RAPSODI RAdiation Protection with Silicon Optoelectronic Devices and Instruments

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1 RAPSODI RAdiation Protection with Silicon Optoelectronic Devices and Instruments Massimo Caccia Universita dell Insubria Como (Italy) on behalf of The RAPSODI collaboration 11th Topical Seminar on Innovative Particle and radiation detectors,,siena October 1-4, 2008

RAPSODI RAdiation Protection with Silicon Optoelectronic Devices and Instruments Funded by the EC under the Sixth Framework Program (Co-operative research) Start-time Oct 2006; End-time: Jan 2009

2 RAPSODI RAdiation Protection with Silicon Optoelectronic Devices and Instruments Funded by the EC under the Sixth Framework Program (Co-operative research) Start-time Oct 2006; End-time: Jan 2009 Main objectives: Silicon Photo Multipliers development and optimization for three well defined applications: Dosimetry in Mammography, Radon Monitoring, illicit traffic of radioactive material (homeland security) Consortium composition: 4 Small and Medium Enterprises + 3 R&D performers SensL (IE) PTW (DE) UNICO (IT) (Leading organization) AGH (PL) Plch SMM (CZ) ITEP (RU) ForimTech (CH)

Silicon Photon Multipliers SiPM = High density (~103/mm2 ) matrix of

advantages over traditional photo-detectors: high sensitivity

ns) compactness, robustness, low operating voltage and power

cells V working DCR GAIN PDE (%) (green) SensL 3x3 20 x 20 8640 30 6

3 Silicon Photon Multipliers SiPM = High density (~103/mm2 ) matrix of diodes with a common output, working in Geiger-Müller regime advantages over traditional photo-detectors: high sensitivity (single photon discrimination) high speed (Trise~ 1 ns; Tfall ~ 50 ns) compactness, robustness, low operating voltage and power consumption, low cost Producer Area (mm2) Pixel size (µm) No. cells V working DCR GAIN PDE (%) (green) SensL 3x3 20 x MHz Hamamatsu 1x1 17 x khz 3 x CPTA 1x1 30 x MHz

4 Full characterization protocol I-V measurements (leakage current, quenching resistor, breakdown voltage) Noise measurements (vs over voltage and vs temperature): dark counting rate (DCR) vs bias voltage optical cross-talk (DCR vs threshold) Analysis of (Poissonian photon) spectrum (vs temperature) resolution power (how many photons can I distinguish?) & gain working point optimization (at low and large flux) noise measurement (not DCR) optical cross-talk (deviations from the Poissonian distribution) linearity & dynamic range Spectral response (PDE vs λ, PDE vs temperature) timing properties and time resolution (not relevant for RAPSODI but in progress)

Basic Equipment USB-VME Bridge CAEN V171816ch QDC CAEN V792N DC power supply Agilent 6645A Scope Agilent 54624A Pulse Generator Agilent 33250A [50 MHz] Lecroy 821 NIM discriminator CAEN NIM

5 Basic Equipment USB-VME Bridge CAEN V171816ch QDC CAEN V792N DC power supply Agilent 6645A Scope Agilent 54624A Pulse Generator Agilent 33250A [50 MHz] Lecroy 821 NIM discriminator CAEN NIM level translators SensL Board + ZFL-500-BNC [20 db gain] PDL800-B PicoQuant (green LED) OZ optics coupler & focuser Dark Box +XY stage and manual Z Keithley 4200 SCA C-V meters QS+HF

6 Photon Spectrum & Gain Light source: Pico Quant PDL light at ~ 510 nm (green) peak Gain ~ 106 > 20 room T Peak width: System noise Cell-to-cell gain variation (process uncertainties) Ileak fluctuations Spurious hits in the QDC integration time width count Xtremely good resolution power!

Dark Count Rate & Xtalk Threshold scan The Dark Counts (DCR)

initiated by thermal emission. > 0.5 ph 0.5 ph 1.5 ph 2.5 ph > 1.

5 ph an avalanche generation can fire another cell by a photon;

7 Dark Count Rate & Xtalk Threshold scan The Dark Counts (DCR) measure the rate at which a Geiger avalanche is randomly initiated by thermal emission. > 0.5 ph 0.5 ph 1.5 ph 2.5 ph > 1.5 ph fixed threshold (0.5 phe-) > 2.5 ph an avalanche generation can fire another cell by a photon; measuring the DCR for different thresholds is possible to define and evaluate the Optical Cross talk as:

8 Photon Detection Efficiency (PDE) PDE Pico Quant PDL 800 Ligth guide Ø 1 mm clear fiber (divergence 15 ) Light source calibrated with a reference PMT (H5783) and tuned to have 200 ph/burst The PDE has to be corrected for the Optical Cross Talk as: FC connector SiPM sensor FC to guarantees the reproducibility of the fiber tip to SiPM surface distance and alignment (acceptance control)

9 Temperature Dependence Gain vs bias voltage Pico Quant PDL 800 ~ 510 nm Cooling Box + Temperature control Gain vs temperature SensL 9k: 23.2 mv/ C ± 1.4 mv/ C SensL 04k : 23.6 mv/ C ± 0.9 mv/ C

10 Gain stabilization vs. T Breakdown Voltage rescaled accounting for the temperature variation

11 Flashing an Application: Dosimetry in mammography Dosimetry in mammography is utmost important and this is somehow proven by the ongoing debate on the relevance of mammography screening but currently existing instruments are limited: Standard Termo-Luminescent Detectors require to be analyzed after examination, degrade with time MOSFET detectors suffer from low stability and degrade with each irradiation Ionization chamber devices need relatively high voltage (cannot be used in contact with the patient), not tissue equivalent precise measurements of the actual dose being received by a patient without distorting the X-ray beam and introducing any artefacts in the image Some functional requirements: dose rate range (2 150 mgy/s) dose range (0.5 mgy mgy) sensitivity (5%) overall accuracy (±10%) tolerance to environmental variation & stability

Prototype qualification Conceptual design of the prototype tested @ PTW secondary standard lab for dosimetry: Scintillator (tile or fiber) Ligth guide Ø 1 mm clear fiber FC connector & SiPM

12 Prototype qualification Conceptual design of the prototype PTW secondary standard lab for dosimetry: Scintillator (tile or fiber) Ligth guide Ø 1 mm clear fiber FC connector & SiPM Electronics Trace plot: typical mammo SiPM output (continuous photons flux pulse duration of each sample100 ms) PHISYCAL OBSERVABLE: buffered signal sum Sum of samples signals selected by an edge detector algorithm + left & right buffer BUFFERED SUM proportional to the DOSE ~TIME

13 Executive summary of the results Two different set-up (optimized for dynamic range & λ): 1mm scintillator tile coupled with SensL SiPM (9k cells, 3x3 mm2) Blue scintillator fiber coupled with Hamamatsu (400 cells, 1x1 mm2) Irradiation: 0, mgy/s Tile + SensL Fiber + Hamamatsu Precision(%) 1.95 ± ± 0.03 SensitivityA (mgy/s) 2.60 ± ± 0.03 MDSB (mgy/s) ± ± Linear Dinamic range (mgy/s) 160 > 200 A Sensitivity: Precision / system gain B MDS: minimum signal distinguishable from the noise

14 The quest for invisibility Slicing one row. Possibly fair enough for a physicist, not for a Medical Doctor

15 Conclusions Within the RAPSODI project, a laboratory for SiPM and light sensors characterization has been setup at the University of Insubria. The lab has developed both the expertise and the instrumentation to perform all the measurements to fully characterize SiPM. This expertise has been used also in the test of a mammography dosimeter instrument being developed in collaboration with PTW. The performances of the first MammoDos prototype are according to specification and this will lead to the final product before the end of the project. The prototype of the Radon Concentration Measurement device has been qualified (Intellectual Property issues force me not to say more ) RAPSODI is also finalizing a start-up kit for interested users (Fast LED, Scintillator tile, Ampli, discri & logic and more) By now, I m really convinced the fun sith SiPM (SPM, MMPC and any other possible brand name) ] has just started!

Introducing the CAEN Silicon Photomultiplier Kit: a flexible, modular system for sensor testing & education

Massimo Caccia Universita dell Insubria @ Como massimo.caccia@uninsubria.it On behalf of Introducing the CAEN Silicon Photomultiplier Kit: a flexible, modular system for sensor testing & education NDIP