K-40 (Potassium-40) Radiation Safety Data

Source: Ionactive Radiation Protection Resource

K-40 (Potassium-40)

Half life: 1,300,000,000 years

Specific activity: 1.54×105 Bq/g

Decay product: Ca-40 (89%) & Ar-40 (11%) (both non-radioactive)

Significant emissions (keV) [K-40 (Potassium-40)]

In the data below, % refers to the probability of emission of a particular type of radiation at a specified energy

Gamma / x-ray: 1461 keV (11%)

Beta (Emax): 1312 keV (89%)

Electrons: 3 keV (7)%, negligible for radiation protection purposes.

Alpha particles: n/a

External exposure (in air) K-40 (Potassium-40)

The values below are specified as mSv/h for either 1 MBq of activity or an area source of 1 MBq/m2 depending on the geometry. Unless specified below, any bremsstrahlung dose rate is not specified. (HP 0.07) represents a skin dose rate and (HP 10) represents an 'at depth' tissue dose rate (> 10mm).

Point source (at 30cm)

Point source : 0.107 mSv/h (beta dose rate) [negligible above background]

Infinite place source (at 10 cm)

Beta (HP 0.07) : 0.10 mSv/h

Photon (HP 0.07) : 0.00094 mSv/h

Photons (HP 10) : 0.00088 mSv/h

External exposure (arising from personal contamination) K-40 (Potassium-40)

The values below are either for uniform contamination on the skin (for 1 kBq/cm2) or as a single droplet (1 kBq) and are specified in mSv/h. It is assumed that no PPE is being worn which would attenuate the radiation.

Uniform deposit on the skin: 1.65 mSv/h (beta dose rate)

0.05ml droplet on the skin: 1.12 mSv/h (beta dose rate)

Shielding (external radiation) K-40 (Potassium-40)

In the data below beta shielding is specified as mm of material to provide 100% absorption of the beta particle (or electron). Gamma (and x-ray) shielding is specified in terms of mm of material relating to 1 TVT or 1 HVT. The TVT is the thickness of material (in mm) which will reduce the radiation intensity (dose rate) down to 1/10 of the pre-shielded dose rate. The HVT is the thickness of material (in mm) which will reduce the radiation intensity down to 1/2 of the pre-shielded dose rate

Beta radiation (for 100% absorption)

Glass: 2.4 mm

Plastic: 4.5 mm

Typical PPE (glove): negligible absorption (but don't rely on gloves to shield for external radiation, they are a contamination control method).


Gamma / x-ray radiation (TVT and HVT)

Lead: 20mm (HVT) and 58mm (TVT)

Steel: 41mm (HVT) and 111mm (TVT)


Internal exposure [K-40 (Potassium-40)]

The data featured below is derived for employees who work with ionising radiation (and are therefore subject to dose limits specified by the Ionising Radiations Regulations 2017 in the UK, and similar regulation around the world). Whilst not directly applicable to public exposure (e.g. exposure resulting from environmental releases - either planned or accidental), the data will provide a good indication of likely exposures and is therefore adequate for general research, illustration and asking 'what if?' type questions. If you need professional advice, please consider consulting a Radiation Protection Adviser (RPA).

Internal radiation exposure generally means the intake of a radioactive substances by inhalation, ingestion or through cuts (or absorption) in the skin. For this resource assume cuts / absorption are similar to the ingestion values.

This data provides the dose delivered (committed effective dose equivalent) for an intake of [K-40 (Potassium-40)] by inhalation or ingestion to yield 1mSv effective dose. The dose value provided assumes that all the dose is delivered in the first year of intake, in reality this will vary greatly with radioisotope due to a combination of physical half-life, biological half-life and the biochemical behaviour of the particular radioactive substances in the body.

Target organ: Lungs

Inhalation dose (1 mSv): 0.335 MBq

Ingestion dose (1 mSv): 0.16 MBq

The following additional resource may be of interested:

Radioactive bananas (Banana equivalent dose) [contain naturally occurring K-40]

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