Herbert R. Faust

The level structure of 114Cd from (n, γ) and (d, p) studies☆

Abstract Gamma rays and conversion electrons have been measured following thermal neutron capture in 113 Cd using the crystal spectrometers GAMS and the β-spectrometer BILL at the High Flux Reactor of the ILL at Grenoble. Primary γ-rays following thermal and average resonance neutron capture at E n = 2 keV and 24 keV were recorded at the High Flux Beam Reactor at the Brookhaven National Laboratory. The 113 Cd(d, p) 114 Cd reaction was studied with the Q3D spectrograph at the Munich tandem accelerator. Combining all these experimental results an almost complete level scheme of 114 Cd was constructed up to 3.3 MeV including 48 excited levels with spin and parity information. The level scheme is discussed in terms of particle-hole excitations across the Z = 50 closed shell coupled to collective states, as well as in an interacting boson configuration mixing scheme.

The importance of intruder states in 114Cd

Abstract The origin and decay properties of levels in 114Cd, with special emphasis on the quintuplet of states around 1.2 MeV excitation energy, are invesigated both theoretically and experimentally. An almost complete set of reduced transition probabilities B(E0) and B(E2) is established by means of (n, γ) and (n, e−) spectroscopy. Cofiguration mixing between vibrational-like and rotational-like states, extracted from proton two-particle-two-hole (2p-2h) core coupling calculations, is found to be crucial for explaining the peculiar level properties.

Ternary fission yields of 241Pu(nth,f)

Abstract Ternary events in the thermal neutron induced fission of 241Pu(n,f) were studied with the recoil separator LOHENGRIN at the high-flux reactor of the Institut Laue Langevin in Grenoble. Yields and energy distributions could be determined for most isotopes of the elements hydrogen to oxygen. Also several heavier nuclei up to 30Mg could be observed. Yields were measured for 42 isotopes, for further 17 isotopes upper limits could be deduced. For the first time the halo nuclei 11Li, 14Be and 19C were found in neutron induced fission with yields of some 10−10 per fission.

Level structure of 191Os: Coexisting oblate and prolate configurations

Abstract An extensive level scheme for the transitional nucleus 191 Os has been constructed on the basis of (n, γ), (n, e − ) and (d, t) reaction data. γ-rays following thermal capture and average resonance capture (ARC) were detected with pair spectrometers. Secondary γ-ray spectra were obtained with the GAMS bent crystal spectrometers. The high precision of the resultant energies was the critical factor in developing a level scheme on the basis of Ritz combinations. γγ coincidences were obtained from both primary and secondary transitions. Conversion electrons, detected with the BILL spectrometer, gave multipolarity information. The (d, t) reaction measured with a Q3D magnetic spectrometer gave additional information on the hole states in 191 Os. A discussion of the resulting level scheme briefly reviews the fragmentation of negative-parity strength but focuses mostly on a rare example of an anti-aligned decoupled set of coexisting positive-parity states. For these, triaxial particle-plus-rotor calculations are carried out. Reasonable agreement is obtained and the calculations also explain the unusually strong population in (n, γ) of this set of mostly medium spin states.

The Munich Fission Fragment Accelerator

For the new Munich high-flux reactor FRM-II a fission fragment accelerator is under design. The accelerator will deliver intense mass-separated beams of very neutron-rich fission fragments with energies at and beyond the Coulomb barrier. One main physics goal will be the investigation of very heavy neutron-rich nuclei produced in fusion reactions.

In-pile arrangements of reactor-based RIB facilites

Abstract Two Radioactive Ion Beam facilities are projected at high-flux reactors: PIAFE at the Institut Laue Langevin in Grenoble and the Munich Fission Fragment Accelerator at the FRM-II in Garching. Both will operate with a “nuclear heated” target-ion-source assembly (fission rate ≈ 1014 S−1) in an in-pile position in a neutron flux of the order 1014 cm−2 s−1. The expected beam intensities are several orders of magnitude higher than those of existing ISOL facilities which use thermal neutron-induced fission. The major difference between the in-pile parts of the projects is the type of beam tube: PIAFE will use a single-ended tube where target change and ion extraction are done to the same side — at the FRM-II a tube with access from both sides will be used, allowing a spatial decoupling of target handling and ion extraction. Different methods to master the new technical challenges arising from the high neutron flux are discussed.

Near-yrast structure of N = 93 neutron-rich lanthanide nuclei

Two neutron-rich N=93 isotones, {sup 155}Sm and {sup 153}Nd, have been studied by delayed gamma-ray and conversion-electron spectroscopy at the Lohengrin mass spectrometer. A half-life of 2.9(5) mus has been measured for the nu5/2{sup +}[642] state at 16.5 keV in {sup 155}Sm. The decay of a 1.17(7)-mus isomer in {sup 153}Nd, at 191.7 keV, has been remeasured and its spin has been reassigned as (5/2){sup +}. This state contains a strong component of the nu5/2{sup +}[642] Nilsson orbital. In addition, a new 1.00(8)-mus isomeric state at 538.6 keV, with a probable nu11/2{sup -}[505] Nilsson configuration, has been observed in {sup 155}Sm. Triple gamma-ray coincidence data from the spontaneous fission of a {sup 252}Cf source placed inside the Gammasphere array were used to extend the collective band on top of the (5/2{sup +}) isomeric state of {sup 153}Nd, and a new band with the same bandhead spin has been observed in {sup 151}Ce. The observation of this new band and an additional new transition in the ground-state band has led us to change the ground-state spin of {sup 151}Ce to (3/2{sup -}). Calculations using the quasiparticle-rotor model successfully reproduce the majority of the features of the gamma decays of these nuclei,morexa0» including branching ratios and isomeric half-lives. Because this model uses a reflection-symmetric core, we conclude that the polarizing effect of the odd particle is responsible for the dipole moment present in the nu5/2{sup +}[642] states of the three nuclei studied and the nu11/2{sup -}[505] level of {sup 155}Sm.«xa0less