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Biaxially stretched composite polyethylene naphthalate (PEN) films (BSCPF) embedded with submicron lithium fluoride (6LiF) particles and luminescent molecules were fabricated to make large area scintillation films (≈1 m × 1 m) for thermal neutron detection. BSCPF had 20.2% higher neutron light yield as compared to unstretched composite film (UCPF), and were 2.46 ± 1.47 times more efficient for detecting thermal neutrons than lithiated glass GS20 above lower level discriminator corresponding to an intrinsic efficiency for gamma <10−6. MCNPX simulations for a layered BSCPF detector resulted 6.1 cps for 1 ng 252Cf, thus meeting the Pacific Northwest National Laboratory criteria for absolute neutron detection efficiency and intrinsic gamma-neutron discrimination. BSCPF have alpha to beta ratio of 0.25, which is higher than that for UCPF (0.11), and also for GS20 (0.22), which offers the possibility of excellent neutron/gamma discrimination. [ABSTRACT FROM AUTHOR]

A methodology for simulating a neutron detector's pulse-height spectra (PHS) utilizing semiempirical equations for the light yield nonproportionality of organic scintillators is described. Using these simulations, suitable material synthesis techniques are established for optimizing the performance of neutron scintillators. A MATLAB program suite was developed to automate the process of generating the PHS by pairing these semi-empirical equations with results generated using Monte Carlo radiation transport code (MCNPX) particle track (PTRAC) output files. This is accomplished by first calculating the energy deposited in a detector from each charged-particle reaction product generated from a neutron absorption event by postprocessing the MCNPX PTRAC output files. The energy deposited from each charged particle is then used in semiempirical light yield equations to determine the fluorescent light energy output by each charged particle. Finally, the individual contributions from each charged particle are recombined to accurately simulate the pulse generated from the neutron absorption event. [ABSTRACT FROM AUTHOR]

Quantification of uncertainties in doses from intakes of radionuclides is important in risk assessments and epidemiologic studies of individuals exposed to radiation. In this study, the uncertainties in the doses per unit intake (i.e., dose coefficients) for ingestion of 131I, 137Cs, and 90Sr by healthy individuals have been determined. Age-dependent thyroid dose coefficients were derived for 131I. The analysis for 131I uses recent measurements of thyroid volume obtained by ultrasonography, which indicate a thyroid mass lower than that previously obtained using autopsy measurements. The coefficients for 137Cs are determined using the relationship between the biological half-lives and the amount of potassium in the human body. The most recent International Commission on Radiological Protection biokinetic model was employed to determine the uncertainties for 90Sr. For 137Cs and 90Sr, the dose coefficients represent exposure in adulthood and they were determined for all organs of radiological importance. The uncertainty in the estimated dose coefficients represent state of knowledge estimates for a reference individual, and they are described by lognormal distributions with a specified geometric mean (GM) and geometric standard deviation (GSD). The estimated geometric means vary only slightly from the dose coefficients reported by ICRP publications. The largest uncertainty is observed in the dose coefficients for bone surface (GSD = 2.6), and red bone marrow (GSD = 2.4) in the case of ingestion of 90Sr. For most other organs, the uncertainty in the 90Sr dose coefficients is characterized by a GSD of 1.8 (or less for some organs). For 131I, the uncertainty in the thyroid dose coefficients is well represented by a GSD of 1.7 for both sexes and all ages other than infants for whom a GSD of 1.8 is more appropriate. The lowest uncertainties are obtained for the dose coefficients from ingestion of 137Cs (GSD = 1.24 for males; 1.4 for females). A dominant source of uncertainty in the ingestion dose coefficients is the variation of the biokinetic parameters. For 131I, the largest contribution to the uncertainty comes from the variation in the thyroid mass, but the contribution of the biokinetic parameters is comparable. The biokinetic parameters with the largest contribution to the uncertainty are (a) the fractional uptake from blood to thyroid in the case of ingestion of 131I, (b) the absorbed fraction from the gastrointestinal tract (f1) in the case of 90Sr, and (c) the amount of potassium in the body for 137Cs. The contribution to the uncertainty of the absorbed fraction (which accounts for the fraction of energy deposited in the target organ) is the smallest contributor to the uncertainty in the dose coefficients for most organs. To reduce the uncertainty in the dose estimated for a real individual, one should determine the above-mentioned parameters for the specified individual rather than to rely on assumptions for a reference individual. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we report on optical and scintillation properties of a new scintillation material CsGd2Cl7:Ce. Crystals were grown in vacuum sealed ampoules, and the response to gamma rays and thermal neutrons was characterized. The scintillation light yield was ∼38,000ph/MeV, and the primary decay time was 60ns under γ-ray excitation. A thermal neutron response resulting from capture by 157Gd and 155Gd and subsequent emission of conversion electrons and X-rays was observed. The crystals exhibited a layered structure with cleavage planes and relatively low hygroscopicity. [Copyright &y& Elsevier]