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Acrylic board with 5 holes Collimated surface barrier detector for counting primary particles
Source collimator
Internal side
External side
Semiconductive cathode
Plate of 8 mm thickness5 holes of 1.5 mm diameter 6 mm pitch
Test of acrylic plate (Propane)Measurements with Am241 source: correlation of the hole signal with the alpha signal
Signal from surface barrier detector (primary particle)
Signal from the holes (ions)
Signal from the holes enlarged view
In propane at 2 mBar, HV 2kV signal amplitude ~ 50 mV
Measurements at PTB microbeam
• Protons: 3 MeV, 10 MeV Alphas: 5 MeV, 8 MeV, 20 MeV
• Beam size: 3 um at vacuum window
• Adjustable frequency from ~ 10 Hz
• Next beam time end of October
Efficiency vs primary frequency (alphas)
Ions/alpha expected in the volume at 3 mBar
20 MeV: ~1008 Mev ~ 200
(not including beam and detector geometry)
__ mean counts/trigger
--- counts/trigger (only trigger with signal)
__ % of empty triggers (triggers with no signal)
% o
f e
mp
ty t
rig
ge
rs%
of
em
pty
tri
gg
ers
Goals of the testsImprovement of ion detection
efficiency
Long dead time:
- cathode recharge time test of cathode materials - Dupont kapton XC: uncontrolled discharges (more layers?) - A. Breskin RPWELL materials
- charge-up of hole walls glass GEM – Y. Mitsuya: OK for thick structure (1cm T, 1mm D)
- dark rategas impurities (water scintillation, photo-effect) - PEEK, glassfield emission - cathode material
Low probability for ion-impact ionization:
- thicker boards
- compare efficiency with different LET radiation (p, alpha, different energies @ PTB)
PEG3 PEG3C
Ohm·cm 8.5 × 1012 4.5 × 1014
Additional tests• Test different gasses-Ar -ArCO2
-Ar-methane
• Test different board thicknessesAcrylic of 10 mm, 8 mm, 6 mm - measure of efficiency (counts/primary) and dark rate
• Measure the signal amplitude as a function of the applied HV. to study the signal generation mode
Tests with Argon – 3.5 mBar
Lower peak at higher pressure
Hole signal has smaller amplitude than in propane
Preliminary measurements – 3.5 mBar
E/P [V/cm/mBar] dark rate [Hz] SNR counts/trigger
714 39.20 1.77 0.19
893 45.90 1.93 0.18
1071 63.50 2.00 0.27
1250 75.00 1.85 0.19
E/P [V/cm/mBar] dark rate [Hz] SNR counts/trigger464 5.93 3.86 0.18811 46.22 0.36936 61.17 1.13 0.25
1071 117.78 1.04 0.30
Argon
Propane
Purpose:Development of a device for characterization of radiation track structure for study of radiation biological effectiveness
Simple damage REPARABLE
Complex damage IRREPARABLE
50 base pairs~ 16 nm
~ 2 nm
• Evidences that the local clustering of energy transfer points, in particular ionizations, is important for the production of initial damage to cells
• MC simulations show high LET radiation induced large ionization clusters are responsible for complex DNA damage.
• Experimental characterization for benchmarking MC simulations and characterize mixed or unknown fields
• Ideal detector would provide information on spatial distribution of ionization events with single ionization resolution in nanometric volumes of biological tissue (water)
The track imaging detectorAnode providing drift voltage
Ed
Ea
RTGEM-like detector, 2D array of ion
countersSensitive
volume: low pressure
propane gas 1-5 mbar
~100s nm track length in
water
Cathode providing accelerating voltage
Secondary electron avalanche moving towards
the PCB surface
Primary ion producing ion impact
ionization
Readout strips
X
y
hit
Bashkirov, V. A., Hurley, R. F., Schulte, R. W.A novel detector for 2D ion detection in low-pressure gas and its applications. NSS/MIC Conference Record, IEEE, 694-698, 2009
Prototype characterization – Detector signal
Detector signal on 50Ω load
Diode signal
Pulse of 5mV and 400 ns gain of ~108
• Source:
• Am241 alphas 2mm beam
• Working gas:
• propane
• PCB:
• 3.3 mm G10 board with common top electrode (gold plated)
• Holes 0.8mm, pitch 2mm
• Cathodes:
• high resistivity glass
• semi-conductive glass
P = 4 mbarHV = -800 VEd = 10 V/cm
Semiconductor glass Mean counts/trigger = 18
High resistivity glass Mean counts/trigger = 14
● beam Ø= 2 mm ● propane at P= 4 mbar ● Ed and Ea neglected
Semiconductive glass
● Different distribution shape, peak shifted to larger counts number
● Smaller number of empty triggers● Shorter recharge time● Still signal disappears below 2
mbar● Still low number of detected ions
G4 simulations of g
Including geometrical efficiency
ideal
Including geometrical efficiency
ideal
Ionizations/alpha
Measurements results:Measure of efficiency with 3 detector versions varying gas pressure and accelerating field intensity
Ion impact probability ÷ E/P
percentage of primaries producing at least one ionization in one of the holes
Efficiency vs plate thickness 2/2
Measurements results:Measure of efficiency with 3 detector versions varying gas pressure and accelerating field intensity
Ion impact probability ÷ E/P
percentage of primaries producing at least one ionization in one of the holes
Efficiency vs plate thickness 2/2
Efficiency vs plate thickness 2/2Measurements results:Measure of efficiency with 3 detector versions varying gas pressure and accelerating field intensity
Ion impact probability ÷ E/P
percentage of primaries producing at least one ionization in one of the holes
Chamber (Aluminum+plastic lid)
Swagelok fitting
MKS Baratron 626
Control valve MKS 248A
Swagelok fitting
Swagelok tee
Swagelok tee
Fast evacuation valve
Needle control valve
Propane cylinder
Working pressure: 1-3 mbar propane, continuous flow Chamber internal dimensions: 20 x 10 x 7.5 cm^3 Flow for normal operation controlled by metering valve swagelok SS-SS4 0.004 Cv max flow ~ 1-4 std cc/min Evacuation before injecting propane (minimum P = 0.05 mbar). Fast evacuation valve (Diaphragm valve swagelok SS-DSS4 0.3 Cv) Tubing stainless steal ¼''
Pump
Pressure controller MKS 250
Gas System
Hole signal