TIDE TESTS AT GDD LAB M. Casiraghi and F. Vasi

New detector configuration

Low pressure chamber

anode

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

PEEK plate

Tests with Argon - 2.5 mBar

Acquisition gate

Hole signal

Alpha signal + scintillation ?

Tests with Argon – 3.5 mBar

Lower peak at higher pressure

Hole signal has smaller amplitude than in propane

4 mbar6.5 mbar

Test with Argon with previous detector

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

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

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

Experimental set-up at LLU

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