Lifetime measurement of neutron-rich even-even molybdenum isotopes

Background: In the neutron-rich A approximate to 100 mass region, rapid shape changes as a function of nucleon number as well as coexistence of prolate, oblate, and triaxial shapes are predicted by various theoretical models. Lifetime measurements of excited levels in the molybdenum isotopes allow the determination of transitional quadrupole moments, which in turn provides structural information regarding the predicted shape change. Purpose: The present paper reports on the experimental setup, the method that allowed one to measure the lifetimes of excited states in even-even molybdenum isotopes from mass A = 100 up to mass A = 108, and the results that were obtained. Method: The isotopes of interest were populated by secondary knock-out reaction of neutron-rich nuclei separated and identified by the GSI fragment separator at relativistic beam energies and detected by the sensitive PreSPEC-AGATA experimental setup. The latter included the Lund-York-Cologne calorimeter for identification, tracking, and velocity measurement of ejectiles, and AGATA, an array of position sensitive segmented HPGe detectors, used to determine the interaction positions of the gamma ray enabling a precise Doppler correction. The lifetimes were determined with a relativistic version of the Doppler-shift-attenuation method using the systematic shift of the energy after Doppler correction of a gamma-ray transition with a known energy. This relativistic Doppler-shift-attenuation method allowed the determination of mean lifetimes from 2 to 250 ps. Results: Even-even molybdenum isotopes from mass A = 100 to A = 108 were studied. The decays of the low-lying states in the ground-state band were observed. In particular, two mean lifetimes were measured for the first time: tau = 29.7(-9.1)(+11.3) ps for the 4(+) state of Mo-108 and tau = 3.2(-0.7)(+ 0.7) ps for the 6(+) state of Mo-102. Conclusions: The reduced transition strengths B(E2), calculated from lifetimes measured in this experiment, compared to beyond-mean-field calculations, indicate a gradual shape transition in the chain of molybdenum isotopes when going from A = 100 to A = 108 with a maximum reached at N = 64. The transition probabilities decrease for Mo-108 which may be related to its well-pronounced triaxial shape indicated by the calculations

Determination of the B(E3, 0(+) -> 3(-))-excitation strength in octupole-correlated nuclei near A approximate to 224 by the means of Coulomb excitation at REX-ISOLDE

Volume: 533Peer reviewe

Do nuclei go pear-shaped? Coulomb excitation of Rn-220 and Ra-224 at REX-ISOLDE (CERN)

Volume: 93The IS475 collaboration conducted Coulomb-excitation experiments with post-accelerated radioactive Rn-220 and Ra-224 beams at the REX-ISOLDE facility. The beam particles (E-beam: 2.83 MeV/u) were Coulomb excited using Ni-60, Cd-14, and Sn-120 scattering targets. De-excitation gamma-rays were detected employing the Miniball array and scattered particles were detected in a silicon detector. Exploiting the Coulomb-excitation code GOSIA for each nucleus several matrix elements could be obtained from the measured gamma-ray yields. The extracted matrix element allows for the conclusion that, while Rn-220 represents an octupole vibrational system, Ra-224 has already substantial octupole correlations in its ground state. This finding has i(m)plications for the search of CP-violating Schiff moments in the atomic systems of the adjacent odd-mass nuclei.Peer reviewe

Coulomb excitation of re-accelerated 208Rn and 206Po beams

Volume: 63Peer reviewe

Letter dated 11 December 1967 from William F. Thoele to Lorenzo A. Richards

Letter dated 11 December 1967 from William F. Thoele to Lorenzo A. Richards, inviting him and his wife Zilla to a Christmas dinner-dance on 23 DecemberDECEMBER I I, 1967 DR. L. A. RICHARDS ^55 FIFTH STREET RIVERSIDE, CALIFORNIA DEAR DR. RICHARDS: ON SATURDAY NIGHT, DECEMBER 23, MOIST O'MATIC WILL HAVE A CHRISTMAS DINNER-DANCE TO V/HICH YOU AND YOUR WIFE ARE CORDIALLY INVITED. THE LOCATION IS THE NAVAL ORDINANCE CLUB - IF YOU DESIRE INSTRUCTIONS ON HOW TO GET THERE, PLEASE CALL AND LET US KNOW. FESTIVITIES WILL BEGIN WITH A COCKTAIL HOUR AT 6:30, FOLLOWED BY A BUFFET DINNER AT 8:00, AND DANCING WILL BE FROM 9 - 1:00 AM. IF YOU CAN MAKE IT TO THE PARTY, WILL YOU PLEASE LET US KNOW SO THAT A RESERVATION CAN BE MADE FOR YOU AND YOUR WIFE. VERY TRULY YOURS, WILLIAM F. THOELE CONTROLLER WFT:GB \J TORO MANUFACTURING CORPORATION • 5825 JASMINE STREET, RIVERSIDE, CALIFORNIA • 92504 • P. O. BOX 489 • 688-9221 MOIST O'MATIC DIVISIO

The valence band electronic structure of rhombohedral like and tetragonal like BiFeO3 thin films from hard X ray photoelectron spectroscopy and first principles theory

We investigate the electronic structure of rhombohedral like R and tetragonal like T BiFeO3 thin films using high energy X ray photoelectron spectroscopy and first principles electronic structure calculations. By exploiting the relative elemental cross sections to selectively probe the elemental composition of the valence band, we identify a strong Bi 6p contribution at the top of the valence band in both phases, overlapping in energy range with the O 2p states; this assignment is confirmed by our electronic structure calculations. We find that the measured occupied Bi 6p signal lies closer to the top of the valence band in the T phase than in the R phase, which we attribute, using our electronic structure calculations, to lower Bi O hybridization in the T phase. We note, however, that our calculations of the corresponding densities of states underestimate the difference between the phases, suggesting that matrix element effects resulting from the different effective symmetries also contribute. Our results shed light on the chemical nature of the stereochemically active Bi lone pairs, which are responsible for the large ferroelectric polarization of BiFeO

Evolution of quadrupole collectivity in N=80 isotones toward the Z=64 subshell gap: The B(E2; 2(1)(+) -> 0(1)(+)) value of Sm-142

It was shown that the evolution of the B(E2; 2+1 → 0+1 ) values in N = 80 isotones from Te to Nd is affected by the underlying subshell structure. This manifests itself in the observation of the local suppression of the B(E2) value at Z = 58 with respect to the neighboring nuclei 136Ba and 140Nd. To investigate this shell sensitivity toward the Z = 64 subshell gap, the B(E2; 2+1 → 0+1 ) value of the unstable nucleus 142Sm was measured utilizing the projectile Coulomb excitation technique. The radioactive ion beam (RIB) experiment was performed at the REX-ISOLDE facility at CERN. The B(E2) value of 32 (4) W.u. reflects the impact of the π(1g7/2 2d5/2) subshell closure at Z = 64 with respect to a linear scaling of collectivity with valence proton number.status: publishe