Well, now I am pretty sure that I am seeing alphas from a smoke detector
source ($5.50 - ~1uc americium) , with a once upon a time very good ~.1"
sq quad pin photodiode (it's been kicked around for ~ten years on my
bench with no lid , dirty, one bond wire wiped off , rats chewi...)
I hooked one end of the diode to a 9 volt battery, the other end of the
diode to the scope probe, the probe ground clip to other end of battery.
I guess the scope is a 1 mohm load. (How in bloody h&ll did they ever
get started with "w" for ohms??? )
Scope seems to have ~1.5mv of noise, pulses from diode = ~1.5 to ~3.5 mv
~300 usec decay time, ~1k pulse/s.
I don't think you need a $20 op amp for that.
Now I have to find a $.10 photodiode in a can - well <$5.00 any way :-)
I have not gotten any transistors to detect yet but will keep trying

To be 100% sure, I need a graceful means to place and remove an alpha
blocker (piece of paper) without disturbing the light leakage and etc
and etc -- the epoxy is curing as I type. My early setup was photodiode
sticking up in a proto strip with the source (and it's "native" housing)
balanced on the diode and then a bit of tape (alpha blocker) or not ---
juggle, drop, blast, hold tongue just right, DON'T TOUCH the americium
AT ALL with ANYTHING, DON'T touch the photodiode !!

Man, I really wish that turkey hadn't stolen my geiger counter the other
night - But then I may not have played with the photodiode ??

-- 

Looking forward,
Al Shinn







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