Bias Effects on g- and s-Factors in Westcott Convention

For accuracy improvement of neutron activation analysis and neutron capture cross sections, bias effects are investigated on g- and s-factors in the Westcott convention. As origins of biases, a joining function shape, neutron temperature, and sample temperature have been investigated. Biases are quantitatively deduced for two 1/v isotopes (197Au, 59Co) and six non-1/v isotopes (241Am, 151Eu, 103Rh, 115In, 177Hf, 226Ra). The s-factor calculated with a joining function deduced recently by a detailed Monte Carlo simulation is compared to s-factors calculated with traditional joining functions by Westcott. The results show the bias induced by the sample temperature is small, in the order of 0.1% for the g-factor and in the order of 1% for the s-factor. On the other hand, the bias size induced by a joining function shape for the s-factor depends significantly on both isotopes and neutron temperature. As a result, the reaction rates are also affected significantly. The bias size for the reaction rate is given in the case of an epithermal neutron index r = 0.1, for the eight isotopes.

In situ measurement of neutron temperature for the extended k0 NAA at FRM II

The neutron temperature at different irradiation positions in the research reactor FRM II was measured using thermometer labels together with lutetium standards. This was the first time to measure the local temperature at the irradiation positions with this combination. The simplified Westcott formalism was used to calculate the neutron temperature using Lu and g(Tn) factors from different data sources. The results showed agreement between neutron temperature according to the Lu method and the temperature showed on the labels. They can be used as a reliable alternative to determine the neutron temperature instead of using Lu standards in the extended k0 NAA.

Study on Moderation Properties of Cold Mesitylene using KUANS

Neutron moderation properties from the cold mesitylene moderator have been studied. Kyoto University Accelerator driven Neutron Source has been used for these experiments. The container of the mesitylene moderator is situated in front of the polyethylene moderator and the change of the time of flight spectrum has been recorded as a function of the temperature of the mesitylene moderator. By fitting the Maxwell distribution to the obtained TOF spectra, the neutron temperature corresponding to the mesitylene temperature is estimated.

Change in Primordial Abundances Due to a Change in the Primordial Plasma Energy Density

We recently showed that the energy density of a plasma is appreciably different than previously thought when high frequency plasma fluctuations, ω ≥ kB/ħ, are taken into account (M. Opher &R. Opher, 1999). A change in the primordial plasma energy density changes the primordial expansion rate of the universe, the neutron temperature freeze-out, and the primordial nucleosythesis abundances. The change in the primordial abundances due to the change in the primordial plasma energy density is evaluated, taking into account the high frequency, as well as the low frequency fluctuations of the plasma.