Path: utzoo!mnetor!uunet!iscuva!jimc
From: jimc@iscuva.ISCS.COM (Jim Cathey)
Newsgroups: sci.electronics
Subject: Re: electronic time capsule
Message-ID: <1184@iscuva.ISCS.COM>
Date: 22 Feb 88 18:48:49 GMT
References: <3a623999.44e6@apollo.uucp>
Organization: ISC Systems Corporation, Spokane, WA
Lines: 28

In article <3a623999.44e6@apollo.uucp> nelson_p@apollo.uucp writes:
>  This is potentially a very good idea, having many advantages 
>  over my other proposals.  Questions:  How can I sense the 
>  radioactivity?  G-M tubes are not particularly long-lived devices;
>  depending on how they're quenched and how much radiation they're
>  exposed to, they may be good for a few decades at best.  Are there
>  reliable solid-state detectors?   Also what materials would have a 
>  sufficiently short half-life to be suitable?  

I have an old gamma counter at home (medical surplus).  I think it uses
a sodium iodide crystal as a scintillation detector followed by a
photomultiplier tube as the active ingredients.  I don't know if there
are any more modern optical sensors than the PM tube that are solid
state.  (I think the PM tube was heaterless, so it might be ok so far
as life went, but it does require HV to operate.)

The only radioactive thing I had that tickled the thing was Coleman
lantern mantles.  I think they're dipped in thorium oxide.  Anybody
know the half-life of this stuff?  I don't have my CRC handbook nearby.

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