Editor’s Note: the following article was recently presented at the 25^th International Gemological Conference (October 1995) held at the Rayong Resort Conference Center in Rayong, Thailand. It is reprinted here as part of JewelSiam’s continuing effort to provide our readers with interesting and informative articles on current gemstone enhancement techniques and technologies.

 

Abstract

            The most complex and least understood device presently used to enhance the color of various gemstones is the high-energy electron beam linear accelerator (linac). Linacs are used to generate highly energetic electrons (i.e. beta particles) which produce color changes in many types of gemstones. The effects of these color changes range from subtle to quite pronounced, with corresponding changes in the gemstones’ intrinsic value. The purpose of this paper is to provide an overview of such linacs and explain how they are used for gemstone color enhancement. This paper will also describe a commercial linacs facility presently being installed in Bangkok, Thailand.

 

Overview

            Few people outside of the gemstone industry realize that nearly all faceted blue topaz has been bombarded (i.e. irradiated) with subatomic beta particles (i.e. electrons) to produce its desirable blue hues. In fact, it is safe to state that nearly every piece of blue topaz presently for sale in jewelry stores throughout the world has been treated in an electron beam linear accelerator facility and then heat treated to produce the attractive blue color. Generally, the public reaction upon learning such knowledge is initial disbelief, often followed by the disclaimer that they would rather not have known. On the other hand, scientists and engineers nearly always brighten up upon hearing this fact, anxious to understand the processes and techniques involved in such an interesting application of fundamental science.

            Many of the colored gemstones extracted from the earth owe their natural color to having been irradiated by naturally occurring radioactive sources over millions of years. Some of these sources of radiation may have been radioactive constituents (impurities) within the gemstones themselves, radioactive components of the soil of matrix around the gem material, and cosmic radiation which continually bombards the earth. The radiation striking the gemstone atoms can cause color centers which involve either an excess or a deficit of electrons from their normal positions within the atomic structure of the gemstone material. The selective emission or absorption of visible light striking the gemstone actually produces the appearance of what humans refer to as “color”, as it is perceived by our eyes and brain. In this context, the enhancement of gemstone colors with radiation is certainly not unnatural. Electron beam linac technology merely serves to greatly speed up this natural color enhancement process so that the beauty of the stones can be enjoyed much sooner.

            It is interesting to note that written processes to enhance the color and appearance of gemstones date back to long before the birth of Christ (and even before Buddha). There is written evidence that as early as 2,000 BC the Minoans modified the color of gemstones Regarding the enhancement of gemstones, Pliny (23-79 AD) wrote that: “To tell the truth, there is no fraud or deceit in the world which yields greater gain and profit than that of counterfeiting gems.” The knowledge of gemstone enhancement methods grew and was gradually recorded. Two centuries after Pliny, the Emperor Diocletian angrily ordered that all such texts be burned. Later manuscripts, dating back fifteen centuries, provide simple recipes for counterfeiting the color of gems using such tools as fire, goats’ blood, the milk of a white bitch dog, bile from tortoises and cattle, garlic, and the urine of an uncorrupted youth. As time went on, the level of gemstone treatment knowledge and methodologies progressed. In the last century, gemology became a more systematic science. At the turn of this century scientists discovered radioactivity and the curious effects various types of radiation had on certain materials, including gemstones. Recently, gemstone color enhancement techniques have mushroomed due to the existence and increased availability of advanced technological tools and techniques. The most complex of these is the use of electron beam linacs to enhance the color of various gemstones including topaz, tourmaline, quartz, beryl, zircon, and diamond, among others.

 

Lina Technical description

            Charged particle accelerators played a key role in the early days of atomic and nuclear physics, and still do. The first charged particle accelerator was built in 1932 by two British physicists, Cockroft and Walton. It was used to accelerate protons up to the then unheard of speed (energy) of 150 keV. An electron accelerated through a potential difference of one volt is said to have energy of 1 electron volt (i.e. 1 eV). On the atomic scale, the electron volt is a basic unit of energy. Larger energies are typically expressed as a thousand electron volts (keV), a million electron volts (MeV), a billion electron volts (GeV), and a trillion electron volts (BeV). Today, large circular accelerators funded and developed by consortiums of nations, and costing literally billions of dollars, have the ability to accelerate particle beams to energies exceeding the average energy of cosmic radiation (about 10 Gev) by two orders of magnitude.

            Sixty years of accelerator research and development have resulted in several new accelerator technologies. Used to accelerate a wide range of charged particles. Electrons are the particles most usually accelerated for commercial applications. They are also the lightest particle accelerated; approximately 9.109 x 10^-31kilograms apiece. These stable particles have a rest energy of 511 keV (0.511 MeV) and are about 1,836 times lighter than the next lightest particle, the proton. Highly energetic electrons are often referred to simply as “Beta” particles.

Of the many technologies used to accelerate electrons, the one most commonly used for commercial applications is that of the radiofrequency (rf) powered linac.

Figure 1 is the front panel of a modern graphical computer interface used to control and monitor an rf linac. It is divided into three distinct regions to simplify the monitoring and control of the linac. The top one third of this control panel represents the actual electrical control cabinets and electronic racks located in the plant. If one or more of these systems has an alarm condition, the corresponding system flashes red on the screen, and the operator can select it with the computer’s mouse to receive more specific details and additional supporting information. The middle one-third of the control panel is a graphical representation of the major linac components located in the shielded bunker area. The linac operator can simply select a component of interest with the mouse and will immediately receive detailed information associated with a particular component. The bottom one-third of the control panel allows the linac operator to select and/or monitor particular linac parameters including the actual desired electron energy, desired dose, dose rate, etc. the linac operator can control the machine remotely from the control room using this control panel, or control it locally through the electronic cabinets and electrical racks located in the plant. An rf linac is an extremely complex system which normally includes at least twenty major subsystems including the:

                               

Electron beam linear accelerators evolved from microwave radar developments during World War II. The source of microwave power, the klystron, was invented at Stanford University during the war. This vacuum tube device, about the size of a human, revolutionized radar and communications. Its most immediate application was to power shipboard radar units. In the late 1940’s a high power klystron was incorporated into the design of a radio frequency (rf) powered linac which was used for particle physics research. In the mid-1950’s, the first medical linac suitable for treating deep-seated cancerous tumors in humans was built. It is interesting to note that the basic technology of rf linacs has not changed significantly in over forty years.

            You may recall that the magnitude and polarity of an alternating voltage changes regularly and repeats itself periodically in time in a cyclic pattern called a sine wave. The number of complete sine wave cycles per second is called the frequency and is expressed in hertz (Hz), kilohertz (kHz), or megahertz (MHz). One hertz is defined as one cycle per second. For reference, the frequency of electric power in Thailand is 50 Hz. A typical broadcast radio wave could be around 1,000 kHz (i.e. 1 MHz).

            The klystron, as the source of energizing power for a typical rf linac, operates at around 3,000 MHz. In other words, it completes a single cycle in 1/3,000^th of one microsecond. Such a high frequency is commonly referred to as “microwave energy” and falls under the frequency classification of “S-band”. The klystron is simply a powerful electron tube which provides the source of microwave power used to accelerate the electrons along the linear accelerator structure.

            As shown in Figure 2, the klystron is surrounded by a large magnetic focusing coil and feeds its microwave power into the rectangular copper waveguide which transfers the microwave energy to the accelerator structure and ultimately into the resonant cavities within the accelerator structure. The hollow copper waveguide confines the microwaves by reflecting them forward off the waveguide walls like water in a hose. The waveguide is kept pressurized with sulfur hexafluoride gas (SF₆) to minimize electrical discharge. Ceramic windows, essentially transparent to microwaves, separate the pressurized waveguide from the high vacuum of the klystron and the accelerator structure. Both the klystron and the accelerator structure make extensive use of resonant microwave cavities. These cavities are nothing more than very accurately machined concave copper cylinders about 10 centimeters in diameter and several centimeters in length. The cavities are made of copper because of its high electrical and thermal conductivity. They are enormously efficient devices in which relatively small amounts of electrical power create intense electric force fields.

This resonance phenomenon occurs at a fixed frequency which is determined by the dimensions of the cavity. In the case of 3,000 MHz, the cavity has the approximate size and shape of a small can of tuna fish. An electric current flows on the inner walls of the cavity, moving electric charge from one end of an individual cavity to the other end of the cavity. These end regions of dense charges give rise to intense electric force fields along the cylindrical axis of the cavity. The polarity of the electric charge, the current, and the direction of the electric force fields reverse direction twice each microwave cycle, that is, six billion times each second.

A small opening (about 1 centimeter diameter) is drilled through the center of each resonant cavity. In the accelerator structure, hundreds of these concave copper cavities are brazed together, end to end. The focused electron beam travels through these central cavity holes as it makes its way down the accelerating structure. The overall length of the accelerator structure is a major determining factor for the resultant energy level of the emerging electron beam. Typically, rf linacs are designed with a fixed electron beam energy (usually around 10--> 16 MeV) to maximize their efficiency.

Figure 3 shows the accelerating structure of one of Bets Color, Ltd.’s rf linacs inside a concrete bunker. The bunker provides the necessary radiation shielding when the machine is operating. One such bunker built by the author consisted of over 70 tons of structural steel and about 1.4 million pounds of solid concrete blocks. With such a shielded facility, it is possible to stand outside the bunker during operations and not be able to detect any radiation above the normal background level using standard radiation detection equipment. Consequently, such machines need not be located in remote, isolated locations.

The source of electrons for the rf accelerator is referred to as the electron gun. Figure 4 shows the electron gun which is attached to the end of the accelerating structure where it injects the electrons. It is basically a simple heated filament (like a light bulb) which literally boils off electrons which are injected into the accelerator structure. The electron gun filament operates at a potential difference of about 80,000 volts and is pulsed via an electronic trigger circuit which also simultaneously pulses the cathode of the klystron. The pulse repetition frequency can be either fixed or variable, and typically ranges from one pulse per second (i.e. 1 Hz) to 300 Hz. The width (i.e. duration) of an individual pulse is quite short, typically around 5 microseconds.

The pulsed electron beam from the electron gun passes through the small openings in the center of the rf cavities, along the cylindrical axis of the accelerator, pushed along (i.e. accelerated) by the electric force field generated within the resonant cavities. Almost immediately after the electron gun injection point is the point where the microwave waveguide feeds the rf power from the klystron into the resonant cavities of the accelerating structure.

Normally, about one-third of the injected electrons are captured and accelerated by the microwave electric force field in the accelerator structure. As they gain energy, the electrons travel faster and faster, approaching the speed of light! Since they cannot ever attain the speed of light, their mass actually increases as they gain energy. You may recall the E=mc². This is Einstein’s famous mass-energy equivalence equation. For example, a 2 MeV electron moves at 98% the speed of light. Its mass in motion is nearly 5 times greater than its mass at rest. A 15 MeV electron has a mass about 30 times greater than its rest mass.

The inside of the accelerator structure is kept under a strong vacuum (approximately 10^-7Torr) so that there are very few stray particles to interfere with the focused electron beam. If there were no vacuum, the beam of accelerated electrons would collide with air molecules and lose energy. The electron beam is tightened (i.e. focused) via magnetic fields generated by electric magnets surrounding the accelerator structure.

As shown in Figure 5, at the end of the accelerating structure the electron beam is allowed to drift along inside of a stainless steel tube (still under a vacuum) and enter a bending magnet system which serves to turn (i.e. steer) the beam to the desired location where it will exit the vacuum system. The accelerated beam of electrons (about 1 centimeter in diameter) emerges from the end of the bending magnet system through an extremely thin titanium-vanadium-aluminum foil window (about 0.05 mm thick) where it is directed onto the target material (i.e. the gemstones) with a magnetic scanning device, similar to the raster scan of a television screen.

The rf linac is basically a source of high energy electrons which can be turned on and off at will. A portion of the electronics associated with the rf linac is shown in Figure 6. This ability to turn the source of radiation on and off as desired is quite unique and advantageous. Unlike a Cobalt-60 (gamma) source, or a nuclear reactor (neutron) source, the rf linac (electron) source is only generating electromagnetic radiation when it is turned on and all of its subsystems are working properly. The rf linac has further advantages over other sources of radiation. In a properly configured rf linac, the high-energy beam of electrons can be used to generate a secondary, less powerful source of gamma radiation and / or neutrons which can be turned on and off as required.

On the other hand, due to the complexity of the systems involved, it is often difficult to keep an rf linac operating for long periods of time. Costly periods of down-time can result. Additionally, it requires a highly educated and technically skilled support staff. A commercial rf linac facility typically costs between about US$3,000,000--> US$6,000,000(75,000,000--> 150,000,000 Baht) for the initial capital costs of equipment and facility. Operating costs can become prohibitive if major components fail before the end of their expected lifetimes. For example, replacement Klystrons for an S-band rf linac cost approximately US$100,000 (2,500,000 Baht) each. As you might imagine, linacs are not designed and manufactured primarily for the color enhancement of gemstones! They have many other interesting primary uses. Electron beam linacs have applications in the following diverse fiends:

• particle physics                      

• medical applications

- medical radiation therapy devices for cancer treatments

- sterilization of medical and pharmaceutical products such as bandages, gauze, latex gloves, tongue depressors, thermometers, gowns, saline solutions, ointments & gels, petri dishes, and test tubes before their use

- sterilization of single-use disposable surgical products such as scalpel blades, sutures, syringes, catheters, and surgery kits before their use

- sterilization of consumer products such as baby powder, soap & shampoo, cotton balls, insect spray, jewelry boxes, tampons, infant wear, eye lashes & shadow, etc. (before use)

- sterilization of medical waste prior to release for permanent disposal

- production of short-lived radioisotopes for research, hospital and clinical applications

• food preservation

- control salmonella and other food-borne bacteria in poultry

- sterilize fruit flies on papayas for quarantine purposes

- extend shelf lives of seasonal products such as strawberries, dates, figs, potatoes, onions, garlic, pistachio nuts, flowers, etc.

- insect disinfestations of bulk products (herbs, spices, cereals, grains, animal feeds, etc.)

• government and private sector electronics

- electronically harden and improve switching speeds and recovery times of transistors

-  does rate characterization testing of integrated circuits, transistors and diodes (i.e. piece parts) for satellite system components

• high energy X-ray sources for non-destructive industrial radiography

- dynamic inspection of jet and rocket motor engines

- non-destructive testing of ordnance (i.e.bombs)

- checking integrity of oil rig drill casings and transcontinental pipelines

- inspecting solidified nuclear waste, solid rocket fuel, space shuttle booster engines, etc.

- inspecting integrity of pre-stressed concrete structures (bridges, etc.) in place

- screening cargo containers and trucking vans for contraband

- inspecting small castings, automotive engines, and parts from defects

• industrial electron beam processing

- enhance chemical catalytic processes

- induce color in glass containers and decorative material (including gemstones)

- cross-linking and polymerization of plastics such as catheters; wire and cable covering; and piping to improve strength, fire resistance, etc.

- curing of rubber and resin in composite parts

- rapid curing of lacquer coatings on furniture and other wood products

- adiabatic hardening of steel alloy surfaces

- sterilization / processing of animal vaccines, human bone & tissue, rawhide dog treats, emery boards, and tennis racket strings

- sterilization / processing of food packaging such as dairy cartons, heat shrinkable film, plastic food wrap, wine corks and plastic bottles.

 

Topaz treatment

            At this point, it might be useful to discuss the general topic of topaz treatment. In the late 1940’s researchers described the use of gamma radiation from a Cobalt-60 source to enhance the color of blue topaz. The resultant blue color was not very intense and it exhibited a steely gray appearance which was considered unattractive by many. However, it was the primary technology used to modify the color of blue topaz for over one decade. The use of linac-produced electrons to enhance the color of blue topaz began on a large scale (i.e. commercially) in the early 1970’s in California. The resultant color become known in the gemstone trade as “Sky Blue”. By the end of the 1970’s this process was also being employed at a linac facility in New York. In the mid-1980’s linac treated topaz began to come out of both England and Germany. Since then, the knowledge and application has spread to a number of linac facilities around the world. In the mid-1970’s a laboratory in England developed a process using neutrons from a nuclear reactor to create a dark sapphire-like blue color in topaz referred to as “London Blue”. In the early 1980’s this process was duplicated, on a much larger scale, in California where millions of carats per month were produced. Around the same time, the technology became known to take the neutron-treated material from the reactor and subject it to large doses of electrons from a linear accelerator. The resultant color was an intense electric blue which came to be called “Swiss Blue”.

            Topaz is an all chromatic gemstone in which the color is derived from defects in the crystal structure rather than from any essential element in its chemistry. Irradiating topaz with high energy electrons induces color centers by creating the absence (or the excess) of electrons within the crystal structure. Loosely held electrons can react with the electromagnetic fields of light traveling through the topaz, preferentially absorbing some frequencies. Since this process generally occurs in the visible and ultraviolet range of the energy spectrum, the result is the appearance of various shades of blue to the human eye.

            The electron beam dose necessary to significantly modify the color of topaz is quite large. A typical dose range would be 8,000 to 9,000 Megarads (MRADs), a unit for measuring absorbed dose, With a typical linac topaz batch (target) size of about 10,000 carats (i.e. about 2 kilograms), such a dose could take several days of continuous operation to achieve, the stones must be water cooled during the irradiation, since the resultant internal heat in the stones is sufficient to anneal (i.e. eliminate) the color centers as they are formed; as well as crack the stones from internal thermal stress. If the gemstones were not cooled during the electron beam treatment process, they would experience tremendous temperature changes as large as one hundred degrees Celsius per minute. In addition, the electrons must have enough energy to completely penetrate the stones without stopping. For example, a 10 MeV electron will only penetrate approximately 16 millimeters (about 5/8 inch) into solid topaz before it is totally stopped. Since topaz is an excellent electrical insulator, a large negative charge builds up within the stones as each stopped electron deposits its negative charge. Eventually the growing electrical charge discharges to an electrical ground and destructively fractures the gemstone. The use of higher-energy electrons basically eliminates this problem, allowing the treatment of larger stones without fear of damaging the gemstones. On the average, a 22 MeV electron will penetrate approximately 36 millimeters (about 1 3/8 inch) into solid topaz before it is stopped.

            Naturally occurring topaz, an aluminum fluorosilicate [AI₂SiO₄F_2-x (OH) _x], normally contains only very small (i.e. trace) amounts of impurities. Both natural topaz and electron beam treated topaz is insignificantly radioactive. However, like nearly everything else in the world (including the human body) natural topaz is slightly radioactive due to its trace elements, some of which are naturally radioactive. The amount of radioactivity is well within legally acceptable limits. The electron beam irradiation of topaz creates insignificant induced radioactivity when using electrons with energies less than about 15 MeV. This is below the threshold energy for most of the electron beam activation reactions that would be of concern in a linac facility. Usually, the treated material can be safely handled within ten minutes of being treated, and may be released to the public within a few days.

            The use of higher energy electrons (>15 MeV) to irradiate topaz creates a number of short-lived (i.e. short half-life) radioactive byproducts in the topaz, and the treated material generally reaches legal release levels within two to three weeks, It is the impurities in the topaz which become activated (i.e. radioactive). Previous experience with our linacs, and machines of similar energy capability, indicate that high-energy operations result in minor activation of the experimental device (especially any copper or brass fixtures), but no significant activation along the beam line. Additionally, internal contamination and room contamination are not problems. Written operation procedures typically require that the linac operator perform an initial entry radiation survey in the treatment room after operating with electron energies above 15 MeV.

            For operations below 15 MeV, no initial entry radiation survey is typically required unless a high-Z material has been used as a brehmstrahlung (i.e. braking radiation) converter in the target area. In such a case, the dense high-Z material (i.e. material with a high atomic number) is used to convert the highly energetic electrons to X-rays (photons) through a slowing-down mechanism. The resultant photons may have enough energy to enter the nucleus of an atom and make it radioactive (i.e. photo activation). Subsequently a neutron could be emitted from the radioactive atom (i.e. a photo neutron reaction) and make another atom radioactive. Photo neutron reactions are only produced above a certain energy referred to as the activation threshold. While high-energy electron beam linac irradiation of topaz poses no significant problem, care must be taken when irradiating gemstones containing the elements beryllium, lithium, uranium and thorium in a high energy linac as they have low activation energy thresholds for photo neutron reactions.

            Although electron beam linac irradiated topaz presents no danger to the general public, neutron irradiated topaz treated in a nuclear reactor facility can present a potential health hazard, if not properly controlled. This differentiation between treatment technologies is fundamental and important. The impurities (i.e. trace elements) in topaz become quite radioactive when bombarded by neutrons in a nuclear reactor; and must be monitored carefully. Typical topaz impurities which result in activation products with longer half-lives include tantalum, scandium and manganese. Depending on the length of time the topaz was bombarded by neutrons, it might be several months to several years before such material reaches a releasable level of activity. The bright blue topaz referred to as “Swiss Blue” is created by first bombarding the topaz with neutrons in a nuclear reactor, then irradiating the same topaz with electrons using an rf linac, and then heat treating the topaz in ovens. The normally clear natural topaz becomes an ugly green/brown shade after neutron bombardment, so that its neutron treatment is readily apparent to the eye. This gross discoloration is generally a good indication that radiation monitoring is necessary before handling the material further. Generally, such topaz is not released from the nuclear reactor facility until it has reached an acceptable, legal activity level. It is then sent to a linac facility for electron beam treatment, followed by heat treatment.

            If such material is above the acceptable activity levels, it must only be released to an individual or company which has the necessary possession license for radioactive material. Since it is possible that such material may find its way into a linac facility for further treatment, care should be taken to test and monitor such material carefully to insure it is not released to anyone not properly licensed to possess it. The legal release levels, normally expressed in units of NanoCuries per gram (nCi/gm), vary from country to country; for example, Great Britain (2.7nCi/gm); Wist Germany, Italy, Japan, Taiwan and Hong Kong (2.0nCi/gm); U.S. and Canada (1.0nCi/gm). Since topaz is not actually consumed (i.e. eaten) by the consumer, the U.S. limit is considered far too stringent a guideline by many experts in this area, with the European and Asian limits appearing to be much more realistic values. In fact, the more stringent U.S. limits have resulted in a severe impact on the blue topaz market in the U.S., forcing production and jobs overseas.

 

New Linac Facility

            The first commercial high-energy electron beam linear accelerator facility in Southeast Asia is presently being built in Bangkok, Thailand.

            The company, Beta Color, Ltd., is a majority Thai owned private limited company owned and operated by a group of key businessmen in the international colored gemstone marketplace. Upon completion, it will be the first linac facility in the world built and operated specifically for gemstone color enhancement. Beta Color, Ltd. Will begin business as a manufacturing services company providing electron beam treatment services to enhance the color of various gemstones, particularly topaz and diamond. It is expected that the facility will be available to the gem trade industry in mid-1996.

            Jewellery News Asia (September 1992) reported that Thailand exported 15,843,407 carats of polished topaz in 1991; up 6.4% from 1990[Source: Department of Business Economics, Thailand]. According to this report, 19.7% (by carat weight) of all the polished gemstones exported from Thailand in 1991 were topaz. The four primary mining sources of rough topaz worldwide are Brazil, Sri Lanka, Nigeria and China. Examination of the world topaz market indicates that about 50,000,000 carats are treated each year. These figures indicate that over 30% of the world’s topaz is presently exported from Thailand. The previously mentioned report shows that about 65% is sent to the U.S., 6% to Japan, 9% to the U.K., 11% to Germany, and 9% to other countries. The key point is that all of the topaz presently faceted in Thailand is now being sent out of the country for electron beam treatment. Most of these stones are then returned to Thailand for further processing, including repolishing as necessary, and eventual setting in jewelry. Once the Beta Color, Ltd. Facility is operational, faceted topaz will no longer have to be sent out of Thailand to accelerator facilities in North America, U.K. or Germany and then returned to Thailand for additional processing.

            According to Thai Board of Investment (BOI) documents “The Royal Thai Government accords a top priority to boost Thailand to be ranked among the world’s leading gem and jewelry centers.” The Thai gemstone and jewelry industry is diligently pursuing a projected export target of 100,000 milling Baht (US$ 4billion) by the year 1995. In order to take advantage of Thailand’s unique, well known position as one of the de facto centers for the world gemstone industry, the principals of Beta Color, Ltd. Funded the acquisition and refurbishment of two variable-energy electron beam rf linacs. The machines were initially manufactured in France and installed in major cancer treatment centers in the United States in the late 1970’s. In the early 1990’s they were replaced by newer, but less powerful machines, and were acquired by Beta Color, Ltd. The machines were then shipped to Canada for extensive design modifications and refurbishment prior to being imported into Thailand. They are presently being installed in a new facility conveniently located in Bangkok’s gemstone district. The company has also imported a third linac to Thailand for spare parts; and has two additional linacs stored at its U.S. subsidiary company, Beta Color, Inc. in southern California. As we saw earlier, most rf linace are designed to operate at a single, fixed electron beam energy level, usually somewhere between 10 MeV to 16 MeV, to maximize their efficiency. The Beta Color, Ltd. Machines have undergone extensive modifications to allow for variable, operator controlled electron beam energies from the low MeV range (particularly useful for work with diamonds) up to the mid-30 MeV range. These linacs are most efficient when operated between about 16 MeV--> 26 MeV (particularly useful for work with topaz). This variable energy capability should greatly facilitate planned research and development efforts.

            In addition to gemstone color enhancement, the new Bangkok facility will also serve as a pilot plant for investigation the feasibility of installing a much larger scale facility devoted to other applications such as cross linking polymers, sterilizing medical products and pharmaceuticals, enhancing semiconductor characteristics, enhancing semiconductor characteristics, etc. One purpose of such a pilot plant is to determine if the marketplace will support such a large-scale facility in Thailand. Despite the many commercial applications of electron beams, Beta Color, Ltd. Management intends to concentrate its startup resources on the gemstone color enhancement market based upon the principals’ extensive knowledge and experience in the colored stone marketplace. However, it is reassuring to know that there are numerous back up markets we could pursue to more fully utilize our machines, if necessary.

            This multi-year effort has required extensive upfront capital for the acquisition and refurbishment of the machines and the construction of an appropriate facility. In addition to substantial funding provided by both of the principals, Beta Color, Ltd. Has a number of private Thai and American investors, some of whom are heavily involved in the colored stone industry. The principals of the company are:

             Chairman – Mr. Henry Ho, alias Park Satienrapat, age 37, is a graduate of the Gemological Institute of America. He is President of the Asian Institute of Gemological Sciences head quartered in Bangkok, and is Vice President of the Thai Gem and Jewelry Traders Association. Mr. Ho is also the President of Bijoux D’Amour, a leading Jewelry company listed on the Thai Stock Exchange. Additionally, he is the Managing Director of Jewelry Realty, Ltd., developer of the 59-story Jewelry Trade Center in the heart of the Silom Road gemstone District in Bangkok.

            President – Mr. Douglas J. Parsons, age 40, has a graduate degree in Nuclear Engineering from the Pennsylvania State University where he was a member of Phi Beta Kappa, Tau Beta Pi (the engineering honor society), and the nuclear engineering honor society. While in the U.S. Navy’s nuclear power program, he acquired extensive hands-on technical experience in the operation and maintenance of electrical and mechanical equipment nuclear power plant systems and components, radiochemistry and radiation health physics. He previously served as a licensed nuclear reactor operator on a university research reactor, and a field engineer for a nuclear service firm. Mr. Parsons has founded and managed a number of successful private sector ventures including a nuclear utility company engineering firm, a retail computer store, and an import/export company supplying fine gem and mineral specimens to museums and private collections worldwide.

 

Summary

            High-energy electron beam linacs are highly complex electronic devices which can be used to modify the characteristics of a wide range of materials. One of their least understood applications is the color enhancement of various gemstones; primarily topaz. It is hoped that this paper will clarify this particular application, providing the reader with a better understanding of the technology and its application in the gem industry.

 

References • Ashbaugh, Charles E. (1988) Gemstone Irradiation and Radioactivity. Gems & Gemology,    Vol.24, No.4, pp. 196-213. • Hoover, D.B. (1992) Topaz. Butterworth-Heinemann Ltd. Oxford, Great Britain. • Nassau, Kurt (1984) Gem Enhancements; Heat, Irradiation, Impregnation, Dyeing, and other Treatments which alter the Appearance of Gemstones, and the Detection of such Treatments. Butterworth’s, Stoneham. Massachusetts, U.S.A • Scharf, Wald mar H. (1989) Particle Accelerators –Applications in Technology and Research. Research Studies Press, Somerset, England. • Scott, Allan W. (1993) understanding Microwaves. John Wiley & Sons, Inc. New York.