Units of Radioactivity
What is Radioactivity?
Formula of Radioactivity
The formula for radioactivity, often referred to as the decay law, quantifies the rate at which an unstable atomic nucleus decays. It is expressed by the equation:
N(t) is the number of undecayed nuclei at time t,
N₀ is the original number of nuclei,
e is the base of the natural logarithm,
λ (lambda) is the decay constant specific to each radioactive substance,
t is the time elapsed.
What are the Units of Radioactivity?
The units of radioactivity measure the rate at which radioactive decays occur in a sample of radioactive material. The primary unit used is the becquerel (Bq), defined as one decay per second. This unit is part of the International System of Units (SI) and was named after Henri Becquerel, one of the discoverers of radioactivity.
Another commonly used unit, especially in the medical field and older literature, is the curie (Ci), which is larger than the becquerel. One curie is defined as 3.7×10¹⁰ decays per second, which is approximately the activity of one gram of radium-226, a historically significant radioactive substance.
These units quantify the activity of a radioactive sample without directly measuring the energy released during decay. They provide a way to express the stability of the nuclei and the potential intensity of the radiation emitted.
SI Unit of Radioactivity
It measures the activity of a quantity of radioactive material and is defined as one decay or disintegration per second.This unit reflects the rate at which unstable atomic nuclei undergo radioactive decay.
CGS Unit of Radioactivity
This unit was originally based on the activity of one gram of radium-226 and is still commonly used in medicine and older scientific literature, despite the SI system’s preference for the becquerel.
List of Units of Radioactivity
| Unit | Symbol | Equivalent to |
|---|---|---|
| Becquerel | Bq | 1 Bq = 1 disintegration per second |
| Curie | Ci | 1 Ci = 3.7×10103.7×10¹⁰ Bq |
| Rutherford | Rd | 1 Rd = 1 million Bq |
| Gray | Gy | 1 Gy = 1 joule/kg |
| Sievert | Sv | 1 Sv = 1 joule/kg (adjusted for radiation type) |
| Rad | Rad | 1 Rad = 0.01 Gy |
| Rem | Rem | 1 Rem = 0.01 Sv |
Becquerel (Bq)
The SI unit of radioactivity, symbolized as Bq. It is defined as one disintegration or decay per second. This unit directly measures the activity of a radioactive substance without reference to the energy of the radiation emitted.
Curie (Ci)
A traditional unit of radioactivity, symbolized as Ci. One curie is equivalent 3.7×10¹⁰ to becquerels. The curie is based on the radioactivity of one gram of radium-226 and is still widely used in medicine and industry.
Rutherford (Rd)
Less commonly used today, this unit is symbolized as Rd. One Rutherford equals one million becquerels (1 million disintegrations per second), and it was historically used to measure significant levels of radioactive activity.
Gray (Gy)
A unit of absorbed radiation dose, symbolized as Gy. One gray is the absorption of one joule of radiation energy per kilogram of matter. It quantifies the amount of radiation energy absorbed by the tissue.
Sievert (Sv)
The unit of radiation dose equivalent, symbolized as Sv. It measures the health effect of ionizing radiation on human tissue, taking into account the type and energy of the radiation. One sievert equals one joule per kilogram, adjusted for biological effectiveness.
Rad
An older unit of absorbed dose, where one rad is equivalent to 0.01 gray (100 rad = 1 gray). Symbolized as Rad, it is still used in some contexts within the United States.
Rem
Similar to the sievert, the rem (Roentgen equivalent man) measures the biological effects of ionizing radiation. Symbolized as Rem, one rem is equivalent to 0.01 sievert.
Conversion of Units of Radioactivity
| From Unit | To Unit | Conversion Factor |
|---|---|---|
| Curie (Ci) | Becquerel (Bq) | 1 Ci = 3.7×10¹⁰ Bq |
| Becquerel (Bq) | Curie (Ci) | 1 Bq = 2.7027×10⁻¹¹ Ci |
| Rutherford (Rd) | Becquerel (Bq) | 1 Rd = 1×10⁶ Bq |
| Becquerel (Bq) | Rutherford (Rd) | 1 Bq = 1×10⁻⁶ Rd |
From Curie (Ci) to Becquerel (Bq)
1 curie is approximately equal to 37 billion becquerels. This conversion factor is used to translate between the traditional unit (curie) and the SI unit (becquerel) of radioactivity.
From Becquerel (Bq) to Curie (Ci)
1 becquerel is approximately equal to 2.7027 x 10^-11 curies. This allows for the conversion from the SI unit back to the traditional unit of radioactivity.
From Rutherford (Rd) to Becquerel (Bq)
1 Rutherford, a less commonly used unit, is approximately equal to 1 million becquerels, used mainly in historical or specific scientific contexts.
From Becquerel (Bq) to Rutherford (Rd)
This conversion allows for the transition from the SI unit of radioactivity to the older, less common unit of Rutherford, facilitating understanding and calculations in diverse contexts.
FAQ’s
What are the 7 types of radiation?
The seven types of radiation include alpha, beta, gamma, X-ray, neutron, positron, and proton radiation, each with unique properties and interactions with matter.
How do you measure radioactivity?
Radioactivity is measured using devices like Geiger counters, scintillation counters, and ionization chambers, which detect and quantify radioactive decay particles and radiation.
Why are there so many units for radiation?
Multiple units for radiation exist to address different measurement needs, historical developments, and scientific and medical applications, enhancing precision and context relevance.
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