The performance evaluation of gamma- and neutron-sensitive superheated emulsion (bubble) detectors.

The superheated emulsion (bubble) detectors have been developed at Defence Laboratory, Jodhpur (DLJ), India, for measurement of gamma doses. The developed detectors have been tested at Radiation Safety and System Division (RSSD), Bhabha Atomic Research Center (BARC), Mumbai (India) and DLJ having ISO-17025 accredited facility for testing and calibration of Radiation Monitors. A series of experiments were conducted to determine the gamma and neutron sensitivity of these detectors, i.e. batch homogeneity, reproducibility, dose equivalent rate effect, gamma/neutron dose equivalent response, gamma/neutron energy response and change in gamma sensitivity as a function of temperature. All the results were within +/- 20% of themselves. It is observed that the response of the detector is dependent upon temperature. The recommended ideal working temperature range of the detector is 20-28 degrees C, but a temperature correction is required beyond approximately 30 masculineC. The temperature compensation may be possible up to 45 degrees C in improved version using specially prepared reversible thermo-sensitive polymer gel. The detector may have applications in radio-diagnosis, R&D laboratories, and health physics as well as an indicator of gamma radiation for dirty bomb to be useful for first responder in any radiological emergency.

Accidental gamma dose measurement using commercial glasses.

Commercial glasses have been investigated for their application in accidental gamma dose measurement using Thermoluminescent (TL) techniques. Some of the glasses have been found to be sensitive enough that they can be used as TL dating material in radiological accident situation for gamma dosimetry with lower detection limit 1 Gy (the dose significant for the onset of deterministic biological effects). The glasses behave linearly in the dose range 1-25 Gy with measurement uncertainty +/- 10%. The errors in accidental dose measurements using TL technique are estimated to be within +/- 25%. These glasses have shown TL fading in the range of 10-20% in 24 h after irradiation under room conditions; thereafter the fading becomes slower and reaches upto 50% in 15 d. TL fading of gamma-irradiated glasses follows exponential decay pattern, therefore dosimetry even after years is possible. These types of glasses can also be used as lethal dose indicator (3-4 Gy) using TL techniques, which can give valuable inputs to the medical professional for better management of radiation victims. The glasses are easy to use and do not require lengthy sample preparation before reading as in case of other building materials. TL measurement on glasses may give immediate estimation of the doses, which can help in medical triage of the radiation-exposed public.

A new chlorophycean nickel hyperaccumulator.

Bioremediation of nickel by chlorophycean bioremediator, Chlorococcum hemicolum was investigated. The growth rates at various concentrations of Ni2+ were assessed in terms of protein level and 12 mg L(-1) of the Ni2+ is the tolerance limit (46.76% level of growth kinetics). Absorption/adsorption kinetics was estimated after 240 h of Ni2+ treatments. Absorptions were higher than adsorption with maximum accumulation factor (AF) of 1.37. Ni2+ concentration and absorption were linearly related (r=0.98; p>0.01). Other biochemical parameters like total sugar, chlorophyll and carotenoids were also quantified to correlate the state of metabolism and these exhibited reduction due to heavy metal stress.

Application of commercial glasses for high dose measurement using the thermoluminescent technique.

Commercial glasses under this study showed linear thermoluminescence (TL) response in gamma dose range 100 Gy to 10 kGy, glow peaks between 175 and 200 degrees C, fading under dark and room light 2.86-7.36% and 10.42-20.82%, respectively, in 24h and 34.86-70.80% under sunlight in 5h after exposure. The TL glass dosimetric results have been found to be reproducible within +/- 6.0%. Glasses have been observed as thermally unstable and its TL sensitivity reduces after annealing. The TL response of the glasses has been found to reduce by 7.40-51.49% after first annealing of the samples at 400 degrees C for 15 min. The trace element study suggests that presence of impurities has no role in TL sensitivity of glasses rather imperfections and dislocations in the lattice are the major contributor in the formation of TL centers. Commercial glasses can serve as good TL material for gamma irradiator and gamma chamber dosimetry. The various radiation parameters for glass TL dosimetry have been studied in detail and presented.

Evaluation of dose distributions in gamma chamber using glass plate detector.

A commercial glass plate of thickness 1.75 mm has been utilized for evaluation of dose distributions inside the irradiation volume of gamma chamber using optical densitometry technique. The glass plate showed linear response in the dose range 0.10 Kilo Gray (kGy) to 10 kGy of cobalt-60 gamma radiation with optical sensitivity 0.04 Optical Density (OD) /kGy. The change in the optical density at each identified spatial dose matrix on the glass plate in relation to the position in the irradiation volume has been presented as dose distributions inside the gamma chamber. The optical density changes have been graphically plotted in the form of surface diagram of color washes for different percentage dose rate levels as isodose distributions in gamma chamber. The variation in dose distribution inside the gamma chamber unit, GC 900, BRIT India make, using this technique has been observed within +/- 15%. This technique can be used for routine quality assurances and dose distribution validation of any gamma chamber during commissioning and source replacement. The application of commercial glass plate for dose mapping in gamma chambers has been found very promising due to its wider dose linearity, quick measurement, and lesser expertise requirement in application of the technique.

Gamma-irradiated onions as a biological indicator of radiation dose.

Post-irradiation identification and dose estimation are required to assess the radiation-induced effects on living things in any nuclear emergency. In this study, radiation-induced morphological/cytological changes i.e., number of root formation and its length, shooting length, reduction in mitotic index, micronuclei formation and chromosomal aberrations in the root tip cells of gamma-irradiated onions at lower doses (50-2000 cGy) are reported. The capabilities of this biological species to store the radiation-induced information are also studied.