Test of a Micromegas TPC

for imaging by fast neutrons

Test of a Micromegas TPC

for imaging by fast neutrons

Luxing An1, David Attié2, Yonghao Chen1, Paul Colas2, M. Riallot2, Huaya Shen1, Wenxin Wang1,2, Xiaodong Wang1, Chunhui Zhang2,

Xiaodong Zhang1,3, Yi Zhang1

1. College of Nuclear Science and Technology, Lanzhou University, Lanzhou, China;2. IRFU-CEA, Saclay, France;3. Department of Nuclear Engineering, University of Tennessee, Knoxville, USA;

2

Neutron cross-sections are higher for light elements: see hydrocarbons through metals or glass.

Applications to rocket engines, etc…

Motivation

3

T2K TPC electronics

• Electronics designed in CEA/Irfu for the T2K TPC

• AFTER-based electronics (72 channels/chip): – low-noise (700 e-) pre-amplifier-shaper– 100 ns to 2 µs tunable peaking time– full wave sampling by SCA– frequency tunable from 1 to 100 MHz (most data at 50 MHz)– 12 bit ADC (rms pedestals 4 to 6 channels)– zero-suppression capability

• 6 Front-End Cards (FEC) readout by aFront-End Mezzanine (FEM)

• 4 AFTER chips per FEC

• Spark protection

FEC with 4 AFTER chips

4

Detector + electronics setup

4

David.Attie@cea.fr

1

A

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2

3

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BCDEFGH

23

4

IJKLMNOP

IJKLMNOP

5

6

7

8

56

78

400

400

174,6

143

96

64

65

231

Trigger fromthe mesh signalFEM

FEC

Shielding

Window for x-rays source

5 Micromegas TPC for neutron imaging

Gas: Argon + 5% Isobutane

128 µm HVmesh

Eamp ~ 23 kV/cm

15 mmHVdrift

Edrift ~ 160 V/cm

PE

• Detector layout: 1728 (48×36) pads of 1.75 mm×1.50 mm

+ bulk Micromegas• Elastic scattering on hydrogen n

p+ masks (PE)

PCB Micromegas

n

p

Aluminized polyethylene 1 mm

between 2 layers (0.5 µm) of Al

57.4 mm

88.6

mm

Cosmics

(x, y, t)

II. Other Micromegas TPC application: neutron imaging

6 Simulation for converter efficiency Neutronproton recoiling efficiency in a

polyethylene [C2H4]n layer coming from 241Am-9Be source

Incident neutron spectrum

According to ISO 8529(*)

* INTERNATIONAL STANDARD ISO 8529. Reference neutron radiations – Part 1: Characteristic and methods of productions. International Standard ISO 8529-1 (2001).

II. Other Micromegas TPC application: neutron imaging

7 Reconstruct track

Garfield

Avalanches

Drift lines from

primary ionization

e-

Proton track

\\

II. Other Micromegas TPC application: neutron imaging

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Experiment and Simulation Results-- n-g discrimination

Two Methods to discriminate the neutron and gamma events with Am-Be neutron source:

1. Time2. Energy

With Convertor

W/O Convertor

75 keV Threshold

9 Test with a 241Am-9Be neutron source

Letters “CEA” or “LZU” • 8 cm thickness • 4-4.5mm width

2.5mm

3 mm

3.5mm

4 mm

II. Other Micromegas TPC application: neutron imaging

10 Neutron imaging

Integrating the ADC of all events in one pad.

Reconstructed using the time information.

II. Other Micromegas TPC application: neutron imaging

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A new detector has been used to detect neutrons: a ‘flat’ TPC with O(mm) pixels and with a CH2 converter.

The time measurement along the proton track allows determination of the conversion point and improves image resolution.

Conclusion