Fast Neutron Resonance Radiography in a Pulsed Neutron Beam · pickup electrode • integrated...
Transcript of Fast Neutron Resonance Radiography in a Pulsed Neutron Beam · pickup electrode • integrated...
V. Dangendorf, 10.02.03 1
V. V. DangendorfDangendorf, G. , G. LaczkoLaczko, C. , C. KerstenKersten
PhysikalischPhysikalisch--Technische Bundesanstalt Technische Bundesanstalt //BraunschweigBraunschweig, Germany, Germany
A. A. BreskinBreskin, R. , R. ChechikChechik, D. , D. VartskyVartsky
WeizmannWeizmann Institute / Institute / RehovotRehovot, Israel, Israel
Fast Neutron Resonance RadiographyFast Neutron Resonance Radiography
in a Pulsed Neutron Beamin a Pulsed Neutron Beam
V. Dangendorf, 10.02.03 2
Radioscopy / RadiographyRadioscopy / Radiography
Radiationsource
X-raysneutrons
PositionSensitiveDetector
Object
V. Dangendorf, 10.02.03 3
Digital Subtraction Radiography Digital Subtraction Radiography
A
B
E
σσ∆E1 ∆E2
Mat A
Mat B
Rad ∆E1
Rad ∆E2
V. Dangendorf, 10.02.03 4
Properties of Fast NeutronsProperties of Fast NeutronsPROsPROs::
• high penetration powercomparable to MeV photons)
• low Z-dependence of cross sections(compared to Z - Z5 dependence of photons)
• isotope (element)-specific cross section characteristics
CONsCONs::
• complex and expensive neutron source installations
reactor, accelerator, target, shielding ...
• comparably weak sourcesneutron flux of strongest reactors is still comparable to photon flux of a candle
• difficult and little developed imaging techniquesproblems: efficiency, scattering, acquisition speed, time resolution ...
V. Dangendorf, 10.02.03 5
2 4 6 8 100
1
2
3
4
C
cros
s se
ctio
n / b
arns
Neutron Energy / MeV
Cross sections of C, N, O Cross sections of C, N, Oin the in the MeV MeV regionregion
2 4 6 8 100
1
2
N-14
cro
ss s
ect
ion
/ b
arn
s
Neutron Energy / MeV
2 4 6 8 100
1
2
3
4O-16
cros
s se
ctio
n /
barn
s
Neutron Energy / MeV
V. Dangendorf, 10.02.03 6
Fast-NeutronFast-Neutron Applications IApplications I Exploiting high penetration through high-Z material:
Imaging of low-Z structures behind massive high-Z shielding material
Example: (J.Hall, LLNL)
1” thick ceramic and polyethylenepolyethylene structure
behind shielding of
1” thick 238U
10 MeV neutron 8 MeV e--Bremsstrahlung
V. Dangendorf, 10.02.03 7
Applications IIApplications IIExploiting cross section structure (resonance imaging):
Small objects of specific element distributions behind massive shielding
Examples:
1.) Detection of Diamonds enclosedin Mineral (Kimberlith)
Guzek et al (DeBeers / RSA)
Method: High intensity dual-energy neutron beam
utilising cross section structureof C around 8 MeV
2.) Luggage and Cargo inspection: by measuring C, N, O - distribution
• Overley et al (Ohio-University)
Method: white neutron beam with TOFtechniques for energy dependent transmission radiography
• Lanza et al (MIT):
Method: imaging with monoenergetic neutrons at several discrete energies
V. Dangendorf, 10.02.03 8
Experimental
Technique
V. Dangendorf, 10.02.03 9
- Transmission Image with selected, quasi-monoenergetic Neutron Energy
- Successive images at different energies
VariableVariable Monoenergetic Monoenergetic Neutron Beam Neutron Beam
deuteron beam
deuterongas target
neutron beam
Example:
deuterium projectile hitting gaseous deuterium target:
Requirements:
• high intensity deuteron beam (0,5 - 10 mA)
• 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
Pulsed deuteronbeam
Be target
Pulsed neutronbeam
~ 1 µs
~ 1 ns
2TOF
2N
N 2 t
dmE
⋅=
tTOF
En(tTOF)Deuteron pulses:
• 1 ns width
• 0.5 - 1 µs distance
V. Dangendorf, 10.02.03 12
1. Accelerator:
• Cyclotron (TCC-CV28)
• Ion beams: p → 2 - 24 MeV
d → 3 - 14 MeV
• Pulsing: via pulsed injection
- 1,5 ns (fwhm) wide - 500 ns pulse separation for TOF
• Beam current available:
- unpulsed: IB up to 25 (200) µA
- pulsed: IB up to 2 µµA
PTB Fast Neutron FacilityPTB Fast Neutron Facility
1
2
V. Dangendorf, 10.02.03 13
2. N-production:(“high current” station with collimator)
• reaction: Be (d,n)
• Ed = 13 MeV
• thickness Be-Target: 3 mm
• beam spot: < 3 mm (but at present no online control)
Fast Neutron ProductionFast Neutron Production
2 4 6 8 10 120
200
400
600
800
1000
1200
YΩ
, E /
Q /
[1012
/(sr
C M
eV)]
energy / MeV
Forward Neutron Yield:
Y = 10 16 / (sr C)
For typical experimental setup distance source - detector: 3 m beam current: 2 µA
Differential forward neutron yield fromthick target Be(d,n) / Brede (89):
neutron flux at detector position:
ϕϕ ~ 3* 105 s-1 cm-2
V. Dangendorf, 10.02.03 14
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
V. Dangendorf, 10.02.03 23
Imaging properties (FANGAS)Imaging properties (FANGAS)
Radiographic images of Carbonsamples obtained with FANGASintegrated over all neutron energies
Images obtained after correcting for
flatness of field andefficiency and linearity inhomogeneities of detector
d= 5 mm
l=20 mm3 cm
V. Dangendorf, 10.02.03 24
Imaging properties (FANGAS)Imaging properties (FANGAS)
Differential Imaging withFANGAS
a) “off” resonance image
b) “on” resonance image
c) differential image (smoothed)
Comment:
(taken from earlier paper of Watterson et al):
“...because of the difficulties withsources and the low efficiencies ofdetectors, images are often limited byPoisson statistics”
_
=
V. Dangendorf, 10.02.03 25
Imaging properties (OTIFANTI)Imaging properties (OTIFANTI)
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
V. Dangendorf, 10.02.03 27
NewDetector
Development
V. Dangendorf, 10.02.03 28
Detector Development: FANGASDetector Development: FANGAS
Efficiency problem:
larger efficiency by stackingof detectors ⇒ 25 Dets provide 5 %
Requirements:- simple and industrial production- robust and easy to operate- cheap high rate readout system
(several 100 kHz / module)
1 2 3 . . . . . .25
neutrons
V. Dangendorf, 10.02.03 29
Detector Development IDetector Development IFANGASFANGAS
• neutrons scatter with protons in PE-radiator
• protons produce electrons in conversion gap
• electrons are amplified in multistage GEM structures
• final electron avalanche is collected on resistive layer
• moving electrons induce signal on pickup electrode
• integrated delayline structures encode position information
GEMsPE-radiator
(neutron-converter)
resistive layeron insulator
multilayer PCB(pickup, delay lines)
neutron
proton
conversion gap
~ 12 mm
V. Dangendorf, 10.02.03 30
conversionand drift
amplification
transfer andsignal induction
Cross section view of 1 hole
All photos taken from F. Saulis webpage: http://gdd.web.cern.ch/GDD/
∅ hole ~80 µm, ∅ hole center ~70 µm,
hole spacing: 140 µm
~70 µm
80 µm
V. Dangendorf, 10.02.03 31
Detector Development IIDetector Development IIOTIFANTIOTIFANTI
Modifications of Otifanti:
• Optical Preamplifier to increase light detection efficiency
• Modifying ULTRA8 to-enable repetitive triggering for about 1s with > 1 MHz rate- increase sensitivity in near UV
• Replace ULTRA8 by separate cameras which can be individually triggered with 2 MHz repetition rate
mirror
PM
lens
scintillatorscreen
fast framingcamera (ULTRA 8)
optical preamp(image intensifier)
lens
V. Dangendorf, 10.02.03 32
OPTICAL PREAMPLIFIEROPTICAL PREAMPLIFIER
photocathode
MCPselectron amplifier
phosphor
hν
hν’
e-
∅ 75 mm
ιd < 2 ns
t →
Fast light decay in phosphorto preserve time resolution
I
-250 V 0 V
2 kV
8 kV
!
V. Dangendorf, 10.02.03 33
ULTRA 8 - REQIREMENTSULTRA 8 - REQIREMENTS
Further use of ULTRA8 depends on
• Achieving sensitivity in UV to avoid wavelenght shifter(namely in the λ= 370 - 470 nm region)
- new beam splitter (proposed by manufactuer)
• Implementation of fast (> 1 MHz) repetitive photocathode-pulsing
- upgrade of pulser electronics by manufacturer
• Implemetation of more flexible trigger schemes
- external access to HV-pulsers
- modification of camera firmware by manufacturer
V. Dangendorf, 10.02.03 34
Individual ICCD CamerasIndividual ICCD Cameras
PM
lens
mirrorBC400 screen
(22*22 cm2
d = 10 mm )
separate ICCDcameras
optical preamp(image intensifier)
lens
Individual Intensified CCD cameras (ICCD) view preampintensifier at slight angles to optical axis
each ICCD is independently triggered and read out
modular from 1 up to 9 cameras (first step: 1 camera for testing concept)
Estimate of optical efficiency: (assuming standard ICCD)90 pe- / n (fiberplate outp. window)720 pe- / n (fused silica outp.window)
Problems to be solved:Funding (~ 25 k$ per camera)PC-Pulser with 2 MHz repetition rate (e.g. Photek GM 150-20 (modified) DEI HV Modules