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'[EE]: Re: Alpha particles detector with PIC logger'
2002\09\15@125842 by Alan B. Pearce

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>I tried a silicon solar cell once, it didn't work as well as a signal
>transistor with the metal case hacked off (2n2222). Power transistors like
a
>2N3555 didn't work either. I thought with all the area a power transistor
>has it would, but it didn't work with alpha anyways.

This does not surprise me. Consider that there was not a problem (AFAIK)
with radiation problems and 8K dynamic memory, the problem only appeared
when the early 16k chips came out, with their finer chip geometry. Device
geometry has quite an effect on how radiation affects components.

Then if you to real fine geometries then you go back to having no radiation
problems. My understanding is that geometries finer than 0.25 micron are
considered intrinsically rad hard for use in space and other radiation
critical uses.

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2002\09\16@083020 by Russell McMahon

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> Then if you to real fine geometries then you go back to having no
radiation
> problems. My understanding is that geometries finer than 0.25 micron are
> considered intrinsically rad hard for use in space and other radiation
> critical uses.

I hadn't heard this and I must say it isn't intuitive to me. Can someone
explain the mechanism and/or confirm this immunity. (I could go Googling but
presumably people here who work regularly in with such areas will have the
facts at their fingertips).



       Russell McMahon

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2002\09\16@154818 by Attila Muhi

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Hi,

I've heard one guy use a vacuum tube HVDC rectifier, DY87 I think, as a detector. A certaion voltage was applied between plate and cathode. No heating voltage was applied, and the radiation and following ionization triggered small current pulses.

Don't know if an alpha particle is too big to pass through the glass, beta particles and gamma-radiation should pass without problems. Perhaps you can break the glass if you have to...

regards

Attila Muhi - SM4RAN

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2002\09\17@133444 by Peter L. Peres

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On Mon, 16 Sep 2002, Attila Muhi wrote:

*>Hi,
*>
*>I've heard one guy use a vacuum tube HVDC rectifier, DY87 I think, as a
*>detector. A certaion voltage was applied between plate and cathode. No
*>heating voltage was applied, and the radiation and following ionization
*>triggered small current pulses.

Following ionisation of what ? DY87 is a kenotron tube rated 20kV reverse
voltage afair, and that means it has VERY high vacuum. The only thing that
could ionize in it would be the metal of the anode (the cathode being very
small).

OTOH certain large gas tubes MIGHT work as detectors. F.ex. a fluorescent
tube might do it but it would not be self extinguishing like a Geiger
tube.

It would be interesting for someone who has a calibration source to set up
a neon bulb relaxation oscillator and see if putting the source close to
it woulld up the frequency.

*>Don't know if an alpha particle is too big to pass through the glass,
*>beta particles and gamma-radiation should pass without problems. Perhaps
*>you can break the glass if you have to...

And suck a vacuum using a soda straw afterwards.

Peter

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2002\09\18@090126 by Marco Genovesi

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I'm sorry if I reply only now,  I have lot of problems at work and a very
short time for read the mail on PIC List...

Well, very thanks for the replies to my question about the alpha Detector, I
have found a lot of useful informations related to rad. detectors.
With sincerity, I really doubt to obtain the right detector for my use
without a lot of troubles (and money..), however i will start to buid the
two (simplest?) projects founded:

http://www.zetex.com/frame.asp?page=http://www.zetex.com/3.0/3-8-2a.asp
(DN12 Ionizing Smoke Detector)

http://www.ibutton.com/images/wideband.pdf
(Photodiode and OP Amps form wideband radiation monitor).

The 2.nd link seems to me interesting, even if the author says that is
difficult to distinguish, for  this detector,  Alpha particles from the
other types of radiations. However, in the caves environment (where i test
the logger) Alpha is usually the highest source of rad.
A point that i haven't realized is that for Alpha is sufficient a normal
photodiode and not a PIN diode (ok?).
Also, is there a better (an not expensive) alternative for LM3900 Op Amp or
is adequate?  I'm a beginner in electronics, even if my hairs are grey...
sorry for possible mistakes.

regards
Marco

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2002\09\18@152009 by Peter L. Peres

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On Wed, 18 Sep 2002, Marco Genovesi wrote:

*>http://www.ibutton.com/images/wideband.pdf
*>(Photodiode and OP Amps form wideband radiation monitor).

>opamp 3900

The 3900 is a Norton opamp (has current inputs). Use something else (TL074
will work on 9V battery and outperform LM3900 in this circuit - you need
to redesign the bias circuits. Adding another 2M resistor to ground for
each of the first 2 amps inputs should do this. Also remove the zener
diode and its polarisation resistor (reduces quiescent power drain), feed
the upper 2M resistors directly from 9V. The TL074 may drift more than the
3900 in this circuit but the integrator will work better ;-). I think that
a 2M resistor should be used to shunt the 0.1u cap but I am not sure. Try
it.

hope this helps,

Peter

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2002\09\19@044143 by Marco Genovesi

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Peter, thank you very much for these useful tips !!
I have only a little experience in electronics, so your contribute is very
appreciate.

An ultimate question: with my logger (16F84A based) i can read only a
frequency /pulse input, so i suspect that the A4 section of OP-Amp  (and
speaker, led..) may be missed.  Is correct?

Best regards,
Marco



{Original Message removed}

2002\09\19@162325 by Peter L. Peres

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On Thu, 19 Sep 2002, Marco Genovesi wrote:

*>An ultimate question: with my logger (16F84A based) i can read only a
*>frequency /pulse input, so i suspect that the A4 section of OP-Amp  (and
*>speaker, led..) may be missed.  Is correct?

No but you can forget the transistor and connect the logger input to the
output of the last opamp (without a capacitor, but with a suitable
resistor, like 22k or so). You will need to experiment. I have some doubts
about how that circuit behaves 'in nature'. The noise of the diode may be
enough to generate output pulses and it will be tricky to tell what is
what without a calibration source and a climatic box at least (to test
over temperature).

good luck,

Peter

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2002\09\20@031011 by Marco Genovesi

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Peter, thanks for the suggestions... obviously a sort of calibratin will be
needed. A point favourable is that to a great extent of the caves the
temperature (in the internal regions, where i want to take the measures) has
only small variations over the year ( 2 - 1 degree C. , often less) and also
very low noise from other sources (RF...), whereas humidity may be a
problem, not only for the sensor but also for the logger.

many thanks again
Marco



{Original Message removed}

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