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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. - PowerPoint PPT Presentation
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Romualdo Santoro
Università dell’Insubria
Integration of SiPM in a high-pressure noble gas scintillation detector for homeland
security
M. Caccia, V. Chmill, S. Martemiyanov – Insubria
R. Chandra, G. Davatz, U. Gendotti – Arktis
13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy
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MODES_SNM
R. Santoro
Modular Detector System for Special Nuclear Material
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
13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy
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Baseline technology
R. Santoro
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 wrt 3He
44 cm diameter x 47 cm sensitive length 180 bar 4He sealed system maintaining
gas purity
R. Chandra et al., 2012 JINST 7 C03035
13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy
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MODES_SNM System overview
R. Santoro
Modular system optimized for: Fast neutron (4He) Thermal neutron (4He with Li
converter) Gamma (Xe)
All components are being integrated, we are approaching the
commissioning and qualification phase
With γ-ray spectroscopy
capability
13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy
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MODES_SNM R&D
R. Santoro
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
13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy
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SiPM
R. Santoro
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
Signals from SiPM
13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy
7
SiPM
R. Santoro
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
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
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Lab charcterization to fullfill the simulation hints
R. Santoro
Minimum detectable light Detector sensitivity (i.e. S/N or capability to
discriminate an “event” against noise )
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
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Lab charcterization to fullfill the simulation hints
R. Santoro
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)
≈ 250 ph @ 25°C ≈ 60 ph @ 21.6°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
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)
R. Santoro
13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy
11
Counting measurements
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
R. Santoro
1st Trigger Scheme
2nd Trigger Scheme
typical γ event typical n event
13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy
12
Counting measurements
R. Santoro
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 ]
Result for the different trigger scheme @ 28°C
13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy
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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:1. 400 events without radioactive sources
2. 6000 events with 60Co source in contact
3. 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
neutronsR. Santoro
13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy
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Sample composition: (% of Background and signal)
R. Santoro
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 peakDefinition of Fast and
Slow Component
BKG
Co60
Cf252 The areas underneath the fits are used
to measure sample composition These numbers are used to estimate
the selection efficiency and bkg rejection power
13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy
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A multivariate Bayesian analysis
R. Santoro
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.)
∫∞−= ix
iiiii dxxhxI~
)()~( : signal over noise distributions)( ii xh
€
P = Π⋅(−logΠ)i
i!i=0
3
∑ ,Π = I1⋅ I2⋅ I3⋅ I4
13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy
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1st Step
R. Santoro
c.d.f. obtained for one of the selected variables (total charge), based on the bkg data-set
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
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1st Step
R. Santoro
c.d.f. obtained for one of the selected variables (total charge), based on the bkg data-set
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
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1st step: bkg rejection
R. Santoro
Selection for the 2nd step
Selection for the 2nd step
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
€
P = Π⋅(−logΠ)i
i!i=0
3
∑ ,Π = I1⋅ I2⋅ I3⋅ I4
Repeat the exercise for all the quantities and combine the c.d.f. as follow
13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy
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2nd step
R. Santoro
after the Bkg has been filtered out, the ratio between γ and n events in 252Cf can be measured:
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
20
2nd step: γ rejection
R. Santoro
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
R. Santoro
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
13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy
22
Customized electronics
R. Santoro
≈ 60 ph @ 19.6°C
≈ 30 ph @ 19.6°C
Pedestal
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
13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy
23
Conclusion
R. Santoro
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
13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy
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Spares
R. Santoro
13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy
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Typical events with PMTs
R. Santoro
Neutron/γ discrimination is based on the difference between the fast/slow component of the scintillation light
Typical neutron and gamma events
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
26
Bkg_rejection
R. Santoro
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
R. Santoro
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
R. Santoro
€
εn _ select =Ncf _ sig _ sel −ε bkg _ rej * Ncf _ total _ bkg
Ncf _ total _ signal
P_value=0.995Neutron eff = 94%γ rejection power= 92%
€
γrej _ power =1 −ε bkg _ rej
€
εbkg _ rej =Nco60 _ sel
Nco60 _ total _ signal
measured with a data-set with pure bkg
13th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD13) 7-10 Oct. 2013, Siena, Italy
29
Few spectra used in the linearity plot
R. Santoro