β decay of 69 Kr and 73 Sr and the rp process Bertram Blank CEN Bordeaux-Gradignan

1. β decay of 69Kr and 73Sr and the rp process Bertram Blank CEN Bordeaux-Gradignan

2. Motivation 69Kr – rp-Process Drip-Line Nucleus 69Br • Measurement of the 69Br ground state. • Constraints on the 68Se rp-process “waiting point”. 73Sr – rp-Process Drip-Line Nucleus 73Rb • Measurement of the 73Rb ground state. • Constraints on the 72Kr rp-process “waiting point”.

3. 69Br and the rp process • The rapid proton, or rp process, is thought to mainly occur during Type I X-ray bursts (timescale of ~10-100 s). • Burst properties and nucleosynthesis of heavy nuclei is significantly influenced by “waiting-point” nuclei. • T1/2(68Se)=35.5s and 69Br is proton unbound. • How strongly can the 68Se waiting point be bypassed via 2p captures? • 2p-capture rate depends exponentially on Sp. • ⇒Need spectroscopy beyond the drip line. A. Rogers, ANL

4. Previous measurements A. M. Rogers et al. P. Schury et. al • Non-observation: Upper limit on the 69Br lifetime estimated from 78Kr fragmentation cross sections T1/2<100 nsSp < -450 keV (Blank et al., 1995) T1/2<24 nsSp < -500 keV (Pfaff et al., 1996) • Indirect: High-precision penning trap mass measurements of 68Se and 69Se + CDE (Coulomb Displacement Energy) Sp= -636 105 keV (Brown et al., 2002; Schury et al., 2007; Savory et al., 2009) • Direct: Kinematic reconstruction of the 69Br protondecay Sp= -785+35-40 keV (A.M. Rogers et al., 2011)

5. Populating 69Br via 69Kr β decay • Method: Populate the 69Br g.s. in the β decay of 69Kr and look at β-p correlations • Monoenergetic protons. • Clean and selective technique. • Problem: Decay to the Isobaric Analog State is favored over the g.s. -- X.J. Xu et al. Phys. Rev C 55, R533 (1997) • However, a few percent of the decay flux may go to the g.s.

6. Setup CSS2 CSS1 LISE3 • Fragmentation of 78Kr primary beam. • E=70 MeV/A Intensity ~ 3-4 eμA. • Utilized the LISE3 spectrometer with an Al (100μm) degrader and a Wien filter. LISE Target: natNi 200 mg/cm2 EXOGAM Clovers • Implant-decay experiment using β-p and β-γ event tagging. • ToF from RF and MCP's. • Si detector for energy loss of heavy ions. • Heavy ions are implanted into a 16x16 strip DSSD (3 mm pitch, 500 μm thick). • γ's are measured using four germanium clover detectors. DSSSD E ToF ΔE MCP CENBG, GANIL, ANL

7. Setup Fragmentation of 78Kr primary beam. E=70 MeV/A Intensity ~ 3-4 eμA. Utilized the LISE3 spectrometer with an Al (100μm) degrader and the Wien filter. • Identified 211 69Kr implantation events →87 69Kr/day. • Clean PID based on redundant identification parameters.

8. Measurements of known half-lives • Known T1/2(62Ga) = 116.12 (23) ms. • Negligible additional decay components. • Known T1/2(67Se) = 136 (12) ms • So far there is good agreement with most easily measured half-lives.

9. 65Se β decay preliminary results • Batchelder et al (Phys. Rev. C 47, 2038 1996) identified a single proton group at 3.55 (0.03) MeV. • We also observe a proton peak at an energy of 3.51 MeV.

10. 69Kr β decay preliminary results

11. 69Kr β decay preliminary results X. J. Xu et al, Phys. Rev. C 533, 1997 • Half-life previously measured by X.J. Xu et al, Phys. Rev. C R533, 1997 of T1/2=32 (10) ms. • Also claimed to observe a single proton group at 4.07 (0.05) MeV.

12. 69Kr β decay proton spectrum • Half-life previously measured by X.J. Xu et al, Phys. Rev. C R533, 1997 of T1/2=32 (10) ms. • Also claimed to observe a single proton group at 4.07 (0.05) MeV. • We observe proton decays to excited states. • However, IAS is observed at E=2.97 MeV. • We do not observe 69Br ground-state proton decays.

13. We observe proton decays to excited states. However, IAS is observed at E=2.97 MeV. We do not observe 69Br ground-state proton decays. 69Kr β decay preliminary results • Half-life previously measured by X.J. Xu et al, Phys. Rev. C R533, 1997 of T1/2=32 (10) ms. • Also claimed to observe a single proton group at 4.07 (0.05) MeV.

14. Level Scheme

15. 73Sr 73Rb 69Kr 72Kr 69Br 68Se Measurement aims: • Study of decay of 73Sr to 73Rb and 72Kr • Study of decay of 69Kr to 69Br and 68Se Known Properties: • 73Sr decay: - Proton line at 3.75(4) MeV assumed to be IAS (Batchelder et al., PRC48 (1993) 2593) • 73Rb: - half-life T1/2 < 30ns (Janas et al., PRL82 (1999) 295)

16. Production: • 92Mo fragmentation at the FRS at 500 MeV/u, 4g/cm2, 9Be target, 5e9pps • expected rates: • 73Sr: 250 per day • 69Kr: 200 per day in same setting  5-7 days experiment  Factor of 5 more statistics than at GANIL for 69Kr  First data for 73Sr decay (beyond IAS) • setup: • DSSSD setup • Gamma-ray detection B. Fernandez-Dominguez et al.

18. Correlation method • For any given implant there are uncorrelated decay events that follow implantation. • One of the events will be a true correlation while the others are false/uncorrelated. • SPATIAL CORRELATION: Requirement that the implant and decay occurs in the same DSSD pixel. • TIME CORRELATION:Requirement that the decay occurs within an adjustable time correlation window. • False correlations add to a randomly distributed continuous background.