Title: The pixel ionisation chamber: a detector for beam monitor and dosimetry
1The pixel ionisation chamber a detector for beam
monitor and dosimetry
- A.Boriano 1,2, F.Bourhaleb 2,3, R. Cirio 2, M.
Donetti 2,4, - F. Marchetto 2, C. Peroni 2, C.J. Sanz Freire 2
- 1 ASP, Torino, Italy
- 2 University and INFN, Torino, Italy
- 3 ICSC WorldLab, Lausanne, Switzerland
- 4 TERA Foundation, Novara, Italy
- partially supported by IBA, Louvaine- la-Neuve,
Belgium - PTCOG XXXV PMRC Tsukuba November 15 2001
2Improving the Magic Cube (3D dosimeter for
hadron beams)
The Magic Cube can be bought at Physalus
(furio.gramatica_at_physalus.it)
3The pixel chamber
- parallel plate ionization chamber
- anode segmented in 1024 square pixels
- pixel dimension 7.5 X 7.5 mm2
- sensitive area 24 X 24 cm2
- 1 mm water equivalent thickness
- front-end electronics, located around the
chamber, perform analog to digital conversion
4Front-end electronics
- located around the chamber
- we have developed a full custom chip (TERA05)
- every chip has 64 channels that convert the
collected charge in digital output
5TERA05
- Very Large Scale Integration (VLSI)
- i?f conversion
- output ? Qint
- 100 fCltcharge quantumlt800 fC
- Imax 4 ?A
- 64 channels
- 16 bit wide counters
- multiplexed digital output
- dead-time free readout
- max read out 10 MHz
6Linearity at 100 fC charge quantum
- 20 pA lt I lt 0.6 ?A
- Linearity better than 0.7
7Linearity at 600 fC charge quantum
- 10 pA lt I lt 2 ?A
- Linearity better than 0.3
8Spread of charge quanta
9Reproducibility of charge quantum
- I 49.96 nA
- Qc 600 fC
- 24 ºC lt T lt 27 ºC
- 1 month
- 6 measures
10Data acquisition
- connection detector-data acquisition by twisted
pair flat cables (100 m maximum lenght) - max rate transfer 10 MHz 40 Mb/s
- read out transfer time 50 ?s
- read out cycle total time 100 ?s
- real time operating system
11Beam test at GSI
12Spatial resolution
13Homogeneity of response
14Beam test at PSI
15Comparison with PSI proton beam transverse profile
16very good for IMRT with photons too !(cfr.
collaboration with IBA/Wellhofer/Scanditronix)
Field shape varying with time 6 MV Elekta
accelerator at S.Anna hospital in Torino 1.2x1.2
cm2 square field going to 12.4x12.4 cm2 square
field
17Conclusions
- parallel plate pixel ionization chamber
- big sensitive area
- 1024 independent measurements
- VLSI electronics dead-time free readout
- one dead-time free readout of all 1024 channels
every 100 ?s - ?GOOD MONITOR FOR SCANNED BEAMS
- Next step might be a real-3D-Magic Cube (?
dosimeter)