GRID lifetime measurements in59, 61, 63Ni following thermal neutron capture

Abstract

The GRID-method has been used to measure the lifetimes of ten excited states in 59, 61, 63Ni following thermal neutron capture in Ni targets of natural isotopic composition. Four of the lifetimes have been determined for the first time, the other six lifetimes can be compared with the results of conventional DSA-measurements following charged particle induced reactions. Cascade feeding effects have been included in the analysis. Level energies and electromagnetic properties of negative parity states in 59Ni have been compared with the results of shell model calculations in 3pOh and 4plh model spaces. Statistical model estimates of the lifetimes as function of excitation energy and spin are also given.

Thermal neutron capture?-ray spectroscopy of59Ni and61Ni

“…With the high neutron flux available at the ILL reactor and a high resolution pair spectrometer we hoped to be able to identify the missing portions of the primary spectra Supported by Deutsches BMFT of the 5s'6~ 7) reactions, to identify new excited states and make spin-parity assignments. This information, together with the results from charged-particle induced reactions then should allow us to derive level densities and ~-ray strength functions in the semi-magic Z=28 nickel isotopes, and compare them to findings for N ~_ 20, 28 and 50 neutron magic nuclei [4][5][6][7][8][9].This present work complements our previous studies of the 6~Ni(n, ~)63Ni and 6ZNi(2 n, 7)64Ni reactions [10] and the GRID lifetime measurements in 59'61Ni by U1-big et al [11]. In this latter work, assumptions concerning the feeding mechanism of several excited states had to be inferred which now can be checked with the present data.…”

“…(9) 0.165(9) 4977.00 (9) 0.253 (13) 5044.89 (11) 0.030(2) 5068.63 (9) 0.109(6) 5078.92 (12) 0.024(1) 5109.06 (9) 0.108(5) 5115.93 (30) 0.007(1) 5140.76 (16) 0.026(2) 5145.18 (9) 0,131(7) 5152.30 (10) 0.047(3) 5167.55 (28) 0.007(1) 5223.38 (13) 0,027(2) 5237.0 (6) 0.003(1) 5268.56 (9) 0.337(17) 5277. 35(15) 0.021(1) 5292.69 (13) 0.038(2) 5312,64 (9) 1.74(9) 5362.67 (11) 0.045(2) 5384.52 (13) 0.025 (2) 5435.77 (10) 0.631 (32) 5458.74 (10) 0.079(4) 5546.62 (1 I) 0.066 (3) 5565.96 (24) 0.019(2) 5590.0 (5) 0.005(1) 5617.04 (12) 0.075(4) 5621.41 (11) 0.126 (7) 5631.99 (22) Only transitions which were placed into the level scheme and the strongest (I >__ 0.1% per captured neutron) unplaced lines are given "The 7-energies are not corrected for recoil. The given errors include systematic errors of 10ppm for 0MeV<E~__<3 MeV and 15 ppm for E~>3 MeV b The intensities are given in units of v-transitions per 100 captured neutrons.…”

“…In this latter work, assumptions concerning the feeding mechanism of several excited states had to be inferred which now can be checked with the present data. Ulbig and co-authors [11,12] also performed extensive shell model calculations of the negative parity states in 59Ni. …”

Double neutron capture in62Ni

“…(7) 0.40 (8) 4765.17(9) 1637.03 (13) 0.30 (6) 4788.96 (8) (7) 0.312 (16) 3648-* 0 7380.62(13) 3696.28 (8) 0,234 (12) 7393.01(36) 3748.77 (8) 0,160 (8) 3749--* 0 7427.6(7) 3768.51 (9) 0.130 (7) 7437.6(8) 3798.74 (7) 0,516 (26) (6) 0.304 (15) 4573-* 0 0.456 (23) 4616-* 0 0.623(31) 464t-* 0 0.373 (19) 4.61 (23) 9658 -*4869 0.149 (7) 4869-* 0 0.378 (19) 1.19 (6) 9658-* 4704 1.13 (6) 9658--,4641 0.735 (37) 9658---,4616 1.02 (5) 9658-*4573 0.122(6) 0.126 (6) 1.31 (7) 0.143 (7) 5418-* 0 0.173(9) 0.160 (8) 0.402 (20) 9658--, 3749 0.141 (7) All energies are given in keV. (7) 0.40 (8) 4765.17(9) 1637.03 (13) 0.30 (6) 4788.96 (8) (7) 0.312 (16) 3648-* 0 7380.62(13) 3696.28 (8) 0,234 (12) 7393.01(36) 3748.77 (8) 0,160 (8) 3749--* 0 7427.6(7) 3768.51 (9) 0.130 (7) 7437.6(8) 3798.74 (7) 0,516 (26) (6) 0.304 (15) 4573-* 0 0.456 …”