Krypton-85 (⁸⁵Kr) is a

radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferr ...

krypton Krypton (from grc, κρυπτός, translit=kryptos 'the hidden one') is a chemical element with the symbol Kr and atomic number 36. It is a colorless, odorless, tasteless noble gas that occurs in trace amounts in the atmosphere and is often ...

. Krypton-85 has a

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...

of 10.756 years and a maximum

decay energy The decay energy is the energy change of a nucleus having undergone a radioactive decay. Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting ionizing particles and radiation. This decay, or loss of energy ...

of 687

keV Kev can refer to: Given name * Kev Adams, French comedian, actor, screenwriter and film producer born Kevin Smadja in 1991 * Kevin Kev Carmody (born 1946), Indigenous Australian singer-songwriter * Kev Coghlan (born 1988), Scottish Grand Prix moto ...

. It decays into stable

rubidium Rubidium is the chemical element with the symbol Rb and atomic number 37. It is a very soft, whitish-grey solid in the alkali metal group, similar to potassium and caesium. Rubidium is the first alkali metal in the group to have a density higher ...

-85. Its most common decay (99.57%) is by beta particle emission with maximum energy of 687

and an average energy of 251 keV. The second most common decay (0.43%) is by beta particle emission (maximum energy of 173 keV) followed by

gamma ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...

emission (energy of 514 keV). Other decay modes have very small probabilities and emit less energetic gamma rays. Krypton-85 is mostly synthetic, though it is produced naturally in

trace Trace may refer to: Arts and entertainment Music * ''Trace'' (Son Volt album), 1995 * ''Trace'' (Died Pretty album), 1993 * Trace (band), a Dutch progressive rock band * ''The Trace'' (album) Other uses in arts and entertainment * ''Trace'' ...

quantities by

cosmic ray spallation Cosmic ray spallation, also known as the x-process, is a set of naturally occurring nuclear reactions causing nucleosynthesis; it refers to the formation of chemical elements from the impact of cosmic rays on an object. Cosmic rays are highly ener ...

. In terms of

radiotoxicity Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...

, 440 Bq of ⁸⁵Kr is equivalent to 1 Bq of

radon-222 Radon-222 (222Rn, Rn-222, historically radium emanation or radon) is the most stable isotope of radon, with a half-life of approximately 3.8 days. It is transient in the decay chain of primordial uranium-238 and is the immediate decay product of ...

, without considering the rest of the radon decay chain.

Presence in Earth atmosphere

Natural production

Krypton-85 is produced in small quantities by the interaction of

cosmic ray Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...

s with stable

krypton-84 There are 34 known isotopes of krypton (36Kr) with atomic mass numbers from 69 through 102. Naturally occurring krypton is made of five stable isotopes and one () which is slightly radioactive with an extremely long half-life, plus traces of radio ...

in the atmosphere. Natural sources maintain an equilibrium inventory of about 0.09 PBq in the atmosphere.

Anthropogenic production

As of 2009 the total amount in the atmosphere is estimated at 5500 PBq due to anthropogenic sources. At the end of the year 2000, it was estimated to be 4800 PBq, and in 1973, an estimated 1961 PBq (53 megacuries). The most important of these human sources is

nuclear fuel reprocessing Nuclear reprocessing is the chemical separation of fission products and actinides from spent nuclear fuel. Originally, reprocessing was used solely to extract plutonium for producing nuclear weapons. With commercialization of nuclear power, the ...

, as krypton-85 is one of the seven common

medium-lived fission product Long-lived fission products (LLFPs) are radioactive materials with a long half-life (more than 200,000 years) produced by nuclear fission of uranium and plutonium. Because of their persistent radiotoxicity it is necessary to isolate them from man ...

s. Nuclear fission produces about three atoms of krypton-85 for every 1000 fissions (i.e., it has a fission yield of 0.3%). Most or all of this krypton-85 is retained in the

spent nuclear fuel Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor (usually at a nuclear power plant). It is no longer useful in sustaining a nuclear reaction in an ordinary thermal reactor an ...

rods; spent fuel on discharge from a reactor contains between 0.13–1.8 PBq/Mg of krypton-85. Some of this spent fuel is reprocessed. Current nuclear reprocessing releases the gaseous ⁸⁵Kr into the atmosphere when the spent fuel is dissolved. It would be possible in principle to capture and store this krypton gas as

nuclear waste Radioactive waste is a type of hazardous waste that contains radioactive material. Radioactive waste is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, rare-earth mining, and nuclear weapons r ...

or for use. The cumulative global amount of krypton-85 released from reprocessing activity has been estimated as 10,600 PBq as of 2000. The global inventory noted above is smaller than this amount due to radioactive decay; a smaller fraction is dissolved into the deep oceans. Other man-made sources are small contributors to the total. Atmospheric

nuclear weapons test Nuclear weapons tests are experiments carried out to determine nuclear weapons' effectiveness, yield, and explosive capability. Testing nuclear weapons offers practical information about how the weapons function, how detonations are affected by ...

s released an estimated 111–185 PBq. The 1979 accident at the Three Mile Island nuclear power plant released about . The Chernobyl accident released about 35 PBq, and the Fukushima Daiichi accident released an estimated 44–84 PBq. The average atmospheric concentration of krypton-85 was approximately 0.6 Bq/m³ in 1976, and has increased to approximately 1.3 Bq/m³ as of 2005. These are approximate global average values; concentrations are higher locally around nuclear reprocessing facilities, and are generally higher in the northern hemisphere than in the southern hemisphere. For wide-area atmospheric monitoring, krypton-85 is the best indicator for clandestine plutonium separations. Krypton-85 releases increase the electrical conductivity of atmospheric air. Meteorological effects are expected to be stronger closer to the source of the emissions.

Uses in industry

Krypton-85 is used in arc discharge lamps commonly used in the entertainment industry for large HMI film lights as well as

high-intensity discharge lamp High-intensity discharge lamps (HID lamps) are a type of electrical gas-discharge lamp which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tu ...

s. The presence of krypton-85 in discharge tube of the lamps can make the lamps easy to ignite. Early experimental krypton-85 lighting developments included a railroad signal light designed in 1957 and an illuminated highway sign erected in

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...

in 1969. A 60 μCi (2.22 MBq) capsule of krypton-85 was used by the random number server HotBits (an allusion to the

radioactive element A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transfe ...

being a

quantum mechanical Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, qua ...

source of entropy), but was replaced with a 5 μCi (185 kBq)

Cs-137 Caesium-137 (), cesium-137 (US), or radiocaesium, is a radioactive isotope of caesium that is formed as one of the more common fission products by the nuclear fission of uranium-235 and other fissionable isotopes in nuclear reactors and nucl ...

source in 1998. Krypton-85 is also used to inspect aircraft components for small defects. Krypton-85 is allowed to penetrate small cracks, and then its presence is detected by autoradiography. The method is called "krypton gas penetrant imaging". The gas penetrates smaller openings than the liquids used in

dye penetrant inspection Dye penetrant inspection (DP), also called liquid penetrate inspection (LPI) or penetrant testing (PT), is a widely applied and low-cost inspection method used to check surface-breaking defects in all non-porous materials (metals, plastics, or cer ...

and

fluorescent penetrant inspection Fluorescent penetrant inspection (FPI) is a type of dye penetrant inspection in which a fluorescent dye is applied to the surface of a non-porous material in order to detect defects that may compromise the integrity or quality of the part in que ...

. Krypton-85 was used in cold-cathode voltage regulator electron tubes, such as the type 5651. Krypton-85 is also used for Industrial Process Control mainly for thickness and density measurements as an alternative to Sr-90 or

Sealed Sources for Industrial Gauging. M85K01 Series Kr-85 Beta Sources (PDF) Retrieved on 2021-09-10

References

{{Reflist Fission products Krypton-085