After reading this essay you will learn about:- 1. Measurement of Radioactivity 2. Effects of Radioactivity 3. Impact.
Essay on the Measurement of Radioactivity:
Radioactivity can be measured by a Geiger-Muller counter. The type commonly used consists of an aluminium tube which acts as the negative electrode, while a wire down the center forms the positive electrode (Fig. 22.1).
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The gas inside the tube consists of argon at low pressure with an added trace of bromine. A thin mica window at the end permits the entry of active particles. If one of these enter the tube, the gas is ionized. By the time the electrons from the ionization process reach the central electrode, they are moving so fast under the high potential gradient that they create an avalanche of extra ions by collision.
This process of gas amplification as it is called increase the sensitivity of the tube, enabling it to record the entry of beta (β-) particles and gamma (γ) photons which, on their own, produce far fewer ion-pairs per centimetre of their path than do alpha (α) particles (Table 22.2).
The current pulses from the tube are amplified and used to operate either a dekatron counter or scalar or else a rate meter. The former counts and records the pulses on a micro ammeter calibrated in counts per second.
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The Geiger-Muller counter is connected to a combined power unit and scaler and the voltage adjusted to the recommended value specified for the tube. The scalar is switched on and allowed to warm up. A random count is recorded which is the background count and comes from radioactive material in the earth and nearby surrounding together with cosmic radiations which pernetrate the earth’s atmosphere from outer space.
The background count is timed over a period of at least 2 minutes and, after this, radiations from the source is measured. Nowadays portable battery operated Geiger tubes are available.
Essay on the Effects of Radioactivity:
It is well-known that some chemical elements possess different kinds of atomic structure by modification of their nuclear composition (i.e., number of protons, neutrons, etc.). Isotopes are capable of emitting radiant energy, which is called radioactivity.
Some isotopes are, of course, non-emitting type. Uranium, Radium and Thorium are the most commonly known isotopes that are capable of emitting radioactive emissions.
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On emission of radiation from isotopic elements, there will be loss of weight of the element. The loss of weight and its conversion into energy is illustrated by Einstein’s famous equation E = mc2 (E = Energy, m = mass of the object, and c = speed of light emission). Thus mass can be converted into energy.
Environmental hazards from nuclear power plants are the release of radioactive substances which could happen at the slightest error or negligence. Radioactive isotopes are also known as radionuclides. These emitted radiations that are capable of damaging the protoplasmic system of living system. The emitted radiations may be alpha, beta and gamma rays.
These rays enter the environment thus from nuclear fallouts from nuclear power plant wastes and certain other sources. The relative contribution of different sources of radiation in our environment is given in Fig. 22.2.
Essay on the Impact of Radioactivity:
The radioactivity effect may be:
(i) Instantaneous,
(ii) Prolonged, or
(iii) Delayed types.
Even it could be carried to future generations or production of defective embryos. All kinds of impact depends on two major factors’, doses of radiation exposure and duration of exposures. The radiation effect is thus grouped at effects on different cellular component level.
The details are discussed separately under the following heads:
(a) Radiation effect on DNA,
(b) Radiation effect on chromosome,
(c) Radiation effect on cellular level,
(d) Tissue response to radiation, and
(e) Radioactive fallouts.
In addition there are a number of gross physiological effects on whole body including defects of circulatory, digestive and neurotic systems too.
(a) Radiation Effects on DNA:
There are four categories of changes:
1. Base damage—change or loss of a base.
2. Single-strand breaks (SSB) — break in the backbone of one chain of the DNA molecule.
3. Double-strand break (DSB) — break in both chains of DNA molecule.
4. Cross-links — either within the DNA molecule (instrastrand) or from one molecule to another (DNA-inserted or DNA-protein)
There may be an immediate or delayed effect depending on the doses of exposure.
(b) Radiation Effects on Chromosomes:
These effects include a number of structural changes on chromosomes.
The details are:
1. A single break in one chromosome or chromatid,
2. A single break in separate chromosomes or chromatids,
3. Two or more breaks in the same chromosome or chromatid.
4. “Stickiness” or dumping of the chromosomes.
The general consequence to the cell of these structural changes may be one of the following:
1. The broken ends may re-join with no visible damage. This is restitution.
2. Loss of part of the chromosome or chromatid at the next mitosis giving rise to an aberration.
3. Rearrangement of the broken ends, which can produce a grossly distorted chromosome viz., ring chromosomes, dicentric chromosomes and anaphase bridges.
4. Rearrangement of the broken ends without visible chromosomal damage; the genetic material has been rearranged.
(c) Radiation Effect on Cellular Level:
One of the three things can happen to a cell after irradiation:
1. It can be delayed from going through division; appropriately, the term used to define this response is division delay.
2. It can die before it divides, during interphase. This response is also appropriately named interphase death.
3. It can die when attempting mitosis; this response is termed reproductive failure.
The details of extent of damage is shown below:
(d) Tissue Response to Radiation:
The radiation effect at tissue level are:
1. Acute and chronic morphogenic effects on tissues.
2. Total body radiation syndrome viz., N-V-D syndrome (Nausea, Vomiting, Diarrhea).
3. Three general effects of radiation on the embryo and fotus: viz. lethality; congenital abnormalities present at birth and long-term effects on body after birth.
4. Late radiation effects, i.e., induction of carcinogenesis.
(e) Radioactive Fallouts:
Radioactive fallouts are the input of radioactive dust from the atmosphere on ground surface. The source of such dusts are usually nuclear bombs. Atomic bombs based on fission of uranium and plutonium release fission products that cause enormous effect on living system. Radioactive dust thus generated accumulate on living system through food chain and thereby cause serious damage to the life processes.