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# aqa unit 5 decay question Watch

1. X has 1.8 x 10^15 atoms and its half life is 8h, after 24h its gonna have 2.25 x 10^14 atoms left.

what is the energy transfer from the sample in 24h if the isotope emits alpha particles of energy 5MeV.

so i know energy transfer = AE,

A = N/t so the atoms that had decayed after 24h is 1.575 x 10^15, so that divided by (24 x 60 x 60) is 1.8 x 10^10, and that multiplied by 5MeV, i thought would give me the answer but it didn't.

what am i doing wrong?
2. Why are you dividing by 24 x 60 x 60
3. (Original post by Stonebridge)
Why are you dividing by 24 x 60 x 60
oh im guessing you dont do that because the time taken had already been taken into consideration.
so the activity is just the total number of atoms that had decayed in a certain time?
4. (Original post by cooldudeman)
oh im guessing you dont do that because the time taken had already been taken into consideration.
so the activity is just the total number of atoms that had decayed in a certain time?
Yes you just need the total number decayed in the 24hr time interval.

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