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Research paper Caterbury Chist Church University May, 22, 2008

Radiation Used in Industry

History The first example of ionizing radiation is X-rays. It was accidentally discovered on November 8, 1895 by Wilhelm Conrad Röntgen. He is also the first man who received the first Nobel Prize in Physics in 1901. The hand in following picture（picture 1） shows different degrees of absorption in soft tissue and bone under X-rays.

The discovery was immediately applied in medicine. With the other kind of ionizing radiation were developed successively, more important discoveries have been made. These ionizing rays are also used in many applications. Introduction “In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. Two types of radiation are commonly differentiated in the way they interact with normal chemical matter: ionizing and non-ionizing radiation.”

As the Non-ionizing radiation is not included in our course “Introduction to radiation physics”, then the Non-ionizing radiation part will not be the major component in this paper. The ionizing radiation and its applications will be emphasized.

Neutron radiation Neutron radiation is composed by free neutrons, produced by spontaneous or induced nuclear fission, nuclear fusion or other nuclear reactions. Neutron non-ionizing radiation cannot ionize atoms, but if collision with different elements of the nuclear, a neutron excitation will occur, resulting in an unstable isotope with radioactive.

Electromagnetic radiation Electromagnetic radiation is transferred in the common space with the composition of electric energy and magnetic energy, and the energy was produced by moving charges; for example, the antenna is transmitting radio frequency signals emitted by moving electric charge and it will produce electromagnetic of energy. Electromagnetic spectrum includes all kinds of electromagnetic radiation, from extremely low frequency electromagnetic radiation to extremely high frequency electromagnetic radiation. In between the two radio waves, microwaves, infrared, visible and ultraviolet light and so on are also electromagnetic radiation.

Thermal radiation (heat) Ideal black-body radiation is radiation emitted by the radiation of a specific wavelength at a specific temperature with maximum amount of radioactive radiation. Meanwhile, the blackbody is an object absorbs all incident radiation and does not reflect any radiation, it is absolutely black body. Theoretically, black body can radiate all the wavelengths of the electromagnetic waves on the spectrum. Wien's displacement law is to describe the electromagnetic radiation flux density peak wavelength of the blackbody and the law of its temperature dependence.

Alpha particles α-particles is a radioactive particle, it is formed by two protons and two neutrons and does not bring any electron, which is equivalent to the core of He-4, or after the ionized He-4, He2 +.

Usually radioactive chemical elements with a larger atomic weight will produce α-particles emitted by α-decay, which becomes lighter elements until the element is stable. Alpha particles travel at speeds in excess of 5% of the speed of light, α-particles has a relatively large size, and with two positive charges, it is easy to ionizing other substances. Therefore, its energy is also lost fast and has the weakest penetration compare with the other ionizing radiation particles, the human skin or a piece of paper has been able to stop a α-particle.

α-particles released from the radioisotope is not dangerous at the outside of human body. However, the material (radium, uranium, etc.) which can release α-particle would be very dangerous once they are inhaled or injected, it. It can damage the cells of internal organs directly. Beta particle β particles is high-energy electrons released when β-decay  radioactive occurred, and the speed is up to 90% of the speed of light.

In the β-decay process, radioactive nuclei emit electrons and neutrinos and transfer to another core, the product of the electron is called a β particle. In the positive β-decay, the proton change to a neutron in the nucleus while release a positron. In the negative β-decay, the neutron changes to a proton in the nucleus and releasing an electron, that is β particles.

Since the electron mass is much lighter than proton and neutron, when β particles through an electric field, if it is negative electron, its path will twist to the positive direction. Through the magnetic field, if the magnetic field direction is from the inside out, the particles will twist counter-clockwise with curved path.

Gamma rays Gamma rays are electromagnetic photons with frequencies 1019 Hz and above, so it has relatively small wavelength. Gamma-ray does not have the charge and rest mass, it has a relatively weak ionizing ability compare with α particles and β particles. The gamma rays has extremely penetrating power and with high energy. Gamma rays can be stopped by high atomic number nucleus, such as lead or depleted uranium.

With its high energy and penetration, it can breaks the DNA within the cell and thus cause cell mutations, loss of hematopoietic function, cancer and other diseases. It can kill cells, and therefore can be used for medical purposes, to kill cancer cells.

X-ray X-ray is the electromagnetic wave with wavelength range from 0.01 nm to 10 nm, with wave-particle duality. Electromagnetic energy transmits in the form of photons. When the X-ray photon collision with an atom, the atom can absorb the energy and the atomic electron can jump to a higher orbit energy level, atom can be ionized by single photon if the photo has relatively high energy (greater than the ionization energy of electrons). In general, the larger atoms have a better chance to absorb the X-ray photons. Human soft tissue is formed by smaller atoms and bones include higher atoms as it containing more calcium atoms, so the bones are easy to attract x-rays. Therefore, X-ray can be used to check the human body structure.

Atomic battery Radioisotope 63 Ni (half-life of 100 years) and copper metals can be used as long-life battery materials, the principle is nickel-63  will continually  release β-rays  to copper, so copper will gain negative charges, and nickel -63 will have positive charge, when an external voltage constitute a loop, nickel-copper battery will begin to work continuously and generate electricity. By the half-life of 100 years Ni -63 radioisotopes, the battery can work for at least 50 years. As the small battery size, and with long life, so it can be widely used on in artificial organs, for the artificial heart, artificial kidneys and other devices to provide long-term power.

The following picture shows the atomic battery contains layers of silicon carbide and metal foil embedded with the radioactive isotope tritium.

Medical radiography Radiography is the use of ionizing electromagnetic radiation to view objects. The largest use of ionizing radiation in Radiography is x-rays. Technically, imaging modalities like PET and MRI are not radiographic techniques, but sometimes they have grouped in radiography because the radiology department of hospitals handles all forms of imaging. [11]

The reason why the x-ray can make the body film and form images on the screen, on the one hand is based on the characteristics of x-ray, that is, its penetration, fluorescence effects and photographic effects; the other hand, is based on human organization have different density and thickness. Because of this difference, when the x-ray through the body at different organizational structures, the x-ray is absorbed in different levels, so the amount of x-ray to reach the screen film is different. In this way, images with different black and white contrast will form on screen or x-ray film.

Therefore, x-ray image formation should have the following three basic conditions: First, x-ray should have a certain penetration, so as to penetrate the organizational structure of human; Second, the penetration of the organizational structure, there must be differences in density and thickness, so that in the process of penetrate, some of the x-rays being absorbed, and the amount of remainder x-rays is a difference; third, the difference remaining x-rays, is not visible, because the X-ray fluorescent effect and sensitive effect, after imaging process, will be able to get the X-ray imaging on the fluorescent plate or film with a black and white contrast and differences in color levels.

Organization structure of the human body is composed with different elements, depending on various organization have different sum of the elements and different densities in unit of volume size. The density of human organization structure can be summarized into three categories: there is a high density of bone organization and calcification, etc.; medium-density cartilage, muscle, nerve, organ and body fluids, etc.; low-density fatty organization and gas presented in the respiratory tract, gastrointestinal tract, sinuses.

The uniform intensity x-ray penetration of different densities structure, due to different levels of absorption, in the x-ray films showing with black white contrast, differences in levels of x-ray images on the screen.

In the body structure, chest ribs have high density, on the x-ray absorptiometry and more photos showing the white; the lungs with the low gas density, x-ray absorptiometry less, the picture shows shadow.

X-ray penetration of low-density organization, only a few x-rays will be absorbed, the remaining x-ray will be more sensitive to the x-ray film, more metal silver will be produce by the reduction photochemical reaction, then the x-ray film showed a shadow; the more fluorescent were produced on the fluorescent screen, brighter on the screen. It is exactly opposite for high-density organization.

Pathological changes can also change the density of human tissue. For example, tuberculosis lesions in the low-density lung tissue of origin can produce the medium density fibrous and high density calcification. In the chest radiograph, Shadow in the background of the lung lesions appeared on behalf of the white. Therefore, organizations in different density with pathological changes can produce the corresponding pathological x-ray images.

Human tissues and organs form the structure of different thickness is also inconsistent. The thick and thin parts, some has clear boundaries, some with the gradual migration. Thickest part has more x-ray absorption and less x-ray get through, opposite for thin part, in the x-ray film and the screen, the brightness contrast differences between black and white or from light to dark, it has clear or unclear boundaries, and they are related to the thickness of the differences.

Overall, differences in density and thickness is the foundation to generate image contrast, is a basic condition for x-ray imaging. It should be noted that the dominant of density and thickness in the role of imaging is dependent. For example, the chest and rib are thin but with high density, and cardiac vascular has low density but its thick, and thus the great vessels in heart has brighter image than the image of ribs. Similarly, the large number of effusion in pleural has medium density, but thick, so its image than the image of the white ribs (see in picture 3). It should be noted that the density of human tissue structure and x-ray image density are two different concepts. The former refers to the human tissue within the mass of unit volume, while the latter represents the image shown on the x-ray film in black and white. However, the proportion of the material itself is proportional to its density; material with high density, high proportion, more amount of x-ray absorbed, and the image was a white shadow in the photo. On the contrary, low-density material, with low proportion, less x-ray absorption, the image showed a shadow in the photo. Although has connection with the thickness of the object, but the white or the black shadows on the photo may reflect the level of different density. In terms, usually use density levels to expression the image in white and black. For example, high-density, medium density and low density express in white, grey and black shadow respectively, and present the density also. The tissue density is changed, and then the increased density or reduced density is used to express the image of the white and black shadow.