ENHANCED RADIOACTIVE CONTENT OF 'BALANCE' BRACELETS.

During a routine whole body counting measurement of a worker at the Nuclear Research Center Negev, abnormal activities of (232)Th and (238)U were measured. After a thorough investigation, it was found that the radioactivity was due to a rubber bracelet ('balance bracelet') worn by the worker during the measurement. The bracelet was counted directly by an high pure germanium gamma spectrometry system, and the specific activities determined were 10.

Fast determination of ⁹⁰Sr/⁹⁰Y activity in milk by Cherenkov counting.

Cherenkov counting of the ⁹⁰Sr/⁹⁰Y pure beta emitters is an attractive method for ⁹⁰Sr activity determination, but the color quenching effect may be significant, especially for strongly colored or semi-opaque media. A quench correction method based on the external source of some liquid scintillation systems (named ESAR - external source area ratio) was proposed and checked for aqueous solutions and was proved to be effective also for urine samples. In the present work, the application of the ESAR method for fast determination of ⁹⁰Sr/⁹⁰Y activity in milk samples is described.

Determination of 90Sr-90Y activity in urine samples by using Cherenkov counting.

Cherenkov counting of the (90)Sr-(90)Y pure beta emitters in aqueous samples is an attractive method; but color quenching correction is needed, this being especially significant for urine which is characterized by a strong coloration. A quench correction method based on the external source of some liquid scintillation systems (named ESAR-External Source Area Ratio) was proposed for aqueous solutions. In the present work, the application of the ESAR method for determination of (90)Sr-(90)Y in human urine samples is described.

A comparative study of color quenching correction methods for Cerenkov counting.

The color quenching correction for Cerenkov counting is normally based on indexes defined for liquid scintillation spectra. Because of the differences in the spectrum shapes, these indexes are not optimal, and a different method was proposed based on the integral counting of the external (152)Eu source spectra of a 1200 Quantulus system. We have shown that this method, named ESAR (external source area ratio), is superior to all the other correction methods, offering the highest sensitivity and the widest range of application.

Color quench correction for low level Cherenkov counting.

The Cherenkov counting efficiency varies strongly with color quenching, thus correction curves must be used to obtain correct results. The external (152)Eu source of a Quantulus 1220 liquid scintillation counting (LSC) system was used to obtain a quench indicative parameter based on spectra area ratio. A color quench correction curve for aqueous samples containing (90)Sr/(90)Y was prepared.

Determination of the solubility and size distribution of radioactive aerosols in the uranium processing plant at NRCN.

Inhalation is the main route of internal exposure to radioactive aerosols in the nuclear industry. To assess the radiation dose from the intake of these aerosols, it is necessary to know their physical (aerodynamic diameter distribution) and chemical (dissolution rate in extracellular lung fluid) characteristics. Air samples were taken from the uranium processing plant at the Nuclear Research Center, Negev.

Determination of radioiodine activity in charcoal cassettes.

Sampling of radioiodine in air is accomplished by passing an air sample through an activated charcoal cassette. A mathematical model was developed, which assumes that radioiodine distribution along the cassette axis can be expressed by an exponential function. The model was validated experimentally for cassettes used for air sampling of radioiodine production boxes.

Normalisation of spot urine samples to 24-h collection for assessment of exposure to uranium.

For dose assessment of workers at Nuclear Research Center Negev exposed to natural uranium, spot urine samples are analysed and the results are normalised to 24-h urine excretion based on 'standard' man urine volume of 1.6 l d(-1). In the present work, the urine volume, uranium level and creatinine concentration were determined in two or three 24-h urine collections from 133 male workers (319 samples) and 33 female workers (88 samples).

An improved method for Organic Bound Tritium (OBT) determination in urine samples.

The Organic Bound Tritium (OBT) amount in the body may induce changes in the evaluation of the internal exposure to tritium, due to its different retention time relative to HTO. OBT measurements for urine are not performed routinely, mainly because of the lengthy work needed in preparation of the samples, when using the standard oxygen combustion method. A simpler and more rapid method based on liquid scintillation counting (LSC) was employed, and an evaluation was performed to check its suitability for urine samples.

Improved localization of a 'hot spot' in the lungs for an array of four HPGe detectors--the isotopic ratio effect.

Considerable errors in the determination of radioactivity in lungs are caused by the usual assumption of homogeneous distribution, while actually the radioactive contamination can be distributed, and even in the form of a 'hot spot'. Modern lung counter systems use several HPGe detectors, and the ratio of the different count rates of the detectors can be used to locate a 'hot spot' and apply correction algorithms for activity calculation. In the present work it is shown that the variability of the isotopic composition of the uranium source has a major effect on the process of localization of the 'hot spot' in the lungs.

MDA improvement technique for lung counter measurements of uranium workers.

A practical and simple method was employed to improve the minimum detectable activity (MDA) for lung counting measurements by summing several accumulated spectra. The method was checked for natural uranium, which produces peaks due to photon energies of 63.3, 92.

Improved determination of the position and activity of a radioactive point source inside a bulky medium using several detectors. The special case of a lung counter--a general view.

A method is described to locate a radioactive point source in a lung using a commercial array of lung detectors. The method takes advantage of the fact that modern commercial systems consist of several Ge detectors, each connected to a multi-channel analyzer, and the information from each detector can be analyzed separately. The system is calibrated with point sources placed in various locations in the lungs of a phantom.

Determination of quality parameters from statistical analysis of routine TLD dosimetry data.

Following the as low as reasonably achievable (ALARA) practice, there is a need to measure very low doses, of the same order of magnitude as the natural background, and the limits of detection of the dosimetry systems. The different contributions of the background signals to the total zero dose reading of thermoluminescence dosemeter (TLD) cards were analysed by using the common basic definitions of statistical indicators: the critical level (L(C)), the detection limit (L(D)) and the determination limit (L(Q)). These key statistical parameters for the system operated at NRC-Negev were quantified, based on the history of readings of the calibration cards in use.

The virtual point detector concept for HPGe planar and semi-planar detectors.

The virtual point detector assumption was validated for planar and semi-planar detectors. The distance of the virtual point detector from the detector face is larger than the thickness of the detector, which means that the virtual detector position is outside the volume of the detector.

Establishing schedules for repeated doses of strontium and for concurrent chemotherapy in hormone-resistant patients with prostate cancer: measurement of blood and urine strontium levels.

Strontium-89 (Sr-89) alone or with concurrent chemotherapy has a role in the treatment of patients with prostate cancer (PCP). The schedules for repeated doses of Sr-89 or for concurrent chemotherapy is undetermined. The objective of this study was to measure the effective half-life (Te) of Sr-89 using a detector available in a nuclear research facility.

Determination of parameters relevant to alpha spectrometry when employing source coating.

The recoil fragments from an alpha-emitting source may cause significant detector contamination. The simplest method to avoid the problem is to use a source coating. The influence of Mylar film coatings of different thickness on the resolution, efficiency and minimum detection level of an alpha spectrometry system was investigated.

Locating a "hot spot" in the lungs when using an array of four HPGe detectors.

Considerable errors in the activity determination in lungs can be induced for the case of a "hot spot". Modern lung counter systems use several HPGe detectors, and the count rate ratios of the detectors can be used to locate the "hot spot" and apply correction algorithms. Some criteria for location determination of a point source in the lungs were investigated, and it is shown that an average error of up to about 10% can be achieved.

The validity of the virtual point detector concept for absorbing media.

The concept of representing the detector volume by a virtual point detector in order to facilitate efficiency evaluations was proposed in the past for non-absorbing media. The validity of the model was expanded also to absorbing media present between the detector and a point source in front of it. Empirical values were determined based on experiments with aluminum, copper, iron and lead.

The interference of medical radionuclides with occupational in vivo gamma spectrometry.

Radiation workers undergo routine monitoring for the evaluation of external and internal radiation exposures. The monitoring of internal exposures involves gamma spectrometry of the whole body (whole body counting) and measurements of excreta samples. Medical procedures involving internal administration of radioactive radionuclides are widely and commonly used.

REM need in adolescents as indicated by resistance to REM deprivation.

The hypothesis that adolescents have an exceptionally strong need for REM sleep was tested by measuring their resistance to REM deprivation. Ten adolescents (aged 16 to 17 yr.) were compared with 12 young adults (aged 25 to 27 yr.