Hazards of radiation

Ionizing radiation

These kinds of radiation can damage cells by knocking electrons out of molecular bonds--creating ions: charged molecules & free radicals.

Your body repairs some damage.

Biggest risk is to growing / dividing cells:

fetuses and cancers

 damage potentialblocked by
alpha, `{::}_2^4He` high paper
beta, `e^-` medium Al sheets
gamma low thick lead
x-ray low moderate lead

Alpha emissions are easily blocked. Problems occur when radioactive isotopes get inside your body--through eating or respiration--and can then emit alphas right next to a living cell.

Smoke detectors typically contain a small amount of an alpha emitter: The alpha's knock electrons off of air molecules.

Your skin's natural defense: It's already dead, and you're going to shed it before long.

Radiation in you and me

Many atoms in your body have a small probability of being radioactive isotopes. The two main ones are:

  • Potassium-40: 0.01% of all potassium; $\beta$ emitter; ~1,000 explosions / sec.
  • Carbon-14: 0.00000000001% of all carbon; $\beta$ emitter; ~3,000 explosions / sec.

Cell damage

Cell damage is measured in Sieverts (Sv). 1 Sv is approximately equivalent to 200 billion gamma rays penetrating each 1 square cm of an average body. The following are full body doses.

0.00001 Sv - Approximate dose from one dental x-ray. Well, this one is concentrated on your jaw, not spread out.

0.00016 Sv - "Self" radiation.

0.003 Sv - U.S. average annual dose.

0.100 Sv - EPA says a sudden dose of this much leads to 0.8% increase in risk of cancer according to the Linear Hypothesis.

0.2 Sv - Approx dose received by each of 52,000 Hiroshima survivors.

0.260 Sv - annual naturally occurring radiation exposure in Ramsar, Iran.

0.5 Sv - peak civilian exposure (est) from one nuclear test in Kazakhstan.

1-2 Sv - nausea, loss of hair, rarely fatal.

5 Sv - 50% chance of death after sudden exposure to this much radiation. Read more about the Goiania accident in Brazil.

25 Sv - "Cancer dose"

Really means: if you expose a larger group of people to 25 Sv, there will be one more death than would have occurred otherwise.

Hiroshima and cancer [Writing]

Human beings in Hiroshima, Japan, when the Allies exploded the first atomic bomb

50,000-150,000 killed within days
  • Killed in initial blast
  • Killed by fire
  • Received a high enough dose to die of radiation sickness
~52,000 survivors Survived, but received an average radiation dose of ~0.2 Sv

Total dose to survivors: 0.2 Sv * 52,000 $\approx$ 10,400 Sv.

According to the Linear Hypothesis, there should be one extra death due to cancer for each 25 Sv a population receives:

  1. Figure out the number of excess cancers expected due to this radiation dose. It may help to think about units when you decide what to multiply or divide by what:

    10,400 Sv

    $\frac{25 \,{\rm Sv}}{1\, {\rm cancer}}$

    ______ excess cancers--the units are "cancers"(well really, deaths due to cancer.) Hint: If you get *more* deaths due to cancer than 52,000 (the number of exposed people) something is wrong with your calculation!

    ______ % Using the low figure of 50,000 immediate deaths, what percentage is this (excess cancers) / (immediate deaths)?

  2. Your lifetime probability of developing cancer is about 20%. So, how many of these 52,000 survivors would you have expected to die of cancer even without the Hiroshima bomb?

    ______ number of "naturally occurring" cancers.

The Linear Hypothesis is cautious. It probably overestimates the dangers of radiation. Some people believe it would be more appropriate to use a _threshhold model_ for the dangers of radiation exposure.

Infectious irradiation?

Irradiating food involves killing off bacteria (dividing cells) by shining `gamma` radiation on the food.

If the main effect of the radiation is to ionize cells.... would you expect that the food would be more radioactive than it was before?

Is someone exposed to radiation to treat their cancer radioactive after treatment?

Everyday radiation

Most important source is Radon gas.

Risks in daily life


  1. It seems that it is safer to travel by car than by bicycle. If that's the case... why are so many more people killed in car accidents than in bicycle accidents each year?

  2. The chance of death by car accident is 1 in a million for each 50 km driven. The average car in the U.S. is driven ~ 12,500 miles in a year. What are the chances of death from a car accident over the course of a year for a person who drives this much over the course of a year? (1 mile = 1.6 km)

Motor vehicle deaths by year, U.S.A.

Suggested exercises

Chapter 14, Conceptual exercises: 37, 39, 43, 44

Image credits

ionizing radiation, Tosaka, Nick Sherman, Ɓukasz Strachanowski