medipix2 meeting dec. 2005 medipix activity at berkeley john vallerga, jason mcphate, anton tremsin...
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Medipix2 meeting Dec. 2005
Medipix Activity at BerkeleyMedipix Activity at Berkeley
John Vallerga, Jason McPhate, Anton Tremsin
and
Bettina Mikulec
Medipix2 meeting Dec. 2005
ContentsContents
Tube Fabrication Progress– Header
– Body
– Medipix bake to 350 C
Neutron Detector Concept
Medium Infra-red ( = 5 m) APD array
Medipix2 meeting Dec. 2005
High Temperature BakeHigh 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
Medipix2 meeting Dec. 2005
Neutron sensitive MCPsNeutron 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 m in glass
Can also be made with Gd203 dopant and used as a passive collimator
Medipix2 readout useful for high flux, fast tomography
Medipix2 meeting Dec. 2005
10B neutron capture reaction10B neutron capture reaction
10B(n,)7Li reaction =3837 barns for thermal neutrons
and 8500 for cold neutrons
Medipix2 meeting Dec. 2005
Neutron capture reactionNeutron capture reactionn
7Li4He
n
Secondary electrons
10B
Secondary electrons
10B(n,)7Li reaction, =3837 barns
Medipix2 meeting Dec. 2005
Angular selective neutron detectionAngular selective neutron detection
Secondary electrons
Secondary electrons
No bias applied to front MCP
Angular selective
Bias applied to front MCP
All neutrons are detected
Medipix2 meeting Dec. 2005
Infra-red sensitive Medipix!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
Medipix2 meeting Dec. 2005
Status of ideaStatus 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