Charge Exchange reactions with Unstable Nuclei

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1 Charge Exchange reactions with Unstable Nuclei Sam Austin and Remco Zegers Sam Austin, Daniel Bazin, Alex Brown, Christian Diget, Alexandra Gade, Carol Guess, Marc Hausmann, Wes Hitt, Meredith Howard, Michael King, Rhiannon Meharchand, David Miller, Shumpeji Noji, Yoshi Shimbara, Kris Starosta, Clarisse Tur, Phil Voss, Dirk Weishaar, John Yurkon, Remco Zegers

2 (n,p)-type Charge-exchange Probes Forward kinematics (stable targets) (n,p) reaction (d, 2 He) reaction (t, 3 He) reaction ( 7 Li, 7 Be) reaction ( 12 C, 12 N) reaction ( reaction ( 12 B, 12 C) reaction Need to extract: excitation energy angular distributions Must be: background free single step, direct reaction Inverse kinematics (rare isotopes) (p, n)-two applications (d, 2 He) reaction ( 7 Li, 7 Be) reaction Motivations Nuclear structure studies Gamow-Teller transitions Astrophysics electron capture rates in stellar evolution

3 Inverse Kinematics For p( 56 Ni, 56 Cu)n Charge Exchange B(GT - ) =B(GT + ) ΔE = 1 MeV Need to cover broad range of angles, observe low energy neutrons. Approved experiment at NSCL, run early next year

4 LENDA--Low-Energy Neutron Detector Array 24 plastic scintillators (2.5x4.5x30cm) Neutrons > 150 kev E 20 kev for E n =200 kev lab < 2 o Efficiency >30% for E n <4 MeV Construction finished Summer 2009 G. Perdikakis, et al, IEEE Transactions On Nuclear Science, 56, 1174 (2009) 4

5 LENDA Response 252 Cf Cutoff 130 kev G. Perdikakis, IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 56, NO. 3, JUNE 2009

6 EC Strength from A(p, n) Charge Exchange Ni(p,n) Example Analog Transitions Ni (p,n) Decay T forbidden Problem no isospin meter. Use inelastic scattering to identify T > states. σ(p n)/σ(p, p ) to analogs depends on isospin, always differs by at least x 2 Fujita et al. have studied in detail. Requires good resolution to identify states.

7 60 Ni(p, n) 60 Cu(T > ) IUCF Caurier et al LSSM has no strong states below 1.5 MeV?? Can one achieve sufficient statistics and resolution for unstable nuclei Anantaraman et al., Phys.Rev.C78:065803,2008 7

8 Si via 7 Li ( P, Si) 7 Be + Neighboring the island of inversion Ground-state is sd-like but low-lying pf-intruders Study the intrusion/mixing of the pf-shell into the sd shell

9 The ( 7 Li, 7 Be+ ) reaction Proportionality between GT cross section and B(GT) Calibrate with -decay The transition to the excited state provides a spin-transfer filter Good B(GT)- GT 65 AMeV S. Nakayama et al., PRC 60, (1999)

10 Experimental principle 7 Li ( P, Si) 7 Be + Si-S800 ( 7 Li, 7 Be+ ) SeGA P beam

11 Experiment

12 S800 Beam line operated in dispersion matched mode P 14+) (H-like) charge state convenient to determine: energy scale energy resolution 1:00 (1 MeV) angular resolution ~1 mrad FWHM (dispersive) 20 mrad FW (non-dispersive) Particle ID ΔE vs TOF P 14+ Si 33 Si Most Si events are not result of CE more complex reactions need tag TOF relative to RF

13 BarrelSeGA P Si SeGA ( 7 Li target) Based on simulation by P. Mantica 15 detectors close to target High efficiency = 12% main aim: 7 Be 430 kev line Si Doppler shifted lines Resolution for Doppler broadened lines: 6-8% at 1 MeV large beam spot on target closeness of detectors to target 2x10 6 pps on target 77% DAQ lifetime

14 P( 7 Li, 7 Be+ ) Si * γ s from SeGa (lab frame) Proof of Principle The 430 kev gamma tag isolates S = 1 transitions Si line shapes well described by simulations (not shown) 2+, 5.33 MeV, From S800 SI From S800 14

15 Conclusions The ( 7 Li, 7 Be+ ) reaction in inverse kinematics can be used as tool to extract GT strength distributions in the (n,p) direction for unstable nuclei. The GT strength distribution for P Si was extracted via the P( 7 Li, 7 Be+ ) reaction in inverse kinematics.

16 Outlook Next experiment coming up! Improvements for future experiments: Better angular resolution Short-term solution-clever tuning-focus before target Long-term solution: high-rate tracking (diamond detectors?) S800-7 Be(430 kev) - ejectile -coincidences Would allow for correction of decay-in-flight effects Better reconstruction of -decay scheme Heavier RI beams (astrophysics/giant resonances) Improvement in dispersion matching is a challenge Probably need combination with tracking Need to deal with high charge-state yield (S800 hodoscope?) Measurements above neutron-decay threshold: Measure decay neutrons (MoNA) Improvement of reaction theory General for composite CE probes

17 Experiment Y. Fujita, M. Fujiwara, H. Ejiri, T. Adachi et al. (Osaka/RCNP), H. Sakai, S. Shimoura, et al. (Univ. of Tokyo), Y. Shimbara (NSCL, now Niigata U.) D. Frekers et al. (Univ. of Münster), M. Harakeh (KVI) Jenna Deaven, Carol Guess, Rhiannon Meharchand, Du Nguyen, Amanda Prinke, LeShawna Uher Wes Hitt (MSU Students) S. M. Austin, D. Bazin, A. Cole[now Kalamazoo], A. Gade, B.M. Sherrill, K. Starosta, D. Weisshaar, Remco Zegers(MSU) Theory M. Horoi (CMU), B.A. Brown (MSU) G. Colo, S. Fracasso (Milano) Astrophysics E. Brown, D. Chamulak (MSU) S. Gupta (MSU, now LANL) Those involved NSF PHY & PHY (JINA) 17