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Direct Reactions with ORRUBA and GRETINA

Direct Reactions with ORRUBA and GRETINA. Steven D. Pain Oak Ridge National Laboratory. GRETINA Workshop, ANL, February 2013. Particles and gamma rays in coincidence in direct measurements. Measure excitation energies of unknown states to a much higher precision Extra tag for selectivity

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Direct Reactions with ORRUBA and GRETINA

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  1. Direct Reactions with ORRUBA and GRETINA Steven D. Pain Oak Ridge National Laboratory GRETINA Workshop, ANL, February 2013

  2. Particles and gamma rays in coincidence in direct measurements • Measure excitation energies of unknown states to a much higher precision • Extra tag for selectivity • In nuclei with a sufficiently high level density, gammas provide a handle on which states are populated, constraining the analysis of the particle spectra (probe fragmentation of single-particle strengths) • Measure through which states the states populated decay (branching ratios), knowing the populated state from the particle energy • Allows (statistics dependent) gamma-gamma analysis to be employed • Surrogate measurements • Not just (d,p) measurements! Other light-ion transfer reactions (pickup, two-nucleon transfer), transfer reactions using heavy-ion targets (proton transfer), light-ion inelastic scattering, … Study particle and hole states in same experiment

  3. Level Densities Level spacings as low as 20 keV 134Te(9Be,8Be)135Te

  4. Example (d,pg) measurements with CARIBU beams Example - track the fragmentation of SP energies along the Xe chain Measurement of particle and hole states at same time Factor of ~2 below GS in efficiency

  5. TIARA Performance – 24Ne(d,p)25Ne 2x105 pps 24Ne 1 mg/cm2 CD2 target 2 mm beam spot

  6. TIARA Performance Only core signals from EXOGAM clovers, limiting Doppler correction to 65 keV broadening g 2x105 pps 24Ne 1 mg/cm2 CD2 target 2 mm beam spot p

  7. TIARA Performance Only core signals from EXOGAM clovers, limiting Doppler correction to 65keV broadening g p

  8. ORRUBA and Gammasphere 25 mb cross section, 105 pps on 100mg/cm2 CD2 1500 counts/day (singles) (~150 proton-g coincidences per day) Improved particle resolution compared to TIARA, T-REX, etc (improved angular resolution, larger barrel) Heavy recoils in < 1 degree cone Recoil tagging (fast ionization counter, PPAC, MCP, diamond, FMA) for mixed beams

  9. ORRUBA and Gammasphere • Equipment development time proposal accepted (April 2011) • 4 (+2) days • End cap detector • Compact recoil detector ORRUBA 173 mm chamber radius

  10. November 2011 – ANL tests • In preparation for the equipment development beam time: a trip to Argonne in November 2011 to run source tests • Three types of ORRUBA detector (65um NR, 500um R and 1000um R) • GS chamber mount for standard configuration • Aims • physical checks • resolution checks • readout/instrumentation checks • GS coincidence checks

  11. November 2011 – ANL tests Signals run the length of the FMA (2 x 25 ft cables) Instrumented with RAL shaping amplifiers, and CAMAC ADCs of Darek Sewerniak Data also taken with Darek’s GRETINA digitizers (14 bit, 100 MHz) 228Th source for calibration of the ORRUBA detectors, and 249Cf was used to perform an a-g coincidence measurement Digital Analog

  12. November 2011 – ANL tests

  13. November 2011 – ANL tests Gamma-gated alpha spectra E(a) ~5.8 MeV E(a) ~5.9MeV Gamma Energy [keV] Alpha Energy [keV]

  14. Transfer experiments feasible with beams of ~105 pps (or lower!) Combined high-resolution particle array and high-resolution gamma-ray array critical for the full utilization of RIBs Level assignments and simple decay schemes Tool for using surrogate methods for informing statistical (n,g) cross sections Improved resolution Improve on excitation energy measurements Push transfer experiments to nuclei with higher level densities Coupling ORRUBA to Gammasphere could be a stepping stone to coupling an array to Gretina Both have large internal radii, avoiding compromising the performance of the particle array Improved Doppler-corrected resolution of Gretina will increase resolving power What more do we need beyond current arrays? Space constraints could be quite tough for a highly segmented array (eg sORRUBA) Acquisition merging challenges Forward angle detectors for pickup reactions Recoil detector(s) Ge + Si + recoil + gas jet target? Summary

  15. TIARA Setup Barrel Si 36 < lab < 144  Target Changing Mechanism Beam VAMOS Target position Forward Annular Si (S1+S2) 5.6 < lab < 28  Backward Annular Si 144 < lab < 168.5 

  16. 78Zn(d,pg)79Zn at ISOLDE • ~3 MeV/A • ~1x105 pps • 60 – 70% 78Zn (Ga, Rb contaminants) • CD2 targets (100 mg/cm2 and 1 mg/cm2) • ~8% g efficiency Si Si

  17. Miniball +T-REX setup • ~8 clusters • (of 3 segmented crystals)

  18. Proton singles spectra ORRUBA standalones ORRUBA telescopes PRELIMINARY d p • Si telescopes forward and backward of 90° (140 mm dE and 1000 mm E) • Annular endcap at backward angles (d,p) d elastics p

  19. Proton-gamma coincidences PRELIMINARY LASER ON LASER ON Gamma ray energy Excitation Energy from protons Gamma ray energy LASER OFF LASER ON Gamma ray energy Excitation Energy from protons

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