LED Materials Dept.

Radiation

Radiation can be roughly divided into the following two categories.

  1. 1.Electro-magnetic radiation
    It is an electromagnetic wave with a very short wavelength. Due to the extremely short wavelength, it has high permeability, which is useful for inspection etc. On the other hand, there is a danger of public exposure, due to this high permeability. Electro-magnetic radiation includes X-rays and gamma rays (γ- rays).
  2. 2.Particle radiation
    It is movement of particles with mass that includes various elementary particles constituting an atom, and the atomic nucleus themselves. Particle radiation includes;
    1. 1)Particle beam with charge  -alpha rays (α-rays), beta rays (β-rays), electron rays, proton rays, heavy particle rays etc,
    2. 2)Particle beam without charge -neutron rays

  3. Some radiations will be explained below;

    1. X-rays
      X-rays are electromagnetic waves with their wavelength of 1 pm - 10 nm, generated from atoms (due to the orbital electron transition). It is used for X-rays photography, analysis of crystal structure using diffraction phenomena and so on. Together with gamma rays, it can be screened with lead.
    2. Gamma rays (γ-rays)
      Gamma rays are electromagnetic waves with wavelength longer than 10 pm and with high transparency. They are originated from the transition of the energy level in the nucleus (when the unstable nucleus shifts to a more stable state). “Gamma ray” was discovered by Paul Ulrich Villard of France, and then named by Ernesto Rutherford of England.
    3. Alpha rays (α-rays)
      Alpha rays are particles (helium nuclei consisting of two protons and two neutrons) released from nuclei. They are also called “Alpha particles”. Alpha rays can be screened with a piece of paper.
    4. Beta rays (β- rays)
      Beta rays are electrons emitted from nuclei, and are also called “Beta particles”. Beta rays can be screened with a metal plate such as an aluminum plate.
    5. Neutron rays
      Neutron is one of the particles making up nucleus, and neutron rays are the flow of neutrons. Neutron rays can be screened by substances containing a lot of hydrogen like water or concrete.
    6. Electron rays
      Electron rays are the flow of electrons with negative charges. When a voltage is applied to the opposing electrode in vacuum condition, the vicinity of the cathode emits light, the cause of which is the electrons emitted from the electrode. It was first observed by German physicist Wilhelm Hittorf and they were called cathode rays. They are also called electron beam and have been for CRT display.
    7. Proton rays
      Proton rays are the bundle flows of accelerated protons, which are the nucleus of hydrogen having positive charges. They can be accelerated with an accelerator, and when they enter a substance, they have a characteristic that they are concentrated at a specific depth depending on their energy. By making use of this, they are utilized for radiotherapy.

    Medical imaging diagnosis

    This is the diagnosis method to measure the conditions of disease in the body (such as position, shape, size, distribution etc.) utilizing images taken by special cameras and special inspection devices from the outside of the body. More accurate disease information can be obtained by this, and then can be used to evaluate diagnosis and treatment effect. It is also called “Modality”, and many kinds of medical imaging diagnosis methods are used recently. Some methods are shown below.

    1. Simple X-rays examination
    2. CT scan
    3. Ultrasonic echography
    4. MRI (Magnetic Resonance Imaging )
    5. Nuclear medicine scan (This is also called Isotope examination or RI examination. PET examination is a representative nuclear medicine scan.)

    Radiation Medical Care

    Radiation use in the medical field is divided into “Radiographic examination” and “Radiation treatment”. Scintillators are used in radiographic examinations. (Explained already)

    Radiation therapy is to irradiate the lesion with radiations in order to damage and then to treat the lesion. This is mainly used for cancer treatment. As irradiation methods of radiations;

    1. External irradiation
      • Radiation is irradiated from the outside of the body
      • High energy radiation therapy with linac (linear accelerator), three dimensional conformal radiation therapy (3D-CRT), intensity modulated radiation therapy (IMRT), stereotactic radiotherapy (SRT) etc.
    2. Internal irradiation
      • The radiation source is sealed and introduced into the body, transported to the affected area and its vicinity and then irradiation treatment is done.
      • Sealed brachytherapy etc.

    The type of radiation used varies from X-rays to heavy particle rays. Using special equipment, proton rays treatment and heave particle rays treatment are more advanced methods, and can be performed focusing on the identified lesion. So regarding these methods it is said that there is less bad influence which happens in X-rays treatment, in which normal tissues around irradiation paths are exposed and affected more.

    Reference;National Cancer Research Center/ Cancer Information Service[別窓表示]

    Non-destructive inspection

    Structures such as bridges, manufacturing equipment in production plants such as chemical industry and steel industry, or mechanical parts of public transportation machines like airplanes and trains, are subject to deterioration and abrasion depending on usage time and its harsh operating environment. Sudden failures such as breaking may occur, and this may lead to a great deal of damage.

    Troubles like existence of defeat or progress of wear should be inspected periodically, to determine the condition whether it is normal or abnormal, and continuation or stopping of the operation. Since the inspection must be accomplished without breaking the object, various inspection methods in which objects are not broken (non-destructive of inspection) are developed and used alone or in combination.

    As the representative non-destructive inspection,

    1. Visual testing (VT)
    2. Radiographic Testing (RT)
    3. Ultrasonic Testing (UT)
    4. Eddy Current Testing (ET)
    5. Magnetic particle Testing (MT)
    6. Strain Measurement (SM)
    7. Acoustic Emission (AE)
    8. Penetration Testing (PT)
    9. Infrared Ray thermography Testing (IRT)
    10. Hammering test, and Auscultation

    etc.

    RT (Radiographic Testing) uses X-rays and can grasp internal defects as images, so it is possible to conduct highly reliable inspection, in spite of lacking convenience on site. Moreover, industrial X-rays CT apparatus (non-destructive inspection for mechanical parts decomposed periodically and those immediately after manufacture) and continuous X-rays inspection apparatus (foreign matter inspection system for such as food on the belt) are already indispensable inspection methods. In these devices, scintillators play an important role.