Epithermal neutron self-shielding factors in foils for collimated beams.

An epithermal neutron self-shielding factor must be introduced to take into account the absorption of a neutron beam crossing a sample. This factor depends on the geometry and dimension of the sample, as well as on the physical and nuclear properties of the nuclides. On the basis of a dimensionless variable, which includes the relevant characteristics of the sample, universal curves for monoenergetic and 1/E collimated neutron beams are proposed, which enable the determination of the self-shielding factor for isolated resonances of high absorber nuclides.

Monte Carlo calculation of epithermal neutron resonance self-shielding factors in foils of different materials.

Epithermal neutron resonance self-shielding factors in foils of materials used as activation detectors or as targets for radionuclide production have been calculated using the MCNP code. Two irradiation conditions have been considered: (a) foils immersed into an isotropic neutron flux and (b) foils submitted to a collimated neutron beam. The self-shielding factors, Gres(t), for gold, indium, manganese and cobalt have been compared with available published values. The self-shielding factor depends on various physical and nuclear parameters. However, it is shown that for the isotropic case and for high absorber elements submitted to a collimated beam, a dimensionless variable could be adopted that describes the self-shielding factors of different materials by quasi "universal curves". Gres(t) for the collimated beam are always higher than those for the isotropic case.

Monte Carlo calculation of epithermal neutron resonance self-shielding factors in wires of different materials.

Epithermal neutron resonance self-shielding factors in wires of materials used as activation detectors or as targets for radionuclide production have been calculated using the MCNP code. The energy dependent self-shielding factor depends on the ratio scattering/capture cross sections. The self-shielding factors for cobalt and gold have been compared with available values. The self-shielding factor depends on various physical and nuclear parameters. However, an adimensional variable can be adopted that describes the self-shielding factors of different materials by a quasi "universal curve".

On the fission interference correction and its dependence on the epithermal to thermal neutron flux ratio in thermal NAA of molybdenum.

The present work aims at the following: (1) analyzing the experimental fission interference factor for molybdenum, FMo, obtained by the authors, who have described the irradiation conditions used as concerns the epithermal to thermal neutron flux ratio, phi epi/phi 0; (2) establishing a simple calculation model that describes the dependence of FMo on phi epi/phi 0 in an adequate way, to provide a satisfactory basis to explain the scatter found in the existing experimental data; and (3) clearly indicating the basic recommendations to take into account in order to obtain with high accuracy the concentration of molybdenum in samples containing uranium.

Comparison of the argon tunable dye laser with the flashlamp pulsed dye laser in treatment of facial telangiectasia.

BACKGROUND: A prospective, side-by-side comparison study of the argon tunable dye laser (ATDL) and the flashlamp pulsed dye laser (FPDL) for the treatment of solar-induced telangiectasia was carried out in 14 patients with symmetrical bilateral cheek telangiectasias. OBJECTIVE: The objective was to compare the efficacy of treatment by the two lasers. METHODS: Patients were treated and examined at weeks 2, 4, and 6. Evaluation was done by direct observation and questionnaire, as well as by photographic slides projected to an impartial panel. RESULTS: Final evaluation at week 6 showed 11 of 14 patients with excellent results at sites treated with the FPDL, compared with four of 14 with the ATDL. However, only six of 13 patients preferred the FPDL, due to the purpura and postinflammatory hyerpigmentation. CONCLUSION: We conclude that the objective final results favor the FPDL over the ATDL for treatment of facial telangiectasia, but that the ATDL is still an important option for patient acceptance.

Factor for correcting the ruthenium interference in instrumental neutron activation analysis of barium in uraniferous samples.

The fission spectral interference of ruthenium on the instrumental neutron activation analysis of barium in samples containing uranium is extensively discussed. In particular the dependence of the correction factor on the phi epi/phi th ratio is studied. An excellent agreement between experimental and calculated values is achieved. A procedure is suggested for the resolution of multiple interferences in the general case where uranium, barium and/or ruthenium are present in samples to be analysed.

Determination of selenium in duplicate diets of residents of Pinhel, Portugal, by neutron activation.

A rapid cyclic instrumental neutron activation analysis (CINAA) method has been used to determine the selenium content of 27 duplicate diet samples from each of the 27 districts surrounding Pinhel, Portugal. The accuracy and precision of the CINAA method have been evaluated by analyzing certified reference materials and observed to be within +/- 5-10% for samples containing at least 40 ppb of selenium. The detection limit has been found to vary between 26-42 ppb selenium depending on the sample composition. The average daily dietary intake has been calculated as 37 micrograms of selenium per day.

Determination of trace elements in reference materials by the k(0)-standardization method (INAA).

Instrumental neutron activation analysis was applied to four reference materials: NBS 1573 (Tomato Leaves), NBS 1645 (Citrus Leaves), NBS 1645 (River Sediment), and IAEA MA-A-2 (TM) (Fish Flesh). The k(0)-standardization method was used. The results are compared with (i) reference values (mostly non-certified) and (ii) published values obtained by other methods. Good agreement is found for most of the elements. For some elements, large discrepancies are observed.