Analysis of experimental data on the neutron yield from muons
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EMENTARY PARTICLES AND FIELDS Experiment
Analysis of Experimental Data on the Neutron Yield from Muons N. Yu. Agafonova and A. S. Malgin* Institute for Nuclear Research, Russian Academy of Sciences, pr. Shestidesyatiletiya Oktyabrya 7a, Moscow, 117312 Russia Received July 26, 2012; in final form, October 4, 2012
Abstract—Experimental data accumulated over 60 years of studying the yield of cosmogenic neutrons in a liquid scintillator (YLS ), iron (YFe ), and lead (YPb ) were analyzed. This analysis revealed that the main part of the results on the yield YLS were overestimated by about 30%. With allowance for this ¯μα , where the ¯μ , A) = bn Aβ E circumstance, all experimental data can be described by the dependence Y (E α ¯ stands for the energy spent by a muon on neutron production. The exponents of α = 0.78 product bn E μ and β = 0.95 are determined by the properties of the medium and by neutron production in showers. DOI: 10.1134/S1063778813050025
1. INTRODUCTION Measurements of neutron production induced by cosmic-ray muons started in the 1950s. The objective of those measurements was to study the photonuclear interaction of muons. Because of its small cross section of about 10−30 cm2 /nucl, this interaction became sizable at muon energies in excess of about 10 GeV, which correspond to the depth of more than 20 mwe. The average value of the product of the cross section σ and the neutron multiplicity ν per nucleon, νσ/A [cm2 /nucl] (see [1–4]), or per nucleus, νσ (see [5, 6]), was measured as a rule. After the appearance of the article by Zatsepin and Ryazhskaya [7] in the mid-1960s, investigations of neutron production by muons in underground experiments acquired a new meaning—study of background sources in low-background underground experiments, which has remained important to date in connection with vigorous neutrino investigations and searches for dark-matter particles. As a quantitative measure, a unit of “the number of neutrons produced by a single muon in 1 g/cm2 of matter” was introduced in [7]. Later, this unit was called a “neutron yield”: Yn = Nn /(lμ ρ) [(g/cm2 )−1 ], where Nn is the number of neutrons produced by a muon of energy Eμ over the length of lμ in matter of density ρ. Interest in the problem of the neutron yield has been quickened in the past years. This was due to increasing demands on the accuracy in determining the background in underground experiments, on one hand, and to the growing potential of computational facilities, on the other hand. Computational facilities *
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are used to seek the dependence of the yield on Eμ and on the atomic number of matter, A, with the aid of the FLUKA and GEANT universal codes and their modifications [8–10]. At the present time, we do not have at our disposal an expression that one could use to calculate the yield in question and which would relate the energy loss of a muon in matter, the nuclear properties of matter, and processes of neutron production in hadron (h) and electromagnetic (em) muon-initiated showers developin
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