A New Decay Path in the C+16O Radiative Capture Reaction Institut Pluridisciplinaire Hubert Curien, Strasbourg, France
Outline Narrow Resonances, C +16O Detailed study of the C(16O,γ)28Si resonant radiative capture reaction Towards novel detection systems?
Resonant Structures Resonance phenomena at energies up to ~ 5 MeV per nucleon C+C, 14C+14C, 16O+16O, 24Mg+24Mg, 28Si+28Si C+16O system, narrow resonance Width 100-200 kev at the CB, low spin (0+-6+), at Ex(28Si) ~ 25 MeV Radiative capture reactions C(16O, )28Si, gamma decay through doorway states Molecular states and resonances Molecules and deformation : search for signatures in the decay Specificity of the gamma decay of resonant structures But / is (very) weak: 10-4 10-6 Experimentally Courtin Sandrine
C+16O, starting points Si breakup states into 28 C+16O C+16O cluster breakup states in 28Si up to EX = 45 MeV C.J. Metelko et al., J. Phys. G29 (2003), 697. Reaction C(20Ne,C16O) at ANL Dedicated equipment : Position Sensitive DSS RC Successful C+C study / doorway states S. Courtin et al.,fusion06, AIP Conf. Proc.853 (2006) 154. D.G. Jenkins et al., PRC76 (2007) 044310.
C+16O, theoretical predictions Hartree-Fock, GCM, cluster models, AMD Si(C-160) Ohkubo and Yamashita, Phys.Lett. B 578 (2004) 304. 28 Links between low-lying members of these cluster bands?
Radiative Capture and Heavy-Ions Nuclear Astrophysics, light particles Inverse kinematics Heavy Ions, a few systems only GSI, 90Zr(90Zr,γ)180Hg, = 40 pb, (J.G. Keller, K.H. Schmidt et al. PRC 29, 1569 (1984)) Argonne, 89Y(90Zr,,γ) Au, (F. Camera et al., PLB 560, 155 (2003)) 179 Light heavy-ions : C+C -> 24Mg + γ and C+16O -> 28Si + γ Sandorfi et al. (Brookhaven ~ 1980) Resonances NaI, Eγ > 18 MeV, no recoil, deexcitation to the low-lying states of and 28Si Mg, 24
C+16O experimental study To the ground state band Capture cross-sections To the prolate excited band C(16O,γ)28Si 16 O, 10 pna C, 40 µg.cm-2 ECM = 8.5, 8.8, 9 MeV A.M. Sandorfi, in Treatise on Heavy-Ion Science, D.A. Bromley, Vol II, sec. 3. M.T. Collins, A.M. Sandorfi and D.H. Hoffmann, Phys.Rev. Lett. 49 (1982), 1553
C+C and C+16O experimental studies DSSSD Recoil spectrum Si 28 D.A. Hutcheon et al., NIM A 498, 190 (2003). First Stage Second Stage ISAC I : RNBs / Stable (OLIS) 0 spectrometer Tof on 17 m Beam rejection 1013 Acceptance : cone ½ angle 20 mrad gas/solid target system recoil detectors (DSSSD, ) BGO array (ε = 50 % @ 5 MeV)
C+16O results of the Dragon experiment 2+ 0+ 3-0+ 4+ 2+ ~ 14 MeV E1(MeV) BGO spectrum ECM = 8.5 MeV E0(MeV) E0(MeV) E*(28Si) ~ 25 MeV 10 11 MeV states involved in the decay <fold> = 2.5 cascades 3- state strongly fed directly (p-h excitation) Complexity of Dragon s acceptance simulations to obtain quantitative results (GEANT)
Fusion process C+16O fusion cross-section Normalized Triumf data σ ECM = 8.5 MeV ECM = 8.8 MeV ECM = 9. MeV Spin ECM(MeV) E0(MeV)
Monte-Carlo simulations vs data, C+16O Resonance Jπ = 0+,1-, 2+, 3-, 4+, 5-, 6+ Ex : Jπ = 0+ 25 MeV n 0+ only αα p Ne 19.3 MeV 20 α 10 MeV 9.3 MeV Mg 24 E0(MeV) simulation Si 28 experiment Counts g.s. Very well known sd shell nucleus E0(MeV)
Monte-Carlo simulations vs data, C+16O Entrance spin distribution for fusion 28 Si known states / branching ratios Mean Γγ (E1), (M1), (E2) E0(MeV) Entrance spin mixing 5- - 6+ simulation simulation experiment experiment E0(MeV)
States fed in the decay 16 MeV gated 7.2 MeV 7.2 MeV E0(MeV) Direct feeding of the 43+ (prolate) at 9.164 MeV? 4+3 9.2 MeV 2+1 1.8 MeV g.s. Si 28 E1(MeV) 25 MeV E0(MeV)
Status Cascade decay Compound nucleus deexcitation (1p, 1α ), statistical calculations Role of the isospin in the decay in this N = Z nucleus? Resonances strongly correlated to 28 Si states Large part of the flux via states around 10-11 MeV (α threshold = 9.3 MeV) Si well known sd shell nucleus / detected at the focal plane (g.s.) simulations 28 States with a specific structure (3-, 4+)? Decay of the resonances : link with molecules at lower energies, astrophysics factor
What s next? Needs Low cross-sections (σ ~10 nb ) Recoils @ 0 Large range of γ-ray energies Multistep decays / which states? Near future FMA + Gammasphere project? Dragon + Tigress project? Mean / long term γ-array with high efficiency and and good resolution (ex LaBr3(Ce))
PARIS - Photon Array for studies with Radioactive Ions and Stable beams www.paris.ifj.edu.pl A. Maj et al. / 42 labs. / SPIRAL2 Novel type of calorimeter / LaBr3 + CsI? Eγ = 100 kev 50 MeV Cubic / Spherical designs under study LaBr CsI GEANT4 simulations Different possibilities / spherical design
PARIS - Photon Array for Studies with Radioactive Ions and Stable Beams www.paris.ifj.edu.p GEANT4 simulations, first step LaBr + CsI spherical PARIS (LaBr3 layer) vs BGO array Eγ = 20 MeV (RC) BGO array PARIS
Collaboration S. Courtin, D. Lebhertz, F. Haas, A. Michalon, C. Beck, M. Rousseau, M.- D. Salsac IPHC, Strasbourg, France D.G. Jenkins, P. Marley, B. Fulton University of York, United-Kingdom C.J. Lister Argonne National Laboratory, USA D.A. Hutcheon and the DRAGON collaboration Triumf, Vancouver, Canada