Andrea Pola. Dipartimento di Energia, Politecnico di Milano, via Ponzio 34/3, Milano INFN, Sezione di Milano, via Celoria 16, Milano

Transcription

1 Andrea Pola Dipartimento di Energia, Politecnico di Milano, via Ponzio 34/3, Milano INFN, Sezione di Milano, via Celoria 16, Milano

2 SILICON DEVICES for: Neutron spectrometry Solid state microdosimetry

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4 NEUTRON SPECTROMETRY WITH SILICON DEVICES Polyethylene radiator Si device Spectroscopy Chain Recoilproton spectrum Unfolding Procedure Analytical Response Matrix Neutron spectrum Advantages: High Spatial resolution Good energy resolution Low cost Compactness Limitation: Maximum Detectable energy Radiation Damage Application: Low-energy ionaccelerators facilities

5 A Recoil-proton spectrometer n Polyethylene Thickness = 1 mm p P-i-n diode (ex. Hamamatsu S Thickness = 500 μm Sensitive area = 9 x 9 = 81 mm 2 )

6 Typical response of silicon diodes irradiated with mono-energetic neutrons 0,1 En = 4.8 MeV 0,01 Photons Response (cm 2 ) 1E-3 1E-4 1E-5 Recoil-protons 1E-6 1E Deposited energy (kev)

7 Silicon diode response to mono-energetic neutrons at different energies Response (cm 2 ) x10-4 1x10-5 = MeV = MeV = MeV = MeV = MeV = MeV E n = MeV = MeV = MeV = MeV = MeV = MeV = MeV = MeV = MeV = MeV = MeV = MeV = MeV = MeV = MeV E n = MeV = MeV Deposited energy (kev)

8 Silicon diode response: comparison with analitycal model Counts per unit neutron fluence (cm 2 ) 10-3 Monoenergetic 2.73 MeV neutrons Experimental Analitical Deposited energy (kev)

9 UNFOLDING ALGORITHM An iterative unfolding algorithm based on a non-linear least-squared method (GRAVEL) is employed to reconstruct the primary neutron spectra The response matrix R j (E de ) is composed by the set of analytical response functions to monoenergetic neutrons R j (E de ) = p j (E de ) π j ( ) with j = 0... N Guess: distribution uniform in energy

10 Energy distribution of the yield of neutrons generated at 0 by 5.0 MeV protons striking a thick beryllium target 5x10 8 Neutrons from 9 Be(p,n) 9 B at 0 4x10 8 3x10 8 Diode spectrometer Time of flight (Massey et al. ) Neutron yield (sr -1 MeV -1 μc -1 ) 2x Neutron energy (MeV)

11 Energy distribution of the yield of neutrons generated at 0 by 5.0 MeV protons striking a thick beryllium target 5x10 8 Neutrons from 9 Be(p,n) 9 B at 0 4x10 8 3x10 8 Diode spectrometer Time of flight (Massey et al. ) Neutron yield (sr -1 MeV -1 μc -1 ) 2x Neutron energy (MeV)

12 Pulse Shape Discrimination (PSD) with silicon diodes 80 V out_preamplifier (mv) t rise =30 ns 1 MeV photon (uniform distribution) 1 MeV photon (triangular distribution) 1 MeV proton t rise =45 ns Time (ns) 90% t rise =70 ns 10%

13 PSD: Electronic chain -V Low Noise Preamplifier Spectroscopy Amplifier (τ slow ) ADC Filter Amplifier CR-RC (τ fast ) Filter Amplifier CR-RC (τ fast ) Constant Fraction Discriminator Pulse Shape Analyzer Start Time-to- Amplitude Converter Stop Timing chain

14 Timing spectra 1 Photons = 1.3 MeV Counts per unit charge (μc -1 ) 0,1 0,01 with polyethylene without polyethylene Recoil Protons T start-stop (ns)

15 A NEUTRON SPECTROMETER BASED ON A PIN-DIODE DIODE: Measurement of Continuos Neutron Spectra Energy distribution of the yield of neutrons generated at 0 by 5.0 MeV protons striking a thick beryllium target 10 9 Time-of-flight (TOF) PIN-Diode without PSD PIN-Diode with PSD Neutron yield (μc -1 sr -1 MeV -1 ) 10 8 Neutron yield above 1.1 MeV (µc -1 sr -1 ) This work TOF (2.25±0.10)x10 8 (2.64±0.07)x Neutron energy (MeV) TOF: Howard, W.B., Grimes, S.M., Massey, T.N., Al-Quraishi, S.I., Jacobs, D.K., Brient, C.E., Yanch, J.C., Measurement of the Thick-Target 9 Be(p,n) Neutron Energy Spectra, Nucl. Sci. Engineering 138(2) (2001)

16 MONOLITHIC SILICON TELESCOPE ΔE-E (ST-Microelectronics) [1] Sensitive area: 1 mm 2 p + n + ΔE stage ΔE thickness: ~2 μm p E thickness: ~500 μm + E stage n + The ΔE triggers the E stage for secondary electron discrimination Converter ΔE E Charge sensitive preamplifier Charge sensitive preamplifier ΔE chain E chain Spectroscopy Amplifier (τ = 3 μs) Spectroscopy Amplifier (τ = 2 μs) Multiparameter MCA [1] Tudisco, S., et al. A new large area monolithic silicon telescope. Nucl. Instrum. Meth. A 426, (1999). Neutron Spectrometry with a Monolithic Silicon Telescope

17 Monolithic Si - E/E detector (ST-Microelectronics & LNS INFN) 1 MeV Boron (Projected range ~ μm) Doping profile 500 μm N - Dopant concentration (cm -3 ) Boron Depth (μm) Neutron Spectrometry with a Monolithic Silicon Telescope

18 Monolithic Si - E/E detector Process (ST-Microelectronics & LNS INFN ) ~2 μm Arsenic N - Dopant concentration (cm -3 ) Doping profile Arsenic Boron Depth (μm) Phosphor Neutron Spectrometry with a Monolithic Silicon Telescope

19 Monolithic Si - E/E detector ~2 μm ~500 μm N - Dopant concentration (cm -3 ) Doping profile Arsenic Boron Depth (μm) Neutron Spectrometry with a Monolithic Silicon Telescope

20 Monolithic Si - E/E detector ~2 μm ~500 μm N - Dopant concentration (cm -3 ) Doping profile Arsenic Boron Depth (μm) Neutron Spectrometry with a Monolithic Silicon Telescope

21 Monolithic Si - E/E detector ~2 μm ~500 μm N - Dopant concentration (cm -3 ) Arsenic Doping profile X eff ~ 2 μm x depl Boron Depth (μm) E stage: E E stage: PIN diode substrate, x ~ 500 μm N on P diode micrometric thickness, x depl ~ 1 μm Capacitance ~ 10 nf cm -2 Charge collection: fast vertical drift charge division x eff ~ 2 μm Neutron Spectrometry with a Monolithic Silicon Telescope

22 Recoil Proton Spectrometer = MeV hν E = n = MeV MeV Converter Si Diode p E E -1-1 p(e p(e d ) cm 2 d ) (MeV cm ) 2 ) Analytical Experimental n e E E d (MeV) hν Neutron Spectrometry with a Monolithic Silicon Telescope

23 E/E Recoil Proton Spectrometer = MeV hν 10-3 = MeV Converter cm 2 ) 10-4 E E (trigger) E stage p p(e d E ) (MeV n e E d E (MeV) hν Neutron Spectrometry with a Monolithic Silicon Telescope

24 E/E Recoil Proton Spectrometer = MeV 300 = 1715 kev Counts per unit neutron fluence 3.0E-4 6.0E-4 Converter E E stage E stage e hν p (kev) E d ΔΕ Protons E d E (MeV) 9.0E-4 1.2E-3 1.5E-3 1.8E-3 1.8E-3 2.4E-3 3.5E-3 electrons n hν 10-3 = MeV cm 2 ) 10-4 E/E discrimination p(e d E ) (MeV Neutron Spectrometry with a Monolithic Silicon Telescope E d E (MeV)

25 ΔE E E COINCIDENCE TECNIQUE AND PARTICLE DISCRIMINATION E stage response function to MeV neutrons Response per unit neutron fluence (MeV -1 cm 2 ) Without coincidence technique ΔE - E coincidence After off-line discrimination = MeV E d E (MeV) Neutron Spectrometry with a Monolithic Silicon Telescope

26 ΔE E E SCATTER PLOTS AT DIFFERENT NEUTRON ENERGIES 300 = 680 kev Counts per unit neutron fluence 300 = 996 kev Counts per unit neutron fluence 3.0E-4 3.0E-4 5.1E-4 5.1E-4 7.2E-4 7.2E-4 9.4E-4 (kev) E-4 1.2E-3 1.4E-3 1.6E-3 1.8E-3 2.0E-3 (kev) E-3 1.4E-3 1.6E-3 1.8E-3 2.0E-3 E d ΔΕ 100 E d ΔΕ E d E (kev) E d E (kev) 300 = 1306 kev Counts per unit neutron fluence 3.0E = 1715 kev Counts per unit neutron fluence 3.0E-4 6.4E-4 6.0E-4 9.8E-4 9.0E E-3 1.7E E-3 1.5E-3 2.0E-3 1.8E-3 (kev) E d ΔΕ E-3 2.7E-3 3.0E-3 (kev) E d ΔΕ E-3 2.4E-3 3.5E E d E (kev) E d E (kev) Neutron Spectrometry with a Monolithic Silicon Telescope

27 MONOLITHIC SILICON TELESCOPE: ANALYTICAL MODEL of RESPONSE FUNCTIONS 1. Assumptions: elastic scattering isotropic in the centre-of-mass system; a parallel beam of monoenergetic neutrons; a uniform probability of interaction in the polyethylene; the contribution of recoil carbon ions is neglected at the energies accounted for 2. Taking into account the actual geometrical structure of the telescope (dead layer 0.4 μm, ΔE stage 1.9 μm and E stage ) 3. Starting from range-energy and stopping power energy relations taken from ICRU report n 49 Bivariate probability density distribution per unit neutron fluence of the energy E d ΔE and E d E deposited in the ΔE and E stage, respectively Prob( E d ΔE, E de ) Neutron Spectrometry with a Monolithic Silicon Telescope

28 p(e ΔE d,e E d ) = R MONOLITHIC SILICON TELESCOPE: ANALYTICAL MODEL of RESPONSE FUNCTIONS 2 h poly 3 (E n ) (R Si (E ΔE d + E 1 E d ) R Si (E E d )) 4 S S Si poly E E Si R R Si Si Si (E E d (E a + h ) + h E d a + h ) + h Si ΔE E Si E ( R (E + E ) R (E )) d S (E ΔE d + E Si E Si ΔE E Si E S (E ) ( R (E E ) R (E )) d + d d d d d Si E d ) = 2.7 MeV p(e d ΔE,E d E ) (kev -2 cm 2 ) 7.0E E E E-12 Bivariate distribution normalized to unit neutron fluence (kev) E E E-10 E ΔE d E E The model does not take into account statistical uncertainties (straggling, electronic noise) E E d (kev) Neutron Spectrometry with a Monolithic Silicon Telescope

29 MONOLITHIC SILICON TELESCOPE: FLUKA SIMULATIONS 400 En = 2727 kev 2.000E E E-12 (kev) E ΔE d E E E E E E E E d (kev) Neutron Spectrometry with a Monolithic Silicon Telescope

30 MONOLITHIC SILICON TELESCOPE: FLUKA simulation and analitycal model Comparison between analytical model and simulation 400 = 2.7 MeV p(e d ΔE,E d E ) (kev -2 cm 2 ) 300 Analytical 2.000E E E E-11 (kev) E E E-11 E ΔE d 1.125E E E E d (kev) Neutron Spectrometry with a Monolithic Silicon Telescope

31 MONOLITHIC SILICON TELESCOPE: FLUKA simulation and analitycal model Comparison between analytical model, simulation and experimental = 2.7 MeV Counts per unit neutron fluence (kev -2 cm 2 ) 2.000E E E E-12 (kev) E E E-11 E ΔE d 4.488E E E E d (kev) Neutron Spectrometry with a Monolithic Silicon Telescope

32 IRRADIATIONS WITH MONOENERGETIC NEUTRONS (at INFN LNL - Legnaro): comparison with simulations and analytical model 10-4 Experimental Analytical (this work) FLUKA Simulation cm 2 ) p(e d E ) (MeV = MeV = MeV = MeV = MeV E E d (MeV) Neutron Spectrometry with a Monolithic Silicon Telescope

33 MONOLITHIC SILICON TELESCOPE: DETECTION EFFICIENCY Detector Sensitive Area : 1 mm 2 1.5x10-5 Counts per unit neutron fluence (cm 2 ) 1.0x x10-6 Analytical Experimental (MeV) Neutron Spectrometry with a Monolithic Silicon Telescope

34 MEASUREMENTS OF CONTINUOUS SPECTRA Energy distribution of the yield of neutrons generated at 0 by 5.0 MeV protons striking a thick beryllium target Howard et al. (TOF) Monolithic Silicon Telescope Neutron yield (MeV -1 μc -1 sr -1 ) Neutron energy (MeV) Time-of-Flight: Howard, W.B., Grimes, S.M., Massey, T.N., Al-Quraishi, S.I., Jacobs, D.K., Brient, C.E., Yanch, J.C., Measurement of the Thick-Target 9 Be(p,n) Neutron Energy Spectra, Nucl. Sci. Engineering 138(2) (2001) Neutron Spectrometry with a Monolithic Silicon Telescope

35 MEASUREMENTS OF CONTINUOUS SPECTRA Energy distribution of the yield of neutrons generated at 0 by 4.0 MeV protons striking a thick beryllium target Howard et al. (TOF) Monolithic Silicon Telescope Neutron yield (MeV -1 μc -1 sr -1 ) Neutron energy (MeV) Time-of-Flight: Howard, W.B., Grimes, S.M., Massey, T.N., Al-Quraishi, S.I., Jacobs, D.K., Brient, C.E., Yanch, J.C., Measurement of the Thick-Target 9 Be(p,n) Neutron Energy Spectra, Nucl. Sci. Engineering 138(2) (2001) Neutron Spectrometry with a Monolithic Silicon Telescope

36 MEASUREMENTS OF CONTINUOUS SPECTRA Energy distribution of the yield of neutrons generated at 0 by 3.7 MeV protons striking a thick beryllium target Howard et al. (TOF) Monolithic Silicon Telescope Neutron yield (MeV -1 μc -1 sr -1 ) Neutron energy (MeV) Time-of-Flight: Howard, W.B., Grimes, S.M., Massey, T.N., Al-Quraishi, S.I., Jacobs, D.K., Brient, C.E., Yanch, J.C., Measurement of the Thick-Target 9 Be(p,n) Neutron Energy Spectra, Nucl. Sci. Engineering 138(2) (2001) Neutron Spectrometry with a Monolithic Silicon Telescope

37 MEASUREMENTS OF CONTINUOUS SPECTRA Energy distribution of the yield of neutrons generated at 0 by 3.4 MeV protons striking a thick beryllium target Howard et al. (TOF) Monolithic Silicon Telescope Neutron yield (MeV -1 μc -1 sr -1 ) Neutron energy (MeV) Time-of-Flight: Howard, W.B., Grimes, S.M., Massey, T.N., Al-Quraishi, S.I., Jacobs, D.K., Brient, C.E., Yanch, J.C., Measurement of the Thick-Target 9 Be(p,n) Neutron Energy Spectra, Nucl. Sci. Engineering 138(2) (2001) Neutron Spectrometry with a Monolithic Silicon Telescope

38 MEASUREMENTS OF CONTINUOUS SPECTRA Energy distribution of the yield of neutrons generated at 0 by 3 MeV protons striking a thick beryllium target Howard et al. (TOF) Monolithic Silicon telescope Neutron yield (MeV -1 μc -1 sr -1 ) Neutron energy (MeV) Time-of-Flight: Howard, W.B., Grimes, S.M., Massey, T.N., Al-Quraishi, S.I., Jacobs, D.K., Brient, C.E., Yanch, J.C., Measurement of the Thick-Target 9 Be(p,n) Neutron Energy Spectra, Nucl. Sci. Engineering 138(2) (2001) Neutron Spectrometry with a Monolithic Silicon Telescope

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40 Conventional microdosimeter: TEPC (Tissue Equivalent Proportional Counter), spherical or cylindrical proportional counter filled with tissue- equivalent gas MICRODOSIMETRY (ICRU REPORT n 36) Conceptual framework (and corresponding experimental methods) for the systematic analysis of the microscopic distribution of energy deposition in irradiated matter Tissue- equivalent gas Tissue-equivalent plastic Central anode and grid (charge collection and confinement) Principle: to simulate a microscopic volume of tissue by replacing it by a much larger cavity filled with tissue-equivalent gas of much lower density Applications: radiation biology, radiation chemistry, radiation protection, radiation therapy and dosimetry Semiconductor Detectors for Neutron Spectrometry and Microdosimetry

41 SOLID STATE MICRODOSIMETERS Si-devices can provide sensitive zones of the order of a micrometer CHALLENGING DEVICES FOR MICRODOSIMETRY HOW a Si-DEVICE BASED MICRODOSIMETER? Tissue-equivalent converter Silicon device Spectroscopy Chain Spectrum of the energy imparted per event in silicon Data Analysis Analytical corrections Microdosimetric spectrum in tissue Semiconductor Detectors for Neutron Spectrometry and Microdosimetry

42 SILICON MICRODOSIMETRY PN diodes [1] J. F. Dicello, H. I. Amols, M. Zaider, and G. Tripard, A Comparison of Microdosimetric Measurements with Spherical Proportional Counters and Solid-state Detectors, Radiation Research 82 (1980) [2] M. Orlic, V. Lazarevic, and F. Boreli, Microdosimetric Counters Based on Semiconductors Detectors, Radiat. Prot. Dosim. 29 (1989) [3] A. Kadachi, A. Waheed, and M. Obeid, Perfomance of PIN photodiode in microdosimetry, Health Physics 66 (1994) [4] A. Kadachi, A. Waheed, M. Al-Eshaikh, and M. Obeid, Use of photodiode in microdosimetry and evaluation of effective quality factor, Nuc. Instrum. Meth. A404 (1998) The differences from the lineal energy spectra measured with the TEPC (Tissue Equivalent Proportional Counter) were mainly ascribed to the shape and the dimensions of sensitive volumes Complex charge collection process, field funneling effect

43 FIELD FUNNELING EFFECT (FFE) : p-n DIODES FFE is due to a local distortion of the electric field in the depletion layer leading to the collection of charge produced in the non-depleted zone 2 µm@2v Field Funneling Effect Recoil proton Depletion Layer P-Layer N + Depletion layer thickness: 2 2 V Response (cm 2 ) neutrons from 0 1x10-5 with polyethylene - ASIC V cc =-2 V = MeV = MeV = MeV E 10-6 n = MeV = MeV 10-7 The higher the incident neutron energy, the higher the maximum energy deposited by recoil-protons Energy (kev) Active thickness: ~ 12 μm!!!

44 PN diodes in SOI wafer [1] B. Rosenfeld, P. Bradley, I. Cornelius, G. Kaplan, B. Allen, J. Flanz, M. Goitein, A.V. Meerbeeck, J. Schubert, J. Bailey, Y. Tabkada, A. Maruashi, Y. Hayakawa, New silicon detector for microdosimetry applications in proton therapy, IEEE Trans. Nucl. Sci. 47(4) (2000) [2] P. Bradley, A.B. Rosenfeld, B.J. Allen, J. Coderre, and J. Capala, Performance of silicon microdosimetry detectors in boron neutron capture therapy, Radiation Research 151 (1999) [3] P.D. Bradley, The Development of a Novel Silicon Microdosimeter for High LET Radiation Therapy, Ph. D. Thesis, Department of Engineering Physics, University of Wollongong, Wollongong, Australia (2000).

45 MONOLITHIC SILICON TELESCOPE (ST-Microelectronics)(1) Sensitive area: 1 mm 2 ΔE thickness: E thickness: ~1.9 μm ~500 μm Dopant concentration (cm -3 ) 1E20 1E19 1E18 1E17 1E16 1E15 1E14 1E13 ΔE charge collection thickness 1E Depth (μm) As B The p + cathode acts as a watershed for the charge collection Minimization of the field-funneling effect (2) (1) Tudisco, S., et al. A new large area monolithic silicon telescope. Nucl. Instrum. Meth. A 426, (1999). (2) Agosteo, S., Fallica P.G., Fazzi, A., Pola, A., Valvo, G., Zotto, P. A feasibility study of a solid-state microdosimeter. Applied Radiation Isotopes. 63, (5-6) (2005).

46 IRRADIATIONS WITH MONOENERGETIC NEUTRONS (at INFN LNL - Padova): comparison with simulations and analytical model 7.0x x x10-4 En = 680 kev Experimental FLUKA Simulation Analytical En = 996 kev Experimental FLUKA Simulation Analytical 7.0x x x x x x x x x10-4 p(ε) ε 2 (kev cm 2 ) 1.0x x x x En = 1306 kev Experimental FLUKA Simulation Analytical 100 En = 1715 kev Experimental FLUKA Simulation Analytical 1.0x x x x x x x x x x x x ε (kev)

47 SOLID STATE MICRODOSIMETER Advantages: Simple, low cost system Transportability Low power consumption Integration of multiple detectors In-vivo design But, the realization of a microdosimeter based on a silicon device involves some problems, mainly: 1. Silicon is not tissue tissue equivalence criteria and correction; 2. The sensitive volume is usually a rectangular parallelepiped; 3. The electronic noise imposes the minimum detectable energy.

48 TISSUE EQUIVALENCE CORRECTION The tissue equivalence of silicon device requires: 1. the minimization of the contribution of secondaries generated by direct interactions of neutrons with silicon, i.e. most events shuold be crossers or stoppers Relevant reactions that can generate starters or insiders: Fast neutrons Elastic scattering with silicon nuclei 28 Si(n,α) 25 Mg 28 Si(n,p) 28 Al One order of magnitude lower than the one due to recoil-protons In commercial PIN diodes the contribution is of the order of a few percent Thermal neutrons 10 B(n,α) 7 Li Implantation of pure 11 B The spectrum of the energy imparted in the ΔE E detector is due to secondaries generated in the converter

49 TISSUE EQUIVALENCE CORRECTION The tissue equivalence of silicon device requires: 2. a suitable correction to the measured distribution in order to obtain a spectrum equivalent to that acquired with an hypothetical tissue ΔE detector Analytical procedure for tissue-equivalence correction E Tissue d (E p, l) = E Si d (E p, l) S Tissue S Si (E (E p ) p ) Energy deposited along a track of length l by recoil-protons of energy E p in a tissue-equivalent ΔE detector Scaling factor : stopping powers ratio

50 TISSUE-EQUIVALENCE EQUIVALENCE CORRECTION The scaling factor S S Tissue (E) (E) depends on the energy and the type of the impinging particle Si S Tissue (E)/S Si (E) Protons Electrons E stage of the telescope and E-E scatter-plot E (kev) Limits: the thickness of the E stage restricts the TE correction to recoilprotons below 8 MeV (alphas below 32 MeV) Electrons release only part of their energy in the E stage Mean value over a wide energy range (0-10 MeV) = 0.53

51 The scaling factor TISSUE-EQUIVALENCE EQUIVALENCE CORRECTION S Tissue S Si ( Ep) depends on the energy of recoil-proton E ( E ) p p E p can be measured event-by-event by exploiting the E-stage of the telescope 0,8 0,7 Before correction After correction 0,6 0,5 ε d(ε) 0,4 0,3 0,2 0,1 0, ε (kev)

52 COMPARISON WITH SIMULATIONS (FLUKA code) A tissue-equivalent detector with the same geometrical structure of the monolithic silicon telescope was modelled and irradiated with a parallel beam of 2.7 MeV neutrons. 0,8 0,7 Experimental FLUKA simulation 0,6 0,5 ε d(ε) 0,4 0,3 0,2 0,1 0, ε (kev)

53 SHAPE ANALYSIS Objetive: compare the distributions measured with the monolithic silicon telescope and with a cylindrical TEPC It is necessary to adopt some criteria for choosing the dimensions of simulated tissue cylinder The equivalent cylindrical dimensions are calculated by equating the dosemean energy imparted per event. ε D Assuming a constant linear energy transfer L: ε D = L 0 l 2 p(l)dl l Ratio of the first and second moments of the track length distributions

54 INTER-COMPARISON WITH A CYLINDRICAL TEPC Preliminary results of the irradiation with 2.7 MeV mono-energetic neutrons (INFN-LNL Van De Graaff accelerator) 0,8 0,7 0,6 0,5 Solid state microdosimeter Cylindrical TEPC (2.67 μm) ε F ε D (kev) (kev) TEPC 66.8 ± ± 4.2 Si-Telescope 71.6 ± ± 6.3 ε d(ε) 0,4 0,3 0,2 0,1 0, ε (kev) Despite the shape equivalence correction,, the inherent difference in the track length distributions still subsists

55 MONOLITHIC SILICON TELESCOPE: NEW DETECTOR DESIGN A matrix of cylindrical E elements (about 2 µm thick) implanted on a single E stage (500 µm thick) was designed and constructed. 14 μm E element 9 μm E stage More than 7000 pixels are connected in parallel to give an effective detection area of the E stage of about 0.5 mm 2

56 IRRADIATION WITH 2.7 MeV MONOENERGETIC NEUTRONS ΔE stages and E stage were acquired by a 2-channel ADC in coincidence mode 250 Counts Energy imparted in the ΔE stage (kev) Recoil-protons Recoil-protons due to track length distribution Secondary electrons Energy imparted in the E stage (kev)

57 IRRADIATION WITH DIFFERENT CONVERTERS: Tissue-equivalent equivalent plastic (A150) Cylindrical TEPC (2.7 μm site) Silicon device + A150 plastic 0.6 y d(y) y (kev μm -1 )

58 Thanks for your attention!!! and thanks to my colleagues: S. Agosteo 1,2, A. Fazzi 1,2, M.V. Introini 1,2 G. D Angelo 1,2, A. Foglio Para 1, P.Zotto 3 1 Dipartimento di Ingegneria Nucleare, Politecnico di Milano, via Ponzio 34/3, Milano, Italy 2 INFN, Sezione di Milano, via Celoria 16, Milano, Italy 3 Dipartimento di Fisica, Università di Padova and INFN Sezione di Padova, via Marzolo 8, Padova, Italy