On Fri, 11 Nov 2011 22:30:49 +0000, Steve Walker wrote:

On 11/11/2011 18:01, 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.

Alpha emitters are very safe, even safe to handle - as you say, alpha
particles are stopped incredibly easily. However, they are NOT safe if
swallowed, inhaled or they enter the body through a cut, as there they
can remain for lengthy periods, irradiating a small area - alpha is
actually highly damaging.

SteveW

yes - a very common GCSE level question - which is the most dangerous type
of radiation? low penetrating power but hgh ionisation potential means
alpha is the safest outside and most dangerous inside the body,Gamma Low
ionistion potential but very penetrating - less damage but difficult to
shield from, Beta meduim penetration and medium ionisation potential -
worst of both world in effect
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