H. Mach

Single-neutron states in Sn-133

The location of several single-neutron states in Sn-133 has been identified. The P-3/2, h(9/2), and f(5/2) states were found at 853.7, 1560.9, and 2004.6 keV, respectively, by measuring gamma rays in coincidence with delayed neutrons following the decay o

g-factor measurements of μs isomeric states in neutron-rich nuclei around 68Ni produced in projectile-fragmentation reactions

We report the first g factor measurement on microsecond isomers of neutronrich nuclei produced in projectile-fragmentation reactions at intermediate energies. The nuclides in the vicinity of 68 Ni were produced and spin oriented following the fragmentation of a 76 Ge, 61.4 MeV u −1 beam at GANIL. The LISE spectrometer was used to select the nuclei of interest. The time-dependent perturbed angular distribution (TDPAD) method was applied in combination with th eh eavy-ion–gamma correlation technique to measure the g factors of 69m Cu (J π = 13/2 + , T1/2 = 350 ns) and 67m Ni (J π = 9/2 + , T1/2 = 13.3 µs). Specific details of the experimental technique and the comparison of the results (|g( 69m Cu) |= 0.225(25) and |g( 67m Ni) |= 0.125(6)) with theoretical calculations are discussed. These results provide another indication of the importance of proton excitations across the Z = 28 shell gap.

Enhanced and quenched B(E1) transition rates between parity doublet bands in 227Ra

Abstract The fast timing βγγ ( t ) method has been used to measure level lifetimes in the parity doublet bands in 227 Ra populated in the β − decay of 227 Fr. In particular T 1 2 = 254(9) ps , 236(30) ps , ⩽41 ps and 16(13) ps have been measured for the 3 2 − and 5 2 − members of the K π = 3 2 − band and for the 1 2 − and 3 2 − members of the K π = 1 2 − band, respectively. These results indicate surprisingly fast B (E1) rates in this octupole transitional nucleus with the average | D 0 | value of ⩾ 0.11 e ·fm for the K π = 1 2 − band and | D 0 |= 0.10 e ·fm for K π = 3 2 − band. The general enhancement (and occasional quenching) of E1 intra-doublet and some enhanced extra-doublet transitions in 227 Ra are interpreted within the quasiparticle-plus-phonon model with the inclusion of Coriolis coupling. Similar calculations, performed for 223 Ra, are found to be in good agreement with the experimental data.

Application of Ultra-fast Timing Techniques to the Study of Exotic and Weakly Produced Nuclei

Ultra-fast time-delayed techniques have been recently applied in a number of studies where exotic nuclei were identified using advanced selection techniques. These include large Compton-suppressed ...

Coupling of valence particles/holes to 68,70Ni studied via measurements of the B(E2) strength in 67,69,70Ni and 71Cu

Coupling of valence particles/holes to 68,70Ni studied via measurements of the B(E2) strength in 67,69,70Ni and 71Cu.

The Nuclear Structure of 229Th

E. Ruchowska,1,∗ W. A. Plociennik,1,† J. Żylicz,2 H. Mach,3 J. Kvasil,4 A. Algora,5 N. Amzal,6 T. Back,7 M. G. Borge,8 R. Boutami,8 P. A. Butler,6 J. Cederkall,9 B. Cederwall,7 B. Fogelberg,3 L. M. Fraile,9,‡ H. O. U. Fynbo,9 E. Hagebo,10 P. Hoff,10 H. Gausemel,10 A. Jungclaus,8 R. Kaczarowski,1 A. Kerek,7 W. Kurcewicz,2 K. Lagergren,7 E. Nacher,5 B. Rubio,5 A. Syntfeld,1 O. Tengblad,8 A. A. Wasilewski,1 and L. Weissman9 1The Andrzej Soltan Institute for Nuclear Studies, PL 05-400 Świerk, Poland 2Institute of Experimental Physics, University of Warsaw, PL 00-681 Warsaw, Poland 3Department of Radiation Sciences, University of Uppsala, SE-751 21 Uppsala, Sweden 4Department of Nuclear Physics, Charles University, CZ-18000 Prague 8, Czech Republic 5Instituto de Fizica Corpuscular, CSIC-University Valencia, E-46100 Burjassot, Spain 6Oliver Lodge Laboratory, University of Liverpool, Liverpool L69 3BX, United Kingdom 7Physics Department, Royal Institute of Technology, SE-106 91 Stockholm, Sweden 8Instituto de Estructura de la Materia, CSIC, E-28006 Madrid, Spain 9ISOLDE, CERN, CH-1211 Geneva 23, Switzerland 10Department of Chemistry, University of Oslo, Post Office Box 1033 Blindern, N-0315 Oslo, Norway (Received 28 December 2005; published 26 April 2006)

Octupole correlations in 229Ra

Abstract The structure of 229 Ra has been studied in the β − decay of 229 Fr. Spins and parities have been determined from the conversion electron measurements, while half-lives for the 137.5, 142.7, 168.8, 213.0 and 479.0 keV levels have been measured in the ps and ns ranges via the fast timing βγγ ( t ) method. Our data confirm the previous results and enrich the knowledge of the structure of this nucleus by 25 new states and several strong transitions. Structural similarities are established between 229 Ra and its N = 141 isotone 231 Th. The experimental results are compared with the theoretical predictions of the quasiparticle-phonon model with inclusion of Coriolis coupling. The reduced transition probabilities, and especially the moderately fast B (E1) rate for the 137.5 keV transition connecting the band-heads of the K π = 5 2 ± parity doublet bands, reveal the presence of significant octupole correlations in 229 Ra.

The nuclear structure of 227Fr

The γ-rays following the β− decay of 227Rn have been investigated by means of γ-ray singles and γγ-coincidence measurements using an array of 12 Compton-suppressed Ge detectors. The fast-timing βγγ(t) method has been used to measure six level lifetimes. Multipolarities of 32 transitions in 227Fr have been established by measuring conversion electrons with a mini-orange electron spectrometer. Most of the observed transitions have been placed in a level scheme comprising 38 excited states of 227Fr. The low-lying levels are interpreted in terms of seven rotational bands. The observed E1 strengths for two transitions connecting the Kπ = 32± bands are consistent with the transitional character of 227Fr, and confirm the presence of octupole correlations in this nucleus.

Isomeric and two-quasiparticle states in the neutron-excess odd-odd nucleus 134Sb

Detailed theoretical calculations of the properties of the neutron-excess odd-odd nucleus 134Sb are performed by using different theoretical approaches. A comprehensive comparison with the recent experimental data is performed; this comparison suggests the presence of isomeric states among the low-lying levels of this nucleus. These states are the twins of the corresponding levels of the odd-odd nucleus 210Bi that is situated near the stability line. The obtained results manifest the similarity of nuclear structure in the region of the “remote” doubly magic nucleus 132Sn and in the region of the classical stable doubly magic nucleus 208Pb.

Quenched E1 transition rates in 231Th

Abstract The fast timing βγγ(t) method has been used to measure lifetimes of the low-lying levels in 231Th populated in the β− decay of 231Ac. The half-life of the K π = 5 2 − band-head at 185.7-keV was measured as T 1 2 = 1073(79) ps , yielding D0 = 1,76(8) × 10−2 e·fm and 1.65(6) × 10−2 e·fm for the E1 transitions to the 7 2 + and 5 2 + members respectively of the K π = 5 2 + ground state band. Furthermore, T 1 2 ⩽ 74 ps and ⩽ 74 ps were measured for the K π = 3 2 + and 1 2 + band-heads at 221.4- and 247.6-keV, and T 1 2 = 503(12) ps and 98(36) ps for the 1 2 − and 3 2 − states at 554.7- and 593.6-keV, members of the K π = 1 2 − band. The latter results consistently yield D0 values of the order of 1.1 × 10−2 e·fm for three transitions connecting the K π = 1 2 ± bands. The observed transition rates have been interpreted within the quasiparticle-phonon model with the inclusion of Coriolis coupling.