Specific Activity Converter
Convert Bq/kg, Ci/g, dps/g, and other units for radioactivity per unit mass.
Result
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Base Unit
Relative Value
*Diagram shows values relative to the selected base unit (Bq/kg).
Unit Information
What is Becquerels per kilogram (Bq/kg)?
Becquerels per kilogram (Bq/kg) is the SI unit for specific activity. It represents the number of radioactive decays (Becquerels) occurring per second within one kilogram of a substance. This unit provides a standardized way to compare the radioactivity concentrations of different materials.
What is Becquerels per gram (Bq/g)?
Becquerels per gram is another metric unit, often used for smaller samples or materials with higher concentrations of radioactivity. 1 Bq/g is equal to 1000 Bq/kg.
What is Curies per gram (Ci/g)?
Curies per gram (Ci/g) is a non-SI unit of specific activity, combining the older unit of activity (Curie) with a unit of mass (gram). One Curie is 3.7 × 10¹⁰ Becquerels. This unit expresses a very high concentration of radioactivity and might be encountered in older literature or specific applications in the US.
What are dps/g and dpm/g?
'dps/g' stands for 'disintegrations per second per gram' and is equivalent to Bq/g. 'dpm/g' stands for 'disintegrations per minute per gram' and is equivalent to (1/60) Bq/g. These are direct measures of decay rate per gram.
What are compound units like mCi/g and kBq/kg?
These units simply combine standard prefixes (kilo-, milli-, micro-) with the base units. For example, mCi/g means millicuries per gram. These are used to express specific activity in a range of magnitudes suitable for different applications, from environmental monitoring to high-activity medical sources.
Formulas
1 Ci/g = 3.7 × 10¹³ Bq/kg
This formula shows the conversion between the very high-concentration unit of Curies per gram and the SI base unit of Becquerels per kilogram.
1 Bq/g = 1000 Bq/kg
Converts between the common specific activity units of Becquerels per gram and Becquerels per kilogram.
1 mCi/g = 3.7 × 10¹⁰ Bq/kg
Converts the commonly used millicuries per gram to the SI base unit.
dps/g = Bq/g
Disintegrations per second per gram is equivalent to Becquerels per gram.
SA = (A × N_A) / M
Theoretical specific activity (SA) can be calculated where A is the decay constant, N_A is Avogadro's number, and M is the molar mass.
Key Reference Points
- Potassium-40 in natural potassium: ~31 Bq/g.
- Potassium-40 in a human body: ~55 Bq/kg.
- Carbon-14 (pure): ~1.65 × 10¹¹ Bq/g or ~4.46 Ci/g.
- Cobalt-60 (pure, medical/industrial source): ~4.2 × 10¹⁶ Bq/kg or ~1100 Ci/g.
- Uranium-238 (pure): ~12,400 Bq/kg.
- Exemption limit for some radioactive material transport: May be around 100 Bq/g.
- Specific activity of natural granite (due to U/Th): ~1 Bq/g.
- Specific activity of coffee beans (due to K-40): ~1 Bq/g.
- A medical tracer dose might have a very high specific activity but a very small total mass.
- Low-level radioactive waste typically has a specific activity in the range of kBq/g to MBq/g.
Did You Know?
The specific activity of a radioisotope is inversely proportional to its half-life and its atomic weight. Isotopes with short half-lives and low atomic weights will generally have very high specific activities because a larger fraction of their atoms decay per unit time. For example, Technetium-99m (half-life ~6 hours) has a much higher specific activity than Uranium-238 (half-life ~4.5 billion years).
A 'carrier-free' radioisotope is theoretically pure, containing only the radioactive isotope and no stable isotopes of the same element. This results in the maximum possible specific activity for that radioisotope.
High specific activity radiopharmaceuticals are desirable in nuclear medicine because they allow a sufficient amount of radioactivity to be delivered to a target tissue (e.g., a tumor) with a minimal mass of the chemical compound, reducing potential chemical toxicity.
In Gabon, Africa, there is evidence of a natural nuclear fission reactor that was active about 2 billion years ago. The high concentration (specific activity) of Uranium-235 in the ore, combined with groundwater acting as a moderator, allowed a self-sustaining nuclear chain reaction to occur.
In carbon-14 dating, the specific activity of carbon-14 (e.g., in Bq/g of carbon) in an ancient organic sample is measured and compared to the specific activity in modern living organisms to determine its age.
The Banana Equivalent Dose (BED) is an informal unit of radiation exposure, intended to place a dose in perspective with the natural radiation from eating one average banana. Bananas are naturally radioactive due to their potassium-40 content, with a specific activity of about 130 Bq/kg.
The site of the first atomic bomb test, the Trinity Site in New Mexico, still has slightly elevated levels of radioactivity. The specific activity of certain isotopes in the soil is a key measure used to monitor the site's safety.
Mixing a radioactive substance with a non-radioactive substance (a 'carrier') will decrease its specific activity (activity per gram) but will not change its total activity (total decays per second).
In biological and environmental research, isotopes with a known specific activity are used as 'tracers'. By following the radioactivity, scientists can track the path and metabolic fate of a substance through a complex system.
Depleted uranium, a byproduct of uranium enrichment, has a lower specific activity than natural uranium because it has had most of the more radioactive U-235 isotope removed. It is very dense and is used in armor plating and munitions.
Conversely, enriched uranium, used in nuclear reactors and weapons, has a higher proportion of the U-235 isotope, giving it a much higher specific activity than natural uranium.
Many ionization-type smoke detectors contain a tiny amount of the radioactive isotope Americium-241, an isotope with a very high specific activity. The alpha particles it emits ionize the air in a chamber, and smoke particles disrupt this process, triggering the alarm.
In the early 20th century, watch dials were painted with radium-laced paint to make them glow. The workers, mostly young women, ingested radium by licking their brushes to a fine point. The high specific activity of radium led to severe health consequences, and their story was crucial in establishing worker protection laws.
Specific energy is a related but different concept, referring to the energy released per unit mass of a substance, often used for fuels (e.g., Joules/kg). Specific activity refers only to the rate of radioactive decay.
Medical isotopes are often produced in nuclear reactors or particle accelerators. The goal is to produce the desired isotope with a very high specific activity, separating it from the original target material and any byproducts.
This is a common laboratory technique for measuring the activity of low-energy beta-emitting isotopes. The sample is mixed with a 'scintillation cocktail' that emits flashes of light when it interacts with radiation. The rate of flashes gives the activity, which can be used to calculate specific activity.
NORM stands for Naturally Occurring Radioactive Material. TENORM is Technologically Enhanced NORM, where industrial processes (like mining or oil and gas extraction) concentrate these natural materials, increasing their specific activity and potentially creating a radiation hazard.
Specific Activity is also known as 'activity concentration by mass'. For fluids and gases, 'activity concentration by volume' (e.g., Bq/L or Bq/m³) is also commonly used.