Investigation of delayed neutron precursors of As, Sb and Ge
Abstract
As, Sb and Ge are separated in a few seconds as hydrides from the bulk of the thermal neutron fission products of 235U. A 2·15 ± 0·15 sec delayed on half-life is observed contributing 4 oer cent to the total yield of delayed neutrons formed in fission. It is assigned to 85As as delayed neutron precursor, with a neutron emission probability of 11 ± 3 per cent, on the grounds of the fine structure of the fission mass-yield curve. 87As is excluded, its half-life being ⩽ 1·5 sec. An upper limit to any contribution of a Sb delayed neutron precursor to this activity is 25 per cent. A 10 ± 2 sec delayed neutron half-life observed under the same conditions is discussed and cannot be attributed to these elements.
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Nuclear Data Sheets for A = 87
2015, Nuclear Data SheetsThe evaluated experimental data are presented for 14 known nuclides of mass 87 (Ga, Ge, As, Se, Br, Kr, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru). New datasets have been added for 87Ga, 87Se, 87Kr, 87Rb, 87Sr, 87Nb, and 87Tc. The observation of and new lifetime measurements for 87As at the NSCL Coupled Cyclotron Facility and the Oak Ridge Isochronous Cyclotron at the HRIBF–ORNL Facility are included in the adopted levels for this isotope. The new evaluation also includes an isomeric level at unknown energy for 87Tc, changes to the adopted levels for 87Nb based on newly published data including an extension of the high spin levels and new lifetime measurements, and new heavy ion data for 87Kr. New high spin levels for 87Rb were observed, indicating possible neutron core excitations. In addition, the ground state lifetime of 87Rb has been revised and a new lifetime measurement for an excited level in 87Rb indicates a possible proton spin flip. New excitation levels have been observed for the first time in 87Se. New direct and precise measurement of atomic masses of 87Tc, 87Mo, 87Nb, 87Zr, 87Mo and 87Tc have greatly improved the Q value landscape in this mass region. This work supersedes the previous A=87 evaluation published in 2002He09, and Q values for all isotopes were updated to incorporate the mass evaluation in 2012Wa38.
Nuclear Data Sheets for A = 86
2015, Nuclear Data SheetsThe experimental nuclear spectroscopic data for known nuclides of mass number 86 (Ga, Ge, As, Se, Br, Kr, Rb, Sr, Y, Zr, Nb, Mo, Tc) have been evaluated and presented together with Adopted properties for levels and γ rays. New high-spin data are available for 86Se, 86Br, 86Kr, 86Sr, 86Y, 86Zr and 86Mo; and lifetime data for high-spin states in 86Y and 86Zr. No significant new data since the 2001 NDS for A=86 have been reported for 86Rb and 86Nb. No data are yet available for excited states in 86Ga and 86As. The decay scheme of radioactive 86Ge is unknown, while those for 86Ga, 86As, 47.4 min isomer of 86Y, 86Nb and 86Tc are deemed as incomplete. Isomerism in 86Nb remains unconfirmed. This work supersedes the data presented in the previous NDS evaluation of A=86 published by 2001Si43.
Nuclear data sheets for A = 85
2014, Nuclear Data SheetsEvaluated experimental data are presented for 13 known nuclides of mass 85 (Zn, Ga, Ge, As, Se, Br, Kr, Rb, Sr, Y, Zr, Nb, Mo). Since the previous 1990 evaluation of , 85Zn, 85Ga, 85Ge and 85nuclides are newly added here. Excited state data for 85Se, 85Zr have become available from radioactive decay and in–beam γ–ray studies. New and improved high–spin data are available for 85Br, 85Kr, 85Rb, 85Y, 85Nb and 85Mo. New direct and precise measurement of atomic masses of 85Ge, 85As, 85Se, 85Br, 85Rb, 85Zr, 85Nb and 85Mo have greatly improved the landscape of β decay–Q values and separation energies in this mass region.
In spite of extensive experimental work on the isobaric nuclei of this mass chain several deficiencies remain. No excited states are known in 85Zn, 85Ga, 85As. Only a few excited state are assigned in 85Ge from 85Ga β– decay. From radioactivity studies, the decay schemes of 85Zn and 85Mo are not known, and those for 85Ga, 85Ge, 85As and 10.9–s isomer of 85Zr are incomplete. Level lifetimes are not known for excited states in 85Se, 85Br, 85Nb and 85Mo. The 85Tc nuclide has not been detected in fragmentation experiments at GANIL, alluding to its unbound nature for proton emission. The 85Kr, 85Rb, 85Sr, and 85Y nuclides remain the most extensively studied from many different reactions and decays.
The evaluation of nuclides has been done after a span of 23 years, thus includes an extensive amount of new data for almost each nuclide. This work supersedes the data for nuclides presented in earlier full NDS publication by J. Tepel in 1980Te04 and a later one published in an update mode by H. Sievers in 1991Si01
Discovery of the arsenic isotopes
2010, Atomic Data and Nuclear Data TablesTwenty-nine arsenic isotopes have been observed so far and the discovery of these isotopes is discussed here. For each isotope a brief summary of the first refereed publication, including the production and identification method, is presented.
Nuclear Data Sheets for A = 84
2009, Nuclear Data SheetsThe evaluated spectroscopic data are presented for 12 known nuclides of mass 84 (Ga, Ge, As, Se, Br, Kr, Rb, Sr, Y, Zr, Nb, Mo). Except for the stable nuclides 84Sr and 84Kr, extensive new data are available for all the other nuclides since the 1997 evaluation by J.K. Tuli (1997Tu02) of A = 84 nuclides. Many precise Penning-trap mass measurements since AME-2003 for A = 84 nuclides (2009Re03,2008Ha23,2008We10,2007Ke09,2006Ka48,2006De36,2006Ri15) have resulted in improved Q values and separation energies. However, many deficiencies still remain. Some examples are given below. Excited-state data for 84Ga and 84As are nonexistent, and those for 84Ge are scarce. The radioactive decay schemes of 84Ga, 84Ge, 84Se, 84Y (39.5 min), 84Y (4.6 s), 84Zr and 84Nb suffer from incompleteness and that for 84Mo decay is not known at all. The energy ordering of the two activities (39.5 min and and 4.6 s) of 84Y is not well established, although, high-spin with tentative spin-parity of (6+) is adopted here as the ground state of 84Y based on weak arguments. From a conference report published in 2000, it is clear that extensive experiments were done to investigate decays of 84Zr and 84Y, but details of these studies never appeared in literature and none were made available to the evaluators when requested from original authors.
This evaluation was carried out as part of ENSDF workshop for Nuclear Structure and Decay Data Evaluators, organized and hosted by the “Horia Hulubei” National Institute for Physics and Nuclear Engineering, Bucharest, Romania during March 30, 2009 – April 3, 2009. Names of the evaluators principally responsible for evaluation of individual nuclides are given under the respective Adopted data sets.
Nuclear Data Sheets for A = 135
2008, Nuclear Data SheetsThe evaluated experimental data are presented for 17 known nuclides of mass 135 (In, Sn, Sb, Te, I, Xe, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb). For 135In, 135Eu, 135Gd and 135Tb, only the half-lives and isotopic identifications are established without any knowledge of their level structures and β decay schemes. Extensive high-spin structures are known for 135Te, 135I, 135Ba, 135La, 135Ce, 135Pr, 135Nd, 135Pm and 135Sm; including a superdeformed structure in 135Nd. Only limited high-spin data are available for 135Sb and the data for 135La are from a thesis only. Neutron capture γ-ray data are available in detail for 135Ba (thermal and resonance energies) and marginally for 135Cs (thermal neutrons). Single particle-transfer data exist for 135Xe and 135Ba; and marginally for 135I and 135La. In the opinion of the evaluators, the decay schemes from β decays of 135Sn, 135Xe, 135Pr, 135Pm isomers and 135Sm are not well established. The absolute level energies in 135Pm and 135Sm are not known. This work supersedes earlier (1998Se07,1987Se11,1975He12) evaluations of A = 135.