Nuclear reactions are key to making radioisotopes. They change atoms into different elements or isotopes. Understanding these reactions helps scientists produce the right radioactive materials for various uses.

There are different types of nuclear reactions, like neutron capture and charged particle reactions. Each has its own quirks and uses. Knowing the ins and outs of these reactions is crucial for making radioisotopes efficiently and safely.

Nuclear Reaction Types

Transmutation and Neutron Capture Reactions

• Nuclear transmutation occurs when an atomic nucleus is transformed into another nucleus through a nuclear reaction
• Involves the change of one chemical element or isotope into another, resulting in significant changes in the atomic number and mass number
• Neutron capture is a type of nuclear reaction where an atomic nucleus absorbs or captures a neutron
• The target nucleus combines with the neutron, forming a heavier isotope of the same element (e.g., $^{58}Fe + n \rightarrow ^{59}Fe$)
• Neutron capture reactions are the most common method for producing radioisotopes due to the high probability of interaction between neutrons and nuclei

Charged Particle and Photonuclear Reactions

• Charged particle reactions involve the interaction of a charged particle (such as a proton, deuteron, or alpha particle) with a target nucleus
• These reactions can induce nuclear transformations, leading to the production of different isotopes or elements (e.g., $^{18}O(p,n)^{18}F$)
• Charged particle reactions often have a higher threshold energy compared to neutron capture reactions
• Photonuclear reactions occur when a high-energy photon (gamma ray) interacts with an atomic nucleus
• The photon can cause the ejection of nucleons (protons or neutrons) from the nucleus, resulting in the formation of a different isotope or element (e.g., $^{9}Be(\gamma,n)^{8}Be$)

Reaction Parameters

Cross-Section and Q-Value

• Cross-section is a measure of the probability of a specific nuclear reaction occurring between a projectile and a target nucleus
• Expressed in units of area (barns), with larger cross-sections indicating a higher likelihood of the reaction taking place
• The Q-value represents the amount of energy released or absorbed in a nuclear reaction
• Positive Q-values indicate an exothermic reaction (energy released), while negative Q-values indicate an endothermic reaction (energy absorbed)

Threshold Energy and Yield

• Threshold energy is the minimum kinetic energy required for a projectile to induce a specific nuclear reaction
• Reactions with higher threshold energies require more energetic projectiles to occur
• Yield refers to the amount of a specific radioisotope produced in a nuclear reaction
• Expressed as a percentage or fraction of the total number of target nuclei that undergo the desired reaction
• Yield depends on factors such as the reaction cross-section, target material, and irradiation conditions

Radioisotope Properties

Specific Activity and Radionuclidic Purity

• Specific activity is a measure of the radioactivity of a radioisotope per unit mass
• Expressed in units of radioactivity per mass (e.g., Bq/g or Ci/g)
• Higher specific activities indicate a greater concentration of the radioisotope in a given sample
• Radionuclidic purity refers to the fraction of the total radioactivity in a sample that is attributed to the desired radioisotope
• Expressed as a percentage, with higher values indicating a more pure radioisotope preparation
• Impurities can arise from contaminants in the target material or from competing nuclear reactions during production