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The production of Neptunium-236g.

Jerome, S M; Ivanov, P; Larijani, C; Parker, D J*; Regan, P H (2014) The production of Neptunium-236g. J. Environ. Radioact., 138. pp. 315-322.

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The isotope 236gNp is of interest both as a long-lived odd-odd isotope and as a chemical yield tracer. The parallel and anti-parallel couplings of the final unpaired proton and neutron in this nucleus gives rise to two competing states with the same internal, single-particle configuration, which have assigned spin/parity Ip=(6-) and (1-) respectively. The higher-spin, `high-K' coupling has been established as the ground state of this prolate deformed nucleus and decays with a half-life of 1.55×105 years. The anti-parallel coupling of the same orbitals giving rise to the metastable, but considerably shorter-lived Ip=Kp=(1-) state, which has an evaluated decay half-life of 22.5 hours. Both of these states decay to excited states in 236U (by electron capture) and 236Pu (by ß- decay). The spin/parity of the decaying state has been established by the identification of electromagnetic transitions from high spin (Ip=6+) and low-spin (Ip=2+) states respectively which are populated in the daughter nuclei. The excitation energy difference between these the Ip=6- ground state and Ip=1- excited state has not been experimentally established to date but evaluations suggest an energy difference of the order of 60 keV. This energy difference would give a direct measurement of the Nilsson orbital dependent proton-neutron residual interaction in this nucleus.
The radiochemical analysis of 237Np is important in a number of fields of activity, such as nuclear forensics, environmental analysis and measurements throughout the nuclear fuel cycle. However analysis is complicated by the lack of a stable isotope of neptunium. Although various tracers have been used, including 235Np, 239Np and even 236Pu, none are entirely satisfactory. However, 236gNp would be a better candidate for a neptunium yield tracer, as its long half-life means that it is useable as both a radiometric and mass spectrometric measurements. This radionuclide is notoriously difficult to prepare, and limited in scope. In this paper, we examine the options for the production of 236gNp, based on work carried out at NPL since the last MARC conference. However, this work was primarily aimed at the production of 236Pu, and not 236gNp and therefore the rate of production are based on the levels of 236Pu generated in the irradiation of (i) 238U with protons, (ii) 235U with deuterons, (iii) 236U with protons and (iv) 236U with deuterons. The derivation of a well-defined cross section is complicated by the relevant paucity of information on the variation of the 236mNp:236gNp production ratio with incident particle energy. Furthermore, information on the purity of 236gNp so produced is similarly sparse. Accordingly, the existing data is assessed and a plan for future work is presented.

Item Type: Article
Keywords: Neptunium, radiochemical analysis, irradiation, odd-odd nucleus
Subjects: Ionising Radiation
Ionising Radiation > Radioactivity
Identification number/DOI: 10.1016/j.envrad.2014.02.029
Last Modified: 02 Feb 2018 13:13
URI: http://eprintspublications.npl.co.uk/id/eprint/6493

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