Nuclei · Question 29

A mixture consists of two radioactive materials A1 and A2 with half lives of 20 s and 10 s respectively. Initially the mixture has 40 g of A1 and 160 g of A2. The amount of the two in the mixture will become equal after

1. 60 s
2. 80 s
3. 20 s
4. 40 s

Two radioactive nuclei P and Q, in a given sample decay into a stable nucleus R. At time t = 0, the number of P species is 4N0 and that of Q is N0. Half-life of P (for conversion to R) is 1 minute whereas that of Q is 2 minutes. Initially there are no nuclei of R present in the sample. When number of nuclei of P and Q are equal, the number of nuclei of R present in the sample would be

1. 2N0
2. 3N0
3. 9N02
4. 5N02

The power obtained in a reactor using 235U disintegration is 1000 kW. The mass decay of 235U per hour is

1. 10 microgram
2. 20 microgram
3. 40 microgram
4. 1 microgram

Fusion reaction takes place at high temperature because

1. nuclei break up at high temperature
2. atoms get ionised at high temperature
3. kinetic energy is high enough to overcome the Coulomb repulsion between nuclei
4. molecules break up at high temperature

The half life of a radioactive isotope X is 50 years. It decays to another element Y which is stable. The two elements X and Y were found to be in the ratio of 1 : 15 in a sample of a given rock. The age of the rock was estimated to be

1. 150 years
2. 200 years
3. 250 years
4. 100 years

A nucleus mnX emits one particle and two particles. The resulting nucleus is

1. m-6n-4Z
2. m-6nZ
3. m-4nX
4. m-4n-2Y

The binding energy per nucleon in deuterium and helium nuclei are 1.1 MeV and 7.0 MeV, respectively. When two deuterium nuclei fuse to form a helium nucleus the energy released in the fusion is

1. 23.6 MeV
2. 2.2 MeV
3. 28.0 MeV
4. 30.2 MeV

The decay constant of a radioisotope is . If A1 and A2 are its activities at times t1 and t2 respectively, the number of nuclei which have decayed during the time (t1 - t2)

1. A1t1 - A2t2
2. A1 - A2
3. (A1 - A2)/
4. (A1 - A2)

The mass of a 73Li nucleus is 0.042 u less than the sum of the masses of all its nucleons. The binding energy per nucleon of 73Li nucleus is nearly

1. 46 MeV
2. 5.6 MeV
3. 3.9 MeV
4. 23 MeV

The activity of a radioactive sample is measured as N0 counts per minute at t = 0 and N0/e counts per minute at t = 5 minutes. The time (in minutes) at which the activity reduces to half its value is

1. e 25
2. 5 e 2
3. 5 10 2
4. 5 e 2