Gemstone irradiation

Process to enhance a gemstone's optical properties

Pure diamonds, before and after irradiation treatment

* A: Initial (2×2 mm size)
* B: Irradiated by different doses of 2 MeV electrons
* C: Irradiated by different doses and then annealed at 800 °C (1,470 °F)

Gemstone irradiation is a process in which a gemstone is intentionally exposed to large amounts of ionizing radiation in order to enhance its optical properties. Large amounts of ionizing radiation can rearrange the gemstone's crystal structure, altering its optical properties.[1] This can significantly alter the gemstone's color or lessen the visibility of its inclusions.

The process, widely practiced in jewelry industry,[2] is done in either a particle accelerator for electron bombardment, a gamma ray facility using the radioactive isotope cobalt-60, or a nuclear reactor for neutron bombardment.[1][3] 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

[edit]

See also: Induced radioactivity and Neutron activation

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 caused by exposure to natural radiation in the earth, which is usually alpha or beta particles.[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 rays or neutrons 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.[9] So neutron-treated gemstones are set aside afterward for a couple of months to several years to allow the residual radioactivity to decay,[3][10] 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.[12][13] After having been kept there for 16 months, the diamond became olive green.[12] This method produces a dangerous degree of long-term radioactive contamination and is no longer in use.[14] 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,[14] the scintillation counter,[15] or the semiconductor detector[15]—are so high in radiation emission that they may darken photographic film in minutes.[16]

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.[17] In Thailand, the Office of Atoms for Peace (OAP) did the same, irradiating 413 kilograms (911 lb) of gemstones from 1993 to 2003,[18] until the Thailand Institute of Nuclear Technology was established in 2006 and housed the Gem Irradiation Center to provide the service.[19][20]

## Materials and results

[edit]

Effects of irradiation on
various gemstone materials

Material | Starting color | Ending color
Amber | Light yellow | Orangey red,[21]
orangey yellow[21]
Beryl | Colorless  | Yellow[22]
Blue  | Green[22]
Colorless
to pale pink
(Maxixe-type) | Deep blue[1]
Diamond | Colorless or
yellow
to brown | Green to blue[23]
Fluorite | Colorless | Various[22]
Pearl | Light colors | Brown,[22]
gray to black[22]
or gray-blue[24]
Quartz | Colorless to
yellow or
pale green | Amethyst,[23][22]
brown,[22] rose,[22]
"smoky" (light gray)[23]
Sapphire | Pink with
blue tint | Tint removed[25]
Topaz | Yellow
to orange  | Intensify colors[22]
Colorless

pale blue  | Brown,[22]
dark blue,[26]
green,[22]
sky blue[26]
Tourmaline | Colorless

pale colors  | Brown,[22]
green-red (bicolor),[22]
intense pink,[20]
pink,[20][22] red,[22]
yellowish orange[20]
Pink  | Intense pink,[20]
orangey pink[20]
Blue  | Purple[22]
Zircon | Colorless | Brown to red[22]

London Blue (left), one of the neutron-bombarded varieties of topaz,[26] compared to a natural blue topaz (right). Intensely blue topaz does not exist in nature and is caused by artificial irradiation.[27]

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 caused by artificial irradiation.[27] 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.[28] Dark-blue varieties of topaz, including American Super Blue and London Blue, are caused by neutron bombardment,[26] while lighter sky-blue ones are often caused by electron bombardment.[26] Swiss Blue, subtly lighter than the US variety, is caused by a combination of the two methods.[26]

Diamonds are mainly irradiated to become blue-green or green, although other colors are possible.[29] When light-to-medium-yellow diamonds are treated with gamma rays they may become green; with a high-energy electron beam, blue.[23] The difference in results may be caused by local heating of the stones, which occurs when the latter method is used.[23]

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.[30]

Pearls are irradiated to produce gray blue or gray-to-black colors.[24] Methods of using a cobalt-60 gamma ray facility to darken white Akoya pearls were patented in the early-1960s.[31] 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.[31] Most black pearls available in markets prior to the late-1970s had been either irradiated or dyed.[31]

### Uniformity of coloration

[edit]

Gemstones that have been subjected to artificial irradiation generally show no visible evidence of the process,[32] although some diamonds irradiated in an electron beam may show color concentrations around the culet or along the keel line.[32]

### Color stability

[edit]

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.[33] 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

[edit]

1. ^ Generally speaking, either photons having energy of at least 10 MeV or neutrons are needed to induce significant radioactivity in a material.[8]
2. ^ As of 1987[update], 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).[11] As of 2022[update], the release limit of the European Union is 2.7 nanocuries per gram (100 Bq/g).[10]

## References

[edit]

### Citations

[edit]

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

### Works cited

[edit]

* Ashbaugh III, Charles E. (Winter 1988), "Gemstone Irradiation and Radioactivity", Gems & Gemology, vol. 24, no. 4, Gemological Institute of America, pp. 196–213, Bibcode:1988GemG...24..196A, doi:10.5741/GEMS.24.4.196, ISSN 0016-626X, archived (PDF) from the original on November 19, 2008, retrieved March 11, 2025
* Crowningshield, Robert (Winter 1981), "Irradiated Topaz and Radioactivity" (PDF), Gems & Gemology, vol. 17, no. 4, Gemological Institute of America, pp. 215–217, Bibcode:1981GemG...17..215C, doi:10.5741/GEMS.17.4.215, ISSN 0016-626X, archived (PDF) from the original on October 18, 2022, retrieved November 13, 2022
* Department of Geological Sciences (1998), Pearl, University of Texas at Austin, archived from the original on June 16, 2021, retrieved November 12, 2022
* Fielding, P. E. (March 1970), "The distribution of uranium, rare earths and color centers in a crystal of natural zircon" (PDF), American Mineralogist, vol. 55, no. 3–4, pp. 428–440, archived (PDF) from the original on May 6, 2022, retrieved November 21, 20223–4&rft.pages=428-440&rft.date=1970-03&rft.aulast=Fielding&rft.aufirst=P.+E.&rft_id=http://www.minsocam.org/ammin/AM55/AM55_428.pdf&rfr_id=info:sid/en.wikipedia.org:Gemstone+irradiation" class="Z3988">
* Hurlbut, Cornelius S.; Kammerling, Robert C. (1991), Gemology (PDF), Wiley-Interscience, ISBN 0-471-52667-3, archived from the original (PDF) on January 9, 2025, retrieved November 4, 2022 – via LibreTexts.
* Jewelers Circular Keystone, ed. (December 1990), "NRC Cracks Down on Irradiated Topaz", Jewelers Circular Keystone, vol. 161, no. 12, Reed Business Information, Inc. (US), p. 39, ISSN 1534-2719, archived from the original on November 13, 2022, retrieved March 11, 2025 – via Gale OneFile
* Journal of Physics: Conference Series, ed. (February 4–6, 2019), "International Nuclear Science and Technology Conference: About Thailand Institute of Nuclear Technology (Public Organization)", Journal of Physics: Conference Series, vol. 1285, no. 1, IOP Publishing Ltd, p. 011001, Bibcode:2019JPhCS1285a1001., doi:10.1088/1742-6596/1285/1/011001, ISSN 1742-6596
* King, John M.; Shigley, James E. (2003), "An Important Exhibition of Seven Rare Gem Diamonds" (PDF), in King, John M. (ed.), Gems & Gemology in Review: Colored Diamonds, Gemological Institute of America, pp. 43–49, ISBN 0-87311-052-8, archived (PDF) from the original on October 24, 2021, retrieved October 21, 2022 – via E-Library of the Dubai Municipality website.
* Li, Yan; Wang, Yamei; Chen, Quanli (Spring 2022), "Characteristics of amber with irradiation treatment" (PDF), Gems & Gemology, vol. 58, no. 1, Gemological Institute of America, pp. 133–136, ISSN 0016-626X, archived (PDF) from the original on June 4, 2022, retrieved November 13, 2022
* Nassau, K. (Fall 1980), "Irradiation-Induced Colors in Gemstones" (PDF), Gems & Gemology, vol. 16, no. 2, Gemological Institute of America, pp. 343–355, ISSN 0016-626X, archived from the original (PDF) on December 6, 2008
* Nuclear Regulatory Commission (April 2019), Backgrounder on Irradiated Gemstones, The U.S. Nuclear Regulatory Commission, archived from the original on September 1, 2022, retrieved November 12, 2022  This article incorporates public domain material from websites or documents of the United States government.
* Office of Atoms for Peace (2006), Gems Enhancement by Irradiation Technique, Office of Atoms for Peace, archived from the original on December 22, 2006, retrieved December 4, 2008
* Omi, Nelson M.; Rela, Paulo R. (2007), Gemstone Dedicated Gamma Irradiator Development: Proceedings of the INAC 2007 International Nuclear Atlantic Conference (PDF), Associação Brasileira de Energia Nuclear, ISBN 978-85-99141-02-1, archived (PDF) from the original on October 21, 2022, retrieved October 21, 2022
* Parthasarathy, K. S. (February 4, 2008), Radiation Technology in India, The Press Trust of India Ltd., archived from the original on November 12, 2022, retrieved November 12, 2022 – via Gale OneFile
* Rossman, George R. (Summer 1981), "Color in Gems: The New Technologies" (PDF), Gems & Gemology, vol. 17, no. 2, Gemological Institute of America, pp. 60–72, Bibcode:1981GemG...17...60R, doi:10.5741/GEMS.17.2.60, ISSN 0016-626X, archived from the original (PDF) on November 12, 2022
* Schröck, Thomas (August 31, 2022), "Irradiation of Gemstones", The Natural Gem, archived from the original on November 21, 2022, retrieved November 21, 2022
* Skuratowicz, Arthur Anton; Nash, Julie (2005), Working with Gemstones: A Bench Jeweler's Guide, MJSA/AJM Press, ISBN 978-0971349544
* Sofianides, Anna S.; Harlow, George E. (1991), Gems and Crystals: From the American Museum of Natural History, Simon & Schuster, ISBN 978-0671687045, retrieved September 14, 2023 – via Internet Archive
* Soonthorntantikul, Wasura; Vertriest, Wim; Palke, Aaron (Spring 2023), "Chromophore Behaviors (Including the 880 nm Absorption Band) in an Irradiated Pink Sapphire" (PDF), Gems & Gemology, vol. 59, no. 1, Gemological Institute of America, pp. 160–162, ISSN 0016-626X, archived (PDF) from the original on May 24, 2023, retrieved July 27, 2023
* Suwanmanee, Waratchanok; Sutthirat, Chakkaphan; Wanthanachaisaeng, Bhuwadol; Utapong, Teerawat (2021), "Colour Enhancement of Pink Tourmaline from Nigeria by Electron-Beam and Gamma Irradiation", The Journal of Gemmology, 37 (5), London: 514–526, Bibcode:2021JGem...37..514S, doi:10.15506/JoG.2021.37.5.514, ISSN 1355-4565, S2CID 234194204, retrieved November 13, 2022 – via ResearchGate
* Thomadsen, Bruce; Nath, Ravinder; Bateman, Fred B.; Farr, Jonathan; Glisson, Cal (November 2014), "Potential Hazard Due to Induced Radioactivity Secondary to Radiotherapy: The Report of Task Group 136 of the American Association of Physicists in Medicine", Health Physics, vol. 107, no. 5, pp. 442–460, doi:10.1097/HP.0000000000000139, PMID 25271934, S2CID 26289104
* Tilden, William A. (1917), Chemical Discovery and Invention - In the Twentieth Century, London: G. Routledge and Sons; New York: E.P. Dutton, OCLC 1041782335, retrieved October 21, 2022 – via Internet Archive This article incorporates text from this source, which is in the public domain.

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