Jan Wauters

Beams of short lived nuclei produced by selective laser ionization in a gas cell

Abstract An on-line laser ion source has been developed for the production of elemental and isobaric pure beams of radioactive ions. It is based on selective resonant laser ionization of nuclear reaction products thermalized and neutralized in a noble gas at high pressure. The ion source has been tested in a wide range of recoil energies going from 1.3 MeV to ∼ 90 MeV. Efficient schemes of two step laser ionization through autoionizing states have been found for nickel, cobalt and rhodium. Residence times of the reaction products in a gas cell have been measured for helium and argon as buffer gas. Elementally pure beams of 54,55Ni and 54Co, produced in a light-ion induced fusion-evaporation reaction, and of 113Rh, produced in proton-induced fission of 238U, were obtained. An efficiency of the ion source of 6.6% for fusion reactions and of 0.22% for fission reactions has been obtained. A selectivity of the ion source of 300 for fusion and 50 for fission reactions has been achieved.

Identification of the doubly-magic nucleus 100Sn in the reaction 112Sn+natNi at 63 MeV/nucleon

Abstract We report on the production of the doubly-magic nucleus 100 Sn and other proton-rich nuclei in the A ∼ 100 region in the reaction 112 Sn + nat Ni at 63 MeV/nucleon. The experiment was carried out using the high acceptance device SISSI and the Alpha and LISE3 spectrometers at GANIL. The identification of the reaction products ( A , Z and Q ) was made using the measurements of time-of-flight, energy-loss and kinetic energy.

Identification of μs-isomers produced in the fragmentation of a 112Sn beam

Abstract Decays of over forty short-lived ( T 1 2 from ≈ 50 ns to 70 μs) isomeric states including a new isomer 66mAs produced in the fragmentation of a 112Sn beam (58 A·MeV, 63 A·MeV) on a natNi target were observed at the final focus of the LISE3 spectrometer at GANIL. Their detection, based on the slow (≈ 10 μs) time correlation of identified ions with the characteristic γ-radiation, represents a novel method to search for new isomers and can be used for unambiguous isotope identification for projectile fragment separator experiments. Isomeric yields and isomer-to-total production ratios were determined.

Life time measurements of 0+ intruder states in 190,192,194Pb

Abstract The fine structure in the α-decay of mass-separated 194,196,198 Po is studied. Feeding to the 0 + ground state and the first excited 0 + intruder state in 190,192,194 Pb is observed. From α-e-t coincidences between the feeding α-ray and the E0 transition, the half life of the 0 + intruder state in 190,192,194 Pb is measured. The mixing between intruder state and ground state is deduced.

INTRUDER STATES IN ODD ODD TL NUCLEI POPULATED IN THE ALPHA-DECAY OF ODD ODD BI ISOTOPES

The alpha-decay of mass separated Bi-190,192,194,196 isotopes has been studied with the LISOL on-line separator. Time sequential alpha-singles spectra were taken and for Bi-190,192,194, alpha-Xt and alpha-gamma-t coincidences were collected. Transition probabilities of levels in Tl-186,188,190 were measured using a fast timing alpha-gamma-t and alpha-e-t coincidence set up. The alpha-decay of 196Bi and the beta-decay of 190Bi are observed for the first time. In all the Bi nuclei presently studied, unhindered alpha-decay of Bi starting from the high- (10-) and low-spin (3+) isomer populating intruder-based states in Tl was observed. The excitation energy of these intruder states is comparable with the intruder states in the neighboring odd-even and even-even nuclei.

ALPHA-DECAY STUDY OF PB-188 AND HG-180,HG-182

Theα decay of mass-separated188Pb and180,182Hg has been studied at the GSI on-line mass separator. Alpha singles spectra as well asα-X-t andα-e-t coincidence events were collected. Fine structure in theα decay of188Pb was measured for the first time, feeding the 21+ and 02+ states in184Hg. Theα decay of180,182Hg feeds low-lying states in176−178Pt. One of these states could be identified as a 0+ state. The deexcitation pattern could be established. As a by-product an alpha-decay scheme of180Au towards levels in176Ir is given.Theα decay of mass-separated188Pb and180,182Hg has been studied at the GSI on-line mass separator. Alpha singles spectra as well asα-X-t andα-e-t coincidence events were collected. Fine structure in theα decay of188Pb was measured for the first time, feeding the 21+ and 02+ states in184Hg. Theα decay of180,182Hg feeds low-lying states in176−178Pt. One of these states could be identified as a 0+ state. The deexcitation pattern could be established. As a by-product an alpha-decay scheme of180Au towards levels in176Ir is given.

The alpha-branching ratios of the pb-188, pb-190, pb-192 isotopes

Theα-branching ratios (bα) of192,190,188Pb are measured using mass-separated sources. Different experimental set-ups are used — one detector as well as two detector set-ups — thereby detecting theα particles from the parent and/or viaα decay formed daughter nuclei, theβ-delayed gamma radiation from the parent and/or viaβ decay formed daughter nuclei and the Tl KX rays from electron capture decay. Values forbα of 6.2(6) 10−5 and 4.0(4) 10-3 were found for192,190Pb respectively. For188Pb, limits on thebα values were obtained: 0.03<bα<0.10. A careful analysis of the previously reportedbα values showed that the discrepancies in thebα values were not due to inadequate correction procedures, as was suggested, but to experimental uncertainties in the efficiency determination of the different detection set-ups and to an unreliableβ-decay scheme for188Pb. Thebα obtained in this work show that the leadα decay is not faster than the Hgα decay and that there is no need to assume a disappearance of theZ=82 shell closure halfway betweenN=82 andN=126.

Identification of 100Sn and others proton drip-line nuclei in the reaction 112Sn(63 MeV/nucl.)+natNrmNi

Abstract Six new neutron-deficient nuclei 103Sb, 104Sb, 98In, 91Pd, 89Rh and 87Ru have been identified among the products of quasi-fragmentation of a 112Sn beam (63 MeV/nucl.), in addition to the previously reported 100Sn and 102Sn. Decays of over forty short-lived ( T 1 2 from ≈50 ns to 70μ s ) isomeric states including new isomer 66mAs were observed in the same reaction.

Activation volumes for horseradish peroxidase compound ii reactions

The activation volumes for the reactions of horseradish peroxidase compound II with L-tyrosine, 3-iodo-L-tyrosine, p-aminobenzoic acid and ferrocyanide were determined by using a high-pressure stopped-flow technique at 25 degrees C and pH 7. For the tyrosines, the solvent electrostriction accompanying substrate ionization and H+ transfer from the substituted phenol to a basic group of the enzyme can account for the observed negative activation volumes. For p-aminobenzoic acid a simple electron transfer without H+ transfer appears to occur. The positive activation volume for ferrocyanide may be explained in terms of electron transfer associated with a large change in electrostriction of the inorganic redox couple.

Effects of pressure and temperature on the reactions of horseradish peroxidase with hydrogen cyanide and hydrogen peroxide.

Reactions of ferric horseradish peroxidase with hydrogen cyanide and hydrogen peroxide were studied as a function of pressure. Activation volumes are small and differ in sign (delta V = 1.7 +/- 0.5 ml/mol for peroxidase + HCN and -1.5 +/- 0.5 ml/mol for peroxidase + H2O2). The temperature dependence of cyanide binding to horseradish peroxidase was also determined. A comparison is made of relevant parameters for cyanide binding and compound I formation.