131I dose coefficients for a reference population using age-specific models.

Age-specific dose coefficients are required to assess internal exposure to the general public. This study utilizes reference age-specific biokinetic models of iodine to estimate the total number of nuclear disintegrations ã(rS,τ) occurring in source regions (rS) during the commitment time (τ). Age-specific S values are estimated for 35 target regions due to131I present in 22rSusing data from 10 paediatric reference computational phantoms (representing five ages for both sexes) published recently by the International Commission of Radiation Protection (ICRP). Monte Carlo transport simulations are performed in FLUKA code. The estimated ã(rS,τ) and S values are then used to compute the committed tissue equivalent dose HT(τ) for 27 radiosensitive tissues and dose coefficients e(τ) for all five ages due to inhalation and ingestion of131I. The derived ã(rS,τ) values in the thyroid source are observed to increase with age due to the increased retention of iodine in the thyroid. S values are found to decrease with age, mainly due to an increase in target masses. Generally, HT(τ) values are observed to decrease with age, indicating the predominant behaviour of S values over ã(rS,τ). On average, ingestion dose coefficients are 63% higher than for inhalation in all ages. The maximum contribution to dose coefficients is from the thyroid, accounting for 96% in the case of newborns and 98%-99% for all other ages. Furthermore, the estimated e(τ) values for the reference population are observed to be lower than previously published reference values from the ICRP. The estimated S, HT(τ) and e(τ) values can be used to improve estimations of internal doses to organs/whole body for members of the public in cases of131I exposure. The estimated dose coefficients can also be interpolated for other ages to accurately evaluate the doses received by the general public during131I therapy or during a radiological emergency.

Development of a rapid technique for sequential separation of plutonium/americium in nasal swab using solvent extraction and liquid scintillation spectrometry.

A rapid radiochemical method has been developed for estimation of plutonium and americium in nasal swab using extractive liquid scintillation spectrometry. The method involves solvent extraction of plutonium and americium from pre-treated nasal swab using 0.2 M Di-(2-ethylhexyl)phosphoricacid prepared in toluene scintillator & back extraction of americium in aqueous phase using 0.35 M HNO3. Activity assessment was carried out using liquid scintillation spectrometry. Overall recovery obtained was 96% for plutonium and 76% for americium with a sample turnaround time of 3 h.

Creatinine as a normalization factor to estimate the representativeness of urine sample - Intra-subject and inter-subject variability studies.

In-vitro bioassay monitoring generally involves analysis of overnight urine samples (~12 h) collected from radiation workers to estimate the excretion rate of radionuclides from the body. The unknown duration of sample collection (10-16 h) adds to the overall uncertainty in computation of internal dose. In order to minimize this, IAEA recommends measurement of specific gravity or creatinine excretion rate in urine. Creatinine is excreted at a steady rate with normally functioning kidneys therefore, can be used as a normalization factor to infer the duration of collection and/or dilution of the sample, if any. The present study reports the chemical procedure standardized and its application for the estimation of creatinine as well as creatinine co-efficient in normal healthy individuals. Observations indicate higher inter-subject variability and lower constancy in daily excretion of creatinine for the same subject. Thus creatinine excretion rate may not be a useful indicator for extrapolating to 24 h sample collection.

Application of alpha track registration technique for plutonium estimation in bioassay samples.

Bioassay monitoring is carried out for occupational workers handling plutonium (Pu) in nuclear facilities. In India, presently Pu estimation in bioassay samples is done by alpha spectrometry. The minimum detectable activity (MDA) of alpha spectrometry is 0.5mBq for a counting period of 1 day. To reduce the load of sample counting on alpha spectrometry, an alternative method based on alpha track registration in solid state nuclear track detectors (SSNTDs) is developed in the present paper. For this purpose, few urine samples of normal subjects spiked with known amounts of Pu in the range of 0.5-5.5mBq were exposed to CR-39 SSNTDs. The total number of alpha tracks seen in the CR-39 films of the sample and the standard were used to calculate the amount of Pu in the sample. The results of alpha track registration technique were also compared with that obtained by the well-established alpha spectrometry and were found to agree well within +/-30%. The minimum amount of Pu that can be analyzed by this method is 0.18mBq for an exposure period of 45 days.