Superdeformation and High Spin Spectroscopy Studies on \u3csup\u3e174\u3c/sup\u3eHf

High-spin states of the nucleus 174Hf were populated using the heavy-ion reactions at the Atlas accelerator facility at the Argonne National Laboratory and the 88 cyclotron facility at the Lawrence Berkeley National Laboratory. The de-exciting [gamma] rays are detected with the GAMMASPHERE spectrometer. In this nucleus, eight superdeformed bands are observed for the first time. Studies on these bands as well as eight bands with normal deformation are performed. The hypothesis for presence of a triaxial shape at high deformation in 174Hf is tested via lifetime measurements of the states of the superdeformed structures. The deduced quadrupole moments of four of these bands are compared with the Ultimate Cranker calculations and an additional search for transitions that depopulate these structures is carried out. Discussion on the possibility that these bands manifest triaxiality in 174Hf is presented. The study of the bands with normal deformation employed an extensive systematics of crossing frequencies, alignments, and Routhians. CSM and TRS calculations are performed and compared with these observables. Quasiparticle configurations for all of the bands with normal deformation are proposed, and B (M1) / B (E2) and B (E1) / B (E2) transition strength ratios are analyzed

Towards \u3csup\u3e26\u3c/sup\u3eNa via (d,p) with SHARC and TIGRESS and a novel zero-degree detector

Nucleon transfer experiments have in recent years begun to be exploited in the study of nuclei far from stability, using radioactive beams in inverse kinematics. New techniques are still being developed in order to perform these experiments. The present experiment is designed to study the odd-odd nucleus 26Na which has a high density of states and therefore requires gamma-ray detection to distinguish between them. The experiment employed an intense beam of up to 3×107 pps of 25Na at 5.0 MeV/nucleon from the ISAC-II facility at triumf. The new silicon array SHARC was used for the first time and was coupled to the segmented clover gamma-ray array TIGRESS. A novel thin plastic scintillator detector was employed at zero degrees to identify and reject reactions occurring on the carbon component of the (CD)2 target. The efficiency of the background rejection using this detector is described with respect to the proton and gamma-ray spectra from the (d,p) reaction. © Published under licence by IOP Publishing Ltd

A study on the transition between seniority-type and collective excitations in 204Po and 206Po

Low-lying yrast states in 204Po and 206Po have been investigated by the γ-γ fast timing technique with LaBr3(Ce) detectors. Excited states of these nuclei were populated in the 197Au(11B,4n) and the 198Pt(12C,4n) fusion-evaporation reactions, respectively, at the FN-Tandem Facility at the University of Cologne. The lifetimes of the 4+1 states in both nuclei were measured, along with an upper limit for the 2+1 state in 204Po. The preliminary results are discussed in the scope of the systematic behavior of the transition strengths between yrast states in polonium isotopes

Coulomb Excitation of Proton-rich N = 80 Isotones at HIE-ISOLDE

A projectile Coulomb-excitation experiment was performed at the radioactive ion beam facility HIE-ISOLDE at CERN. The radioactive ¹⁴⁰Nd and ¹⁴²Sm ions were post accelerated to the energy of 4.62 MeV/A and impinged on a 1.45 mg/cm²-thin ²⁰⁸Pb target. The γ rays depopulating the Coulomb-excited states were recorded by the HPGe-array MINIBALL. The scattered charged particles were detected by a double-sided silicon strip detector in forward direction. Experimental γ-ray intensities were used for the determination of electromagnetic transition matrix elements. Preliminary results for the reduced transition strength of the B(M1;23+→21+)=0.35(19)μN2 of ¹⁴⁰Nd and a first estimation for ¹⁴²Sm have been deduced using the Coulomb-excitation calculation software GOSIA. The 2³₊ states of ¹⁴⁰Nd and ¹⁴²Sm show indications of being the main fragment of the proton-neutron mixed-symmetry 2⁺₁,ms state

Search for Isovector Valence-Shell Excitations in 140Nd and 142Sm via Coulomb excitation reactions of radioactive ion beams

Projectile Coulomb excitation experiments were performed at HIE-ISOLDE at CERN with the radioactive ion beams of 140Nd and 142Sm. Ions with an energy of 4:62 MeV/A were impinging on a 1.45 mg/cm2 thick 208Pb target. The γ-rays depopulating the Coulomb-excited states were recorded by the HPGe-array MINIBALL and scattered particles were detected by a double-sided silicon strip detector. Experimental intensities were used for the determination of electromagnetic transition matrix elements. A preliminary result of the B(M1; 2+3 → 2+1) of 140Nd and an upper limit for the case of 142Sm are revealing the main fragments of the proton-neutron mixed-symmetry 2+1;ms states

Search for Isovector Valence-Shell Excitations in Nd-140 and Sm-142 via Coulomb excitation reactions of radioactive ion beams

Projectile Coulomb excitation experiments were performed at HIE-ISOLDE at CERN with the radioactive ion beams of 140Nd and 142Sm. Ions with an energy of 4.62 MeV/A were impinging on a 1.45 mg/cm2 thick 208Pb target. The γ-rays depopulating the Coulomb-excited states were recorded by the HPGe-array MINIBALL and scattered particles were detected by a double-sided silicon strip detector. Experimental intensities were used for the determination of electromagnetic transition matrix elements. A preliminary result of the B(M1; 2+ 3→2+ 1 ) of 140Nd and an upper limit for the case of 142Sm are revealing the main fragments of the proton-neutron mixed-symmetry 2+ 1,ms states.peerReviewe

SHARC: Silicon Highly-segmented Array for Reactions and Coulex used in conjunction with the TIGRESS gamma-ray spectrometer

The combination of gamma-ray spectroscopy and charged-particle spectroscopy is a powerful tool for the study of nuclear reactions with beams of nuclei far from stability. This paper presents a new silicon detector array, SHARC, the Silicon Highly-segmented Array for Reactions and Coulex. The array is used at the radioactive-ion-beam facility at TRIUMF (Canada), in conjunction with the TIGRESS gamma-ray spectrometer, and is built from custom Si-strip detectors utilising a fully digital readout. SHARC has more than 50% efficiency, approximately 1000-strip segmentation, angular resolutions of Delta theta approximate to 1 : 3 deg and Delta phi approximate to 3.5 deg, 25-30 keV energy resolution, and thresholds of 200 keV for up to 25 MeV particles. SHARC is now complete, and the experimental program in nuclear astrophysics and nuclear structure has commenced