TIDE TESTS AT GDD LAB M Casiraghi and
TIDE TESTS AT GDD LAB M. Casiraghi and F. Vasi
New detector configuration Low pressure chamber anode
Acrylic board with 5 holes Internal side Source collimator Collimated surface barrier detector for counting primary particles External side Semiconductive cathode Plate of 8 mm thickness 5 holes of 1. 5 mm diameter 6 mm pitch
Test of acrylic plate (Propane) Measurements with Am 241 source: correlation of the hole signal with the alpha signal Signal from the holes (ions) Signal from surface barrier detector (primary particle) Signal from the holes enlarged view In propane at 2 m. Bar, HV 2 k. V signal amplitude ~ 50 m. V
Measurements at PTB microbeam • Protons: 3 Me. V, 10 Me. V Alphas: 5 Me. V, 8 Me. V, 20 Me. V • Beam size: 3 um at vacuum window • Adjustable frequency from ~ 10 Hz • Next beam time end of October
20 Me. V: ~100 8 Mev ~ 200 (not including beam and detector geometry) __ mean counts/trigger --- counts/trigger (only trigger with signal) __ % of empty triggers (triggers with no signal) % of empty triggers Ions/alpha expected in the volume at 3 m. Bar % of empty triggers Efficiency vs primary frequency (alphas)
Goals of the tests Improvement 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 (1 cm T, 1 mm D) Ohm·cm - PEG 3 C 8. 5 × 1012 4. 5 × 1014 dark rate gas impurities (water scintillation, photo-effect) - PEEK, glass field emission - cathode material Low probability for ion-impact ionization: - thicker boards - compare efficiency with different LET radiation (p, alpha, different energies @ PTB)
Additional tests • Test different gasses -Ar. CO 2 -Ar-methane • Test different board thicknesses Acrylic 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
PEEK plate
Tests with Argon - 2. 5 m. Bar Acquisition gate Hole signal Alpha signal + scintillation ?
Tests with Argon – 3. 5 m. Bar Lower peak at higher pressure Hole signal has smaller amplitude than in propane
Test with Argon with previous detector 6. 5 mbar 4 mbar
Preliminary measurements – 3. 5 m. Bar Argon E/P [V/cm/m. Bar] dark rate [Hz] SNR 714 39. 20 893 45. 90 1071 63. 50 1250 75. 00 counts/trigger 1. 77 0. 19 1. 93 0. 18 2. 00 0. 27 1. 85 0. 19 Propane E/P [V/cm/m. Bar] dark rate [Hz] 464 811 936 1071 SNR 5. 93 46. 22 61. 17 117. 78 counts/trigger 3. 86 0. 18 0. 36 1. 13 0. 25 1. 04 0. 30
Simulations Argon Propane
Back-up slides
Purpose: Development of a device for characterization of radiation track structure for study of radiation biological effectiveness Simple damage REPARABLE • 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. 50 base pairs ~ 16 nm • 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) Complex damage IRREPARABLE ~ 2 nm
The track imaging detector Anode providing drift voltage Readout strips RTGEM-like detector, 2 D array of ion counters Ed Sensitive volume: low pressure propane gas 1 -5 mbar X hit ~100 s nm track length in water Ea y Cathode providing accelerating voltage Primary ion producing ion impact ionization Secondary electron avalanche moving towards the PCB surface Bashkirov, V. A. , Hurley, R. F. , Schulte, R. W. A novel detector for 2 D ion detection in low-pressure gas and its applications. NSS/MIC Conference Record, IEEE, 694 -698, 2009
Experimental set-up at LLU
Prototype characterization – Detector signal • Source: • Am 241 alphas 2 mm beam • Working gas: • propane • PCB: • 3. 3 mm G 10 board with common top electrode (gold plated) • Holes 0. 8 mm, pitch 2 mm • Cathodes: • high resistivity glass • semi-conductive glass Diode signal Detector signal on 50Ω load P = 4 mbar HV = -800 V Ed = 10 V/cm Pulse of 5 m. V and 400 ns gain of ~108
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 Semiconductor glass Mean counts/trigger = 18 High resistivity glass Mean counts/trigger = 14 G 4 simulations of g beam Ø= 2 mm ● propane at P= 4 mbar ● Ed and Ea neglected ● Including geometrical efficiency ideal Ionizations/alpha
Efficiency vs plate thickness 2/2 Measurements results: Measure of efficiency with 3 detector versions varying gas pressure and accelerating field intensity percentage of primaries producing at least one ionization in one of the holes Ion impact probability ÷ E/P
Efficiency vs plate thickness 2/2 Measurements results: Measure of efficiency with 3 detector versions varying gas pressure and accelerating field intensity percentage of primaries producing at least one ionization in one of the holes Ion impact probability ÷ E/P
Efficiency vs plate thickness 2/2 Measurements results: Measure of efficiency with 3 detector versions varying gas pressure and accelerating field intensity percentage of primaries producing at least one ionization in one of the holes Ion impact probability ÷ E/P
Gas System Chamber (Aluminum+plastic lid) Swagelok fitting Propane cylinder Needle control valve Swagelok fitting Swagelok tee Control valve MKS 248 A Pump Hole signal Pressure controller MKS 250 Fast evacuation valve MKS Baratron 626 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-SS 4 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-DSS 4 0. 3 Cv) Tubing stainless steal ¼''
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