Application fields of scintillators
Basic principles of radiation detection
Radiation, such as X-ray (Roentgen), has high penetrating power and this property is useful in various fields. Scintillators convert it into visible light which then can be easily transformed to electrical signal by photomultiplier or avalanche photodiode. Finally, information including an imaging, a spectrum, and timing is processed by computer.
Rapid increase in the number of patient suffering from cancer is an acute problem for all industrially developed countries including Japan. However, cancer can be treated and successfully cured if found at the early stage. Positron Emission Tomography (PET) is a very effective tool in cancer diagnosis. Because cancer cells grow fast, it consumes much more glucose than healthy ones. If a chemical analog of glucose-fluorodeoxyglucose marked with the positron emitter 18F is prescribed to a patient with cancer, cancer cells emit higher level of radiation which can be detected with PET providing an image of a cancer tumor. Besides clinical oncology, PET is used in cardiology, neurology and psychiatry. We develop not only crystal scintillators for such applications, but also imaging devices in cooperation with other groups.
Scintillators are frequently used in astrophysics. Stars are born in dense and thick molecular gases observed in the optical wavelength. The upper left figure shows an image of massive star forming region NGC2264 where stars are blocked behind the expanding gas. However, newly-born stars emit intense X-ray radiation passing through the gas and with help of scintillators they can be clearly distinguished, see the upper right figure.
Hunting for mineral resources
Scintillators are employed to discover oil or mineral resources. It was found that layers with excessive content of radioactive isotopes exists near the oil strata. The radiation informs us the position of the oil pool, and we can drill precisely without any wasting. Scintillators used in such environment should possess sufficient mechanical strength in addition to high light yield and fast decay.
Scintillators are used in homeland security applications such as the airport luggage screening machines shown in the figure. Its principle of operation is similar to the medical X-ray equipment.
Particle and high energy physics
Nuclear fusion is the process by which multiple atomic particles join together to form a heavier nucleus. It is the most important process in nature because it powers all the stars like our Sun, where two hydrogen atoms collide to become one atom of helium and release enormous energy required to support life on the Earth. Scientists are trying to reproduce such a process on the Earth looking for the new ecological sources of the energy. An example of such experiment is shown on the picture. Accompanied with the nuclear fusion, a large number of neutrons is generated. Scintillators are used to evaluate the amount of these neutrons helping to monitor and control the artificial nuclear fusion.
High penetrating power of radiation enables us to examine different kind of materials including delicate cultural objects or even animals without destructing them.
Land mine location
Gun powder of land mines contains a lot of nitrogen. If it is irradiated with neutrons, nuclear reaction between nitrogen and neutrons produces gamma-rays detected with scintillators and land mine location can be found out.