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 > 109 K, ρ ~ 106 g/cm3)

- Thermonuclear runaway

© David A. Hardy/www.astroart.org

The rp-process

http://www.nscl.msu.edu/~schatz/

- Extreme conditions allowunstable 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 1038 erg/s (105 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 0o by Argonne FMA

24MgTarget

40Ca 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

62Ge 62Ga 62Zn

τ1/2 ~ 100ms τ1/2 ~ 100ms

62Cu

τ1/2 ~ 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

62Ga62Ga

62Ga

Cou

nts

Cou

nts

Energy (keV)

Energy (keV)

Further increase in sensitivity using Microball

- Addition of the Microball [2], a CsI charged particle detector inside Gammasphere target chamber, in March 2011

- Microball allows us to veto charged particle evaporation channels

- Reaction used: 58Ni(45Sc,3n)100In, e.g. 3p channel 100Pd suppressed by >97%

- Higher recoil rates possible

[2] D.G. Sarantites et al., NIMA 381 (1996) 418-432

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 100In data in early stages

3) Future: use system to study Tz=-1 nuclei, produced in 2n evaporation channels, in region of rp-process e.g. 62Ge

Conclusions

Collaboration for 62Ga

G.Lotay1, P.J. Woods1, D. Seweryniak2, M. Carpenter2, C.J. Chiara2, H.M. David1, T. Davinson1, C. Hoffman2, R.V.F

Janssens2, D. Jenkins3, T.L. Khoo2, T. Lauritson2, C.J. Lister2, Z. Liu1, E. A. McCutcheon2, A. Rodgers2,

J.P. Wallace1 and S. Zhu2

Collaboration for 100In

C.J. Chiara2, D. Seweryniak2, W.B. Walters4, M. Carpenter2, H.M. David1, C.N. Davids2 T. Davinson1, C. Hoffman2, R.V.F Janssens2, T.L. Khoo2, T. Lauritson2, C.J. Lister2, Z. Liu1, G.Lotay1, E. A. McCutcheon2,W. Reviol5 A. Rodgers2, D.G.

Sarantites5, P.J. Woods1 and S. Zhu2

1University of Edinburgh, Edinburgh, EH9 3JZ, UK2Physics Division, Argonne National Laboratory, Argonne IL 60439, USA

3Department of Physics, University of York, Heslington, York YO10 5DD, UK4Department of Chemistry and Biochemistry, University of Maryland, College Park MD 20742, USA

5Department of Chemistry, Washington University, St. Louis MO 63130, USA