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Joined: 11 Jun 2011
Posts: 2
Location: mexico

 Posted: Sun Jun 12, 2011 1:06 am    Post subject: radioactivity 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
hepcj

Joined: 23 Jun 2007
Posts: 125

 Posted: Sun Jun 12, 2011 11:46 am    Post subject: 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

Joined: 11 Jun 2011
Posts: 2
Location: mexico

 Posted: Sun Jun 12, 2011 11:04 pm    Post subject: cheers mate
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