V. Dangendorf, 10.02.03 1 V. V. Dangendorf Dangendorf , G. , G. Laczko Laczko , C. , C. Kersten Kersten Physikalisch Physikalisch- Technische Bundesanstalt Technische Bundesanstalt / Braunschweig Braunschweig, Germany , Germany A. A. Breskin Breskin , R. , R. Chechik Chechik , D. , D. Vartsky Vartsky Weizmann Weizmann Institute / Institute / Rehovot Rehovot , Israel , Israel Fast Neutron Resonance Radiography Fast Neutron Resonance Radiography in a Pulsed Neutron Beam in a Pulsed Neutron Beam
34
Embed
Fast Neutron Resonance Radiography in a Pulsed Neutron Beam · pickup electrode • integrated delayline structures encode position information GEMs PE-radiator (neutron-converter)
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
V. Dangendorf, 10.02.03 1
V. V. DangendorfDangendorf, G. , G. LaczkoLaczko, C. , C. KerstenKersten
• high pressure windowless deuterium gas targets(e.g. 2 bar buffered towards 10-6 mbar beam tube)
• time structure of beam not relevant (DC, pulsed..)
• neutron energy selection by projectile energy or collision kinematics → variable energy accelerator→ angular variation of object & imaging system
• separate beam dump for several kW thermal powerEn ~ Ed + Q
Q(d(d,n)H3) ~ 3 MeV
V. Dangendorf, 10.02.03 10
Planned at the LLNL Neutron Radiography facility
Example for Radiography System based on aExample for Radiography System based on aVariable Variable MonoenergeticMonoenergetic Neutron Beam: Neutron Beam:
V. Dangendorf, 10.02.03 11
Multiple Transmission Images with Neutron Energy selected by
Neutron Time-Of-Flight (TOF)
Time-Of-FlightTime-Of-Flight MethodMethod
Requirements:
• “Medium” intensity deuteron beam (20 - 200 µA)
• solid Target (e.g Be)
• requires nanosecond beam pulsing
• neutron TOF ⇒⇒ neutron energy
• target acts also beam dump (i.e. needs cooling for about 1 kW thermal power
• need for imaging system with fast timing capability
Selection of Sample MaterialSelection of Sample Material
3 4 5 6 7 8 90
1
2
3
4
SMAX
1
SMIN
1
SMAX
2
SMIN
2
cros
s se
ctio
n / b
arns
Neutron Energy / MeV
Carbon cross section and energybins for resonance imaging:
V. Dangendorf, 10.02.03 15
Experimental Experimental SetupSetup of Fast Neutron of Fast NeutronRadiography ExperimentRadiography Experiment
C-samples
Be-target
collimator
neutron beamdeuteron beam
position sensitive-detectors:
FANGAS OTIFANTI
3 -3,5 m
5 - 100 cm
neutron flux per uA beam at detector position 3 m:
ϕϕ ~ 1,5 * 105 / (µµA s cm2)
V. Dangendorf, 10.02.03 16
OTIFANTI:OpTIcal FAst NeuTronImaging system
Experimental Experimental SetupSetup of Fast Neutron of Fast NeutronRadiography ExperimentRadiography Experiment
pulsed neutron sourcewith collimator(13 MeV d→Be)
FANGAS: FAstNeutronGAS-filledimaging chamber
Sample: stack ofgraphite cylinders
V. Dangendorf, 10.02.03 17
Detectors
Present Status
V. Dangendorf, 10.02.03 18
Imaging Techniques with Imaging Techniques withTime-Of-FlightTime-Of-Flight MethodMethod
Task:Task: Simultaneous acquisition ofPosition Coodinates (X,Y) and TOF
1. Neutron Counting Imaging Techniques:
• Each Neutron is individually registered
• relevant parameters (X,Y, TOF) are measured andstored in
- 3-dimensional Histogramm- List Mode file
Advantage:
Full Information is obtained and available offline (forLM storage)
Disadvantage:- Slow (several MHz max speed)
- For LM storage: excessive diskspace required
- Dedicated Detector development necessary
2. Integrating Imaging Techniques:
• Image is captured in segmented (“pixeled”) detectors
• quantum structure is lost, only integrated “currents” intoimage cells are measured
• Requires storage structures of sufficient size and dimension(e.g. X,Y, TOF: multiple frame CCD, each frame captures image for different energy window)
Advantage:• Very high data capture rate
• Based almost entirely on industrially available techniques
Disadvantage:• requirement for proper adjustment of exposure
timing at runtime
• Fast high frequency exposure system needs some development
V. Dangendorf, 10.02.03 19
FANGASFANGAS Principle of OperationPrinciple of Operation
• Neutrons interact (sometimes) in thinfoil converter (1mm PE)
• recoil protons escape from foil
• protons ionise gas along track
• electrons from gas in region close tofoil surface are amplified in ParallelPlate Avalanche Chamber (PPAC)
• wire chamber (MWPC) for finalamplification and localisation bycathode delayline readout
• TOF and position are stored inListmode or 3-d matrix
FAst NeutronGAS-filled
imaging chamber
V. Dangendorf, 10.02.03 20
OTIFANTIOTIFANTIPrinciple of OperationPrinciple of Operation
• Neutrons interact in scintillatorBC400 (NE102)
• recoil protons are stopped within fewmm and produce local light spot
• optics (mirror and lens) transferimage to photon counting imageintensifier or fast framing camera(Hadland ULTRA 8)
• separate photomultiplier (PM)delivers fast trigger signal
OpTIcal FAst NeuTron Imaging system
PM
lens
Mirror
BC400(22*22 cm2
d = 10 mm )
image intensifieror fast framing
camera (ULTRA 8)
V. Dangendorf, 10.02.03 21
OTIFANTI with ULTRA8OTIFANTI with ULTRA8Fast Framing CameraFast Framing Camera
• Intensified CCD camera
• segmented photocathode with 8 indepen-dently gatable frames (a 512*512 px)
• Short gating time (down to 10 ns per shot)
• Long integration time (about 1 s withreasonable noise)
• Repetitive (periodic) exposure phase-locked to beam pulse⇒ simultaneous integration of images withneutrons of up to 8 selected energy bins∆
E1
∆E
2
∆E
3
∆E
4
∆E
5
2 4 6 8 10
0
200
400
600
800
1000
1200
energy / MeV
YΩ,
E /
Q /[
1012
/(sr
C)]
∆E
6
∆E1 ∆E2
∆E3 ∆E4
∆E1
∆E5 ∆E6 ∆E6
∆E4
V. Dangendorf, 10.02.03 22
OTIFANTI with ULTRA8OTIFANTI with ULTRA8Fast Framing CameraFast Framing Camera
Images with OTIFANTI and intensified UV-CCD camera
d-beam current: 20 µA
no energy windows selected, exposure time: 30 s (300 imagesat 100 ms / frame)
3 cm
V. Dangendorf, 10.02.03 26
Summary of present statusSummary of present status
FANGAS: . - Detector worked well but has low detection efficiency: εFA ~ 0,2 % - Data Acquististion slow : ~ 104 s-1 at present
required : 106 s-1
OTIFANTI:
a) with Ultra8 framing camera: - small optical efficiency due to problem with image splitter - limited pulsing possibility (present frame exposure rate: ~ 2500 s-1, required: 2*106 s-1 )
b) with present standard intensified camera: - due to integrating system →→ high acquisition speed
- only single frame possible, i.e. 1 energy range per exposure cycle- optical efficiency needs improvement (at present ~ 60 % QE per absorbed neutron