physics homework?

Question

1 . A 10.0mg sample of strontium-90 is found to have an activity of 24 Bq. Its halrd-life is 28.5 years. Calculate:
a) the fraction of undecayed atoms of Sr-90 remaining after 114years.
b) the activity of the sample after this time.

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2-The radioactive isotope gold-198 is a B- (Beta) emitter and is often used as a radioisotipic tracer. It can be used, for instance, by health engineers to trace the flow of sewage. it is found that its activity drops to 1/8 of its original value in just over 8 days.
a) Write the B-decay equation for this isotope (198 over 79 Au). You will need to refer to a periodic table.
b) Calculate its approximate half-life.
c) Estimate the fraction of gold-198 remaining after 2 weeks.
d) Why do you think gold-198 may be chosen as a tracer to study the flow of sewage?



If you know the answer, plz write it down.. and i really appreciate it! Thanks alot!

Answer 1

You must be kidding.

S a = L N0
S - 24Bq
a = 10.0 mg
N- number of decaying atoms
N0 - initial number of atoms

L= ln(2)/ H
L- decay constant
H- half life time

So
N0= S a /L = S a H/ ln(2)
finally

N(t)= S a H/ ln(2) exp( - t L)
N(t)= S a H/ ln(2) exp( - t ln(2)/ H )

Now you are ready to compute for t=114 years
just keep in mind that
1 year = 365 x 24 x 3600= 31,536,000 sec (common year)

Answer 2

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