[APD] APD news 9/29/2004

[Mary Bishai]

Dear All,

Since there werent enough bodies around for todays meeting, I thought I
drop a line as to the status of our APD effort:

1) Mark has successfully integrated the Keithley 6485 into our labview I-V
   testing program. We can now take I-V curves automatically

2) Mark verified that we get the same continuous light gain with 2V on the
   LED even without the LCR meter hooked up. So my hypothesis that the low
gains observed could have to do with the LCR meter sourcing current while
in the test circuit has been proven wrong.


3) Mike has obtained a weak microcurie Fe-55 source for use in gain
   calibrations. Joe Vignola indicated that only GERT training is required
   to handle this source, so long as the sign indicating the precsence of
   the source is prominantly displayed wherever it happens to be located.


4) Today, I noticed the Kiethley picoammeter is displaying some
   measurement problems. The current measurements on the 20nA scale
   (lowest possible with the APD dark currents) are unreliable. I verified
   that on the 200nA, 2micro amp and 20 microamp scale the ammeter reads
   the same value, and that this value agrees with the reading from the
   old 486 picoammeter. On the 20nA scale the value is 50% to 1/2 the
   value on all the other scales.  This seems to be an instrument problem.
   After being on hold with Keithley tech-support (I think they are in the
   US ;)) for 15 mins I gave up and will try e-mailing my contact
   instead.

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Mary Bishai                          Office: 3-181
Assistant Physicist                  Pager:
Brookhaven National Laboratory       Tel: 631-344-4877
Bldg 510E, P.O. Box 5000             FAX: 631-344-4741
Upton, NY 11973-5000                 E-mail: mbishai at bnl.gov
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