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 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

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

Example (d,p  ) 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

TIARA Performance – 24 Ne(d,p) 25 Ne 2x10 5 pps 24 Ne 1 mg/cm 2 CD 2 target 2 mm beam spot

TIARA Performance Only core signals from EXOGAM clovers, limiting Doppler correction to 65 keV broadening p  2x10 5 pps 24 Ne 1 mg/cm 2 CD 2 target 2 mm beam spot

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

ORRUBA and Gammasphere 25 mb cross section, 10 5 pps on 100  g/cm 2 CD 2  1500 counts/day (singles) (~150 proton-  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

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

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 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 Digital Analog November 2011 – ANL tests Data also taken with Darek’s GRETINA digitizers (14 bit, 100 MHz) 228 Th source for calibration of the ORRUBA detectors, and 249 Cf was used to perform an  -  coincidence measurement

November 2011 – ANL tests

E(  ) ~5.9MeV E(  ) ~5.8 MeV Gamma Energy [keV] Alpha Energy [keV] Gamma-gated alpha spectra

Transfer experiments feasible with beams of ~10 5 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,  ) 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

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

78 Zn(d,p  ) 79 Zn at ISOLDE ~3 MeV/A ~1x10 5 pps 60 – 70% 78 Zn (Ga, Rb contaminants) CD 2 targets (100  g/cm 2 and 1 mg/cm 2 ) ~8%  efficiency Si

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

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

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