Experimental simulation of personal dosimetry in production of medical radioisotopes by research reactor

Due to their work conditions, research reactor personnel are exposed to ionising nuclear radiations. Because the absorbed dose values are different for different tissues due to variations in sensitivity, in this work personal dosimetry has been performed under normal working conditions at anatomical locations relevant to more sensitive tissues as well as for the whole body by employing a Rando phantom and thermoluminescent dosemeters (TLDs). Fifty-two TLDs-100H were positioned at high-risk organ locations such as the thyroid, eyes as well as the left breast, which was used to assess the whole-body dose in order to study the absorbed doses originating from selected locations in the vicinity of the reactor. The results have employed the tissue weighting factors based on International Commission on Radiological Protection ICRP 103 and ICRP 60 and the measured results were below the dose limits recommended by ICRP. The mean effective dose rates calculated from ICRP 103 were the following: whole body, 30.64-6.44 μSv h(-1); thyroid, 1.22-0.23 μSv h(-1); prostate, 0.085-0.045 μSv h(-1); gonads, 1.00-0.51 μSv h(-1); breast, 3.68-0.77 μSv h(-1); and eyes, 33.74-7.01 μSv h(-1).     

Determination of the mass fraction of crystals in partly frozen hydrocarbon fuels

The per cent by mass of crystalline solid in a partly frozen hydrocarbon fuel cannot be determined by a filtration experiment alone because the precipitate retained by the filter entraps large amounts of the liquid phase. A technique has been developed which augments the filtration experiment with an independent determination of the amount of liquid in the precipitate and hence allows calculation of the true value of the mass percent of crystalline solid, %S. This method involves the addition to the initial fuel of a small amount of a non-crystallizing dye as a tracer and the determination of the amount of entrapped liquid in the precipitate fraction by a spectrophotometric comparison of the dye concentrations in the precipitate and filtrate. The technique has been tested at several temperatures on both a diesel and a jet fuel. %S increased with decreasing temperature below the melting point. The %S values for the jet fuel were in good agreement with results obtained in another laboratory using a filtration/g.c. analysis method. Precipitates obtained by filtration of the partly frozen fuels were found to contain 50–80% entrapped liquid.     

STRONTIUM ISOTOPE STRATIGRAPHY OF THE ASMARI FORMATION (OLIGOCENE - LOWER MIOCENE), SW IRAN

The Asmari Formation has been studied in the subsurface at the Bibi Hakimeh, Marun and Ahwaz oilfields and in an outcrop section from the Khaviz anticline. It consists of approximately 400 m of cyclic platform limestones and dolostones with subordinate intervals of sandstone and shale. The method of Sr‐isotope stratigraphy is well suited for dating these strata because of the rapid rate of change of marine ⁸⁷Sr/⁸⁶Sr during Asmari deposition (roughly 32‐18 Ma) and the common presence of well‐preserved macrofossils. Profiles of age against depth in the four areas show a decrease from higher stratigraphic accumulation rates in the lower Asmari to lower rates in the middle to upper part of the formation. There is also a trend towards less open‐marine depositional conditions and increasing early dolomitization and anhydrite abundance above the lower part of the formation. These changes reflect the dynamics of platform progradation across the areas studied, from early deposition along relatively high accommodation margin to slope settings to later conditions of lower accommodation on the shelf top. Ages of sequence boundaries are estimated from the age‐depth profiles at each locality, providing a framework for stratigraphic correlation. Asmari deposition began in early Rupelian time (34‐33 Ma) in the Bibi Hakimeh area, when the studied areas to the NW were accumulating basinal marl facies. Progradation of the platform across the Marun and Ahwaz areas took place in mid‐Chattian time (27‐26 Ma) and somewhat later (26‐25 Ma) in the more basinward Khaviz area. Depositional sequences have durations of 1‐3 Ma, whereas component cycles represent average time intervals of 100‐300 Ky. Sr analyses of most dolomite, anhydrite and celestite samples plot close to or below the macrofossil age‐depth trend for each locality, indicating formation from waters preserving seawater ⁸⁷Sr/⁸⁶Sr approximately contemporaneous with or slightly younger than the time of sediment deposition. Local deviations from this trend are interpreted as indicating episodes of seepage‐reflux and also a contribution of Sr from non‐marine sources during formation of the Gachsaran cap rock anhydrite.     

Fabrication of single-mode chalcogenide optical fiber

Long lengths (>150 m) of single-mode chalcogenide optical fiber were fabricated by a double crucible technique. Single-mode transmission through 10 m of continuous fiber was demonstrated using an F-center laser at 2.7 μm. The optical loss of this fiber was measured by a standard cutback technique using an FTIR spectrometer and also using an F-center laser, A minimum loss of less than 1 dB/m was obtained