jason hodges, yacouba diawara, cai-lin wang, rick riedel · 2013. 2. 15. · 3 managed by...
TRANSCRIPT
n-Source Needs
Jason Hodges, Yacouba Diawara, Cai-Lin Wang, Rick Riedel
Instrument and Source Design Division, Oak Ridge National Laboratory
August 1st, 2012
2 Managed by UT-Battelle for the U.S. Department of Energy Presentation_name
He3-Shortage
• Major Uses
– neutron scattering instruments
– portal monitors (US & overseas)
• ‘Gold Standard’ Characteristics
– high detection efficiency
– good gamma discrimination
– nontoxicity (cf. alt. BF3)
– detector stability
– low cost prior to shortage
3 Managed by UT-Battelle for the U.S. Department of Energy Presentation_name
He3 Production & Demand
• US Production
– Decay 6% / yr of H3 in US NNSA tritium stockpile (1980-95, 2003-08)
– Reduction in nuclear weapons has reduced supply of He3
– Estimated annual production 2011-18 is 8,000-10,000 liters
• US Demand
– Large SNS instrument requires ~ 7,000 liters
– DOE has a modest stockpile for neutron detectors
– Portal monitor ~45 liters each
– Policy committee eliminated allocation of He3 for domestic portal monitors FY2010
– US annual deficit expected to be ~5,000 liters, yrs 2011-18
• Extremes in Pricing, World [May 2011, Physics Today]
– Prior to shortage: US ~$100 liter
– Current: US $600 government, $1000 commercial
– March 2011: UK supplier ~$4500 liter
4 Managed by UT-Battelle for the U.S. Department of Energy Presentation_name
Large Scale Themes for US n-Source
Detector Development
NB: Spallation source instruments – are all Time-of-Flight (ToF) instruments
Reactor source instruments – mainly nonToF instruments but some are ToF
• He3-alternative technologies whenever possible
• 1 microsecond time resolution \ event based detection mode
– Required for all ToF instruments
– Vast majority of detector modules will be for Spallation sources, therefore ToF
– Event time stamping detectors can be used at non-TOF instruments
– Event detection leads to highest possible dynamic range and background suppression
– Event based corrections are applicable to all instruments
• Changing conditions at sample, source
• Stroboscopic experiments
5 Managed by UT-Battelle for the U.S. Department of Energy Presentation_name
5
6 Managed by UT-Battelle for the U.S. Department of Energy Presentation_name
Detector Characteristics?
- Brief Survey of ORNL Instruments
Pixel dimension (mm)
Array size (m^2) High Eff.
Beamline Name < 1.0 ~ 5.0 ~ 10.0 ~ 0.3 ~ 1.0 > 2.0 l < 1Å
1B NOMAD X X X
2 BASIS X X
3 SNAP X X
4A MagRef X X
4B LiqRef X X
5 EQ-SANS X X X
6 CNCS X X
7 VULCAN X X X
8 VENUS X X
9 CORELLI X X X
11A POWGEN X X X
11B MaNDi X X X
12 TOPAZ X X X
14B HYSPEC X X
15 NSE X X
16B VISION X X X
17 SEQUOIA X X
18 ARCS X X X
CG2 Gen-SANS X X
CG3 Bio-SANS X X
HB-1 Pol-TAS X X
HB-1A TAS X X
HB-2A NPD X X X
HB-2B NRSF2 X X
HB-3 TAS X X X
HB-3A 4C-SCD X X
CG-4C Cold-TAS X X
CG-4D IMAGINE X X
HB-2C WAND X X
29 instruments
when sorted 90% of this table
collapses to just four types of
detector
6 out of 7 large arrays
are 10 – 40 m2
7 Managed by UT-Battelle for the U.S. Department of Energy Presentation_name
Detector Characteristics?
- Brief Survey of ORNL Instruments
• Almost equal instrument split between 10, 5 & 1 mm pixel resolution requirements
• Just 4 detector types are used for all except 2 instruments
– 1-D He3 tube detectors, these can be arrayed close to form pseudo 2D detector
– 2-D wire He3 detectors
– Scintillator WLSF and Anger camera detectors
• Exceptions:
– Imaging [ inc.Tomography] req. 50 um pixel and very high count rate
– Laue SCD gained $ advantage by using 100 mm pixel resolution of flat plate technology
IMPROVEMENTS / ALTERNATIVES
NEEDED FOR ALMOST ALL
INSTRUMENT TYPES
8 Managed by UT-Battelle for the U.S. Department of Energy Presentation_name
1-D He3 Detectors:
• Backscattering & Triple –Axis Spectrometers
– Array size range 0.02 - 0.4 m2
– 1-D He3 still the most appropriate technology
– Total He3 demand anticipated is small
• TOF Chopper Spectrometers
– Array size range 20 - 40 m2
– Reserve of He3 is inadequate
– Alternative has to be developed
• WLSF is a possibility
- Increased pixels = increased PMT anodes per module
- Multianode PMT modules
- Gamma sensitivity?
9 Managed by UT-Battelle for the U.S. Department of Energy Presentation_name
1x1-D He3 Detectors
• SANS, Neutron Spin Echo, SESANS
– Array size range 1 - 3 m2
– Reserve of He3 is adequate at ORNL
– Flux near beamstop saturates detector
• Very high count rate 2-D detector required for central area
-- see next slide
10 Managed by UT-Battelle for the U.S. Department of Energy Presentation_name
2-D He3 Detectors
• Reflectometers, GISANS, NSE, SCD
– Detector size range ~ 1 m2
– Efficiency limited due to He3 pressure
– SCD: expensive to tile reciprocal space
– Refl: Count rate required is x100 current technology
• Parallel Plate Avalanche Chamber Technology
- 1 Mcps in 1 cm2
- 100 mm resolution capability
- ~0.5 Mcps measured in HFIR beam (He3)
- He3-free version under development
• Anger camera a possibility for Reflectometers
- new high throughput FPGA needs to be developed
11 Managed by UT-Battelle for the U.S. Department of Energy Presentation_name
Li6F:ZnS Wavelength Shifting Fiber Detectors
• Powder Diffractometers
– Array size range 4 - 40 m2
– Efficiency cf. 10 atm He3 1” tubes
– Current pixel size = 5 x 55 mm2
– Ghosting at ~ 0.5% level
– Pixel resolution limited by number of PMTs
– More PMTs = more HV supplies + interconnects + weight = $$/ module
0.1 0.2 0.3 0.4 0.5 0.6 0.7
0
10000
20000
30000
40000
50000
60000
70000
80000
co
un
ts
d-spacing (Å)
V2 Module on POWGEN
1g diamond powder
x 25
Each module
– 0.3 m2
– 40 kg
– ~ $110,000
POWGEN:
– 23 of 148 possible modules currently installed
12 Managed by UT-Battelle for the U.S. Department of Energy Presentation_name
WLSF: Detector Development
Component Current Pro Con Alternate Improvement Requirement Scintillator Single
corrugated
easily
exchanged expensive Sandwich of
two flats
Cost saving =
$15,000
PMTs 32 single
ended
can be
individually
balanced
Requires 32
HV power
supplies and
magnetic
shields
4 Multianode
PMTs
Cost saving =
$20,000
New
processing
algorithm
Algorithm 154 x 7 pixels Doesn’t meet
high angle
requirement
308 x 13 pixels Spatial
resolution
Algorithm No individual
fiber efficiency
correction
responsible for
some ghosting
Flat field to
fiber efficiency
weighting
scheme
Decreases
ghosting and
permits use
of MA PMTs
Further development for Chopper Spectrometer instruments is anticipated
- symmetric pixels
- lower background
Total savings: ~ $35,000 per module & weight reduced by 50%
13 Managed by UT-Battelle for the U.S. Department of Energy Presentation_name
Anger Camera Detectors
• Single Crystal Diffractometers
– Array size range ~ 1 m2
– Efficiency is 90% at 1 Å
– Max. count rate > 100 kcps
– Current spatial resolution avg. 1.0 mm
– Pixel resolution limited by scintillator brightness
– greater spatial resolution means larger crystal unit cells; more complex proteins
More details on Anger Cameras & WLSF will be given by Rick Riedel
14 Managed by UT-Battelle for the U.S. Department of Energy Presentation_name
VENUS: Versatile Neutron Imaging
Instrument at the SNS
• Detector Requirements
– Size: min. 0.08 m2
– Efficiency: 50% at 1 Å
– Temporal: 100 ms
– Resolution: acceptable 200 mm
desired 20 mm
– Count rate: 10 Mcps
• Candidate Technologies
– Anger Camera: 3 mm anodes but brighter scintillator needed => 200 mm
– Parallel Plate: in development; size and tiling may be limited
– MCP (Nova Sci.): highest resolution ~ 20 mm plate is size limited
• May need to use a combination of two detectors
15 Managed by UT-Battelle for the U.S. Department of Energy Presentation_name
Conclusions
• Anticipated user demand for neutron detectors esp. He3 alternatives is very high
• All current ORNL alt-He3 detector technologies are 1st generation
– they can meet many ‘acceptable level’ requirements for certain instruments
– however, current cost per module (inc. engineering for stands) is too high for the largest instruments
– both Anger Camera and WLSF types need significant improvements for 2nd generation
• reduce cost and reduce weight
• increase spatial resolution, increased count rate capability and reduced background:
This will allow use in
larger arrays > 100 modules: powder & disordered material diffractometers,
expanded suite of instrument types: imaging, SANS, reflectometers, chopper spectrometers
• Biggest deficiency exists for TOF Imaging Instrument: VENUS
16 Managed by UT-Battelle for the U.S. Department of Energy Presentation_name
Opportunities
• Polarized Beam Instruments: Mag. Refl, NSE, Chopper Spec., SCD
– All could benefit (x2) from detectors that measure the neutron polarization
• Photo-detectors
– Solid-State PMTs: requires noise suppression
– Multi-multi anode PMTs: alleviates gaps => large size format