The algorithm used for isotope identification onboard a radioisotope identifier (RIID) plays a key role in obtaining a correct identification. The majority of RIIDs deployed by the United States Department of Homeland Security are based on NaI spectrometers. Their performance in isotope identification has been well-documented. It has been demonstrated that the secondary analysis of spectra by a trained spectroscopist is frequently necessary to resolve problems in the RIIDs identification. It is also clear that trained spectroscopists are capable of identifying complicated, multiple-line sources with even the poorest resolution detectors such as Nal. This paper seeks to understand the factors in detector performance such as energy resolution that play an important role in isotope identification.

Since September 11, 2001, there has been increasing interest in providing first responders with radiation detectors for use in the search for and isotope identification of potentially-smuggled special nuclear material (SNM) or radiological dispersal devices (RDDs). These devices are typically comprised of low-resolution detectors such as NaI, thus limiting their identification abilities. We present a new technique of wavelet analysis of low-resolution spectra for the use in isotope identification. Wavelet analysis has the benefit of excellent feature localization while, unlike with Fourier analysis, maintaining the signal frequency and time characteristics. We will demonstrate this technique with a series of gamma-ray spectra obtained from typical hand-held isotope identifiers, illustrate figures-of-merit to be applied to these results, and discuss future algorithm optimization.

A critical mass experiment using a 6-kg {sup 237}Np sphere has been performed. The purpose of the experiment is to get a better estimate of the critical mass of {sup 237}Np. To attain criticality, the {sup 237}Np sphere was surrounded with 93 wt % {sup 235}U shells. A 1/M as a function of uranium mass was performed. An MCNP neutron transport code was used to model the experiment. The MCNP code yielded a k{sub eff} of 0.99089 {+-} 0.0003 compared with a k{sub eff} 1.0026 for the experiment. Based on these results, it is estimated that the critical mass of {sup 237}Np ranges from kilogram weights in the high fifties to low sixties.

A portable instrument designed for use in treaty verification has been developed. A multichannel analyzer connected to a NaI(Tl) detector provides a rate meter, a background analyzer, a plutonium detector, and an energy-windowed scanner. The presence of plutonium is detected by excess counts in the 400 keV region. An energy calibration is automatically determined using either of two calibration sources. The simple operator interface is implemented with four lights and pushbuttons.< >

Automated in-field radioisotope identification presents many challenges, including difficult choices in detector technology, the need for high-reliability low-power electronics, and imprecise analysis methods. To meet these challenges, we have developed ruggedized large-volume CdZnTe (CZT) detectors that are coupled to state-of-the-art low-power electronics to perform radioisotope identification with fuzzy logic in real time. The analysis is presented in a simple straightforward manner that enables first responders, customs agents, or other nonexperts to detect, locate, and identify sources of radiation

Radioactive waste containing fissile material is frequently encountered in decontamination and decommissioning activities. For the most part, this waste is placed in containers or drums and stored in storage facilities. The amount of fissile material in each drum is generally small because of criticality safety limits that have been calculated with computer transport codes such as MCNP,1 KENO,2 or ONEDANT.3 To the best of our knowledge, no experimental critical mass data are available to verify the accuracy of these calculations or any calculations for systems containing fissile material (U-235, Pu-239, U-233) in contact with matrix material such as Al2O3, CaO, SiO2, Al, MgO, etc. The experiments presented in this paper establish the critical masses of highly enriched uranium foils diluted to various X/235U ratios with polyethylene and SiO2, polyethylene and aluminum, polyethylene and MgO, polyethylene and Gd, polyethylene and Fe, and moderated and reflected with polyethylene. In addition, these critical mass experimental data will be used to validate cross section data.

This experiment demonstrated how the neutron multiplication of a system increases as moderated material is placed between highly enriched uranium foils. In addition, this experiment served to demonstrate the hand-stacking technique and approach to criticality be remote operation. This experiment was designed by McLaughlin in the mid-seventies as part of the criticality safety course that is taught at the Los Alamos Critical Experiments Facility. The H/{sup 235}U ratio for this experiment was 215, which is the ratio at which the minimum critical mass for this configuration occurs.

Experiments were performed to measure a variety of parameters for SHEBA: behavior of the facility during transient and steady-state operation; characteristics of the SHEBA fuel; delayed-critical solution height vs solution temperature; initial reactor period and reactivity vs solution height; calibration of power level vs reactor power instrumentation readings; flux profile in SHEBA; radiation levels and neutron spectra outside the assembly for code verification and criticality alarm and dosimetry purposes; and effect on reactivity of voids in the fuel.

In June, 1995, Los Alamos National Laboratory hosted the 23rd U.S. Department of Energy sponsored Nuclear Accident Dosimetry Study at the Los Alamos Critical Experiments Facility. The participants tested their facilities accident dosimeters under a variety of neutrons fields produced by the Solution High Energy Burst Assembly (SHEBA) and the Godiva IV fast burst assembly. To provide useful information for the evaluation of the results, the neutron energy Spectrum was determined and the delivered absorbed dose to tissue. The measurement of the neutron energy spectrum on Godiva provides a unique problem in that the burst, which is nearly Gaussian in time, has a full width at half maximum of around 50 microseconds. The neutron spectrum was first determined at low-power while running at delayed critical using a standard set of Bonner spheres. At the same time, the response of a set of TLD dosimeters were measured. After that, measurements were conducted during a burst with another set of TLDs and with sulfur pellets.

The NAVI-2 is a rugged, lightweight, and waterproof portable radiation analyzer developed by the Advanced Nuclear Technology group at Los Alamos National Laboratory. It was originally developed for a specific application: performing confirmatory measurements on plutonium removed from dismantled nuclear weapons as part of the O`Leary-Mikhailov mutual reciprocal inspections agreement. Since that time the hardware has stabilized into a mature package while several additional software packages have been developed. Now, in addition to the original software for performing confirmatory measurements, software is available that will allow the NAVI-2 to be used for scanning of extended sources, searching for hidden sources, and monitoring of items in a portal monitoring sense. This report will provide hardware and software details for owners and users of the NAVI-2.

A new version of the SHEBA assembly is described. Several experiments are proposed for the facility.

The Los Alamos Critical Experiments Facility (LACEF) is now operating after a lengthy period of shutdown that lasted from November 1989 until June 1991. Since June 1991, the efforts of the staff have concentrated on bringing the assemblies back to operational status. The facility is fully operational and performing experiments. This progress report nominally covers the second quarter of FY93 (first quarter of calendar year 1993). It has sections on nuclear criticality safety classes, SHEBA II Project, Godiva IV activities, Skua activities, basic neutron physics measurements, etc.

The relative photodetachment cross section for decay into the H(N = 2) channel by the 1P-degrees shape resonance in H- was measured, as well as that for decay into all channels. The branching ratio sigma(N = 2)/sigma(total) was computed for a series of energies between 10.95 and 11.3 eV after normalizing the cross sections to theoretical peak amplitudes. The maximum branching ratio (almost-equal-to 0.8) appears at an energy about 20 meV higher than the central energy of the resonance. Results are compared with recent theoretical calculations.

Historically, alpha-particle detectors have been limited by the very short range of alpha particles in air. This results in a number of problems inherent to alpha contamination detectors, such as relatively poor sensitivity, geometry limitations, and inefficient monitoring techniques. In this paper, we document tests of a new long-range alpha detector. The charges generated by the interaction of alpha particles with air can be transported over significant distances (several meters) in a moving current of air generated by a small fan. An ion chamber located in front of the fan measures the current carried by the moving ions and, hence, detects the alpha decays.