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- Policing Futures: The Police, Law Enforcement and the Twenty-First Century?
- How Does Radiation Affect Humans?.
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Ionizing radiation, health effects and protective measures
Weidner, S. Maschnik, K. John, F. Hemez, B. Ballard, H. Bach, E. Birnbaum, L. Bitteker, A. Couture, D. Dry, M. Fassbender, F. Nortier, Appl. Engle, J. For example, a typical ionization releases six to seven times the energy needed to break the chemical bond between two carbon atoms.
The same amount of raw energy, distributed more broadly in nonionizing form, would have much less effect. For example, the amount of energy in a lethal dose of ionizing radiation is roughly equal to the amount of thermal energy in a single sip of hot coffee. What is DNA? Of all the molecules in the body, the most crucial is DNA deoxyribose nucleic acid , the fundamental blueprint for all of the body's structures.
The DNA blueprint is encoded in each cell as a long sequence of small molecules, linked together into a chain, much like the letters in a telegram. DNA molecules are enormously long chains of atoms wound around proteins and packed into structures called chromosomes within the cell nucleus. When unwound, the DNA in a single human cell would be more than 2 meters long.
It normally exists as twenty-three pairs of chromosomes packed within the cell nucleus, which itself has a diameter of only 10 micrometers 0. Each cell is continually reading various parts of its own DNA as it constructs fresh molecules to perform a variety of tasks. It is worth remembering that the structure of DNA was not solved until , nine years after the beginning of the period studied by the Advisory Committee. We now have a much clearer picture of what happens within a cell than did the scientists of What effect can ionizing radiation have on DNA?
Ionizing radiation, by definition, "ionizes," that is, it pushes an electron out of its orbit around an atomic nucleus, causing the formation of electrical charges on atoms or molecules. If this electron comes from the DNA itself or from a neighboring molecule and directly strikes and disrupts the DNA molecule, the effect is called direct action.
This initial ionization takes place very quickly, in about 0.
However, today it is estimated that about two-thirds of the damage caused by x rays is due to indirect action. This occurs when the liberated electron does not directly strike the DNA, but instead strikes an ordinary water molecule. This ionizes the water molecule, eventually producing what is known as a free radical.
A free radical reacts very strongly with other molecules as it seeks to restore a stable configuration of electrons. A free radical may drift about up to 10,,, times longer than the time needed for the initial ionization this is still a very short time, about 0. This also increases the possibility that other substances could be introduced that would neutralize free radicals before they do damage.
A fast neutron will bypass orbiting electrons and occasionally crash directly into an atomic nucleus, knocking out large particles such as alpha particles, protons, or larger fragments of the nucleus. The most common collisions are with carbon or oxygen nuclei. The particles created will themselves then set about ionizing nearby electrons. A slow neutron will not have the energy to knock out large particles when it strikes a nucleus.
Instead, the neutron and the nucleus will bounce off each other, like billiard balls. In so doing, the neutron will slow down, and the nucleus will gain speed. The most common collision is with a hydrogen nucleus, a proton that can excite or ionize electrons in nearby atoms.
All of these collisions and ionizations take place very quickly, in less than a second. It takes much longer for the biological effects to become apparent. If the damage is sufficient to kill the cell, the effect may become noticeable in hours or days. Cell "death" can be of two types. First, the cell may no longer perform its function due to internal ionization; this requires a dose to the cell of about gray 10, rad. This requires a dose of 2 gray rad , which will cause reproductive death in half the cells irradiated hence such a quantity is called a "mean lethal dose.
Death may also result if cell reproduction ceases in parts of the body where cells are continuously being replaced at a high rate such as the blood cell-forming tissues and the lining of the intestinal tract. A very high dose of gray 10, rad to the entire body causes death within twenty-four to forty-eight hours; a whole-body dose of 2. These effects were once called nonstochastic; they are now called deterministic. What long-term effects can radiation have? The effect of the radiation may not be to kill the cell, but to alter its DNA code in a way that leaves the cell alive but with an error in the DNA blueprint.
The effect of this mutation will depend on the nature of the error and when it is read. Since this is a random process, such effects are now called stochastic. How can ionizing radiation cause cancer?