Chapter 13: Nuclei

Suppose we consider a large number of containers each containing initially 10000 atoms of a radioactive material with a half-life of 1 year. After 1 year

(a) all the containers will have 5000 atoms of the material

(b) all the containers will contain the same number of atoms of the material but that number will only be approximately 5000

(c) the containers will, in general, have different numbers of the atoms of the material but their average will be close to 5000

(d) none of the containers can have more than 5000 atoms

The gravitational force between an H-atom and another particle of mass m will be given by Newton’s law: F = G M.m/r² , where r is in km and

(a) M = mproton + m electron

(b) M = mproton + melectron – B/c² (B = 13.6 eV)

(c) M is not related to the mass of the hydrogen atom

(d) M = mproton + m electron |V |/c² – (|V | = magnitude of the potential energy of electron in the H-atom)

When a nucleus in an atom undergoes radioactive decay, the electronic energy levels of the atom

(a) do not change for any type of radioactivity

(b) change for α and β radioactivity but not for γ-radioactivity

(c) change for α-radioactivity but not for others

(d) change for β-radioactivity but not for others

Mx and My denote the atomic masses of the parent and the daughter nuclei respectively in a radioactive decay. The Q-value for a β– decay is Q1 and that for a β + decay is Q2. If me denotes the mass of an electron, then which of the following statements is correct?

Tritium is an isotope of hydrogen whose nucleus Triton contains 2 neutrons and 1 proton. Free neutrons decay into

(a) Triton energy is less than that of a He³ nucleus

(b) the electron created in the beta decay process cannot remain in the nucleus

(c) both the neutrons in triton have to decay simultaneously resulting in a nucleus with 3 protons, which is not a He³ nucleus

(d) because free neutrons decay due to external perturbations which is absent in a triton nucleus

Heavy stable nuclei have more neutrons than protons. This is because of the fact that

(a) neutrons are heavier than protons

(b) electrostatic force between protons are repulsive

(c) neutrons decay into protons through beta decay

(d) nuclear forces between neutrons are weaker than that between protons

In a nuclear reactor, moderators slow down the neutrons which come out in a fission process. The moderator used to have light nuclei. Heavy nuclei will not serve the purpose because

Fusion processes, like combining two deuterons to form a He nucleus are impossible at ordinary temperatures and pressure. The reasons for this can be traced to the fact:

(a) nuclear forces have short-range

(b) nuclei are positively charged

(c) the original nuclei must be completely ionized before fusion can take place

(d) the original nuclei must first break up before combining with each other

Samples of two radioactive nuclides A and B are taken. λA and λB 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?

The variation of the decay rate of two radioactive samples A and B with time is shown in the figure. Which of the following statements are true?

dN/dt P

B

A