“DOSIMETRY” Measuring Radiation National 5

Why should we measure radiation?

What can be measured? We are concerned with 3 quantities of measurement in radioactivity We are concerned with 3 quantities of measurement in radioactivity Activity Activity Absorbed Dose Absorbed Dose Equivalent Dose Equivalent Dose

Activity of a source

The activity (A) of a radioactive source is the number of decays per second and is measured in becquerels The activity (A) of a radioactive source is the number of decays per second and is measured in becquerels One becquerel (1Bq) is one decay per second. One becquerel (1Bq) is one decay per second.

Example A radioactive source gives off 300 radioactive emissions in 2 minutes. What is the activity of the source in Becquerels? Activity = Number of emissions  time(s) A = 300 / 120 Activity = 2.5 Bq

Absorbed Dose

Not all of the emissions from a radioactive source will be absorbed by a body. Not all of the emissions from a radioactive source will be absorbed by a body. Much of the ‘activity’ from a radioactive source will miss the body. Much of the ‘activity’ from a radioactive source will miss the body. Some will pass straight through without being absorbed. Some will pass straight through without being absorbed.

Absorbed Dose The absorbed dose (D) is the energy absorbed by each kg of the body. The absorbed dose (D) is the energy absorbed by each kg of the body. The gray (Gy) is the unit of absorbed dose. The gray (Gy) is the unit of absorbed dose. One gray is one joule per kilogram. (1 Gy = 1J/kg) One gray is one joule per kilogram. (1 Gy = 1J/kg)

Example “Exposure to a radiation dose of four Gray will typically kill about half of all healthy adults.”

Equivalent Dose

Biological effects of radiation The actual effect of the radiation on a body will depend on several factors; The actual effect of the radiation on a body will depend on several factors; 1. How much energy is absorbed (the absorbed dose: D) 2. What kind of tissue receives the radiation (bone, muscle, brain, etc.) 3. What type of radiation the tissue is exposed to ( , neutron, proton)

Equivalent dose The equivalent dose (H) takes into account the type of radiation and the total energy absorbed. The equivalent dose (H) takes into account the type of radiation and the total energy absorbed. Equivalent dose is measured in sieverts (Sv). Equivalent dose is measured in sieverts (Sv).

Typical levels of Equivalent Dose Radiation Dose Effect 2 mSv/yr (millisieverts per year) Typical background radiation experienced by everyone (average 1.5 mSv in Australia, 3 mSv in North America) 9 mSv/yr Exposure by airline crew flying New York-Tokyo polar route 20 mSv/yr Current limit (averaged) for nuclear industry employees

Typical levels of Equivalent Dose Radiation Dose Effect 50 mSv/yr Former routine limit for nuclear industry employees. It is also the dose rate which arises from natural background levels in several places in Iran, India and Europe 100 mSv/yr Lowest level at which any increase in cancer is clearly evident. 350 mSv/lifetime Criterion for relocating people after Chernobyl accident

Typical levels of Equivalent Dose Radiation Dose Effect 1,000 mSv single dose (1 Sievert) Causes (temporary) radiation sickness such as nausea and decreased white blood cell count, but not death. Above this, severity of illness increases with dose 5,000 mSv single dose (5 Sieverts) Would kill about half those receiving it within a month

Summary QuantityUnit Unit symbol Definition Activity (A) BecquerelBq Number of disintegrations per second Absorbed dose (D) GrayGy Energy absorbed per kg Equivalent dose (H) SievertSv Measure of biological effect of radiation Equivalent dose rate (H) Sievert per hour Svh -1 Biological effect per unit time.

Comparison with rain! QuantityDefinition If it was rain it would be…. Activity Number of disintegrations per second How much rain is falling Absorbed dose Energy absorbed per kg How much rain is hitting you Equivalent dose Measure of biological effect of radiation How wet you get

Safety with Radioactivity

What are the safety procedures necessary when handling radioactive substances. What are the safety procedures necessary when handling radioactive substances. What are the 3 methods of reducing the equivalent dose What are the 3 methods of reducing the equivalent dose Include the radioactive hazard sign and state where it should be displayed Include the radioactive hazard sign and state where it should be displayed