This blog post examines the principles and applications that led nuclear physics—the study of atomic nuclei—to modern medical technologies like radiation therapy and PET scans, via cyclotrons and radioactive isotopes.
Why did nuclear physics lead to medicine and experimental science?
Nuclear physics is the study of atomic nuclei. However, many people tend to perceive nuclear physics solely as the field dealing with nuclear fission phenomena occurring in nuclear power plants. Contrary to this perception, various byproducts generated during nuclear physics research enabled experiments previously impossible in other areas of chemistry or physics, and they also hold practical value in the medical field.
Cyclotron: Just a Simple Particle Accelerator?
For example, consider the cyclotron, an accelerator developed for nuclear physics experiments. A cyclotron is a particle accelerator that induces particles into circular motion. Structurally, it is a relatively simple device consisting of two D-shaped vacuum chambers made of copper plates. This device uses high-frequency alternating current voltage to accelerate the flow of charged particles.
The structural characteristics of the cyclotron can be broadly divided into two main features. The first feature is that, unlike conventional linear particle accelerators, the cyclotron is a circular particle accelerator with two D-shaped semicircular plates spaced apart. The second characteristic is that within the cyclotron, the direction of the alternating voltage’s frequency changes each time particles pass through one of the semicircular plates. To accelerate the particle flow, the alternating voltage flows between two semicircular metal electrodes inside the vacuum chamber. These semicircular plates are spaced apart at a fixed interval to ensure particles, injected into the center of this space, have room to move freely. The semicircular plates are positioned between the poles of an electromagnet generating an electromagnetic field perpendicular to the electrode plates. The resulting magnetic field causes the particles’ paths to curve into a circular shape due to the Lorentz force acting perpendicular to their direction of motion. Furthermore, each time particles pass through the gap between the semicircular plates, the direction of the electric field frequency changes. This alteration ensures the electric field is oriented appropriately to accelerate the particles’ velocity. Consequently, the particles are guided to follow circular orbits of progressively larger radii under the influence of the electric force.
Particles accelerated in this manner can be utilized in experiments upon leaving the cyclotron, such as colliding them with various materials or inducing nuclear reactions to observe the creation of new particles. However, particles generated in a cyclotron serve not only for simple experimentation but also play a crucial role in the medical field. In other words, the ion beam ejected from a cyclotron can be utilized for cancer treatment, aligning with the core principle of a medical technology commonly known as radiation therapy. The method of irradiating a patient’s tumor site with protons accelerated to approximately 60 percent of the speed of light in a cyclotron to destroy cancer cell DNA offers the advantage of minimizing the impact on healthy tissue during its passage through the body, compared to conventional radiation therapy. Furthermore, the treatment process is relatively swift and causes less discomfort to the patient, which is another significant characteristic. Thus, the application of nuclear physics demonstrates that it is not confined to the limited field of electricity generation but can extend into diverse areas.
Nuclear Physics in Medical Technology
Radioactive isotopes, commonly handled in nuclear physics experiments, are also actively utilized in medical technology. Innovative medical devices have been developed that utilize radioactive isotopes to obtain more detailed information about the human body’s internal workings. Beyond conventional X-ray imaging, computed tomography (CT), and magnetic resonance imaging (MRI), a technology called positron emission tomography (PET) has emerged that can visualize the brain’s functional activity itself. PET is a device that uses substances labeled with radioactive isotopes to obtain images of various regions of the brain. The principle behind collecting PET images utilizes the physiological phenomenon that glucose metabolism increases in activated brain regions, leading to a corresponding increase in blood flow. In this process, water molecules containing an isotope with an extremely short half-life of approximately two minutes are used to measure changes in blood flow. The examination compares the brain’s response in a state without specific stimulation to its activation state when stimulation is applied, conducted using a tomographic imaging method. Such examples clearly demonstrate how nuclear physics can positively influence the advancement of other academic fields.
The Applicability of Nuclear Physics
Both the technology for generating electricity using nuclear fission reactions and the medical application of particle accelerators called cyclotrons are results of applying scientific principles discovered during the exploration of atomic nuclei. In this sense, nuclear physics is not merely a discipline focused on elucidating the properties of particles; it is a field that drives the advancement of other academic disciplines based on the knowledge accumulated during its research. In conclusion, nuclear physics can be summarized as a versatile discipline that not only explores atomic nuclei but also contributes to the progress of science and technology as a whole by applying the principles revealed in the process to various fields.
