#### Question - 1

The activity of a radioactive sample is measured as 1750 counts/min at t = 0 and as 975 counts/min at t = 5 min. The decay constant is approximately

• A 0.922/min
• B 0.691/min
• C 0.461/min
• D 0.230/min

#### Question - 2

Samples of two radioactive nuclides A and B are taken. ${ \lambda }_{ A }$ and ${ \lambda }_{ B }$ are the disintegration constants of A and B, respectively. In which of the following cases, the two samples can simultaneously have the same decay rate at any time?

• A Intial rate of decay of A is twice the initial rate of decay of B and ${ \lambda }_{ A }$ = ${ \lambda }_{ B }$
• B Intial rate of decay of A is twice the initial rate of decay of B and ${ \lambda }_{ A }$ > ${ \lambda }_{ B }$
• C Intial rate of decay of B is twice the initial rate of decay of A and ${ \lambda }_{ A }$ < ${ \lambda }_{ B }$
• D Initial rate of decay of B is always same

#### Question - 3

If radioactive substasnce decays for time interval equal to its mean life, then the fraction of the substance remaing undecayed, will be

• A $\frac { 1 }{ e }$
• B $\frac { 1 }{ { e }^{ 2 } }$
• C $\ { e }^{ 2 }$
• D e

#### Question - 4

Two Cu64 nuclei touch each other. The electrostatic replulsive energy of the system will be

• A 0.788 MeV
• B 7.88 MeV
• C 126.15 MeV
• D 788 MeV

#### Question - 5

The graph of log $\frac { R }{ { R }_{ 0 } }$ versus A (R = radius of a nucleus and A = mass number) is

• A a circle
• B an ellipse
• C a parabola
• D a straight line

#### Question - 6

Which stable nucleus has radius one third of that of Os189 ?

• A Be9
• B Li7
• C F19
• D None of these

#### Question - 7

If the nuclear radius of 27Al is 3.6 fm, the approximate nuclear radius of 64Cu in Fermi is

• A 2.4
• B 1.2
• C 4.8
• D 3.6

#### Question - 8

The half-life of a radioactive material is 3 h. If the initial amount is 300 g, then after 18 h, it will remain

• A 4.68 g
• B 46.8 g
• C 9.375 g
• D 93.75 g

#### Question - 9

The half-life of a radioactive isotope X is 50 yr. It decays to another element Y whichis 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 estimed to be

• A 200 yr
• B 250 yr
• C 100 yr
• D 150 yr

#### Question - 10

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 Aand 160 g of A2. The amount of the two in the mixture will become equal after

• A 60 s
• B 80 s
• C 20 s
• D 40 s