Progress on DESCANT DEuterated SCintillator Array for Neutron Tagging

Paul Garrett

University of Guelph

for the DESCANT Collaboration

NEDA collaboration 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 deuterated scintillator; 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 1.08p sr

• 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

11.65 cm

14.30 cm 13.45 cm

6.12 cm

5.62 cm

12.83 cm 13.40 cm

12.22 cm

15.14 cm

7.63 cm 4.79 cm

Green is truncated White shape

En = 3.0 MeV

BC537

BC501A

Test results from 10cm diameter, 2.5cm deep cell with monoenergetic neutrons

En = 4.3 MeV

• 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

Prototype White Detector

Energy Resolution

• Measured energy resolution using 137Cs, 22Na and 60Co

• Each source placed 30 cm from front face

137Cs60Co

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

FOM = 1.2

g

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-1 keVee-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

Mounting of DESCANT detectors

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

DSP for n-g determination

c

tbt

at

CeBeAeNtL

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/cm2 13C 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