P. Hornshøj

Decay characteristics of short-lived radio-nuclides studied by on-line isotope separator techniques

Abstract Short-lived isotopes of argon, krypton, silver, cadmium, tin, iodine, xenon, platinum, gold, mercury, polonium, radon and francium have been studied by the on-line isotope separator technique. Nuclear decey data are presented.

ALPHA DECAY OF NEUTRON-DEFICIENT RADON AND POLONIUM ISOTOPES.

Abstract The use of mass-separated samples of neutron-deficient radon isotopes, produced at the ISOLDE on-line mass-separator facility at the CERN 600 MeV synchro-cyclotron, has permitted precise half-life determinations and unambiguous mass assignments for a range of light radon isotopes. Alpha/EC-branching ratios are extracted for several radon and polonium isotopes through the use of genetic relationships. The systematics of the α-widths is discussed.

BETA-DELAYED PROTON EMISSION FROM HEAVY NUCLEI. II. THE CALCULATION OF SPECTRAL SHAPES AND INTENSITIES IN A COMPOUND-NUCLEUS MODEL.

Abstract Beta-delayed proton emission from isotopes of xenon and mercury is investigated in a statistical calculation. The absolute proton intensities, the branching ratios to final levels, and the approximate spectral shapes are in good agreement with experiment if the β-strength function is assumed to be a constant with a low-energy cut-off. For the xenon isotopes an improved fit is obtained if the β-strength function is taken to have a broad peak centred at 5 MeV. This peak is tentatively interpreted as evidence for intermediate structure involving the ( g p 9 2 ) −1 g n 7 2 state.

Alpha-decay widths of neutron-deficient francium and astatine isotopes

Abstract The use of mass-separated samples of neutron-deficient francium isotopes, produced at the ISOLDE on-line mass-separator facility at the CERN 600 MeV synchro-cyclotron, has permitted precise determinations through genetic relationships of α /(EC+ β + ) branching ratios for a range of light francium and astatine isotopes. The experiments verify previous mass assignments and provide improved values for the half-lives. The systematics of α-widths and of β-strength functions is surveyed.

Widths for s- and d-wave α-decay of neutron-deficient isotopes with Z ≦ 82

Abstract The α-decay of the nucleides 188–192Pb, 180Hg, and 176Pt has been studied after on line mass separation of spallation products from reactions with 600 MeV protons. For the lead isotopes, the K X-ray/α ratios were determined, and from these partial α half-lives were deduced. In the decay of 6 sec 176Pt, a 1.4% α-branch was found to the 228 keV 2+ level of 172Os, while for 180Hg an upper limit of 10−3 (relative to the ground-state α-branch) could be put on the intensity of an assumed rotational fine-structure component. The systematics of reduced s-wave (0+ → 0+) α-widths is discussed. The lead isotopes show a surprising trend: the reduced s-widths vary from a very small value for 186Pb (deduced from the heavy-ion cross sections of Gauvin et al.) to a quite large value for 192Pb. The systematics of d-wave (0+ → 2+) hindrance factors (relative to the ground-state branch) shows that these range from 1 to 4 for the actinides, while for platinum and mercury one finds 8 and ≈ 50, respectively.

Beta-delayed proton emission from heavy nuclei: (I). The observation of coincidences between protons and γ-rays

Abstract Coincidences have been detected between γ-rays and β-delayed protons emitted after the decay of very neutron-deficient nuclei. In the three cases studied the decay proceeds to the ground state with branches to the first excited (2 + ) state of the even daughter nucleus of (58±7) % ( 115 Xe to 709 keV in 114 Te), (14±3) % ( 117 Xe to 679 keV in 116 Te), and (50±10) % ( 181 Hg to 158 keV in 180 Pt). Upper limits of 2 and 6 % can be placed on the branches to the 4 + states of 114 Te and 180 Pt. For the cases of 115,117 Xe, coincidences with annihilation radiation were also observed; the measured positon/proton ratio determines the difference Q — B p , between the energy available for electron capture and the proton separation energy for the daughter. For 115 Xe the result is 6.20±0.13 MeV, for 117 Xe 4.10±0.20 MeV.

The β2p decay mechanism of 31Ar

Abstract We have measured the beta-decay of 31 Ar with a high granularity setup sensitive to multiparticle decay branches. Two-proton emission is observed from the isobaric analog state in 31 Cl to the four lowest states in 29 P and furthermore from a large number of states fed in Gamow–Teller transitions. The mechanism of two-proton emission is studied via energy and angular correlations between the two protons. In all cases the mechanism is found to be sequential yielding information about states in 30 S up to 8 MeV excitation energy. Improved data on the β -delayed one-proton branches together with the two-proton data provide precise information about the beta-strength distribution up to 15 MeV excitation energy.

Beta decay of 31Ar

Abstract A complete study of 31 Ar beta decay has been made by high-resolution charged-particle and gamma-ray spectroscopy. Beta-delayed radiation was detected by an array of three charged-particle detectors and a large-volume germanium detector. Fifteen new energy levels were discovered in 31 Cl. The beta-strength distribution, measured to 14.5 MeV, is compared with a shell-model calculation in the full sd space. The quenching of the Gamow-Teller strength and the isospin impurity of the IAS in 31 Cl are discussed.

Observation of the Li-11(beta d) decay

Experimental data from the decay of Li-11 show for the first time the presence of beta-delayed deuterons with a branching ratio larger than 10(-4). To distinguish between beta d and beta t events the decays of the daughter nuclei Li-9 and Li-8 were identified in the energy and decay time spectra. Furthermore, a time correlation analysis between the beta d events and the subsequent daughter decays was performed.

Projectile coulomb excitation with fast radioactive beams

We report a search for γ rays emanating from Coulomb excitation of fast (30–46 MeV/u) radioactive projectiles8He,11,12,14Be interacting with a lead target. These are clearly identified by their Doppler shift. The 320 keV 1/2− → 1/2+ γ transition from11Be was observed with a cross-section of 191±26 mb which is noticeably less than expected from the known lifetime and in the perturbation limit of pure Coulomb excitation. In the other nuclei rather stringent upper limits of 0.01 to 0.2 Weisskopf units, are placed on the hypothetical transition to 1− states.