FR2460119A1 - Changing the colouring of hard and gem stones - using high energy level rapid neutrons and gamma particles - Google Patents

Abstract

Gem stones are treated in a reactor by neutrons and the gamma-particles accompanying them. Rapid neutrons having an energy of >=0.5 MeV are applied in integral doses of 5 x 1015 to 1 x 1018 neutrons/cm2, together with gamma-particles in integral doses of 5 x 106- 1 x 109 R at 300 degrees C. In the process, thermal neutrons with an energy 0.5 MeV are filtered out by foils of Cd, and colours are obtd. which are highly valued in the jewellery trade. The colours are resistant to UV light, and the induced radioactivity approaches the base level very quickly.

Description

The present invention relates to the treatment of substances by irradiation and more particularly to a process for changing the color of hard stones and of articles produced from such stones used in jewelry.

 The invention can find its application both for coloring hard colorless stones and for changing the color of stones which have no colors, shades or intensities of coloration appreciated in jewelry.

 There are methods for coloring hard stones using ionizing and corpuscular radiation.

There is a process for coloring hard stones by bombardment with gamma particles.

 This process resides in the coloring of hard stones by bombardment with gamma particles at integral doses from 105 to 108 R. This process uses relatively weak ionizing radiation, which makes it possible to reveal only the potential centers of coloring of hard stones.

There is also a process for e> loration of hard stones by electronic irradiation.

This process does not produce a color resistant to light and heat.

 This process also uses relatively weak ionizing radiations which make it possible to reveal only the potential centers of coloring of hard stones. However, in certain hard stones the centers of coloring necessary appear only for the action of powerful irradiations like a neutron radiation or the radiation of a reactor which represents the set of neutron radiations and those of gamma particles which l 'accompany.

 We know a process for coloring hard stones, especially diamonds, which consists of treating hard stones in a reactor with neutrons and gamma particles which accompany them.

 In this process, a beam of neutrons with an energy of between 0.005 and 0.01 eV is used and at integral doses greater than 1018 neutrons / cm 2, which in turn makes it possible to obtain a color resistant to light and heat. but on the other hand, causes the treated samples to become significant sources of induced radioactivity, which requires their prolonged storage after treatment or else makes them completely unusable.

 The invention relates to a process for changing the coloring of hard stones and articles made with such stones, used in jewelry, in which the choice of treatment regimes would make it possible to obtain colors, shades and intensities resistant to light and heat and most appreciated in jewelry while exhibiting minimal induced radioactivity.

It therefore relates to a process for changing the coloring of hard stones and of articles produced with such stones used in jewelry, which consists in treating hard stones in a neutron reactor and accompanying gamma particles, characterized in that that the treatment is carried out using fast neutrons with an energy equal to at least 0.5 MeV, in integral doses of 5.1015 to 1.1 o18 neutrons / cm2 and gamma articulations in integral doses of 5.1 o6 to 1.109 R at temperatures below 3000C.

 This invention makes it possible to improve the decorative qualities of hard stones and of the articles produced with them used in jewelry and, consequently, to increase their commercial value.

 The process for coloring hard stones and articles made with such stones used in jewelry resides in the following.

The hard stones to be treated are placed in the channel of a fast neutron reactor and are subjected to bombardment by a beam of fast neutrons of energy equal to at least 0.5 MeV at integral doses of 5.1015 to 1.1018 neutrons / cm2 and by gamma particles at integral doses from 5.106 to 1.109 R. The thermal neutrons forming part of the radiation of the reactor are filtered using cadmium sheets. The temperature of the samples is maintained at 3000C at most.

 As a result of this operation, the varieties of coloring which are impossible to obtain using other types of radiation are obtained, without induced radioactivity.

This process is most effective for hard stones whose coloring centers are essentially formed under the simultaneous action of a beam of fast neutrons and gamma particles which accompany them.

 The invention will become apparent from the following description with reference to the following exemplary embodiments.

Example I
Cut stones made of weakly colored chrysolite crystals were subjected to a treatment in the channel of a reactor at a temperature of 2800C.

 The treatment is carried out using fast neutrons at an integral dose of 5.lu15 neutrons / cm2 and of gamma particles, at an integral dose of 5.106 R. As thermal neutron filter with energy lower than 0.5 MeV we used cadmium sheets. Greenish-brown items more popular in jewelry were obtained. The color obtained was shown to be resistant to light (ultra-violet) and to heat (up to 4000C). The induced radioactivity approached background level after two weeks.

Example 2
Cut stones made of weakly colored chrysolite crystals were subjected to a treatment in the channel of a reactor at a temperature of 2800C using fast neutrons at an integral dose of 1.1017 neutrons / cm2 and gamma particles which accompany at a full dose of 1.108 R.

As thermal neutron filter with energy lower than 0.5
MeV we used cadmium sheets. There were obtained articles of greenish brown color (more intense than in Example 1) more appreciated in jewelry. The coloring obtained was shown to be resistant to light (ultra-violet) and to heat (up to 400 ° C.). The induced radioactivity approached background level in three weeks.

Example 3
Cut stones made of weakly colored chrysolite crystals were subjected to a treatment in the channel of a reactor at a temperature of 2800C using fast neutrons at an integral dose of i.î018 neutrons / cm2 and gamma particles which accompany them at a full dose of 1.109 R.

As thermal neutron filter with energy lower than 0.5 MeV, cadmium sheets were used. We obtained yellowish brown items more appreciated in jewelry. The color obtained was shown to be resistant to light (ultra-violet) and to heat (up to 4000C). The induced radioactivity approached background level after four weeks.

Example 4
Cut stones made of weakly colored beryl crystals were subjected to a treatment in the channel of a reactor at a temperature of 2800C using fast neutrons at an integral dose of 6.1015 neutrons / cm2 and 6 gamma cells. at an integral dose of 6.106 R. Cadmium sheets were used as thermal neutron filters with energy lower than 0.5 MeV. We obtained items of greenish yellow color more appreciated in jewelry and close to analogous colorings of natural beryls. The coloring obtained was shown to be resistant to light (ultra-violet) and to heat (up to 3500C). The induced radioactivity exceeded the background level by 40% two weeks after treatment.

Example 5
Cut stones made of weakly colored beryl crystals were subjected to a treatment in the channel of a reactor at a temperature of 1500C using fast neutrons at an integral dose of 1.1 o18 neutrons / cm2 and gamma particles which accompany them at a full dose of 1.109 R.

As the thermal fast neutron filter with an energy of less than 0.5 MeV, cadmium sheets were used. We obtained articles of golden yellow color more appreciated in the jewelry and identical to that of natural beryls of heliodore type. The coloration obtained was shown to be resistant to light (ultraviolet) and to heat (up to 3500C). The induced radioactivity exceeded the background level by 30% 0 four weeks after treatment.

Example 6
Cut stones made of weakly colored beryl crystals were subjected to a treatment in the channel of a reactor at a temperature of 150 C using fast neutrons at an integral dose of 5.1017 neutrons / cm2 and gamma particles. accompanying at a full dose of 5,108 R.

As thermal fast neutron filters with an energy of less than 0.5 MeV, cadmium sheets were used. We got more popular yellow items in jewelry. The color obtained was shown to be resistant to light (ultraviolet) and to heat (up to 3500C). The induced radioactivity dropped by 40 ffi to the background level three weeks after treatment.

Example 7
A colorless phenacite crystal was subjected to a treatment in the channel of a reactor at a temperature of 1800C using fast neutrons at an integral dose of 1.1017 neu 2 trons / cm2 and gamma particles accompanying them at a dose integral of 1.108 R. As thermal neutron filter of energy lower than 0.5 MeV one used sheets of cadmium. We obtained a light yellow crystal more appreciated in jewelry. The coloring was shown to be resistant to light (ultraviolet) and heat (up to 3000C). The induced radioactivity exceeded the background level by 40% two weeks after treatment.

Example 8
A colorless phenacite crystal was subjected to a treatment in the channel of a reactor at a temperature of i800C using fast neutrons at an integral dose of 1.1018 neutrons / cm2 and gamma particles at an integral dose of 1.109 R.

As thermal neutron filter with energy lower than 0.5 MeV, cadmium sheets were used. We obtained a brown-yellow crystal more appreciated in jewelry. The coloring was shown to be resistant to light (ultraviolet) and heat (up to 300 C). The induced radioactivity exceeded the background level by 50% four weeks after treatment.

Example 9
A colorless phenacite crystal was subjected to a treatment in the channel of a reactor at a temperature of 1800C using fast neutrons at an integral dose of 7.1015 neutrons / cm2 and gamma particles at an integral dose of 7.106 R .

Cadmium sheets were used as thermal neutron filters with an energy of less than 0.5 MeV. A crystal of light yellow color (less intense than in Example 7) was obtained, which is more appreciated in jewelry. The induced radioactivity approached background levels two weeks after treatment.

Thus, this invention provides the necessary colors and intensities, resistant to light and heat and minimal induced radioactivity.

Claims (1)

CLAIM  Process for changing the color of hard stones and of articles produced with such stones, used in jewelry, which consists in treating hard stones in a neutron reactor and accompanying gamma particles, characterized in that the treatment is carried out at using fast neutrons with an energy of 0.5 MéV at least, at integral doses of 5.1 o15 to 1.1 o18 neutrons / cm2, and gamma particles, integral doses of 5.106 to 1.109 R, at temperatures below 3000C.