The Silicon Photo-Multiplier (SiPM) being yet in its infancy, a full protocol for the sensor characterization has been developed and implemented at the Physics Department of Universita\u2019 dell\u2019Insubria. Sensors from different producers have been analyzed and compared, in view of the integration in the instruments for radiation detection. Exemplary illustrations are reported here, together with the first results on real-time dosimetry in mammography

A.  Bulgheroni

A.  Golubev

A.  Kantsyrev

A.  Martemianov

C.  Cappellini

C.  Pychlau

F.  Risigo

J.  W\ufcrfel

M.  Caccia

M.  Jastrzab

N.  Fedyushkina

N.  Markov

V.  Chmill

The Silicon Photo-Multiplier (SiPM) being yet in its infancy, a full protocol for the sensor characterization has been developed and implemented at the Physics Department of Universita’ dell’Insubria. Sensors from different producers have been analyzed and compared, in view of the integration in the instruments for radiation detection. Exemplary illustrations are reported here, together with the first results on real-time dosimetry in mammography

F. Risigo

C. Cappellini

V. Chmill

N. Fedyushkina

A. Golubev

M. Jastrzab

A. Kantsyrev

N. Markov

A. Martemianov

C. Pychlau

J. Würfel

BULGHERONI, ANTONIO

CACCIA, MASSIMO

Archivio istituzionale della ricerca - Università dell'Insubria

ARTICLE IN PRESSNuclear Instruments and Methods in Physics Research A 607 (2009) 75–77Contents lists available at ScienceDirectNuclear Instruments and Methods inPhysics Research A0168-90doi:10.1 CorrE-m1 ht2 ht3 htjournal homepage: www.elsevier.com/locate/nimaSiPM technology applied to radiation sensor developmentF. Risigo a,, A. Bulgheroni b, M. Caccia a, C. Cappellini a, V. Chmill a, N. Fedyushkina c, A. Golubev c,M. Jastrzab a,d, A. Kantsyrev c, N. Markov c, A. Martemianov c, C. Pychlau e, J. Wu¨rfel ea Physics and Mathematics Department, University of Insubria, via Valleggio 11, Como 22100, Italyb Istituto Nazionale Fisica Nucleare, INFN sez. Milano, via Celoria 16, 20133 Milano, Italyc ITEP, Institute of Theoretica and Experimental Physics, B. Cheremushkinskaya 25, 117259 Moscow, Russiad Electronics Department, AGH-University of Science and Technology, al. Mickiewicza 30, Krakow 30059, Polande PTW-Freiburg, Physikalisch-Technische Werkstaetten Dr. Pychlau Gmb, Loerracher Str. 7, 79115 Freiburg, Germanya r t i c l e i n f oAvailable online 1 April 2009Keywords:Silicon Photo-MultipliersRadon monitoring02/$ - see front matter & 2009 Elsevier B.V. A016/j.nima.2009.03.209esponding author. Tel.: +390312386142; faxail address: fabio.risigo@uninsubria.it (F. Risigtp://www.sensl.comtp://www.hamamatsu.comtp://www.zao-cpta.ru/a b s t r a c tThe Silicon Photo-Multiplier (SiPM) being yet in its infancy, a full protocol for the sensorcharacterization has been developed and implemented at the Physics Department of Universita’dell’Insubria. Sensors from different producers have been analyzed and compared, in view of theintegration in the instruments for radiation detection. Exemplary illustrations are reported here,together with the ﬁrst results on real-time dosimetry in mammography.& 2009 Elsevier B.V. All rights reserved.1. IntroductionThe Silicon Photo-Multipliers (SiPM) [1] consist of a high-density(103mm2) matrix of diodes with a common output. Each diode isoperated in a limited Geiger–Mu¨ller regime [2], in order to achievegain at the level of 106. As a consequence, these detectors aresensitive to single photons (even at room temperature), feature adynamic range well above 100photons/burst and have reasonablephoton detection efﬁciency (PDE). Moreover, the SiPMmeasures thelight intensity simply by the number of ﬁred diodes.Compactness, robustness, low cost, low operating voltage andpower consumption represent the numerous advantages overtraditional photodetectors.Various SiPMs from three producers (Hamamatsu1, SensL2 andCPTA3) have been qualiﬁed and compared. As exemplary illustra-tion, the main characteristics of the two sensors that have been usedfor the measurements described in Section 3 are reported in Table 1.Fig. 1 shows a typical oscilloscope output and the correspondentspectrum of the integrated signal for the Hamamatsu SiPM: theindividual peaks are clearly separated from each other, allowing astraightforward photon counting.2. SiPM characterizationThe SiPM characterization procedure implemented at Universita’dell’Insubria has been performed on existing devices with the mainll rights reserved.: +39 0312386258.o).goal to deﬁne an exhaustive protocol and to produce a comparativestudy. The tests have investigated parameters such as dark countrate (DCR), optical crosstalk, gain, photo detection efﬁciency andtheir temperature dependence. The characterization of the detectorsis a major task with application-speciﬁc key ﬁgures.For instruments designed for the detection of low-intensitylight pulses, the photon detection efﬁciency and the dark countrate are the major ﬁgures. The former is determined by thequantum efﬁciency, the ﬁll factor and the avalanche triggeringefﬁciency, obviously linking it to the dark count rate. The DCRresults from avalanches initiated by thermally generated carriers;however, because of the optical crosstalk [3], more cells can beﬁred in a correlated way, making the technology and operationaloptimization non-trivial. As exemplary illustration, values of thePDE versus overvoltage are shown in Fig. 2 for the detectors usedin mammography (Table 1) and tested with green light at 524nm.The ‘‘staircase’’, measuring the DCR versus the discriminationthreshold, is shown in Fig. 3, where levels corresponding to thepeak amplitude of the single, double and triple cells are evident.For instruments sampling a ‘‘continuous’’ light ﬂux, where thetime scale is deﬁned with respect to the single-cell signaldevelopment (see Fig. 1 for a typical pulse shape), the key ﬁgureis essentially the linear dynamic range, where signiﬁcant devia-tions may be expected as long as the probability to hit a cellduring its recovery time is not negligible. For these applications,single-cell signal piling-up is not an issue as long as theproportionality with the input stimulus is preserved.Tests, performed with a focus on the dosimeter for mammo-graphy, prove the linearity of the sensors under test till avalanchetriggering frequencies in excess of the GHz level.For every application (whether oriented to the detection ofpulses or sampling a continuous ﬂux), thermal stability is anasset.ARTICLE IN PRESSFig. 1. Oscilloscope output and the correspondent multipeak spectrum for the Hamamatsu SiPM.over voltage (%)1 1.5 2 2.5 3 3.5 4PDE (%)246810121416PDE (%)PDE corrected (%)Fig. 2. PDE dependence versus overvoltage, for the Hamamatsu SiPM MPPCS010361-050; the plot shows the value for uncorrected PDE and corrected for theoptical crosstalk.Table 1Main characteristics of a SensL SiPM SMPScint1000 04 and Hamamatsu SiPMMPPC S010361-050.SensL SiPM Hamamatsu SiPMNumber of diode 8640 400Single-diode dimension 20mm20mm 50mm50mmBreakdown voltage 28.04V 70.56VDark count rate 8MHz 270kHzOptical crosstalk 22.5% 10%Gain 106 7.5105PDE 4% l ¼ 520nm) 50%(l ¼ 400nm)Measurements refer to room temperature and a working overvoltage of +2V.Threshold [mV]50 100 150 200 250 300Frequency [kHz]110102Fig. 3. DCR versus threshold for the Hamamatsu SiPM.F. Risigo et al. / Nuclear Instruments and Methods in Physics Research A 607 (2009) 75–7776Results do suggest that, apart from the obvious solutions ofoperating in a temperature-controlled environment, the possibi-lity to implement a feedback procedure on the bias voltage is aviable option. Detailed measurements will be the subject of aforthcoming publication.3. Real-time dosimetry in mammographyThe real-time dose measurement in mammography is anexemplary application of the SiPM sensors.This instrument is meant to be used during every mammo-graphy scan to monitor the dose delivered to the patient. Itconsists of a sensitive volume of scintillating, a Silicon Photo-Multiplier light sensor and a small local display of the recordeddose.Two prototypes were characterized at PTW-Freiburg: Blue light-emitting plastic tile, optically coupled to a wave-length shifting ﬁber, in order to match the SiPM peaksensitivity. A green-emitting scintillating ﬁber, coupled to a clear ﬁberconveying the light to a SiPM.ARTICLE IN PRESSTable 2Characterization results for the mammography device.Set-up Precision (%) Gain (QDC/mGy/s) Sensitivity (mGy/s) MDS (mGy/s) Max. dose rate (mGy/s)o5% o7.5% o10%Tile-SensL 1.9570.05 0.0050070.00001 0.4570.01 2.37870.05 40 – –Fiber-SensL 3.1770.05 0.0328670.00001 2.6770.04 0.72370.007 115 155 190Fiber-Hama 2.0770.03 0.0169170.00001 1.8270.02 0.21670.002 170 200 –The precision is computed as the standard deviation of the measurements, corrected for the correlation factor. The linearity was evaluated ﬁtting the data up to half of thescanned range and then evaluating the deviations from the extrapolated linear ﬁt. The dose rates corresponding to 5%, 7.5% and 10% deviation level have been computed andretained as indicators.sample0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000QDC - pedestal-200020040060080010001200140016001800Fig. 4. The signal for a typical data set is shown as a function of the samplenumber. The integration time for the reported data was 3000ns for a dose rate of21mGy/s.F. Risigo et al. / Nuclear Instruments and Methods in Physics Research A 607 (2009) 75–77 77For the tile only the SensL SiPM sensor was used while the ﬁbersystem was also interfaced to the multi-pixel photon counterproduced by HAMAMATSU (see Table 2).The prototypes were exposed to the X-ray beam of a referencemammography unit and dose rates spanning from less than1mGy/s to a few hundreds mGy/s have been used to irradiate thedevice in realistic conditions.The charge from the sensor has been integrated and sampled at30 kHz by a QDC (charge digitizer), a transimpedance ampliﬁca-tion stage (the QDC conversion capacitance is 0.11pC per QDCunit). Typical integration times were ranging between 500 and5000ns while the irradiation times were of 0.1 s. For eachirradiation, the effective dose rate and exposure time havesimultaneously been measured with calibrated sensors.The typical output signal from the prototype is displayed inFig. 4, where the samples corresponding to the tile irradiation areclearly distinguishable.The characterization of the prototype has been performedrelying on four main ﬁgures of merit:meOptprecision, deﬁned as the standard deviation of the measure-ments for constant radiation conditions; sensitivity, namely the minimum detectable variation in thedose rate; minimum detectable signal (MDS), differing from the sensi-tivity since it accounts as well for the spread in the offset and linearity, measured against the dose rate in the region ofinterest.The system response to increasing dose rates has beenmeasured and compared with the values provided by theUNIDOS.4 The precision and the linearity have been evaluatedfrom these sets of measurements using both the tile and the ﬁberset-up.A hint of the system performances, for the three conﬁgura-tions, is given in Table 2 while a complete report of themeasurements procedure and results can be found in [4].4. Conclusion and outlookThe working prototype described here has been designed andcharacterized during a research project funded by the EuropeanCommission within the sixth framework program.5 The project issuccessfully entering its last phase, and by the end of it all theworking prototypes will be completely qualiﬁed.References[1] A. Adikinov, et al., Nucl. Instr. and Meth. A 387 (1997) 231.[2] K.G. McKay, Phys. Rev. 94 (1954) 877.[3] F. Zappa, S. Cova, M. Ghioni, A. Lacaita, C. Samori, Appl. Opt. 35 (12) (1996)1956.[4] C. Cappellini, et al., The RAPSODI project: SiPM development for appliedresearch in radiation protection, in: 2008 NSS-MIC Conference Record.4 The UNIDOS, an ultrahigh-sensitive electrometer for charge and currentasurement, produced by PTW-Freiburg.5 Contract number: COOP 32993 – RAPSODI (RAdiation Protection with Siliconoelectronic Devices and Instruments).

SiPM technology applied to radiation sensor development

SiPM technology applied to radiation sensor development

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