Test of a Micromegas TPC for imaging by

Test of a Micromegas TPC for imaging by fast neutrons Luxing An 1, David Attié 2, Yonghao Chen 1, Paul Colas 2, M. Riallot 2, Huaya Shen 1, Wenxin Wang 1, 2, Xiaodong Wang 1, Chunhui Zhang 2, Xiaodong Zhang 1, 3, Yi Zhang 1 1. 2. 3. College of Nuclear Science and Technology, Lanzhou University, Lanzhou, China; IRFU-CEA, Saclay, France; Department of Nuclear Engineering, University of Tennessee, Knoxville, USA;

2 Motivation v Neutron cross-sections are higher for light elements: see hydrocarbons through metals or glass. v Applications to rocket engines, etc…

T 2 K TPC electronics 3 • Electronics designed in CEA/Irfu for the T 2 K 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 a Front-End Mezzanine (FEM) • 4 AFTER chips per FEC • Spark protection FEC with 4 AFTER chips

Detector + electronics setup 4 Window for x-rays source Shielding C FE FEM Trigger from the mesh signal David. Attie@cea. fr 4

Micromegas TPC for neutron imaging 5 • Detector layout: 1728 (48× 36) pads of 1. 75 mm× 1. 50 mm • Elastic scattering on hydrogen n p + masks (PE) n PE 15 mm Gas: Argon + 5% Isobutane p + bulk Micromegas Aluminized polyethylene 1 mm between 2 layers (0. 5 µm) of Al Edrift ~ 160 V/cm 128 µm HVdrift HVmesh Eamp ~ 23 k. V/cm 88. 6 mm 57. 4 mm (x, y, t) Cosmics PCB II. Other Micromegas TPC application: neutron imaging Micromegas

6 Simulation for converter efficiency q Neutron proton recoiling efficiency in a polyethylene [C 2 H 4]n layer coming from 241 Am-9 Be 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

Reconstruct track 7 \ Garfield Drift lines from primary ionization e- Proton track Avalanches II. Other Micromegas TPC application: neutron imaging

Experiment and Simulation Results -- n-g discrimination 8 Two Methods to discriminate the neutron and gamma events with Am-Be neutron source: 1. Time 2. Energy 75 ke. V Threshold With Convertor W/O Convertor

9 Test with a 241 Am-9 Be neutron source 4 mm 3. 5 mm 3 mm 2. 5 mm Letters “CEA” or “LZU” • 8 cm thickness • 4 -4. 5 mm width 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

11 Conclusion v A new detector has been used to detect neutrons: a ‘flat’ TPC with O(mm) pixels and with a CH 2 converter. v The time measurement along the proton track allows determination of the conversion point and improves image resolution.