Intrinsic neutron background of nuclear emulsions for directional Dark Matter searches

TL;DR

This paper estimates the intrinsic neutron background in nuclear emulsions used for directional Dark Matter detection, showing it is low enough for practical experiments and highlighting the importance of understanding radioactive contamination.

Contribution

It provides the first detailed estimation of neutron background from radioactive contamination in nuclear emulsions for Dark Matter searches using GEANT4 simulations.

Findings

Neutron background is approximately 0.06 neutrons per year per kilogram.

Background levels are compatible with a 10 kg×year exposure.

Radioactive contamination is a manageable background for directional Dark Matter detection.

Abstract

Recent developments of the nuclear emulsion technology led to the production of films with nanometric silver halide grains suitable to track low energy nuclear recoils with submicrometric length. This improvement opens the way to a directional Dark Matter detection, thus providing an innovative and complementary approach to the on-going WIMP searches. An important background source for these searches is represented by neutron-induced nuclear recoils that can mimic the WIMP signal. In this paper we provide an estimation of the contribution to this background from the intrinsic radioactive contamination of nuclear emulsions. We also report the induced background as a function of the read-out threshold, by using a GEANT4 simulation of the nuclear emulsion, showing that it amounts to about 0.06 neutrons per year per kilogram, fully compatible with the design of a 10 kg$\times$year exposure.