Calculation of half-life for ^79Se decay

1 Introduction The 79Se is one of the fission products with long half-life. It is an important nuclide of radioisotope ap-plications and radioactive waste-treatments, and is also used as the fission monitor. The measurement of its half-life is very difficult, because the differences of half-lives in different experiments are very large. Therefore, it is highly important and interesting to calculate its half-life with Log f 1ut systematics. The calculated half-life has also been compared with…     

Temperature and symmetry energy of neutron-rich fragments in the 1A GeV124,136Xe＋Pb reactions

In this work we study the symmetry-energy coefficient of neutron-rich nuclei, and the temperature dependence of nuclear symmetry energy at low temperatures. An isobaric method is used to extract the symmetry-energy coefficients of neutron-rich nucleus （asm） at zero temperature （T） and asym/T at nonzero temperature in the measured 1A GeV 124＇136Xe＋Pb reactions. T of fragment is obtained from the ratio of its asym to asym/T. The results show that, for fragment with the same neutron-excess （I=N-Z）, the heavier the fragment is, the higher T it has, and T tends to saturate around 1 MeV for the large mass fragments. It is also shown that the more neutron-rich the isobar is, the higher temperature it has. The T2 dependence of symmetry energy of finite nucleus at low temperatures is verified by the extracted results.     

Experimental test of a new neutron threshold detector and its application

The Possibility of using 209Bi as a new threshold detector to measure high-energy neutrons was investigated for the first time.At the same time the experiment measured successfully the emitted neutron fluence rate,energy spectrum and dose equivalent rate distributions in the heavy ion target area using a detector complex including 209Bi,^115In,^27Al,^19Fand ^12C samples.     

Measurements of neutron spectra from iron and boron—in—polyethylene bomareded with 14MeV nuetrons

The leakage spectra of 14MeV neutrons from spheres of iron and boron-inpolyethylene with three differnet mass ratios of boron carbide to polyethylene were measured over the energy range of 20 keV to 16MeV by using proton recoil method.The integral leakages and removal cross sections at different lower cut-off energy were given.     

Measurements of fast—neutron capture cross sections for ^159Tb and ^169Tm

The neutron capture cross sections for ^159Tb and ^169Tm relative to the ^197Au (n,γ)^198Au reaction are measured at neutron energies of 0.57,1.10 and 1.60 MeV by using the activation method.The activities of the products are measured with a high resolution HPGe detector gamma-ray spectrometer.The errors of the present work are 5-6% for Tb,6-7% for Tm.The recommended data in energy region of 0.4-3.0MeV are given as compared with other data published previously.     

Elemental analysis of rain－and fresh water by neutron activation analysis

Analysis of rain-and fresh water for trace constitutents is a mandatory part of environmental monitoring.This text gives a survey of neutron activation analysis(NAA) within the framework of current environmental water research programmes.based on the practice developed in co-operation with the Dutch Energy Research Centre at Petten(ECN).While the procedures reported in literature cover obout thirty five elements,our routine procedures of instrumental neutron activation analysis(INAA) is limited to ten to fifteen elements.THe use of some dedicated radiochemical separations(RNAA) adds another six,some of which are speciated as well.Current contributions of NAA to water analysis center on determination and speciation of anionic trace elements,notably Br.I,As,and Se,on the assay of some ultra traces like Ag,Au and Hg and on validation.     

The level structure of ＆76Se from ^76Br γ—decay

The decay of ^76Br has been investigated for further study of the ^76Se levels.Gamma ray singles were measured with HpGe-NaI compton-suppressed spectrometer,Coincidence spectra were collected with two HpGe detectors coupled to a three-parameter system.There were 138 γ-rays observed.and 120 of these were fitted into 46 levels in ^76Se.37 γ-rays and 15 new energy levels were found for the first time.     

Exploring the sensitivity of α-decay half-life to neutron skin thickness for nuclei around ~(208)Pb

Based on the newest experimentally extracted nuclear density distributions for double-magic nucleus208Pb(Tarbert et al. in Phys Rev Lett 112:242502, 2014),the sensitivity of α-decay half-life to nuclear skin thickness is explored in the vicinity of the shell closure region around208 Pb, i.e., isotopes of Z ? 82 and isotones of N ? 126.With the two-parameter Fermi(2PF) density distributions and an analytically derived formula, the α-decay half-life is found to be closely related to the magnitude of nuclear skin thickness. For a decays to the Z ? 82 isotopes, the α-decay half-life is found to decrease with the increasing neutron skin thickness, while the opposite behavior is found for a decays to the N ? 126 isotones. Therefore, it could be a possible way to extract the nuclear skin thickness from measured α-decay half-lives.     

Proton and neutron alignments of the k^ π=5/2^- band in ^79Kr

An experimental study of high-spin states in ^79Kr has been performed at the GASP array using the reaction ^55Mn(^20Si, αpn),Nine new states along with 10 new gamma ray transitions were found in the k^ π=5/2^- band in ^79Kr Three band crossings,associated with the allignments of a πg9/2 pair and a πg9/2 pair and also a high-j 5h11/2 intrude orbital,were observed at rotational frequency h=0.50,0.65 and 0.90 MeV,respectively ,A cranked shell model analysis has been made to interpret the experimental results.     

Effect of concrete buildings on the environmental neutron flux by using the reaction^197 Au （n,γ）^198Au and extremely low level gamma ray spectroscopy

The activation of gold by environmental neutrons through the reaction^197Au (n,γ)^198Au was used to study the effect of concrete buildings on the neutron flux, and to estimate the thermal neutron flux inside and outside these buildings. The results showed that three ceilings of thickness 34 g/cm^2 decrease the fast neutrons to 26% from its original value. However, the same reinforced concrete decreases the slow neturon flux to only 62% of its original value. The thermal neutron flux at 283 m from the center of Training Reactor of Kinki University, was twice higher than the environmental neutron background.     

Investigation of decay modes of superheavy nuclei

A detailed investigation of different decay modes,namely alpha decay,beta decay,cluster decay,including heavy particle emission(Zc＞28),and sponta-neous fission,was carried out,leading to the identification of new cluster and beta-plus emitters in superheavy nuclei with 104≤Z≤126.For the first time,we identified around 20 beta-plus emitters in superheavy nuclei.Heavy-particle radioactivity was observed in superheavy elements of atomic number in the range 116≤Z≤126.292-293 Og were identified as 86Kr emitters,and 298122 and 300122 were identified as 94Zr emitters,whereas heavy-particle radioactivity from 91Y was also observed in 299123.Fur-thermore,the nuclei 300124 and 306126 exhibit 96Mo radioactivity.The reported regions of beta-plus and heavy-particle radioactivity for superheavy nuclei are stronger than those for alpha decay.The identified decay modes for superheavy nuclei are presented in a chart.This study is intended to serve as a reference for identifying possible decay modes in the superheavy region.     

Study of delayed neutron decay curves from thermal neutron induced fission of U and Pu

The results of measurements of the delayed neutron decay curves obtained from the thermal neutron induced fission of ²³⁵U and ²³⁹Pu are presented. The data were obtained by the periodical irradiation method on the pulsed reactor IBR-2 during the time interval 5 to 730 msec following irradiation. A comparison of these newly measured decay curves with the curves calculated using several standard delayed neutron sets was then performed. Based on these measurements, a new 7-group delayed neutron model is proposed.     

Measurement of the Po production induced by thermal neutron capture on Bi

A measurement of the polonium production in a solid Bi target, placed in a high thermal neutron flux of 2.3 × 10¹³ n/cm²/s, was performed. Two different activation methods, based on α and γ spectroscopy, were used to cross check the results. Values of (16.08 ± 1.8) mb and (18.4 ± 0.9) mb for the ²¹⁰Po (i.e. ^210gsBi) formation cross-section were obtained and a recommended value of (17.9 ± 0.8) mb was proposed. Our results are in disagreement with adopted cross-section values in the main nuclear data libraries, namely smaller by 25% for ^210gsBi. These new values will account for more precise evaluations of ²¹⁰Po formation in moderated spallation targets containing ²⁰⁹Bi.     

Preliminary measurements of the prompt neutron decay constant in MASURCA

Pulse counting techniques have been used to measure the prompt decay constant = (β - ) / Λ in the MASURCA reactor of CEA at critical state. The data has been analyzed in time domain using Rossi- and Feynman- techniques, and in frequency domain using the cross power spectral density.

The Rossi- technique has been studied using one and two detectors. Due to the strong inherent spontaneous fission source, the one-detector variant gives a very strong white-noise signal, which is absent in the two-detector method. Because each neutron detected recorded not only a pulse, but also an echo after 120 ns, corrections had to be made to the theory applied.

The Feynman- technique is even more sensitive to the echo in the signals, and quite large corrections had to be made. Nevertheless the results obtained are in reasonable agreement with those of the correlation methods. For both measurement techniques, experiments of long duration are needed to get accurate results. The results obtained agree within 10% with calculations.

The prompt decay constant has also been measured with a continuous current technique. From the cross power spectral density thus obtained, the -value is in agreement with that of the pulse counting techniques.