M. Osipenko INFN 2 Dicember 203 INFN-E/RILF * Introduction ToF Experiment Conclusion * CVD diamonds for fast neutron detection and spectroscopy in high flux environment INFN-E/RILF M.Osipenko etal.,m.pillon 2 etal.,r.cardarelli 3 etal., G.VeronaRinati 3 etal. INFNGenova, 2 ENEAdiFrascati, 3 UniversitàdiTorVergata HeRe in Italy,Frascati, 203
2 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF * Introduction ToF Experiment Conclusion * Motivation φ n cm -2 s - 2 9 8 7 6 5 4 3 2 Goal: to monitor neutron spectrum inside reactor core. Solution: single crystal CVD diamond detectors. Fast Reactor neutron flux -8-7 -6-5 -4-3 -2 - T n MeV Advantages: 0 µmcrystalwilllastfor severalyearsat 9 n/cm 2 /s, fast signals good for background rejection, compact detectors do not influence reactor kinetics. Problems: small signals.
Principle of Detection 3 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF Charged particle crossing diamond creates e-hpairs, To collect pairs the bias voltagehastobe applied across the diamond, Current pulses are generated on electrodes, To become measurable thesignalshavetobe amplified. Electrodes Charged Particle Diamond e-h Creation Amplifier V bias
Crystal Properties 4 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF High bandgap, low capacitance, high carrier mobility fast, low-noise signals cvd Diamond Si GaN 4H-SiC Bandgap[eV] 5.47.2 3.39 3.27 e-h creation energy[ev] 3 3.6 8-8.4 Displacement energy[ev] 43 3-20 -20 25 Electronmobility[µm 2 /V/ns] 200 50 0 80 Holemobility[µm 2 /V/ns] 260 45 20 2 Density[g/cm 3 ] 3.52 2.33 6.5 3.2 Resistivity[Ωcm] > 2.3 5 4 8 Breakdown field[mv/cm] 0.3 5 3-5 Dielectric constant 5.7.9 9.5 9.7
Signal Formation 5 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF ForkeVofdeposited energyn eh =77e-h pairs are created; Statistical uncertainty on created charge is F Neh (3%forkeV), wheref 0.08is diamond Fano factor; Charges drift towards electrodes generating currentfortimet c : I(t) = Q(t) d µe(x(t)) d-thickness; e,h-mobility: µ = d2 t c V bias
Time of Flight Technique 6 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF Measure the coincidence between two subsequent neutron interactions: T n = T n + M n 2 ( d c t ) 2 T n -energylostinfirstinteraction, t-timeintervalbetweentwo interactions. Threshold deposited energy is critical: n h CDV minimalaccessibleneutronenergyt min n 5E thr, efficiencyloss ǫ(e thr )/ǫ(e thr =0) (T n /7E thr ) 2. d n CVD2 n
ToF Energy Resolution 7 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF AssumeToFresolution δ t =30psatMeV. AssumeE dep resolution δ E =50keV. Requires development of a new, high precision coincidence electronics. Edep resolution Distance resolution ToF resolution d=.2 cm E dep =0.2MeV d= cm δt n /T n δt n /T n d=2 cm d=3 cm - - T n MeV T n MeV
ToF Efficiency 8 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF Geant4 simulations of the detector were performed, usingadsneutronflux 9 n/cm 2 /sand50kev detection threshold, attofdistanced =2cm(cm)integrated coincidence rate: 0.6 khz(2.5 khz), efficiency ǫ 2 A =5 6 (ǫ 2 A =2 5 ). Events 5 4 3 2-2 -3-4 -5-6 d=cm d=2cm -7 0.5.5 2 2.5 MeV E dep -8-9 -2 - T n MeV
Accidental Coincidences 9 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF Assumingtriggerwindow t =ns: R acc =Rsingle 2 t =70kHz () 28(d=cm)-25(d=2cm)timeshigherthansignal rate. However, only 0.026 accidental signals appear in an opennsgate. General the trend of Signal-to-Noise-Ratio: SNR = πφ n d 2 t (2)
CVD Diamond Crystals M. Osipenko INFN 2 Dicember 203 INFN-E/RILF Diamond Detectors Ltd. SO-274: 4.7 4.7mm 2 surfaceareaand 500 µm thick; Atomic impurities: N<5 ppb, B<<5 ppb(spectroscopic grade), SurfacescanRMSforside:.37nm,side2:0.7nm; DLC(-3 nm)/pt(50 nm)/au (0 nm) ohmic contacts, area22mm 2,C D =2.2pF; Brass/aluminum casing with two SMA-F connectors. HW GW cvd HW GW
Experimental Setup M. Osipenko INFN 2 Dicember 203 INFN-E/RILF FNG in D-D mode(2.5 MeV monocromatic neutron beam), neutronfluxof 6 n/cm 2 /s, twocvdcrystalswereplacedatdistanced =.2 cm, signals preamplified by fast transimpedance amplifiers(see R. Cardarelli talk) connected trough 5 mcabletothesecondaryamplifierp/s774. DAQ: NIM crate(power supplier, secondary amplifier), VME crate(5 Gs/s digitizer, controller/pc).
2 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF * Introduction ToF Experiment Conclusion * Pictures Two DDL diamonds attached
3 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF * Introduction ToF Experiment Conclusion * Results 20 coincidence events/540 s- expected 0.25 Hz, 5%accidentals( t =2ns)-asexpected, ToFis0.6ns,withtimingresolutionsof0.36ns(δ t =250 psoftwoamplifiersatmev)and0.ns(distance), observedpeakrmsis0.4ns,inagreementwith estimates(0%t n resolution). ADC channel [2 mv] 00 900 800 700 600 CVD CVD2 E dep =743 kev E dep =59 kev Events 25 20 5 Coincidence 500 5 400 0 50 0 50 200 250 300 350 400 Sample [0.2 ns] 0-25 -20-5 - -5 0 5 5 20 25 t ns
Results cont. 4 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF energy thresholds were set 0.25 MeV, deposited energy resolution 50 kev, only backscattered n were detected in CVD (threshold for forward n 7 27 kev), incvd2flatangulardistribution, θn CM >70, within covered energy range ToF variation < ps. 8 6 4 CVD CVD2-6 -7-8 Events 2 8 t ns -9-6 - 4-2 2-3 0 0 200 400 600 800 00 200 400 600 800 2000 Edep [kev] -4 550 600 650 700 750 800 850 900 950 00 CVD E dep [kev]
Amplifier Test 5 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF compared five fast amplifiers: DBA IV, CAEN A423, Cividec C2, Wisnam µta40 and Cividec C6, 24 Am(α,5MeV)and 90 Sr(β <2.3MeV)sources, CVD diamond detector read out independently from two sides, 5 Gs/s(2 GHz BW) digitizer recorded the signals. V G HV- 750 700 650 CVD V2 G2 HV+ ADC channel [2 mv] 600 550 500 450 400 350 300 250 χ 2 /N.d.F.=0.9 E dep =627 kev χ 2 /N.d.F.= E dep =5 kev 220 240 260 280 300 320 340 Sample [0.2 ns]
Amplifier Energy Resolution 6 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF measured noise level in terms of energy deposited in diamond, obtainedpeakshape5mev αfrom 24 Amsource, among fast amplifiers best resolution Cividec C6(0 MHzBW). FWHM of noise E dep [kev] 400 350 300 250 200 50 0 50 DBA IV CAEN A423 Cividec C2 Wisnam uta40 Cividec C6 Cividec Cx Events 5000 4500 4000 3500 3000 2500 2000 500 00 500 α 5.05 MeV DBA IV CAEN A423 Cividec C2 Wisnam uta40 Cividec C6 Cividec Cx 0 Amplifier 0 4600 4800 5000 5200 5400 E dep [kev]
Amplifier Timing Resolution 7 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF coincedence between two electrodes, 24 Am(α,5MeV)and 90 Sr(β <2.3MeV)sources, Cividec C6 has best timing resolution, energy dependence of timing resolution agrees with σ t = t rise S/N 2 β 0.8 MeV DBA IV CAEN A423 Cividec C2 Wisnam uta40 Cividec C6 200 00 Cividec C6 Events FWHM t [ps] 800 600 90 β Sr 400 200 270 ps/(e / MeV) dep α 24 Am - -0.5 0 0.5 t [ns] 0 3 E dep [kev]
8 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF * Introduction ToF Experiment Conclusion * Summary sccvd diamonds were proposed for ToF neutron spectrometer( 5 < φ n < 9 n/cm 2 /s), test measurement at FNG demonstrated feasibility of technique, number of commercial amplifiers were tested, noise level of existing amplifiers has to be improved by afactorof. Future: develop better signal amplifier, optimize detector geometry, test at FNG and research reactors.
Backup Slides 9 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF
Resolution vs. Distance 20 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF Two500 µmcrystalsatdistanced; AssumeToFresolution δ t =0.2ns; AssumeE dep resolution δ E =50keV. T n =0.3 MeV T n = MeV T n =5 MeV d= cm δt n /T n δt n /T n d=2 cm d=3 cm - - - d cm T n MeV
Resolution Contributions 2 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF Ford >2cmandT n >0.4MeVToFresolution dominates; Develop high precision coincidence technique; 25 ps resolution has been achieved with diamonds. Edep resolution Distance resolution ToF resolution Edep resolution Distance resolution ToF resolution δt n /T n δt n /T n - - d cm T n MeV
ToF Resolution Cont. 22 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF InregionofinterestToFvaryfrom0.5to7ns. T n =0. MeV T n = MeV T n =5 MeV t ns t ns d= cm d=2 cm d=3 cm - - d cm - - T n MeV
Conversion Cross Sections 23 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF Hydrogen and Carbon have highest cross sections.
Conversion Efficiency 24 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF Assuming % of range convertor thickness. ε conv -3-4 -5-6 -7-8 2 C H 6 Li(t) 6 Li(d) B 4 N -3-2 - T n MeV Deposited energy threshold not considered, Acceptance of diamonds seen from converter not included, %ofrange probably gives poor resolution.
Other Active Detectors 25 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF In fluxes < 2 n/cm 2 /s Diamond detector can substitute Fission Chamber as active monitor. Fission Diamond Chamber Detector ChargeMobility 0.3-0.4cm 2 /V/s 2000cm 2 /V/s Charge Collection time 5-7 µs 2- ns Counting Rate 20 khz MHz Size 4 mm 2 2 2mm 2 Converter U,Th,Pu H, Li, B Efficiencyat0.5MeV.barn 0.4barn( 6 Li) SignalSize 200fC 60fC( 6 Li) Spectroscopy unfolding direct( 6 Li) EnergyRange entire <7MeV( 6 Li)
26 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF * Introduction ToF Experiment Conclusion * Robustness Diamonds are radiation hard. RD42 Neutrons: up to 4 5 of4.8 MeVn/cm 2 0.25 MGy, Photons:upto MGy, MIPs(24 GeV p): upto4 5 p/cm 2.25MGy,
Signal Collection 27 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF Electrode contacts can be ohmic or Schottcky (rectifying); Ohmic contacts: charge canflowthrough(tior Cr which form carbide at500 annealing followedbyptandau); Schottcky(rectifying) contacts: charge remain in detector bulk (e.g.al). φ s :C4.8-5.8eV(p-type); φ m :Al4.eV,Ti4.3eV,Cr4.5 ev,au5.ev,pt5.7ev; p-typeohmic: φ s < φ m
Signal Description 28 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF Spacecharge(τ sc )andtrapping τ e,h lifetimes( 40ns): Drift velocity: I e,h (t) e ±t/τsc e,h t/τ e,h v drift = d t c Charge collection distance: ccd d = Q Q 0 d Q = I(t)dt 2τ e,h v drift E(x) I(t) pa V/d 9 8 7 6 5 4 3 2 (V-V c )/d e 0-2 - 0 2 3 4 5 6 t ns x /τ sc -/τ e e h -/τ sc -/τ h t c h d
* Appendix * For Further Reading I 29 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF Edited by R.S. Sussmann CVD Diamond for Electronic Devices and Sensors. Wlley, 2009. D. Meier, CVD Diamond Sensors for Particle Detection and Tracking, CERN 999. H.Perneggeretal.,J.ofApp.Phys.97,073704(2005). P.Moritzetal.,Diam.Relat.Mater.,765(200). H. Frais-Kölbl, E. Griesmayer and H. Pernegger, Nucl. Inst. Meth. A535, 8(2004).