View source for Physics:Gemstone irradiation

{{Short description|Process to enhance a gemstone's optical properties}}
{{Annotated image 4 | align=right | caption=Pure diamonds, before and after irradiation treatment<br>'''A''' Initial (2×2&nbsp;mm size)<br>'''B''' Irradiated by different doses of 2&nbsp;[[Physics:MeV|MeV]] electrons<br>'''C''' Irradiated by different doses and then annealed at {{convert|800|C}}| image=irrdiamond.jpg| width=220 | height=150 | image-width=220 | image-left=0 | image-top=0
| annotations =
{{Annotation|32|109|<span style{{=}}"color:black">'''A'''</span>}}
{{Annotation|30|38|<span style{{=}}"color:white">'''B'''</span>}}
{{Annotation|96|37|<span style{{=}}"color:white">'''B'''</span>}}
{{Annotation|169|35|<span style{{=}}"color:white">'''B'''</span>}}
{{Annotation|172|104|<span style{{=}}"color:white">'''C'''</span>}}
{{Annotation|100|107|<span style{{=}}"color:white">'''C'''</span>}}
}}
'''Gemstone irradiation''' is a process in which a [[Earth:Gemstone|gemstone]] is artificially [[Biology:Irradiation|irradiated]] in order to enhance its [[Physics:Optical properties|optical properties]]. High levels of [[Physics:Ionizing radiation|ionizing radiation]] can change the atomic structure of the gemstone's [[Physics:Crystal lattice|crystal lattice]], which in turn alters the optical properties within it.<ref name="Hurlbut p170">{{Harvnb|Hurlbut|Kammerling|1991|p=170}}</ref> As a result, the gem{{shy}}stone's color may be significantly altered or the visibility of its inclusions may be lessened. 

The process, widely practiced in jewelry industry,<ref name="Omi Rela 2021 p1">{{Harvnb|Omi|Rela|2007|p=1}}</ref> is done in either a [[Physics:Nuclear reactor|nuclear reactor]] for [[Physics:Neutron|neutron]] bombardment, a [[Physics:Particle accelerator|particle accelerator]] for [[Physics:Electron|electron]] bombard{{shy}}ment, or a [[Physics:Gamma ray|gamma ray]] facility using the radioactive isotope [[Physics:Cobalt-60|cobalt-60]].<ref name="Hurlbut p170" /><ref name="NRC 2019">{{Harvnb|Nuclear Regulatory Commission|2019}}
</ref> The irradiation treatment has enabled the creation of gemstone colors that do not exist or are extremely rare in nature.<ref name="Hurlbut p170" /> However, the process, particularly when done in a nuclear reactor, can make gemstones radioactive. Health risks related to the residual radioactivity have led to government regulations in many countries.

==Radioactivity and regulations==
[[File:Alfa beta gamma neutron radiation.svg|thumb|upright|Alpha ('''α''') radiation is [[Physics:Stopping power (particle radiation)|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'' is a broad one, which covers bombardment by [[Physics:Subatomic particle|subatomic particle]]s as well as the use of the full range of [[Physics:Electromagnetic radiation|electromagnetic radiation]], including (in order of increasing [[Physics:Frequency|frequency]] and decreasing [[Wavelength|wavelength]]) [[Physics:Infrared|infrared radiation]], [[Physics:Visible spectrum|visible light]], [[Physics:Ultraviolet|ultraviolet radiation]], [[Physics:X-ray|X-ray]]s, and [[Physics:Gamma ray|gamma ray]]s.<ref name="Nassau p343">{{Harvnb|Nassau|1980|p=343}}</ref> Certain natural gemstone colors, such as blue-to-green colors in [[Chemistry:Diamond|diamond]]s<ref name="King p48" /> or red colors in [[Chemistry:Zircon|zircon]],<ref name="Fielding p428">{{Harvnb|Fielding|1970|pp=428-429}}</ref> are the results of the exposure to natural radiation in the earth, which is usually [[Physics:Alpha particle|alpha]] or [[Physics:Beta particle|beta particle]].<ref name="King p48">{{Harvnb|King|Shigley|2003|p=48}}</ref> The limited penetrating ability of these particles result in partial coloring of the gemstone's surface.<ref name="King p48" /> Only high-energy radiation such as gamma ray or [[Physics:Neutron|neutron]] can produce fully saturated body colors,<ref name="King p48" /> 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.<ref name="Hurlbut p172">{{Harvnb|Hurlbut|Kammerling|1991|p=172}}</ref>{{Ref label|A|a|none}} Neutrons penetrate the gemstones easily and may cause visually pleasing uniform coloration, but also penetrate into the [[Physics:Atomic nucleus|atomic nucleus]] and cause the [[Physics:Excited state|excited nucleus]] to [[Physics:Radioactive decay|decay]], thereby inducing radioactivity.<ref name="Nassau p346">{{Harvnb|Nassau|1980|p=346}}</ref> So neutron-treated gemstones are set aside afterward for a couple of months to several years to allow any residual radioactivity to decay,<ref name="NRC 2019" /><ref name="Schröck 2022" /> until they reach a safe level of less than {{convert|1|nCi/g|Bq/g|lk=on}} to {{convert|2.7|nCi/g|Bq/g}} depending on the country.{{Ref label|B|b|none}}

The first documented artificially irradiated gemstone was created by English chemist Sir William Crookes in 1905 by burying a colorless diamond in powdered [[Chemistry:Radium bromide|radium bromide]].<ref name="Tilden p145">{{Harvnb|Tilden|1917|pp=[https://archive.org/details/chemicaldiscover00tildrich/page/145/mode/1up 145-146]}}</ref><ref name="Hurlbut p158">{{Harvnb|Hurlbut|Kammerling|1991|p=158}}</ref> After having been kept there for 16&nbsp;months, the diamond became olive green.<ref name="Tilden p145" /> This method produces a dangerous degree of long-term residual radioactivity and is no longer in use.<ref name="Hurlbut p216">{{Harvnb|Hurlbut|Kammerling|1991|p=216}}</ref> Some of these radium-treated diamonds—which are still occasionally put on sale and can be detected by [[Physics:Particle detector|particle detector]]s such as the [[Organization:Geiger counter|Geiger counter]],<ref name="Hurlbut p216" /> the [[Physics:Scintillation counter|scintillation counter]],<ref name="Ashbaugh 1988 p207">{{Harvnb|Ashbaugh III|1988|p=207}}</ref> or the [[Physics:Semiconductor detector|semiconductor detector]]<ref name="Ashbaugh 1988 p207"/>—are so high in radiation emission that they may darken [[Engineering:Photographic film|photographic film]] in minutes.<ref name="Crowningshield p216">{{Harvnb|Crowningshield|1981|p=216}}</ref>

The concerns for possible health risks related to the residual radioactivity of the gemstones led to government regulations in many countries.<ref name="Hurlbut p170" /> 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.<ref name="NRC 2019" /> 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.<ref name="NRC 2019" /> 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.<ref name="Parthasarathy 2008">{{Harvnb|Parthasarathy|2008}}</ref> In Thailand, the [[Organization:Office of Atoms for Peace|Office of Atoms for Peace]] (OAP) did the same, irradiating {{convert|413|kg}} of gemstones from 1993 to 2003,<ref name="OAP 2006">{{Harvnb|Office of Atoms for Peace|2006}}</ref> until the [[Organization:Thailand Institute of Nuclear Technology|Thailand Institute of Nuclear Technology]] was established in 2006 and housed the Gem Irradiation Center to provide the service.<ref name="JOP 2019 p1">{{Harvnb|Journal of Physics: Conference Series|2019|pp=1-2}}</ref><ref name="TINT 2021 p517">{{Harvnb|Suwanmanee|Sutthirat|Wanthanachaisaeng|Utapong|2021|p=517}}</ref>

==Materials and results==
<div style="float:right; margin:5px;">
{| class="wikitable" style="text-align:center"
|- bgcolor=#CDC0B0
! colspan=3|Effects of irradiation on<br/>various gemstone materials 
|- bgcolor=#EEDFCC
| Material || Starting color || Ending color
|-
| [[Earth:Amber|Amber]] || Light yellow || Orangey red,<ref name="Li 2022 p133"/><br />orangey yellow<ref name="Li 2022 p133">{{Harvnb|Li|Wang|Chen|2022|p=133}}</ref>
|-
|rowspan=3| [[Chemistry:Beryl|Beryl]] 
| Colorless 
| Yellow<ref name="Ashbaugh 1988 p201"/>
|-
| Blue 
| Green<ref name="Ashbaugh 1988 p201"/>
|-
| Colorless<br />to pale pink<br /><small>(Maxixe-type)</small>
| Deep blue<ref name="Hurlbut p170"/>
|-
| [[Chemistry:Diamond|Diamond]] || Colorless or<br />yellow<br />to brown || Green to blue<ref name=Rossman_70/>
|-
| [[Chemistry:Fluorite|Fluorite]] || Colorless || Various<ref name="Ashbaugh 1988 p201"/>
|-
| [[Chemistry:Pearl|Pearl]] || Light colors || Brown,<ref name="Ashbaugh 1988 p201"/><br />gray to black<ref name="Ashbaugh 1988 p201"/><br />or gray-blue<ref name="Sofianides 1991 p178"/>
|-
| [[Chemistry:Quartz|Quartz]] || Colorless to<br />yellow or<br />pale green ||  [[Chemistry:Amethyst|Amethyst]],<ref name=Rossman_70/><ref name="Ashbaugh 1988 p201"/> <br />brown,<ref name="Ashbaugh 1988 p201"/> rose,<ref name="Ashbaugh 1988 p201"/><br />"smoky"<small> (light gray)</small><ref name=Rossman_70/>
|-
| [[Chemistry:Sapphire|Sapphire]] || Pink with<br />blue tint || Tint removed<ref name="Soonthorntantikul 2023 p160">{{Harvnb|Soonthorntantikul|Vertriest|Palke|2023|p=160}}</ref>
|-
|rowspan=2| [[Chemistry:Topaz|Topaz]] 
| Yellow<br />to orange 
| Intensify colors<ref name="Ashbaugh 1988 p201"/>
|-
| Colorless<br />to<br />pale blue
| Brown,<ref name="Ashbaugh 1988 p201"/><br />dark blue,<ref name="JCK 1990 p39"/><br />green,<ref name="Ashbaugh 1988 p201"/><br />sky blue<ref name="JCK 1990 p39"/>
|-
|rowspan=3| [[Chemistry:Tourmaline|Tourmaline]] 
| Colorless<br />to<br />pale colors
| Brown,<ref name="Ashbaugh 1988 p201"/><br />green-red <small>(bicolor),</small><ref name="Ashbaugh 1988 p201">{{Harvnb|Ashbaugh III|1988|p=201}}</ref><br />intense pink,<ref name="TINT 2021 p517"/><br />pink,<ref name="TINT 2021 p517"/><ref name="Ashbaugh 1988 p201"/> red,<ref name="Ashbaugh 1988 p201"/><br />yellowish orange<ref name="TINT 2021 p517"/>
|-
| Pink
| Intense pink,<ref name="TINT 2021 p517"/> <br />orangey pink<ref name="TINT 2021 p517"/>
|-
| Blue
| Purple<ref name="Ashbaugh 1988 p201"/>
|-
| [[Chemistry:Zircon|Zircon]] || Colorless || Brown to red<ref name="Ashbaugh 1988 p201"/>
|- 
|}
</div>
{{multiple image| align = right|direction = horizontal|header =|header_align = left/right/center|footer = London Blue (left), one of the neutron-bombarded varieties of topaz,<ref name="JCK 1990 p39"/> compared to a natural blue topaz (right); Intensely blue topaz does not exist in nature and is the result of artificial irradiation.<ref name="Sofianides 1991 p82"/>|footer_align = left|image2 = Lepidolite-Topaz-vlt-6b.jpg |width2 = 108 |caption1 =|image1 = London blue topaz.JPG|width1 = 151|caption2 =}} 
The most commonly irradiated gemstone is [[Chemistry:Topaz|topaz]], which usually becomes blue after the process.<ref name="NRC 2019" /> Intensely blue topaz does not exist in nature and is the result of artificial irradiation.<ref name="Sofianides 1991 p82">{{Harvnb|Sofianides|Harlow|1991|p=82}}</ref> According to the American Gem Trade Association, approximately 30&nbsp;million carats ({{convert|6000|kg|abbr=on|disp=or}}) of topaz are irradiated every year globally, 40&nbsp;percent of which were done in the United States as of 1988.<ref name="Ashbaugh 1988 p205">{{Harvnb|Ashbaugh III|1988|p=205}}</ref> Dark-blue varieties of topaz, including American Super Blue and London Blue, are the results of neutron bombardment,<ref name="JCK 1990 p39">{{Harvnb|Jewelers Circular Keystone|1990|p=39}}</ref> while lighter sky-blue ones are often those of electron bombardment.<ref name="JCK 1990 p39"/> Swiss Blue, subtly lighter than the US variety, is the result of a combination of the two methods.<ref name="JCK 1990 p39"/>

Diamonds are mainly irradiated to become blue-green or green, although other colors are possible.<ref name="Skuratowicz p13">{{Harvnb|Skuratowicz|Nash|2005|p=13}}</ref> When light-to-medium-yellow diamonds are treated with gamma rays they may become green; with a high-energy electron beam, blue.<ref name=Rossman_70/> The difference in results may be caused by local heating of the stones, which occurs when the latter method is used.<ref name=Rossman_70>{{Harvnb|Rossman|1981|p=70}}</ref>

Colorless [[Chemistry:Beryl|beryl]]s, also called goshenite, become pure yellow when irradiated, which are called golden beryl or heliodor.<ref name="Hurlbut p170" /> [[Chemistry:Quartz|Quartz]] crystals turn "smoky" or light gray upon irradiation if they contain an [[Chemistry:Aluminum|aluminum]] impurity, or [[Chemistry:Amethyst|amethyst]] if small amounts of iron are present in them; either of the results can be obtained from natural radiation as well.<ref name=Rossman_69>{{Harvnb|Rossman|1981|p=69}}</ref>

[[Chemistry:Pearl|Pearl]]s are irradiated to produce gray blue or gray-to-black colors.<ref name="Sofianides 1991 p178">{{Harvnb|Sofianides|Harlow|1991|p=178}}</ref> Methods of using a cobalt-60 gamma ray facility to darken white [[Biology:Pinctada fucata|Akoya pearls]] were patented in the early-1960s.<ref name=Department_of_Geological_Sciences>{{Harvnb|Department of Geological Sciences|1998}}</ref> But the gamma ray treatment does not alter the color of the pearl's [[Biology:Nacre|nacre]], therefore is not effective if the pearl has a thick or non-transparent nacre.<ref name=Department_of_Geological_Sciences/> Most black pearls available in markets prior to the late-1970s had been either irradiated or dyed.<ref name=Department_of_Geological_Sciences/>

=== Uniformity of coloration ===
Gemstones that have been subjected to artificial irradiation generally show no visible evidence of the process,<ref name=Hurlbut_127>{{Harvnb|Hurlbut|Kammerling|1991|p=127}}</ref> although some diamonds irradiated in an [[Physics:Electron beam|electron beam]] may show color concentrations around the [[Engineering:Culet|culet]] or along the keel line.<ref name=Hurlbut_127/>

=== Color stability ===
In some cases, the new colors induced by artificial irradiation may fade rapidly when exposed to light or gentle heat,<ref name=Hurlbut_057>{{Harvnb|Hurlbut|Kammerling|1991|p=57}}</ref> so some laboratories submit them to a "fade test" to determine color stability.<ref name=Hurlbut_057/> 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.<ref name="Hurlbut p170" />

== Notes ==
{{refbegin}}
'''a.''' {{Note label|A|a|none}} Generally speaking, an energy of at least 10 [[Physics:MeV|MeV]] is needed to induce radioactivity in a material.<ref>{{Harvnb|Thomadsen|Nath|Bateman|Farr|Glisson|2014}}</ref>

'''b.''' {{Note label|B|b|none}} {{As of|1987}}, most developed countries regarded {{convert|2|nCi/g|Bq/g}} as safe to release to the public while the U.S. federal release limits for most nuclides were {{convert|1|nCi/g|Bq/g}} or less, and that of the United Kingdom was {{convert|2.7|nCi/g|Bq/g}}.<ref name="Ashbaugh 1988 p212">{{Harvnb|Ashbaugh III|1988|p=212}}</ref> {{As of|2022}}, the release limit of the European Union is {{convert|2.7|nCi/g|Bq/g}}.<ref name="Schröck 2022">{{Harvnb|Schröck|2022}}</ref>
{{refend}}

== References ==
=== Citations ===
{{reflist|15em}}

=== Works cited ===
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{{refend}}

{{Nuclear technology}}

[[Category:Gemstones]]
[[Category:Nuclear technology]]
[[Category:Radiation]]

{{Sourceattribution|Gemstone irradiation}}