Greta with in-flight separated fast beams

Transkripsi

1 Greta with in-flight separated fast beams SeGA Greta ε γ (1.3 MeV): 2% 55% Resolution x 1/5 Count rate examples for CCF, SCF (200 MeV 238 U, 100 kw) Physics examples Evolution of nuclear shells and details of wave function in exotic nuclei 78 Ni, 100 Sn Evolution of proton- and neutron collectivity in exotic nuclei Greta WS 2006 FSU 1

2 Evolution of nuclear shells and details of wave function Single-nucleon knockout and two-nucleon knockout Wave function information on hole states in weakly and deeply bound systems extending (e,e p) work on stable targets (orbital angular momenta, spectroscopic factors) Single-nucleon pickup Wave function information on particle states (orbital angular momenta, spectroscopic factors) Under development g-factor measurements Transfer reactions with thick targets (d,pγ) Greta WS 2006 FSU 2

3 Greta advantage: Single particle states around 78 Ni Greta at CCF: maybe hole states 9 Be( 78 Ni, 77 Ni)X, beam rate 0.02 Hz 9 Be( 78 Ni, 77 Co)X 78 Ni Greta at SCF: hole states, particle states 9 Be( 78 Ni, 79 Ni)X, beam rate 9 Hz 9 Be( 78 Ni, 79 Cu)X Greta WS 2006 FSU 3

4 Greta advantage: Single particle states around 100 Sn Greta at SCF: hole states 9 Be( 100 Sn, 99 Sn)X, beam rate 2 Hz 9 Be( 100 Sn, 99 In)X Greta at RIA: particle states 9 Be( 100 Sn, 101 Sn)X, beam rate 25 Hz 100 Sn Greta WS 2006 FSU 4

5 Slowed beams: High-velocity transient field method Perturbation of γ-ray angular distribution by Δθ due to interaction of magnetic moment (g=μ/i) in large hyperfine field external field φ. Δθ = gφ μ φ = h N T T 2 1 B tf ( t) e t τ dt magnet beam SeGA arrangement detection of Doppler-shifted gamma rays and angular distribution measurements The high-velocity transient field method uses a thick Au interaction target that serves to both slow down and Coulomb excite the secondary beam. The Fe layer is polarized and induces the transient field Energy (MeV/A) Fast ion Davies et al., Phys. Rev. Lett. 96, (2006) Au Fe Slowed ion Greta WS 2006 FSU 5

6 Evolution of proton- and neutron collectivity in exotic nuclei Intermediate-energy Coulomb excitation Transition matrix elements (E1, E2, E3, possibly M1) to low-lying excited states provides measure of proton collectivity Proton scattering Transition matrix elements provide measure of mainly neutron collectivity with some proton collectivity admixed (depends on energy) Combination with e.m. probe or isoscalar probe allows isolation of proton and neutron collectivity Lifetime measurements with plunger ( Kris Starosta s contribution) Transition matrix elements Greta WS 2006 FSU 6

7 Greta advantage: Collectivity around 78 Ni and 100 Sn Greta at CCF: Coulex and proton scattering on 104 Sn and possibly 102 Sn Greta at SCF: Coulex and proton scattering on 50 Ni 80 Ni and 100 Sn Greta WS 2006 FSU 7

8 γ-ray detection with fast (v=0.4c) rare-isotope beams Clean trigger event-by-event (need 0-deg spectrometer) Luminosity gain over low-energy beam due to thick target Trend towards longer experiments to answer very focused science questions Raises capacity question Multiple experiments at once in same setup Incoming beam PID Reacted beam PID Greta WS 2006 FSU 8

9 Greta advantage: Added Value in detailed spectroscopic information in all experiments γ-ray angular distributions Transition multipolarities γ-ray polarization Parity changes l I i I f I ii SeGA example Data: γ-ray transition in Coulomb excitation of 40 Ar (absolute measurement and calculation) H. Olliver et al. PRC 68 (2003) , PRC 69 (2004) Greta WS 2006 FSU 9

10 48 Ca fragments + Hydrogen (80 mg/cm 2, 1mm liquid) at 95 MeV/nucleon Incoming beam PID About 20 different incoming fragments C.M. Campbell et al. PRL (2006) in print Greta WS 2006 FSU 10

11 48 Ca fragments + Hydrogen (80 mg/cm 2, 1mm liquid) at 95 MeV/nucleon Gated on incoming 40 S - Reacted beam PID in S800 About 3-4 channels per incoming fragment Greta WS 2006 FSU 11

12 48 Ca fragments + Hydrogen (80 mg/cm 2, 1mm liquid) at 95 MeV/nucleon Gated on incoming 40 S Gammas in coincidence with identified reacted beams Greta WS 2006 FSU 12

13 Greta advantage: Increase in scientific capacity For each experiment there will be many parasitic channels Example here About 20 different incoming fragments About 3-4 channels per incoming fragment Greta s increase in efficiency and angular resolution over SeGA will provide enough sensitivity to study also the weaker channels, taking advantage of all rare isotopes transmitted and reaction products detected. Multiple observables per run, collider model Amortize high cost of long, focused experiments Greta highly leverages investment in facility Greta WS 2006 FSU 13