D. Alber

A 2π neutron multiplicity filter for in-beam γ-ray spectroscopy of neutron deficient nuclei

Abstract A 2π neutron multiplicity filter consisting of 16 detectors filled with NE213 liquid scintillator has been designed and assembled for in-beam γ-ray spectroscopy of neutron deficient nuclei. Results are presented for the efficiency for single and multiple events, detector cross talk by scattering and n-γ discrimination, both, for a 252Cf source and a typical (hi, xn yp zα) reaction.

In-beam spectroscopy of exotic nuclei with OSIRIS and beyond

Abstract The experimental techniques and recent results of nuclear structure studies in-beam close to 100Sn are reviewed. The structure of the nuclides 97Ag, 100Cd and 104Sn, so far the nuclei of closest approach to 100Sn with known excited states, is discussed within the spherical shell model. The basic shell model parameters of 100Sn, single particle binding energies and two-body matrix elements, as deduced from the shell model analysis, are summarized. From the available structure information conclusions are drawn for the design and expected phenomena of future experiments towards the far-from-stability doubly magic 100Sn.

In-beam spectroscopy of104Sn

The very neutron deficient nucleus 104Sn has been identified in in-beam spectroscopy using the reaction50Cr(58Ni, 2p2n) and neutron and charged particle multiplicity filter detectors. Excited states up to I ≈ 10 and Ex=4 MeV were observed and the level scheme is discussed in the frame work of the spherical shell model.

Nuclear structure study of the neutron deficient cadmium isotopes100, 101, 102Cd

The neutron-deficient nuclei100,101Cd were identified for the first time in — beam following the reactions58Ni +46,48Ti and58Ni +50Cr at 230 MeV and 245 MeV bombarding energy of the58Ni beams. Theγ-decay of the isotopes100,101,102Cd was studied inpγ, ppγ,nγ, nnγ, andnγγ prompt and delayed coincidence spectra. Isomers were found with spin and half life {ie1-01}=8+, T1/2=52(5) ns in100Cd, {ie1-02}=(19/2+), T1/2=4.6(4) ns in101Cd and {ie1-03}=8+, T1/2=56(4) ns in102Cd. In a PAD experiment theg-factor of the {ie1-04}=8+ isomer in100Cd was measured to be g=1.24(6). Using the reaction36Ar +70Ge at 135 MeV energy of the36Ar beam, theg-factor and the quadrupole moment of the {ie1-05}=8+ isomer in102Cd were measured to be g=1.29(3) and Q=87(10) fm2, respectively. The spectroscopic results are discussed within a shell model approach using a100Sn core, which accounts well for the electromagnetic properties of the proton aligned isomers. The structure of the spherical neutron states, dominated by the close lying vd5/2, g7/2 orbitals, and the gradually developing quadrupole collectivity are reproduced by the shell model calculations.

Recoil distance lifetime measurements in 125Xe

Lifetimes of excited states in 125Xe populated in the (12C, 3n) reaction on 116Cd were measured by the recoil distance method. A delayed tagging technique was employed to preferentially detect the non-yrast transitions in the νg72 band system built on the Iπ = 72+, T12 = 140 ns isomer in 125Xe. The following mean lifetimes τ(I)π, Ex) were obtained: 115 ± 25ps (92+, 597 keV), 11.3 ± 1.1 ps (112+, 871 keV), 4.2 ± 1.5ps (132+, 1210 keV), 3.8 ± 1.3ps (152+, 15360 keV); 12.5 ± 1.3 ps (152−, 797 keV). The results are well described within the triaxial-rotor-plus-particle model.

Nuclear structure studies of the neutron deficientN=50 nucleus96Pd

The neutron deficient nucleus96Pd, four proton holes below the doubly magic100Sn, has been studied in the reaction64Zn (36Ar, 2p 2n). Innγ andγγ coincidences levels up to 7 MeV excitation energy were established, and a new neutron core-excited isomer with T1/2=35(4)ns and g=0.83 (5) was identified. A detailed shell model study yields excellent agreement for states within the π(p1/2,g9/2) configuration space but fails to reproduce the isomerism andg-factor for the core-excited state.

Spectroscopy of198,199Po

Excited states in198,199Po have been studied by in-beamγ-ray spectroscopy. These nuclei were produced in the 4n and 5n reaction channels for 115 MeV20Ne on183W-targets. Multipolarities and mixing ratios ofγ-transitions were determined from DCO-ratios, leading to spin/parity assignments. In198Po,γ-cascades have been observed above several excited levels that are similar to the vibration-like structure built on the ground state. In199Po, the coupling of the oddi13/2 neutron seems to favor the spherical shape of the even core; no levels resembling the intruder states of the even nuclei are found. A semi-quantitative evaluation of the cross-sections for nuclei produced in fission and multi-particle transfer is presented.

First in-beam observation of97Ag — The three-proton-hole spectrum in100Sn

Excited states in97Ag have been identified for the first time following the reactions46Ti(58Ni,α p 2n and64Zn(36Ar,p 2n. The population cross sections were 1.0(5) mb and 0.7(3) mb, respectively. Theγ-decay of the seniorityΝ=3 states below theIπ=(17/2−) and (21/2+) isomers was investigated. In a search for short lived isomers half lives oft1/2=5(2) ns and 2.5(5) ns were found in theN=50 isotones97Ag,Iπ=(17/2−) and/or (21/2+) and95Rh,Iπ=(21/2+). A new isomer was identified in97Pd,Iπ=17/2+ witht1/2=2.3(5) ns. The implication of the three-proton hole spectrum in100Sn for the empirical residual interaction and shell model predictions is discussed.

In-Beam study of neutron deficient100Cd

The very neutron deficient nucleus100Cd52 has been identified in the reaction46Ti (58Ni, 2p2n) and its level scheme was studied up to Ex=4.3 MeV and I ≈12. A T1/2=40−10+20ns isomer was found at Ex=2.548 MeV with Iπ=(8+).

The g-factor and the electric quadrupole moment of the 7/2+ isomer in125Xe

The time differential perturbed angular distribution method (PAD) was used to measure theg-factor and the electric quadrupole interaction in a Cd single crystal for thet1/2=140 ns,Iπ=7/2+ isomer in125Xe. Theg-factor isg=+0.264(10) and the quadrupole coupling constante2Qq/h=122.1 (6) MHz at 552 K. The lifetime of theIπ=11/2+ state was measured to beτ=11.3 (1.1) ps by the recoil distance method (RDM). From an analysis of the spectroscopic data using the triaxial-rotor-plus-particle (TRPP) model the quadrupole moment of the 7/2+ isomer is deduced to beQ=1.40 (15) b yielding an electric field gradient (efg)eq=3.6(4)·1017 V/cm2 for XeCd.