Andreas Oberstedt

On the β -decay of 9 C

In beta -decay experiments on C-9 at CERN/ISOLDE the beta -strength was determined to the ground state, the 12.2 MeV excited state and the Isobaric Analog State (IAS) at 14.655 MeV in B-9. A large beta -strength asymmetry is deduced for the mirror transitions of C-9 and Li-9 to states around 12 MeV excitation energy. A satisfactory description of the three-body decay from a narrow energy region around the 12.2 MeV resonance is obtained within a sequential model involving the ground and first-excited states of Li-5 and Be-8. From the study of angular correlations the spin of the 12.2 MeV state is determined as 5/2(-). For the first time the population of the IAS is observed in beta -decay and new information on the decay of this state is obtained. The advantages of a closely packed. highly segmented detector setup are demonstrated

New information on b-delayed neutron emission from 12,14Be

The β-delayed neutron branches from neutron-rich Be-isotopes have been measured with a setup sensitive down to thermal energies. For 14Be a new value of Pn = 101 ± 4% has been found for the total neutron-emission probability and an upper limit of 2.4% (95% confidence level) is imposed on the combination P2n + 3P3n of multi-neutron emission probabilities. Moreover, an improved value of Pn = 0.50 ± 0.03% has been obtained for 12Be. A time-correlation method, previously developed for a continuous radioactive beam to determine neutron branching ratios, has been revised and adapted to the pulsed secondary beam at ISOLDE, CERN.

Light exotic isotopes: recent beam developments and physics applications at ISOLDE

This paper is divided in three parts: (i) the measurement of yields and decay losses of Li and Be isotopes released from a thin foil tantalum target at the CERN/ISOLDE PS-Booster; (ii) results from β-decay experiments on 12Be and 14Be, an improved half-life of 21.49(3) ms has been obtained for 12Be; (iii) the β-decay of 9C. An outline of the analysis procedure to determine the branching at high excitation energies is given. The ground-state branch has been determined to 54.1(15)%.

Silicon thermal detectors for single quanta of radiation: fabrication, statistical fluctuations of phonons, physical properties and operation

Abstract Fabrication of a thermal detector designed for high resolution spectroscopy of low-energy radiation is described. Details of the micromachining of pure silicon are given including the etching of the 0.1 mm 3 absorber and the doping process to obtain the temperature sensing thermistor which is an integrated part of the absorber. The cryogenic system, the signal processing at working temperatures around 50 mK and the data acquisition system are discussed. Theoretical aspects of the intrinsic resolving power are presented. The relation between the intrinsic detector resolution and particle energy at different working temperatures is derived. Measured resistance vs temperature is shown for thermistors made with different dopings on wafers with different initial wafer resistivity. The influence of the initial wafer purity on the R - T characteristic curves is discussed. The optimal implantation dose was determined for thermistors implanted in high purity wafers.

Silicon microcalorimeters for high energy resolution spectroscopy

Abstract Integrated bolometers of a volume of about 0.05 mm 3 are fabricated by the technique of silicon micromachining. As thermistor serves a heavily phosphorus doped area implanted in the absorber surface. The optimum thermistor doping was determined with respect to a high resistance gradient, but at the same time with resistance values low enough for providing signals which are reasonably high. Measurements of low-energetic γ-rays and conversion electrons indicated the high sensitivity of our detectors, however unfortunately for picking up noise, too. The steps to improve the current energy resolution are reported.

β-delayed neutron emission from 12,14Be

The existence of {beta}-delayed particle emission allows one to study the {beta}-strength distribution, and thereby the ground-state structure, of exotic drip-line nuclei. A time-correlation method has been applied to recent data on the heaviest Be-isotopes to determine their neutron branches. Improved results were obtained for {sup 12}Be and new results were found for the very short-lived neutron-emitter, {sup 14}Be.

On the beta-decay of C-9

In beta -decay experiments on C-9 at CERN/ISOLDE the beta -strength was determined to the ground state, the 12.2 MeV excited state and the Isobaric Analog State (IAS) at 14.655 MeV in B-9. A large beta -strength asymmetry is deduced for the mirror transitions of C-9 and Li-9 to states around 12 MeV excitation energy. A satisfactory description of the three-body decay from a narrow energy region around the 12.2 MeV resonance is obtained within a sequential model involving the ground and first-excited states of Li-5 and Be-8. From the study of angular correlations the spin of the 12.2 MeV state is determined as 5/2(-). For the first time the population of the IAS is observed in beta -decay and new information on the decay of this state is obtained. The advantages of a closely packed. highly segmented detector setup are demonstrated

On the

In beta -decay experiments on C-9 at CERN/ISOLDE the beta -strength was determined to the ground state, the 12.2 MeV excited state and the Isobaric Analog State (IAS) at 14.655 MeV in B-9. A large beta -strength asymmetry is deduced for the mirror transitions of C-9 and Li-9 to states around 12 MeV excitation energy. A satisfactory description of the three-body decay from a narrow energy region around the 12.2 MeV resonance is obtained within a sequential model involving the ground and first-excited states of Li-5 and Be-8. From the study of angular correlations the spin of the 12.2 MeV state is determined as 5/2(-). For the first time the population of the IAS is observed in beta -decay and new information on the decay of this state is obtained. The advantages of a closely packed. highly segmented detector setup are demonstrated

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In beta -decay experiments on C-9 at CERN/ISOLDE the beta -strength was determined to the ground state, the 12.2 MeV excited state and the Isobaric Analog State (IAS) at 14.655 MeV in B-9. A large beta -strength asymmetry is deduced for the mirror transitions of C-9 and Li-9 to states around 12 MeV excitation energy. A satisfactory description of the three-body decay from a narrow energy region around the 12.2 MeV resonance is obtained within a sequential model involving the ground and first-excited states of Li-5 and Be-8. From the study of angular correlations the spin of the 12.2 MeV state is determined as 5/2(-). For the first time the population of the IAS is observed in beta -decay and new information on the decay of this state is obtained. The advantages of a closely packed. highly segmented detector setup are demonstrated