Centre Etudes Nucléaires de Bordeaux Gradignan

date: June 2000

Interest

Predictions based on the rp process require a knowledge of the half-lives, binding energies and relevant reaction cross sections for the nuclei along the path. For high temperatures and densities, the extend of the rp process is not yet very well known due to some lacks of the knowledge about proton-rich nuclei in the A=60-100 mass region . Rp process path is shown on.
In a recent experiment, we extended the study of nuclei in the cobalt-to-krypton region with isospin projections between Tz = 0 and Tz = -3/2. All these nuclei are along the path of the rp process according to the calculations of Champagne and Wiescher, Rev. Nucl. Part. Sci. 42, 39 (1992). Here we present the results of our half-life measurements. A possible rp process path is shown on Figure 1 .

Figure 1: Rp process path in the Cu-Sr region. Circles: nuclei with half-lives measured in this experiment.

Experimental Method

At GANIL with the LISE spectrometer: ⁷⁸Kr at 73 MeV/A & 2 mA impinging on a 177 mg/cm² thick Be target, a Si telescope with a 16x16 Si strip detector as implantation device, four Ge detectors for gamma-ray registration are presented on Figure 2.

Spectroscopie dans l’entourage du ⁷⁰Br (E346) : final results of half-lives

Figure 2: Experimental set-up used to measure half-lives with a Silicium detector for implantation surrounded by 2 Germaniums detectors, 1 clover and the LEPS detector.

Results

Half-life values were obtained by pixel-to-pixel correlations of decay events with the implantation events of identified nuclei during a time delay of 5 seconds. Figure 3 shows an implantation profile in the 16 x16 silicon strip detector.

Figure 3: X and Y correlations in stripped Silicium.

23 nuclei were produced with half-lives less than a second:
4 new half-life values were obtained for the Tz = -1 nuclei ⁶⁶Se, ⁶⁴As, ⁶²Ge and ⁶⁰Ga, key nuclei of the rp process.

Experimental time spectra obtained for all nuclei are presented in Figure 4.

Figure 4: Half-lives measurements for Co-Kr nuclei.

A summary of the half-life measurements and a comparison with previous results from the literature is given in Table 1. Half-life values obtained for the first time in this work are compared to the Gross Theory (T. Tachibana et al., Prog. Theor. Phys. 84, 641 (1990)).

Table 1: Experimental half-lives compared with previous values.