If an atom or a nucleus flies at a fast speed, it can be put inside something else just like a baseball thrown at a fast speed gets nailed into a sandy plain. The phenomena that occur differ according to the speed of light within matter. In the case of protons, if they fly at the speed of about 900 km per second and collide with metal they hit the surface of the metal and make the atoms of the metal come out quickly. This is called Sputtering. If the speed of the proton is faster by about five times, it penetrates a molecule and gets stuck in between atoms, which is called Implanting. In order to make a proton particle penetrate an atom and stick inside nuclei, a nuclear reaction, the speed must reach 45,000 km per second, which is about 10 times faster than when passing in between atoms. If the speed of a proton particle reaches one third the speed of light, it spallates the nucleus and generates high-speed neutrons.
Dr. Carlo Rubia, a Nobel laureate, had asserted that the problem of nuclear waste with long half-lives can be solved in this way. Hence, a lot of scientists have been waiting for the construction of a large-scale particle accelerator for realizing this plan.
What kind of equipment is an accelerator The equipment that makes particles fly at a fast speed is the particle accelerator. The principle is simple. There are electrons that go around the nucleus positioned in the center of the atom or around the surroundings of the nucleus. If two of these are separated, the cathode nucleus of the electron gets anode electricity.
If you want to heighten the speed of the electron, you should prepare many electrodes and positively electrify the first electrode.
Then the electron gets pulled. And the moment that the electron goes through the electrode, the change is made to a negative charge. The electron gets pushed out.
If the next electrode is positively charged, the electron moves at a faster speed.
If this is repeated, the particle moves at faster and faster speeds, to the extent that it approaches the speed of light. If there are electrodes in a straight line, the accelerator is called a linear accelerator.
If the electrodes are manufactured in a straight line, there are space limitations. Hence, the movement of the particle is bent by using an electromagnet. If the electrodes are placed into a round shape, the accelerator is called a circular accelerator.
However, if the electrons are accelerated without any relation to the form of the accelerator, the accelerator is an electron accelerator. If protons, the nuclei of hydrogen, are accelerated, the accelerator is a proton accelerator. If atomic nuclei which are heavier than hydrogen atoms such as helium, carbon, oxygen-calcium, gold, or uranium are accelerated, the accelerator is a heavy ion accelerator.
For most accelerators, the use is different according to the size of the energy. The 10 to 100 MeV class is used for industrial use, including materials engineering, and for medical diagnosis usage. The 100 MeV to 1 GeV class is used for nuclear science research and particle therapy. Enormous accelerators of over 10 GeV to the TeV range reach tens of kilometers in diameter.
Such accelerators are used for high-energy particle physics research to find out the principle of the formation of the universe.
Among these, the accelerator worth paying attention to for medicinal and industrial purposes is the cyclotron. The cyclotron is an accelerator comprised of electromagnets, a high-frequency electric power generator, vacuum equipment and an ion source. Compared to the amount of energy, the size is small. The quality of the accelerator beam is good.
The price is low. Hence, it is suitable for the production of radioisotopes.
A 10 MeV to 30 MeV cyclotron that produces radioisotopes with short life spans for nuclear medicine use, including the high-tech cancer diagnosis equipment PET/CT and SPECT has been developed.
Radioisotopes are classified into nuclides with excessive protons and nuclides with excessive neutrons according to the subject causing the nuclear reaction.
As accelerator nuclides irradiate protons and go through nuclear reactions caused by protons, they are called nuclides with excessive protons. In contrast, nuclear reactor nuclides are caused by the neutrons of the nuclear reactor, and therefore they are nuclides with excessive neutrons. The nuclear character of these nuclides is mutually complementary.
Hence, most of the accelerator nuclides engage in electron capture or positron emission decay, also called beta decay. As such, they are mainly used for disease diagnosis. In contrast, nuclear reactor nuclides engage in emission decay. Therefore, they are used for medical treatments.
Differently from nuclear reactor nuclides, the accelerator nuclides not only have high carrier-free non-radioactivity, or Specific activity, but also decay through electron capture or positron emission. Hence, the radioactivity hitting patients can be considerably reduced, and images good for diagnosis can be obtained. Therefore, nuclear medicine prefers accelerator nuclides for diagnostic use. In addition, positron emission nuclides are used for Positron Emission Tomography (PET). Because of this, they are used for research on the metabolism of the human body, cancer diagnosis, diagnosis of the abnormalities of the heart, and the diagnoses of many kinds of diseases caused by neurological abnormalities.
The beam energy of the cyclotron for exclusive use with PET is low at 10 MeV. Such a cyclotron can produce radioactive nuclides for positron emission. And the gamma ray emission nuclides need proton energy of over 20 MeV. As a result, a cyclotron of the 10 MeV class cannot produce SPECT nuclides. It can only produce PET nuclides.
