DISTRIBUTION OF RADIONUCLIDES IN RIVER SEDIMENTS OF KATHMANDU VALLEY, NEPAL AND THE EVALUATION OF ASSOCIATED RADIATION HAZARD.

The natural radioactivity in our living environment is mainly due to radionuclides of 40K, 232Th and 238U. We studied the distribution of these radionuclides in the sediment of different rivers and streams throughout the Kathmandu valley. The activity concentrations were determined by using digiBase NaI(TI) gamma-ray spectrometer, and further they were used to calculate radiological hazard indices to estimate the risk associated with the use of these sediments. The average activity concentrations for 40K, 232Th and 238U were found to be 378.54 ± 109.06, 45.95 ± 18.47 and 26.90 ± 9.61 Bq per kg, respectively. The average concentrations and calculated hazard indices have been compared with the respective reported activity concentration in different countries. This study reveals that there is no radiological threat using these local sediments as building materials and for other purposes.

UNCERTAINTY EVALUATION IN MEASUREMENT OF THE PERSONAL DOSE EQUIVALENT AT NINE INDIVIDUAL MONITORING SERVICES IN ASIA AND THE PACIFIC REGION.

This paper presents the results of the evaluation of the uncertainty in measurement of the personal dose equivalent, Hp(10), at nine individual monitoring services (IMSs) in Asia and the Pacific region. Different types of passive dosemeters were type-tested according to the International Electrotechnical Commission 62387 requirements. The uncertainty in measurement was calculated using the Guide to the Expression of Uncertainty in Measurement approach. Expanded uncertainties ranged between 24 and 86% (average = 38%) for Hp(10) values around 1 mSv and between 14 and 40% (average = 27%) for doses around the annual dose limit, Hp(10) = 20 mSv. The expanded uncertainties were lower than the 1.5 factor in either direction proposed by the International Commission on Radiological Protection for doses near the relevant dose limits. This indicates an acceptable level of uncertainty for all participating IMSs. Uncertainty evaluation will help the IMSs to acknowledge the accuracy of their measurements.

RESULTS OF THE JOINT IAEA/ARPANSA INTERCOMPARISON EXERCISE ON WHOLE BODY DOSEMETERS FOR PHOTONS IN ASIA AND THE PACIFIC REGION.

An intercomparison exercise (IC) on whole body dosemeters to determine the quantity personal dose equivalent Hp (10) in photon radiation fields was jointly organised and conducted by the International Atomic Energy Agency (IAEA) and the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) for individual monitoring services (IMS) in Asia and the Pacific region. This was arranged to help the IMS in the region to achieve a more accurate dosimetry service and to improve their performance. Twenty-four IMS participated in this IC. Four sets of dosemeters were irradiated using X-ray and gamma radiation qualities at 0° and 20° angle of incidence, respectively. All the IMS provided results that were within the acceptable limits defined by the IAEA. However, only a minority of participants reported confidence intervals that included the reference dose, for each exposure scenario. For few systems, the overall performance could be significantly improved by reviewing calibration procedures.

Pressure-accelerated dissociation of amyloid fibrils in wild-type hen lysozyme.

The dynamics of amyloid fibrils, including their formation and dissociation, could be of vital importance in life. We studied the kinetics of dissociation of the amyloid fibrils from wild-type hen lysozyme at 25°C in vitro as a function of pressure using Trp fluorescence as a probe. Upon 100-fold dilution of 8 mg ml(-1) fibril solution in 80 mM NaCl, pH 2.2, no immediate change occurred in Trp fluorescence, but at pressures of 50-450 MPa the fluorescence intensity decreased rapidly with time (k(obs) = 0.00193 min(-1) at 0.1 MPa, 0.0348 min(-1) at 400 MPa). This phenomenon is attributable to the pressure-accelerated dissociation of amyloid fibrils into monomeric hen lysozyme. From the pressure dependence of the rates, which reaches a plateau at ~450 MPa, we determined the activation volume ΔV(0‡) = -32.9 ± 1.7 ml mol(monomer)(-1) and the activation compressibility Δκ(‡) = -0.0075 ± 0.0006 ml mol(monomer)(-1) bar(-1) for the dissociation reaction. The negative ΔV(0‡) and Δκ(‡) values are consistent with the notion that the amyloid fibril from wild-type hen lysozyme is in a high-volume and high-compressibility state, and the transition state for dissociation is coupled with a partial hydration of the fibril.