F. Buchinger

Development and operation of gas catchers to thermalize fusion–evaporation and fragmentation products

Abstract A new approach to the production of low energy radioactive beams involves the stopping of fast beams produced by fragmentation, in-flight fission or fusion–evaporation reaction into a large gas catcher where the reaction products are thermalized in high-purity helium and extracted as singly charged ions for post-acceleration. This removes the limitation present in standard ISOL technique for species that are difficult to extract from the target/ion source assembly. This approach has been implemented at Argonne since 1998 to inject fusion–evaporation products in an ion trap system. Via a series of improvements since then, we now reach efficiencies for these devices of close to 50% with delay times below 10 ms. In preparation for the RIA project, a larger device for stopping fragmentation products is in preparation. The basic principles behind these devices together with results obtained and experience gained operating these devices will be presented. Preparation for a test of the large gas cell at the full RIA energy at GSI will also be presented.

The Temperature of Buffer-gas Colled Ions in a Paul Trap

Abstract A measurement of the temperature of a typical ion cloud in a Paul trap with buffer gas cooling has been made using time-of-flight of the extracted ion cloud. A temperature of 0·3 ± 0·1 eV was obtained for 20 00039K ions in a trap of potential well depth 60 eV with helium buffer gas at 3 × 10−2 Pa. This value is intermediate by a factor of about 10 in each direction between that of other published works using different observational methods on Paul traps operated under similar conditions. Explanations for the discrepancies are suggested. In any case, the present work indicates that sub-electronvolt temperatures can be achieved, at least for small trap loadings. The result considerably eases the design of transport systems for such ion clouds and greatly enhances the possible uses of a Paul trap collection device for highly sensitive precise experiments.

Improvements in the injection system of the Canadian Penning trap mass spectrometer

Abstract The Canadian Penning Trap (CPT) mass spectrometer is designed to make precise mass measurements on a variety of stable and short-lived isotopes. Modifications to the injection system of the CPT have been implemented in recent months, the purpose being to more efficiently collect and transfer weakly-produced reaction products from the target to the Penning trap. These include a magnetic triplet situated after the target chamber to increase the acceptance of the Enge spectrograph, a velocity filter to more effectively separate the beam from the reaction products and the replacement of the Paul trap with a linear trap resulting in more efficient capture and accumulation of ions from the ion cooler. This paper will discuss these recent modifications and how they have increased our ability in making mass measurements on isotopes of low abundance, including those from a 252 Cf fission source.

Nuclear ground state properties of 99Sr by collinear laser spectroscopy with non-optical detection

Collinear fast-beam laser spectroscopy, with improved sensitivity for ions with hyperfine split transitions, is performed to measure the hyperfine structure and the isotope shift of the well deformed short-lived 99Sr. The new method consists in ground state depopulation by a two-step optical pumping sequence prior to state selective neutralization and fast-atom counting. A definitive nuclear spin value I = 32, the change in mean square charge radius δ〈r2〉98,99 and the nuclear moments are derived. These results are compared to nuclear spectroscopy information and are interpreted in the frame of the particle plus deformed core model.

First experimental determination of the charge radius of 74Rb and its application in tests of the unitarity of the Cabibbo-Kobayashi-Maskawa matrix.

Collinear-laser spectroscopy with the bunched-beams technique was used for the study of neutron deficient Rb isotopes, out to (74)Rb (N = Z = 37) at TRIUMF. The measured hyperfine coupling constants of (76,78m)Rb were in agreement with literature values. The nuclear spin of (75)Rb was confirmed to be I = 3/2, and its hyperfine coupling constants were measured for the first time. The mean-square charge radius of (74)Rb was determined for the first time. This result has improved the isospin symmetry breaking correction term used to calculate the Ft value, with implications for tests of the unitarity of the Cabibbo-Kobayashi-Maskawa matrix.

The mean square nuclear charge radius of

We report on a collinear laser spectroscopy measurement of the nuclear charge radius of (I = 3/2), yielding . Within the experimental accuracy, the N = 20 neutron shell closure has no influence on the charge radii of the calcium isotopes.

Nuclear moments of strongly deformed strontium isotopes

Nuclear spins, moments and mean square charge radii of78–100Sr have been obtained by fast ion-beam collinear laserspectroscopy. The experiments performed at ISOLDE have been extended to include99Sr, measured by a non-optical detection scheme with a two-step optical pumping sequence. The results for the strongly deformed isotopes are discussed in the frame of the particle-plus-deformed core model.

Identification of individual bistable defects in avalanche photodiodes

The effects of individual bistable defects on the dark counting rate of avalanche photodiodes have been monitored and their temperature dependence studied. The presence of a bistable defect in the diode is indicated by the repeated random switching of the counting rate between two well‐defined rates. Four of the defects studied were produced via reaction with a single neutron from a Be–Am source, while two were found to exist without irradiation. Results were analyzed in terms of the activation energies of the electron generating capabilities of the defects, and the effective potential barriers between the two structural configurations of the bistable states. Among the six defects studied, two of them could be of the same type.

Nuclear electric quadrupole moment of 9Li using zero-field β-detected NQR

A ?-detected nuclear quadrupole resonance (NQR) spectrometer becomes a powerful tool to study changes in nuclear ground-state properties along isotopic chains when coupled to a laser excitation beamline to polarize the nuclei of interest. Recently, the ?-NQR technique in a zero magnetic field has been applied for the first time to measure the ratio of static nuclear quadrupole moments of 8, 9Li, Q9/Q8 = 0.966?75(9) denoted by Q8 for 8Li and Q9 for 9Li, respectively. This shows agreement with present literature values but with significantly improved precision. Based on the literature, the quadrupole moment for 8Li has been re-evaluated to be |Q8| = 32.6(5)?mb. From this, the quadrupole moment for 9Li is calculated as |Q9| = 31.5(5)?mb with the error being dominated by the error of Q8.

Nuclear moments of the neutron-deficient thallium isotopes

The nuclear moments of the neutron-deficient187,188Tl isotopes were determined by measuring the hyperfine structure splittings of the λ=535 nm line in neutral thallium. An optical efficiency of 2×10−4 photons per radioactive ion was achieved using collinear fast beam laser spectroscopy with a large solid angle fiber optical array detector. Most of the moments can be interpreted fairly well in the single particle model.