Measurement of the quenching factor of Na recoils in NaI(Tl)

TL;DR

This study measures the quenching factor of sodium recoils in NaI(Tl) crystals using neutron scattering, providing data crucial for dark matter detection experiments and comparing results with theoretical models.

Contribution

The paper provides new measurements of sodium recoil quenching factors in NaI(Tl) crystals at low energies, aligning with previous data and theoretical predictions.

Findings

Quenching factors range from 19% to 26% for 10-100 keVnr

A specific quenching factor of 25.2% ± 6.4% at 10 keVnr

Pulse shape analysis distinguishes electron and nuclear recoils down to 2 keVee

Abstract

Measurements of the quenching factor for sodium recoils in a 5 cm diameter NaI(Tl) crystal at room temperature have been made at a dedicated neutron facility at the University of Sheffield. The crystal has been exposed to 2.45 MeV mono-energetic neutrons generated by a Sodern GENIE 16 neutron generator, yielding nuclear recoils of energies between 10 and 100 keVnr. A cylindrical BC501A detector has been used to tag neutrons that scatter off sodium nuclei in the crystal. Cuts on pulse shape and time of flight have been performed on pulses recorded by an Acqiris DC265 digitiser with a 2 ns sampling time. Measured quenching factors of Na nuclei range from 19% to 26% in good agreement with other experiments, and a value of 25.2 \pm 6.4% has been determined for 10 keV sodium recoils. From pulse shape analysis, the mean times of pulses from electron and nuclear recoils have been compared down to 2 keVee. The experimental results are compared to those predicted by Lindhard theory, simulated by the SRIM Monte Carlo code, and a preliminary curve calculated by Prof. Akira Hitachi.