Calculation of neutron background for underground experiments

TL;DR

This paper estimates neutron backgrounds in underground dark matter detectors by calculating neutron yields from radioactive materials, aiding in the design of more sensitive experiments.

Contribution

It introduces a detailed method for calculating neutron production spectra from materials using Empire2.19 and Sources4A, improving background estimation accuracy.

Findings

Neutron spectra from various isotopes were calculated and compared with experimental data.

Estimated neutron background event rates for a hypothetical Ge-based dark matter detector.

Derived radiopurity requirements for detector materials to minimize neutron backgrounds.

Abstract

New generation dark matter experiments aim at exploring the 10e-9 - 10e-10 pb cross-section region for the WIMP-nucleon scalar interactions. Neutrons produced in the detector components are one of the main factors that can limit detector sensitivity. Estimation of the background from this source then becomes a crucial task for designing future large-scale detectors. Energy spectra and production rates for neutrons coming from radioactive contamination are required for all materials in and around the detector. In order to estimate neutron yields and spectra, the cross-sections of (a,n) reactions and probabilities of transitions to different excited states should be known. Cross-sections and transition probabilities have been calculated using Empire2.19 for several isotopes, and for some isotopes, a comparison with the experimental data is shown. The results have been used to calculate the neutron spectra from materials using the code Sources4A. Neutron background event rates from some detector components in a hypothetical dark matter detector based on Ge crystals have been estimated. Some requirements for the radiopurity of the materials have been deduced from the results of these simulations.