Chapter 20: Nuclear Physics

Question 1

What’s a nucleon?

Answer 1

A nucleon refer to either a proton or a neutron in the nucleus.

Question 2

State what is meant by nucleon number

Answer 2

Nucleon Number (mass number), A, of an element is the total number of nucleons in the nucleus (i.e. protons + neutrons)

Question 3

State what is meant by atomic number

Answer 3

Atomic Number (proton number), Z, of an element is the number of protons in the nucleus.

Question 4

State what is meant by neutron number

Answer 4

Neutron number, N, of an element is the number of neutrons in the nucleus.

Question 5

What is a nuclide?

Answer 5

A nuclide is a class of nuclei that have a particular nucleon number and
a particular proton number.

Question 6

What is an isotope?

Answer 6

Isotopes are nuclei of atoms of a particular element containing the same number of protons but different number of neutrons.

Question 7

What is the atomic mass unit?

Answer 7

The atomic mass unit (u) is defined as 1/12th of the mass of a carbon-12 atom.
u = 1.66 × 10–27 kg

Question 8

Define relative atomic mass

Answer 8

The relative atomic mass Mr of a substance is the ratio of the mass of one atom of this substance to 1/12th of the mass of a carbon-12 atom.

Question 9

Define mass defect

Answer 9

Mass defect, Δm is defined as the difference between the total mass of the
separate nucleons in a nucleus and the combined mass of the nucleus.

Question 10

What is binding energy?

Answer 10

Binding Energy is defined as the energy required to separate the nucleons in a
nucleus to infinity. It is also the energy equivalent of the mass defect of a nucleus.

Note: It is also the energy released when nucleons come together to form a nucleus
from infinity.

Question 11

State what is meant by binding energy

Answer 11

The binding energy per nucleon is defined as the average energy per nucleon needed to separate a nucleus into its constituent nucleons to infinity.

Question 12

What is nuclear fission?

Answer 12

Nuclear Fission is the splitting of a heavy nucleus into two lighter nuclei of approximately the same mass.

Question 13

What is nuclear fusion?

Answer 13

Nuclear Fusion is the process where two light nuclei combine to form a nucleus of greater mass.

Question 14

State what is meant by radioactive decay

Answer 14

Radioactive decay is a spontaneous and random process in which an unstable
nucleus emits alpha particles, beta particles or gamma radiation to become more
stable.

Question 15

What is an exponential decrease?

Answer 15

An exponential decrease refers to a situation where a quantity reduces at
a rate proportional to its current value.

Question 16

State what is meant by the decay constant

Answer 16

The decay constant λ is the probability per unit time of the decay of a nucleus.

Question 17

What is activity?

Answer 17

The activity, A of a radioactive source is defined as the number of nuclear disintegrations per unit time in the source. (rate of decay of the radioactive nuclei)

Question 18

What is count rate?

Answer 18

The count rate (C) is defined as the rate at which emissions from a radioactive source
are detected.

Question 19

State what is meant by the half-life

Answer 19

The half-life t1/2 of a radioactive nuclide is the average time taken for the number of undecayed nuclei to be reduced to half its original number.