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Unified framework for precise background modeling to enhance rare event detection at the Kuo-Sheng nuclear reactor laboratory

Subhasis Parhi, Lakhwinder Singh, Venktesh Singh, Henry Tsz-King Wong

TL;DR

The paper develops a Geant4-based background-modeling framework for the TEXONO KSNL setup to achieve precise background characterization in rare-event searches. By confining specific radioisotopes to detector components and the surrounding environment and simulating five million events per confinement, it constructs a complete background spectrum that closely matches measurements after optimizing decay-chain activities and energy resolution. The dominant background arises from $^{238}$U/$^{232}$Th decay chains in the HPGe front-end electronics, with notable but smaller contributions from $^{40}$K and $^{137}$Cs, while environmental isotopes like $^{60}$Co, $^{54}$Mn, and $^{135}$Xe are mitigated by shielding. The validated framework supports detailed background suppression, shielding optimization, and robust spectral interpretation critical for low-threshold, rare-event analyses such as CEvNS and neutrino/dark matter searches at KSNL.

Abstract

A background model has been designed for TEXONO experiment using Geant4 sim- ulation software. The contamination of different radioactive isotopes in the detector background has been considered from both the detector set-up and the environment. 238 U and 232 Th have been confined in the front end electronics of the HPGe detector. These two isotopes are confined by breaking the complete chains into constituent decay chains on the basis of half-life of the isotopes. 235 U isotope is also confined in the front end electronics of the pre-amplifier. 40 K gets confined in NaI(Tl) Anti-Compton Veto (ACV) detector where 137 Cs has been confined in CsI(Tl) ACV detector. The detector environment gets confined with 60 Co, 54 Mn, and 135 Xe. Five million events have been considered in each confinement. The amplitudes of the experimental and simulated peaks have been matched by adjusting the activity of the simulated decay chain.

Unified framework for precise background modeling to enhance rare event detection at the Kuo-Sheng nuclear reactor laboratory

TL;DR

The paper develops a Geant4-based background-modeling framework for the TEXONO KSNL setup to achieve precise background characterization in rare-event searches. By confining specific radioisotopes to detector components and the surrounding environment and simulating five million events per confinement, it constructs a complete background spectrum that closely matches measurements after optimizing decay-chain activities and energy resolution. The dominant background arises from U/Th decay chains in the HPGe front-end electronics, with notable but smaller contributions from K and Cs, while environmental isotopes like Co, Mn, and Xe are mitigated by shielding. The validated framework supports detailed background suppression, shielding optimization, and robust spectral interpretation critical for low-threshold, rare-event analyses such as CEvNS and neutrino/dark matter searches at KSNL.

Abstract

A background model has been designed for TEXONO experiment using Geant4 sim- ulation software. The contamination of different radioactive isotopes in the detector background has been considered from both the detector set-up and the environment. 238 U and 232 Th have been confined in the front end electronics of the HPGe detector. These two isotopes are confined by breaking the complete chains into constituent decay chains on the basis of half-life of the isotopes. 235 U isotope is also confined in the front end electronics of the pre-amplifier. 40 K gets confined in NaI(Tl) Anti-Compton Veto (ACV) detector where 137 Cs has been confined in CsI(Tl) ACV detector. The detector environment gets confined with 60 Co, 54 Mn, and 135 Xe. Five million events have been considered in each confinement. The amplitudes of the experimental and simulated peaks have been matched by adjusting the activity of the simulated decay chain.

Paper Structure

This paper contains 12 sections, 12 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Experimental set-up at KSNL
  3. Monte Carlo Simulation using Geant4
  4. Radioactive contamination present in various components of the detector setup
  5. Fission and its activity in the Decay Chains of $^{238}$U and $^{232}$Th
  6. Confinement of $^{238}$U and $^{232}$Th decay chains and $^{235}$U isotope
  7. Confinement of $^{40}$K isotope
  8. Confinement of $^{137}$Cs isotope
  9. Confinement of isotopes in detector environment
  10. Summing of Individual Spectra from Isotope Confinement
  11. Comparison of simulated and experimental spectra
  12. Discussions and Conclusions

Figures (12)

  • Figure 1: Schematic layout of the HPGe detector with its anti-Compton detectors as well as internal shielding and radon purge system Wong(2007).
  • Figure 2: Schematic layout of the electronics and data acquisition systems of the HPGe and the associated ACV and CRV detectors Wong(2007).
  • Figure 3: Semicircular angle view of the modeled detector setup and associated active shielding. $L$ denotes length, $D$ denotes diameter, $T$ denotes thickness, and $OD$ denotes outer diameter.
  • Figure 4: A visual representation of the entire detector setup simulation including auxiliary edges.
  • Figure 5: Simulated spectra of $^{238}$U, $^{232}$Th and $^{235}$U with ACV suppression.
  • ...and 7 more figures