Chemistry 2

Measuring Radiation and Health Affects

  1. There are several units for measuring radiation. Below are some of the most common ones:
    1. Measuring radioactivity
      1. We can monitor and count every time a substance emits a radioactive particle or a gamma ray.
      2. If a substance emits more radiation per minute than another substance we consider it to be more radio active than another substance.
      3. The common unit for measuring this radioactivity is the Becquerel (Bq) and the SI unit is the Curie (Ci).
      4. For example, a typical gram of radium emits 1,000,000 times more radiation than 1 gram of uranium


      5. A Bq = 1 particle of radiation released per second. A Ci = 37 billion particles of radiation released per second.
      6. The Ci (Curie) is related to Marie Curie who did her first work with radium. 1 Ci = number of particles of radiation released per second by 1 gram of radium.
    2. Measuring energy absorption
      1. Each particle of radiation (the gamma ray included) carries a certain amount of energy. Sometimes you might want to know how much energy is being absorbed by surrounding objects instead of how many particles of radiation are being emitted.
      2. The measurement of energy absorbed is also given in two different units. The common unit is the radiation absorbed dose (rad) and the SI unit is the Gray (Gy).
      3. Depending on the type of radiation absorbed (alpha, beta, gamma, or neutrons) the amount of energy absorbed could be different. Alpha particles and gamma rays can have very similar energies. For example, a person exposed to the same number of alpha particles or gamma rays may absorb the same amount of radiation.



      4. In the example above the gamma rays each carry the same energy as the alpha particles. This is not always true, but may be true. Therefore, in the case above the same number of particles absorbed equals the same amount of energy absorbed.
      5. Rads and Gys are related in the following way: 1 Gy = 100 rad.
    3. Measuring Biological Effects
      1. Although the amount of energy absorbed may be equivalent, the biological effect of different particles can be very different. That is why we need a different measurement of "dosage", one that will make it easier to compare different exposures to radiation.
      2. The units used for measuring biological dosage come in two varieties as well. The common unit is the roentgen equivalent man (rem) and the SI unit is the Sievert (Sv).
      3. Depending on the type of radioactive particle (or ray) that is absorbed, varying amounts of biological damage can be done.
      4. For example, alpha particles tend to concentrate all their energy in one small region while the energy absorbed from a gamma ray may be spread out over a larger volume. This means that absorbing and equal number of alpha particles can be much more dangerous than absorbing the same number of gamma rays.


      5. As you can see the same number of alpha particles, carrying the same amount of energy can do much more biological damage. Because we most care about how much radiation will affect us, this is the most common type of measurement used.
      6. While the Sv is the SI unit, the most commonly used unit is the rem. 1 Sv = 100 rem.
    4. Background Radiation
      1. Radiation exists all around you. Humans have evolved with this normal amount of natural radiation, so our bodies have some built in repair mechanisms which allow us to deal with these normal levels of radiation. This normal level of radiation is called "Background Radiation".
      2. Below is a table of the typical sources of background radiation an average person receives each year:
        Background Radiation Sources
        Natural Sources:
        - Radon
        200 mrem
        - Cosmic Rays
        28 mrem
        - Rocks and Soil
        28 mrem
        - Internal Sources: natural found in the human body
        40 mrem
        Human created sources:
        - Medical X-Rays
        40 mrem
        - Nuclear Medicine
        14 mrem
        - Consumer Products
        10 mrem
        - Other
        3 mrem
        Total -->
        363 mrem

        *Radon is a naturally occurring radioactive element.
        -Cosmic rays are high energy particles or rays that hit the Earth's atmosphere causing many other high energy particles to be produced.
        - Rocks and soil (as well as building materials) contain naturally occurring radioactive elements like uranium, thorium, and radium.
        - Internally, one major source is potassium-40 a naturally occurring radioactive isotope of potassium.

        **Many smoke detectors contain small amounts of radioactive material.
        - Sitting in front of computer monitors and TVs also raise your dosage very slightly. TV adds about 10 mrem per year for the average person.
      3. To get a sense of how specific activities affect our exposure see the table below:
        Typical activities and their exposure:
        - Chest X-Ray
        8.0 mrem
        - Cross country round trip airplane ride
        5.0 mrem
        - Watch TV for an hour
        0.15 mrem
        - Live outside a nuclear power plant for a year
        0.10 mrem
    5. Health Effects
      1. There is a debate about how much small amounts of radiation can affect our health. Some people feel that any radiation above the natural background is too much while others argue that our bodies were designed to tolerate a certain level of radiation, so very low exposures have no effect.
      2. So background radiation is about 360 mrem or 0.36 rem. Below is some of what we know happens at higher doses:
        Acute effect of whole-body irradiation*
        Dose in rem Effect
        0 - 0.360
        		 Little to none. This is normal background radiation.
        5-20
        		 Possible late effect; possible chromosomal aberrations
        20 - 100
        		 Temporary reduction in leukocytes (white blood cells); after 50 rem temporary sterility in men
        100-200
        		 Mild radiation sickness within a few hours: vomiting, diarrhea,fatigue; reduction in resistance to infection; possible bone growth retardation in children
        200 - 300
        		 Serious radiation sickness; effects as in 100 - 200 above and also bone marrow syndrome (loss of blood producing tissue), hemorrhage; 10 - 35% will die within 30 days
        300 - 400
        		 Serious radiation sickness as above; also marrow and intestine destruction; permanent sterility in women; 50 - 70% will die within 30 days
        400 - 1000
        		 Acute illness, early death; 60 - 95% will die within 30 days
        1000 - 5000
        		 Acute illness, early death in days; 100% will die within 10 days
        Over 5000
        		 Acute illness; death in hours to days; central nervous system syndrome; 100% will die within 2 days.

        *from "Nuclear Arms Race" by Paul P. Craig and John A. Jungerman

      3. These doses are extremely high and not something you are likely to ever encounter. Only people close to a nuclear explosion or a major nuclear accident would ever experience such high doses of radiation. Keep in mind that background radiation is only 0.36 rem.