Ned A. Wogman

Precise trace rare earth analysis by radiochemical neutron activation

A rare earth group separation scheme followed by normal Ge(Li), low energy photon detector (LEPD), and Ge(Li)−NaI(Tl) coincidence-noncoincidence spectrometry significantly enhances the detection sensitivity of individual rare earth elements (REE) at or below the ppb level. Based on the selected γ-ray energies, normal Ge(Li) counting is favored for140La,170Tb and169Yb; LEPD is favored for low γ-ray energies of147Nd,153Sm,166Ho and169Yb; and noncoincidence counting is favored for141Ce,143Ce,142Pr,153Sm,171Er and175Yb. The detection of radionuclides152mEu,159Gd and177Lu is equally sensitive by normal Ge(Li) and noncoincidence counting;152Eu is equally sensitive by LEPD and normal Ge(Li); and153Gd and170Tm is equally favored by all the counting modes. Overall, noncoincidence counting is favored for most of the REE. Precise measurements of the REE were made in geological and biological standards.

Natural Contamination in Radionuclide Detection Systems

Through the use of low-level gamma-ray spectrometry, clean material for construction of radionuclide detection systems has been identified. In general aluminum contains high quantities of 232Th and 238U with minimal quantities of 40K. Stainless steels contain 60Co. The radioactive contents of foams, cements, and light reflective materials are quite variable. Molecular sieve materials used in germanium spectrometers contain from 4-9 dpm/g. Only through a judicious choice of materials can a spectrometer with the lowest achievable background be assembled.

Evaluation of a Phoswich Detector for the in Situ Analysis of 90Sr

A Phoswich detector system which employs a 3.45 mm thick by 12.5 cm diameter CaF2(Eu) crystal coupled to a 6.4 cm thick NaI(Tl) crystal was evaluated for the detection of 90Sr(90¿) in the presence of 106Ru (106Rh) and 137Cs and for its ability to measure 238pu, 239pu, 241Am and 244Cm. The radioactive species were studied, both as surface contamination and contamination distributed in sediments, as a function of overburden thickness for different materials. The CaF2(Eu) crystal detects beta or low energy photon emissions while the NaI(Tl) crystal only detects higher energy photons from radionuclide decay or bremsstrahlung radiation. As little as 9 d/m/cm2 of 90Sr as surface contamination can be measured in a 1000 second counting period in the presence of comparable concentrations of 137Cs and 106Ru. The Phoswich system is specifically designed for the measurement of 90Sr(90¿) and does not detect the transuranic species well. The operating parameters and use of the Phoswich system for identification of specific radionuclides in shallow land waste burial environments are discussed.

Prospects for the introduction of wide area monitoring using environmental sampling for proliferation detection

The International Atomic Energy Agency (IAEA) is committed to strengthening and streamlining the overall effectiveness of the IAEA safeguards system within the context of the Non-Proliferation Treaty (NPT). The IAEA has investigated the use of environmental monitoring techniques and a variety of techniques were studied as part of extensive field trials. The efficacy of long-range monitoring depends on the availability of mobile signature isotopes or compounds and on the ability to distinguish the nuclear signatures from background signals and attribute them to a source. The Comprehensive Nuclear Test Ban Treaty (CTBT) also requires a variety of environmental sampling and analysis techniques. This paper serves as a scientific basis to start discussions of environmental sampling techniques that could be considered for wide-area monitoring for the detection of undeclared nuclear activities within the NPT or for the possible future use within the CTBT.

Wide-area aquatic sampling and analysis for the detection of nuclear proliferation

Nuclear proliferation signature radionuclides can be delivered to the aquatic environs via direct liquid discharges or atmospheric routes. The candidate radionuclides for detection are 3H, 90Sr, 95Nb, 95Zr, 99Tc, 106Ru, 125Sb, 129I, 134Cs, 137Cs, 144Ce, 147Pm, NatU, 238U, 235U, 237Np, 239Pu, 240Pu, and 241Pu. The criteria for detection are the limits of radionuclide analysis, the nature and variability of background oncentrations, and the transport characteristics between the source and sample site. The type of sample to be taken is determined by the signature radionuclides sorption on/in the media sampled. Non-sorbing radionuclides such as 3H, 99Tc, and 129I are in the water, whereas the Pu radionuclides are in the transported sediments. Results are discussed for monthly releases of radionuclides such as 90Sr, 137Cs, and 239Pu for variable flow-rate conditions with typical backgrounds and typical detection limits.

The 76Ge double beta decay experiment at Homestake

An ultralow background intrinsic Ge detector has been developed over several generations of experiments. The radioactive background from construction materials has been reduced by more than two orders of magnitude. The sources of background in a standard commercial cryostat have been identified and eliminated. Data taken with this 135 cm3 prototype installed in the Homestake Gold Mine are presented. A large (1440 cm3) detector and data acquisition system now under construction are also described.

Screening of potential sites for undeclared nuclear facilities in environmental monitoring for nuclear proliferation

The sensitivity of environmental sampling and analysis for the estimated atmospheric concentrations of radionuclides in effluents from clandestine nuclear facilities may require many sampling sites and exorbitant costs to monitor such large areas. An assessment has been made of the key factors necessary to support the operation of a nuclear facility, e.g., the existence of a nearby transportation network, main electrical power supply, and population centers. Screening, the subject of this paper, evaluates how cartographic data and satellite imagery can be used to identify areas most capable of supporting undeclared nuclear operations. As a result, large geographical areas can be eliminated from environmental monitoring and sampling. This leads to reduced costs, a reduction in the number of sampling sites required, and a reduction in the overall level of effort required to accomplish effective environmental monitoring. The screening methodology and techniques are described and examples given.

Double Beta Decay: Recent Developments and Projections

A report of recent events in both theoretical and experimental aspects of double beta decay is given. General theoretical considerations, recent developments in nuclear structure theory, geochronological determinations of half lives and ratios as well as laboratory experiments are discussed with emphasis on the past three years. Some projections are given.

Status of the Battelle‐Carolina 76Ge Double beta decay experiment

The status of the development of the Battelle−Carolina 76−Ge double beta decay experiment is presented. Emphasis in this article is on background studies. (AIP)