Radiation from chapter environment from Park textbook of spm
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Here is the complete chapter on Radiation from the Environment section of Park's Textbook of Preventive and Social Medicine (SPM):
RADIATION
(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
(a) Cosmic Rays
- Originate in outer space; weakened as they pass through the atmosphere
- At ordinary living altitudes: ~35 mrad/year
- A commercial jet pilot receives ~300 mrad/year from cosmic radiation
- Above 20 km, cosmic radiation becomes important
(b) Environmental
- Terrestrial radiation: Radioactive elements (thorium, uranium, radium, K⁴⁰) present in soil, rocks, buildings - ~50 mrad/year
- In Kerala (India), rock formations with uranium can deliver up to 2,000 mrad/year
- Atmospheric radiation: Radioactive gases radon and thoron - ~2 mrad/year (small)
(c) Internal Radiation
- Radioactive matter stored in body tissues: uranium, thorium, K⁴⁰, Sr⁹⁰, C¹⁴
- Inflicts ~25 mrad/year (may be as high as 70-80 mrad/year)
- Total natural radiation: ~0.1 rad/year for the average person
B. Man-Made Sources
| Natural | Man-Made |
|---|---|
| Cosmic rays | Medical and dental: X-rays, Radioisotopes |
| Terrestrial | Occupational exposure |
| Atmospheric | Nuclear: radioactive fall-out |
| Internal (K⁴⁰, C¹⁴) | Miscellaneous: TV sets, radio-active dial watches, luminous markers |
(a) X-rays - Greatest man-made source for the general population
- Skin dose from a single X-ray film: 0.02 to 3.0 rad
(b) Radioactive Fallout
- Nuclear explosions release important isotopes: C¹⁴, I¹³¹, Cs¹³⁷, Sr⁹⁰
- Cs¹³⁷ and Sr⁹⁰ are most important (released in large amounts, remain radioactive for years)
- Half-life of Sr⁹⁰: ~28 years; Cs¹³⁷: ~30 years
(c) Miscellaneous - TV sets, luminous wrist watches (currently too small to be important)
2. Types of Radiation
Ionizing radiation - has the ability to penetrate tissues and deposit energy within them. Divided into:
- Electromagnetic radiations - X-rays and gamma rays
- Corpuscular radiations - alpha particles, beta particles (electrons), protons
Non-ionizing radiation - electromagnetic radiation of wavelengths longer than ionizing radiation (less energy)
Penetrating Ability of Common Environmental Radiations
| 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 |
| Cosmic rays | - | Some components very high | - |
Key points:
- Alpha particles are 10 times as harmful as X-rays, beta particles, or gamma rays
- Alpha particles have little penetrating force, but dangerous if inhaled or ingested
- Gamma rays and X-rays have short wavelengths - deep penetrating radiations
- X-rays are man-made; gamma rays are emitted spontaneously by radioactive elements during disintegration
- No material difference between gamma rays and X-rays otherwise
3. Radiation Units
Activity:
- Becquerel (Bq) = 1 disintegration per second (SI unit)
- Old unit: Curie (Ci); 1 Bq ≈ 27 picocuries
Potency is measured in three ways:
| Old Unit | SI Unit | Measures |
|---|---|---|
| Roentgen | Coulomb/kg (C/kg) | Exposure (ions in 1 ml air); 1 R = 2.58 × 10⁻⁴ C/kg |
| Rad | Gray (Gy) | Absorbed dose (energy/gram tissue); 1 rad = 0.01 Gy |
| Rem | Sievert (Sv) | Dose equivalent (potential danger); 1 Sv = 100 rem |
Dose Equivalent (H):
H = D × Q
- H = dose equivalent (Sieverts)
- D = absorbed dose (Grays)
- Q = quality factor (depends on ionization density in tissue)
- Q for X-rays, gamma rays, electrons = 1
- Q for alpha particles = 20
4. Biological Effects of Radiation
Two categories:
- High dose / Short-term - acute effects (cell killing, organ damage)
- Low dose over extended period - chronic/long-term effects
Effects are Somatic or Genetic:
Dose-Response Relationship (High Dose):
| Dose | Effect |
|---|---|
| < 5 rad | No immediate observable effects |
| 5-50 rad | Slight blood changes detectable on medical evaluation |
| 50-150 rad | Blood changes noted; nausea, fatigue, vomiting likely |
| 150-1,100 rad | Severe blood changes; symptoms appear immediately. At 300-500 rad, up to half the people die within 60 days without intensive care. Death due to destruction of blood-forming organs (bone marrow). |
| 1,100-2,000 rad | 100% probability of death within 1-2 weeks. GI system destroyed; once this fails, nothing can be done. |
| >2,000 rad | Death certain. Above 5,000 rad, CNS (brain and muscles) can no longer control body functions. |
Somatic effects:
- Immediate: Radiation sickness, Acute radiation syndrome
- Delayed: Leukaemia, Carcinogenesis, Foetal developmental abnormalities, Shortening of life
Genetic effects (manifest in offspring):
- Chromosome mutations (associated with sterility)
- Point mutations (affect genes)
5. Radiation Protection
- Natural background radiation: ~0.1 rad/year - no current hazard
- Permissible additional dose from man-made sources: should not exceed 5 rad/year
- X-rays constitute the greatest man-made hazard
- In routine fluoroscopy, 4 rad is delivered to a body part in ~1 minute
Protective Measures:
- Avoid unnecessary X-ray examinations, especially in children and pregnant women
- Adequate control and surveillance of X-ray installations
- Lead shields and lead rubber aprons (0.5 mm lead reduces scattered X-rays by over 90%)
- Workers must wear a film badge or dosimeter (shows accumulated radiation exposure)
- Periodic medical examinations, regular working hours, recreation, and holidays for workers
International Recommendations:
- ICRP, IAEA, WHO are active in setting standards
- ICRP recommendation: genetic dose to whole population from all additional sources should not exceed 5 rems over 30 years
- WHO has published permissible radiation levels in drinking water
- This field is called Radiation Hygiene - the youngest branch of hygiene
6. Radiation Hazards (Occupational - from Chapter on Occupational Health)
Industries at risk: radium painting, luminous dial manufacture, radioactive ore mining (monazite sand), medical/industrial X-ray, arc welding (UV rays), glass blowing and foundry work (infrared rays)
Effects of Occupational Radiation Exposure:
- Acute: Burns, dermatitis, blood dyscrasias
- Chronic: Malignancies, genetic effects
- Lung cancer in uranium mine workers (radioactive dust inhalation)
Preventive Measures (Occupational):
- Avoid inhalation, swallowing, or direct skin contact
- X-ray shielding of adequate thickness and material
- Employee monitoring every 6 months with film badge or pocket electrometer
- Protective clothing to prevent contact
- Adequate ventilation of workplace
- Medical examination of workers every 2 months; if harmful effects found, transfer to non-radiation work
- Pregnant women should not work where there is continuous radiation exposure
Park's Textbook of Preventive and Social Medicine, pp. 844-847
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