1. Recoil Separator Techniques J.C. Blackmon, Physics Division, ORNL RMS - ORNL WF QT QD Q D Target FP ERNA - Bochum WF Target D QT FP DRS ORNL QD VF D VAMOS GANIL ã Recoil separator basics DRAGON ISAC ã How do recoil separators compete? ã Why underground?

2. ã Combination of magnetic and and electrostatic elements that spatially disperse charged reaction products by m/q What is a recoil separator? Dipole magnet B  = p q ã SPIRAL at GANIL ã large acceptance ã rotatable 6 m Wien filter E B = p m + dispersed q m no p dispersion

3. An alternate approach Dipole magnet B  = p q + Electrostatic deflector E q V  = 1 2 dispersed q m no p dispersion FMA at ATLAS ã very high selectivity 78 Kr 64 Zn 135 Tb   < nb

4. Some recoil separator properties ã High selectivity ã Good energy acceptance ã Modest angular acceptance ã Well-suited for inverse kinematics p recoil ~ p beam  <1  *apertures only

5. Capture in Inverse Kinematics Carbon foil MCP e-e- e-e- Compact Windowless H 2 Target 50 (10 -15 eV)cm 2 - this measurement 74.3 (10 -15 eV)cm 2 - SRIM2003 Length = 20 cm  10 19 atoms/cm 2

6. What might be studied underground? 12 C( ,  ), 16 O( ,  ) Supernovae ~ He burning 20 Ne, 24 Mg, 28 Si, 32 S, 36 Ar, 40 Ca( ,  ) Supernova nucleosynthesis 14 N( ,  ) 18 O( ,  ) 22 Ne( ,  ) AGB stars ~ s process 14 N(p,  ) 17 O(p,  ) 17 O(p,  ) Red giants ~ CNO cycle 22 Ne(p,  ) 23 Na(p,  ) 24 Mg(p,  ) Globular clusters ~ Ne/Mg/Na cycles

7. (p,  ) reactions 17 O(p,  ) 18 F Oxygen ratios in presolar grains Galactic production of 17 O Oxygen ratios in red giant atmostpheres Gamma rays from 18 F decay in novae Search for 180-keV resonance  p  < 6  eV Dominate uncertainty for 1x10 8 K < T < 3x10 8 K Measure in inverse kinematics with a recoil separator?

8. 17 O H2H2 17 O(p,  ) 18 F in inverse kinematics Daresbury Recoil Separator EE  E+E  = 0.8 eV (4x10 -8 )*Incident 680-keV resonance ã clean identification of reaction products much more difficult as beam energy decreases

9. Beam rejection at low energies 10 -8 * 1 p  A  60 kHz 21 Na(p,  ) @ 220 keV/u (Bishop et al.) ã recoil-gamma coincidence  High selectivity without Z identification

10. (p,  ) vs. inverse kinematics ã Energies < 200 keV/u ã gamma detection required in both cases ã no Z identification of heavy ion ã separator TOF can tag events of interest ã large recoil angle - transmission difficult ã poor beam suppression  high FP count rate   A of HI beam vs. mA of protons It is difficult for inverse kinematics to compete with a high current proton accelerator underground.

11. 12 C(  ) 16 O Kunz et al. (01) Plaga et al. (87) Azuma et al. (94) S E1 (300 keV) ~ S E2 (300 keV) ~ 80 keV  b ã limited by gamma backgrounds mA 4He  4 fusions/month  Need  (300 keV) ~ 0.1 fb

12. 4 He( 12 C,  ) 16 O with a recoil separator 3x10 -10 E cm = 3.2 MeV How low in E cm can this technique be pushed?

13. ã E cm > 1.4 MeV  recoil provides clear 16 O tag ã E cm < 1.4 MeV  E-E identification of recoil Z is lost Increasing recoil cone must be accepted Beam suppression is more difficult If 10 -10 beam suppression & 1000 cosmics/day  10 recoil-gamma background events/day 12 C(  ) fusion rate underground probably 10 times > inverse kin. 12 C(  ) 16 O vs. inverse kinematics

14. 12 C(  ) 16 O - My perspective ã Unique astrophysical importance ã Measurements in inverse kinematics will clearly improve our understanding ã Measurements in inverse kinematics will not measure the cross section near the Gamow window anytime soon  (  ) measurements above ground are limited by ambient backgrounds ã Measurements underground would clearly be a substantial improvement ã Issues: Level of beam induced background Robustness of solid carbon targets  Would measuring 4 He( 12 C  ) 16 O underground be more sensitive than 12 C(  ) 16 O? More robust/stable target, less background ( 13 C)

15. (  ) on N=Z nuclei ã Important for understanding supernova nucleosynthesis  -rich freeze-out,  -ray production ( 44 Ti, 56 Ni) ã Sparse experimental information, especially for heavier nuclei  Statistical model calculations somewhat more uncertain due to low energy  N optical potentials. Rauscher et al. (00) ã Some of these reactions have significant target issues (stability under high beam currents) ã Measurement with a heavy ion beam on an alpha target could be easier and cleaner

16. Conclusions  It is difficult for recoil separator measurements of (p,  ) reactions to compete with high-intensity proton beams for stable targets due to the very low energies. A compelling case can clearly be made for measuring these reactions underground. ã LUNA and other facilities have the capability to measure these reactions, but the list of interesting measurements is extensive, and the pace of measurements is slow.  Improvements in our understanding of 12 C(  ) 16 O will be made through measurements in inverse kinematics above ground. However, these measurements are exponentially more difficult at low energies. Measurements at an underground facility are compelling and should be vigorously pursued.  The capability to measure such (  ) reactions at low energies currently does not exist anywhere. A strong case can be made for a new underground accelerator facility to address this important physics.  mA beam of 4 He  High intensity heavy (A<40) ion beam & He jet target?