New Data on Photoneutron Reaction Cross Sections for 76,78,80,82 Se Nuclei
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CLEI Experiment
New Data on Photoneutron Reaction Cross Sections for 76,78,80,82Se Nuclei V. V. Varlamov1)* , A. I. Davydov2), and B. S. Ishkhanov1), 2) Received May 16, 2018; revised May 23, 2018; accepted May 23, 2018
Abstract—The problem of reliability of the cross section data obtained for partial photoneutron reactions on 76,78,80,82 Se nuclei in beams of quasimonoenergetic annihilation photons by means of neutron multiplicity sorting is discussed by employing objective physical criteria. It is shown that, because of substantial systematic uncertainties, experimental data on the (γ, 1n) and (γ, 2n) cross sections are unreliable. New data satisfying the reliability criteria are obtained for the partial photoneutron reaction cross sections for 76,78,82 Se nuclei by an experimental–theoretical method for evaluating such cross sections and are compared with experimental data and with data evaluated earlier for the isotope 80 Se. The evaluated integrated cross sections for the total photoneutron reactions on 76,78,80,82 Se nuclei are compared with the predictions of the Thomas–Reiche–Kuhn classical dipole sum rule. DOI: 10.1134/S1063778819010186
1. INTRODUCTION
average discrepancy between the cross sections for the neutron yield reaction (γ, xn) = (γ, 1n) + 2(γ, 2n) + 3(γ, 3n) + . . . (1)
Cross sections for photoneutron reactions leading to the emission of various numbers of particles are widely used in fundamental nuclear physics studies, as well as in various applications in the realms of nuclear physics, astrophysics, geology, chemistry, and medical sciences [1–3]. These are, primarily (γ, 1n), (γ, 1n1p), (γ, 2n), and (γ, 3n), reactions. The majority of relevant data were obtained by means of photoneutron multiplicity sorting in beams of quasimonochromatic annihilation photons at the Lawrence Livermore National Laboratory (USA) and at the Nuclear Research Centre in Saclay (France) [1, 2, 4].
turns out to be about 10%. This means that, in the cross sections for the above partial reactions, there are significant systematic uncertainties associated with drawbacks of the method based on photoneutron multiplicity sorting. An experimental–theoretical method for evaluating partial reaction cross sections was proposed in [8] with the aim of finding out which data are reliable. In employing this method, the experimental cross section that corresponds to the neutron yield reaction (1) and which is independent of problems inherent in the method of neutron multiplicity sorting since it takes into account all neutrons emitted in this reaction is separated for the partial reaction contributions,
Significant systematic discrepancies were found [5–7] in the (γ, 1n) + (γ, 1n1p) and (γ, 2n) cross sections for 19 nuclei from 51 V to 232 Th that were studied in these two laboratories. It turned out that, as a rule, the (γ, 1n) + (γ, 1n1p) cross sections were larger (by about 60% to 100%) in Saclay, while the (γ, 2n) cross sections were on the contrary larger in Livermore. For the aforementioned nuclei, the average value of the ra
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