Pooling techniques for bioassay screening

Pooling techniques commonly are used to increase the throughput of samples used for screening purposes. While the advantages of such techniques are increased analytical efficiency and cost savings, the sensitivity of measurements decreases because it is inversely proportional to the number of samples in the pools. Consequently, uncertainties in estimates of dose and risk which are based on the results of pooled samples increase as the number of samples in the pools increases in all applications. However, sensitivities may not be seriously degraded, for example, in urinalysis, if the samples in the pools are of known time duration, or if the fraction of some attribute of the grab urine samples to that in a 24-hour composite is known (e.g., mass, specific gravity, creatinine, or volume, per 24-h interval). This paper presents square and cube pooling schemes that greatly increase throughput and can considerably reduce analytical costs (on a sample basis). The benefit-cost ratios for 5{times}5 square and 5{times}5{times}5 cube pooling schemes are 2.5 and 8.3, respectively. Three-dimensional and higher arrayed pooling schemes would result in even greater economies; however, significant improvements in analytical sensitivity are required to achieve these advantages. These are various other considerations for designing a pooling scheme, where the number of dimensions and of samples in the optimum array are influenced by: (1) the minimal detectable amount (MDA) of the analytical processes, (2) the screening dose-rate requirements, (3) the maximum masses or volumes of the composite samples that can be analyzed, (4) the information already available from results of composite analysis, and (5) the ability of an analytical system to guard against both false negative and false positive results. Many of these are beyond the scope of this paper but are being evaluated

HEU age determination

A new technique has been developed to determine the age of highly enriched uranium (HEU) in solids. Uranium age is defined as the time since the uranium-containing material was last subjected to a process capable of separating uranium from its radioactive-decay daughters. [Most chemical processing, uranium enrichment, volatilization processes, and phase transformations (especially relevant for uranium hexafluoride) can result in separation of the uranium parent material from the decay-product daughters.] Determination of the uranium age, as defined here, may be relevant in verifying arms-control agreements involving uranium-containing nuclear weapons. The HEU age is determined from the ratios of relevant uranium daughter isotopes and their parents, viz {sup 230}Th/{sup 234}U and {sup 231}Pa/{sup 235}U. Uranium isotopes are quantitatively measured by their characteristic gamma rays and their daughters by alpha spectroscopy. In some of the samples, where HEU is enriched more than 99%, the only mode of HEU age determination is by the measurement of {sup 231}Pa since there is negligible quantity of {sup 230}Th due to very low atom concentrations of {sup 234}U in the samples. In this report the methodology and the data for determining the age of two HEU samples are presented

HEU age determination

A technique has been developed to determine the Highly Enriched Uranium (HEU) Age which is defined as the time since the HEU was produced in an enrichment process. The HEU age is determined from the ratios of relevant uranium parents and their daughters viz {sup 230}Th/{sup 234}U and {sup 231}Pa/{sup 235}U. Uranium isotopes are quantitatively measured by their characteristic gammas and their daughters by alpha spectroscopy. In some of the samples where HEU is enriched more than 99%, the only mode of HEU age determination is by the measurement of {sup 231}Pa since there is negligible quantity of {sup 230}Th due to very low atom concentrations of {sup 234}U in the sample. In this paper we have presented data and methodology of finding the age of two HEU samples

Measurement of fallout {sup 239}Pu levels in urine samples by fission track analysis

A Fission Track Analysis (FTA) method for assessing 239Pu in urine samples was first developed at Brookhaven National Laboratory (BNL) in 1988; it then had a detection limit of 100 aCi (3.7 {micro}Bq). Since that time, several steps were introduced that increased chemical recovery and lowered the detection limit to less than 1O aCi per sample. These improvements include a process of micro-column separation of plutonium in the final stages. The improved FTA method was applied to 22 urine samples from male staff at BNL. The results showed that 239Pu from fallout excreted in urine was 33 +/- 11 aCi (1.2 {micro}Bq) per day