Underground Physics and the Nonlinear Delayed Barometric Effect of the Gamma-Ray Background
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Underground Physics and the Nonlinear Delayed Barometric Effect of the Gamma-Ray Background Yu. V. Stenkina,b,*, V. V. Alekseenkoa†, A. V. Igoshinc, D. A. Kuleshova, K. R. Levochkina, V. I. Stepanova, V. P. Sulakovc, V. V. Ruleva, and O. B. Shchegoleva aInstitute
for Nuclear Research, Russian Academy of Sciences, Moscow, 117312 Russia MEPhI National Research Nuclear University, Moscow, 115409 Russia c Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, 119991 Russia *e-mail: [email protected] b
Received March 31, 2020; revised April 10, 2020; accepted April 12, 2020
Abstract—The gamma-ray background problem is known to be acute in any low-background underground experiment. The variations of this background depend on many parameters and should be taken into account when interpreting the results of experiments combined under the term “underground physics”. This paper is devoted to studying the long-term variations of the gamma-ray background in an underground laboratory with a scintillation detector based on a CsI crystal. Our studies have revealed a new effect in underground physics—a delayed nonlinear pumping effect for the gamma-ray background in an underground room that can lead to a significant rise of this background at an anomalously low atmospheric pressure. DOI: 10.1134/S1063776120090095
1. INTRODUCTION The background problem in low-background experiments is solved by various methods using passive and active shields. However, it can never be solved completely both due to the presence of naturally radioactive nuclides in any material and due to the activity inside the shield induced by penetrating cosmic rays. In our previous paper [1] on this subject we described the detection of a large delayed barometric effect for the neutron background in an underground laboratory related to the diffusion and the pumping effect of radioactive radon gas in soil. This study has revealed another new effect—a delayed nonlinear barometric pumping effect for the gamma-ray background in the same laboratory of the EAS–MSU array [2] at the Institute of Nuclear Physics of the Moscow State University (MSU) at a depth of 25 m water equivalent. The effect is also related to the diffusion of radon in the surrounding soil and manifests itself only when the atmospheric pressure drops, but the diffusion parameters are different from those for neutrons. The relative magnitude of the effect is also much smaller than that observed for neutrons; nevertheless, the effect is quite significant. The pumping effect has been known to geophysicists for more than 100 years [3] and there is extensive literature on this subject (for an overview, see, e.g., [4] and references therein). The effect is as follows: during † Deceased.
periodic atmospheric pressure fluctuations the underground gases are pumped out into the atmosphere and, conversely, the air is pumped into the soil. Actually, this effect is general in nature and manifests itself at an interface between two media like atmosphere–water and atmosp
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