Several incidences of nuclear smuggling during the past
few decades
have raised the demand for the development of a strong “on-site”
nuclear forensic infrastructure. High-resolution γ-ray spectrometry
(HRGRS) plays an important role in nuclear forensics. However, the
existing methodologies, developed primarily for nuclear fuel cycle
applications, are relative and rely on the availability of a standard,
limiting their use for the absolute assay of special nuclear materials
in nonstandard geometry samples with an unknown matrix, which is vital
to make a quick “on-site” decision on the severity,
potential radiological threat, and intended use of an interdicted
package. In this work, a methodology has been developed using HRGRS
for quantifying fissile (235U, 239Pu) and other
radioisotopes, which is applicable to sealed packages without requiring
the knowledge of the sample geometry and the matrices. By combining
experiments and Monte Carlo simulations, an iterative methodology
has been proposed for “point” to “extended”
source absolute efficiency transformation and demonstrated further
for the absolute isotopic assay of uranium and plutonium standards,
mock-up nuclear forensic samples, and an unknown nuclear material
mixture with a nonstandard geometry, compound matrices, and a wide
variation in the elemental and isotopic compositions with a view to
imitate an “on-site” experience. The present methodology
requires an assay time of only a few minutes to an hour and thus promises
“on-site” nuclear forensic analysis of suspected flagged
packages at borders and ports using high-resolution γ-ray spectrometry.
Furthermore, the present methodology is versatile and can also be
adopted for wider applications, beyond nuclear forensics.