Radiophysics at its Basics
Radiation is defined as emission of energy as electromagnetic waves or as moving subatomic particles, especially high energy particles which cause ionization and Radioactivity is the term used to describe disintegration of atoms. The latter one is a part of our earth – it has existed all along. Naturally occurring radioactive materials are present in earth’s crust, the floors, and walls of our college, schools, or office and in food we eat and drink. There are radioactive gases in the air we breathe. Our own bodies contain naturally occurring radioactive materials.
Man has always been exposed to natural radiation arising from the earth as well as from outside earth (The radiation we receive from outer space is called cosmic radiation or cosmic rays). They are also received by exposure from manmade radiation, such as X-rays, radiations used to diagnose diseases and for cancer therapy.
Moving on to the science behind this; the atom can be characterized by the number of protons in the nucleus. Some natural elements are unstable. Therefore, their nuclei disintegrate or decay thus, releasing energy in the form of radiation. This physical phenomenon is called radioactivity and the radioactive atoms are called nuclei. The radioactive decay is expressed in units called becquerels. One becquerel equals one disintegration per second. The radio nuclides decay at a characteristic rate that remains constant regardless of external influences, such as temperature or pressure. The time it takes for half the radio nuclides to disintegrate or decay is called half-life. This differs for each radio element, ranging from fractions of a seconds to billions of years. For example, half-life of
Uranium 238 is
4.5 billion years.
The term radiation is broad and can be classified into many ways. Referring to mainly ionizing radiation (radiations get ionized when it passes through matter.) it can be classified into 4 types. The first one being Alpha radiations which consists of heavy positively charged particles emitted by atoms of elements such as uranium and radium. The second one, Beta radiation that consists of electrons. They are more penetrating than alpha particles and can pass 1-2 cm of water. The third one, Gamma radiation, are electromagnetic radiation similar to X-rays, depending on their energy, can pass right through the human body, but can be stopped by thick walls of concrete. The last one, Neutrons, are uncharged particles and do not produce ionization directly. But, their interaction with the atoms of matter can give rise to alpha, beta, gamma or X-rays which then produce ionization.
The main topic of this article Radio physics is defined as the branch of physics that deals with the ionizing and nonionizing radiations and its effects on interaction with matter along with their properties. Health physics, radiological health or radiological engineering are synonym terms for that area of public health and environment health engineering that deals with the safe use of ionizing and nonionizing radiation in order to prevent harmful effects of the radiation to individuals, to population groups, and to the biosphere. Health physics is a science and hence is a systematic organization of knowledge about the interaction between radiation and organic and inorganic matter. Radiation ranks among the most thoroughly investigated etiologic agents associated with disease. Contrary to the popular belief that our experience with the radiation bioeffects started with the nuclear weapons project during world war 2, our experience goes back to the very earliest days of radiation use. As early as
1906, two French physiologists published the results of their studies on the sensitivity of various tissues and organs to radiation. They found that “the sensitivity of cells to irradiation is in direct proportion to their reproductive activity and inversely proportional to their degree of differentiation”. Although much still needs to be learned about the interaction between ionizing radiation and living matter, more is known about the mechanism of radiation effects on the molecular, cellular and organ system levels than is known for most other environmental stressing agents. Observed radiation effects (or effects of other noxious agents) may be broadly classified into two categories, namely, Stochastic (Effects that occur randomly, and whose probability of occurrence rather than the severity of the effect, depends on the size of the dose. Stochastic effects such as cancer, are also seen among persons with no known exposure to the agent associated with that effect.) and Non stochastic, or deterministic effects. Most biological effects fall into the category of deterministic effects. Deterministic effects are characterized by the three quantities stated by the Swiss physician and scientist Paracelsus about
500 years ago when he wrote “the size of the dose determines the poison.” First one being that a certain minimum dose must be exceeded before the particular effect is to be observed. Second being the magnitude of the effect increases with the size of the dose. Third one being that there is a clear, unambiguous causal relationship between exposure to the noxious agent and the observed effect.
The effects of radiation at high doses and dose rates are reasonably well documented. A very large dose delivered to the whole body over a short time will result in the death of the exposed person in few days. Much has been learned by studying the health records of the survivors of the bombing of Hiroshima and Nagasaki. This tells that some of the health effects do not appear unless a certain quite large dose is absorbed. However, many effects such as cancer are detectable and occur more often in those with moderate doses. At lower doses and dose rates, there is a degree of recovery in cells and in tissues.
Every one faces challenges in life. It is impossible to eliminate them all, but possible to reduce them. Any individual exposed to carcinogenic pollutants will carry some risk of getting cancer. Strenuous attempts are made in the nuclear industry to reduce such risks to as low as reasonably achievable. The use of radiation and nuclear techniques in medicines, industry, agriculture, energy and other scientific and technological fields has brought tremendous benefits to the society. The benefits in medicine for diagnosis and treatment in terms of human lives saved are enormous. Radiation is a key tool in the treatment of certain kinds of cancer. Three out of every four patients hospitalized in the industrial countries benefit from some sort of nuclear medicine. The beneficial impacts in other fields are similar. No human activity or practice is totally devoid of associated risks. Radiation should be viewed from the perspective that the benefit from it to mankind is less harmful than from many other agents.
- Research Papers BARC.
- Introduction to Health Physics by HERMAN.