In article , Derek Geldard
wrote:
On Wed, 23 Sep 2009 10:02:01 +0100 (BST), "Dave Liquorice"
wrote:


Of course it depends on the substance how long the half life is, they
vary from seconds to thousands of years but most are fairly short and
the level of radiation decreases over time as well. The nature of the
radiation is important as well, alpha particles are easyly stopped for
example.

Common misconception, along with "If an isotope has a long half life
it's not very radioactive", -erm no 1 millicurie is 1 millicurie .

It may be even a more common misconception to confuse the millicurie with a
unit of mass. :-)

Yes, 1 millicurie is 1 millicurie. But if one isotope has a half life
billions of times lower than another, then one gram of one of them would
have to be matched with many tons of the other (all at a similar distance
to you) to irradiate you with the same number of particles per time.

How many milllicuries does the Earth contain? Does the large number of the
answer mean we must all leave the Earth immediately because we are being
fried? :-)

The reality is that we are surrounded with large amounts of materials with
very long half lives. Including our own bodies.

Slainte,

Jim

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