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Integration of SiPM in a high-pressure noble gas scintillation detector for homeland security

Integration of SiPM in a high-pressure noble gas scintillation detector for homeland security. Romualdo Santoro Università dell’Insubria. M. Caccia , V. Chmill , S. Martemiyanov – Insubria R. Chandra , G. Davatz , U. Gendotti – Arktis. MODES_SNM.

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Integration of SiPM in a high-pressure noble gas scintillation detector for homeland security

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  1. Integration of SiPM in a high-pressure noble gas scintillation detector for homeland security Romualdo Santoro Universitàdell’Insubria M. Caccia, V. Chmill, S. Martemiyanov – Insubria • R. Chandra, G. Davatz, U. Gendotti – Arktis

  2. MODES_SNM Modular Detector System for Special Nuclear Material 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy • Approved by the European Commission within the Framework Program 7 • The Main Goal is the development of a system with detection capabilities of “difficult to detect radioactive sources and special nuclear materials” • Neutron detection with high γ rejection power • γ-rays spectrometry • Other requirements • Mobile system • Scalability and flexibility to match a specific monitoring scenario • Remote control, to be used in covert operations

  3. Baseline technology • 44 cm diameter x 47 cm sensitive length • 180 bar 4He sealed system maintaining gas purity 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy • The Arktis technologies is based on the use of 4He for the neutrons detection • The main key features of 4He • Reasonably high cross section for n elastic scattering • Good scintillating properties • Two component decays, with τ at the ns and μs levels • Cheaper and easier to be procured wrt3He R. Chandraet al., 2012 JINST 7 C03035

  4. MODES_SNM System overview With γ-ray spectroscopy capability • All components are being integrated, we are approaching the commissioning and qualification phase 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy Modular system optimized for: Fast neutron (4He) Thermal neutron (4He with Li converter) Gamma (Xe)

  5. MODES_SNM R&D 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy • The project baseline is based on PMTs coupled with scintillating material • R&D activities was planned since the beginning to investigate the possibility of using SiPM as light detector • Why SiPM is so appealing? • high sensitivity (single photon discrimination) • compactness, robustness, • low operating voltage and power consumption • low cost

  6. SiPM Signals from SiPM 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy SiPM is a High density (~103/mm2 ) matrix of diodes with a common output, working in Geiger-Müller regime Common bias is applied to all cells (few % over breakdown voltage) Each cell has its own quenching resistor (from 100kΩto several MΩ) When a cell is fired an avalanche starts with a multiplicative factor of about 105-106 The output is a fast signal (Trise~ns; Tfall ~ 50 ns) sum of signals produced by individual cells SiPM works as an analog photon detector

  7. SiPM The selected device is a large area (13.6 x 14.3 mm2) monolithic array of SiPM units produced by Hamamatsu: S11829-3344M 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy SiPM is a High density (~103/mm2 ) matrix of diodes with a common output, working in Geiger-Müller regime Common bias is applied to all cells (few % over breakdown voltage) Each cell has its own quenching resistor (from 100kΩto several MΩ) When a cell is fired an avalanche starts with a multiplicative factor of about 105-106 The output is a fast signal (Trise~ns; Tfall ~ 50 ns) sum of signals produced by individual cells SiPM works as an analog photon detector

  8. Lab charcterization to fullfill the simulation hints Model developed by Arktis • We expect 255 photons / matrix for 100 keV deposited energy assuming the 95% of reflectivity 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy Minimum detectable light Detector sensitivity (i.e. S/N or capability to discriminate an “event” against noise )

  9. Lab charcterization to fullfill the simulation hints ≈ 60 ph @ 21.6°C ≈ 250 ph @ 25°C • We expect 255 photons / matrix for 100 keV deposited energy assuming the 95% of reflectivity 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy Firing the matrix with a calibrated photon flux, we measured the minimum detectable light a two different temperatures (different performances due to a combined effect of increased noise and gain drift)

  10. Experimental set-up for proof of principle A short tube (19 cm) used for the proof of principle Filled with 4He at 140 bar, an integrated wavelength shifter and two SiPMs mounted along the wall (by ARKTIS) Two SIPMs read-out through the Hamamatsu electronic board (C11206-0404FB) 2-channels 3-stage amplification with leading edge discrimination (SP5600A – CAEN) Digitizer with a sampling rate of 250 Ms/s 12 bit digitization (V720 – CAEN) 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy

  11. Counting measurements 1st Trigger Scheme 2nd Trigger Scheme typical γ event typical n event Test performed measuring: • Background, n and γ counting rate using 252Cf and 60Co source in contact Two triggering scheme: • Trailing edge discrimination in coincidence • Trailing edge and delayed gate of each single SiPM in coincidence • Few parameters to be optimized: • Leading and trailing threshold • Delay time (ΔT) • Gate aperture 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy

  12. Counting measurements Result for the different trigger scheme @ 28°C An amazing result, corresponding to a γ rejection power at the 106 level [ 10 counts in 1000s, for a number of γ given by acceptance*activity*time = 1/3 * 3 * 104 * 103 ~ 107 ] 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy

  13. Off-line data analysis • Data recorded with a minimum bias trigger • Low threshold on the pulse height discrimination • No coincidence between the two SiPMs • For each triggered events we digitize signal of both SiPMs with sample rate of 125 MS/s and a total duration of 4μs. • Three data set: • 400 events without radioactive sources • 6000 events with 60Co source in contact • 10000 events with 252Cf source in contact • Analysis strategies: • Identify an observable allowing to measure the ratio between noise & particle induced triggers in samples 2 & 3 • Filter noise from particle induced events through a multivariate analysis • Identify the ratio between γ and n events in sample 3 • Filter γ from n through a multivariate analysis • Measure the rejection power of interacting γ and the selection efficiency of interacting neutrons 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy

  14. Sample composition: (% of Background and signal) BKG Co60 Definition of Fast and Slow Component • The areas underneath the fits are used to measure sample composition • These numbers are used to estimate the selection efficiency and bkg rejection power Cf252 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy Each signal is baseline subtracted in the integrated time windows FAST and SLOW component is calculated as the integral of the signal to the left / right side of the peak

  15. : signal over noise distributions A multivariate Bayesian analysis 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy The strategy: • Select 4 no-correlated variables where bkg, γ and n appear to be “reasonably” different • TOT_Diff, Charge Diff, Charge Skewness, Full_charge • Bkg data-set is used to build the experimental probability density functions (p.d.f.) • The corresponding cumulative distributions function (c.d.f.) Ii is then constructed: • The four Ii’s are combined to get the final distribution: Two step procedure: • 1st step: the selection criteria based on P is used to remove the background from n and γ induced events • 2nd step: the procedure is reiterated to define the n/γ selection criteria (60Co sample used to build the p.d.f.)

  16. 1st Step bkg data-set As expected we have a random quantity with a flat distribution 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy c.d.f. obtained for one of the selected variables (total charge), based on the bkg data-set

  17. 1st Step Moving towards a different p.d.f (60Co or 252Cf), we have an accumulation of events on the right part of the histogram which allows as to separate the signal form bkg 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy c.d.f. obtained for one of the selected variables (total charge), based on the bkg data-set

  18. 1st step: bkg rejection • Repeat the exercise for all the quantities and combine the c.d.f. as follow • These two plots show that almost all the signal is on the right part of the histograms (peak) while the bkg is a flat component on the left • The bin at P>0.995 contains ~78% of the γ events • The bin at P>0.995 contains ~99% of the γ +n events for Cf Selection for the 2nd step Selection for the 2nd step 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy

  19. 2nd step • γ- events in the 60Co data-set • n and γ composition in the 252Cf data-set 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy after the Bkg has been filtered out, the ratio between γ and n events in 252Cf can be measured:

  20. 2nd step: γ rejection • The procedure is reiterated using the 60Co data-set to build the cumulative distributions to identify γ over n in the 252Cf data-set Results for a P cut of 0.995 • Results are well beyond the expectation which are pushing us to continue with • Further test to measure the neutron detection efficiency and to qualify the γ/n separation using TOF technique • Tube layout optimization • Improved electronics (see next slide) 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy

  21. Customized electronics 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy • Adjustable bias voltage for each of 16 channels • SiPM temperature readout and gain compensation • The thermo-chip placed onto the SiPM generates a digital pickup noise which cannot be removed • The frequency of the temperature readout is settable • The board include a lemo connector that can be used for veto trigger • Improved minimum detectable light and dynamic range

  22. Customized electronics ≈ 30 ph @ 19.6°C Pedestal ≈ 60 ph @ 19.6°C 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy • Adjustable bias voltage for each of 16 channels • SiPM temperature readout and gain compensation • The thermo-chip placed onto the SiPM generates a digital pickup noise which cannot be removed • The frequency of the temperature readout is settable • The board include a lemo connector that can be used for veto trigger • Improved minimum detectable light and dynamic range

  23. Conclusion 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy The Proof of Concept of SiPM arrays in the tube has been successfully completed The tube design optimization is certainly required A new front-end electronics (designed at Uni. Insubria) has been characterized in the lab and fulfils the requirements New test campaign is on the way to optimize the on-line and off-line analysis

  24. Spares 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy

  25. Typical events with PMTs Typical plot from the 4He detectors showing the discrimination between neutrons (Am-Be) and gamma (60Co) 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy Neutron/γ discrimination is based on the difference between the fast/slow component of the scintillation light Typical neutron and gamma events

  26. Bkg_rejection • Bkg flat distribution (1st selection) • Co60 flat distribution (2nd selection) 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy

  27. 2nd step Distributions of the four discriminant variables used in the second step of the procedure after having filtered the noise induced events 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy

  28. 2nd step: γ rejection measured with a data-set with pure bkg P_value=0.995 Neutron eff = 94% γ rejection power= 92% 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy

  29. Few spectra used in the linearity plot 13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy

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