Thursday, April 11, 2013

NaI Scintillators in Liquid Helium

After yesterday's attenuation calculations, I'm trying to find out if I can place the scintillator directly into the liquid helium Dewar to avoid the attenuation of flux due to the Dewar walls and solenoid windings.  I came across an interesting article that was a portion of Fernand Bedard's PhD dissertation in 1956.  It's interesting for lots of reasons.  First, Bedard was working with Hans Meissner.  Second the article mentions currents across insulating junctions with superconductors on either side in 1956, several years before Josephson would do his Nobel prize winning work on Josephson junctions.  Finally, Dr. Bedard wound up working for the NSA!

Then, there's the pragmatic stuff.  It looks like they did place their NaI crystal in the Dewar.  The article also mentions that they were able to load 2 liters of liquid helium using only 5.5 liters.  They apparently lost only 3.5 liters to boil off!  The article also has an excellent description of their procedure and of issues they had with their photomultiplier tube.  A diagram of their Dewar is shown below, (picture 1).

1.  Bedard on Dewar and photomultiplier usage and of course, electrons from superconductors
Bedard F., Meissner H. & Owen G. (1956). Investigation of Electron Emission from Superconductors, Physical Review, 102 (3) 667-670. DOI:

Other Handy References on NaI Detectors
Link to nice article in ROSI on NaI detectors

Increased counts down to 0 C

Temp vs. response time

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