Atom – basic building block of matter
Atoms contain 3 types of particles – protons (+); neutrons
(no charge), and electrons (-). Electrons are in orbit
around the nucleus.
All matter is made up of elements – fundamental
substances that cannot be broken down by chemical
Radiation – light energy that travels and spreads out as it goes
- energy in transit in the form of particles and
Electromagnetic radiation – all the wavelengths of light energy
that make up visible light, radio and TV waves, ultraviolet
waves, microwaves, and ionizing radiation
Visible light, radio and TV waves, ultraviolet waves,
microwaves – do not carry enough energy to separate molecules
or remove electrons from atoms
Ionizing radiation – radiation with enough energy to remove
tightly bound electrons from their orbits, causing the atom to
become charged or ionized (electrically charged ions formed)
Can destroy chemical bonds in tissue and in DNA.
Sources of ionizing radiation:
sun, rocks, soil, past nuclear weapons,
radioactive medical and industrial wastes, nuclear and
coal power plants; security check devices
Exposed to higher amounts at high altitudes, in certain
jobs, certain medical treatments
Categories of origin:
1. Cosmic radiation from sun and space
More at high altitudes – atmosphere (ozone layer) helps
protect earth. Denver > LA or Boston
2. Radioactive materials in earth’s crust – soils, rocks, sands.
Radioactive gases escape from these (Radon) and enter air
3. Manmade – for industrial, medical (Xrays and labeled drugs)
and dental, and consumer use; Nuclear weapons; nuclear
Radon gas is considered “an enhanced natural source” –
concentrates in houses and mine shafts, etc due to human
Estimated that 82% of our exposure is from natural and
enhanced “natural” sources. Harm relates to type and
4 types of ionizing radiation:
Alpha particles; beta particles; gamma rays, x-rays
Differ by particle source, energy and speed,
penetrability, and consequent ability to do harm.
Gamma and x-rays are worst.
1. Alpha particles
- fast moving bits of atoms that are given off by a radioactive
substance (fragments contain 2 protons and 2 neutrons)
- Velocity is 1/20th
the speed of light (slow)
- Natural elements can be alpha emitters – uranium-238;
thorium-232; radium-226; radon-222; polonium-210: found
in rocks , soils, and water
- Useful in some medical and industrial processes
Radium-226 used to treat cancer by putting it into the tumor
to kill the cells; Polonium-210 used as a static eliminator in
paper mills (alpha particles attract loose electrons and reduce
static charge); Americium-241used to create a current in
smoke detectors. Smoke breaks the current and sets off
- Released during some mining operations
- For most, greatest exposure is radon gas or smoking
Health Effects: lack energy to penetrate skin; problem if inhaled
or ingested; or if enter blood through a wound.
Lung and other cancer risks.
2. Beta Particles
-Fragments of atoms that originate from nucleus and become like
- A little smaller than alpha particles
- Speed varies over a wide range
- technetium-99; phosphorus-31; tritium H-3; carbon-14, strontium-
90; cobalt-60; iodine-129 and 131
- used in medical diagnosis, imaging, and treatment; luminous dials
on gauges, and wrist watches; carbon-14 used to date matter up to
30,000 years of age; other industrial measuring instruments
Health effects: can burn skin; travel further into tissues than alpha
particles; ingestion and inhalation a worse problem than for alphas
Don’t play with instruments or devices that are marked with
3. Gamma rays
- very short wavelengths; fastest in natural spectrum
- travel at speed of light
- easily pass through many materials – lead shield needed
- differ from X rays in that gamma rays come from the nucleus and x-
rays come form the electron field surrounding the nucleus
- most widely used radiation source
- cesium-137; cobalt-60; technetium-99m (shorter half-life)
Cesium-137 – cancer trt; investigate deep in earth for oil
wells; measure soil density at construction sites; quality control of fill
levels in food and drug packaging
Cobalt-60 – sterilization of medical equipment; pasteurization
of foods and spices; gauge metal thickness in steel manufacturing;
Technetium -99m – common radioactive isotope in medicine
- Gamma ray trts also improve durability of wood and plastics
3. Gamma rays (cont)
-Used to check seals on welds; to inspect jet engine blades and parts
Common sources of exposure: natural occurrence in potassium in
soil, water, bananas, meats; nuclear medicine for bone, thyroid, lung
Medical trts; discarded medical or industrial devices.
External exposure; inhalation; ingestion – all a problem.
Penetrate tissue more deeply – can cause radiation sickness at high
doses (possibly lethal); lower doses – cancer and neural damage, etc.
4. X rays – manmade source
Most exposure through diagnostic medical and dental x-rays.
Like Gamma, but different source.
- chief concerns are contaminated dust, smoke, or gases (like
- mostly alpha and beta particles
- particles can lodge in lungs and remain for a long time
- if particles decay slowly, exposure continues over a long time
The amount of time it takes to decay one half of the radioactive
atoms in a group to another form is called half-life.
- Alpha and beta are of most concern
- energy released directly to tissue (digestive; kidney, and
3. External exposure
- little concern about alpha particles; more about Beta; most
about Gamma and xray.
Gamma and x ray can penetrate the entire body.
(should be shielded by lead apron or container; soil covering
Amount and duration of exposure determines health effects.
I. Acute effects – short term effects from high doses
Radiation sickness – nausea, vomiting, weakness, hair loss, skin
burns, diminished organ function
II. Chronic – long term, low level
Cancer is a primary health effect
1910 – understood that radiation causes skin cancer
Best studies of chronic effects are on Japanese atomic bomb
survivors; natives of Marshall Islands (where bomb testing was
done); and uranium miners.
Radiation changes DNA – mutationa caused.
Health Effect Time to Onset
5-10 changes in blood chemistry
50 nausea hours
75 hair loss 2-3 weeks
400 death from fatal doses within 2 months
1,000 destruction of intestinal lining
death 1-2 weeks
2,000 damage to central nervous system
loss of consciousness minutes
death hours to days