Fast Neutron Resonance Radiography in a Pulsed Neutron Beam V. Dangendorf,, G. Laczko,, C. Kersten Physikalisch-Technische Bundesanstalt /Braunschweig,, Germany A. Breskin,, R. Chechik,, D. Vartsky Weizmann Institute / Rehovot,, Israel V. Dangendorf, 10.02.03 1
Radioscopy / Radiography Object Radiation source X-rays neutrons Position Sensitive Detector V. Dangendorf, 10.02.03 2
Digital Subtraction Radiography B Rad E1 A Rad E2 s E1 E2 Mat A Mat B E V. Dangendorf, 10.02.03 3
PROs: Properties of Fast Neutrons high penetration power comparable to MeV photons) low Z-dependence of cross sections (compared to Z - Z 5 dependence of photons) isotope (element)-specific cross section characteristics CONs: complex and expensive neutron source installations reactor, accelerator, target, shielding... comparably weak sources neutron flux of strongest reactors is still comparable to photon flux of a candle difficult and little developed imaging techniques problems: efficiency, scattering, acquisition speed, time resolution... V. Dangendorf, 10.02.03 4
cross section / barns 4 3 2 1 Cross sections of C, N, O in the MeV region O-16 0 2 4 6 8 10 Neutron Energy / MeV cross section / barns 4 3 2 1 0 2 4 6 8 10 Neutron Energy / MeV C N-14 cross section / barns 2 1 0 2 4 6 8 10 Neutron Energy / MeV V. Dangendorf, 10.02.03 5
Fast-Neutron Applications I Exploiting high penetration through high-z material: Imaging of low-z structures behind massive high-z shielding material 10 MeV neutron 8 MeV e - -Bremsstrahlung Example: (J.Hall, LLNL) 1 thick ceramic and polyethylene structure behind shielding of 1 thick 238 U V. Dangendorf, 10.02.03 6
Applications II Exploiting cross section structure (resonance imaging): Small objects of specific element distributions behind massive shielding Examples: 1.) Detection of Diamonds enclosed in Mineral (Kimberlith) Guzek et al (DeBeers / RSA) Method: High intensity dualenergy neutron beam utilising cross section structure of 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 TOF techniques for energy dependent transmission radiography Lanza et al (MIT): Method: imaging with monoenergetic neutrons at several discrete energies V. Dangendorf, 10.02.03 7
Experimental Technique V. Dangendorf, 10.02.03 8
Variable Monoenergetic Neutron Beam - Transmission Image with selected, quasi-monoenergetic Neutron Energy - Successive images at different energies Example: deuterium projectile hitting gaseous deuterium target: deuteron beam deuteron gas target neutron beam E n ~ E d + Q Q (d(d,n)h3) ~ 3 MeV 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 power V. Dangendorf, 10.02.03 9
Example for Radiography System based on a Variable Monoenergetic Neutron Beam: Planned at the LLNL Neutron Radiography facility V. Dangendorf, 10.02.03 10
Time-Of-Flight Method Multiple Transmission Images with Neutron Energy selected by Neutron Time-Of-Flight (TOF) Requirements: Pulsed deuteron beam ~ 1 µs ~ 1 ns Deuteron pulses: 1 ns width 0.5-1 µs distance Be target E N Pulsed neutron beam t TOF m d = 2 t 2 N 2 TOF E n (t TOF ) 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 V. Dangendorf, 10.02.03 11
PTB Fast Neutron Facility 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 2 Beam current available: - unpulsed: I B up to 25 (200) µa - pulsed: I B up to 2 ma 1 V. Dangendorf, 10.02.03 12
Fast Neutron Production 2. N-production: ( high current station with collimator) reaction: Be (d,n) E d = 13 MeV thickness Be-Target: 3 mm beam spot: < 3 mm (but at present no online control) Forward Neutron Yield: Y = 10 16 / (sr C) For typical experimental setup distance source - detector: 3 m beam current: 2 µa Y Ω, E / Q /[10 12 /(sr C MeV)] 1200 1000 800 600 400 200 0 Differential forward neutron yield from thick target Be(d,n) / Brede (89): 2 4 6 8 10 12 energy / MeV neutron flux at detector position: j ~ 3* 10 5 s -1 cm -2 V. Dangendorf, 10.02.03 13
Selection of Sample Material Carbon cross section and energy bins for resonance imaging: 4 S MAX 1 cross section / barns 3 2 1 S MIN 1 S MIN 2 S MAX 2 0 3 4 5 6 7 8 9 Neutron Energy / MeV V. Dangendorf, 10.02.03 14
Experimental Setup of Fast Neutron Radiography Experiment collimator position sensitive-detectors: FANGAS OTIFANTI deuteron beam neutron beam C-samples Be-target 5-100 cm 3-3,5 m neutron flux per ua beam at detector position 3 m: j ~ 1,5 * 10 5 / (ma s cm 2 ) V. Dangendorf, 10.02.03 15
Experimental Setup of Fast Neutron Radiography Experiment pulsed neutron source with collimator (13 MeV d Be) FANGAS: FAst NeutronGAS-filled imaging chamber OTIFANTI: OpTIcal FAst NeuTron Imaging system Sample: stack of graphite cylinders V. Dangendorf, 10.02.03 16
Detectors Present Status V. Dangendorf, 10.02.03 17
Imaging Techniques with Time-Of-Flight Method Task: Simultaneous acquisition of Position Coodinates (X,Y) and TOF 1. Neutron Counting Imaging Techniques: Each Neutron is individually registered relevant parameters (X,Y, TOF) are measured and stored in - 3-dimensional Histogramm - List Mode file Advantage: Full Information is obtained and available offline (for LM 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 into image 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 18
FANGAS Principle of Operation FAst NeutronGAS-filled imaging chamber Neutrons interact (sometimes) in thin foil converter (1mm PE) recoil protons escape from foil protons ionise gas along track electrons from gas in region close to foil surface are amplified in Parallel Plate Avalanche Chamber (PPAC) wire chamber (MWPC) for final amplification and localisation by cathode delayline readout TOF and position are stored in Listmode or 3-d matrix V. Dangendorf, 10.02.03 19
OTIFANTI Principle of Operation PM lens image intensifier or fast framing camera (ULTRA 8) BC400 (22*22 cm 2 d = 10 mm ) Mirror OpTIcal FAst NeuTron Imaging system Neutrons interact in scintillator BC400 (NE102) recoil protons are stopped within few mm and produce local light spot optics (mirror and lens) transfer image to photon counting image intensifier or fast framing camera (Hadland ULTRA 8) separate photomultiplier (PM) delivers fast trigger signal V. Dangendorf, 10.02.03 20
OTIFANTI with ULTRA8 Fast Framing Camera Y Ω, E / Q /[10 12 /(sr C)] 1200 1000 800 600 400 200 0 E1 E1 E2 E3 E4 E4 E5 E6 E6 E 1 E 2 E 3 E 4 E 5 E 6 2 4 6 8 10 energy / MeV Intensified CCD camera segmented photocathode with 8 independently gatable frames (a 512*512 px) Short gating time (down to 10 ns per shot) Long integration time (about 1 s with reasonable noise) Repetitive (periodic) exposure phaselocked to beam pulse simultaneous integration of images with neutrons of up to 8 selected energy bins V. Dangendorf, 10.02.03 21
OTIFANTI with ULTRA8 Fast Framing Camera V. Dangendorf, 10.02.03 22
Imaging properties (FANGAS) Radiographic images of Carbon samples obtained with FANGAS integrated over all neutron energies 3 cm d= 5 mm l=20 mm Images obtained after correcting for flatness of field and efficiency and linearity inhomogeneities of detector V. Dangendorf, 10.02.03 23
Imaging properties (FANGAS) _ = Differential Imaging with FANGAS 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 with sources and the low efficiencies of detectors, images are often limited by Poisson statistics V. Dangendorf, 10.02.03 24
Imaging properties (OTIFANTI) 3 cm Images with OTIFANTI and intensified UV-CCD camera d-beam current: 20 µa no energy windows selected, exposure time: 30 s at 100 ms / frame) (300 images V. Dangendorf, 10.02.03 25
Summary of present status FANGAS:. - Detector worked well but has low detection efficiency: ε FA ~ 0,2 % - Data Acquististion slow : ~ 10 4 s -1 at present required : 10 6 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*10 6 s -1 ) b) with present standard intensified camera: - due to integrating system fi 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 26
New Detector Development V. Dangendorf, 10.02.03 27
Detector Development: FANGAS Efficiency problem: larger efficiency by stacking of detectors 25 Dets provide 5 % Requirements: - simple and industrial production - robust and easy to operate - cheap high rate readout system (several 100 khz / module) neutrons 1 2 3......25 V. Dangendorf, 10.02.03 28
Detector Development I conversion gap FANGAS resistive layer on insulator neutrons scatter with protons in PEradiator neutron proton 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 PE-radiator (neutron-converter) GEMs multilayer PCB (pickup, delay lines) integrated delayline structures encode position information ~ 12 mm V. Dangendorf, 10.02.03 29
hole ~80 µm, hole center ~70 µm, hole spacing: 140 µm 80 µm ~70 µm conversion and drift amplification transfer and signal induction Cross section view of 1 hole All photos taken from F. Saulis web page: http://gdd.web.cern.ch/gdd/ V. Dangendorf, 10.02.03 30
Detector Development II OTIFANTI scintillator screen PM lens optical preamp (image intensifier) lens fast framing camera (ULTRA 8) mirror 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 V. Dangendorf, 10.02.03 31
OPTICAL PREAMPLIFIER -250 V 0 V hν photocathode 75 mm MCPs 2 kv 8 kv e - hν electron amplifier phosphor ι d < 2 ns! Fast light decay in phosphor to preserve time resolution I t V. Dangendorf, 10.02.03 32
ULTRA 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 33
Individual ICCD Cameras BC400 screen (22*22 cm 2 d = 10 mm ) mirror Individual Intensified CCD cameras (ICCD) view preamp intensifier 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) PM lens optical preamp (image intensifier) lens separate ICCD cameras 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 V. Dangendorf, 10.02.03 34