Ph. Dessagne

Projectile fission at relativistic velocities: a novel and powerful source of neutron-rich isotopes well suited for in-flight isotopic separation

Abstract Projectile fission of 238U was investigated at a bombarding energy of 750 A·MeV using a Pb target. Forward emitted fragments from 80Zn up to 155Ce were analyzed with the Fragment Separator (FRS) and unambigously identified by their energy-loss and time-of-flight. The magnetic selection of the largest momenta acted as a trigger of the low-energy fission component. More than forty new nuclear species were identified. The related isotopic production cross-sections are presented.

Identification of more than a 100 new isotopes from 238U projectile fission and beams of neutron-rich nuclei at BRENDA

Abstract Projectile fission of 238U was investigated at a bombarding energy of 750 A·MeV using Pb and Be targets. The fully stripped forward emitted fragments from Ti to Cs were analyzed with the Fragment Separator (FRS) and unambiguously identified by their energy-loss and time-of-flight. The magnetic selection of the largest momenta acted as a trigger of the low-energy fission component. More than a hundred new nuclear species were identified including the 78Ni, for which a cross-section of 300 pb was measured.

The delayed proton emission in the A≃65–77 mass region, statistical aspects and structure effects

Abstract In the decay of the series of T Z =1/2 nuclei, 65 Ge, 69 Se, 73 Kr and 77 Sr, a statistical analysis was applied to the β delayed proton emission to obtain nuclear structure information. New results emerge from this study, in the light of improvements in the experimental techniques and developments of the analysis method. Experimental results are analysed by comparison with a statistical model, in order to extract information on level densities and partial transition widths of the proton emitting nuclei. Limitations of the existing descriptions of processes for nuclei far from stability are pointed out.

Beta-delayed neutron decay of 33Na

Abstract Beta-delayed neutron decay of 33 Na has been studied using the on-line mass separator ISOLDE. The delayed neutron spectra were measured by time-of-flight technique using fast scintillators. Two main neutron groups at 800(60) and 1020(80) keV were assigned to the 33 Na decay, showing evidence for strong feeding of states at about 4 MeV in 33 Mg. By simultaneous β–γ–n counting the delayed neutron emission probabilities P 1n =47(6)% and P 2n =13(3)% were determined. The half-life value for 33 Na, T 1/2 =8.0(3) ms , was measured by three different techniques, one employing identifying gamma transitions and two employing beta and neutron counting.

Separation and implantation of relativistic86Kr-fragments at the FrS; half-life measurement by ion-? time-correlations

Neutron-rich Co and Fe isotopes produced by86Kr projectile fragmentation at 500 MeV/u were separated and identified using the fragment separator (FrS) in a bunched energy mode.66Co and65Fe ions were selectively implanted in a double PIN-diode array where theβ-decay signals were measured. The half-lives were deduced from time correlations between implantation andβ-decay signals. The remeasurement of the66Co half-life confirms the isotope identification. The value of the65Fe half-life was found to be 0.45±0.15 s.

Beta decay and structure of exotic nuclei in the mass regions N=Z, A ~ 70 and near the N=20 closed shell

This paper describes two beta decay experiments performed at the CERN/ISOLDE mass separator. The structure of 74Kr has been studied using a total absorption g spectrometer (TAgS). The measured Gamow-Teller strength is presented and compared to HFBCS+QRPA calculations. The 33Na decay is also presented. The structure of the 33Mg daughter nucleus is compared to shell-model calculations, showing for the first time an inversion of states in the A~35 mass region.

A new isomeric state in 65Ni

Abstract A new isomeric state has been observed in 65Ni. Its properties are described and discussed. Comparison is made with other isomers already observed in this mass region, and theoretical approaches are considered.

The β+ and EC decay of 69Se, possible shape‐coexistence and superdeformation effects in 69As

The β+ and electron‐conversion decay of 69Se to 69As and the subsequent γ and proton emissions have been investigated by means of the 40Ca(32S,2pn)69Se reaction with a 100 MeV beam delivered by the Strasbourg MP tandem. Direct proton spectra and proton‐X rays coincidence have been registered in a closed geometry with a proton resolution of 20keV. (AIP)

Gamow‐Teller beta decay of 29–31Na comparison with shell‐model estimates

Gamma rays and delayed‐neutron processes subsequent to beta decay of the neutron‐rich 29–31Na isotopes are studied in singles an coincidence mode with mass‐separated sources at ISOLDE. Improved level schemes are presented for mass 29 and 30, whose features substantially agree with shell‐model predictions. The deduced Gamow‐Teller strengths are discussed as well as the occurrence of negative parity intruder states in the daughter nuclei.

Experimental mass excess of 49,50K and 40,42Cl

Detection of the β–decay of fission fragments produced from 600 MeV proton induced fission of a uranium carbide target has been used to measure the mass excess of 49,50K and 40,42Cl. The experimental data is presented. (AIP)