SRS Unit 1.2 ATAR Physics - Ionising Radiation & Nuclear Reactionc

WIP - til Decay Series

Bohr’s Atomic Model

• The nuclear model where protons and neutrons are contained in a nucleus and electrons are orbiting it in shells

Proton

Charge:

• + 1.602×10⁻¹⁹ 𝐶

• +1 𝑒

Location:

• Nucleus

Mass:

• 1.6726 ×10⁻²⁷ 𝑘𝑔

• 1.007276 𝑎𝑚𝑢

Neutron

Charge:

• 0C

• 0 e

Location:

• Nucleus

Mass:

• 1.6749 ×10⁻²⁷ 𝑘𝑔

• 1.008665 𝑎𝑚𝑢

Electron

Charge:

• −1.602×10−19 𝐶

• −1 𝑒

Location:

• Outside nucleus

Mass:

• 9.1094 ×10−31 𝑘𝑔

• 0.000549 𝑎𝑚𝑢

Nucleons

• A collective term for protons and neutrons found in the nucleus.

Nuclides

• The range of atomic nuclei associated with a particular atom, which is defined by the atomic number and the various isotopes of that atom as identified by the mass number.

Isotopes

• Two or more types of atoms that have the same atomic number and position in the periodic table but different number of neutrons.

Atomic Number (Z)

• The number of protons that defines the element

Atomic Mass Number

• The total mass of protons (Z) and neutrons (N) of an atom in Atomic Mass Units (amu)

Neutron Number (N)

• Atomic Mass Number (rounded) - Atomic Number

Electrostatic Force (EF)

• An attractive and repulsive force between particles caused by their electric charges

• Like charges repel, opposites attract

• Also referred to as Coulomb’s force

Strong Nuclear Force (SNF)

• The “glue” holding protons and electrons together in the nucleus together

• Exists within quarks, which form protons and neutrons

SNF > EF

• If the Strong Nuclear Force is stronger than the Electrostatic Force, nuclei will be stable

• However, if this delicate balance is interfered with, nuclei will become unstable and decay

Stable nuclide

• A nuclide that will never (or close to never) decay

Unstable nuclide

• A nuclide that will decay

• It will keep decaying until the balance of protons and neutrons is stable

Radioactive decay

• The process by which an unstable atomic nucleus loses energy by radiation and the emission of subatomic particles

Radioisotope

• A radioactive isotope

Beta Positive/Plus Decay (β⁺)

• Occurs when the nucleus has too many protons

• Therefore the Electrostatic Force overpowers the Strong Nuclear Force

• The proton decays into a neutron to release excess EF and stabilise the nucleus

• Due to this, the nucleus emits a positron (anti-electron) known as a Beta Positive Particle along with a neutrino

Beta Negative/Minus Decay (β^-)

• Occurs when the nucleus has too many neutrons

• Therefore the Strong Nuclear Force overpowers the Electrostatic Force

• The neutron decays into a proton to gain additional EF and stabilise the nucleus

• Due to this, the nucleus emits an electron known as a Beta Negative Particle along with an anti-neutrino

Alpha Decay (α)

• Occurs when the nucleus is too heavy to naturally be stable (every element above Bismuth)

• The nucleus releases two protons and two neutrons at the same time - an Alpha Particle

• An Alpha Particle is the same as a Helium-4 nucleus

Gamma Decay (γ)

• Occurs when nucleus has excess energy but the correct ratio of protons to neutrons

• The nucleus emits energy Gamma Radiation - gamma waves

Segre Plot

• A graph/visualisation of the stability in nuclei showing all known isotopes of each element and their radioactivity/stability

• y axis is number of neutrons (N), x axis is number of protons (Z)

• Beyond element 82 (Lead) there are no more stable isotopes

• The number of radioactive isotopes for each element exceeds the number of stable ones

Penetrating ability

• How well radiation can pierce through matter

Ionisation ability

• How well radiation can ionise atoms

• Ionisation is the process by which an atom loses or gains an electron, thus resulting in a net positive or negative charge

Alpha Particle (α)

Mass:

• 4.001 506 u

Charge:

• +2e

Penetrating Ability:

• Low

Ionisation Ability:

• High

Beta Positive/Plus Particle (positron) (β⁺)

Mass:

• 0.000549 u

Charge:

• +1e

Penetrating Ability:

• Medium

Ionisation Ability:

• Medium

Beta Negative/Minus Particle (electron) (β^-)

Mass:

• 0.000549 u

Charge:

• -1e

Penetrating Ability:

• Medium

Ionisation Ability:

• Medium

Gamma Particle (γ)

• High energy light/electromagnetic wave

Mass:

• 0 u

Charge:

• 0e

Penetrating Ability:

• High

Ionisation Ability:

• Low

• Can only ionise atoms if it strikes an electron directly and knocks it loose

Nuclear Equation formats

• LHS → RHS

• Reactants → Products

• Parent Nucleus → Daughter Nucleus + decay particles + energy

Alpha Decay Equation

PN → DN + α + energy

Beta Positive/Plus Decay Equation

PN → DN + β⁺ + v_e + energy

Beta Negative/Minus Decay Equation

PN → DN + β^- + v_e + energy

Gamma Decay Equation

PN* → PN + γ + energy