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Accueil du site > ANGLAIS > Research > Exotic Nuclei > Research topics > Experiments > GANIL (Caen) > Spectroscopic studies around 70Br (E346) - 2000: final results of half-lives


Spectroscopic studies around 70Br (E346) - 2000: final results of half-lives

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)).

 


 

Nucleus  Previous values

or Theory 

Present work
References

71Kr 
64(85) ms [1] 86(45) ms  [1] B. Blank et al., Phys. Let. B364, 8 (1995)
71Kr 100(3) ms " [2] M. Oinonen et al., Phys. Rev. C54, R2924 (1997)
70Kr  57(21) ms [3]  42(31) ms  [3] M. Oinonen et al., Phys. Rev. C61, 035801 (2000)
70Br  78.54(59) ms [4] 79(36) ms "
66Se 58 ms Gross Theo. 64(17) ms 
67Se  107(35) ms [5]  ms 135(10) ms [5] P. Baumann et al., Phys. Rev. C50, 1180 (1994)
64As   21 ms Gross Theo. 18+43-7 ms 
65As  190(+110 -70) ms [6]  126(16) ms [6] J.A. Wigner et al., Phys. Rev. C48, 3097 (1993)
66As   95.77(28) ms [4] 97(2) ms
61Ge 40(15) ms [7]  38(23) ms [7] M.A.C. Hotchkis et al., Phys. Rev. C35, 315 (1987)
62Ge 67 ms Gross Theo.  201(84) ms 
63Ge 95(+23

-20) ms [6] 

150(9) ms cf. [6] 

60Ga 
 70(15) ms [8]  70(13) ms [8] E. Roeckl et al., in ISOL’01 conference
61Ga 150(30) ms [6]   148(18) ms cf. [6] 
62Ga  116.35(35) ms [9] 117(3) ms  [9] C.N. Davids et al., Phys. Rev. C19, 1436 (1979)
57Zn  40(10) ms [10] 38(4) ms [10] A. Jokinen et al., GSI 99-1, 18 (1999)
58Zn 86(18) ms [11]  83(10) ms [11]  A. Jokinen et al., Eur. Phys. J. A3, 271 (1998)
59Zn  182.0(1.8) ms [12] 173(14) ms [12] Y. Arai et al., Nucl. Phys. A420, 193 (1984) 
56Cu  95(3) ms [13]  82(7) ms [13] R. Borcea et al., to be published
57Cu  196.3(7) ms [14] 182(18) ms   [14] D.R. Semon et al., Phys. Rev. C53, 96 (1996)
54Ni  106(12) ms [15]  221(24) ms [15] I. Reusen et al., Phys. Rev. C59, 2416 (1999)
55Ni  204(3) ms [15] 199(7) ms "
53Co 240(20) ms [16] 245(11) ms [16] J. Honkanen et al., Nucl. Phys. A496, 462 (1989)
54Co  193.28(7) ms [17]  172(23) ms [17] V.T. Koslowsky et al., NIM in P. R. A401, 289 (1997)

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