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Recoil Separator Techniques J.C. Blackmon, Physics Division, ORNL

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

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Recoil Separator Techniques J.C. Blackmon, Physics Division, ORNL

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

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

  3. Electrostatic deflector + dispersed no p dispersion p Br = q FMA at ATLAS E q 1 Vr = • s < nb 78Kr 2 64Zn m 135Tb q • very high selectivity An alternate approach Dipole magnet

  4. precoil ~ pbeam q <1 Some recoil separator properties *apertures only • High selectivity • Good energy acceptance • Modest angular acceptance • Well-suited for inverse kinematics

  5. Compact Windowless H2 Target Carbon foil MCP e- e- 50 (10-15 eV)cm2 - this measurement 74.3 (10-15 eV)cm2 - SRIM2003 Capture in Inverse Kinematics Length = 20 cm  1019 atoms/cm2

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

  7. Search for 180-keV resonance (p,g) reactions 17O(p,g)18F Oxygen ratios in presolar grains Galactic production of 17O Oxygen ratios in red giant atmostpheres Gamma rays from 18F decay in novae wgpg < 6 meV Dominate uncertainty for 1x108 K < T < 3x108 K Measure in inverse kinematics with a recoil separator?

  8. (4x10-8)*Incident 17O(p,g)18F in inverse kinematics Daresbury Recoil Separator 17O H2 680-keV resonance wg = 0.8 eV DE • clean identification of reaction products much more difficult as beam energy decreases DE+E

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

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

  11. 12C(a,g)16O SE1(300 keV) ~ SE2(300 keV) ~ 80 keVb Kunz et al. (01) • Need s(300 keV) ~ 0.1 fb mA 4He  4 fusions/month Plaga et al. (87) Azuma et al. (94) • limited by gamma backgrounds

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

  13. 12C(a,g)16O vs. inverse kinematics • Ecm > 1.4 MeV  recoil provides clear 16O tag • Ecm < 1.4 MeV DE-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 12C(a,g) fusion rate underground probably 10 times > inverse kin.

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

  15. (a,g) on N=Z nuclei • Important for understanding supernova nucleosynthesis • a-rich freeze-out, g-ray production (44Ti, 56Ni) • Sparse experimental information, especially for heavier nuclei • Statistical model calculations somewhat more uncertain due to low energy aN optical potentials. Rauscher et al. (00) • Some of these reactions have significant target issues (stability under high beam currents) • 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,g) 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. • 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 12C(a,g)16O 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 (a,g) 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 4He • High intensity heavy (A<40) ion beam & He jet target?

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