Production of Radionuclides (Nuclear Activation)

Introduction to Radionuclide Production

In 1896, Henri Becquerel discovered natural radioactivity, and in 1934, Frédéric Joliot and Irène Curie-Joliot discovered artificial radioactivity. Natural radionuclides are produced through one of four radioactive decay chains, each fed by a long-lived and heavy parent radionuclide. However, the vast majority of radionuclides used in medicine and industry today are produced artificially through a process called nuclear activation.

Nuclear activation involves the bombardment of stable nuclei with energetic particles or high-energy photons to induce a nuclear transformation, resulting in the creation of radionuclides. Various particles or electromagnetic radiation generated by machines are used for this purpose, such as:

Neutrons from nuclear reactors for neutron activation
Protons from cyclotrons or synchrotrons for proton activation
X-rays from high-energy linear accelerators for nuclear photoactivation

Methods of Radionuclide Production

Neutron Activation

Neutron activation is the most widely used method for producing radionuclides, especially for medical applications. It involves the bombardment of stable nuclei with neutrons, typically from a nuclear reactor. This induces the nuclei to capture neutrons and become unstable, thus producing a radionuclide.

Applications of Neutron Activation:

Radiotherapy: Radionuclides used for external beam radiotherapy and brachytherapy are often produced trough neutron activation.
Nuclear Medicine Imaging: Radionuclides for imaging, such as in PET (Positron Emission Tomography), are also produced using neutron activation.

Proton Activation

Proton activation involves bombarding stable nuclei with protons, which can be produced in a cyclotron or synchrotron. The interaction of protons with the nuclei causes the production of various radionuclides.

Applications of Proton Activation:

Positron Emitters for PET Imaging: Proton activation is particularly important in the production of positron-emitting radionuclides used in PET scans.

Nuclear Photoactivation

Nuclear photoactivation occurs when high-energy X-rays (photons) are used to bombard stable nuclei, causing them to emit radiation and become radionuclides. This method is typically employed in radiation protection and in situations where activated materials could pose a risk.

Applications of Nuclear Photoactivation:

Radiation Protection: Nuclear photoactivation is relevant when components of radiotherapy machines, like linear accelerators, become activated during patient treatment and pose a potential radiation risk to medical staff.

Example of Radionuclide Production via Neutron Activation

A common example of neutron activation is the production of iodine-131 (¹³¹I) from stable iodine-130 (¹³⁰I). When stable iodine-130 is bombarded with neutrons in a nuclear reactor, it captures a neutron and becomes iodine-131, a radioactive isotope.

The reaction can be written as:

$I 130 + n \to I 131$

Iodine-131 is used in various medical applications, including thyroid cancer treatment and diagnostic imaging, as it emits beta particles and gamma radiation.

Importance and Applications of Radionuclides

Radionuclides are critical in various fields, particularly in medicine, where they are used in imaging and therapy. The use of artificial radionuclides, produced by nuclear activation, has revolutionized modern diagnostics and treatment:

Therapeutic Nuclear Medicine: Radionuclides are used to target and treat diseases, such as cancer, by delivering localized radiation to tumors.
Diagnostic Imaging: Radionuclides are used in PET scans, SPECT, and other imaging techniques to visualize and diagnose conditions in the body.
Radiation Protection: Understanding how radionuclides are produced and used helps in managing radiation risks, especially in medical facilities and research environments.