Neeraj Sethi

Date of Award


Document Type


Degree Name

Master of Science


Department of Engineering Physics

First Advisor

Benjamin R. Kowash, PhD.


This research utilizes the relationship between source location, background radiation and detector placement to quantify an expected detector response from a 3x3 Sodium Iodide gamma detector. A parametric equation is developed to calculate the detector response as a function of distance and source photon energy. Using MCNP particle current and pulse height tally functions, backscattering photons are quantified as a function of material thickness and energy distribution. Three configurations of source - detector - scattering medium were modeled in MCNP using the pulse height tally functions, integrated over a 70keV - 360keV energy window and plotted as a function of the detector distance from the scattering medium. The resulting fit equations described the effects on detector response from the backscattered photons from any wall in a box shaped space. The superposition of the individual scattering contributions from six surfaces made up the total scattering contribution and predicted the overall expected detector response. The same data sets were also plotted and fitted as a function of distance and energy to produce 3 dimensional parametric equations that predicted detector response over ranges of distance and energy. The normalized superposition and 3D superposition calculated responses were within 4% of the observed responses.

AFIT Designator


DTIC Accession Number


Included in

Nuclear Commons