Units of radioactivity: Difference between revisions

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For the quantitative measurement of  different aspects of [[radioactivity]], there are a substantial number of '''units of radioactivity'''.  The number is relatively high because the aspects include the energy of a radiation source, as well as the effect of [[ionizing radiation]] in air, absorbed in arbitrary materials, and specific effects on biological systems. Doubling the number of units is the reality that they are defined both for the [[International System of Units]] (SI) and in [[U.S. customary units|"traditional" or "customary"]] units.
For the quantitative measurement of  different aspects of [[radioactivity]], there are a substantial number of '''units of radioactivity'''.  The number is relatively high because the aspects include the energy of a radiation source, as well as the effect of [[ionizing radiation]] in air, absorbed in arbitrary materials, and specific effects on biological systems. Doubling the number of units is the reality that they are defined both for the [[International System of Units]] (SI) and in [[U.S. customary units|"traditional" or "customary"]] units.


 
Properly interpreting the units can be quite complex. A given quantum of ionizing radiation will have different effects not only due to the type of radiation, which is considered in the computation of the units of biological effect, sieverts and rems, but also due to the energy level within a radiation type. Fast, medium-speed and slow neutrons, for example, have different biological effects.
 
 




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==Ionization of air==
==Ionization of air==
Roentgens measure the ionization of air from a radioactive source, but knowing that is less important than knowing other measurements.
==Absorption in materials==
==Absorption in materials==
==Biologic effects==
==Biologic effects==
{| class="wikitable"
<center>'''Radiation weighting (WR) factors'''</center><ref name=OHS>{{citation
| url = http://www.ccohs.ca/oshanswers/phys_agents/ionizing.html
| publisher = Canadian Centre for Occupational Health and Safety
| title = Radiation - Quantities and Units of Ionizing Radiation
}}</ref>
|-
! Radiation type
! Energy level
! Biological effect
|-
|Gamma rays and x rays
| All
| 1
|-
| Beta particles
|All
| 1
|-
| rowspan=5| Neutrons
| < 10 KeV
| 5
|-
| > 10 keV to 100 keV
| 10
|-
| > 100 keV to 2 MeV
| 20
|-
| > 2 MeV to 20 MeV
| 10
|-
| > 20 MeV
| 5
|-
| Alpha particles
| All
| 20
|}
==Qualifiers==
==Qualifiers==
==Decay reactions==
==Decay reactions==
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| Rate of emission from a source
| Rate of emission from a source
|  
|  
* Becquerel (Bq)
* becquerel (Bq)
|  
|  
* Curie (Ci)
* curie (Ci)
* Counts per minute
* Counts per minute
|  
|  
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| Air ionization by radiation
| Air ionization by radiation
|  
|  
* G
* grays per hour (Gy/h)
rays per hour (Gy/h)
|   
|   
* Roentgen (R)
* roentgen (R)
|  
|  
* Used for X-rays and gamma radiation
* Used for X-rays and gamma radiation
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| Absorbed dose
| Absorbed dose
|  
|  
* Gray (Gy)
* gray (Gy)
|  
|  
* rad
* rad
|  
|  
* 1 Gray = 100 rad
* 1 gray = 100 rad
|-
|-
| Biological equivalent dose
| Biological equivalent dose
|  
|  
* Sievert (Sv)
* sievert (Sv)
|  
|  
* rem
* rem
|
|
|}
|}

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Relations among units

For the quantitative measurement of different aspects of radioactivity, there are a substantial number of units of radioactivity. The number is relatively high because the aspects include the energy of a radiation source, as well as the effect of ionizing radiation in air, absorbed in arbitrary materials, and specific effects on biological systems. Doubling the number of units is the reality that they are defined both for the International System of Units (SI) and in "traditional" or "customary" units.

Properly interpreting the units can be quite complex. A given quantum of ionizing radiation will have different effects not only due to the type of radiation, which is considered in the computation of the units of biological effect, sieverts and rems, but also due to the energy level within a radiation type. Fast, medium-speed and slow neutrons, for example, have different biological effects.



Activity of a source of radiation

As opposed to most of the other units, the SI unit becquerel[1] (Si) and the common unit curie (Ci) deal with the activity of the source, not the effects on radioactivity reaching its destination. Linked with area or volume measurements, these units are useful in giving a quantitative measurement of contamination of areas of the ground or volumes of water. When the source contains multiple isotopes, as with a reactor accident, it is most useful to state activity of each isotope.

Basic units

1 Bq = 1 event of radiation emission per second. Since this is a very small unit, common measurements are:

  • 1 kBq = 103 Bq
  • 1 MBq = 106 Bq
  • 1 GBq = 109 Bq

The older unit, the Curie (Ci), is equal to 37 GBq. The Curie is a large unit, so common representations are

  • 1 mCi = 10-3Ci
  • 1 uCi = 10-6Ci
  • 1 nCi = 10-9Ci
  • 1 pCi = 10-12Ci

Linking the two sets of units,

1 Bq = 27 pCi


Measuring contamination

Contamination of surfaces, such as the ground near a radiation release, is stated in Bq or Ci units per square metre. Contamination of water is expressed in Bg or Ci per liter.

Refining activity

Neither the Bq nor the Ci measure the energy of release from the source, only its rate. The energy is specified in electronvolts.

Ionization of air

Roentgens measure the ionization of air from a radioactive source, but knowing that is less important than knowing other measurements.

Absorption in materials

Biologic effects

Radiation weighting (WR) factors
[2]
Radiation type Energy level Biological effect
Gamma rays and x rays All 1
Beta particles All 1
Neutrons < 10 KeV 5
> 10 keV to 100 keV 10
> 100 keV to 2 MeV 20
> 2 MeV to 20 MeV 10
> 20 MeV 5
Alpha particles All 20

Qualifiers

Decay reactions

References

  1. ↑ While the abbreviations of units are capitalized, the spelled-out names are not, to avoid confusion with the person they honor.
  2. ↑ Radiation - Quantities and Units of Ionizing Radiation, Canadian Centre for Occupational Health and Safety
Property measured SI unit Other unit Notes
Rate of emission from a source
  • becquerel (Bq)
  • curie (Ci)
  • Counts per minute
Air ionization by radiation
  • grays per hour (Gy/h)
  • roentgen (R)
  • Used for X-rays and gamma radiation
Absorbed dose
  • gray (Gy)
  • rad
  • 1 gray = 100 rad
Biological equivalent dose
  • sievert (Sv)
  • rem
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