Light Yield Response of Neutron Scintillation Screens to Sudden Flux Changes.

Tobias Neuwirth,Bernhard Walfort,Michael Schulz,Simon Sebold

doi:10.3390/jimaging6120134

Abstract

We performed a study of the initial and long term light yield of different scintillation screen mixtures for neutron imaging during constant neutron irradiation. We evaluated the light yield during different neutron flux levels as well as at different temperatures. As high frame rate imaging is a topic of interest in the neutron imaging community, the decay characteristics of scintillation screens are of interest as well. Hence, we also present and discuss the decay behavior of the different scintillation screen mixtures on a time scale of seconds. We have found that the decay time of ZnS:Cu/6LiF excited with a high neutron flux is potentially much longer than typically stated. While most of the tested scintillation screens do not provide a significant improvement over currently used scintillation screen materials, Zn(Cd)S:Ag/6LiF seems to be a good candidate for high frame rate imaging due to its high light yield, long-term stability as well as fast decay compared to the other evaluated scintillation screens.

Highlights

Nondestructive testing is a key feature of neutron imaging [1]
Exposure times in this regime pose challenges with respect to the available neutron flux, the camera system, as well as the decay time of the scintillation materials, which are an essential component of almost all detection systems for neutron imaging
In the 6LiF-based scintillation screens the excitation radiation is the same, we focus on those screens when comparing the light yield changes

Summary

Introduction

Nondestructive testing is a key feature of neutron imaging [1]. The neutron contrast modality depends on the specific nuclear core structure, enabling the analysis of both heavy and light elements, as well as differentiation between isotopes. One focus of neutron imaging is time-resolved imaging in the sub-second regime [2,3,4] Exposure times in this regime pose challenges with respect to the available neutron flux, the camera system, as well as the decay time of the scintillation materials, which are an essential component of almost all detection systems for neutron imaging. The decay time of the light emission of scintillation screens influences the following images, as the light emission generated in one frame may still be emitted during the exposure of the subsequent frame i.e., generating ghost images. This degrades the quality of the measured data. It should be noted that this result differs from previously recorded results, which suggest a decay time of 85 μs to 10% [5] in a ZnS/6LiF scintillation screen

Methods

Results

Conclusion