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Detailed angular distributions for the 230,232Th( d , t )229,231Th reactions were measured with 17 MeV deuterons, using a magnetic spectrograph to analyze the reaction products. Comparisons with distorted wave Born approximation predictions were used to determine l-values and spectroscopic strengths for many levels in both nuclides. These results reconfirm previous assignments for the 3 / 2 + [ 631 ] band in 229Th, with its bandhead unresolved from the 5 / 2 + [ 633 ] ground state, providing support for the existence of the much-sought “3.5 eV” isomer (for which the latest reported energy is 7.6 ± 0.5 eV ). Although 231Th was previously well studied, many new spin-parity assignments have been made and some changes to adopted model assignments are proposed. There is evidence in both isotopes for appreciable mixing of single-particle orbitals with other configurations, as predicted by the Quasiparticle Phonon Model. Single-nucleon transfer strengths are described much better with earlier values for the Nilsson model parameters κ and μ than later values that have been widely used. An earlier 232Th( d , t ) study concluded that serious errors could result in the commonly-used method of predicting cross sections by combining distorted wave Born approximation calculations using spherical form factors with Nilsson wave functions for a deformed potential, but the present work shows this conclusion is not valid because it was based on inadequate knowledge of the 231Th nuclear structure.

Dy161,163(t,α) angular distributions were measured using 17 MeV tritons from the McMaster University FN tandem Van de Graaff accelerator. Reaction products were analyzed with an Enge split-pole magnetic spectrograph. New nuclear structure information is reported for each of the residual odd–odd nuclides 160Tb and 162Tb. Clear assignments can be made for the K=1 and K=4 bands formed by coupling the 32+[411] proton with the 52+[642] neutron of the 161Dy target and with the 52−[523] neutron of the 163Dy target. Bands formed by transfer of the 52+[413] proton can also be assigned. Two new Gallagher–Moszkowski splitting energies are reported. Although large peaks can be attributed to transfer of the 52−[532] and 72−[523] protons, strong Coriolis mixings of the four two-quasiparticle bands formed by these transfers in each nuclide, coupled with the unknown Gallagher–Moszkowski splittings and Newby shifts, limit the interpretation to some tentative assignments. From reaction Q-values the mass of 162Tb is determined to be ∼80 keV higher than reported in the 2003 mass tables.

The properties of high-K isomers have been investigated by measuring γ rays from a source of the 31-year 178Hfm2 isomer and from the decay of implanted 178,179Lu beams. Low-intensity transitions have been identified in the decay of 178Hfm2, demonstrating a consistent extension of K-hindrance systematics to higher multipolarities, and elucidating the spin-dependence of the mixing between the two Kπ = 8- bands. A search is underway for new isomers in 178,179Lu and the preliminary results of the analysis are reported. © 2004 Elsevier B.V. All rights reserved.

The 230,232Th(p,α)227,229Ac reactions were studied using 20 MeV protons and a magnetic spectrograph to analyze the reaction products. Relative populations of levels in 229Ac correlated well with previously published (t,α) results for the same final levels, showing that the similarity of the two reactions observed empirically in the deformed rare earth region extends to actinides. The most strongly populated level in 227Ac is at 639 keV, and is assigned as the 1/2 + [4 0 0] bandhead. The 435 keV level, previously adopted as the 1/2 + [6 6 0] bandhead, also has a significant intensity that is attributed to ΔN=2 mixing between these two K=1/2 proton orbitals. The ΔN=2 matrix element estimated from these data is ∼80 keV, similar to values observed for the same two Nilsson states as neutron orbitals in the dysprosium isotopes.

Lifetimes of excited states in 100 Ru were determined from Doppler-shift attenuation measurements following the 100 Ru(n, n ′ γ ) reaction. Absolute transition rates or limits thereon were extracted for states in the three-phonon region and were compared with an interacting boson model description of this nucleus. Intruder states were identified, and a candidate for the 2 + mixed-symmetry state is suggested.

Efforts to model and measure absolute neutron-induced reaction cross sections have for the most part been limited by experimental techniques to neutron energies found in reactors and light-ion fusion reactions (i.e., t(d,n){alpha} etc.). This can in large part be attributed to the difficulty involved in making high-flux mono-energetic neutron beams with E{sub n} > 14 MeV. The result has been a lack of guidance for (n,xnypz{alpha}) reaction modeling for E{sub n} > 1-2 MeV. These limitations become particularly exacerbated in nuclei where structure effects (i.e., near shell closures, high deformation etc.) or fission complicates the models. The GEANIE spectrometer at LANSCE/WNR fills this gap in experimental technique by allowing for efficient measurement of neutron-induced {gamma}-ray partial cross sections over a wide range of incident neutron energies (1 < E{sub n} (MeV) < 250). GEANIE consists of 20 Compton-suppressed and 6 unsuppressed hpGe detectors located at the 60{sup o} right beam line at the LANSCE/WNR spallation source. Eleven of the GEANIE detectors are Low Energy Planar Spectrometers (LEPS) with excellent timing and energy resolution. LANSCE/WNR provides a white source of neutrons through the spallation of a tungsten target with an 800 MeV 2-5 {micro}amp beam of protons. Neutron energy is determinedmore » from the time-of-flight technique. Early results from GEANIE [Ber98] highlighted the deficiencies in the modeling of neutron-induced reaction modeling on a {sup 196}Pt target. More recently, measurements on a {sup 92}Mo target have identified {gamma}-rays in over 2 dozen reaction products [Gar00a]. In this paper we will present an overview of several recent results from GEANIE, including data on a {sup 92}Mo and two Actinide ({sup 235}U and {sup 239}Pu) targets. The implications of these results for reaction modeling from low to high (E{sub n} < 250 MeV) energy will be presented and plans for future experiments discussed.« less

Nuclear levels in 190 Ir have been investigated with the 192 Os(p,3n γ ) and 192 Os(d,4n e − ) reactions using beams of 18–31 MeV protons and 27.8 MeV deuterons. A series of measurements, including excitation functions, γγ and e − e − coincidences, and life time measurements, was performed. From the singles measurements, a total of 140 γ rays were assigned as belonging to the 192 Os(p,3n) 190 Ir channel. The results of the coincidence measurements show that many of these lines are multiplets. Using information from a previous isomer study and single-nucleon transfer reactions, a level scheme is proposed comprising of 112 γ rays placed between 76 levels. It is shown that most of the γ intensity arises from bands having K π ≥4 + . Several negative-parity bands are also proposed. Calculations performed using values of ϵ and γ characteristic of the region reproduce qualitatively some aspects of the level scheme.

In-beam γ-ray spectroscopy and the decay of 124 I were used to study the nuclear structure of 124 Te. On the basis of γγ-coincidences, a level scheme was constructed with over 100 levels and 170 transitions. The use of excitation functions and angular distributions for the (α, 2n) reaction, and the log( ft ) values for the decay, allowed spin assignments for a large number of the levels to be made. The resulting level scheme was interpreted in the framework of the interacting boson model and the particle-core coupling model.

The nuclear structure of 113 Cd was studied using in-beam γ-ray spectroscopy. A level scheme, consisting of 65 levels and more than 100 transitions, was constructed on the basis of γγ coincidences using five compton-suppressed Ge detectors. Spins were assigned by means of excitation function slopes and angular distribution analysis. The resulting level scheme was interpreted in the framework of the interacting boson-fermion model.

Long-lived isomeric states in 190 Ir have been investigated with the 192 Os(p,3n) 190 Ir and 192 Os(d,4n) 190 Ir reactions using beams of 18–31 MeV protons and 27.8 MeV deuterons, respectively. A series of measurements, including excitation functions, half lives, e − γ coincidences and e − e − coincidences, was performed. Five new transitions were observed, and the results of e − γ and e − e − coincidences indicate that these transitions are fed by the 148.7 keV M4 transition that depopulates the 11 − isomer. The previous decay scheme is shown to be incorrect, and the results allow the ground state parity and mass excess to be determined.

A prediction for the negative-parity states originating from the odd-fermion configurations ( ν3p 1 2 ,ν3p 3 2 , ν2f 5 2 ⊗ πd 3 2 ) coupled to an O (6) boson core is obtained for 194 Ir from the known experimental spectra of the nuclei 192 Os, 193 Os and 193 Ir using the U ν ( 6 12 ) ⊗ U π ( 6 4 ) extended supersymmetry. To test the prediction in detail, the spectroscopic factors for the 193 Ir(d,p) 194 Ir reaction are calculated and compared to experimental values. A comparison of the results with those of the Interacting Boson Fermion Fermion Model is also presented.

The level energy spectra of a set of 26 nuclei presenting a vibrational structure were analyzed using a simple U(5) prescription in the IBM-1 framework. Twelve of these nuclei are relatively well fitted and present level patterns in accordance to the model predictions. They are thus confirmed or possible U(5) nuclei. The analysis suggests that they present extensive multiphonon structures. This implies the survival of such structures at higher energies. The experimental B(E2) values between multiphonon states are shown to agree with the finite N dependence predicted by the IBM. It is also observed that the 21+ energies are quite generally about 15% lower than expected from the global nuclear properties.

Levels in the odd-odd nucleus 190Ir were investigated with the 191Ir(d,t), 189Os(3He,d) and 189Os(α,t) reactions. For the 191Ir(d,t) reaction, spectra were measured at 16 angles with a typical overall resolution of 5–6 keV FWHM. The angular distributions of cross sections were compared with predicted curves from DWBA calculations, and spectroscopic strengths were extracted for the different l-values populating the states. From the ratios of (3He,d) and (α,t) cross sections it was possible to obtain information on the dominant l-value involved in the transfer. Relative excitation energies, parities, possible spin values and spectroscopic strengths were determined for levels up to approximately 1 MeV excitation energy. The large number of peaks observed to be populated in common to both the single-proton and single-neutron transfer reactions is strong evidence for a large amount of configuration mixing. Assignments based on the Nilsson model were made for some low-lying states.

Excited levels of the strongly-deformed odd-odd nucleus 166Tm, populated by the 165Ho(α,3nγ) reaction, were investigated using standard in-beam γ-ray spectroscopy, including measurements of a few conversion electron lines, and by high-resolution curved-crystal spectroscopy. A level scheme consisting of 178 transitions among 6 well-developed and 4 partial rotational bands is proposed. Level spins and parities were determined and the results were interpreted in the framework of the Nilsson model by comparison with predictions. The Gallagher-Moszkowski splitting for the { π 1 2 + [411] ± ν 5 2 + [642] } configuration was determined to be 245(20) keV. An anomalous signature splitting was observed for the {π 7 2 + [404] + ν 5 2 + [642]}K π = 6 + configuration.

The nuclear structure of 194 Ir was investigated via the 193 Ir(d,p) reaction using a 16 MeV deuteron beam. The reaction products were analyzed with a magnetic spectograph and detected with photographic plates. The energy resolutions (FWHM) of the detected particles were typically ≅ 8.9keV. Spectra were recorded at 16 angles. The angular distributions of cross sections were fitted with theoretical curves from DWBA calculations, and the spectroscopic strengths were obtained. Level energies, parities, spectroscopic strengths and possible spin values were determined up to approximately 500 keV excitation energy. The experimental results were compared with the IBFFM and the Nilsson model. It was found that the IBFFM can approximately reproduce the structure of 194 Ir, although there is a serious discrepancy with the level observed at 148.7 keV which has a large amount of l = 3 strength. Predictions with the Nilsson model, made for fixed oblate and prolate deformations, did not reproduce the spectroscopic strengths. When spin-parity information for more levels becomes available it may become feasible to improve the description by considering different deformation values, Coriolis mixing and the effects of the mixed target ground state, but at present an unambiguous set of assignments cannot be made.

The nuclear structure of 192Ir was investigated via the 193Ir(d, t) and 191Ir(d, p) reactions, using beams of 18 and 16 MeV deuterons, respectively. The reaction products were analyzed with a magnetic spectrograph, and detected with photographic plates. The energy resolutions (FWHM) of the detected particles were typically ≅ 5.7 keV for the (d, t) and ≅ 8.9 keV for the (d, p) reactions. Spectra were recorded at a large number of angles (⩾ 15). The angular distributions of cross sections were fitted with theoretical distributions from DWBA calculations, and the spectroscopic strengths were obtained. For the (d, t) reaction, the fits to the angular distributions were performed in many cases with the sum of two l-values. Level energies, parities, spectroscopic strengths, and possible spin values were determined up to approximately 1 MeV excitation energy. Spectra were also recorded at a few select angles for the 193Ir(3He, α)192Ir and 195Pt(p, α)192Ir reactions using beams of 25.5 MeV 3He and 18 MeV protons, respectively. In order to obtain more information regarding the spins of levels in 192Ir, multidimensional scaling programs were applied to known γ-ray intensities. The method appeared to be successful, and spins were suggested for many low-lying levels. The experimental results were compared with the IBFFM and the Nilsson model. It was found that the models can only approximately reproduce the structure of 192Ir.

The 178,180Hf(t,α)177,179Lu reactions have been studied using beams of 17 MeV tritons from the McMaster University tandem Van de Graaff accelerator. The reaction products were analyzed with a magnetic spectrograph. Measured angular distributions, and the population patterns observed for previously known rotational bands in 177Lu, permitted reliable assignments of the 7 2 + [404] , 9 2 − [514] , 1 2 + [411] , and 5 2 + [402] Nilsson orbitals in 179Lu, nuclide for which no information on excited states was available earlier. Assignments for the 7 2 − [523] and 3 2 + [411] proton hole states have been made in both isotopes. As expected from known changes in the hexadecapole deformation, the 9 2 − [514] band-head energy decreases rapidly towards the 7 2 + [404] ground state with increasing neutron number, and in 179Lu is found at only 35±5 keV. This is consistent with the suggestion that the odd proton in the 180Lu ground state is in the 9 2 − [514] orbital. The single-quasiproton energies for 179Lu from this work are useful for estimating the energies of isomeric excited states in 180Lu, that are of interest for 180mTa nucleosynthesis.

Levels in 166 Er have been studied with the 164 Er(t, p) and 168 Er(p, t) reactions using beams of 17 MeV tritons and 18 MeV protons. The reaction products were analysed with a magnetic spectrograph. I π = 0 + levels populated in these reactions could be readily identified from the characteristic L = 0 angular distributions, and new 0 + states have been discovered at 1713 and 1935 keV. The previously known 1460 keV 0 + state and the one at 1713 keV are both strongly populated in the (t, p) reaction. Contrary to the findings of a previous study, the (p, t) reaction also has a large amount of L = 0 strength to excited states in 166 Er, in particular to the 1713, 1935 and 2196 keV levels. These results agree well with the systematics of two-neutron transfer strengths to excited 0 + states in this mass region.

The 160Dy(t, α)159Tb, 162Dy(t, α)161Tb, and 164Dy(t, α)163Tb reactions have been studied using a 17 MeV triton beam from the McMaster University Tandem Accelerator. The α-spectra were analyzed with a magnetic spectrograph and the resolution obtained in the best spectra was 16–19 keV FWHM (full-width half maximum). Transferred l-values were determined by comparing the measured angular distributions with distorted-wave Born-approximation predictions. The results were interpreted in terms of the Nilsson model with pairing and Coriolis-mixing effects included. Prior to these experiments the only information available on excited states of 163Tb was from an unpublished (d, 3He) experiment. Now several rotational bands based on single-proton Nilsson states have been assigned. The 3 2 + [411] , 1 2 + [411] , 5 2 − [532] , 7 2 − [532] , 5 2 + [413], 1 2 + [420] and 3 2 − [541] bands have been observed.