Year
2012
Abstract
Nuclear resonance fluorescence (NRF) is a promising technique for assaying 239Pu in melted fuel from the Fukushima accident and spent nuclear fuel because of its sensitivity and isotope specific nature. It can be extended by using the average resonance properties of the nucleus. In the NRF process, a nucleus resonantly absorbs a ? ray, and then emits a characteristic photon. However, there exists two problem: the first is the ?-ray background from the radioactive nature of the fuel, and the second is the background due to beam- induced atomic scattering. Both backgrounds produce a count rate requirement on the detectors beyond the limits of current detector technologies. We propose two methods for solving these problems. Both methods measure the average nuclear resonance absorption (NRA) of the ?-ray beam due to specifically 239Pu, but differ in how they measure the final signature. The first proposed method measures the NRF ?-ray signature of all excited states. The second proposed method uses a beam energy above the photofission threshold, and measures neutrons from photofission. The second method is directly analogous to the self-interrogation method using neutron beams. We will present the methodology and results of calculations, demonstrating that the average NRA method utilizing the ?-ray signature is an order of magnitude more sensitive than a single resonance self-absorption measurement, and that the fission measurement is comparably sensitive to the single resonance self-absorption measurement while being insensitive to the background from atomic scattering.