The media have begun using a variety of units to measure radiation: sieverts, becquerels, millirems, etc. How many people know all these units and whether 10 sieverts/hour is more or less dangerous than 100 becquerels/hr.? To help with the confusion, here is a conversion table that may be of use:Here is a conversion table for various other units of measure:
Conversion Factors
To convert from | To | Multiply by |
Curies (Ci) | becquerels (Bq) | 3.7 x 1010 |
millicuries (mCi) | megabecquerels (MBq) | 37 |
microcuries (µCi) | megabecquerels (MBq) | 0.037 |
millirads (mrad) | milligrays (mGy) | 0.01 |
millirems (mrem) | microsieverts (µSv) | 10 |
milliroentgens (mR) | microcoulombs/kilogram (µC/kg) | 0.258 |
becquerels (Bq) | curies (Ci) | 2.7 x 10-11 |
megabecquerels (MBq) | millicuries (mCi) | 0.027 |
megabecquerels (MBq) | microcuries (µCi) | 27 |
milligrays (mGy) | millirads (mrad) | 100 |
microsieverts (µSv) | millrems (mrem) | 0.1 |
microcoulombs/kilogram (µC/kg) | milliroentgens (mR) | 3.88 |
Radiation Measurements
| Radioactivity | Absorbed Dose | Dose Equivalent | Exposure | |
| Common Units | curie (Ci) | rad | rem | roentgen (R) |
| SI Units | becquerel (Bq) | gray (Gy) | sievert (Sv) | coulomb/kilogram (C/kg) |
So the answer to the question is neither. A becquerel (Bq) is a measure of the radioactivity in counts per second of a given sample where one count represents the decay of one nucleus. It is an SI (Systeme Internationale) unit of measure related to the older, non-SI unit of Curies (Ci). One Ci is equal to the activity of one gram of radium-226. A sample must be normalized to the atomic mass of the isotope being measured.
The absorbed dose is what is actually important when determining if a radiation level is of concern or not. But the radioactivity is the number that is most easily measured. Different types of ionizing radiation (radiation that will change a neutral atom to an ion by removing an electron - similar to creating a free radical that can then damage cells and DNA and such) are absorbed at different levels. Absorbed Dose is measured in joules per kilogram (grays [Gy]), where joules measure the energy absorbed from the radiation and kilograms is the measure of the mass of the absorbing medium (a person's tissue). The effective dose is determined by multiplying a conversion factor, a weighted average of absorption of different organs (heart, liver, skin, e.g.), times the amount of radiation exposure. It is not a simple calculation nor is it exact.
So when the reporter talks about there being so many becquerels of radiation, he is reporting how many counts are being recorded. It is an indication of how much radioactive material is present. By also determining what isotopes of what elements are present, one can evaluate the relative risk to humans and other living things.
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