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