The plutonium isotope , atomic mass 239.05 u, is produced as a by-product in nuclear reactors and hence is accumulating in reactor fuel elements. It is radioactive, decaying by alpha decay with a half-life of . But plutonium is also one of the most toxic chemicals known; as little as 2.00 mg is lethal to a human. We have to answer the following: (a) how many nuclei constitute a chemically lethal dose? (b) What is the decay rate of this amount? (s) What is its activity in curies?

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(a)

The atomic mass of is 239.05 u. Therefore, number of nuclei of contained in 2.00 mg, which is lethal to human beings, will be

(b)

The plutonium isotope is radio active and decays by alpha decay with a half-life of . Therefore, its disintegrations constant is

Therefore, the decay rate of 2.0 mg of the plutonium isotope will be

(c)

We know that

Therefore, the decay rates in curies is