TRAINING COURSE on EXPERIMENTAL MICRODOSIMETRY. Principle of silicon - based microdosimetry Stefano Agosteo 1,2 , Andrea Pola 1,2 1 Politecnico di Milano, Dipartimento di Energia, piazza Leonardo da Vinci 32, 20133 Milano, Italy .
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Principle of silicon-basedmicrodosimetry
Stefano Agosteo1,2,Andrea Pola1,2
1Politecnicodi Milano,Dipartimento di Energia, piazza Leonardo da Vinci 32, 20133 Milano, Italy.
2Istituto Nazionale di FisicaNucleare, Sezione di Milano, via Celoria 16, 20133 Milano, Italy.
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) 441-453.
 M. Orlic, V. Lazarevic, and F. Boreli, Microdosimetric Counters Based on Semiconductors Detectors, Radiat. Prot. Dosim. 29 (1989) 21-22.
 A. Kadachi, A. Waheed, and M. Obeid, Perfomance of PIN photodiode in microdosimetry, Health Physics 66 (1994) 577-580.
 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) 400-406.
The differencesfrom the linealenergyspectrameasuredwith the TEPC (TissueEquivalentProportionalCounter) weremainlyascribedto the shape and the dimensionsof sensitive volumes
Complex charge collection process
Spectrum of the energy imparted per event in silicon
Microdosimetric spectrum in tissue
Field Funneling Effect
2 µm @ 2V
N+THE FIELD-FUNNELING EFFECT
Depletion layer thickness: 2 m @ 2 V
Active thickness: ~ 12 m
-THE FIELD-FUNNELING EFFECT: SOLUTIONS
~ 10-20 um
Allfigures in this slide
Courtesyof A. Rosenfeld, WollongongUniversity, Australia
Contribution of about 5.5%
electronsSEGMENTED SILICON TELESCOPE: SCATTER-PLOT
Calculated contribution of about 5%
due to the track length distribution!
Charge sharing can be neglected
Analytical procedure for tissue-equivalence correction:
Scaling factor :
stopping powers ratio
Energy deposited along a track of length l by recoil-protons of energy Ep in a tissue-equivalent E detector
the thickness of the E stage limits the TE correction to recoil-protons below 8 MeV (alphas below 32 MeV)TISSUE-EQUIVALENCE CORRECTION
The scaling factor
depends on the energy and type of the impinging particle
E stage of the telescope and ∆E-E scatter-plotallow an energy-dependent correction for protons
Electronsrelease only part of their energy in the E stage
ELECTRONS: average value over a wide energy range (0-10 MeV) = 0.53
The main limitation of the system is the high energy threshold imposed by the electronic noise.
New design of the segmented telescope with a ∆E stage with a lower number of cylinders connected in parallel and an E stage with an optimized sensitive area
A feasibility study with a low-noise set-up based on discrete components was carried out in order to test this possibility
By equating the dose-mean energy imparted per event for the two different shapes considered:
The equivalence of shapes is based on the parametric criteria given in the literature(Kellerer).
By assuming a constant linear energy transfer L:
Dimensions of ∆E stages were scaled by a factor η …
… the lineal energy y was calculated by considering an equivalent mean cord length equal to:
Constant TE scaling factor
Event-by-event TE correction!!!