After long effort, in 1902, Marie and Pierre Curie succeeded in separating from uranium ore the first substantial quantity of radium, 1 decigram (dg) of pure . The radium was the radium isotope , which decays with a half-life of 1600 y. We have to answer the following: (a) how many radium nuclei they had isolated? (b) What was the decay rate of their sample, in Bq? (c) What was the decay rate in curies? The molar mass of Cl is 35.453 g per mol; the atomic mass of the radium isotope is 226.03 u.

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(a)

The molar mass of Cl is 35.453 g per mol; the atomic mass of the radium isotope is 226.03 u. From this data we note that the mass of one molecule of will be

Therefore, the number of radioactive isotopes of contained in 1 dg of pure will be

(b)

The half-life of radium isotope is 1600 y. Therefore, its disintegration constant is

The decay rate of Marie and Pierre Curie’s sample therefore was

(c)

The decay rate in curies was