S. Mattsson

Observation of forward neutrons from the break-up of the 11Li neutron halo

Abstract The cross-sections and forward angular distributions of fast neutrons have been studied for the reaction (11Li, 9Li) at 29 MeV/u on targets of Be, Ni and Au. The cross-sections are large and arise essentially from peripheral reactions. The angular distributions of the neutrons are very narrow and indicate the existence of a neutron halo with radius of about 12 fm.

Alpha decay of neutron-deficient mercury isotopes and their daughters

Abstract Half-lives, decay energies and branching ratios have been measured for the α-decay of neutron- deficient mercury isotopes and their daughters. The lightest mercury isotope, 177 Hg( E α = 6.580MeV), has a half-life of 0.17±0.05sec. The heaviest observed α-emitter is 188 Hg. Coincidences between α-particles and γ-rays were measured and weak transitions to excited states could be determined. The spectroscopic results are interpreted as evidence for rotational structure in the light odd-mass platinum isotopes. The existence of a pronounced even-odd variation in the Q -values for α-decay of mercury isotopes has been confirmed.

Alpha decay of neutron-deficient ytterbium isotopes and their daughters

Abstract Ytterbium isotopes with mass numbers 153–158 have been produced at the ISOLDE on-line mass separator facility. The a-decay energies, half-lives and α-branching ratios were measured. The previously unknown nuclide, 153 Yb, was found to decay with a half-life of 4.0 ± 0.5 sec. Alpha emission was observed for the first time from 158 Yb. For the remaining isotopes, earlier mass assignments were confirmed. The α-decay properties of nuclides that were found as daughters of the ytterbium isotopes were also investigated. Alpha-branching ratios were derived for the nuelides 153 Tm, 152, 153 Er, 152 Hoand 150 Dy. The systematics of α-energies and α-widths are discussed.

The strongly deformed nucleus 100Sr

Abstract Two γ-rays of 129.2 and 288.4 keV observed in the β-decay of 55 ms 100Rb are interpreted as representing the two lowest transitions in the 100Sr ground-state rotational band. The energy ratio of the two levels, 3.23, approaches the value for a rigid rotator. The half-life of the 2+ state is 5.15 ± 0.20 ns corresponding to a deformation parameter ϵ of 0.29. The theoretical implications of these results are discussed on the basis of a Nilsson-Strutinsky calculation.

A new island of α-emission: α-decay energies and widths of neutron deficient tellurium, iodine and xenon isotopes

Abstract Using on-line mass separation, eight α-emitters (given with their α-decay energies in keV) in the trans-tin region were investigated: 108Te, 3300(30); 109Te, 3080(15); 110I, 3424(15); 111I, 3150(30); 112I, 2866(50); 112Xe, 3185(30); 113Xe, 2990(30); 114Cs (or 114Ba), 3226(30). Systematics of Q α values and reduced α-widths for this new island of α-emission are discussed.

Properties of the lighest known caesium isotopes 114–118Cs

Abstract Neutron-deficient caesium isotopes with mass numbers from 114 to 118 have been studied at the ISOLDE facility. Half-lives have been determined from counting of β-particles, β-delayed protons, and γ-rays. A short-lived isomer ( T 1 2 = 0.7 sec ) in 116Cs has been observed and the new delayed-particle precursors 116Cs (protons and α-particles), 115Cs (protons), and 114Cs (protons and α-particles) have been identified. Coincidences between delayed particles and γ-rays have been measured for 118Cs (pγ and αγ) and 116Cs (pγ). A search for the possible proton-radioactive isotope 113Cs has been performed and an upper limit for its production yield is given.

Delayed neutron emission probabilities of 9Li and 11Li

Abstract The Pn values for 9Li and 11Li were determined to be (50 ± 4)% and (95 ± 8)%, respectively, by a beta-neutron coincidence technique. The Pn values of 27–31Na, 93–98Rb and 145–146Cs, which had been deduced by normalization to the older Pn value for 9Li, should thus be raised by the factor 1.43. The β-decay branch to the 320 keV first excited state of 11Be was found to be (9.2 ± 0.7)%. The fraction of one-neutron emission leading to excited states of 10Be was deduced to be (41 ± 4)%. The half-life of 11Li was remeasured to be (8.83 ± 0.12)ms.

New targets for on-line mass separation of nuclei formed in 600 MeV proton and 910 MeV 3He reactions

Abstract The performance of the previously reported UC2-graphite cloth, VC, la and Pb targets, as well as the newly developed ThC2-graphite, UC2-graphite, ScC2-graphite, and CaB6 targets is discussed. Production-yield curves for the elements Li, Na, Ar, K, Ga, Rb, In, Cs, Hg, Tl and Fr are given for 600 MeV protons and 910 MeV 3He. It is shown that the latter projectile gives higher yields for the neutron-deficient isotopes produced in fragmentation and spallation processes.

Beta-delayed two-neutron emission from 30,31,32Na

Abstract Beta-delayed two-neutron emission from mass-separated samples of short-lived sodium isotopes has been detected both by n-n time correlations with a 4π neutron counter and by γ-spectroscopic identification of daughter products with mass A − 2. The observed cases (intensities per beta decay) are 30 Na (1.2 ± 0.2%), 31 Na (0.70 ± 0.25%) and 32 Na (5.1 ± 1.8%) . The results are in good agreement with a simple model of beta-particle emission.

Two-neutron removal reactions for very neutron-rich nuclei

Abstract The two-neutron removal reactions of beams of 11 Li, 14 Be and 8 He upon Be, Ni and Au targets were studied at 30 MeV/u. The cross sections and the neutron forward angular distributions were measured; they correlate strongly with the two-neutron separation energy of the projectile. Even though the coverage of the neutron detectors was limited, a rough neutron-neutron distribution could be extracted. A simplified interpretation of the data is presented.