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Snowcat [4.5K]
3 years ago
6

Cobalt-60 is a strong gamma emitter that has a half- life of 5.26 yr. The co balt-60 in a radiotherapy unit must be replaced whe

n its radioactivity falls to 75% of the original sample. If an original sample was purchased in June 2016, when will it be necessary to replace the cobalt-60?
Chemistry
1 answer:
Alenkasestr [34]3 years ago
3 0

<u>Answer:</u> The sample of Cobalt-60 isotope must be replaced in January 2027

<u>Explanation:</u>

The equation used to calculate rate constant from given half life for first order kinetics:

t_{1/2}=\frac{0.693}{k}

where,

t_{1/2} = half life of the reaction = 5.26 years

Putting values in above equation, we get:

k=\frac{0.693}{5.26yrs}=0.132yrs^{-1}

Rate law expression for first order kinetics is given by the equation:

k=\frac{2.303}{t}\log\frac{[A_o]}{[A]}

where,

k = rate constant = 0.132yr^{-1}

t = time taken for decay process = ? yr

[A_o] = initial amount of the sample = 100 grams

[A] = amount left after decay process =  (100 - 75) = 25 grams

Putting values in above equation, we get:

0.132=\frac{2.303}{t}\log\frac{100}{25}\\\\t=10.5yrs

The original sample was purchased in June 2016

As, June is the 6th month of the year, which means the time period will be 2016+\frac{6}{12}=2016.5

Adding the time in the original time period, we get:

2016.5+10.5=2027

Hence, the sample of Cobalt-60 isotope must be replaced in January 2027

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