RADIATION
Electromagnetic Spectrum
Types of Radiation
Ionizing Radiation
gamma rays, X-rays
Non-ionizing radiation
UV rays, Visible light,
infrared, microwaves,
laser, radiofrequencies
Types of Ionizing Radiation
1. Alpha particles
= He
= 2 protons + 2 neutrons
• Massive particles with the most energy
• Least penetrating
• Dangerous if ingested or inhaled
• Shield?
– Paper, clothing or human skin
2. Beta particles
= electron
• More penetrating than alpha radiation
• Can penetrate only ½ inch into the skin
• Dangerous when ingested or inhaled
• Shield?
– Layer of clothing, few mm of alumnium or other
substances
Types of Ionizing Radiation
3. Gamma rays
• Most penetrating type of ionizing radiation
• Shield?
- dense material such as lead
4. X-rays
• Similar to gamma rays but slightly less penetrating.
Ionizing Radiation: Half-life
Half-life is the time it takes for half of
the amount of radioactive material to
decay and be transformed into
something else.
Ionizing Radiation: Sources
IONIZING RADIATION:
Sources of Exposure
1. Natural sources:
• cosmic radiation
• radioactive minerals in earth’s crust
• radionuclides in the body
2. Enhanced natural sources:
Natural sources of radiation that have become sources of high
exposure levels as a result of human activities.
E.g. Radon
3. Human-Generated sources:
• Medical applications
• Nuclear weapons fallout
• Nuclear power plant emissions
• Consumer products
IONIZING RADIATION:
Health Impacts
Tissues with a high turnover rate are more susceptible
High-sensitivity tissues: thyroid, lung, breast, stomach, colon
and bone marrow
Leukemia is the most common cancer associated with
radiation exposure
Mutations, cancer, birth defects
High-level radiation exposures can cause cell death
Low-level radiation exposure over time can cause mutations
and cancers
Fetuses and children are very sensitive to radiation-induced
damaging effects.
IONIZING RADIATION:
Dosage
Radiation Effective Dose = Absorbed dose x Relative Biological Effectiveness
Sievert (Sv) Gray (Gy)
Or, rad rem
1 Sv = 100 rems
1Gy = 100 rads
Relative Biological Effectiveness (RBE):
• 1 for X-rays and gamma rays
• 1-5 for beta-particles
• 10 for alpha particles. Greatest tissue damaging potential.
IONIZING RADIATION:
Dosage and Health Effects
Dose rate largely affects the potential for health effects from
exposure to radiation.
There is no radiation exposure level below which no health
effect can be detected, therefore levels should always be kept
As Low as Reasonably Achievable (ALARA).
IONIZING RADIATION:
Radiation and Nuclear Power Generation
1. Front-End
2. Power Production
Core meltdown
E.g. Chernobyl incident
3. Back-end
Reprocessing
Low-level radioactive wastes and High-level radioactive
wastes:
Sources
Hazards
Disposal methods
NON-IONIZING RADIATION:
Ultraviolet radiation (40-400 nm)
UVa: longer wavelengths (400-320 nm)
UVb: shorter wavelengths (320-280 nm)
Health effects
– Skin cancer
• Uvb is in the ionizing range and can damage DNA.
• An increase of 1-2% of UVb radiation is associated with an
increase of 2-4% in skin cancer.
• North America - skin cancer has reportedly increased by
400%.
– Skin/eye burns
– Cataract, premature cell aging, reduced immunity,
photosensitivity, blood vessel damage
Are sunscreens protective?
Ultraviolet radiation
NON-IONIZING RADIATION:
Microwaves
Depending on frequency, microwaves are
differentially absorbed by bodily tissues,
mostly as a function of their water content.
• Very low energy (below 150 MHZ) simply pass through the
body without being absorbed.
• Intermediate frequency (150-1200 MHZ)are absorbed by the
deeper tissues without any noticeable heating of the skin.
• As frequency increases, tissue penetration decreases and at
3500 MHZ, warming of the skin can be felt.
NON-IONIZING RADIATION:
Electromagnetic fields
Does cell phone usage pose a health risk?