On Fri, 11 Nov 2011 18:01:52 +0000, The Natural Philosopher wrote:

Andrew Gabriel wrote:
In article ,
writes:
On Nov 11, 3:36 pm, "john east" wrote:
Have an ordinary house smoke alarm. It's about twenty years old and it has
recently gone off in the middle of the night for two days running and for no
apparent reason.

I've heard that it might need a vacuum cleaner applied to it. Is there
likely any truth in that, or is there anything else i might usefully do?

Or does it probably mean that I have to replace it?
There has been some discussion here before, based on half-lives, as to
whether the expiry date is absolute, or just a guideline for people

The 10 year live is because you can't clean the ionisation chamber,
and sticky dirt will eventually short out the ionisation current flow,
causing the alarm to go off.

Don't even think about taking the ionisation chamber apart to clean
it (too risky given the radioactive source in it).

Yes, if you take that apart and swallowed it, you might JUST end up with
a small burn on your anus.

If you took it apart and smoked it, you MIGHT end up with lung cancer.
If you mamaged bnot to cough for several minths.

There is a reason why they use alpha emitters. Because they wont even go
thorough a sheet of cigarette paper, let alone your skin.

the reason they use alpha emitters is because the smoke particles block
them significantly well - beta and gamma are too penetrating - the smoke
makes little difference to the radiation hitting the detector - agree with
TNP observation but its the penetrating power ( or lack of) through smoke
is the reason they use them :-)
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.€¢Â°€¢. Nik .€¢Â°€¢.
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