Gemstone irradiation

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Gemstone irradiation is a process in which a gemstone is exposed to artificial radiation 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. [1] As a result, the gem­stone's color may be significantly altered or the visibility of its inclusions may be lessened.

Contents

The process, widely practiced in jewelry industry, [2] 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. [1] [3] The irradiation treatment has enabled the creation of gemstone colors that do not exist or are extremely rare in nature. [1] However, the process, particularly when done in a nuclear reactor, can make the gemstones radioactive. Health risks related to the residual radioactivity in the irradiated gemstones have led to government regulations in many countries.

Radioactivity and regulations

Alpha (a) radiation is stopped by a sheet of paper. Beta (b) radiation is halted by an aluminium plate. Gamma (g) radiation is eventually absorbed as it penetrates a dense material. Neutron (n) radiation consists of free neutrons that are blocked by light elements, which slow and/or capture them. Alfa beta gamma neutron radiation.svg
Alpha (α) radiation is stopped by a sheet of paper. Beta (β) radiation is halted by an aluminium plate. Gamma (γ) radiation is eventually absorbed as it penetrates a dense material. Neutron (n) radiation consists of free neutrons that are blocked by light elements, which slow and/or capture them.

The term irradiation broadly refers to the exposure of matter to subatomic particles or electromagnetic radiation across the entire spectrum, which includes—in order of increasing frequency and decreasing wavelength—infrared, visible light, ultraviolet, X-rays, and gamma rays. [4] Certain natural gemstone colors, such as blue-to-green colors in diamonds [5] or red colors in zircon, [6] are the results of the exposure to natural radiation in the earth, which is usually alpha or beta particle. [5] The limited penetrating ability of these particles result in partial coloring of the gemstone's surface. [5] Only high-energy radiation such as gamma ray or neutron can produce fully saturated body colors, [5] and the sources of these types of radiation are rare in nature, which necessitates the artificial treatment in jewelry industry. The process, particularly when done in a nuclear reactor for neutron bombardment, can make gemstones radioactive. [7] [a] Neutrons penetrate the gemstones easily and may cause visually pleasing uniform coloration, but also penetrate into the atomic nucleus and cause the excited nucleus to decay, thereby inducing radioactivity. [8] So neutron-treated gemstones are set aside afterward for a couple of months to several years to allow any residual radioactivity to decay, [3] [9] until they reach a safe level of less than 1 nanocurie per gram (37  Bq /g) to 2.7 nanocuries per gram (100 Bq/g) depending on the country. [b]

The first documented artificially irradiated gemstone was created by English chemist William Crookes in 1905 by burying a colorless diamond in powdered radium bromide. [10] [11] After having been kept there for 16 months, the diamond became olive green. [10] This method produces a dangerous degree of long-term residual radioactivity and is no longer in use. [12] Some of these radium-treated diamonds—which are still occasionally put on sale and can be detected by particle detectors such as the Geiger counter, [12] the scintillation counter, [13] or the semiconductor detector [13] —are so high in radiation emission that they may darken photographic film in minutes. [14]

The concerns for possible health risks related to the residual radioactivity of the irradiated gemstones led to government regulations in many countries. [1] 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. [3] All neutron- or electron beam-irradiated gemstones must be tested by an NRC-licensee prior to release for sales; however, when treated in a cobalt-60 gamma ray facility, gemstones do not become radioactive and thus are not under NRC authority. [3] In India, the Board of Radiation and Isotope Technology (BRIT), the industrial unit of the Department of Atomic Energy, conducts the process for private sectors. [15] In Thailand, the Office of Atoms for Peace (OAP) did the same, irradiating 413 kilograms (911 lb) of gemstones from 1993 to 2003, [16] until the Thailand Institute of Nuclear Technology was established in 2006 and housed the Gem Irradiation Center to provide the service. [17] [18]

Materials and results

Effects of irradiation on
various gemstone materials
MaterialStarting colorEnding color
Amber Light yellowOrangey red, [19]
orangey yellow [19]
Beryl ColorlessYellow [20]
BlueGreen [20]
Colorless
to pale pink
(Maxixe-type)		Deep blue [1]
Diamond Colorless or
yellow
to brown		Green to blue [21]
Fluorite ColorlessVarious [20]
Pearl Light colorsBrown, [20]
gray to black [20]
or gray-blue [22]
Quartz Colorless to
yellow or
pale green		 Amethyst, [21] [20]
brown, [20] rose, [20]
"smoky" (light gray) [21]
Sapphire Pink with
blue tint		Tint removed [23]
Topaz Yellow
to orange		Intensify colors [20]
Colorless
to
pale blue		Brown, [20]
dark blue, [24]
green, [20]
sky blue [24]
Tourmaline Colorless
to
pale colors		Brown, [20]
green-red (bicolor), [20]
intense pink, [18]
pink, [18] [20] red, [20]
yellowish orange [18]
PinkIntense pink, [18]
orangey pink [18]
BluePurple [20]
Zircon ColorlessBrown to red [20]
London blue topaz.JPG
Lepidolite-Topaz-vlt-6b.jpg
London Blue (left), one of the neutron-bombarded varieties of topaz, [24] compared to a natural blue topaz (right); Intensely blue topaz does not exist in nature and is the result of artificial irradiation. [25]

The most commonly irradiated gemstone is topaz, which usually becomes blue after the process. [3] Intensely blue topaz does not exist in nature and is the result of artificial irradiation. [25] According to the American Gem Trade Association, approximately 30 million carats (6,000 kg or 13,000 lb) of topaz are irradiated every year globally, 40 percent of which were done in the United States as of 1988. [26] Dark-blue varieties of topaz, including American Super Blue and London Blue, are the results of neutron bombardment, [24] while lighter sky-blue ones are often those of electron bombardment. [24] Swiss Blue, subtly lighter than the US variety, is the result of a combination of the two methods. [24]

Diamonds are mainly irradiated to become blue-green or green, although other colors are possible. [27] When light-to-medium-yellow diamonds are treated with gamma rays they may become green; with a high-energy electron beam, blue. [21] The difference in results may be caused by local heating of the stones, which occurs when the latter method is used. [21]

Colorless beryls, also called goshenite, become pure yellow when irradiated, which are called golden beryl or heliodor. [1] Quartz crystals turn "smoky" or light gray upon irradiation if they contain an aluminum impurity, or amethyst if small amounts of iron are present in them; either of the results can be obtained from natural radiation as well. [28]

Pearls are irradiated to produce gray blue or gray-to-black colors. [22] Methods of using a cobalt-60 gamma ray facility to darken white Akoya pearls were patented in the early-1960s. [29] But the gamma ray treatment does not alter the color of the pearl's nacre, therefore is not effective if the pearl has a thick or non-transparent nacre. [29] Most black pearls available in markets prior to the late-1970s had been either irradiated or dyed. [29]

Uniformity of coloration

Gemstones that have been subjected to artificial irradiation generally show no visible evidence of the process, [30] although some diamonds irradiated in an electron beam may show color concentrations around the culet or along the keel line. [30]

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. [31] 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. [1]

Notes

a. ^ Generally speaking, an energy of at least 10 MeV is needed to induce radioactivity in a material. [32]

b. ^ As of 1987, most developed countries regarded 2 nanocuries per gram (74 Bq/g) as safe to release to the public while the U.S. federal release limits for most nuclides were 1 nanocurie per gram (37 Bq/g) or less, and that of the United Kingdom was 2.7 nanocuries per gram (100 Bq/g). [33] As of 2022, the release limit of the European Union is 2.7 nanocuries per gram (100 Bq/g). [9]

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<span class="mw-page-title-main">Amethyst</span> Mineral, quartz variety

Amethyst is a violet variety of quartz. The name comes from the Koine Greek αμέθυστος amethystos from α-a-, "not" and μεθύσκωmethysko / μεθώmetho, "intoxicate", a reference to the belief that the stone protected its owner from drunkenness. Ancient Greeks wore amethyst and carved drinking vessels from it in the belief that it would prevent intoxication.

<span class="mw-page-title-main">Beryl</span> Gemstone: beryllium aluminium silicate

Beryl ( BERR-əl) is a mineral composed of beryllium aluminium silicate with the chemical formula Be3Al2Si6O18. Well-known varieties of beryl include emerald and aquamarine. Naturally occurring hexagonal crystals of beryl can be up to several meters in size, but terminated crystals are relatively rare. Pure beryl is colorless, but it is frequently tinted by impurities; possible colors are green, blue, yellow, pink, and red (the rarest). It is an ore source of beryllium.

<span class="mw-page-title-main">Emerald</span> Green gemstone, a beryl variety

Emerald is a gemstone and a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium or sometimes vanadium. Beryl has a hardness of 7.5–8 on the Mohs scale. Most emeralds have many inclusions, so their toughness (resistance to breakage) is classified as generally poor. Emerald is a cyclosilicate.

<span class="mw-page-title-main">Gemstone</span> Piece of mineral crystal used to make jewelry

A gemstone is a piece of mineral crystal which, when cut or polished, is used to make jewelry or other adornments. Certain rocks and occasionally organic materials that are not minerals may also be used for jewelry and are therefore often considered to be gemstones as well. Most gemstones are hard, but some softer minerals such as brazilianite may be used in jewelry because of their color or luster or other physical properties that have aesthetic value. However, generally speaking, soft minerals are not typically used as gemstones by virtue of their brittleness and lack of durability.

<span class="mw-page-title-main">Sapphire</span> Gem variety of corundum

Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide (α-Al2O3) with trace amounts of elements such as iron, titanium, cobalt, lead, chromium, vanadium, magnesium, boron, and silicon. The name sapphire is derived from the Latin word sapphirus, itself from the Greek word sappheiros (σάπφειρος), which referred to lapis lazuli. It is typically blue, but natural "fancy" sapphires also occur in yellow, purple, orange, and green colors; "parti sapphires" show two or more colors. Red corundum stones also occur, but are called rubies rather than sapphires. Pink-colored corundum may be classified either as ruby or sapphire depending on the locale. Commonly, natural sapphires are cut and polished into gemstones and worn in jewelry. They also may be created synthetically in laboratories for industrial or decorative purposes in large crystal boules. Because of the remarkable hardness of sapphires – 9 on the Mohs scale (the third-hardest mineral, after diamond at 10 and moissanite at 9.5) – sapphires are also used in some non-ornamental applications, such as infrared optical components, high-durability windows, wristwatch crystals and movement bearings, and very thin electronic wafers, which are used as the insulating substrates of special-purpose solid-state electronics such as integrated circuits and GaN-based blue LEDs. Sapphire is the birthstone for September and the gem of the 45th anniversary. A sapphire jubilee occurs after 65 years.

<span class="mw-page-title-main">Topaz</span> Silicate mineral

Topaz is a silicate mineral made of aluminum and fluorine with the chemical formula Al2SiO4(F, OH)2. It is used as a gemstone in jewelry and other adornments. Common topaz in its natural state is colorless, though trace element impurities can make it pale blue or golden brown to yellow-orange. Topaz is often treated with heat or radiation to make it a deep blue, reddish-orange, pale green, pink, or purple.

<span class="mw-page-title-main">Tourmaline</span> Cyclosilicate mineral group

Tourmaline is a crystalline silicate mineral group in which boron is compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. This gemstone comes in a wide variety of colors.

<span class="mw-page-title-main">Beta particle</span> Ionizing radiation

A beta particle, also called beta ray or beta radiation, is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus, known as beta decay. There are two forms of beta decay, β− decay and β+ decay, which produce electrons and positrons, respectively.

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<span class="mw-page-title-main">Neutron radiation</span> Ionizing radiation that presents as free neutrons

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Irradiation is the process by which an object is exposed to radiation. An irradiator is a device used to expose an object to radiation, notably gamma radiation, for a variety of purposes. Irradiators may be used for sterilizing medical and pharmaceutical supplies, preserving foodstuffs, alteration of gemstone colors, studying radiation effects, eradicating insects through sterile male release programs, or calibrating thermoluminescent dosimeters (TLDs).

<span class="mw-page-title-main">Demantoid</span> Green gemstone variety of the mineral andradite

Demantoid is the green gemstone variety of the mineral andradite, a member of the garnet group of minerals. Andradite is a calcium- and iron-rich garnet. The chemical formula is Ca3Fe2(SiO4)3 with chromium substitution as the cause of the demantoid green color. Ferric iron is the cause of the yellow in the stone.

Diamond enhancements are specific treatments, performed on natural diamonds, which are designed to improve the visual gemological characteristics of the diamond in one or more ways. These include clarity treatments such as laser drilling to remove black carbon inclusions, fracture filling to make small internal cracks less visible, color irradiation and annealing treatments to make yellow and brown diamonds a vibrant fancy color such as vivid yellow, blue, or pink.

<span class="mw-page-title-main">Neutron activation</span> Induction of radioactivity by neutron radiation

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<span class="mw-page-title-main">Radiochemistry</span> Chemistry of radioactive materials

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Induced radioactivity, also called artificial radioactivity or man-made radioactivity, is the process of using radiation to make a previously stable material radioactive. The husband-and-wife team of Irène Joliot-Curie and Frédéric Joliot-Curie discovered induced radioactivity in 1934, and they shared the 1935 Nobel Prize in Chemistry for this discovery.

Iodine-125 (125I) is a radioisotope of iodine which has uses in biological assays, nuclear medicine imaging and in radiation therapy as brachytherapy to treat a number of conditions, including prostate cancer, uveal melanomas, and brain tumors. It is the second longest-lived radioisotope of iodine, after iodine-129.

<span class="mw-page-title-main">Goshenite (gem)</span> Variety of beryl

Goshenite is a colorless gem variety of beryl. It is called the mother of all gemstones because it can be transformed into other like emerald, morganite, or bixbite. Goshenite is also referred to as the purest form of beryl since there are generally no other elements present in the stone. The gem is used as imitation for diamond or emerald by adding colored foil on it.

References

Citations

  1. 1 2 3 4 5 6 7 Hurlbut & Kammerling 1991 , p. 170
  2. ↑ Omi & Rela 2007 , p. 1
  3. 1 2 3 4 5 Nuclear Regulatory Commission 2019
  4. ↑ Nassau 1980 , p. 343
  5. 1 2 3 4 King & Shigley 2003 , p. 48
  6. ↑ Fielding 1970 , pp. 428–429
  7. ↑ Hurlbut & Kammerling 1991 , p. 172
  8. ↑ Nassau 1980 , p. 346
  9. 1 2 Schröck 2022
  10. 1 2 Tilden 1917 , pp.  145-146
  11. ↑ Hurlbut & Kammerling 1991 , p. 158
  12. 1 2 Hurlbut & Kammerling 1991 , p. 216
  13. 1 2 Ashbaugh III 1988 , p. 207
  14. ↑ Crowningshield 1981 , p. 216
  15. ↑ Parthasarathy 2008
  16. ↑ Office of Atoms for Peace 2006
  17. ↑ Journal of Physics: Conference Series 2019 , pp. 1–2
  18. 1 2 3 4 5 6 Suwanmanee et al. 2021 , p. 517
  19. 1 2 Li, Wang & Chen 2022 , p. 133
  20. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Ashbaugh III 1988 , p. 201
  21. 1 2 3 4 5 Rossman 1981 , p. 70
  22. 1 2 Sofianides & Harlow 1991 , p. 178
  23. ↑ Soonthorntantikul, Vertriest & Palke 2023 , p. 160
  24. 1 2 3 4 5 6 Jewelers Circular Keystone 1990 , p. 39
  25. 1 2 Sofianides & Harlow 1991 , p. 82
  26. ↑ Ashbaugh III 1988 , p. 205
  27. ↑ Skuratowicz & Nash 2005 , p. 13
  28. ↑ Rossman 1981 , p. 69
  29. 1 2 3 Department of Geological Sciences 1998
  30. 1 2 Hurlbut & Kammerling 1991 , p. 127
  31. ↑ Hurlbut & Kammerling 1991 , p. 57
  32. ↑ Thomadsen et al. 2014
  33. ↑ Ashbaugh III 1988 , p. 212

Works cited

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