Post on 20-Jan-2016
Direct Reactions with ORRUBA and GRETINADirect 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 measurementsParticles 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 DensitiesLevel Densities
Level spacings as low as 20 keV
134Te(9Be,8Be)135Te
Example (d,pExample (d,p) measurements with CARIBU beams) 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 – TIARA Performance – 2424Ne(d,p)Ne(d,p)2525NeNe
2x105 pps 24Ne
1 mg/cm2 CD2 target
2 mm beam spot
TIARA PerformanceTIARA Performance
Only core signals from EXOGAM clovers,
limiting Doppler correction to 65 keV
broadening
pp
2x105 pps 24Ne
1 mg/cm2 CD2 target
2 mm beam spot
TIARA PerformanceTIARA Performance
pp
Only core signals from
EXOGAM clovers, limiting Doppler
correction to 65keV broadening
ORRUBA and GammasphereORRUBA and Gammasphere
25 mb cross section, 105 pps on 100g/cm2 CD2 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 GammasphereORRUBA 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 testsNovember 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 testsNovember 2011 – ANL tests
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 - coincidence measurement
November 2011 – ANL testsNovember 2011 – ANL tests
November 2011 – ANL testsNovember 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 ~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,) 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?
SummarySummary
TIARA SetupTIARA Setup
Forward Annular Si (S1+S2)5.6 < lab < 28
Backward Annular Si144 < lab < 168.5
Barrel Si36 < lab < 144
Target Changing Mechanism
BeamVAMOS
Targetposition
7878Zn(d,pZn(d,p))7979Zn at ISOLDEZn at ISOLDE
• ~3 MeV/A
• ~1x105 pps
• 60 – 70% 78Zn (Ga, Rb contaminants)
• CD2 targets (100 g/cm2 and 1 mg/cm2)
• ~8% efficiency
Si Si
Miniball +T-REX setupMiniball +T-REX setup
• ~8 clusters
(of 3 segmented crystals)
Proton singles spectraProton 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 standalonesORRUBA telescopes
Proton-gamma coincidencesProton-gamma coincidences
Excitation Energy from protons
Excitation Energy from protonsGamma ray energy
Gamma ray energy
Gam
ma
ray
ener
gy
LASER OFF
LASER ON LASER ON
LASER ON
PRELIMINARY