Radionuclide Production 2025

How are synthetic radionuclides produced?

Bombard stable nuclei with subatomic particles, creating unstable nuclei

3 Sources of artificial radionuclides

1. Nuclear Reactors

2. Particle Accelerators

3. Radionuclide generators

Fuel used in a nuclear reactor

U235

4 main components of a nuclear reactor

Fuel: U235 rods

Moderator: Heavy water or graphite

Control rods: Cadmium or Boron

Coolant: Water

Moderator

Slows neutrons, making them more efficient at initiating fission

Control Rods

Absorb neutrons to limit or stop the chain reaction

Nuclear Meltdown

A runaway chain reaction producing heat faster than it can be dissipated

Neutron Activation

Neutrons strike target atoms and are absorbed by their nuclei

(n, y) reaction (neutron capture)

A neutron is absorbed; the excited nucleus emits a gamma ray; produces an isotope

(n,p) reaction (neutron-proton reaction)

A neutron is absorbed and a proton is ejected; produces a different element (isobar)

Energy each nuclear fission event produces

200-300 MeV of thermal energy

4 factors affecting reactor radionuclide production

1. Neutron intensity

2. Neutron energy

3. Number of target nuclei

4. Activation cross section

Particles cyclotrons accelerate

Protons, deuterons, tritons, alpha particles

What energy must have charged particles to overcome Coulomb forces

10-20+ MeV

Two hollow electrodes in a cyclotron

Dees (accelerate particles across the gap using alternating electrical charges)

Stripping foil in a cyclotron

Removes electrons from H¯, leaving a proton (H→ 2e + p*).

Accelerator-produced radionuclides decay method

Positron emission (β*) or electron capture (EC)

Photonuclear Bombardment

High-energy photons strike target nuclei, ejecting a proton or neutron

Radionuclide generator

An apparatus containing a parent-daughter pair that separates and extracts the daughter

Parent and daughter in a Mo-99/Tc-99m generator

Parent: Mo-99; Daughter: Tc-99m

Activation Cross Section

The effective target area presented by a target nucleus

Activation Cross Section measures

The probability of interaction between bombarding particles and target nuclei

Activation Rate (R)

Rate at which target nuclei become unstable per gram of target per second

3 factors that determine Activation Rate

1. Target Area

2. Beam Intensity

3. Mass of Target