Radiation dosage

1

• Radiation dosage
• Start with the energy given to an electron if it
  flows from the negative terminal of a 1 Volt
  battery to the positive 1 electron volt 1 eV.
• A typical energy of a neutron or gamma ray
  emitted in a radioactive decay is 1 million eV
  1 MeV.
• If every cm2 of your body is exposed to 2 billion
  gamma rays of typical 1 MeV energy, your exposure
  is 1 rem.
• Dental x-ray 0.001 rem
• Typical annual exposure 0.4 rem per year
• Radiation sickness 200 rem
• 50 chance of lethal dose 300 - 450 rem

2

• American Nuclear Society table of exposures
  (http//www.ans.org/pi/resources/dosechart)
• typical US exposure 360 mrem per year
• Dose needed to cause cancer 2500 rem
• 360 rem x 75 year life span / 2500 rem ? 1
  chance of cancer due to natural environmental
  radioactivity
• Estimated 1.4 million new cancer diagnoses
  expected per year in US / 304 million US
  population 0.5
• (570,000 deaths in US per year due to cancer
  ?
• likelihood of dying due to cancer 15
  20,
• significantly higher than rate due to
  natural radioactivity. Radiation causes
  excess deaths above
• 20 level)

3

4

• Body has natural defenses against radiation
• Body repairs damage due to low doses
• Below 100 rem, usually no immediate effects
• Cancer requires that multiple genes be damaged
  before
• unregulated cell multiplication occurs,
  usually requires
• multiple exposures
• For doses above 100 rems, symptoms of radiation
  sickness include
• nausea
• vomiting
• headache
• loss of white blood cells

5

• Doses gt 300 rems
• hair loss
• internal harm (damage to nerve cells and the
  cells that line the digestive tract)
• Loss of white blood cells (body's main defense
  against infection) makes radiation victims
  vulnerable to disease.
• Reduced production of blood platelets (important
  for blood clotting) makes victims of radiation
  sickness vulnerable to hemorrhaging.
• Fever and diarrhea
• Half of all people exposed to 450 rems die.
• Doses of 800 rems always fatal within 2 weeks.
• Immediate survivors still face prospect of
  leukemia (cancer of the blood), lung cancer,
  thyroid cancer, breast cancer, and cancers of
  other organs.

6
Linear dose-cancer hypothesis
100 chance
2500 rem
7

• How do we know relation between radiation
  exposure and cancer?
• Early radiation workers had high incidence of
  cancers. (e.g., Marie Curie, who first isolated
  radium from uranium ore, died of leukemia.)
• In the 1920's, watch dials were painted with
  radium-based luminous paint. Employees often
  licked their paint brushes to give them a sharp
  point and ingested small quantities of paint.
  Radium in bones resulted in bone tumors 8 - 40
  years later.
• 6500 British arthritis patients were treated with
  large doses of x-rays. Of the 6,500 patients, 30
  developed leukemia compared with an expected
  incidence of 7 cases.

http//www.jplabs.com/html/effect_of_radiation.HTM
8

• Survivors of the Hiroshima and Nagasaki attacks
  Of 80,000 survivors of the initial attacks, 126
  died of leukemia, nearly double the normal
  figure. Incidence of leukemia was related to
  distance from the explosion and therefore to the
  radiation dose received. Highest incidence was in
  survivors closest to the explosion. Clear
  evidence of the dose-dependent relationship of
  leukemia to radiation, i.e. the higher the dose,
  the greater the risk. Also seen increase in
  frequency of stomach, lung and breast cancer.
  These have taken much longer to develop and some
  are still appearing now.
• A-bomb data show that there is a delay (called
  the latency) between the radiation exposure and
  death from cancer. Mean latency from leukemia
  10 years, and for other cancers gt 20 years.
  Excess cancer deaths still occurring 40 50
  years after the exposures. (http//www.triumf.ca/s
  afety/rpt/rpt_4/node20.html)

9
But at low doses, linear dose-cancer hypothesis
is conservative. Is there a low-dose
threshold?
100 chance
2500 rem
10

• Why is this important?
• Hiroshima Nagasaki survivors received avg. dose
  20 rems ? 0.8 chance of cancer as a result
• 80,000 survivors have 20 chance of dying of
  cancer anyway ? 16,000 cancer deaths not
  connected to A-bombs
• 0.8 excess cancer death rate ? 640 extra cancers
  due to A-bombs (4 of total cancer deaths, 0.6
  of total A-bomb deaths)

11

• Chernobyl 30 of reactors radioactivity
  released into atmosphere.
• 30,000 people in vicinity received average dosage
  of 45 rem
• ? chance of additional cancer due to Chernobyl
  release
• 45/2500 1.8
• ? 30,000 x .018 540 extra deaths compared to
• 30,000 x 20 6,000 normal cancers (9 excess)

12

• Chernobyl 30 of reactors radioactivity
  released into atmosphere.
• 30,000 people in vicinity received average dosage
  of 45 rem
• ? chance of additional cancer due to Chernobyl
  release
• 45/2500 1.8
• ? 30,000 x .018 540 extra deaths compared to
• 30,000 x 20 6,000 normal cancers (9 excess)
• How about living in Denver?
• Extra exposure 0.025 rem due to cosmic rays at
  5000 ft and 0.040 rem due to radioactivity from
  ground 0.065 rem per year
• ? additional cancer deaths after 10 years of
  exposure 0.065 x 10 / 2500 x 2,400,000 people
  620 people
• If Chernobyl was serious, should Denver be
  evacuated?

13

• Three Mile Island
• Loss of coolant accident in 1979 led to partial
  core meltdown.
• Average dose to 2,000,000 people in area 0.001
  rem according to NRC
• Compare to chest x-ray (0.006 rem) or natural
  background level in Harrisburg area 0.1 rem per
  year
• lt 1 extra cancer death
• Next Read Mullers discussion of Yucca Mountain
  and nuclear waste disposal issue