Decay of individual levels in delayed neutron emitters to excited states in the final nuclei
Abstract
Delayed neutron emission to excited states in 84Se, 93Sr and 134Te has been investigated. Comparison of energies and intensities of neutron and γ-ray transitions observed in the decay of the precursors 85As and 135Sb leads to the localization of individual levels in the delayed neutron emitters, suggesting over and above high selectivity in β−-decay also selectivity in the subsequent neutron emission with substantially higher decay probabilities to excited states in the final nuclei than expected from energetics and angular momentum considerations. Gernmany.
References (13)
- H. Gunther
Nucl. Phys.
(1975) - E. Moll
Nucl. Instr.
(1975) - J.T. Routti et al.
Nucl. Instr.
(1969) - R. Brissot
Nucl. Phys.
(1975) - A. Kerek
Nucl. Phys.
(1972) - H. Franz
Phys. Rev. Lett.
(1974)
Cited by (23)
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
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.
Nuclear data sheets for A = 135
1998, Nuclear Data SheetsThe evaluated experimental data are presented for 15 known nuclides of mass 135 (Sn, Sb, Te, I, Xe, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd). Excited state data are nonexistent for135Sn,135Sb,135Eu and135Gd. High spin excitations are known for135Te,135I,135Ba,135La,135Ce,135Pr,135Nd,135Pm and135Sm; including a superdeformed structure in135Nd. Neutron capture γ-ray data are available for135Ba (thermal and resonance neutrons) and135Cs (thermal neutrons). Single particle-transfer data exist for135I,135Xe,135Ba and135La. Nuclides135In and135Cd have not yet been identified but included in theoretial calculations of 96Bo11 and 97Bo24, respectively. The135In nuclide islisted with T1/2(from syst) = 100 ms (97Au04), 89 ms (97Mo25) and Jπ (from syst) = 9/2+ (97Au04, 97Mo25). This work supersedes earlier (87Se11, 75He12) evaluations of A = 135.
The importance of delayed neutrons in nuclear research-A review
1994, Progress in Nuclear EnergyThis paper presents a comprehensive review of the uses of β-delayed fission neutron information in nuclear research with special emphasis on the energy spectra and reactor applications. A short introduction is followed by a discussion of the applications of delayed neutron properties in nuclear structure and astrophysics. Section 3 gives the delayed neutron requirements for reactor physics purposes and points out the difference between the physical and the mathematical representations of the delayed neutron data. In Sections 4 and 5, respectively, there are discussions of the total delayed neutron yield and the decay constants. Section 6 highlights the importance of and the need for an exact knowledge of delayed neutron energy spectra in high-accuracy criticality calculations and in precise evaluations of reactor kinetic characteristics, particularly the fast breeders. Section 6 also gives a brief description of the principal methods that are commonly used for determining the delayed energy spectra. Section 7 gives a chronological account of the developments in the measurement of delayed neutron energy spectra, both aggregate (composite) and from individual fission product isotopes, and compares the spectra, wherever possible, with the ENDF/B evaluations. A comparison is made of the energy spectra of a few precursors measured at different laboratories. There are discussions on the major spectrometry techniques employed in the measurements of delayed neutron energy spectra as well as on the methods of performing spectral analysis. This covers the response function, the efficiency and the sensitivity of the spectrometers, their merits and demerits, and their applicability. Calculations of delayed neutron energy spectra from precursor data, and decomposition of composite spectra into six-group delayed spectra using summation and/or fitting procedures are described in Section 8. Sensitivity studies of fast reactor kinetic behaviour to delayed neutron energy spectra are reviewed in Section 9. Both direct and adjoint methods are discussed. Section 10 gives a summary of the paper which concludes in Section 11 with a number of recommendations.
The shape of the beta strength function and consequences for nuclear physics and astrophysics
1983, Progress in Particle and Nuclear Physics