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Innovative Infra-Red Neutron Detector Progress in Medipix Activity

This document explores the progress in tube fabrication for Medipix neutron detectors at Berkeley, focusing on medium infra-red APD array image tubes. It covers topics like tube body assembly, bake processes, and use of MCPs with boron dopants for neutron detection. Additionally, it discusses challenges with existing APD arrays and proposes a new solution from DRS Technologies. The text also examines the potential of Medipix2 for high frame-rate IR imaging and adaptive optics applications.

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Innovative Infra-Red Neutron Detector Progress in Medipix Activity

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  1. Medipix Activity at Berkeley John Vallerga, Jason McPhate, Anton Tremsin and Bettina Mikulec

  2. Contents • Tube Fabrication Progress • Header • Body • Medipix bake to 350 C • Neutron Detector Concept • Medium Infra-red ( l = 5 mm) APD array

  3. Image Tube progress Header assembly (interior)

  4. Image Tube progress Glued and wire bonded

  5. Image tube progress Header assembly (exterior)

  6. Image tube progress Tube body stackup before brazing

  7. High Temperature Bake • Vacuum bake Medipix2 mounted on ceramic header • Temperature profile to match tube processing • Class C Medipix2 chip (D9) • Initial bake to 300C for 10 hour (turbo failed) • Used DAC scans and threshold equilisation to characterize chip before and after bake. • No apparent change • Second bake 24 hours, with 10 hours at 350C. • Again no apparent change

  8. Neutron sensitive MCPs • Glass microchannel plates with 10B as a major dopant • Manufactured by Nova Scientific (Sturbridge Mass., USA) • High thermal neutron cross section • High spatial resolution as range of daughter products ~ 3 to 4 mm in glass • Can also be made with Gd203 dopant and used as a passive collimator • Medipix2 readout useful for high flux, fast tomography

  9. 10B neutron capture reaction 10B(n,)7Li reaction =3837 barns for thermal neutrons and 8500 for cold neutrons

  10. n Secondary electrons n 4He 7Li 10B Secondary electrons Neutron capture reaction 10B(n,)7Li reaction, =3837 barns

  11. Secondary electrons Angular selective neutron detection Angular selective All neutrons are detected Secondaryelectrons No bias applied to front MCP Bias applied to front MCP

  12. Infra-red sensitive Medipix! • APD arrays seem a natural match to Medipix style readout • High optical QE, no vacuum tube! • Difficult mechanical/fabrication issues • Backside illumination • Optical and electrical crosstalk between pixels • High excess noise factors • DRS technologies has a new HgxCd1-xTe process that can solve many of these issues concurrently and might be a good match to Medipix • Medium infra-red sensitive • Gain of 1000 ± 31

  13. MWIR APD Arrays DRS Technologies

  14. APD Gain vs Bias l = 4.3 mm, 77K l = 2.2 mm, 273K

  15. Excess Noise Factor

  16. Status of idea • Preliminary discussions with DRS found no obvious problems • Sensor has high dark current so must be operated at 77º K • Questions • Can Medipix2 operate at this low temperature • Is Medipix2 a strong source of IR radiation • Applications • Best IR sensors have ~6 e- readout noise at slow rates • Adaptive optics tip/tilt sensors, wavefront sensors in science bandpass • High frame rate IR imaging

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