date: February 2000
* CEN Bordeaux-Gradignan (France)
* Univ. Jyväskylä (Finland)
Fundamental aspects of the weak interaction can be tested with basic ingredients such as half-lives and β-decay energies. For example, Hardy et al. used the superallowed 0+ to 0+ decay of nuclei from 14O up to 54Co to test the standard model via the Conserved Vector Current (CVC) hypothesis. For these studies, the extracted log ft values must be corrected for radiative and Coulomb effects, with these corrections being calculated using various theoretical approaches.
While these corrections are generally in good agreement with each other for nuclei where experimental data are available, there are considerable differences between the predictions for heavier nuclei. A further question is whether the corrected log ft values have an elemental (Z) dependence. To a large extent, these questions can be addressed by precisely measuring log ft values for Fermi superallowed b-decays in heavier nuclei and using the results to test the different predictions.
The present experiment is a feasibility study of this type of experiments at the IGISOL facility in Jyväskylä with 62Ga.
The secondary beam of 62Ga was produced by the 64Zn(p,3n)62Ga reaction at 45 MeV. The 62Ga isotopes were collected by the IGISOL facility and deposited on a moving tape. This tape position was surrounded by a high-efficiency b-plastic scintillator. In close geometry, three germanium detectors were mounted with each of them having a 2 mm thick veto plastic detector.
Fig. 1: Experimental setup at the end of the IGISOL beam line
for the half-life studies of 62Ga.
Due to a rather low primary-beam intensity (1000 nA), a slightly too high beam energy and an IGISOL efficiency of about 1%, the counting rate of 62Ga was only about 1 count per second. The spectrum obtained in about 36 h is shown in figure 2.
Fig. 2: Experimental spectrum for half-life determination of 62Ga. Grow-in and decay parts are visible. The half-life obtained from this spectrum is 116(2) ms.
An increase in primary-beam intensity of about a factor 100, reachable after the installation of a new H- source should yield an increase for 62Ga of about a factor of 10. In addition, lowering the primary-beam energy to about 40 MeV will also considerably increase the counting rate. Finally, the IGISOL efficiency of 62Ga has to be studied carefully.
Another route to produce 62Ga is the use of heavy-ion induced reactions e.g. using primary beams of 16O or 36Ar. The use of a heavy-ion beam would allow to use much larger effective target thicknesses and should thus increase in a sensitive way the production rates of proton-rich odd-odd N=Z nuclei.
Further projects are the measurement of half-lives of 66As and of 70Br.
Participants from CENBG
Participants from the CEN Bordeaux-Gradignan during a cold afternoon in Finland.
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