• Sources of Radiation
1. Natural
2. Man made
Natural
1. Cosmic rays:
– Enter from the outer space & fade thru atmosphere
– Usual exposure low but at higher than 25 km altitude; it becomes and important source of radiation
– A Commercial jet pilot is exposed to 10 times the usual exposure i.e.. 300 mrad/yr. as compared to 35 mrad/year for an average person
2. Terrestrial radiation:
– Thorium, Uranium, K40 etc. present in the environment
– Certain areas in India e.g. Kerala; Uranium deposits are present
3. Atmospheric radiation: radioactive gases present in minute amounts in the atmosphere
– Rodon and
– Thoron
4. Internal radiation: minute quantities of uranium, Thorium etc. stored in the body
Exposure of an average person to natural radiation is appx. 0.1 rad/year
Man – made sources of radiation
A. X – rays: Major source presently
– Medical and
– Dental x-rays
Two types of people affected
1. Patients
2. Radiologist and technicians
Single x-ray: 0.02 to 3.0 rads
B. Radioactive fall out
– Nuclear explosions release:
• Tremendous energy
• C14, I131, Cs137, Sr90
These have very long half lives
Half-lives of Sr and Cs is 30 yr. and 28 yr respectively
• The radioactive particles released in air, float down to earth some years later
• These get distributed fairly evenly throughout the human race
– Nuclear accidents: accidental leaks in atomic energy plants or nuclear test sites
Biological Effects of Radiation
Exposure can be of two types:
1. High doses in a short time: exposure to a high dose of radiation during a short period of time is considered as an acute exposure
A. High acute dose is likely to destroy cells, causing organ injury
B. The Whole body response to this is called "Acute Radiation Syndrome“ or “Radiation Sickness”
2. Low doses over prolonged duration
Biological Effects of Radiation
1. Somatic
– Immediate
• Radiation sickness
• Acute radiation syndrome
– Delayed
• Leukaemia
• Carcinogenesis
• Fetal developmental abnormality
• Shortening of life
2. Genetic
– Mutations
• Chromosomal mutations – associated with sterility
• Point mutations – affect the genes
The biological response depends upon the dosage absorbed:
<5 rad: No immediately apparent symptoms/signs
5-50 rad: Slight changes in blood counts
50 -150 rad: nausea, fatigue, vomiting etc. & some changes in blood counts
150 -1,100 rad: symptoms arise immediately & severe blood changes seen
– Several of the exposed might die approximately 2 weeks later
300-500 rad: up to ½ of the exposed will die within 2 months if no intensive medical care is given
– Cause of death is infections due to lack of white blood cells, as a result of damage to blood forming organs
• Near the lower end of the dose range: if infection can be prevented and controlled by isolation, antibiotics and transfusions; may allow time for the bone marrow, to generate new blood cells and full recovery is possible.
• At the higher end of the dose range, a bone marrow transplant may be the only option for producing new blood cells.
1,100-2,000 rad: There is almost 100% likelihood of death within 1 – 2 weeks.
• The first symptoms appear immediately.
• Within a few days, condition deteriorates fast as the gastrointestinal system is destroyed.
– Once the GI system stops operating, not much can be done, and only comforting care can be given
>2,000 rad: very low chance of survival.
> 5,000 rad: the CNS loses control over muscles and body functions, including breathing and blood circulation.
• Condition deteriorates very fast and
– Nothing much is possible except palliative care for comfort
Radiation Protection
Radiation from:
• Outer space and
• Background radiation
Do not pose a hazard. Estimated to be only 0.1 rad a year.
Among man-made sources, X- rays greatest hazard
• Routine fluoroscopy: the body part is exposed to a dose of 4 rad/min
• If possible, X-rays should be avoided, especially in children & pregnant women
The power of dispersed X-rays can be reduced by > 90% by use of:
– Lead shields and
– Lead rubber aprons
– should be worn by all workers regularly associated with X-ray procedures
Film badge: dosimeter which shows accumulated exposure to radiation since last time the instrument was charged
In addition, the following must be ensured to workers to maintain their state of health:
• Periodic medical examinations
• Fixed working hours
• Recreation and
• Day off
International agencies responsible for control
• IAEA (International Atomic Energy Agency)
– Promote peaceful uses of atomic energy and
– Ensure that these uses do not jeopardize peace or health.
– Sponsored symposia on radioactive waste disposal & related topics
• ICRP (International Commission on Radiological Protection)
– Recommendations on radiation dose levels for occupational workers & general population; adopted by many countries
– It recommends: genetic dose from all sources apart from natural background radiation, should not exceed 5 rems over a period of 30 years
• World Health Organization (WHO): published permissible radiation levels in drinking water.
Reference
• Park’s Textbook of PSM. 25th ed. 2019 Bhanot Publishers, Jabalpur
• Acute Radiation Syndrome: A Fact Sheet for Clinicians. CDC website. Available at: https://www.cdc.gov/nceh/radiation/emergencies/arsphysicianfactsheet.htm, accessed on 22nd March 2021; 12:12 PM
• United States Nuclear Regulatory Commission, Biological effects of Radiation, Reactor Concept Manual
Noise & Health: http://www.ihatepsm.com/blog/noise-and-health
Radiation & Health: http://www.ihatepsm.com/blog/radiation-health