Abrupt change in radiation-width distribution for 147Sm neutron resonances.

We obtained the total radiation widths of s-wave resonances through an R-matrix analysis of (147)Sm(n,γ) cross sections. Distributions of these widths differ markedly for resonances below and above E(n)=300 eV, which is in stark contrast to long-established theory. We show that this change, as well as a similar change in the neutron-width distribution reported previously, is reflected in abrupt increases in both the average (147)Sm(n,γ) cross section and fluctuations about the average near 300 eV. Such effects could have important consequences for applications such as nuclear astrophysics and nuclear criticality safety.

New precision measurements of the 235U(n,γ) cross section.

The neutron capture cross section of (235)U was measured for the neutron incident energy region between 4 eV and 1 MeV at the DANCE facility at the Los Alamos Neutron Science Center with an unprecedented accuracy of 2-3% at 1 keV. The new methodology combined three independent measurements. In the main experiment, a thick actinide sample was used to determine neutron capture and neutron-induced fission rates simultaneously. In the second measurement, a fission tagging detector was used with a thin actinide sample and detailed characteristics of the prompt-fission gamma rays were obtained. In the third measurement, the neutron scattering background was characterized using a sample of (208)Pb. The relative capture cross section was obtained from the experiment with the thick (235)U sample using a ratio method after the subtraction of the fission and neutron scattering backgrounds. Our result indicates errors that are as large as 30% in the 0.5-2.5 keV region, in the current knowledge of neutron capture as embodied in major nuclear data evaluations. Future modifications of these databases using the improved precision data given herein will have significant impacts in neutronics calculations for a variety of nuclear technologies.

Lisina digestível na ração de frangos de corte tipo caipira na fase de crescimento / Dietary digestible lysine in free-range broiler chickens during the growth phase

O presente experimento foi conduzido para determinar as exigências de lisina digestível para frangos de corte (linhagem Redbro), machos e fêmeas, durante o período de crescimento. Foram utilizados 630 frangos, alojados em 30 boxes com acesso à área de pastejo. O delineamento experimental utilizado foi o inteiramente ao acaso, em esquema fatorial 5x2 (lisina e sexo), e três repetições com 21 aves cada. Os níveis de lisina digestível avaliados foram: 7,07; 8,07; 9,07; 10,07 e 11,07g/kg. Avaliou-se o consumo de lisina, o consumo de ração, o ganho de peso e a conversão alimentar. Observou-se efeito de interação (P<0,05) entre os níveis de lisina e sexo para o ganho de peso. Houve efeito (P<0,01) dos níveis de lisina sobre o consumo de lisina, o ganho de peso e a conversão alimentar. Verificou-se que todas as variáveis foram influenciadas (P<0,05) pelo sexo dos frangos. Recomendam-se 10,08 e 9,49g de lisina digestível/kg de ração, correspondendo ao consumo estimado de 21 e 20g de lisina, para machos e fêmeas, respectivamente, para melhor ganho de peso das aves. Para melhor conversão alimentar, recomendam-se 9,61g de lisina digestível/kg, para frangos de ambos os sexos, correspondendo ao consumo estimado de 20g de lisina.(AU)

This experiment was conducted to determine the requirements of digestible lysine in male and female free-range broiler chickens (Redbro lineage) during the growth phase. Six hundred and thirty broiler chickens were allocated in 30 pens with access to the pasture area. The experimental design was completely randomized in a 5x2 (lysine and gender) factorial arrangement with 3 repetitions with 21 chickens each. The levels of digestible lysine evaluated were: 7.07, 8.07, 9.07, 10.07 and 11.07g/kg. The performance traits evaluated were lysine intake, feed intake, weight gain and feed conversion ratio. An interaction effect (P<0.05) was observed between dietary lysine level and gender for body weight gain. There was an effect (P<0.01) of the levels of lysine on lysine intake, body weight gain and feed conversion ratio. It was found that all the variables were affected (P<0.05) for the gender of chickens. We recommended 10.08 and 9.49 g of digestible lysine/kg diet, corresponding to the estimated intake of 21 and 20g of lysine, for males and females, respectively, for better body weight gain of chickens. For better feed conversion ratio, the recommendation is of 9.61 g of lysine/kg of diets, for chickens of both genders, corresponding to the estimated intake of 20g of lysine.(AU)

Prompt radiochemistry at the National Ignition Facility (invited).

Understanding mix in inertial confinement fusion (ICF) experiments at the National Ignition Facility requires the diagnosis of charged-particle reactions within an imploded target. Radiochemical diagnostics of these reactions are currently under study by scientists at Los Alamos and Lawrence Livermore National Laboratories. Measurement of these reactions requires assay of activated debris and tracer gases from the target. Presented below is an overview of the prompt radiochemistry diagnostic development efforts, including a discussion of the reactions of interest as well as the progress being made to collect and count activated material.

Parity violation observed in the beta decay of magnetically trapped 82Rb atoms.

Laser cooling and atomic trapping techniques have been employed to confine polarized 82Rb atoms ( T1/2 = 75 s) in a magnetic time-orbiting-potential (TOP) trap. We have observed the parity-violating correlation between the emitted positron momentum and the parent nuclear spin as a continuous function of angle and positron energy for this pure Gamow-Teller (GT) transition. These proof-of-principle measurements demonstrate the utility of exploring fundamental symmetries in a TOP trap and the steps required to improve sensitivity in the search for physics beyond the standard model.