Image credit: NASA/Dana Berr

X-ray bursts - Close binary system: very dense neutron star and main sequence companion star - Matter accreted onto surface of neutron star - Extreme temperature and density conditions (T > 10 9 K, ρ ~ 10 6 g/cm 3 ) - Thermonuclear runaway © David A. Hardy/

The rp-process - Extreme conditions allow unstable nuclei to undergo reactions - Study highlighted key ‘waiting points’ [1] for example ~A=62 - Low level densities near proton dripline - Reaction rates may be dominated by a single resonance - Structure information required for key nuclei at waiting points [1] A. Parikh et al. ApJ Suppl. Ser., 178, 110 (2008)

X-ray burst properties - Burst recurrence time of hours to days - Burst duration of tens to hundreds of seconds - Peak luminosity ~ 3 x erg/s (10 5 times more than the sun!) Figure from Lewin, W.H.G., van Paradijs, J. & Taam, R.E., 1993, Sp Sci Rev, 62, 223

Producing exotic rp-nuclei - Compound nucleus formed in fusion reaction - Mass A=62 fusion evaporation products analysed at 0 o by Argonne FMA 24 Mg Target 40 Ca beam

Gammasphere - an array of ~100 HPGe γ-ray detectors with almost 4π geometric coverage - γ-rays from nuclei of interest swamped by background from other nuclei - Need more selectivity which are produced much more prolifically

What next? - Take advantage of fast β-decays exhibited by many exotic nuclei in the region of the rp-process 62 Ge 62 Ga 62 Zn τ 1/2 ~ 100ms 62 Cu τ 1/2 ~ 9hrs

New highly segmented implantation detector - Implant recoils into highly segmented 160x160 DSSD (double-sided silicon strip detector) and wait for them to decay β Beam Recoils See also A.N. Steer et al. NIM A, 565, 630, (2006)

Looking for correlations Recoils are implanted into DSSD Recoil Segment of DSSD Subsequent β-decay Path of β Pixel with largest energy deposition selected from nearest neighbours

Results from test experiment γ spectrum measured in coincidence with implanted recoils which were followed by fast decays 62 Ga Counts Energy (keV)

Further increase in sensitivity using Microball - Addition of the Microball [2], a CsI charged particle detector inside Gammasphere target chamber, in March Microball allows us to veto charged particle evaporation channels - Reaction used: 58 Ni( 45 Sc,3n) 100 In, e.g. 3p channel 100 Pd suppressed by >97% - Higher recoil rates possible [2] D.G. Sarantites et al., NIMA 381 (1996)

1) Have demonstrated that new method gives high selectivity on fast β-emitters, and provides ability to produce clean γ-ray spectra 2) Successful introduction of Microball to suppress charged particle channels, analysis of new 100 In data in early stages 3) Future: use system to study T z =-1 nuclei, produced in 2n evaporation channels, in region of rp-process e.g. 62 Ge Conclusions

Collaboration for 62 Ga G.Lotay 1, P.J. Woods 1, D. Seweryniak 2, M. Carpenter 2, C.J. Chiara 2, H.M. David 1, T. Davinson 1, C. Hoffman 2, R.V.F Janssens 2, D. Jenkins 3, T.L. Khoo 2, T. Lauritson 2, C.J. Lister 2, Z. Liu 1, E. A. McCutcheon 2, A. Rodgers 2, J.P. Wallace 1 and S. Zhu 2 Collaboration for 100 In C.J. Chiara 2, D. Seweryniak 2, W.B. Walters 4, M. Carpenter 2, H.M. David 1, C.N. Davids 2 T. Davinson 1, C. Hoffman 2, R.V.F Janssens 2, T.L. Khoo 2, T. Lauritson 2, C.J. Lister 2, Z. Liu 1, G.Lotay 1, E. A. McCutcheon 2,W. Reviol 5 A. Rodgers 2, D.G. Sarantites 5, P.J. Woods 1 and S. Zhu 2 1 University of Edinburgh, Edinburgh, EH9 3JZ, UK 2 Physics Division, Argonne National Laboratory, Argonne IL 60439, USA 3 Department of Physics, University of York, Heslington, York YO10 5DD, UK 4 Department of Chemistry and Biochemistry, University of Maryland, College Park MD 20742, USA 5 Department of Chemistry, Washington University, St. Louis MO 63130, USA