Nuclear Physics: Forces, Decay, and Energy Principles

Posted on May 5, 2026 in Chemistry

Forces in the Nucleus

  • Gravity: Force of attraction.
  • Weak nuclear: Weak interaction.
  • Strong nuclear: Strong interaction.

The strong force is attractive at very short distances and repulsive at slightly longer distances as a residual effect of holding together electrons and nucleons. Isotopes have the same number of protons but a different number of neutrons.

Half-Life Calculations

Half-Life FormulaFinding Number of Half-Lives

N = N0 x (1/2)n

n = T / t1/2

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N = number of nuclei or mass remaining

N0 = start amount

n = number of half-lives

n = number of half-lives

T = total time

t1/2 = length of time for one half-life

Alpha Decay

Alpha DecayFormula
An unstable parent nucleus emits an alpha particle (2 protons, 2 neutrons) to become more stable.
This releases energy and changes the atom to a new element.

Beta Radiation

Beta DecayFormula
β⁻: A neutron changes to a proton and emits an electron (atomic number increases by 1).
β⁺: A proton changes to a neutron and emits a positron (atomic number decreases by 1).

Beta radiation is caused by the weak nuclear force.

Gamma Radiation

Gamma RadiationFormula
Nucleus emits energy in the form of gamma radiation.

Penetration and Human Damage

RadiationPenetrating PowerSource Outside BodySkin PenetrationSource Inside Body
ALPHALOWNONELOWHIGH
BETAMEDLOWMEDHIGH
GAMMAHIGHHIGHHIGHLOW

Absorbed Dose

Ionising: Ability to damage cells.

Absorbed DoseFormula

D = Absorbed dose in (Gy)

Er = Energy absorbed in (J)

m = mass in (kg)

D = Er / m

Equivalent Dose

Equivalent DoseFormula

H = equivalent dose

D = absorbed dose in (Gy)

Wr = radiation weighting factor

H = D x Wr

Radiation weighting factors:

Alpha = 20, Beta = 1, Gamma = 1

Energy Equation

EquationVariables
E = mc²

E = Energy in (J)

m = Mass

c = Speed of light (3×10⁸ m/s)

Note: Find the mass that has disappeared to calculate energy released.

Nuclear Fission and Fusion

ProcessNotes
SubcriticalNumber of reactions is decreasing.
CriticalNumber of reactions is constant.
SupercriticalNumber of reactions is increasing.
Control Methods
  1. Increase mass to increase collisions.
  2. Increase surface area to decrease collisions.
  3. Control rods absorb neutrons to decrease collisions.
  4. Neutron moderator slows down neutrons to increase collisions.
Nuclear PowerPro: No greenhouse gases. Con: Produces radioactive waste.
ComparisonFusion: Two light elements join. Fission: One heavy element splits. Fission is easier to control than fusion.