Neutron-C-19 scattering near an Efimov state

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Armazenagem em atmosfera modificada passiva de carambola azeda (Averrhoa carambola L.) cv. 'Golden Star'

Este trabalho avaliou o efeito das embalagens de polietileno de baixa densidade (PEBD), em diferentes espessuras, no prolongamento da vida útil pós-colheita de carambolas cv. 'Golden Star'. Os frutos foram colhidos fisiologicamente maturos, sendo selecionados pela ausência de defeitos e acondicionados nas embalagens de PEBD, constituindo os seguintes tratamentos: T1 - controle (sem embalagem); T2 - PEBD de 6 mim; T3 - PEBD de 10 mim; T4 - PEBD de 15 mim. Os frutos foram armazenados a 12 +/- 0,5 ºC e 95 +/- 5% de UR, por 45 dias, e mais 5 dias a 22 +/- 3ºC e 72 +/- 5% de UR. Vinte e quatro horas após a colheita e a cada nove dias, amostras eram retiradas do armazenamento refrigerado (AR), mantidas por 12 horas em condições ambiente (22 +/- 3ºC e 72 +/- 5% UR) e analisadas quanto à firmeza de polpa (FP), à perda de massa fresca, à coloração da epiderme, aos sólidos solúveis totais (SST), à acidez total titulável (ATT) e à ocorrência de distúrbios fisiológicos. Realizou-se também uma análise sensorial ao final do experimento. A maior firmeza de polpa e acidez total titulável, o melhor padrão de coloração, o menor conteúdo de sólidos solúveis totais, a ausência de manchas e podridões, e a melhor aceitabilidade pelos julgadores foram obtidos com os frutos acondicionados em embalagens de 10 mim.

Qualidade de carambolas azedas cv. 'Golden Star' tratadas com CaCl2 por imersão e armazenadas sob refrigeração

No presente trabalho, avaliou-se o efeito de diferentes concentrações de CaCl2 aplicadas na pós-colheita de carambolas cv. 'Golden Star, durante o armazenamento refrigerado (AR). Os frutos colhidos fisiologicamente maturos foram selecionados pela ausência de defeitos e imersos em soluções de CaCl2, em diferentes concentrações, em temperatura ambiente (22 °C) por 20 minutos. Após aplicação dos tratamentos T1 - controle (0% de CaCl2); T2 - CaCl2 a 1%; T3 - CaCl2 a 2%; T4 - CaCl2 a 3%, e T5 - CaCl2 a 4%, os frutos foram colocados em câmara frigorífica, por 35 dias, a 12 ± 0,5ºC e 95 ± 3%, e mais 3 dias a 22 ± 3°C e 72 ± 5% de umidade relativa (UR). 24 horas após a colheita e a cada sete dias, amostras foram retiradas da AR, mantidas por 12 horas em condições ambiente (22 ± 3°C e 72 ± 5% UR) e analisadas quanto ao teor de cálcio na polpa, perda de massa fresca, coloração da epiderme, firmeza de polpa (FP), sólidos solúveis totais (SST), acidez total titulável (ATT) e a ocorrência de distúrbios fisiológicos. Ao final do experimento, foi feita uma análise sensorial. Observou-se que os frutos imersos em solução de CaCl2 a 2% apresentaram menor perda de massa fresca e maior firmeza de polpa. As carambolas deste tratamento também não apresentaram manchas e podridões e foram preferidas pelos julgadores no teste de preferência. Os sólidos solúveis totais, a acidez total titulável e a coloração não apresentaram diferença estatística entre os tratamentos. Na análise de teores de cálcio adsorvido pelos frutos, determinou-se que quanto, maior a concentração da solução de CaCl2 aplicada, maior a concentração de cálcio presente na polpa.

Cultivar affects browning susceptibility of freshly cut star fruit slices

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Potentialities and practical limitations of absolute neutron dosimetry using thin films of uranium and thorium applied to the fission track dating

Neutron dosimetry using natural uranium and thorium thin films makes possible that mineral dating by the fission-track method can be accomplished, even when poor thermalized neutron facilities are employed. In this case, the contributions of the fissions of (235)U, (238)U and (232)Th induced by thermal, epithermal and fast neutrons to the population of tracks produced during irradiation are quantified through the combined use of natural uranium and thorium films.If the Th/U ratio of the sample is known, only one irradiation (where the sample and the films of uranium and thorium are present) is necessary to perform the dating. However, if that ratio is unknown, it can be determined through another irradiation where the mineral to be dated and both films are placed inside a cadmium box.Problems related with film manufacturing and calibration are discussed. Special attention is given to the utilization of thin films having very low uranium content. The problems faced suggest that it may be better to substitute these films by uranium doped standard glasses calibrated with thicker uranium films (thickness greater than 1.5 x 10(13) mu m).

Determination of the U-238 spontaneous fission decay constant without neutron irradiation

We have developed a methodology for measuring the decay constant of the spontaneous fission of U-238, lambda(f), using nuclear particle track detectors where thermal neutron irradiation is unnecessary. This methodology is based on the fact that the radiation damage caused by spontaneous fission of trans-uranium elements bearing a mass number close to 238 are similar to U-238 spontaneous-fission ones. Loading a thick source of uranium (thickness greater than the fission fragment range) with a small amount of a suitable trans-uranium element (for instance, Pu-242, which presents a spontaneous fission half-life of 6.75(.)10(10) y), it is possible to determine the observation efficiency of a particle-track detector for fission fragments. Procedures concerning our thick source manufacture and uniformity tests of the trans-uranium distribution are also presented. These results make it possible for the exposure of thick uranium sources (without trans-uranium element) to lead to a lambda(f) value.

Durango apatite fission-track dating using length-based age corrections and neutron fluence measurements by natural thorium thin films and natural U-doped glasses calibrated through natural uranium thin films

In this work, we present an approach for neutron fluence measurements based on natural thorium thin films and natural uranium-doped glasses calibrated through natural uranium thin films to be used for dating with the Fission-Track Method (FTM). This neutron dosimetry approach allows the employment of FTM even when dating is carried out using low neutron themalization facilities. Besides, it makes possible the determination of the Th/U ratio of the mineral to be dated. Durango apatite which is often employed in FTM as an age standard was analyzed. This apatite presented a fairly high Th/U ratio, 29.9 +/- 1.7. Th fissions were 18%, 12% and 10% of the total for irradiations where thermal to fast neutron flux ratios were 2.4, 4.4 and 5,2, respectively. These results show that Th fission must be considered for this apatite, when not well-thermalized irradiation facilities are used. The ratio between spontaneous and induced track length, L(S)/L(1), close to 0.89, indicates a certain amount of rejuvenation of the age of Durango apatite. Therefore, its apparent age should be corrected, the application of a technique based on track-length measurements produced a corrected age of 29.7 +/- 1.1 Ma, consistent with the independent reference age of this apatite (31.4 +/- 0.5 Ma). This result represents a support for viability of the neutron dosimetry approach studied in this work for FTM.(C) 2002 Elsevier B.V. B.V. All rights reserved.

Neutron Diffraction Study of Liquid N-Methylformamide Using EPSR Simulation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

A new technique for thermal neutron detection using pyroelectric ceramics

In this article a new technique for thermal neutron detection using pyroelectric ceramics is described. The detector system is basically constituted of a PZT (lead zirconate titanate) ceramic attached to an uranium disk. The energy released in the uranium fission gives rise to an electrical signal in the detector which is amplified by a lock-in system. The neutron beam impinging on the uranium disk was modulated with a cadmium chopper. Thermal neutron fluxes within the interval of 103 to 106 n/cm2 s have been detected using a U3O8 pellet with 20% enrichment in 235U. © 1992.

Rho-omega mixing and neutron-proton self-energies in the Walecka model

We use the Walecka model to investigate the influence of the charge symmetry breaking ρ0-ω mixing interaction on the neutron-proton self-energy difference in nuclear matter. Using 2mρ〈ρ0|H|ω〉 = -4500 MeV2, and employing the Dirac-Hartree-Fock approximation, we find that the neutron-proton self-energy difference is a decreasing function of the nuclear matter density, and that it has a value of the order of 700 keV at the normal density. The results indicate that the Nolen-Schiffer anomaly might be explained by means of relativistic nuclear models in a similar way as it is explained by means of non-relativistic models.

Problems related to the employment of thin uranium films as neutron dosimeters

Thin uranium films built on muscovite mica basis and obsidian samples having known ages were irradiated with thermal neutrons at the IPEN/CNEN reactor, São Paulo. Comparing thin film performance with the obsidian one, it was observed that the latter feel a greater neutron fluence. Nominal fluences at the used facility are in agreement with the results obtained analysing the obsidian samples. A probable hypothesis to explain this disagreement, namely, the uranium loss from the thin films, was ruled out. © 1995.

Effects of vacuum structure on neutron stars

We study the equation of state for neutron matter using the Walecka model including quantum corrections for baryons and sigma mesons through a realignment of the vacuum. We next use this equation of state to calculate the radius, mass, and other properties of rotating neutron stars.

Neutron-neutron correlations in light exotic nuclei

For light exotic nuclei modeled as two neutrons n and a core A, we report results for the two-neutron correlation functions and also for the mean-square radii, considering a universal scaling function. The results of our calculations for the neutron-neutron correlation functions are qualitatively consistent with recent data obtained for 11Li and 14Be nuclei. The root-mean-square distance in the halo of such nuclei are also consistent with data, which means that the neutrons of the halo have a large probability to be found outside the interaction range. Therefore the low-energy properties of these halo neutrons are, to a large extend, model independent as long as few physical input scales are fixed. The model is restricted to s-wave subsystems, with small energies for the bound or virtual states. For the radii we are also shown results for the 6He and 20C. All the interaction effects, as higher partial wave in the interaction and/or Pauli blocking effect are, to some extend, included in our model, as long as the three-body binding energy is supplied. © 2005 American Institute of Physics.