Gemstone irradiation
Encyclopedia
The gemstone irradiation is a process in which a gemstone
is artificially irradiated
in order to enhance its optical properties. High levels of ionizing radiation
can change the atomic structure of the gemstone's crystal lattice, which in turn alters the optical properties within it. As a result, the gemstone's color may be significantly altered or the visibility of its inclusions may be lessened. The process, widely practised in jewelry industry, is done in either a nuclear reactor
for neutron
bombardment, a particle accelerator
for electron
bombardment, or a gamma ray
facility using the radioactive isotope cobalt-60
. The irradiation enabled creation of certain gemstone colors that do not exist or are extremely rare in nature.
The term irradiation is a very broad one, which covers bombardment by subatomic particle
s as well as the use of the full range of electromagnetic radiation
, including (in order of increasing frequency
and decreasing wavelength
) infrared radiation
, visible light
, ultraviolet radiation
, X-ray
s and gamma ray
s.
Certain natural gemstone colors, such as blue-to-green colors in diamond
s, are the results of the exposure to natural radiation in the earth, which is usually alpha
or beta particle
. The limited penetrating ability of these particles result in partial coloring of the diamond's surface. Only high-energy radiation such as gamma ray or neutron
can produce fully saturated body colors, and the sources of these types of radiation are rare in nature, which necessitates the artificial treatment in jewelry industry.
Irradiation, particularly when done in a nuclear reactor, can make gemstones slightly radioactive, so they are typically set aside for a couple of months to allow any residual radioactivity to decay
. The first documented artificially irradiated gemstone was created by English chemist Sir William Crookes in 1905, by burying a diamond in powedered radium bromide
. After having been kept there for 16 months, the previously colorless diamond became green. This method produced a dangerously high degree of long-term residual radioactivity and is no longer in use. However, radium-treated green diamonds are still occasionally found in markets, which can be detected by a Geiger counter
or by making autoradiograph
s on photographic film
s.
The concerns for possible health risks related to the residual radioactivity of the gemstones led to government regulations in many countries. In the United States, the Nuclear Regulatory Commission
(NRC) has set strict limits on the allowable levels of residual radioactivity before an irradiated gemstone can be distributed in the country. All neutron- or electron beam-irradiated gemstones must be tested by an NRC-licensee prior to release for sales. In India, the Bhabha Atomic Research Centre
started irradiating gemstones in the early 1970s. In Thailand, the Office of Atoms for Peace
(OAP) conducts the process for private sectors, irradiating 413 kilograms (910.5 lb) of gemstones from 1993 to 2003.
|- bgcolor=#EEDFCC
| Material || Starting color || Ending color
|-
|rowspan=3| Beryl
| Colorless
| Yellow
|-
| Blue
| Green
|-
| Colorless
(Maxixe-type)
| Blue
|-
| Diamond
|| Colorless or
yellow to brown || Green to blue
|-
| Fluorite
|| Colorless || Various
|-
| Pearl
|| Light colors || Gray to black
or gray-blue
|-
| Quartz
|| Colorless to yellow
or pale green || Brown, amethyst
,
"smoky", rose
|-
|rowspan=2| Topaz
| Yellow to orange
| Intensify colors
|-
| Colorless to pale blue
| Brown, blue, green
|-
|rowspan=2| Tourmaline
| Colorless to
pale colors
| Yellow, brown,
pink, red,
green-red (bicolor)
|-
| Blue
| Purple
|-
| Zircon
|| Colorless || Brown to red
|- bgcolor=#EEDFCC
| colspan=3 |Source:
|}
Gemstone
A gemstone or gem is a piece of mineral, which, in cut and polished form, is used to make jewelry or other adornments...
is artificially irradiated
Irradiation
Irradiation is the process by which an object is exposed to radiation. The exposure can originate from various sources, including natural sources. Most frequently the term refers to ionizing radiation, and to a level of radiation that will serve a specific purpose, rather than radiation exposure to...
in order to enhance its optical properties. High levels of ionizing radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
can change the atomic structure of the gemstone's crystal lattice, which in turn alters the optical properties within it. As a result, the gemstone's color may be significantly altered or the visibility of its inclusions may be lessened. The process, widely practised in jewelry industry, is done in either a nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
for neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
bombardment, a particle accelerator
Particle accelerator
A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...
for electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
bombardment, or a gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
facility using the radioactive isotope cobalt-60
Cobalt-60
Cobalt-60, , is a synthetic radioactive isotope of cobalt. Due to its half-life of 5.27 years, is not found in nature. It is produced artificially by neutron activation of . decays by beta decay to the stable isotope nickel-60...
. The irradiation enabled creation of certain gemstone colors that do not exist or are extremely rare in nature.
Radioactivity and regulations
Subatomic particle
In physics or chemistry, subatomic particles are the smaller particles composing nucleons and atoms. There are two types of subatomic particles: elementary particles, which are not made of other particles, and composite particles...
s as well as the use of the full range of electromagnetic radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
, including (in order of increasing frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
and decreasing wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
) infrared radiation
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
, visible light
Visible spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm. In terms of...
, ultraviolet radiation
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
, X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s and gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
s.
Certain natural gemstone colors, such as blue-to-green colors in diamond
Diamond
In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...
s, are the results of the exposure to natural radiation in the earth, which is usually alpha
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...
or beta particle
Beta particle
Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay...
. The limited penetrating ability of these particles result in partial coloring of the diamond's surface. Only high-energy radiation such as gamma ray or neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
can produce fully saturated body colors, and the sources of these types of radiation are rare in nature, which necessitates the artificial treatment in jewelry industry.
Irradiation, particularly when done in a nuclear reactor, can make gemstones slightly radioactive, so they are typically set aside for a couple of months to allow any residual radioactivity to decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
. The first documented artificially irradiated gemstone was created by English chemist Sir William Crookes in 1905, by burying a diamond in powedered radium bromide
Radium bromide
Radium bromide is the bromide salt of radium, with the formula RaBr2. It is produced during the separation of radium from uranium ore. This inorganic compound was discovered by Pierre and Marie Curie in 1898, which sparked a huge interest in radiochemistry, especially radiotherapy...
. After having been kept there for 16 months, the previously colorless diamond became green. This method produced a dangerously high degree of long-term residual radioactivity and is no longer in use. However, radium-treated green diamonds are still occasionally found in markets, which can be detected by a Geiger counter
Geiger counter
A Geiger counter, also called a Geiger–Müller counter, is a type of particle detector that measures ionizing radiation. They detect the emission of nuclear radiation: alpha particles, beta particles or gamma rays. A Geiger counter detects radiation by ionization produced in a low-pressure gas in a...
or by making autoradiograph
Autoradiograph
An autoradiograph is an image on an x-ray film or nuclear emulsion produced by the pattern of decay emissions from a distribution of a radioactive substance...
s on photographic film
Photographic film
Photographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and resolution of the film...
s.
The concerns for possible health risks related to the residual radioactivity of the gemstones led to government regulations in many countries. In the United States, the Nuclear Regulatory Commission
Nuclear Regulatory Commission
The Nuclear Regulatory Commission is an independent agency of the United States government that was established by the Energy Reorganization Act of 1974 from the United States Atomic Energy Commission, and was first opened January 19, 1975...
(NRC) has set strict limits on the allowable levels of residual radioactivity before an irradiated gemstone can be distributed in the country. All neutron- or electron beam-irradiated gemstones must be tested by an NRC-licensee prior to release for sales. In India, the Bhabha Atomic Research Centre
Bhabha Atomic Research Centre
The Bhabha Atomic Research Centre is India's primary nuclear research facility based in Mumbai. It has a number of nuclear reactors, all of which are used for India's nuclear power and research programme.- History :...
started irradiating gemstones in the early 1970s. In Thailand, the Office of Atoms for Peace
Office of Atoms for Peace
The Office of Atoms for Peace of Thailand located in Chatuchak district, Bangkok, Thailand, was established in 1961 as the Office of Atomic Energy for Peace, the OAP serves as the main authority in nuclear research in Thailand. The OAP employs approximately 400 people...
(OAP) conducts the process for private sectors, irradiating 413 kilograms (910.5 lb) of gemstones from 1993 to 2003.
Materials and results
various gemstone materials|- bgcolor=#EEDFCC
| Material || Starting color || Ending color
|-
|rowspan=3| Beryl
Beryl
The mineral beryl is a beryllium aluminium cyclosilicate with the chemical formula Be3Al26. The hexagonal crystals of beryl may be very small or range to several meters in size. Terminated crystals are relatively rare...
| Colorless
| Yellow
|-
| Blue
| Green
|-
| Colorless
(Maxixe-type)
| Blue
|-
| Diamond
Diamond
In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...
|| Colorless or
yellow to brown || Green to blue
|-
| Fluorite
Fluorite
Fluorite is a halide mineral composed of calcium fluoride, CaF2. It is an isometric mineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon...
|| Colorless || Various
|-
| Pearl
Pearl
A pearl is a hard object produced within the soft tissue of a living shelled mollusk. Just like the shell of a mollusk, a pearl is made up of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other...
|| Light colors || Gray to black
or gray-blue
|-
| Quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
|| Colorless to yellow
or pale green || Brown, amethyst
Amethyst
Amethyst is a violet variety of quartz often used in jewelry. The name comes from the Ancient Greek ἀ a- and μέθυστος methustos , a reference to the belief that the stone protected its owner from drunkenness; the ancient Greeks and Romans wore amethyst and made drinking vessels of it in the belief...
,
"smoky", rose
|-
|rowspan=2| Topaz
Topaz
Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al2SiO42. Topaz crystallizes in the orthorhombic system and its crystals are mostly prismatic terminated by pyramidal and other faces.-Color and varieties:...
| Yellow to orange
| Intensify colors
|-
| Colorless to pale blue
| Brown, blue, green
|-
|rowspan=2| Tourmaline
Tourmaline
Tourmaline is a crystal boron silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classified as a semi-precious stone and the gem comes in a wide variety of colors...
| Colorless to
pale colors
| Yellow, brown,
pink, red,
green-red (bicolor)
|-
| Blue
| Purple
|-
| Zircon
Zircon
Zircon is a mineral belonging to the group of nesosilicates. Its chemical name is zirconium silicate and its corresponding chemical formula is ZrSiO4. A common empirical formula showing some of the range of substitution in zircon is 1–x4x–y...
|| Colorless || Brown to red
|- bgcolor=#EEDFCC
| colspan=3 |Source:
|}
The most commonly irradiated gemstone is topaz
Topaz
Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al2SiO42. Topaz crystallizes in the orthorhombic system and its crystals are mostly prismatic terminated by pyramidal and other faces.-Color and varieties:...
, which becomes blue after the process. Blue topaz is very rare in nature and almost always the result of artificial irradiation. According to the American Gem Trade Association, approximately 30 million carats (6000 kg (13,227.7 lb)) of topaz are irradiated every year globally, 40 percent of which were done in the United States as of 1988. As of 2011, no topaz is neutron irradiated in the US; major treatment areas are Germany and Poland. A lot of linear accelerated treatment is done in Bangkok.
Diamonds are usually irradiated to become yellow, blue-green or green, although other colors are possible.
Quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
may be irradiated to produce amethyst
Amethyst
Amethyst is a violet variety of quartz often used in jewelry. The name comes from the Ancient Greek ἀ a- and μέθυστος methustos , a reference to the belief that the stone protected its owner from drunkenness; the ancient Greeks and Romans wore amethyst and made drinking vessels of it in the belief...
and other colours.
Colorless beryl
Beryl
The mineral beryl is a beryllium aluminium cyclosilicate with the chemical formula Be3Al26. The hexagonal crystals of beryl may be very small or range to several meters in size. Terminated crystals are relatively rare...
s, also called goshenite, become pure yellow when irradiated, which are called golden beryl or heliodor.
Pearl
Pearl
A pearl is a hard object produced within the soft tissue of a living shelled mollusk. Just like the shell of a mollusk, a pearl is made up of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other...
s are irradiated to produce gray blue or gray-to-black colors. Methods of using a cobalt-60 gamma ray facility to darken white Akoya pearls were patented in the early 1960s. But the gamma ray treatment does not alter the color of the pearl's nacre
Nacre
Nacre , also known as mother of pearl, is an organic-inorganic composite material produced by some mollusks as an inner shell layer; it is also what makes up pearls. It is very strong, resilient, and iridescent....
, therefore is not effective if the pearl has a thick or non-transparent nacre. Most black pearls available in markets prior to the late 1970s had been either irradiated or dyed.
Uniformity of coloration
Gemstones that have been subjected to artificial irradiation generally show no visible evidence of the process, although some diamonds irradiated in an electron beam may show color concentrations around the culetCulet
In gemology, a culet is a flat face on the bottom of a gemstone.During the 14th century, after the adoption of the table cut, a further facet was added to the bottom of the cut parallel to the surface of the table. The term used for these bottom facets derives from the latin word for bottom,...
or along the keel line.
In topaz, some irradiation sources may produce mixtures of blue and yellow-to-brown colors, so heating is required as an additional procedure to remove the yellowish color.
Color stability
In some cases, the new colors induced by artificial irradiation may fade rapidly when exposed to light or gentle heat, so some laboratories submit them to a "fade test" to determine color stability.Sometimes colorless or pink beryls become deep blue upon irradiation, which are called Maxixe-type beryl. However, the color easily fades when exposed to heat or light, so it has no practical jewelry application.