Physics - Radioactivity

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
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