arXiv subjects

M. S. Rahman

Publications and source records attributed to M. S. Rahman.

3 recordsLinked to original sources

arXiv2022

Pulse Shape Discrimination of low-energy nuclear and electron recoils for improved particle identification in NaI:Tl

The scintillation mechanism in NaI:Tl crystals produces different pulse shapes that are dependent on the incoming particle type. The time distribution of scintillation light from nuclear recoil events decays faster than for electron recoil events and this difference can be categorised using various Pulse Shape Discrimination (PSD) techniques. In this study, we measured nuclear and electron recoils in a NaI:Tl crystal, with electron equivalent energies between 2 and 40 keV. We report on a new PSD approach, based on an event-type likelihood; this outperforms the charge-weighted mean-time, which is the conventional metric for PSD in NaI:Tl. Furthermore, we show that a linear combination of the two methods improves the discrimination power at these energies.

physics.ins-det↗

arXiv2021

Quenching factor measurements of sodium nuclear recoils in NaI:Tl determined by spectrum fitting

We have performed measurements of sodium nuclear recoils in NaI:Tl crystals, following scattering by neutrons produced in a $^{7}$Li(p,n)$^{7}$Be reaction. Understanding the light output from such recoils, which is reduced relative to electrons of equivalent energy by the quenching factor, is critical to interpret dark matter experiments that search for nuclear scattering interactions. We have developed a spectrum-fitting methodology to extract the quenching factor from our measurements, and report quenching factors for nuclear recoil energies between 36 and 401 keV. Our results agree with other recent quenching factor measurements that use quasi-monoenergetic neutron sources. The new method will be applied in the future to the NaI:Tl crystals used in the SABRE experiment.

physics.ins-det↗

arXiv2019

Redefinition of site percolation in light of entropy and the second law of thermodynamics

In this article, we revisit random site and bond percolation in square lattice focusing primarily on the behavior of entropy and order parameter. In the case of traditional site percolation, we find that both the quantities are zero at $p=0$ revealing that the system is in the perfectly ordered and in the disordered state at the same time. Moreover, we find that entropy with $1-p$, which is the equivalent counterpart of temperature, first increases and then decreases again but we know that entropy with temperature cannot decrease. However, bond percolation does not suffer from either of these two problems. To overcome this we propose a new definition for site percolation where we occupy sites to connect bonds and we measure cluster size by the number of bonds connected by occupied sites. This resolves all the problems without affecting any of the existing known results.

cond-mat.stat-mech↗