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Cobalt-60 is a strong gamma emitter that has a half-life of 5.26 yr. The cobalt-60 in a radiotherapy unit must be replaced when its radioactivity falls to 75% of the original sample. If an original sample was purchased in June 2013, when will it be necessary to replace the cobalt-60?

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Lelia Lubowitz
Lelia LubowitzLv2
20 May 2020

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Related questions

I did the following two calculations:

Calculation of concentration (M) of 1 mL of cobalt (II) in diluted solution with 9 mL of deionized water

C1*V1 = C2*V2 (I)
0.1 M cobalt * 0.001 L cobalt = C2 * 0.01 L
C2 = (0.1 M * 0.001 L)/0.01 L = 0.01 M

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X = (y-b)/m = (0.22+0.0094)/3.43 = 0.067 M

And I cannot figure out the final calculation:

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I've attached a picture that could provide further context.

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1. A rock from Australia was found to contain 0.435 g of Pb−206to every 1.00 g of U−238.

Assuming that the rock did not contain any Pb−206 at the time of its formation, how old is the rock?

Express your answer using two significant figures.

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