Sensitivity of the calculation of true coincidence summing correction factors in gamma-ray spectrometry

SCK•CEN Mentor

Vidmar Tim, tvidmar@sckcen.be, +32 (0)14 33 21 10

Expert group

Crisis Management and Decision Support

SCK•CEN Co-mentor

Camps Johan , jcamps@sckcen.be , +32 (0)14 33 27 61

Introduction

True coincidence summing (TCS) corrections almost always need to be applied in gamma-ray spectrometry whenever a radionuclide is present in the sample with a complex decay scheme. Namely, in such a case more than one gamma-ray can be emitted by the nucleus at the same time and simultaneously detected, which leads to the loss of counts from the corresponding peak areas of the gamma lines involved when compared to peak areas of equivalent mono-energetic emitters. Since the full-energy peak efficiency, the knowledge of which is required for the computation of the activity of a given radio-nuclide based on its full-energy peak areas, is defined for mono-gamma emitters, the summing effect needs to be corrected for, both in the calibration and in the analysis phase of the measurement.

The TCS correction factors can be measured, but the preparation of the required standards is involved and costly, so computational methods are increasingly being used instead. These are always based on a detector model that never exactly corresponds to the real detector, which introduces an error in the calculation of the TCS correction factors. More specifically, one can speak of the error in the computation of the full-energy peak and total efficiencies, which serve as input to the calculation of the TCS correction factors themselves.

Objective

The aim of the study is to quantify the effect of the uncertainty (error) in the full-energy-peak and total efficiencies on the resulting TCS correction factors. It is well known that due to the nature of the formulae governing the computation of the TCS correction factors any uncertainties in the input efficiencies only have a limited effect on the uncertainties of the final result. However, no large scale study of the phenomenon has ever been conducted. We intend to remedy this.

By a large scale study we mean one that involves many different radio-nuclides and several typical detector and sample models encountered in environmental gamma-ray spectrometry. The EFFTRAN code will be used for this purpose because of its fast computation of TCS correction factors and will be run twice for each combination of a detector model, a sample model and a given radionuclide, once with the default efficiencies, as resulting from its application, and once with the efficiencies increased (or decreased) by a certain percent of the original value.  The full EFFTRAN library of radio-nuclides will be processed in this way. This should give us an insight into which of those are sensitive to inaccuracies in the input efficiencies, and which less so. The result will be of real value to practitioners of gamma-ray spectrometry. 

 

The minimum diploma level of the candidate needs to be

Academic bachelor

The candidate needs to have a background in

Physics

Estimated duration

9-12 months