John Alan Bounds

Long-range alpha detector.

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.

Alpha contamination monitoring of surfaces, objects, and enclosed areas

The usefulness of traditional alpha detectors for contamination monitoring is limited by the size and sensitivity of the detectors and by the short range of alpha particles in air. The long-range alpha detector (LRAD) detects the ions produced by the alpha particles passing through air, rather than the alpha particles themselves, limiting LRAD detection by the range of the ions (tens of meters), rather than the range of the alpha particles (a few centimeters). Since the LRAD collects all ions simultaneously, an LRAD monitor is sensitive to all of the sources of contamination contained within it. The electronic noise within the LRAD can be reduced so that better sensitivity than traditional detectors is also possible. These advantages are used in the object, pipe, and duct, floor, and soil surface monitors discussed. The design of these monitors and field test results are presented. >

Long-range alpha detector (LRAD) for contamination monitoring

The authors describe a novel long-range alpha detector (LRAD) in which alpha particles interact with the ambient air, producing ionization in the air at the rate of about 30000 ion pairs per megaelectronvolt of alpha energy. These charges 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. The LRAD-based monitor is more sensitive and more thorough than conventional monitors. The authors present current LRAD sensitivity limits and results, practical monitor designs, and proposed uses for LRAD monitors.<<ETX>>

Long-range alpha detector (LRAD) sensitivity to beta contamination and soil moisture

Long-range alpha detector (LRAD) systems are designed to monitor alpha contamination by measuring the ionization in air formed by the alphas. Recent tests have been performed to determine the sensitivity of LRAD systems to beta contamination and soil moisture levels. These results and the general technology are discussed in this paper. >

LRAD-based alpha-particle contamination monitoring of personnel and equipment

Traditional alpha-particle contamination monitors are limited in usefulness because of the short range of alpha particles in air. This range limitation makes it impossible to adequately monitor for alpha-particle contamination on uneven surfaces and inside equipment. Personnel must be scanned manually, a procedure that is comparatively uncertain. The long-range alpha detector eliminates many of the difficulties associated with equipment and personnel monitoring by detecting the ions produced by the alpha particles interaction with the air, rather than detecting the alpha particle itself. The personnel and equipment monitors are described in detail, and other potential applications are suggested.

Whole body personnel monitoring via ionization detection

A project between Fernald EMP and LANL is to field a monitor for the detection of alpha-emitting contamination on a human body. Traditional personnel monitoring for alpha emitters involves either frisking with a probe or pressing against large detectors in order to overcome the short range of alpha particles. These methods have a low alpha collection efficiency, and can miss contamination on less accessible surfaces. We have investigated the sensitivity and practicality of measuring the entire subject simultaneously using the technique of ionization monitoring. The goal is to create a booth that personnel step into quickly during egress from radiological facilities. The detection technique relies on a breeze of air passing over the subject. Alpha emission produces copious ions in the ambient air which are transported by the air current to an ion collector, resulting in a small electrical current proportional to the amount of contamination. Results indicate a conservative sensitivity of 3000 disintegrations per minute localized to one of five areas of the body in a measurement lasting less than 2 minutes.

A portable swipe monitor for alpha contamination

A portable swipe monitor has been developed at Los Alamos National Laboratory for the state of New Mexico. The monitor is intended for use at New Mexico ports of entry to detect removable alpha contamination on shipments bound for the proposed Waste Isolation Pilot Plant (WIPP). This detector uses Long-Range Alpha Detection (LRAD) technology, which monitors ionization created by alpha interactions with ambient air, and includes built-in background subtraction of external radiation fields and radon. Its sensitivity to alpha contamination is on the order of a few tens of dpm, and it has excellent linearity throughout its entire range of over 200,000 counts per minute of alpha activity. Designed to be used primarily in the field, the monitor is battery-powered and can operate continuously for up to five hours.

Long-range alpha detector sample monitoring

Abstract Long-range alpha detector (LRAD) systems are designed to monitor alpha sources and contamination by measuring the number of ions created in air by ionizing radiation. Traditional alpha detectors are designed to detect alpha particles directly and must be passed slowly within about 3 cm of an alpha source to operate effectively. LRAD detectors collect the ions created from alpha interactions with air. Therefore, they are better able to monitor equipment and complex surfaces and can be operated at a much greater distance from an alpha source than traditional alpha detectors. Furthermore, because LRAD detectors remain stationary during monitoring, they are less subject to operator error than traditional alpha detectors. This paper will discuss the basic operation as well as recent advances that have been made to LRAD Sample Monitors.

Long-range alpha detector (LRAD) technology, results, and applications

The usefulness of traditional alpha detectors for contamination monitoring is limited by the size and sensitivity of the detectors and by the short range of alpha particles in air. The long-range alpha detector (LRAD) detects the ions produced by the alpha particles passing through air, rather than the alpha particles themselves. Thus, LRAD detection is limited by the range of the ions (tens of meters), rather than the range of the alpha particles (a few centimeters). Since it collects all ions simultaneously, an LRAD monitor will be sensitive to all of the sources of contamination contained within it. In addition, the electronic noise within the LRAD can be reduced so that better sensitivity than that of traditional detectors is possible. Both soil surface and object monitors incorporate these advantages in their designs. Field-test results for these monitors are discussed.<<ETX>>

Lead Void Reactivity Worth in Two Critical Assembly Cores with Differing Uranium Enrichments

Abstract To validate lead (Pb) nuclear cross sections, a series of integral experiments to measure lead void reactivity worths was conducted in a high-enriched uranium (HEU)/Pb system and a low-enriched uranium (LEU)/Pb system using the Comet Critical Assembly at the National Criticality Experiments Research Center. There is a follow-on experiment to measure the lead void reactivity worths in a plutonium/Pb system that is currently under investigation. The critical experiments in the two uranium systems were designed to provide complementary data sets having different sensitivities to scattering cross sections of lead. The larger amount of the 238U present in the LEU/Pb core increases the neutron importance above 1 MeV compared with the HEU/Pb core. Since removal of lead from the core shifts the neutron spectrum to the higher energy region, positive lead void reactivity worths were observed in the LEU/Pb core while negative values were observed in the HEU/Pb core. This technical note is a preliminarily report of the experimental analysis results for the lead void reactivity worths with the Monte Carlo calculation code MCNP® version 6.1 together with nuclear data libraries JENDL-4.0 and ENDF/B-VII.1. The calculation values were found to overestimate the negative reactivity worths for the HEU/Pb core while being consistent for the LEU/Pb core.