Radiation Hazards

Park's Textbook of Preventive and Social Medicine

1. Sources of Radiation Exposure

Radiation is part of man's environment. Sources are divided into two groups:

A. Natural Sources (~0.1 rad/year total)

Source	Dose
Cosmic rays	~35 mrad/year
Terrestrial (soil, rocks, uranium/thorium/K-40)	~50 mrad/year
Atmospheric (radon, thoron gases)	~2 mrad/year
Internal (K-40, C-14, Sr-90 stored in body tissues)	~25 mrad/year

In high-background areas (e.g., Kerala, India), doses can reach up to 2,000 mrad/year due to uranium-containing rock formations.

B. Man-Made Sources

Medical and dental X-rays - the greatest man-made source; skin dose from a single X-ray film = 0.02 to 3.0 rad
Radioactive fallout - nuclear explosions release C-14, I-131, Cs-137, and Sr-90; Sr-90 (half-life 28 yrs) and Cs-137 (half-life 30 yrs) are most important
Occupational exposure - radiologists, medical technicians, industrial workers
Miscellaneous - TV sets, luminous wrist watches (small amounts, not important currently)

2. Types of Radiation

Ionizing Radiation - penetrates tissues and deposits energy within them:

Electromagnetic radiations - X-rays and Gamma rays
Corpuscular radiations - Alpha particles, Beta particles (electrons), Protons

Type	Air	Tissue	Lead
Alpha particles	4 cm	0.05 mm	0
Beta particles	6-300 cm	0.06-4.0 mm	0.005-0.3 mm
Gamma rays	400 metres	50 cm	40 mm
X-rays	120-240 metres	15-30 cm	0.3 mm

Alpha particles are 10x more harmful than X-rays/beta/gamma rays, but have little penetrating force externally. They are dangerous if radioactive substance enters the body (by inhalation or through a wound).
Gamma rays and X-rays have short wavelengths and are deep-penetrating. X-rays are man-made; gamma rays are emitted spontaneously during radioactive disintegration.

Non-ionizing Radiation - electromagnetic radiation with wavelengths longer than ionizing radiation (lower energy): includes ultraviolet rays, infrared rays, microwaves, radio waves.

3. Radiation Units

Rad (Radiation Absorbed Dose) - unit of absorbed dose = 100 ergs of energy absorbed per gram of tissue
Rem (Roentgen Equivalent Man) - biological effectiveness; for X-rays and gamma rays, 1 rad = 1 rem
Roentgen (R) - unit of ionization in air
SI units: Gray (Gy) = 1 J/kg (1 Gy = 100 rad); Sievert (Sv) = equivalent dose (1 Sv = 100 rem)
Becquerel (Bq) - SI unit of radioactivity (1 disintegration/sec); replaces the Curie (1 Ci = 3.7 × 10^10 Bq)

4. Biological Effects of Radiation

Divided into somatic and genetic effects:

Somatic Effects:

Acute (short-term) - skin burns, radiation sickness (nausea, vomiting, hemorrhage, bone marrow depression), cataracts
Chronic (long-term) - malignancies (leukemia, thyroid cancer, lung cancer in uranium miners), aplastic anemia, reduced life expectancy
Threshold effects (erythema, cataracts) vs. Non-threshold effects (carcinogenesis, genetic damage - no safe level)

Genetic Effects:

Radiation causes mutations in germinal (reproductive) cells, transmitted to future generations
Increase in mutation rate is proportional to total accumulated dose
No recovery between doses (cumulative effect)
Mutations are mostly harmful and recessive

5. Radiation Hazards (Occupational)

Industries at risk include:

Painting of luminous dials for watches and instruments
Manufacturing radioactive paints
Mining of radioactive ores, monazite sand workers
Medical and industrial X-ray use
Arc and electric welding (UV ray exposure)
Glass blowing, foundry work (infrared ray exposure)

Effects:

Acute: burns, radiation dermatitis, blood dyscrasias
Chronic: malignancies (lung cancer in uranium miners from inhalation of radioactive dust), genetic effects

6. Radiation Protection

Background radiation (natural) = 0.1 rad/year; does not currently constitute a hazard
Maximum Permissible Dose (MPD):
- Radiation workers: 5 rem/year (whole body)
- General public: 0.5 rem/year
- Gonads/blood-forming organs: 5 rem/year for occupational exposure

Principles (ALARA - As Low As Reasonably Achievable):

Avoid inhalation, swallowing, or direct contact with radioactive material
Shielding - adequate lead/material shielding to reduce exposure below allowable levels
Monitoring - employees monitored at intervals not exceeding 6 months using film badge or pocket electrometer
Protective clothing to prevent contact with harmful material
Adequate ventilation of workplaces to prevent inhalation
Periodic medical examination every 2 months; if harmful effects found, transfer worker to non-radiation work
Pregnant women should not be allowed to work in areas with continuous radiation exposure

Source: Park's Textbook of Preventive and Social Medicine, Chapter on Environmental Health & Occupational Health (Radiation section)

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Radiation Hazards - Summary

Many industries expose workers to radiation through various sources:

Radium/Radioactive substances - used in painting luminous dials (watches, instruments) and manufacturing radioactive paints; also encountered in mining radioactive ores and handling monazite sand
X-rays - used in both medicine and industry
Ultraviolet rays - exposure occurs in arc and electric welding
Infrared rays - produced in welding, glass blowing, foundry work, and heating/drying of painted and lacquered objects (anywhere metal or glass is heated to molten state)

In short: occupational radiation hazards come from ionizing sources (radium, X-rays) and non-ionizing sources (UV and infrared rays), depending on the industry.

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