Complete spectroscopy of51,52V via the50,51V(n, ?) reactions

Abstract

The gamma-ray spectra emitted after thermal neutron capture in highly enriched 5~ and natv targets have been studied using in-pile targets at the ILL high flux reactor and pair and germanium detectors. The neutron binding energies in 51V and 52V were determined to be Bn(51V)=l1051.11(17) keV and Bn(52V) =7311.22(26) keV. The thermal neutron capture cross-section in s~ was measured to be 21_+4 b. From 724 lines attributed to slV, 330 transitions, comprising 90% of the ?-ray flux, were placed into the level scheme. Fifty-nine primary dipole transitions from the 11/2 + or 13/2 + capture states in 51V were established from which the E1 strength distribution was deduced. The energy scaling of these primary transitions was found to follow the El-giant dipole resonance dominance. Many new levels were established; a number of states proposed in previous (d,p) and (n, ?) work were confirmed from their primary population and decaying secondary radiations. The density of levels in the high spin (9/2<_I<_ 15/2) region was parametrized with the Fermi gas model. The spin distributions of 51V were analyzed and a spin cut-off parameter a = 2.8 (3) was deduced. -A nearly complete level scheme of 52V up to 3.5 MeV excitation and similar results concerning the level density and the primary y-ray spectrum were obtained in the 5W (n, ?)52V study. PACS" 21.10.Ma; 23.20.Lv; 25.40.Lw, 27.40. +z I. MotivationIn recent years, "complete" nuclear level schemes have been studied with the aim of testing either specific nuclear models, i.e. to identify all predicted states, or of testing * Supported by Deutsches BMFT under contract 06GO141 ** Present address: Physics Department, Tennessee Technological University, Cockeville, TN 38505, USA statistical (or even chaotic) behavior as visible in the level density distribution, nearest-neighbor level spacings and y-ray strength functions. A test of both aspects appears to be most interesting in nuclei where rather simple rnodels, as for example the shell model, can be assumed or shown to be valid [ 1,2].The present investigation of the s~ y)s~'52V reactions with thermal neutrons was carried out for the following reasons:i) The odd-odd target nucleus 5~ has U= 6 +, leading to spin-parity assignments of either 11/2 + or 13/2 + for the capture state(s) in slV, after s-wave thermal neutron capture. Primary dipole transitions thus populate levels in the spin window 9/2<_1<_15/2. Such high spins are usually not accessible in neutron capture reactions. It was expected that complete spectroscopy in this spin window would allow the measurement of the spin dependence of the level density. ii) Previous (n, y) studies of the G6ttingen-GrenobleMunich collaboration have concentrated on nuclei near the N= 20 and N= 50 neutron shell closures. Krusche, yon Egidy and collaborators [3][4][5] have studied the 4~ isotopes, while Winter et al. [6][7][8] have scanned the isotopes 87"88"89Sr. These experiments gave evidence for shell effects in the level density parameters. Moreover, a comparison of the level den...

Double neutron capture in62Ni

“…The experimental procedure followed the method applied in our previous neutron capture studies on 31p, 50,51V and 86'87'88Str targets [1][2][3][4][5] where further details of the experimental set-up and data analysis are given. The metallic nickel powder target, weighing 784 mg and having 97.5% 62Ni isotope enrichment, was exposed to a thermal neutron flux of 5.5 9 1014 neutrons/cm 2 s near the core of the ILL high flux reactor where it remained during the full breeding period.…”

“…In the course of a systematic investigation of level densities and y-ray strength functions in light and medium nuclei, via thermal neutron capture reactions, we have so far concentrated on targets of the 2s 1 d-shell and near the N= 28 and 50 closed neutron shells [1][2][3][4][5][6]. We now extend these measurements to the Z = 28 closed proton shell nickel isotopes.…”

Thermal neutron capture?-ray spectroscopy of59Ni and61Ni

“…(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.…”

“…For 35 nuclei (see Table 4) we have plotted in Fig. 2 Table 4 (4) a Discrete levels taken from the Nuclear Data Sheets [18,[27][28][29][30][31][32][33][34][35][36] or CTFG parameters taken directly from [20] (2SA1, 29Si, 33S, 348, 3~C1, 4~ 41K, 41Ca, 46Sc, 6~ 67Zn, 75Se, and 77Se), [2] (~2K, 64Cu and 66Cu), [5] (slV and szv), [10] (63Ni and 64Ni) and [13] (3zp); Spin range accessible to primary dipole radiations b s-wave average level spacing Do is taken from [37] ~ spin cut-off parameter was taken as cr = 0.98 A ~ [20] …”

“…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.…”