1) 130 I decays by emission of beta particles to form stable 130 Xe. A 3.00 g io
ID: 798425 • Letter: 1
Question
1)130I decays by emission of beta particles to form stable 130Xe. A 3.00 g iodine sample containing some I-130 was recorded as having 9010 disintegrations per min. k = 0.00094 min -1. How many radioactive I-130 atoms are present in the sample?
2)The radioactive decay of a sample containing an unknown radioactive isotope produced 7520 disintegrations per minute. 9.69 days later, the rate of decay was found to be 2240 disintegrations per minute. Calculate the half-life in days for the unknown radioactive isotope
Explanation / Answer
1)
A = ?N, where, A is no.of decays per unit time, ? is decay constant, N is total no. of particles is sample.
9010 = 0.00094 x N => N = 9010/0.00094 = 9585106.38.
2)
k=(2.303/t) log (a/a-x)
k= (2.303/9.69) log(7520/2240)
= 0.125 day-1
t1/2 = 0.693/k = 0.693/0.125 = 5.54 days
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