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radioactivity

 
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jussi_jaask



Joined: 11 Jun 2011
Posts: 2
Location: mexico

PostPosted: Sun Jun 12, 2011 1:06 am    Post subject: radioactivity Reply with quote

Hi, some help with half lives would be very useful thanks...
"what percentage of a radioactive material, with a half life of 40 seconds, is left after 8 minutes"
what formula do I use to work this one out? thanks
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hepcj
Site Admin


Joined: 23 Jun 2007
Posts: 125

PostPosted: Sun Jun 12, 2011 11:46 am    Post subject: Reply with quote

The level rate of radioactivity in a material is given by

I = I_0 exp(-lambda t) where lambda is the half-life, t is time.
Every 40s the level of radioactivity is reduced by a half.

In 8 minutes, (8*60)/40 = 12 half-lives will have elapsed.
= (1/2)^12 = 1/4096

So the level of radioactivity will be 1/4096 the original level.
Which as a percentage is 1/4096 = 0.024%

See http://www.splung.com/content/sid/5/page/radioactivity
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jussi_jaask



Joined: 11 Jun 2011
Posts: 2
Location: mexico

PostPosted: Sun Jun 12, 2011 11:04 pm    Post subject: Reply with quote

cheers mate Smile
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