Nuclei

A force between two protons is same as the force between proton and neutron. The nature of the force is

• weak nuclear force

• strong nuclear force

• electrical force

• gravitational force

A radioactive decay can form an isotope of the original nucleus with the emission of particles

• one α and one β

• one α and four β

• four α and one β

• one α and two β

The half-life of a radioactive substance is 20 min. The time taken between 50 % decay and 87.5 % decay of the substance will be

• 25 min

• 30 min

• 10 min

• 40 min

A nucleus at rest splits into two nuclear parts having radii in the ratio 1 : 2. Their velocities are in the ratio

• 4 : 1

• 8 : 1

• 2 : 1

• 6 : 1

A radioactive sample of half-life 10 days contains 1000 x nuclei. Number of original nuclei present after 5 days is

• 707 x

• 750 x

• 500 x

• 250 x

An element X decays into element Z by two-step process

                      $$\begin{gathered} \mathrm{X} \stackrel{}{\to } \mathrm{Y} + {}_2{}^4\mathrm{He} \\ \mathrm{Y} \stackrel{}{\to } \mathrm{Z} + 2{\mathrm{e}}^{-}, \mathrm{then} \end{gathered}$$

• X and Z are isobars

• X and Y are isotopes

• X and Z are isotones

• X and Z are isotopes

A nucleus of mass 20 u emits a γ-photon of energy 6 MeV. If the emission assume to occur when nucleus is free and rest, then the nucleus will have kinetic energy nearest to (Take, 1 u = 1.6 × 10^-27 kg)

• 10 keV

• 1 keV

• 0.1 keV

• 100 keV

The particle emitted in the decay of ${}_{92}{}^{238}\mathrm{U}$ to ${}_{92}{}^{238}\mathrm{U}$

• 2 α and 2β

• 1 α and 1 β

• 1 α only

• 1 α and 2 β

The mass defect of ${}_2{}^4\mathrm{He}$ is 0.03 u. The binding energy per nucleon of helium (in MeV) is

• 6.9825

• 27.93

• 2.793

• 69.825

In a nuclear reactor, the function of the moderator is to decrease

• number of neutrons

• speed of neutrons

• escape of neutrons

• temperature of the reactor