ABSTRACT
Advanced instruments and methods need to be developed now to create a technical basis to support the negotiation of future nuclear arms control treaties. One new capability that is anticipated is the ability to confirm either the declared presence or declared absence of high explosive (HE) material in the presence of special nuclear material (SNM). Towards this goal, Passive HE Neutron Inspection (PHENIX) has been developed and demonstrated as a method for confirming the presence or absence of HE in the presence of plutonium. The method exploits the inherent presence of neutrons associated with the decay of plutonium as an internal probe source for performing prompt gamma-ray neutron activation analysis (PGNAA), searching for the presence of HE as revealed by the emission of characteristic gamma rays following neutron absorption in hydrogen and nitrogen which are building blocks of present-day, military-grade HE. Tests using stoichiometrically-correct hemishells of mock HE with plutonium show that a system can be expected to positively confirm the presence or absence of these signatures, supporting determination of HE presence or absence with Pu, in a few hours. To protect other potentially sensitive gamma-ray signatures from a treaty accountable item, an analog information barrier has been conceptualized and tested which physically prevents the collection of gamma-ray spectral data outside of user selected energy windows strategically chosen to view only narrow spectral regions corresponding to the hydrogen (2223.2 keV) and nitrogen (9807.2 keV, 10,318.2 keV, and 10,829.2 keV) PGNAA signatures.
ABSTRACT
Observations of photon and neutron background radiation were made in Rigby, Idaho, during the Great American Eclipse on August 21, 2017. Photon measurements were made using a mechanically-cooled, high-purity germanium gamma-ray spectrometer, segmenting the data into four energy bands of <â¯1â¯MeV, 1-2â¯MeV, 2-3â¯MeV, and 3-7â¯MeV. Neutron measurements were made using 3He proportional counter arrays embedded in polyethylene, either bare or wrapped with Cd or B filters. All data was analyzed in 900-s intervals starting one day before the eclipse and extending to one day after the eclipse. More detailed analyses were made in 90-s intervals for the photon data and 110-s intervals for the neutron data. Meteorological data was simultaneously recorded in 60-s intervals, recording solar radiance, temperature, air pressure, relative humidity, and dew point. For the observations described here, no statistically-significant (> 3σ) variations in signal count rates were observed in either the photon or neutron data. This level corresponds to the lack of observed photon variations exceeding 2.1%, 12.2%, 21.6%, or 43.2% of mean values in the four photon energy groups, respectively; it corresponds to a lack of observed neutron variations exceeding 25.3%, 25.6%, or 16.1% of mean values in the three neutron detector arrays, respectively.
ABSTRACT
A new multiplying test assembly is under development at Idaho National Laboratory to support research, validation, evaluation, and learning. The item is comprised of three stacked, highly-enriched uranium (HEU) cylinders, each 11.4 cm in diameter and having a combined height of up to 11.7 cm. The combined mass of all three cylinders is 20.3 kg of HEU. Calculations for the bare configuration of the assembly indicate a multiplication level of >3.5 (k(eff)=0.72). Reflected configurations of the assembly, using either polyethylene or tungsten, are possible and have the capability of raising the assembly's multiplication level to greater than 10. This paper describes simulations performed to assess the assembly's multiplication level under different conditions and describes the resources available at INL to support the use of these materials. We also describe some preliminary calculations and test activities using the assembly to study neutron multiplication.
