Exact method for determining subsurface radioactivity depth profiles from gamma spectroscopy measurements

TL;DR

This paper presents an exact, polynomial-based method to determine subsurface radioactivity depth profiles from gamma spectroscopy measurements, applicable to environmental, decommissioning, and forensic contexts.

Contribution

It introduces a novel polynomial approach for non-destructively deriving subsurface radioactivity profiles from gamma measurements at multiple angles.

Findings

Successfully applied to models with surface-maximal and subsurface-maximal radioactivity.

Demonstrates potential for accurate, in situ profiling of subsurface radioactivity.

Provides a mathematical framework for analyzing gamma spectroscopy data for depth profiles.

Abstract

Subsurface radioactivity may be due to transport of radionuclides from a contaminated surface into the solid volume, as occurs for radioactive fallout deposited on soil, or from fast neutron activation of a solid volume, as occurs in concrete blocks used for radiation shielding. For purposes including fate and transport studies of radionuclides in the environment, decommissioning and decontamination of radiation facilities, and nuclear forensics, an in situ, nondestructive method for ascertaining the subsurface distribution of radioactivity is desired. The method developed here obtains a polynomial expression for the radioactivity depth profile, using a small set of gamma-ray count rates measured by a collimated detector directed towards the surface at a variety of angles with respect to the surface normal. To demonstrate its capabilities, this polynomial method is applied to the simple case where the radioactivity is maximal at the surface and decreases exponentially with depth below the surface, and to the more difficult case where the maximal radioactivity is below the surface.