Question

The half-life of radon is 3.8 days. Calculate how mach radon will be left out of 1024 milligram after 38 days?

Solution

Correct option is

1.0 mg

By the definition of half-life, if N0 be the initial quantity of radioactive element, then the quantity left (undecayed) after n half-lives is given by   

           

The half-life of radon is 3.8 days. The number of half-lives in 38 days is 

           

               = 10. 

The initial quantity of radon is N0 = 1024 mg (milligram). Therefore, the mass of radon left after 10 half-lives is 

                 

               

               = 1.0 mg.

SIMILAR QUESTIONS

Q1

What is meant by the ‘half-life’ of a radioactive element? What percentage of a given mass of a radioactive substance will be left undecayed after four half-lives? 

Q2

1 milligram radium has . Its half-life is 1620 years. How many radium atoms will disintegrate from 1 milligram of pure radium in 3240 years?

Q3

A sample of radioactive substance has 106 radioactive nuclei. Its half-life time is 20 seconds. How many nuclei will remain after 10 seconds?

Q4

A sample contains 10–2 kg each of the two substances A and B with half-lives 4 seconds and 8 seconds respectively. Their atomic weights are in the ratio of 1 : 2. Find the amounts of A and B after an interval of 16 seconds.

Q5

The half-life of radius is 1600 years. After how many years 25% of a radium block remains undecayed?

Q6

The half-life of polonium is 140 days. In what time will 15 g of polonium be disintegrated out of its initial mass of 16 g?

Q7

The activity of a radioactive element reduces to th of its original value in 30 years. Find the half-life and the decay constant of the element.

Q8

The half-life of thorium-X is 3.64 days. After how many days will 0.1 of the mass of a sample of the substance remain undecayed?

Q9

How much of 5.00 gram of polonium will decay in one year? The half-life of polonium is 138 days.

  

Q10

The half-life of a radioactive substance is  against . Calculate the decay rate for  atoms of the substance.