Development of Monte Carlo Code for Coincidence Prompt Gamma-ray Neutron Activation analysis

Abstract

Prompt Gamma-Ray Neutron Activation Analysis (PGNAA) offers a non-destructive, relatively rapid on-line method for determination of elemental composition of bulk and other samples. However, PGNAA has an inherently large background. These backgrounds are primarily due to the presence of the neutron excitation source. It also includes neutron activation of the detector and the prompt gamma rays from the structure materials of PGNAA devices. These large backgrounds limit the sensitivity and accuracy of PGNAA.

Since Most of the prompt gamma rays from the same element are emitted in coincidence, a possible approach for further improvement is to change the traditional PGNAA detection technique and introduce the gamma-gamma coincidence technique. It is well known that the coincidence technique can eliminate most of the interference backgrounds and improve the signal-to-noise ratio. A new Monte Carlo code CEARCPG is being developed at CEAR to predict coincidence counting in coincidence PGNAA. Compared to the other existing Monte Carlo code, a new algorithm of sampling the prompt gamma rays, which are produced from neutron capture reaction and neutron inelastic scattering reaction, is developed in this work. All the prompt gamma rays are taken into account by using this new algorithm. Before this work, the commonly used method is to interpolate the prompt gamma rays from the pre-calculated gamma-ray table. It works fine for the single spectrum. However it limits the capability to simulate the coincidence spectrum. This new algorithm is to sample the prompt gamma rays from the nucleus scheme. It makes possible to simulate the coincidence spectrum by using Monte Carlo method. The primary nuclear data library used to sample the prompt gamma rays comes from ENSDF library.

Three cases are simulated and the simulated results are checked with the experiments. The first case is the prototype for ETI PGNAA application. This case is designed to check the capability of CEARCPG for single spectrum simulation. The second case and the third case are designed for coincidence simulation. CEARCPG is also applied to optimize the design of coincidence PGNAA device. A new coincidence PGNAA application is proposed in this work. The probability of extending this code is also discussed.

The funding of this work is provided by the Center for Engineering Application of Radioisotopes (CEAR) at North Carolina State University (NCSU) and Nuclear Engineering Education Research.