Nuclear physics
Nucleus before decay – parent nucleus
Nucleus after decay – daughter nucleus
−¿¿
❑ decay: nucleon number decreases by 4 and proton number decreases by 2
❑−¿¿ decay: nucleon number unchanged and proton number increases by 1
❑+¿¿decay: nucleon number unchanged and proton number decreases by 1
Einstein’s mass energy equation
Matter can be considered a form of energy so when energy is supplied to a system its mass
increases and when a system loses mases, its energy decreases. This is known as mass
energy equivalence.
Mass is greater when a particle is moving because its gaining energy
E = mc 2
where m = mass (kg), E = energy (J), c = speed of light
Rest mass – mass of an isolated stationary particle
Mass defect –difference between mass of nucleus and its nucleons which are separated to
infinity
Loss in mass implies that energy was released
Atomic mass unit (u) – 1u is defined as 1/12 of the mass of a neutral atom of carbon-12
1u = 1.6605 x
−27
10
Mass excess = mass in (u) – nucleon number
Since nuclei are made up of neutrons and protons, there are forces of repulsion between the
positive protons, therefore it takes energy (binding energy) to hold nucleons together as a
nucleus
Binding energy – the energy required to separate the nucleons in a nucleus to infinity
Binding energy is not the energy stored in the nucleus
The formation of a nucleus from a system of isolated protons and neutrons is therefore an
exothermic reaction
A higher binding energy per nucleon indicates a higher stability
Finding binding energy per nucleon:
1. Find mass defect for nucleus
2. Use E = mc 2 to find the binding energy of the nucleus
3. Divide binding energy by
number of nucleons to get
binding energy per
nucleon
Nucleus before decay – parent nucleus
Nucleus after decay – daughter nucleus
−¿¿
❑ decay: nucleon number decreases by 4 and proton number decreases by 2
❑−¿¿ decay: nucleon number unchanged and proton number increases by 1
❑+¿¿decay: nucleon number unchanged and proton number decreases by 1
Einstein’s mass energy equation
Matter can be considered a form of energy so when energy is supplied to a system its mass
increases and when a system loses mases, its energy decreases. This is known as mass
energy equivalence.
Mass is greater when a particle is moving because its gaining energy
E = mc 2
where m = mass (kg), E = energy (J), c = speed of light
Rest mass – mass of an isolated stationary particle
Mass defect –difference between mass of nucleus and its nucleons which are separated to
infinity
Loss in mass implies that energy was released
Atomic mass unit (u) – 1u is defined as 1/12 of the mass of a neutral atom of carbon-12
1u = 1.6605 x
−27
10
Mass excess = mass in (u) – nucleon number
Since nuclei are made up of neutrons and protons, there are forces of repulsion between the
positive protons, therefore it takes energy (binding energy) to hold nucleons together as a
nucleus
Binding energy – the energy required to separate the nucleons in a nucleus to infinity
Binding energy is not the energy stored in the nucleus
The formation of a nucleus from a system of isolated protons and neutrons is therefore an
exothermic reaction
A higher binding energy per nucleon indicates a higher stability
Finding binding energy per nucleon:
1. Find mass defect for nucleus
2. Use E = mc 2 to find the binding energy of the nucleus
3. Divide binding energy by
number of nucleons to get
binding energy per
nucleon
