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How do you solve this?

Aimless2007

Hey guys,

I got an exam tomorrow, and since I missed the last week, I don't really know how to solve questions like these:

1 gramm of Ra-226 radiates 3,7*10^10 alpha-particles in a second. Find out the half-life period of Ra-226.

We produce a radioactive Cu-64 and seal it. After 20 days, the activity is 20 Bq. What was the mass in gramm of the Cu-64 when we produced it?

Answers and explanations would be greatly appreciated,

Thanks,

Pear

Reply 1

Ourkid

This may not be of much use now, but here goes anyway:

1)

226 grams of Ra226 = 1 mol
1 gram of Ra226 = 1/ 226 = 0.0044247 mols

no of particles (N) = mols x 6.02x10^23 = 2.66x10^21 particles

activity = - lambda x N
3.7x10^10 = - lambda x 2.66x10^21

Decay constant (lambda) = 1.39x10^-11

half life = ln2 / lambda = ln2 / 1.39x10^-11

Half life = 4.98x10^10 seconds or 1580.15 years approx

2) For this one, I think more info would be needed such as half life of cu-64?

If you had that then you can work out the decay constant, and then use that to calculate the mass.

Unless I just don't know how to. Which is probable.

w00tt