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Progress on DESCANT DE uterated SC intillator A rray for N eutron T agging

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##### Progress on DESCANT DE uterated SC intillator A rray for N eutron T agging

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**Paul Garrett**• University of Guelph • for the DESCANT Collaboration Progress on DESCANTDEuteratedSCintillatorArray for Neutron Tagging NEDAcollaboration meeting Valencia, November 3-5, 2010**Challenges of studies of n-rich nuclei at**RIB facilities Fusion-evaporation or reaction studies using n-rich beams • Low-beam currents • The best beams will have 109, and “good” beams will have 106 ions/s on target – much less than at stable beam facilities • Backgrounds from scattered beam • Must be able to characterize evaporation products in regions where little is known • On neutron-rich side, copious neutron evaporation, charged-particle exit channels suppressed • Some reactions wont have a sufficiently confined recoil cone for efficient detection in recoil separator • Want to make use of all available solid angle • Need for determination of neutron multiplicity**Examples of fusion-evaporation studies**1n gated 2n gated 2n gated with nearest-neighbour rejection 2n gated with nearest-neighbour rejection + TOF analysis Bentley et al., PRC 73, 024304 (2006).**DESCANT**• 70 irregular hexaconical detectors containing liquid deuteratedscintillator; each 15 cm deep • 5 different shapes in 5 rings to achieve close-packing • 20 x White Detector • 10 x Green Detector • 10 x Yellow Detector • 15 x Red Detector • 15 x Blue Detector**DESCANT**• Maximum angle subtended of 65.5o • 92.6% coverage of available solid angle or 1.08psr • Fast neutron tagging from 100’s of keV to ~10 MeV • Digital signal processing • Front face 50.0 cm from the centre of the sphere, back face at 65.0 cm • 4 basic shapes used : White, Red, Blue, Green • The Green and Yellow detectors are mirror images**The DESCANT Detectors**14.30 cm 13.45 cm 6.12 cm 11.65 cm 12.83 cm 13.40 cm 5.62 cm Green is truncated White shape 15.14 cm 12.22 cm 7.63 cm 4.79 cm**Test results from 10cm diameter, 2.5cm deep cell**with monoenergetic neutrons BC501A BC537 En = 3.0 MeV En = 4.3 MeV**PrototypeWhite Detector**• Received prototype June 2010 • Performed acceptance tests using g-sources and a Pu-Be neutron source • Measured neutron response function using mono-energetic neutron beam at University of Kentucky**Energy Resolution**• Measured energy resolution using 137Cs, 22Na and 60Co • Each source placed 30 cm from front face 137Cs 60Co Eres = 25.3% Eres = 25.6%**Time Resolution**• Measured with 60Co source using a fast plastic scintillator FWHM = 0.97 ns**n– Discrimination**• Measured using Pu-Be source placed 1 m from front face • Zero cross-over timing method • FWHMn = 54 chn • FWHMg = 27 chn • Dchannel = 98 chn g FOM= 1.2 n**Other performance tests**• Measured light collection across detector using 137Cs • Source placed directly on the front face at several locations • Measured effective change in gain due to count rate using 137Cs source • Count rate ranged between 4850 s-1 and 32800 s-1 • Noise level defined to correspond to a count rate of 10 counts s-1keVee-1 C / C ~ 1.5% C / C ~ 1.9% Noise Level = 17.3 keVee**Mounting of DESCANT to TIGRESS**• Support shell (nearly) monolithic – all detectors can be mounted into support shell from rear**DESCANT layout – option 1**• 70 element array • 8.9 cm radius opening for beam tube**DESCANT layout – option 2**• 65 element array • 24.3 cm radius opening for beam tube or auxiliaries**DESCANT layout – option 3**• 55 element array • 44.2 cm radius opening for beam tube or auxiliaries**TIG-4G Readout**• Readout of DESCANT detectors by custom built 12- bit 1GHz digitizers built to “TIG” standard • Anode pulse direct to TIG-4G via low-loss cable (LMR400) • On-board pulse-height, event time, and n-g discrimination determination • TIF-4G will be able to trigger DAQ**Real waveform analysis with 1GS/s**g events g+n events B/A**Timeline**• Prototype TIG-4G – Nov. 2010 • First production DESCANT detectors – Jan. 2011 • Delivery of 72 units – Sept. 2011 • Frame construction – Spring 2012 • Commissioning with 18O+13C reaction – late Spring/early summer 2012 • Funding • Canadian Foundation for Innovation – $665k • Ontario Research Fund – $665k • TRIUMF – frame design/construction ~ $370k • Costs • 72 BC537-filled detectors from St. Gobain – $880k • 18 modules TIG-4G – $130k • 2xVME64x crates, CAEN HV supplies, cables/connectors, misc. – $150k**DESCANT Collaboration**• University of Guelph • TRIUMF • University of Montreal: J. P. Martin • University of Kentucky: S. W. Yates, M. T. McEllistrem • Colorado School of Mines: F. Sarazin**Example: fusion evaporation**• Use the most n-rich beam available on a light target • Why a light target (i.e. C)? • The radioactive beams off a UC target are more n-rich than the fused systems • Heavier targets require more beam energy to get over Coulomb barrier – more neutron evaporation from final system so can’t get as neutron rich • C has good physical properties, easy and cheap to fabricate • Simple count rate estimate: • Nc=egetagNtNbs • Lets assume a 1 mg/cm213C target • Maybe we can think about a 14C target • With eg=0.2 and etag=0.2, and count rate of 1 min-1 • Nbs = 0.9×104 b/s • For a 10 mb cross section, we need ~1×106 ion/s • must have at least 109 yield in target (1010 better) • Calculations of neutron-rich beams assuming a 20 g/cm2 U target and 40 mA of proton beam • ALICE calculations of cross sections**Limits**Black line = limit of observation with a production yield of 109 in the U target, a 13C target, and at least 1 mb X-sec. Highlighted squares represent the highest-mass stable isotope. No attention paid to feasibility of producing required beams