Radiation was never one of those good subjects in my life. It usually meant someone was going for treatments at the hospital, tragic accidents at the plant, or even just politics that turned my family sour at the dinner table. So I’ve taken time to research and understand this invisible terror that haunts us so.
Atomic Radiation: Atoms of certain elements emit spontaneously very minute(small) particles and electromagnetic radiation. These tiny particles may carry electric charge, as in the case of alpha or beta rays; they may be neutral as in the case of neutrons. The electromagnetic radiations emitted are X-rays (from atom) and gamma rays (from nucleus) and they do not carry any electric charges. Radioactivity is the result of spontaneous disintegration of an atom during which it emits alpha, beta or gamma particles. Simultaneously, the atom changes into another element which is itself radioactive, and this in turn disintegrates to become something else and the process continues. The sequence of changes is known as the transformation series. The disintegration decay activity of a radioactive element is entirely random. A radioactive element has a definite rate of decay known as the half-life period. Half- life is defined as the time taken for half the atoms in any given sample of the substance to decay.
Alpha rays are helium nuclei, that is, helium atoms which have lost their two orbital electrons, and hence they have a net positive charge. They are all ejected with approximately the same velocity ranging from 1.4 x 109 to 1.7 x 109 cms per second. They have a range of several centimeters in air, but most are stopped by a very thin sheet of aluminum foil, about 0.1 mm thick.
Beta rays are streams of high energy electrons similar to cathode rays. They are emitted with variable velocities, approaching that of light (3 x 108 m/s). They are far more penetrating than the alpha rays and are stopped by a 1 cm thick aluminum sheet.(Hill, J. W. (2012). Chemistry for changing times (14th ed.). Erscheinungsort nicht ermittelbar: Pearson Education.pg.70-71 3.3).Gamma rays consist of electromagnetic radiations of very short wavelength and occupy a band among the X-rays which have the shortest known wavelengths. They have the same velocity as that of light. The highest energy gamma rays are very penetrating and approach absorption (or attenuation) only after traversing few centimeters of lead. Alpha radiation consists of heavy, doubly positive charged particles emitted by atoms of elements such as uranium and radium. Beta radiation consists of electrons. These electrons are much lighter than alpha particles and carry unit negative charge. Gamma rays are a form of electromagnetic radiation similar to X-rays, light and radio waves. Neutrons are uncharged heavy particles contained in the nucleus of every atom heavier than hydrogen. Alpha radiation may just penetrate the surface of the skin: It can be stopped completely by a sheet of paper. Beta particles however need a few millimeters of aluminum sheet for stopping them. Gamma rays are more penetrating but can be shielded by lead slabs, thick concrete or water. X-rays are less penetrating than gamma rays. Neutrons are shielded by concrete and hydrogen-containing substances like wax, water etc.
ii. Natural Background Radiation: Many are unaware of the existence of natural background radiation. The source of these are extra-terrestrial and terrestrial. The extra-terrestrial natural radiation comes from outer space and hence these are called cosmic rays. The terrestrial natural radiation originates from the radioactive substances in the earth’s crust. These radiations irradiate the human body from outside: This exposure is known as External Exposure. ‘Internal Exposure’ arises from both these sources from naturally occurring nuclides which are taken up into the body through normal physiological pathways. A man has about 5,000 Bq* radioactivity in his body mainly due to 40K. (Ionizing radiation: Sources and biological effects. (1982). New York: United Nations.pg.5 15-19)
a. External Exposure: The external exposure of man resulting from cosmic ray component varies slightly with the geomagnetic latitude and, to a great extent, it increases with the altitude above sea-level, the dose rate approximately doubling for each 1.5 km above sea level for the first several kilometers. At sea level, the exposure is 10 per cent lower at the equator compared to those at middle latitudes. The terrestrial component of the natural background is dependent upon the composition of the soils and rocks. On average, population receives an external exposure, from the terrestrial component, of 350 (± 100) μSv per year. These figures are for outdoor exposures. Indoor exposures are generally higher, depending upon the type of houses one lives in e.g. granite houses could give an order of magnitude higher exposure. In India, external dose measurements in over 200 stations from different parts of the country indicate an annual average external exposure of 690 (± 200) μSv/yr.
b. Internal Exposure: Internal exposure results from radio-nuclides entering the body through ingestion or inhalation. These radio-nuclides are either cosmogenic (i.e. produced by the collision of cosmic rays with atoms in the upper atmosphere) or primordial, in the sense that they existed in the earth’s crust throughout its history. Internal exposure from cosmogenic nuclides (such as 4H, 7Be, 14C, 22Na) is very small. The short-lived 222 Rn and its decay products contribute a major fraction of internal dose. Other nuclides like 40 K the decay products of Thorium (220 Ra) and 210 Po contribute to a lesser extent. The internal exposure due to these primordial nuclides is about 1,300 μSv per year. Total annual average exposure of man is 2,000 μSv/yr.
c. Other Exposures: In addition to natural background radiation, man is exposed to sources of radiation that he himself has created; for example, X-rays and other types of radiation used for medical purposes: fallout from testing of nuclear weapons, occupational exposure from nuclear and other industries using ionizing radiation and radioactive materials released in the course of nuclear power production. It is obvious that the contribution due to nuclear discharges is negligible (0.1%). An air travel in a jet plane gives an exposure of 8.5 μSv/hr while in a supersonic it is 16μSv/hr. One chest X-ray may give about 200μSv. The radiation exposure near a nuclear power plant is only few tens micro sievert per year which is negligibly small and lies within the statistical variations in natural background radiation levels. But natural disaster like earthquake, tsunami, or several cyclone may lead to nuclear plant damage and explosion as seen March 2011 at Fukushima, Japan.(Ionizing radiation: Sources and biological effects. (1982). New York: United Nations.pg.7 20-39)
Effects of Radiation: More is known today about effects of exposure to radiation than about any other physical and chemical agent in our environment. The health effects of radiation exposure are not unique. The main effects of radiation are cancer induction and genetic effects. In fact, out of the natural cancer incidence or fatality, only about 10 per cent can be accounted by the exposure to natural background radiation. Thus the effects that can be attributed to low level radiation exposure are also caused by large number of other environmental agents. Effects of radiation exposure to low level radiation should not be disregarded; but it should be viewed as that they are very small compared to risks of similar effects from other known and unknown agents.
At the radiation exposure standards set by nuclear industry for occupational workers as well as members of public, no discernible effects can arise in population groups. Since the disaster caused by Nagasaki and Hiroshima atom bombs in August 1945, people all over the world became aware of the harmful effect of radioactive substances which emit radiation. Ionizing Radiation and Effects on Man: Like radioactive material exposure, ionizing radiation also have deleterious effect on living being specially mankind. The degree of effect however depends on dose and duration of exposure.
“The studies carried out by the Committee in the area of biological effects of ionizing radiation have not resulted in major revisions of the current thinking about genetic risk estimates or the somatic effects analyzed.”
Ionizing radiation: Sources and biological effects. (1982). New York: United Nations.
pg.33 233
For the record, using the quotation for the conclusion was the main effort. It seemed best overall on the basis that just knowing information is one part, proving and improving or disproving these theories can assist with the quality of life that man currently holds dear.
References
(Ionizing radiation: Sources and biological effects. (1982). New York: United Nations.pg.5 15-19, pg.7 20-39, pg. 33, 233)
Ademola, A.K., & Obed, R. I. (2012) Gamma radioactivity levels and their corresponding external exposure of soil samples from Tantalite mining areas in Oke-Ogun, South-western Nigeria. Radioprotection, 47, 243-252
Hill, J. W. (2012). Chemistry for changing times (14th ed.). Erscheinungsort nicht ermittelbar: Pearson Education.
pg.70-71 3.3