Kr-85 (Krypton-85) Radiation Safety Data

Source: Ionactive Radiation Protection Resource

Kr-85 (Krypton-85)

Half life: 10.7 years

Specific activity: 1.45×1013 Bq/g

Decay product: Rb-85 (stable)

Significant emissions (keV) [Kr-85 (Krypton-85)]

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

Gamma / x-ray: 514 keV (<1 %)

Beta (Emax): 687 keV (100%)


Alpha particles:

Medium energy beta emitter in the form of a gas.

External exposure (in air) [Kr-85 (Krypton-85)]

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. (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 : 0.115 mSv/h (115 micro Sv/h) [via beta emissions] and 0.004 micro Sv/h [via rare gamma ray photon]

Infinite place source (at 10 cm)

Beta / electrons (HP 0.07) : n/a

Photon (HP 0.07) : n/a

Photons (HP 10) : n/a

Ionactive note on dose rates for Kr-85. Kr-85 is used in some types of high intensity discharge lamps, where the activity is typically < 500 Bq. This activity is too low to produce measurable external dose rates (individually or aggregated) and so will not be considered further. Kr-85 is also used in 'sealed sources' in the form of an encapsulated gas, where the source capsule has a thin end window allowing the beta particles to pass through. This is then housed in a steel / lead housing with a shutter which can be opened to allow the beta particles to leave the source. The complete Kr-85 sealed source 'gauge' is generally used for thickness / density measurements of thin / low density items (such as material coatings, reconstituted fabrics and leather, medical dressings and similar). The typical activity of such a gauge is 3 GBq, so the potential beta dose rate at 30cm from the gauge with the shutter open could be of the order of 345 mSv/h - however it is unlikely that occupational exposure could actually occur since the gauge shutter is normally interlocked into physical barriers which restricts access (for reasons of both radiation and conventional safety). If the barrier access points are opened then the Kr-85 shutter will close reducing the beta dose rate to background levels. [The 356 mSv/h beta dose calculated here is for a point source totally unshielded. In actual fact the beta beam will be collimated through a small aperture and so the likely beta dose will be about 1/10 of that calculated - so in the region of 35 mSv/h at 30cm].

In the case of a high activity medium energy beta emitter contained in a metal gauge, there is always the potential for bremsstrahlung x-rays. These will to some extent be shielded by the gauge exterior and shutter, but there will not be enough shielding to reduce these to background since the gauge would be too heavy (normally the gauge moves backwards and forwards at reasonable speed across the material being analysed). The bremsstrahlung x-ray photons usually present the more significant detectable radiation dose rates where persons might be located, particularly if the above mentioned barrier perimeter is located near the gauge, or where the gauge is 'offline' and being stored in a secure area.

Typically Ionactive experience is 3-10 micro Sv/h on contact with a typical Kr-85 gauge with 3 GBq of activity.

In the event of a leak the Kr-85 gas (which is an unreactive noble gas) would quickly disperse and not be easily detected during this process. A worse case scenario might be a submersion external dose rate over 1 minute. For Kr-85, if it is assumed that 1MBq is dispersed into 1m3 of air, with the body at the centre of this volume, then the dose rate per minute would be around 0.0153 micro Sv/min. If this value is factored up to a 3 GBq release into the same volume (1m3) for one minute, the dose rate would be 46 micro Sv/min. It is not realistic to calculate this over an hour as the gas would have dissipated far before the initial leak zone.

External exposure (arising from personal contamination) [Kr-85 (Krypton-85)]

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: n/a

0.05ml droplet on the skin: n/a

Kr-85 is a guess and personal contamination will not occur.

Shielding (external radiation) [Kr-85 (Krypton-85)]

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: 1mm

Plastic: 1.9mm

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

Gamma / x-ray radiation (TVT and HVT)

Lead: 6mm (HVT) and 17mm (TVT)

Steel:27(HVT) and 64mm (TVT)

Internal exposure [Kr-85 (Krypton-85)]

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 [Kr-85 (Krypton-85)] 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: n/a

Inhalation dose (1 mSv): n/a

Ingestion dose (1 mSv): n/a

The gaseous nature of Kr-85 means that inhalation and ingestion doses are meaningless. It is true that Kr-85 could be inhaled, but it would then be exhaled. It is unreactive and would not biochemically combine with other body tissues or accumulate in the body. Therefore the submersion dose rate (see above) is the most valid dosimetric value to use if there was a Kr-85 leak.

Physics is, hopefully, simple. Physicists are not

– Edward Teller -