D. E. Appelbe

The GREAT triggerless total data readout method

Recoil decay tagging (RDT) is a very powerful method for the spectroscopy of exotic nuclei. RDT is a delayed coincidence technique between detectors usually at the target position and at the focal plane of a spectrometer. Such measurements are often limited by dead time. This paper describes a novel triggerless data acquisition method, which is being developed for the Gamma Recoil Electron Alpha Tagging (GREAT) spectrometer, that overcomes this limitation by virtually eliminating dead time. Our solution is a total data readout (TDR) method where all channels run independently and are associated in software to reconstruct events. The TDR method allows all the data from both target position and focal plane to be collected with practically no dead-time losses. Each data word is associated with a timestamp generated from a global 100-MHz clock. Events are then reconstructed in real time in the event builder using temporal and spatial associations defined by the physics of the experiment.

K-forbidden transitions from multi-quasiparticle states

Abstract Four-quasiparticle, K π = 12 + states in 172 Hf and 178 W, with half-lives less than 2 ns, are found to decay to their respective K π = 0 + ground-state bands, in competition with transitions to intermediate- K , two-quasiparticle structures. All decay transitions are weakly hindered. When taken together with other K -isomer decay rates, an overall trend of decreasing hindrance with increasing excitation energy is evident. Estimates based on density-of-states considerations approximately reproduce the trend of the data, but also indicate the need to include other K -mixing effects.

Mirror and valence symmetries at the centre of the f7/2 shell

Abstract High-spin states have been investigated in the A=47 mirror pair 4723V24 and 4724Cr23. The Coulomb energy difference (CED) between the two nuclei has been examined up to the band-terminating state of J π = 31 2 − and compared with that of their cross-conjugate nuclei, the mirror pair 4924Cr25 and 4925Mn24. The CED results are interpreted in terms of band-crossing and band-termination phenomena. A comparison of the cross-conjugate pairs indicates for the first time that the CED can reflect the changing nuclear deformation as a function of spin. CED calculations from full pf-shell calculations are presented for the first time and are shown to be in good quantitative agreement with the data.

Neutron–proton pairing, Coulomb effects and shape coexistence in odd–odd N=Z 46V

Abstract High-spin states up to the f 7 2 -shell band termination at J π =15 + have been observed in the odd–odd N = Z =23 nucleus 46 V. A revised and significantly extended level scheme contains two distinct structures corresponding to spherical and prolate shapes. A band exhibiting rotational-like behaviour in the latter structure has excellent correspondence with the yrast sequence in 46 Ti and is therefore assumed to be a T =1 configuration. The difference between excited analogue states in the two nuclei is interpreted as a Coulomb effect and its variation with spin associated with np -pair alignment effects in 46 V. Shell-model calculations have been performed and are in good quantitative agreement with experimental level energies. The competition between T =1 and T =0 structures is also reproduced.

First identification of excited states in 169Ir

Gamma rays populating the alpha-decaying isomeric state in Ir-169 have been observed for the first time. The experiment employed the recoil-decay tagging method using the JUROGAM gamma-ray spectrom ...

High-Spin States and Lifetime Measurements in

Abstract This paper describes the results of two complementary experiments which studied the properties of the well-deformed nucleus 171 Hf. The first experiment, with a thin self-supporting target, extended the rotational bands built upon the [633]7 / 2, [512]5 / 2 and [521]1 / 2 configurations up to spins of 73 / 2–85 /2ℏ . The configurations of these bands and observed band crossings are discussed within the framework of the cranked-shell model. The second experiment employed a backed target in order to measure the lifetimes, by the Doppler Shift Attenuation method, and thereby establish deformations for some of the states in the collective rotational bands. The extracted deformations are found to be consistent with those predicted from theoretical Total Routhian Surface calculations. These deformations provide strong evidence that the high-spin states in 171 Hf, and perhaps more importantly, in the region where the high- K ( K π =19/2 + and K π =23/2 − ) isomeric states decay, retain their well-deformed axial symmetry.

^171

The quadrupole moments and deformations have been measured for six superdeformed bands in Gd-150. The results indicate evidence for deformation driving properties of both the high-hi intruder and a ...

Hf

Abstract: The ridge structure with ΔEγ=±30 keV, observed in the past in coincidence with protons emitted in the reaction 187 MeV 37Cl +120Sn and attributed to an hyperdeformed nuclear shape in 152Dy, has been studied in a new experiment performed with the EUROBALL III array. The ridge is now observed in coincidence with transitions in the yrast superdeformed band of 152Dy but no discrete rotational bands have been identified.

LIFETIMES OF YRAST AND EXCITED SUPERDEFORMED STATES IN 150GD : EFFECT OF PARTICLE-HOLE EXCITATIONS ON THE DEFORMATION

A K{sup {pi}}=8{sup {minus}} strongly coupled rotational band, which is built upon a 23 ns isomeric state, has been established in {sup 170}Hf. The single-particle configuration of the band has been determined from the in-band to out-of-band branching ratios and associated {vert_bar}(g{sub K}{minus}g{sub R}){vert_bar}/Q{sub 0} values. The {gamma}-ray decay of the K{sup {pi}}=8{sup {minus}} isomeric state proceeds through a K{sup {pi}}=6{sup +} intrinsic state, in accordance with the {ital K}-selection rule. A complex array of delayed {gamma}-ray transitions have been observed to link this K{sup {pi}}=6{sup +}, intrinsic bandhead state into the yrast states. In particular, a new {Delta}K=8, 1141 keV, E1 transition links the K{sup {pi}}=8{sup {minus}} isomeric state directly to the ground-state band. The {gamma}-ray reduced hindrance factor for this E1 decay in {sup 170}Hf is the smallest {Delta}K=8 transition observed in the Hf nuclei. However, its value is consistent with that expected on the basis of the increased Coriolis mixing which occurs in the lighter Hf isotopes. {copyright} {ital 1999} {ital The American Physical Society}

Search for hyperdeformed structures populated in the 37Cl+120Sn reaction by using EUROBALL III

Excited states in the neutron-deficient odd-Z nuclide Ta-161 were identified for the first time using the Cd-106(Ni-58,3p gamma) reaction at a beam energy of 270 MeV. The pi h(11/2) band, yrast at ...