Jun Chen Department of Physics and Astronomy, McMaster University, Canada For the McMaster-NSCL and McMaster-CNS collaborations (5.945, 3+ : **) (5.914, 2+/3+ : *) (5.678, 1+ : **) *: D. W. Bardayan et al. PRC. Vol.74, 2006 **: J. A. Caggiano et al. PRC. Vol.65, 2002 Study of Astrophysically important states in 26 Si with 27 Si(p, d) 26 Si * and p( 25 Al, p) 25 Al MOTIVATION At even higher temperatures (grey region in Fig.3) in supernova explosions, 26m Al will be excited to the higher levels by thermal excitation and then quickly gamma- decay to the ground state States in 26 Si in these Gamow windows need to be well understood in order to reduce the remaining uncertainty in the reaction rate (two experiments) Z N Stable Unstable    23 Na 24 Mg 25 Mg 26 Mg 25 Al 26 Al m 26 Al g 27 Al 26 Si 27 Si 28 Si 29 Si 25 Al(p,  26 Si EXPERIMENT ONE: 27 Si(p,d) 26 Si NSCL EXPERIMENT TWO: 25 Al+p elastic scattering with CRIB EXPERIMENT TWO: 25 Al+p elastic scattering with CRIB SeGA Ge array (17 detectors ) ‏ Beam blocker CH 2 target 26 Si 27 Si CH 2 target d 27 S i 26 Si excited 27 Si S800 Focal plane 25 Al beam made by the in-flight method using 24 Mg(d,n) 25 Al reation ~ 5×10 5 pps MeV/u on target Thick CH 2 targets (6.58 mg/cm 2 )‏ Scanned ~ 3.4 MeV in centre-of- mass energy (energy level up to ~ 8.9 MeV) Maximum proton energy ~ 13 MeV mg/cm 2 Carbon target used for background check Primary beam: 150 MeV/u 36 Ar Secondary beam: 89 MeV/u 27 Si Intensity of 1× 10 7 pps with purity of about 36% Target: 250 mg/cm 2 CH 2 foil Detectors: segmented germanium detector array (SeGA) detecting the gamma decay from 26 Si * in coincidence with the recoil at the focal plane (Fig.4) SUMMARY SUMMARY Two different experiments have been performed for the measurements of the astrophysical important states in 26 Si with the aim to reduce the remaining uncertainty in the 25 Al(p,γ) 26 Si reaction rate at nova temperatures. The final analysis for extracting the physical parameters is in progress. References: [1] D. W. Bardayan et al., Phys. Rev. C 65 (2002) [2] J. A. Caggiano et al., Phys. Rev. C 65 (2002) [3] Y. Parpottas et al., Phys. Rev. C 70 (2004) [4] D. W. Bardayan et al., Phys. Rev. C 74 (2006) [5] S. Kubono, Nucl. Phys. A 693 (2001) [6] A. H. Hernandez et al., NMB 143 (1998) [7] S. Kubono et al., Eur. Physi. J. A 13 (2002) [8] J.F. Ziegler, The Stopping and Ranges of Ions in Matter, vols. 3 and 5, Pergamon Press, Oxford, [9] A. M. Lane, and R. G. Thomas, Rev. Mod. Phys. 30 (1958) 257 Galactic 26 Al: important probe for interstellar medium, characterized by the emission of 1.8 MeV gamma rays from the decay of 26g Al (Fig.1)‏ 25 Al(p,γ) 26 Si bypasses the production of 26g Al in nova explosions (red region in Fig.3) since 26 Si decays through 26m Al without the emission of 1.8 MeV gamma rays (Fig.1 & Fig.2)‏ Fig.1: 1.8 MeV Gamma-ray emission from the ground state of 26 Al Fig.2: Reaction paths for 26 Al production in nova explosion Fig.3: Astrophysically important energy levels in 26 Si and its mirror nucleus. In the Gamow window at nova temperature (red region), states are uncertain in resonant energies and spin-parity assignments. Fig.4: Schematic of the spectrometer NSCL Set-up Results Set-up Fig.6: Doppler corrected gamma-ray spectrum Fig.7: A sample γ-γ coincidence spectrum for 1399 keV gamma ray SeGa arrays 90 o array 37 o array Target position Fig.5: Front view of the SeGA germanium detector arrays at NSCL Fig.7: Schematic of the CRIB spectrometer at CNS Fig.8: Configuration of the silicon detectors and PPACs in F3 chamber Forward scattering favored in inverse kinematics 3 ΔE-E telescopes for recoil PID and tracking (Fig.9 & Fig.10) 2 PPACs for beam tracking NaI detectors used above the target for detecting inelastic events Results Fig.9: PID for high energy protons penetrating the ΔE detector Fig.10: PID for low energy protons stopped in the ΔE detector Fig.11: Excitation function in the centre-of-mass frame Fig.12: A sample preliminary R-Matrix fit for resonance at E r = MeV, J π = 3 - Ongoing Analysis Extract cascades from the coincidence analysis Determine the energies and widths for found levels Make spin-parity assignments Calculate the new reaction rate 2 Ge detector arrays at 37 o and 90 o around the target position (Fig.5) 32 segments for each detector providing accurate 3D position for Doppler broadening correction of the measured gamma rays Extract energies, widths, and spin-parities from R-Matrix fits for all found resonances Calculate the new reaction rate The final excitation function was obtained by subtracting the carbon background in the CH 2 target as well as correcting for the energy loss of protons in the target which was simulated by using SRIM calculations. The R-Matrix fit is for single channel only and does not include the inelastic scattering. 89 MeV/nucleon radioactive 27 Si beam 849 keV 993 keV 1400 keV 1537 keV 1796 keV 2647 keV 2355 keV1987 keV 993 keV 1796 keV 2647 keV