Ulf Gruber

ENERGY LEVELS AND GAMMA TRANSITIONS IN Dy 164

The neutron capture Gamma ray spectrum of Dy 164 was measured with the curved crystal spectrometer at the DR-3 reactor at Risø. A level scheme was constructed from the energies (30 keV−1 MeV) and the intensities of the detected lines. The states obtained are: the groundstate rotational band with the levels at 73.392 (0.2+), 242.230 (0.4+), and 501.32 keV (0.6+), the Gamma vibrational levels 761.80 (2.2+), 828.19 (2.3 +), 915.98 (2.4+) and 1024.63 keV (2.5+) and a band withK=2−having the energies 976.88 (2.2−), 1039.30 (2.3-), 1122.76 (2.4−) and 1225.15 keV (2.5−). The precisely determined energies are compared with the collective model. The intensities of the transitions agree with the branching ratios expected from this model.

GAMMA TRANSITIONS AND ENERGY LEVELS IN

220 neutron capture Gamma rays of Dy 165 were measured with the Riso curved crystal spectrometer. The intense transitions permitted the construction of a level scheme for this oddN nucleus. The rotational bandsK=7/2+[633],K=1/2−[521] andK=5/2−[512] were precisely localized, including the spin 11/2 states. Gammavibrational bands built on these Nilsson orbits were observed with their band heads at 538.6, 573.5 and 570.2 keV. TheI=5/2 term at 533 keV can be considered as the 5/2−[523] Nilsson state. The branching ratios allowed the determination of (gK−gR)2-factors for the [633], [521] and [512] bands and yieldedE 1-hindrance factors.Abstract220 neutron capture Gamma rays of Dy 165 were measured with the Risø curved crystal spectrometer. The intense transitions permitted the construction of a level scheme for this oddN nucleus. The rotational bandsK=7/2+[633],K=1/2−[521] andK=5/2−[512] were precisely localized, including the spin 11/2 states. Gammavibrational bands built on these Nilsson orbits were observed with their band heads at 538.6, 573.5 and 570.2 keV. TheI=5/2 term at 533 keV can be considered as the 5/2−[523] Nilsson state. The branching ratios allowed the determination of (gK−gR)2-factors for the [633], [521] and [512] bands and yieldedE 1-hindrance factors.

sup 165

Abstract The low-energy spectrum of the 55 Mn(n, γ) 56 Mn reaction has been studied with a γ-diffraction spectrometer. These data allowed the construction of a level scheme for 56 Mn with two previously unobserved doublets. High-energy γ-transitions to the low-energy states have been measured for different neutron resonances at the BNL fast neutron chopper. For most states a unique spin and parity could be proposed. A shell-model calculation of the structure of the low-lying states of 56 Mn has been carried out with the Oak Ridge-Rochester computer programme; there are plausible theoretical analogues for 11 of the 12 experimentally observed states. Calculated spectroscopic factors and M1 transition probabilities are in qualitative agreement with the experiment.

Dy

Abstract The high energy γ-ray spectrum from thermal neutron capture in natural terbium has been studied over the energy range of 5200 to 6400 keV. Low energy γ-radiation of the same reaction has been observed from 20 to 1230 keV and conversion electrons from 6 to 160 keV. Low energy (n, γγ) coincidences have been measured. A value of 6375.1 ± 0.3 keV has been obtained for the neutron binding energy in 160Tb. The data, when combined with a previous 159Tb (d, p) study, allow a level scheme to be constructed. These levels are assigned to nine rotational bands built on two quasiparticle configurations. The decay of several other levels is discussed. In three cases we have observed both parallel and antiparallel coupled bands with K − = ¦Ω p −Ω n ¦ and K + = Ω p + Ω n , and found the Gallagher-Moszkowski rule to be valid. The energy splitting has been calculated using Nilsson wave functions and a δ-force. Two K = 1 bands with irregular level spacing have been observed.

Energy levels of 56Mn

Abstract Utilizing the Riso bent crystal spectrometer, 47 transitions have been observed from 54 keV to ≈ 1 MeV from the reaction Nb93(n,γ)Nb94. These transitions determine the following levels in Nb94 (energy in keV, spin-parity in parentheses): G.S. (6+, ≈ 40.7 (3+), 58.724 (4+), 78.675 (7+), 113.404 (5+), 314.64 (5+), ≈ 334 (2+) and 640.5 (5+). The 315 keV and 641 keV states probably correspond primarily to the J = 3 2 state of the three neutron configuration coupling to the g 9 2 proton configuration. The other six states result primarily from the coupling of the J = 5 2 state of the three neutron configuration and the g 9 2 proton configuration. Energies of the levels and transition probability ratios are consistent with this interpretation.

Nuclear levels in 160Tb

Abstract103 gamma transitions in Hg 200 have been observed. 37 of them were fitted into a level scheme which comprises 17 states. The energy of the one-phonon vibrational stateI=2+ has been determined to be 367.970±0.020 keV, that of the two-phonon vibrational triplet 947.34±0.07 keV, 1029.37±0.05 keV and 1254.20±0.10 keV. Further levels have been found at energies of 1570.30±0.10 keV, 1571.7±0.6keV, 1594.3±0.4 keV, 1631.5±0.2 keV, 1641.5±0.3 keV, 1718.5±0.2 keV, 1730.8±0.2 keV, 1775.7±1.1 keV, 1842.9±0.8 keV, 1882.9±0.3 keV, 2062.6±0.5 keV and 2082.9±1.0 keV.

Energies and character of low-lying levels in Nb94

ZusammenfassungZur Messung der Energie und Intensität niederenergetischerγ-Strahlung, die Atomkerne nach dem Einfang langsamer Neutronen aussenden, wurde ein Spektrometer mit gebogenem Kristall gebaut und am DR3-Reaktor in Risö, Dänemark, aufgestellt. Dieγ-Strahlung wird an der (110)-Ebene eines Quarzkristalls reflektiert. Häufig können Reflexe in 2., 3. und 5. Ordnung ausgemessen werden, womit sich eine höhere Meßgenauigkeit und ein besseres Auflösungsvermögen als in der 1. Ordnung ergibt. Das Reflexionsvermögen der (110)-Ebene wurde in 1., 2., 3. und 5. Ordnung bestimmt. Es folgt bei höheren Energien (in 1. Ordnung ab rund 300 keV) einemE−2-Verlauf, wie es für einen Mosaikkristall zu erwarten ist.Mit dem Instrument wurde dasγ-Spektrum von Rh104 aufgenommen, und 164 gefundene Linien wurden ausgemessen. Die gewonnenen Ergebnisse gestatten es, unter Berücksichtigung von Koinzidenzdaten das vonBuschhorn vorgeschlagene Niveauschema zu erweitern.

Gammastrahlung vom Einfang thermischer Neutronen in Hg 199

A value ofσ=3, 5±1 is obtained for the spin cut off coefficient in the Fermi gas level density formula from a comparison of calculated and experimental (n, γ)-intensities feeding the observed levels of deformed nuclei in the rare earths region. The model used for the computations is tested at two nuclei with compound states of low spin (Ic=1/2) and high spin (Ic=13/2 or 15/2). The calculations can help to determine spins of nuclear levels in some cases.