Chapter 8: Radiation
Introduction
In physics, radiation is the emission or transmission of energy in the form
of waves or particles through space or a material medium. This includes;
• Electromagnetic radiation
• Particle radiation
When a nucleus is unstable for instance its proton is more than neutron and vice versa it will
disintegrate by emitting radiation or particles to a more stable nucleus.
Any change in the proton number(s) will turn an element into a completely new element. Whereas
changing the number of neutron(s) will result in the formation of isotopes of the same element.
Radioactivity
Radioactivity is defined as the spontaneous disintegration of an unstable nucleus into a more stable
nucleus with the emission of energetic particles or photons.
A nucleus is unstable if it is too big. For nuclei with Z≥ 83 they are no longer stable. This is because
there is not enough neutron that can bind them together. Besides, neutron acts with short-range
force (strong nuclear force) while the repulsion between protons is the long-range force (Magnetic
force).
Nucleon number
𝐴
𝑍𝑋
(mass number)
Chemical symbol
Proton number
(atomic number)
Nucleus
In an electrically neutral atom, the numbers of protons are equal to the numbers of electrons. Ions
are electrically charged atoms, when an atom has more or less than the normal numbers of
electrons. Isotopes are forms of atoms of an element with differing numbers of neutrons in the
nucleus.
• Isotopes- Elements that have the same proton number but different nucleon number. They
have the same chemical properties but different physical properties (Densities and melting
points).
Relative atomic mass
Relative atomic mass is defined as the mass of the atom divided by one-twelve of the mass of carbon
12 atom.
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑎𝑡𝑜𝑚 (𝑖𝑛 𝑔𝑟𝑎𝑚)
𝐴𝑟 = 1
×𝑚𝑎𝑠𝑠 𝑜𝑓 𝑐𝑎𝑟𝑏𝑜𝑛 12 𝑎𝑡𝑜𝑚
12
One relative atomic mass is called 1u. 1𝑢 = 1.66 × 10−27 𝑘𝑔
×
𝑢 𝑘𝑔
÷
, Nucleus radii
The nucleus is very much smaller than the atom. The radius of a nucleus is approximately 10−4
that of the atom it occupies.
A = Nucleon number
1
𝑅𝑎𝑑𝑖𝑢𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑛𝑢𝑐𝑙𝑢𝑒𝑠, 𝑟 = 𝑟0 𝐴3 𝑟0 = 1.2 × 10−15 𝑚
The nucleus density
The volume of the nucleus is approximately 10−12 of the atom. Since most of the mass of the atom
resides in the nucleus, it follows that its density is extremely high, roughly the same for all nuclei
1017 𝑘𝑔 𝑚−3.
Nucleus
Calculation
𝑚𝑎𝑠𝑠 𝑚
𝐷𝑒𝑛𝑠𝑖𝑡𝑦 = = 4 3
𝑣𝑜𝑙𝑢𝑚𝑒 𝜋𝑟
3
1
Since 𝑟 = 𝑟0 𝐴3
𝑚
• 1
4
𝜋(𝑟0 𝐴 3 )3
3
The four fundamental forces
• Strong nuclear force
Short range force
• Weak nuclear force
• Electromagnetic force
• Gravitational force Long range force
Introduction
In physics, radiation is the emission or transmission of energy in the form
of waves or particles through space or a material medium. This includes;
• Electromagnetic radiation
• Particle radiation
When a nucleus is unstable for instance its proton is more than neutron and vice versa it will
disintegrate by emitting radiation or particles to a more stable nucleus.
Any change in the proton number(s) will turn an element into a completely new element. Whereas
changing the number of neutron(s) will result in the formation of isotopes of the same element.
Radioactivity
Radioactivity is defined as the spontaneous disintegration of an unstable nucleus into a more stable
nucleus with the emission of energetic particles or photons.
A nucleus is unstable if it is too big. For nuclei with Z≥ 83 they are no longer stable. This is because
there is not enough neutron that can bind them together. Besides, neutron acts with short-range
force (strong nuclear force) while the repulsion between protons is the long-range force (Magnetic
force).
Nucleon number
𝐴
𝑍𝑋
(mass number)
Chemical symbol
Proton number
(atomic number)
Nucleus
In an electrically neutral atom, the numbers of protons are equal to the numbers of electrons. Ions
are electrically charged atoms, when an atom has more or less than the normal numbers of
electrons. Isotopes are forms of atoms of an element with differing numbers of neutrons in the
nucleus.
• Isotopes- Elements that have the same proton number but different nucleon number. They
have the same chemical properties but different physical properties (Densities and melting
points).
Relative atomic mass
Relative atomic mass is defined as the mass of the atom divided by one-twelve of the mass of carbon
12 atom.
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑎𝑡𝑜𝑚 (𝑖𝑛 𝑔𝑟𝑎𝑚)
𝐴𝑟 = 1
×𝑚𝑎𝑠𝑠 𝑜𝑓 𝑐𝑎𝑟𝑏𝑜𝑛 12 𝑎𝑡𝑜𝑚
12
One relative atomic mass is called 1u. 1𝑢 = 1.66 × 10−27 𝑘𝑔
×
𝑢 𝑘𝑔
÷
, Nucleus radii
The nucleus is very much smaller than the atom. The radius of a nucleus is approximately 10−4
that of the atom it occupies.
A = Nucleon number
1
𝑅𝑎𝑑𝑖𝑢𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑛𝑢𝑐𝑙𝑢𝑒𝑠, 𝑟 = 𝑟0 𝐴3 𝑟0 = 1.2 × 10−15 𝑚
The nucleus density
The volume of the nucleus is approximately 10−12 of the atom. Since most of the mass of the atom
resides in the nucleus, it follows that its density is extremely high, roughly the same for all nuclei
1017 𝑘𝑔 𝑚−3.
Nucleus
Calculation
𝑚𝑎𝑠𝑠 𝑚
𝐷𝑒𝑛𝑠𝑖𝑡𝑦 = = 4 3
𝑣𝑜𝑙𝑢𝑚𝑒 𝜋𝑟
3
1
Since 𝑟 = 𝑟0 𝐴3
𝑚
• 1
4
𝜋(𝑟0 𝐴 3 )3
3
The four fundamental forces
• Strong nuclear force
Short range force
• Weak nuclear force
• Electromagnetic force
• Gravitational force Long range force
