What is Half life? and Why did the early universe only contain hydrogen?

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Thanks for any help! :)

Posted Tue 1st January, 2013 @ 15:43 by :) PurpleJaguar (: - Team GR

3 Answers

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Half life ( if you mean it in a scientific way)
Means the time taken for half the atoms in a
Radioactive substance to decay.
And in reference to why there was only hydrogen in
The early universe is that helium and hydrogen existed
Because all other heavier elements were pulled together
Forming stars. Only when the stars exploded did heavier more
Metallic elements were formed through fusion. There's a lot more
To the why only hydrogen and helium existed but its the gist of it.

Answered Tue 1st January, 2013 @ 22:34 by Hannah Colegate
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Thankyou, this is really helpful :)

Do you know anything about how to work out half life?

Thanks :) 

Answered Wed 2nd January, 2013 @ 10:36 by :) PurpleJaguar (: - Team GR
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Half life can basically be worked out by halfing the number each time so for example:

If a isotope contains 320 atoms of isotop, and we want to find out how much is left after five years..

1st year- 160   (half of 320)

2nd year-80     (we half 160)

3rd year-40      (because we half 80)

4th year-20      (half of 40)

5th year-10     (half of 20)

so we just keep halfing the lastt number by 2

Answered Mon 17th February, 2014 @ 16:31 by fatimaa_p