Properties and Effects of Radiation

1
Properties and Effects of Radiation

• Fear of the Unknown

2
Some Useful Radioactive Isotopes
3
Radiocarbon Dating

• About 1 in every trillion carbon atoms in living
  tissue are carbon-14 (the rest are mostly
  carbon-12)
• Carbon-14 is made in the atmosphere by cosmic
  rays striking CO2 molecules
• Plants convert CO2 to food which animals consume
• Carbon-14 is radioactive with a half-life of 5730
  years and can be detected even in very small
  quantities
• Once an organisms dies, no new carbon-14 is
  added--the amount of carbon-14 that remains
  indicates the age of the organism since its death

4
Example

• 1 g of living tissue results in about 16
  radioactive decays per minute (from carbon-14).
  If a 1 g sample from an archeological dig
  produces 4 decays per minute, how old is it?
• Answer After one half live (about 5700 yrs.) the
  activity will be 8 decays per minute, after two
  half lives (about 11,400 years) the activity will
  be 4 decays per minute
• The sample is about 11,400 years old

5
Dating with Radioactive Isotopes

• Radiocarbon dating is only accurate for ages less
  than about 25,000 years
• Other isotopes can also be used for radiometric
  dating of rocks
• Uranium-238, which has a half-life of 4.5 billion
  years, can be used to date very old rocks
• The oldest rock found on Earth is 3.9 billion
  years old

6
Half-life and Activity

• The activity of a radioactive isotope is the
  number of decays (or disintegrations) per second
• A source with an activity of one Curie (Ci) will
  produce 37 billion disintegrations per second
  (the activity of 1 g of radium)
• The shorter the half-life, the greater the
  activity

7
The Range of Alpha Radiation

• Alpha particles can be blocked by
• A sheet of paper
• One or two inches of air
• The outer layer of the skin
• Thus, materials that emit alpha radiation are
  only dangerous if inhaled or ingested (where they
  can be next to biological tissue)

An alpha particle consists of two protons and two
neutrons
8
The Range of Beta Radiation

• Beta particles can be blocked by
• A thin aluminum plate
• Several feet of air
• The first few layers of the skin
• Thus, beta particles are dangerous if inhaled or
  ingested AND to the cornea, where they can cause
  cataracts

e-
A beta particle is just a high-energy electron
9
The Range of Gamma Radiation

• Gamma particles can be blocked by
• A couple inches of lead
• A few feet of concrete
• Thus, care must be taken to shield oneself from
  gamma radiation
• X-rays are similar to gamma rays but do not
  penetrate as far--you are probably safe if
  separated by a normal wall

A gamma particle is just a high-energy photon
(i.e. piece of light)
10
Radiation Exposure

• Effects of exposure to radiation depends on the
  following factors
• distance from the source
• shielding
• type of radiation
• activity of the source
• part of the body exposed
• exposure time

11
Measuring Radiation Exposure

• A unit of exposure to radiation which includes
  both the total amount of radiation absorbed and
  the type of radiation is the Sievert (Sv)
• Example Your annual dose of radiation from
  natural sources is about 0.003 Sv or 3 mSv

12
Natural Sources of Radiation
Annual natural radiation exposure is 0.003 Sv per
year
13
Radiation Effects Dividing Cells

• Radiation is particularly damaging to cells that
  divide (reproduce) frequently
• Good news Radiation is effective against cancer
  cells, which divide very quickly
• Bad news The lining of the GI tract, the bone
  marrow, and the reproductive organs are
  particularly sensitive to radiation
• Pregnant women should avoid radiation exposure
  since most fetal cells are still dividing

14
Acute and Chronic Exposure

• Acute exposure is a large dose in a short period
  of time
• Acute exposure can result in injury or death
• Chronic exposure is exposure to a small dose of
  radiation over a long period of time
• Chronic exposure can result in cancer later in
  life

15
Biological Effects of Acute Radiation Exposure
Annual natural radiation exposure is 0.003 Sv per
year
16
Radiation and Cancer

• All living cells have enzymes designed to repair
  radiation damage to DNA
• In some cases, radiation-damaged DNA will produce
  cancer cells
• Only estimates of the risk of low-level radiation
  exist

17
Ionizing Radiation

• Only ionizing radiation (i.e. radiation capable
  of breaking apart molecules or disrupting atoms)
  can cause cancer
• Only ultraviolet, x-ray and gamma-ray
  electromagnetic radiation is ionizing radiation

18
Radiation and Mutations

• Radiation can damage a fetus in the womb
• All of the disfigured children born after
  Hiroshima and Nagasaki were in the womb during
  the explosions
• Genetic mutations are passed from parent to
  offspring
• Only after the 1986 Chernobyl accident were
  radiation-induced genetic mutations first
  recorded in humans (none debilitating)