Nuclear levels in152Eu

A systematic study of (n, d), (n, n' p) and (n, pn) reactions at 14.7 MeV

The effect of neutron-proton pairing interaction between the last odd neutron and the last odd proton in the outermost neutron and proton shells of a nucleus has been demonstrated by the last neutron binding energy and the last proton binding energy plots in the heavy nuclei. The n-p pairing interaction has been estimated for nuclei in the region Z>82 and N>126 and it has been successfully used to explain the neutron and proton binding energy plots. The interaction energy seems to decrease with increase in the difference between neutron and proton numbers in the outermost neutron and proton shells respectively for nuclei in the region of Z>82 and N>126.

Spectroscopy of 41K by thermal neutron capture in 40K

Spectroscopy of the ODD-ODD nucleus 76As and its supersymmetric description

The neutron capture gamma-ray spectrum for a natural copper target has been investigated using a Ge(Li) spectrometer. A total of 146 gamma rays were observed, of which about half have been isotopically assigned. Assignment was achieved through the use of coincidence measurements and (d, p) results. The neutron separation energies were found to be 7 914(3) and 7 063(3) keV for 64Cu and 66Cu respectively. The 66Cu gamma-ray transition to low-lying states exhibit exceptionally large radiation widths in a manner similar to the corresponding anomaly in 64Cu.

The decay of Au194

Twenty-seven levels in ${\mathrm{Tm}}^{170}$ have been observed up to an excitation energy of 1153 keV utilizing 12-MeV deuterons and the reaction ${\mathrm{Tm}}^{169}(d,p){\mathrm{Tm}}^{170}$. The ground-state $Q$ value was determined as 4369\ifmmode\pm\else\textpm\fi{}15 keV. Both magnetic Compton and germanium spectrometers have been used to measure 16 high-energy gamma rays up to an excitation energy of 868 keV resulting from the capture of thermal neutrons in the reaction ${\mathrm{Tm}}^{169}(n,\ensuremath{\gamma}){\mathrm{Tm}}^{170}$. The neutron binding energy observed in this reaction is 6595\ifmmode\pm\else\textpm\fi{}2.5 keV. In addition, 177 low-energy gamma rays between 38 and 870 keV have been observed in a bent-crystal spectrograph during irradiation of ${\mathrm{Tm}}^{169}$ with thermal neutrons. The multipolarities of 29 of the transitions were determined from internal conversion measurements with a beta-ray spectrometer. The analysis of these data suggests the existence of 23 levels up to an energy of 720 keV for which assignments have been attempted. Three Nilsson configurations 0, in which the proton orbital ${\ensuremath{\Omega}}_{p}$ remains $\frac{1}{2}+[411\ensuremath{\downarrow}]$ and the neutron orbital ${\ensuremath{\Omega}}_{n}$ is successively $\frac{1}{2}\ensuremath{-}[521\ensuremath{\downarrow}]$, $\frac{7}{2}+[633\ensuremath{\uparrow}]$, and $\frac{5}{2}\ensuremath{-}[512\ensuremath{\uparrow}] 0$, account for 16 states. This analysis leads to the following spectroscopic interpretation (band head energy, keV, in parentheses; spin, parity, and $K$ quantum number in brackets): (ground state), [1-, 1] with superimposed band to 4-; (149.721), [0-, 0] with superimposed band and anomalous spacings of even and odd spin members to 4-; (183.193), [3+, 3] with superimposed rotational members to 5+; (204.452), [2-, 2] with superimposed rotational members to 4-; (447.079), [3-, 3] only member of the band. Seven additional higher energy levels are tentatively assigned, five of which may arise from gamma vibrational bands at 411.45, 661.91, and 719.21 keV built on $K=1\ensuremath{-}$, $K=0\ensuremath{-}$ and $K=3+$ intrinsic bands, respectively. These are the first gamma vibrational bands postulated in odd-odd nuclei. All states below 425 keV from both ($d,p$) and direct high ($n,\ensuremath{\gamma}$) excitation are included in these assignments. The Coriolis coupling between the $K=1\ensuremath{-}$ and $K=0\ensuremath{-}$ bands is clearly observed in the anomalous rotational spacing of the $K=1\ensuremath{-}$ band. Calculation of the energies and ($d,p$) cross sections for the $K=1\ensuremath{-}$ and $K=0\ensuremath{-}$ bands agrees well with experiment and indicates that only the even members of these bands are appreciably mixed. The $M1$ transition probabilities within the $K=0$ rotational band in ${\mathrm{Tm}}^{170}$ are shown to be quite large. It is suggested that the high-energy gamma rays in the reaction ${\mathrm{Tm}}^{169}(n,\ensuremath{\gamma}){\mathrm{Tm}}^{170}$ involve a direct reaction which excludes population of excited proton configurations.

The completely unknown spectrum of excited states of the odd-odd nucleus ${}^{230}$Pa was studied employing the one-neutron transfer reaction ${}^{231}$Pa($d,t$)${}^{230}$Pa at a beam energy of 22 MeV. The excitation energy and the cross section were measured for, in total, 81 states below 1.4 MeV. Level assignments of these states are based on a semiempirical model and comparison with theoretical predictions, based on distorted-wave Born approximation (DWBA) calculations for the cross sections. For 12 rotational bands the band-head energy and the rotational parameter are determined. The $K$ quantum numbers and the Nilsson configurations are established. Empirical values for the Gallagher-Moszkowski splittings and for Newby shifts are obtained.

Level structure of 100Tc

Several measurements in medium mass nuclei have reported a low-energy enhancement in the photon strength function. Although, much effort has been invested in unraveling the mysteries of this effect, its physical origin is still not conclusively understood. Here, a completely model-independent experimental approach to investigate the existence of this enhancement is presented. The experiment was designed to study statistical feeding from the quasi-continuum (below the neutron separation energy) to individual low-lying discrete levels in 95Mo produced in the (d, p) reaction. A key aspect to successfully study gamma decay from the region of high-level density is the detection and extraction of correlated particle-gamma-gamma events which was accomplished using an array of Clover HPGe detectors and large area annular silicon detectors. The entrance channel excitation energy into the residual nucleus produced in the reaction was inferred from the detected proton energies in the silicon detectors. Gating on gamma-transitions originating from low-lying discrete levels specifies the state fed by statistical gamma-rays. Any particle-gamma-gamma event in combination with specific energy sum requirements ensures a clean and unambiguous determination of the initial and final state of the observed gamma rays. With these requirements the statistical feeding to individual discrete levels is extracted on an event-by-event basis. The results are presented and compared to 95Mo photon strength function data measured at the University of Oslo.

We investigate a relation between the energies of nuclear excited levels and its periodic phases for nuclei with A = 14 - 244 in the energy region up to several tens MeV. These levels include neutron and proton resonances, excited levels below neutron and proton separation energies and also vibrational and rotational bands in unstable nuclei. Here we use level periods less than 50 keV. We found that series of parabolic fringes appear in the plots of level energies vs. its periodic phases in various excitation modes. Distinguished fringes can be observed for neutron and proton resonances in nuclei with neutron or proton magic numbers: 37 Cl, 59 Ni, 61 Ni and 62 Ni. For neutron and proton resonances in a wide mass range of nuclei, parabolic fringes with the same periods and scales can be observed at the same incident energies. Each fringe is separated by a phase difference of 1/n , where n is an integer. We interpret the parabolic fringes as a result of interference effects based on time; a quantized phase difference of 1/n can be connected to a discrete time delay of wave pulsations. These fringe spectra were compared between different nuclear excitation modes.

The transfermium nucleus No-254 (Z = 102, N = 152) has been studied in a recoil-decay tagging experiment using the SAGE in-beam spectrometer, RITU gas-filled separator and GREAT focal-plane spectrometer at the Accelerator Laboratory of the University of Jyvaskyla (JYFL). Both γ rays and conversion electrons from the ground-state band of No-254 have been observed with SAGE. Coincidences between them can be seen and it is possible to measure internal conversion coefficients for some transitions in the band. This shows that they have E2 multipolarity, as expected for a rotational band built on a Kπ = 0+ state. The two previously identified K isomers in No-254 have also been seen. In the prompt data tagged on the slow isomer’s decay the prominent 605 keV transition from previous decay spectroscopy experiments is not seen with the expected intensity. This allows one of the previously proposed level schemes to be ruled out. It is possible that this transition is not seen in the in-beam data at all and the peak at this energy is entirely from inelastic neutron scattering reactions within the SAGE germanium detectors. If this is the case the 605 keV transition could directly depopulate the fast isomer into a band built on the slow isomer without any intermediate structure. There is not enough data to measure γ-ray branching ratios in the band built on the slow isomer so a new method has been developed to determine the single-particle structure of the isomer by comparing the in-beam conversion-electron spectrum above it with Geant4 simulations of the same level scheme with a varying single-particle g factor. This suggests that the structure of the slow isomer is the 7/2+[624]ν ⊗ 9/2-[734]ν two-neutron state.

An irradiation of 238U with a beam of reactor fast neutrons permits revealing about 550 gamma transitions associated with the respective (n, n′γ) reaction and with fission fragments. The use of all known data on gamma radiation from fission fragments makes it possible to identify gamma transitions belonging to 238U with a high probability. The scheme of levels and gamma transitions is composed for 238U. New levels (including those of spin-parity Jπ = 0+) at excitation energies below 2 MeV are proposed. The low-lying levels in the rotational band for two-phonon octupole excitations are determined. It is found that a hybrid state is formed upon the crossing of this band and the band based on two-quasiparticle excitations. This hybrid state must involve excitations of both types. A small value of the rotational-band parameter in the isomer of energy 2559.0(4) keV is explained by the contribution to this state from two-quasiparticle configurations belonging to the 1k17/2 subshell. The same circumstance may also be responsible for an enhanced yield of ternary fission for this isomer.

Features of the low-energy level scheme of 229Th as observed in the α-decay of 233U

Excited states of the 193Hg nucleus have been investigated by the reaction 150Nd(48Ca,5n) at a beam energy of 213 MeV. The level scheme has been extended up to 10.7 MeV. Three different level pattern regions have been identified. A lower region with rotational bands, an intermediate region with single-particle character and an upper region with sequences of dipole transitions. The nature and the corresponding nuclear shape in these regions are discussed and compared with similar phenomena in the neighbouring nuclei.