Saturday, April 9, 2011

Prevention and Control of Radiation Hazard

Although it is difficult to eradicate the total effects of radiation, it can be minimized by employing some prevention schemies. These are helpful to control the radiation hazards. Following are the methods for the control of radiation hazards.

1)For the control of radiation hazards form external sources of radiation, it can be done by:
  • Structural shielding design
  • Radiation protection survey
  • Nuclear Regulatory commision regulation
  • Personal monitoring
2) Hazards associated with radioactive nuclides deposited internally are controlled by minimising the absorption, inhalation and injection of radioactive material into the body.

3)Building and fuseliges of aircraft provide little protection from the cosmic rays.
4) Preventing random production
5) Applying ICRP radiation protection principle
6) Applying basic safety standard (BSS) principle
7)Minimising unjustified particles such as

  • Addition of radioactive materials to food, beverages or cosmetics
  • Use radioactive materials in toys and jewellery
8) Reducing nuclear weapons testing and radioactive waste from nuclear power station
9)Minimising the burning of coal
10)Reducing nuclear power industry in number if possible. If not keeping them at seperate place from the public area.
11)By personal monitoring and performing equipment survey in hospitals, power stations etc.

Radaition Hazards-Sources, Prevention and Control of Radiation Hazards.

Radiation is a part of environment. The background radiation is contribute by tree sources namely terrestial radiation, cosmic radiation and radiation from radioactive elements in our bodies. Since ionising radiations have the capacity to ionise the molecules, so when  ionisiong radiation enters into our body, they ionise the tissue molecules and chemical dissocialn takes place. Due to this there is distortion of DNA chain and body cells take place. The cell production rare increases and malignant tumour is formed. These type of radiations are unnecessary to the body. Hence the damages due to such unwanted radiation to the body parts is termed as radiation Hazards. Radiation Hazards mainly take place due to two types of sources.
  1. Internal sources of radiation
  2. External sources of radiation
The damaging of body cells due to radiation from external source of radiation is much less than that of internal sources or radiation.

Radiation Hazard from the Internal source of radiation

This type of radiation hazard are due to:
  • deposition of radioactive nuclide by injection to the body
  • depositions of radioactive nuclide by inhalation in the body
  • deposition of radioactive nuclide bye swallowing

Radiation Hazard from External source of radiation

It is due to the careless handling and use of radioactive source and therapy unit of 60 Co etc.

These two categories of hazards are due to the use of radioactive sources by workers or individuals. Also depending upon the roduction of radiation, the hazards are:
  • Due to natural radiation
  • Due to artifical radiation
Hazard due to natural radiation
  1. Cosmic radiation to earth's atmosphere gives some radiation effect. The global yearly dose (average) due to cosmic radiation is 0.39 MSV.
  2. Earth crust is made of up of radioactive materials such as uranuim. Rock soils contain uranium ie. radioactive material so they irradiate the whole body more or less uniformly. The global dose per year is 0.46 MSV.
  3. Radon is naturally radioactive gas coming from Uranium that is widespread in earth crust. It is emitted from rocks or soils. When radon is inhaled it can lodge in lung and irradiate tissue. The global dose is 1.3 MSV.
  4. Food and water contain radioactive material when food and water are taken, these radioactive materials are taken, they enter int he body and irradiate tissue. The global dose is 0.23 MSV.
Hazard due to artifical source of radiation

The radiation hazard take place due to artificial source of radiation such as:

Medical
Radiation is used in medicine to diagnosis disease and to kill cancer cells. During treatment or diagnosis indivisuals are exposed to radiation that may cause hazards.

Institutions
Many medical institutions discharge radioactive materials into environment that causes radiation hazard.

Environmental radiation
Due to testing of atom bombs and other nuclear activities, radioactive materials set free in atmosphere. These cause irradiation in human due to radioactive material deposition on the ground or from inhalation of air borne radioactivity and from injectio of radioactive material in food and water.

Nuclear power industry
The release radioactive material at each stage int he nuclear fuel cycle.

Non-Nuclear industries
They produce radioactive discharge in the processing of ores containing radiation. The discharged products processing of ores containing radiation. The discharged products transfer throough the food chain from the population.

Accidental release of radioactive material
In normal operation the radioactivity can be widely dispersed accidentally which causes radiation hazard.

Radiation in consumer products
In consumer goods such as smoke detectors, luminious watches, dolls etc may emit radiaton to cause hazard.

Friday, April 8, 2011

Maximum Permissible Dose

The persons who are exposed to radiation should not have the dose greater than upper limit and this limit is called maximum permissible dose (MPD) or smiply the dose limit. The MPD is different for occupationally exposed persons and general public. MPD include contributions from radiation source both inside and outside th ebody but excludes contributions from medical exposure and background radiations. The total dose in rems accumulated by an occupationally exposed person should not exceed 5(N-18) where N is the age of the person in years.

An area where a yearly whole body dose of 1.5 rem or more should be considered as a controlled area. Persons working in a controlled area should carry personal monitors such as TLD, pocket ionisation chamber etc. For the measurement of radiation dose personal monitors are not feasible for members of the public exposed occasionally to radiation. The protective measures for these persons is evaluated indirectly by sampling the air, water, soil and other elements of environment.

Dose Limit and ALARA

Dose limit gives support for the protection principle. Dose limit represents the judgement at the level of the individual harming or not harming which is on the border line of acceptability and unaacceptability. Continued exposure at a level just above a dose limit would result in risks which could be resonably ve described as unacceptable. Thus dose limits are those limits above which any person may cause radiaton hazard. Dose limits for the different people are different according to their employment or their occupation.It is categorized into three,they are:
  1. Employees aged 18 years or above(Employees)
  2. Trainees aged under 18 years(Trainees)
  3. Any other person (Public)
The scientific basis for setting dose limit is  the comparative risk. There are signigicant differences between the risk of radiation and  other occupation al hazards. The persons whose occupation requires exposure to the radiation are called occupational exposure such as radiation oncologist, radiologists,nursing staffs etc working in a radiology or radiotherapy department are occupational exposure. On one hand, the staff has to receive the radiation dose and on other hand, the body has some tolerance limit for occupation of the injured cells. Hence many national and international organizations have recommended the maximum permissible limit radiation.

But ALARA principle should be followed in each department which means the risks we keep as low as reasonably achieavable taking into account the social and economic functions.

Harmful Effects of Ionising Radiation

An individual working with a source of radiation should be familiar with radiation hazards. When ionizing radiation enters the body tissue, it produces ionisation and cause teh chemical dissociation of the tissue molecules. When chemical dissociation takes place in vital components of the body cell, it may be destroyed by the destruction of DNA chain due to unwanted radiation. The cell production rate may be increased and malignant tumor may be formed. Exposure to ionising radiation can produce several effects in an individual depending on:

The type and amount of radiation producing the exposure.
The amount of body that is exposed.
The general helath of the exposed individual.
The quality of medical care available in the event of a relatively high exposure.

The effects of radiation can be divided into following two types:
  1.  Stochastic(long term or delayed ) radiation effect
  2.  Non Stochastic ( Short term or immediate or acute) radiation effect

STOCHASTIC EFFECT:

These are effects which show a random process ie. they can occur at any dose level. The probabililty of the effect occuring is dose dependent. The higher the dose the greater the probability. Stochastic effects are cancer and genetic effects. Of these most important is cancer.

Delayed effects in addition to cancer induction include teratogenesis ( the induction of birth effects by irradiation of foetus). and mutagenesis(the induction of genetic disorders in future generation by irradiation of germ cells). Data on stochastic effects are limited. The most important set of data from the surviors of the atom bo b explosion in Japan at Hirosima and Nagasaki. Cancer birth defects and genetic mutaions all occur naturally at relatively high rates in human population ad identifying an increase in these rates caused by exposure. Too small amoounts of ionising radiation is subject to considerably uncertain.

NON-STOCHASTIC EFFECTS:

The short term effecrts of radiation are associated with the levels of radiation far above those received by persons working in modern radiation facility. Hair loss, skin burns, sterility etc are the examples of deterministic effects. These effects are a result of loss of functional cells, in tisures or organs ie. cell killing. The body may loose its ability to combat infection. Following an absorbed dose of seeral gray diarrhoea, electrolyte imbalance, dehydration adn other gastointestinal effecrts may appear within a few days as a seequence of cell damage.
 Moreover there are some of the serious health harzard caused by heavy exposure to ionising radiations. These are discussed below:

Genetic mutation
When the gene in the DNA chain of a cell is distorted or changed, the same effect is reproduced in the subsequent divisions of the cell. If the affected gene belongs to a cell taking part in reproduction, the progeny(offspring) may show some mental or physical disabilities. The harmful genetic mutatioin get transmitted to the future generation.

Cancer
When there is uncontrolled multiplication of cells whose genes are damaged, a tumor may be formed in any part of the body.

Leucopenia
It is caused when the number of white blood cells in the blood becomes low. This reduces the resistance of the body prone to infections.

Bone Nerosis
It results when the bone marrow is damaged bye the radiations. The bone marrow is responsible for productng red blood cells int he body.

Sterility
It results when there is severe radiaton which damage the gonads.

Epilation
With this,the hair start to fall off which is caused by heavy exposure to radiation, vomiting, fever,  diarrhoea, headache, radiation sickness may result on early effect.