Search

Abstract:: In an experiment performed at the GANIL LISE3 facility, radioactive 27S isotopes have been produced by projectile fragmentation of a 95 AMeV 36Ar primary beam. After selection by means of the LISE3 separator, the isotope of interest was implanted in a silicon-detector telescope where its half-life ( T 1/2 = 15.5(15) ms) and its main decay branches were measured.

Abstract.: A careful investigation of the isomeric transition of the long-lived state at 228.5 keV excitation energy in 80Y has been done. The HIGISOL facility at the Jyväskylä isochronous cyclotron has been used. We used the electron magnetic transporter to prepare an appropriate source and to measure the electron spectra in clean background conditions. The measured internal conversion coefficient αK = 0.50±0.07 allows unambiguous 1- identification for the 228.5 keV first excited isomeric state in 80Y. With a “bare" half-life of 6.8±0.5 s found in this work, this state is strongly populated in the rp-process during X-ray bursts and has therefore to be taken into account in X-ray burst model calculations. However, because of the similarity of the β-decay half-lives of isomeric and ground states, we find a maximum reduction in the effective β-decay lifetime of 80Y of only 17±2%. Our results pave the way for a future investigation of the impact of the isomeric state on the “effective" 80Y proton capture rate.

A new HIGISOL chamber devoted to the study of short-lived products from heavy-ion-induced fusion-evaporation reactions is proposed. It enables, via the extraction of ions by means of a SPIG (SextuPole rf Ion Guide), to improve the mass resolving power by a factor 2.5 compared to the previous system using a skimmer-ring assembly. The gas cell was also equiped with an electric field for faster transportation of recoiling ions to the nozzle where they are ejected with the gas jet. The first results obtained both with a radioactive α-source and cyclotron beam will be reported.

The192Hg nucleus was populated in the160Gd(36S, 4n) reaction at a beam energy of E=159 MeV. Emitted?-rays were detected with the EUROGAM array comprising 43 Compton-suppressed large volume Ge detectors. The level scheme of192Hg has been extended up to an excitation energy of E=10.4 MeV and spin I=34 h. Two new structures, made of competing ?I=1 and ?I=2 transitions have been observed and their connexions with the low-lying levels established. Their lowest levels are located at 6.304 MeV and 6.879 MeV excitation energy. The experimental results are compared with mean-field HF+BCS calculations. It is proposed that the new structures originate from deformation-aligned quasi-proton excitations p(i13/2 * h9/2)K=11 andp (h9/2)K=82, coupled to rotation-aligned quasi-neutron ?(i13/2)n and quasi-proton p(h11/2)2 excitations.

Levels of106Cd, populated by104Pd(a, 2n?)106Cd have been studied measuring direct and delayed?-ray spectra,?-? coincidences and?-ray angular distributions. A decay level scheme is proposed including states up to 4659.8 keV. IntenseE2 transition cascades have been observed. The half-life of an isomeric level located at 4659.8 keV has been measured:T1/2= 62±6ns.

Level structure of102Cd has been studied via both102In decay and nuclear reactions. Using92Mo+14N at 86 MeV, the nucleus102In was identified and its decay (T1/2=24 ±4s) studied with the aid of on-line mass separation techniques. Levels of102Cd were also populated with92Mo+12C at 50 MeV and102Pd+3He at 35 MeV reactions and investigated by means of standard in-beam techniques. A level scheme including states up to 4.5 MeV excitation energy is proposed and then discussed in the frame of available calculations.

Excited states of114, 116Sb have been investigated in the111, 113Cd (7Li, 4n?) reactions. In both level schemes, two independant parts have been exhibited with, mainly, a negative parity band based on 8- or 7- states and a positive parity sequence based on a 11+ state. The interpretation of the significant levels has been performed in the core-particle model and in term of quasiparticle configurations mixing, this last approach being able to give a kind of unified description of the whole spectrum.

Low-lying levels of the 129La isotope have been investigated through the β+/EC decay of 129Ce. The radioactive nuclei were produced in the 94Mo+40Ca reaction at a bombarding energy of 255 MeV and transported with a He-jet system. On-line mass separation was used to select the 129Ce beta-decay γ-γ-t, X- γ- t, e−-γ -tcoincidence measurements as well as time multi-analysis were performed. Internal conversion electrons were recorded with a magnetic selector and multipolarities deduced. The level scheme of 129La is discussed and compared with the calculations made in the frame of the neutron-proton Interacting Boson-Fermion Model (IBFM-2).

Theß-decays of172–175Ir have been studied using a Hejet system through32S induced reactions,ß half-lives have been measured and compared with those given froma decays. The level schemes of osmium nuclei are deduced and for172Os and174Os, the 22+ level is possibly located. The observedß-decay half-lives clearly indicate an isomerism phenomenon occuring in light Ir isotopes.

High spin states in103Rh have been studied using the100Mo(7Li, 4n) reaction. Standard in-beam measurements involving singles?-ray,?-?-t coincidences, angular distribution and linear polarization measurements have been performed. A perturbed band based on a 9/2+ state is interpreted as ag9/2 coupled band. A sequence built on a 1/2- state is related to thep1/2 state. At higher excitation energy, in the range 2.2–3.7 MeV, the strong?I=1 cascade observed, connecting negative parity levels, probably arises from states including three quasi-particle configurations.

The 129Nd activities were produced by bombarding 92,94Mo targets with 210 or 255 MeV 40Ca beams. Mass identification was made using the IGISOL technique. A measured β-decay half-life of 7(1)s was assigned to 129Nd. A new low-lying level scheme has been built for 129Pr. The 11/2−state is proposed to be isomeric at 383 keV excitation energy.

The cross-sections of target-like residues following the14N+27Al reaction at 30 MeV/u have been measured from in-beam and radioactiveγ-ray spectra. The recoil velocities of some fragments have been estimated from theγ-ray Doppler broadening.

Levels in ¹²⁵La have been studied via ⁺/EC decay of on-line mass-separated ¹²⁵Ce using the HIGISOL technique. A new (390 40) ms isomer is definitely attributed to ¹²⁵La by conversion electron measurements of the 107 keV E3 isomeric transition.

Low-spin states in doubly-odd184Au have been populated in the ß+/EC decay of184Hg produced by bombarding184Sm targets with an 185 MeV40Ar beam. Radioactive Hg nuclei were transported by a He jet system. A new level scheme has been established from ?-?-t and X-?-t coincidence measurements. Spin and parity values Ip=5+, Ip =2+ and Ip=3- were assigned to the ground state and the two isomeric states of184Au, respectively. The structure of these states is discussed using B(E1) values.

The lowlying level scheme of the oddodd nucleus132Pr has been investigated for the first time. The radioactive nuclei were produced by bombarding96Mo targets with 225 MeV40Ca beam. Levels have been populated from the132Nd ß- decay. A new value of its halflife has been measured: T1/2=88±7 s. The mass identification has been made with an ionguide coupled with an online isotope separator. ?- ?- t, X-?-t and e--?-t coincidence measurements have been performed. The observed distribution of the level feedings is similar to that of the neighbouring odd-odd nuclei.

Recent data from the EUROGAM array have revealed the population of the yrast superdeformed (SD) band of192Hg in the a4n exit channel of the16O+184W reaction at 113 MeV beam energy. The nucleus assignment was made on the basis of the SD band transition energies, and the observation of characteristic X-rays and lowlying yrast ?-transition of192Hg in coincidence with the SD band ?-rays. Both the feeding and decay-out patterns of the observed SD band have been found similar to the ones previously measured in the (36S,4n) reaction.

New results on the192Hg superdeformed band have been obtained with EUROGAM. The experiment has been performed with the160Gd(36S,4n) reaction at 159 MeV. Above 800 keV the γ-ray energies differ from the previously published ones. Thus the rise of the dynamical moment of inertia above ħω=0.4 MeV is no longer observed. This is in better agreement with recent cranked Hartree-Fock-Bogoliubov calculations.

A controversy has arisen over the existence, or not, of a superdeformed rotational band in192Pb. We have carried out an experiment using the168Er(3OSi, 6n)192Pb reaction at 159 MeV and have observed the coincident? rays in the EUROGAM 2 spectrometer. We confirm the original result of Henry et al. that a superdeformed band exists in192Pb.

From new measurements, a half-live of 4.2±0.3 s has been clearly established in127Pr. This value confirms our first result [4] and rules out other data [5]. The127Pr activity was produced by bombarding92Mo or94Mo targets with 210 MeV40Ca beams. The mass identification has been made using an ion-guide coupled with an on-line isotope separator. The partial level scheme proposed for127Ce has been deduced from ß-gated ? spectra and X?- and ??-coincidences. A new band structure based on a 1/2+ state is established.

Even-A praseodymium activities have been produced and identified in the40Ca +92–96Mo reactions at 5.8 MeV/u:126Pr[T1/2=(3.0 ±0.4)s]128Pr[T1/2=(3.1 ±0.3)s],130Pr[T1/2 =(40.0 ±0.4)s]132Pr[T1/2=1.6 min]. Several new low-energy levels have been populated in even-even cerium nuclei.

A new 12s activity has been produced via the35C1+112Sn reaction at 191 MeV and ascribed to the143Tb EC/ß+ decay. A decay scheme is derived from ?-? and ?-X-ray coincidence measurements.

Radioactive nuclei of127Ce were produced by bombarding92Mo and94Mo targets with 210 and 225 MeV40Ca beams. Two new different half-lifes T1/2=(29±2)s and T1/2=(34±2)s have been measured in the beta-decay of127Ce. Fromβ-gatedγ, conversion electrons andX−γorγ−γcoincidence spectra, a new low-lying level scheme has been deduced for127La. A qualitative description of the data is proposed in the frame of the Interacting Boson Fermion Model (IBFM-2).