1. 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

2. 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

3. 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, (2006).

4. 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

5. 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

6. The DESCANT Detectors 14.30 cm 13.45 cm 6.12 cm 11.65 cm 12.83 cm
Green is truncated White shape
12.22 cm
7.63 cm
4.79 cm

7. Test results from 10cm diameter, 2
Test results from 10cm diameter, 2.5cm deep cell with monoenergetic neutrons
BC501A
BC537
En = 3.0 MeV
En = 4.3 MeV

8. Prototype White 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

9. 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%

10. Time Resolution
Measured with 60Co source using a fast plastic scintillator
FWHM = 0.97 ns

11. n– Discrimination g FOM = 1.2 n
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

12. 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 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

13. Mounting of DESCANT to TIGRESS
Support shell (nearly) monolithic – all detectors can be mounted into support shell from rear

14. Mounting of DESCANT detectors

15. DESCANT layout – option 1
70 element array
8.9 cm radius opening for beam tube

16. DESCANT layout – option 2
65 element array
24.3 cm radius opening for beam tube or auxiliaries

17. DESCANT layout – option 3
55 element array
44.2 cm radius opening for beam tube or auxiliaries

18. 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
Thank-you!

19. DSP for n-g determination

20. Real waveform analysis with 1GS/s
g events
g+n events
B/A

21. Timeline Funding Costs 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

22. 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

25. 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

26. 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