн судалгаа үүссэнээс хойших 100 гаруй жилийн хугацаанд цөмийн бүтэц, урвалын талаар маш олон өгөгдөл, мэдээлэл хуримтлагджээ. Дэлхийн судалгааны лабораториудад янз бүрийн аргаар гарган авсан өгөгдлүүд хоорондоо ихээхэн зөрөх явдал элбэг байдаг. Иймээс, энэ олон өгөгдлүүдээс өөрт хэрэгтэйг олж авах, аль нь үнэн зөв болохыг тогтоох нь хэрэглэгчид ихээхэн төвөг учруулдаг. Цөмийн эрчим хүч, цөмийн технологийг ашиглаж буй ихэнх орнууд өөрсдийн цөмийн өгөгдлийн сантай байдаг бөгөөд тэндээсээ хэрэглэгчдээ найдвартай мэдээллээр хангаж байдаг. Манай улсад цөмийн цацраг, технологийг анагаах ухаан, геологи хайгуул, уул уурхайн үйлдвэрлэл зэрэгт нэвтрүүлэхтэй холбоотойгоор цөмийн өгөгдөл, мэдээллийг хэрэглэгчдийн тоо, эрэлт хэрэгцээ улам өсч байна. Гэвч манайд цөмийн өгөгдөл, мэдээллийн нэгдсэн сан байхгүй учир мэдээллээр гачигдаж, үнэн зөв мэдээлэл олж авахад бэрхшээл учирч байна. Иймээс бид ОУАЭА-ийн EXFOR санд байгаа цөмийн урвалын өгөгдлүүдийн 22579 файл буюу 22579 удаагийн туршилтын мэдээллийг R хэлний орчинд бичигдсэн програм- мын тусламжтайгаар нейтроноор, гамма-квантаар, хөнгөн ба хүнд ионоор явагдах урвалууд гэж ашиглахад эвтэй байдлаар 4 ангилан МУИС-ийн ЦФСТ-ийн компьютерийн “MINATO SERVER”-т байршуулав. Ингэж ангилсан өгөгдлүүдээ цаашид хэрхэн ашиглахын жишээ болгож (n, α), (n, p), (n, t), (n, 2n) болон (γ, n) урвалуудын огтлолын утгуудад системчилсэн анализ хийж, тодорхой зүй тогтлууд байгааг харуулав. Ажиглагдсан зүй тогтлуудыг цөмийн урвалын загвар, механизмуудын тусламжтайгаар тайлбарласан зарим үр дүнг үзүүлэв.
Fast neutron induced nuclear reaction cross section data are necessary for both nuclear energy technology and the understanding of fundamental nuclear physics problems. The information of (n,2n) cross sections is quite essential in nuclear technology as a significant portion of the fission neutron spectrum lies above the threshold of (n,2n) reaction for most of the reactor materials. These cross section data are required in shielding and breeding calculations. Radioactive nuclides produced in the reactor usually have short half-life. So, direct measurement of their neutron cross sections is difficult. Therefore, model formulae are important to predict these cross sections theoretically. In this work, in the framework of the statistical model we deduced some theoretical formulae for the (n,2n) cross section using the evaporation model, constant nuclear temperature approximation and Weizsäker’s formula for binding energy. The model formulae were utilized for systematical analysis of known experimental data of the (n,2n) cross sections at 14 - 15 MeV energy.
In this work we suggest some methods based on the statistical and knock-on models, for evaluation of the α-clustering factor or α-clustering probability in (n, α) reactions induced by slow and fast neutrons. The main purpose of this study is to compare the values of the α-clustering factors obtained by the compound and direct mechanisms for the same nuclear reactions. Also, our results are compared with values estimated by other authors.
In the last years we have been studying the α-clustering in fast and slow neutrons induced (n,α) reactions using the statistical model and knock-on mechanism. In this work in the framework of the compound and direct reaction mechanisms, triton clustering factors (or probabilities) were first obtained for (n,t) reactions. In the case of compound mechanism, the statistical model based on the evaporation model and constant nuclear temperature approximation was used. For the direct reaction mechanism, the knock-on model was utilized. It was shown that the triton clustering factors obtained by the knock-on model are much larger than ones found by the statistical model. At the same time, the triton clustering factors for even-even target nuclei are on an average one order of magnitude lower than ones for odd-even nuclei.
Methods to derive α-clustering factors from the analysis of experimental data for slow (En . 30 keV) and fast (En = 4–6 MeV) neutron-induced (n, α) reactions using the statistical model are described. In this way, the dependence of the α-clustering factor for the (n, α) reaction on the incident neutron energy can be followed. The resulting α-clustering factors are compared with our previous results and those obtained using other approaches.
