Radiative Capture Reaction

Transcription

1 A New Decay Path in the C+16O Radiative Capture Reaction Institut Pluridisciplinaire Hubert Curien, Strasbourg, France

2 Outline Narrow Resonances, C +16O Detailed study of the C(16O,γ)28Si resonant radiative capture reaction Towards novel detection systems?

3 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 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: Experimentally Courtin Sandrine

4 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)

5 C+16O, theoretical predictions Hartree-Fock, GCM, cluster models, AMD Si(C-160) Ohkubo and Yamashita, Phys.Lett. B 578 (2004) Links between low-lying members of these cluster bands?

6 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

7 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

8 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)

9 C+16O results of the Dragon experiment ~ 14 MeV E1(MeV) BGO spectrum ECM = 8.5 MeV E0(MeV) E0(MeV) E*(28Si) ~ 25 MeV 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)

10 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)

11 Monte-Carlo simulations vs data, C+16O Resonance Jπ = 0+,1-, 2+, 3-, 4+, 5-, 6+ Ex : Jπ = 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)

12 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 simulation simulation experiment experiment E0(MeV)

13 States fed in the decay 16 MeV gated 7.2 MeV 7.2 MeV E0(MeV) Direct feeding of the 43+ (prolate) at MeV? MeV MeV g.s. Si 28 E1(MeV) 25 MeV E0(MeV)

14 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 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

15 What s next? Needs Low cross-sections (σ ~10 nb ) 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))

16 PARIS - Photon Array for studies with Radioactive Ions and Stable beams 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

17 PARIS - Photon Array for Studies with Radioactive Ions and Stable Beams GEANT4 simulations, first step LaBr + CsI spherical PARIS (LaBr3 layer) vs BGO array Eγ = 20 MeV (RC) BGO array PARIS

18 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