## Question

### Solution

Correct option is

4221 years

The activity (rate of decay) of a radioactive material at any instant is proportional to the number of atoms left at that instant, that is

Let t be the age of the specimen. The initial (at t = 0) activity R0 was 15 decays/min and the present activity (at tR in 9 decays/min. Thus

= 0.5107

= 4221 years.

#### SIMILAR QUESTIONS

Q1

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?

Q2

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

Q3

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

Q4

The half-life of  against . Calculate the activity of 1 g sample of . Avogadro’s number is .

Q5

The half-life of  is 28 years. How much is the disintegration rate of 15 mg of this isotope? The Avogadro’s number is .

Q6

1 g of particles per second. Find its half-life and average life. Avogadro’s number is .

Q7

Determine the amount of  required to provide a source of -particles of 5 millicurie strength. The half-life of Po is 138 days. The Avogadro’s number is

Q8

The disintegration rate of a certain radioactive sample at any instant is 4750 disintegrations per minute. 5 minute after, the rate becomes 2700 disintegrations per minute. Calculate the half-life of the sample. .

Q9

At a given instant are 25% undecayed radioactive nuclei in a sample. After 10 seconds, the number of undecayed nuclei reduces to 12.5%. Calculate the time in which the number of undecayed nuclei will further reduce to 6.25% of the reduced number.

Q10

A radioactivity sample contains 2.2 mg of pure  which has half-life period of 1224 seconds. Calculate the number of atoms present initially.