Experimental Determination of Slow-Neutron Detection Efficiency and Background Discrimination in Mixed Radiation Fields Using Differential CR-39 Track Detectors

TL;DR

This study develops and tests a method using paired CR-39 detectors to accurately measure slow neutron fluence in mixed radiation fields, effectively discriminating against background charged particles and fast neutrons.

Contribution

The paper introduces a novel approach combining boron coated and uncoated CR-39 detectors to reliably measure slow neutron fluence in complex radiation environments.

Findings

The difference in track density correlates linearly with exposure time.

Boron coated CR-39 detectors alone are insufficient for accurate measurements.

Using both detectors together provides a reliable estimate of thermal neutron flux.

Abstract

Measuring slow neutrons is difficult when the radiation field also contains charged particles and fast neutrons, especially when the radiation composition is not known in advance. In this work, we present a tested method to measure slow neutron fluence using CR-39 solid state nuclear track detectors. Two detectors are used together: a boron coated CR-39 detector and an uncoated CR-39 detector.The uncoated detector records tracks from charged particles and fast neutrons but does not respond to slow neutrons. The boron coated detector additionally detects charged particles produced when slow neutrons react with boron and generate lithium and alpha particles. Subtracting the track density of the uncoated detector from that of the boron coated detector provides a reliable and conservative measure of slow neutrons.Experiments using a reference thermal neutron source show that the difference between the two detectors increases linearly with exposure time. Statistical analysis gives a slow neutron equivalent track rate of 5.84 plus or minus 0.18 tracks per minute, clearly different from zero. The slope of this response is used to determine the detection efficiency of the boron coated detector. The uncoated detector measures the background caused by fast neutron leakage from the source. These results show that boron coated CR-39 detectors cannot be used alone for accurate slow neutron measurements. Reliable neutron fluence determination requires the simultaneous use of an uncoated detector. The difference between the two detectors provides a correct estimate of the thermal neutron flux in mixed radiation fields and where conventional neutron detectors cannot be used.