Data on photoneutron reactions from various experiments for 133 Cs, 138 Ba and 209 Bi nuclei
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CLEI Experiment
Data on Photoneutron Reactions from Various Experiments for 133 Cs, 138 Ba and 209 Bi Nuclei V. V. Varlamov1)* , B. S. Ishkhanov1), 2) , V. N. Orlin1), and N. N. Peskov1) Received November 25, 2015
Abstract—Basic methods for determining cross sections for photoneutron partial reactions are examined. They are obtained directly in experiments with quasimonoeneregetic annihilation photons or from the cross section for the (γ, xn) = (γ, 1n) + 2(γ, 2n) + 3(γ, 3n) + . . . neutron-yield reaction in experiments with bremsstrahlung photons by introducing corrections based on statistical nuclear-reaction theory. The difference in the conditions of these experiments, which leads to discrepancies between their results because of sizable systematic errors, is analyzed. Physical criteria are used to study the reliability of data on the photodisintegration of 133 Cs, 138 Ba, and 209 Bi nuclei. The cross sections for partial and total reactions satisfying the reliability criteria are evaluated within the experimental–theoretical method (σ eval (γ, in) = Fitheor × σ expt (γ, xn)) on the basis of the experimental cross sections σ expt (γ, xn) and the results of the calculations within the combined model of photonuclear reactions. DOI: 10.1134/S1063778816040219
1. INTRODUCTION Experimental data on cross sections for photonuclear reactions are broadly needed in various fields of science and technologies—from fundamental nuclear physics to various applications. Along with data on nuclear reactions induced by neutrons, charged particles, and heavy ions, such data are included in the EXFOR international database of nuclear reactions [1–3]. This database developed and maintained by the IAEA Nuclear Data Centers Network [4] and is well known to users [5]. The well-developed search systems of various versions of this database (Photonuclear Experiment Data Center, Institute of Nuclear Physics, Moscow State University, Russia; IAEA Nuclear Data Section, Austria; and National Nuclear Data Center, United States of America) permit immediate and efficient data processing. In many cases, a comparison of the results of different experiments reveals previously unknown systematics of these results and makes it possible to find systematic discrepancies between them, to perform an analysis of reasons behind them, and develop methods for removing them. In the region of photonuclear reactions, such investigations are of great importance since the conditions under which different experiments with gamma rays are performed are strongly different. This
is due primarily to the absence of monoenergetic photons, with the result that experimentalists have to use various methods for producing quasimonoenergetic photons whose effective spectrum could be interpreted as that which is close to a monoenergetic spectrum. A significant difference in the methods for obtaining data is the reason for substantial systematic errors that exceed greatly statistical errors and which manifest themselves in severalfold distinctions between reaction cross sections determine
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