CVD diamonds for fast neutron detection and spectroscopy in high flux environment

Transcription

1 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 2 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF * Introduction ToF Experiment Conclusion * Motivation φ n cm -2 s Goal: to monitor neutron spectrum inside reactor core. Solution: single crystal CVD diamond detectors. Fast Reactor neutron flux 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.

3 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

4 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] e-h creation energy[ev] Displacement energy[ev] Electronmobility[µm 2 /V/ns] Holemobility[µm 2 /V/ns] Density[g/cm 3 ] Resistivity[Ωcm] > Breakdown field[mv/cm] Dielectric constant

5 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

6 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

7 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

8 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 d=cm d=2cm MeV E dep T n MeV

9 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 accidental signals appear in an opennsgate. General the trend of Signal-to-Noise-Ratio: SNR = πφ n d 2 t (2)

10 CVD Diamond Crystals M. Osipenko INFN 2 Dicember 203 INFN-E/RILF Diamond Detectors Ltd. SO-274: mm 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

11 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).

12 2 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF * Introduction ToF Experiment Conclusion * Pictures Two DDL diamonds attached

13 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] CVD CVD2 E dep =743 kev E dep =59 kev Events Coincidence Sample [0.2 ns] t ns

14 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 CVD CVD Events 2 8 t ns Edep [kev] CVD E dep [kev]

15 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 CVD V2 G2 HV+ ADC channel [2 mv] χ 2 /N.d.F.=0.9 E dep =627 kev χ 2 /N.d.F.= E dep =5 kev Sample [0.2 ns]

16 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] DBA IV CAEN A423 Cividec C2 Wisnam uta40 Cividec C6 Cividec Cx Events α 5.05 MeV DBA IV CAEN A423 Cividec C2 Wisnam uta40 Cividec C6 Cividec Cx 0 Amplifier E dep [kev]

17 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 C Cividec C6 Events FWHM t [ps] β Sr ps/(e / MeV) dep α 24 Am t [ns] 0 3 E dep [kev]

18 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.

19 Backup Slides 9 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF

20 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

21 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

22 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

23 Conversion Cross Sections 23 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF Hydrogen and Carbon have highest cross sections.

24 Conversion Efficiency 24 M. Osipenko INFN 2 Dicember 203 INFN-E/RILF Assuming % of range convertor thickness. ε conv C H 6 Li(t) 6 Li(d) B 4 N T n MeV Deposited energy threshold not considered, Acceptance of diamonds seen from converter not included, %ofrange probably gives poor resolution.

25 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 cm 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 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 MGy, Photons:upto MGy, MIPs(24 GeV p): upto4 5 p/cm 2.25MGy,

27 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 :C eV(p-type); φ m :Al4.eV,Ti4.3eV,Cr4.5 ev,au5.ev,pt5.7ev; p-typeohmic: φ s < φ m

28 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 (V-V c )/d e t ns x /τ sc -/τ e e h -/τ sc -/τ h t c h d

29 * 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, 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).