GB2528303A

GB2528303A - Automated cryogenic measurements of gemstones

Info

Publication number: GB2528303A
Application number: GB1412724.5A
Authority: GB
Inventors: Nicholas Matthew Davies; Andrew John Portsmouth
Original assignee: De Beers UK Ltd
Current assignee: De Beers UK Ltd
Priority date: 2014-07-17
Filing date: 2014-07-17
Publication date: 2016-01-20
Also published as: WO2016009267A1; GB201412724D0

Abstract

Apparatus and method for performing automated cryogenic measurements of parameters of gemstones. The apparatus comprises a cryogenic bath 106 containing liquid cryogen and having a support structure 104 comprising a measurement surface 114 coupled to a fibre optic assembly 109, a transportation means (vacuum wand) 103 for transporting a gemstone to the measurement surface and to one or more bin locations in dependence on a measured parameter, and an optical unit containing one or more light sources and one or more sensors for measuring a parameter of the gemstone when immersed in the bath. A heater system may be used to defrost the vacuum wand between each use.

Description

Automated cryogenic measurements of gemstones

Technical Field

The invention relates to, but is not limited to, methods and apparatus for performing automated cryogenic measurements of parameters of gemstones. I 1

Background

In order to maintain consumer confidence that diamond products are properly disclosed, it is important that the diamond industry has practical methods for testing gemstones to determine whether they are natural diamonds, synthetic diamonds or simulants. Similarly it is important that it has methods for determining whether a diamond has been artificially treated, for example to change its colour.

Apparatus exist that are capable of distinguishing diamond gemstones from simulants, and for measuring a parameter of a diamond to give an indication of whether the diamond is likely to be natural or synthetic, or whether it has been treated, for example to improve its colour. Absorption or photoluminescence spectroscopy may be used to test a gemstone such as a diamond but such testing is generally more sensitive, and in some cases only possible, if the gemstone is cooled below room temperature. For example, it is standard practice for absorption or photoluminescence spectroscopy of diamonds to be carried out with the sample cooled to the temperature of liquid nitrogen. This may be achieved by mounting the diamond to be tested in a cryostat or within a vessel that separates the diamond from the cryogen such as that described in US8477293, but it is generally simpler and quicker to immerse the diamond directly in liquid nitrogen. For example, in a DiamondPLus® instrument the diamond to be tested is mounted on a holder, using which it is pressed against a fibre optic probe at the bottom of a bath filled with liquid nitrogen. The fibre optic probe is used to deliver laser radiation to the cooled stone and to collect the resulting photoluminescence.

In existing automated testing equipment it has been found beneficial to pick, place and dispense stones using a vacuum holder, but the use of such holders tend not to be compatible with immersion in liquid nitrogen because of the problems of liquid nitrogen being pulled through the vacuum holder resulting in deleterious effects to the vacuum system and when a holder is repeatedly immersed in nitrogen from which it is repeatedly removed it will tend to frost up as a result of moisture from the surround air condensing on the cooled holder. Such frosting can have an adverse effect on the measurement and the ability of the holder to function properly. The current invention therefore seeks to solve this problem. I 3

Summary

According to the invention in a first aspect, there is provided an apparatus for performing automated cryogenic measurements of parameters of gemstones Said apparatus may comprise a cryogenic bath containing liquid cryogen and may have a support structure at its base comprising a measurement surface coupled to a fibre optic assembly. The apparatus may comprise a transportation means for transporting the gemstone to the measurement surface and to one or more locations in dependence on a measured parameter. The apparatus may comprise an optical unit containing one or more light sources and one or more sensors. The apparatus may further comprise a de4rosting system.

Optionally the transportation means comprises a handler having a swinging arm configured to have linear and rotary travel and having a vacuum wand connected to a vacuum pump provided at its free end. Optionally the apparatus may further comprise two or more handlers Optionally one or more of the handlers are pivotally mounted on the apparatus.

Optionally the support structure may be coupled to a support arm mounted on a spring loaded support member so as to allow traverse movement of the measurement surface, the fibre optic assembly and the support arm.

Optionally the apparatus may further comprise a displacement body coupled to the support arm so as to allow traverse movement of the displacement body inside the cryogenic bath and having sufficient volume to displace enough liquid cryogen to completely cover a gemstone resting at the measurement surface.

Optionally the cryogenic bath may comprise a single moulded unit comprising a low thermal mass material.

Optionally the cryogenic bath may comprise a vessel insulated with a low thermal mass material.

Optionally the cryogenic bath may further comprise a removable cover.

Optionally the de-frosting system may comprise an electric heating element for heating the vacuum wand 105.

Optionally the de-frosting system may comprise a gas delivery system providing dry heated gas.

Optionally the gas is nitrogen gas.

Optionally the apparatus may further comprise a liquid cryogen storage reservoir.

Optionally the apparatus may further comprising a liquid level sensor located in the cryogenic bath configured to monitor the level of liquid cryogen in the cryogenic bath.

Optionally the liquid level sensor is a thermometer.

Optionally the apparatus further comprises a means to control the flow of cryogenic liquid from the reservoir to the cryogenic bath.

Optionally the means to control the flow of cryogenic liquid from the reservoir to the cryogenic bath may comprise a solenoid valve.

Optionally the means to control the flow of liquid from the reservoir to the cryogenic bath may comprise a heating element.

Optionally the fibre optic assembly is a multifurcated fibre optic cable comprising two or more fibre optic filaments.

Optionally the support structure has a centrally located hole through which the ends of the fibres of the fibre optic assembly terminate to form a measurement surface Optionally the gemstone is in direct contact the ends of the fibres of the fibre optic assembly.

Optionally the measurement surface comprises a transparent window.

Optionally the transparent window is a lens.

Optionally the transparent window is quartz.

Optionally the optical unit may comprise a light source configured to emit light at an emission wavelength or range of wavelengths such that the emitted light illuminates the measurement surface; and a sensor configured to sense light at a sensing wavelengths or range of wavelengths for measuring a parameter, the sensed light being received at the sensor from the measurement surface as a result of illumination of a gemstone located at the measurement surface.

Optionally the optical unit may comprise a plurality light sources each configured to emit light at a different one of a plurality of emission wavelengths or ranges of wavelengths such that the emitted light illuminates the measurement surface; and one or more sensors configured to sense light at a plurality of sensing wavelengths or ranges of wavelengths for measuring the plurality of parameters, the sensed light being received at the sensor assembly from the measurement surface as a result of illumination of a gemstone located at the measurement surface.

Optionally the light source may comprise a broadband light source configured to emit light for measuring the absorption of a gemstone.

Optionally the broadband light source may be configured to emit light at wavelengths in the range from about 300 nm to about 520 nm and the sensor is a spectrometer configured to sense light of a wavelength in the range from 300 nm to 520 nm Optionally the plurality of light sources may comprise one or more laser light sources.

Optionally the one or more laser light sources may comprise a laser light source configured to emit light at a wavelength suitable for stimulating Raman emission spectrum at a detectable wavelength from a cut gemstone.

Optionally the laser light source may be configured to emit light at about 660 nm and the sensor is a spectrometer configured to sense light of a wavelength in the range from 700 nm to 800 nm Optionally the one or more laser light sources may comprise at least one laser light source configured to emit light at a wavelength suitable for stimulating photoluminescence in a cut gemstone.

Optionally the plurality of light sources may comprise one or more LED light sources configured to emit light for measuring fluorescence of a gemstone.

Optionally the LED light source may be configured to emit light in the range 350nm to 400nm and the sensor is a spectrometer configured to sense light of a wavelength in the range 400nm to 520nm.

According to an aspect of the invention there is provided a method for performing automated cryogenic measurements of parameters of gemstones.

The method may comprise the steps of: Transporting a gemstone that is oriented table down from a pick up location to a measurement surface and immersing the gemstone in a liquid cryogen, and taking a measurement of one or more parameters of the gemstone and dispensing the gemstone to an appropriate category bin depending upon the measurement Optionally the parameter that is measured may be one or more of photoluminescence, Raman scattering, fluorescence or absorption Optionally the method may include use of one or more light sources configured to emit light at an emission wavelength or range of wavelengths such that the emitted light illuminates the gemstone; and one or more sensors configured to sense light at a sensing wavelengths or range of wavelengths for measuring a parameter, as a result of illumination of the gemstone.

Optionally the light source may comprise one or more broadband light sources configured to emit light for measuring the absorption of a gemstone.

Optionally the broadband light source may be configured to emit light at wavelengths in the range from about 300 nm to about 520 nm and the sensor may be a spectrometer configured to sense light of a wavelength in the range from 300 nm to 520 nm.

Optionally the light source may comprise one or more laser light sources configured to emit light for photoluminescence or Raman scattering measurements.

Optionally the laser light source may be configured to emit light at a wavelength of about 660 nm and the sensor is a spectrometer configured to sense light of a wavelength in the range from 700 nm to 800 nm.

Optionally the one or more light sources may comprise one or more LED light sources configured to emit light at a wavelength suitable for stimulating fluorescence from a cut gemstone.

Optionally the one or more LED light sources may be configured to emit light between 350 nm and 400 nm and the sensor is a spectrometer configured to sense light of a wavelength in the range from 400 nm to 520 nm.

Optionally the method may further comprise sorting the cut gemstones in dependence on the measured parameters.

Optionally sorting the cut gemstones may comprise identifying whether the gemstones have been treated to improve their colour.

Optionally sorting the cut gemstones may comprise identifying whether the gemstones are diamond or simulant.

Optionally sorting the cut gemstones may comprise identifying whether the gemstones are natural diamond or synthetic.

According to the invention in a second aspect, there is provided a sorting apparatus comprising any apparatus described above and configured to sort cut gemstones in dependence on the measured parameters.

According to the invention in a fourth aspect, there is provided a method for sorting cut gemstones comprising any method described above and further comprising sorting the cut gemstones in dependence on the measured parameters.

According to the invention in a fifth aspect, there is provided a non-transitory computer program product configured to carry out any method described above.

Brief description of the drawings

Exemplary embodiments of the invention are described herein with reference to the accompanying drawings, in which: Figure 1 shows a schematic representation of the top view of an apparatus for performing automated cryogenic measurements of parameters of gemstones Figure 2 shows a schematic representation of the side view of an apparatus for performing automated cryogenic measurements of parameters of gemstones Figure 3 shows a schematic representation of the top view of an apparatus for performing automated cryogenic measurements of parameters of gemstones having a plurality of handlers.

Figure 4 shows a schematic representation of the side view of an apparatus 100 for performing automated cryogenic measurements of parameters of gemstones I 9

Description

Generally, disclosed herein are methods and apparatus for performing cryogenic measurements of parameters of gemstones. In particular, disclosed herein are methods and apparatus for performing automated cryogenic measurements of parameters of gemstones As used herein, the term "parameter" in respect of cut gemstones encompasses the absorption of a gemstone, fluorescence of a gemstone, the Raman and or photoluminescence spectra of a gemstone.

The inventors have appreciated the need to make testing less labour intensive and more efficient, particularly for small gemstones that have less value, such as 2Opts or below. For example, automated screening equipment has been developed to enable natural diamonds to be separated from stones that are potentially synthetics or simulants. Currently, however, at least some of the gemstones referred by such automated equipment need to be further tested using low temperature photoluminescence spectroscopy. It would be beneficial if such further testing could also be automated but this requires a method for automating the immersion of samples within liquid nitrogen and their retrieval for dispensing according to the result of one or measurements carried out when they are immersed in the liquid nitrogen.

In particular exemplary methods and apparatus, an absorption measurement, fluorescence, a Raman or a photoluminescence measurement may each be undertaken automatically.

Instruments are available to assist in identification of natural untreated diamonds, synthetic diamond and treated diamonds. For example, DiamondPLus® is manufactured by De Beers and is used by grading laboratories.

1-2% of diamonds with natural origin are nominally free of nitrogen impurity.

These are called type II diamonds and they form an important category of DiamondSure® referrals to DiamondView®. After the natural origin has been confirmed using DiamondView®, it is necessary to check whether such stones have been artificially treated to improve their colour. The stones are tested using DiamondPLus®, which can be used to make a rapid photoluminescence measurement that significantly reduces the number of type II diamonds that need further, more detailed testing. However the testing requires an operator to manually place and take measurements for of each gemstone Figures 1, 2 and 3 show an apparatus for performing automated cryogenic measurements of parameters of gemstones. The apparatus 100 comprises a housing 104, a handler 101, a cryogenic bath 106, a de-frosting system 105 and an optical unit 112 coupled to the cryogenic bath 106 by a fibre optic assembly 109.

The handler 101 comprises a swinging arm 102 and having a vacuum wand 103 connected to a vacuum pump 112 provided at its free end. The handler 101 is configured to allow traverse movement of the arm 102 and vacuum wand 103. In the exemplary apparatus shown the handler is pivotally mounted on the housing 104. In other embodiments the handler may form a part of a gemstone testing or gemstone orientation system such as that described in W0201 2146913 that is configured to work in co-ordination with the apparatus.

In exemplary apparatus the vacuum wand 103 comprises a low thermal tube made from polyacetal. The vacuum wand 103 has an outside diameter of 4.5 mm and an internal bore of 3.5mm narrowing at one end to 0.6mm and then opening out again to a terminal 1.6mm bore. The width, bores and shape of the terminal end of the vacuum wand 103 may be varied to best accommodate different shapes of cut gemstones ensuring the best seal between the vacuum wand 103 and the gemstone 108 when vacuum is applied.

In the exemplary apparatus shown the de-frosting system 105 comprises a heating element for heating the vacuum wand 103. The heating element comprises a resistor through which current is passed to raise the temperature of the vacuum wand sufficiently to prevent condensation or frosting. In other embodiments the de-frosting system 105 may comprise a system for delivering a jet of dry heated gas such as nitrogen.

The cryogenic bath 106 for holding liquid cryogen 107 preferably liquid nitrogen, comprises a vessel having a small hole 113 at the top sufficiently large for the vacuum wand 103 and a gemstone to pass through and a support structure 104 at the bottom of the bath comprising a measurement surface 114 coupled directly to a fibre optic assembly 109. In the exemplary apparatus shown the cryogenic bath 106 is a single moulded unit. In other embodiments the top of the cryogenic bath may comprise a removable cover for the cryogenic bath 106 The cryogenic bath 106 comprises a low thermal mass material. Alternatively in a further embodiment the cryogenic bath 106 comprises a vessel insulated with a low thermal mass material.

In exemplary apparatus the cryogenic bath 106 is designed with a slope of around 6 degrees at the bottom towards the measurement surface. This allows the level of the liquid cryogen to be fully submerge the gemstones as the liquid cryogen boils away for as long as possible extending the achievable running time of the system. The angle of the slope may be varied to take into account different sizes and shapes of the cryogenic bath, for example the slope may be around 5 degrees or around 10 degrees or around 15 degrees or around 20 degrees.

In the exemplary apparatus shown the support structure 104 has a centrally located hole through which the ends of the fibres of the fibre optic assembly terminate to form a measurement surface 114. In other embodiments the measurement surface may comprise a centrally located transparent window comprising a low thermal mass material to improve longevity of the components.

In exemplary apparatus the fibre optic assembly 109 is a multifurcated fibre optic cable comprising two or more fibre optic filaments. Light is passed to the gemstone on the measurement surface by one of the fibre optic filaments and returned to the sensor for measurement.

In exemplary apparatus the optical unit comprises a light source and sensor coupled to a fibre optic assembly 109. The light source is a laser light source configured to emit light at a wavelength of 660 nm, an example of such a laser source is the Opnext HL6545MG laser diode. The sensor is a spectrometer configured to sense light of a wavelength in the range from 700 nm to 800 nm for photoluminescence or Raman scattering measurements, for example an Ocean Optics QEPro spectrometer.

Alternatively in exemplary apparatus the light source is a broadband light source, for example, a tungsten halogen lamp or an LED. The light source is configured to emit light at a spectrum from 300 nm to 520 nm wavelengths.

The sensor is a spectrometer configured to sense light of a wavelength in the range from 300 nm to 520 nm for absorption measurements.

Alternatively in exemplary apparatus one or more LED light sources are configured to emit light for measuring fluorescence of a gemstone. The LED light source is configured to emit light in the range 350nm to 400nm and the sensor is a spectrometer configured to sense light of a wavelength in the range 400nm to 520nm.

In other embodiments the optical unit may comprise more than one light source to measure different parameters of the gemstone. Each light source may be configured to emit light at a different emission wavelength or range of wavelengths when compared to the other light sources. Alternatively, the emission wavelengths or range of wavelengths of one or more light sources may be coincident or overlap. Also, the plurality of light sources may be provided by a single tuneable light source configured to emit light at one or more of a plurality of wavelengths or ranges of wavelengths. For example, the first and second light sources may be provided by a single tuneable laser.

In other embodiments the optical unit may comprise of more than one light source illuminating a gemstone located at the measurement surface.

Similarly, the optical unit may comprise more than one sensor to measure different parameters of the gemstone. Typically, a separate sensor corresponds to each separate light source. In such apparatus, a sensor is configured to sense light received from the measurement surface 114 as a result of the corresponding light source illuminating a gemstone located at the measurement surface 114. However, in other exemplary apparatus, one sensor may correspond to a plurality of light sources. In such apparatus, a sensor may be configured to sense light received from the measurement surface 114 as a result of a first corresponding light source illuminating a gemstone located at the measurement surface 114 and also configured to sense light received from the measurement surface 114 as a result of a second corresponding light The housing may comprise further components such as the processor and actuators such as the motor for moving the swinging arm 102 and the vacuum pump 112.

In the embodiment shown in figures 1 and 2, the handler 101 has both rotary and linear travel. The vacuum wand 103 will be configured to engage with a gemstone 108 which is orientated table-down from a pick up position 110 and to apply suction from a vacuum pump 112 to retain the gemstone 108 on the wand 103 as the swinging arm 102 is pivoted to a cryogenic bath 106 containing liquid cryogen 107 and pass the gemstone 108 traversely down through a small hold at the top 113. Here it rests on a measurement surface 114 immersed in the liquid cryogen 107. When at this position, the vacuum is turned off. The handler 101 remains in this position with the vacuum wand 103 pressing down on the gemstone to prevent any lateral movement of the gemstone in relation to the measurement surface. While the gemstone 108 is positioned at the measurement surface 114, one or more parameters of the gemstone 108 are measured by passing light from the light sourceinto the gemstone 108 by means of the fibre optic assembly 109. Light is then returned from the gemstone 108 for measurement to the sensor by means of the fibre optic assembly 109.

When the measurement is complete suction from the vacuum pump 112 is once again applied to retain the gemstone 108 on the wand 103 and the handler moves up and transports the gemstone away from the raised measurement surface 114. The gemstone 108 is then dispensed to an appropriate category bin 115 depending upon the measurement that was just made by turning off the vacuum when the handler is above the appropriate category bin 115. After the gemstone 108 is dispensed the handler 101 is pivoted to the defrosting system 105 where the handler is moved traversely down into the de-frosting system 105 and retained in that position to allow the vacuum wand to be heated for a sufficient time and temperature to prevent frosting or condensation of the nozzle with water vapour. The handler then returns to the pickup position 110 to repeat the process.

In exemplary apparatus the de-frosting system comprises of heating pad such as a resistor onto which is mounted with a thin walled thermally conductive cylinder sitting above it touching the surface of the heating pad. Both parts are mounted within a two part insulting case. The heating pad is heated until it reaches around 105 degrees centigrade; this in turn heats the cylinder. The temperature of the heating pad is monitored and once it reaches 105 degrees centigrade the heating pad is turned off. The temperature of the heating pad is monitored and once it has cooled to around 95 degrees centigrade the heating pad is turned on again. This cycle is repeated in order to keep the de-frosting system at approximately 100 degrees ÷/-5 degrees.

The thin walled cylinder is designed to be 0.2mm diameter larger than the vacuum wand which allows the vacuum wand to be inserted inside the cylinder while keeping the side of the vacuum wand very close to the heated surface of the cylinder. The cylinder is designed to be slightly shorter than the vacuum wand but is longer than the distance the vacuum wand submerges into the liquid cryogen. The system is designed so that when the vacuum wand is driven into the cylinder the vacuum wand tip touches the heated pad (resistor). This is to make sure the tip of the vacuum wand is heated and dried as this is the part that comes into contact with the gemstone. When the cryogenic bath is full of liquid cryogen the vacuum wand takes approx. S seconds to dry. This time reduces as the bath empties.

Figure 3 shows an alternative embodiment of the apparatus for performing automated cryogenic measurements of parameters of gemstones. The apparatus further comprises two or more handlers 101. In this configuration the rate of measurement of the parameters may be increased as the handlers are coordinated to allow one handler take a measurement of the gemstone in the liquid cryogen while vacuum wand 103 of the other handlers are being de-frosted by the defrosting system 105. In a further embodiment the apparatus comprises a further handler 117 for transporting a gemstone 108 to the pickup location 110 from an orientation apparatus.

Figure 4 shows an alternative embodiment of the apparatus for performing automated cryogenic measurements of parameters of gemstones.

The apparatus 100 comprises a handler 101 having a swinging arm 102 pivotally mounted on a base 104 and having a vacuum wand 103 connected to a vacuum pump 112 provided at its free end. A cryogenic bath 106 containing liquid cryogen 107 having a small hole 113 at the top of the body of the cryogenic bath 106. A support structure 104 comprising a measurement surface 114 coupled directly to a fibre optic assembly 109 that is supported by a support arm 116 mounted on a spring loaded support member 111 so as to allow traverse movement of the measurement surface 114, the fibre optic assembly 109 and the support arm 110. An optical unit containing a light source and sensor 118.

In the exemplary apparatus shown the support structure 104 has a centrally located hole through which the ends of the fibres of the fibre optic assembly terminate to form a measurement surface 114. In other embodiments the measurement surface may comprise a centrally located transparent window comprising a low thermal mass material to improve longevity of the components. The window may for example be a quartz lens.

In the embodiment shown, the handler 101 has both rotary and linear travel.

The vacuum wand 103 will be configured to engage with a gemstone 108 which is orientated table-down from a pick up position 110 and to apply suction from a vacuum pump 112 to retain the gemstone 108 on the wand 103 as the swinging arm 102 is pivoted to a cryogenic bath 106 containing liquid cryogen 107 and pass the gemstone 108 traversely down through a small hold at the top 113. Here it rests upon the measurement surface 114 this is initially above the level of the liquid cryogen 107. When at this position, the vacuum is turned off such that the gemstone 108 is resting upon the measurement surface 114. The handler 101 then traverses downwards pushing that the gemstone 108 and the support structure 104 down so that the measurement surface 114 and the gemstone 108 become immersed in the liquid cryogen 107. At this point a measurement is made by passing light from the light source into the gemstone 108 by means of the fibre optic assembly 109. Light is then returned from the gemstone 108 for measurement to the sensor by means of the fibre optic assembly 109.

When the measurement is complete the handler 101 returns upwards to its original position so that the measurement surface 114 and the gemstone 108 are removed from the liquid cryogen 107. Suction from the vacuum pump 112 is once again applied to retain the gemstone 108 on the wand 103 as the handler 101 moves up and transports the gemstone away from the raised measurement surface 114. The gemstone 108 is then dispensed to an appropriate category bin 115 depending upon the measurement that was just made.

The Exemplary apparatus of figure 4 may further comprise a displacement body (not shown) coupled to the apparatus so as to allow traverse movement of the displacement body inside the cryogenic bath and having sufficient volume to displace enough liquid cryogen to completely cover a gemstone resting on measurement surface 114 In exemplary apparatus and methods, the gemstone 108 is a diamond.

In exemplary apparatus and methods the liquid cryogen 107 is liquid nitrogen.

In a further embodiment of the current invention the apparatus further comprises a cryogen storage reservoir containing liquid cryogen for re-filling the cryogen bath 106. The reservoir contains a sufficiently large volume of liquid cryogen and is sufficiently insulated to allow for required measurement run times without an operator restocking the liquid cryogen. The reservoir is positioned above the cryogen bath and further comprises a solenoid valve designed to work with cryogenic liquids and configured to control the flow of liquid from the reservoir to the cryogenic bath. The liquid cryogen flows by gravity from the reservoir to the cryogenic bath. The apparatus further comprises a sensor located in the cryogenic bath configured to monitor the level of liquid cryogen in the cryogenic bath. When the sensor detects that the liquid cryogen has fallen below a threshold level the solenoid valve is actuated to release a volume of liquid cryogen into the cryogenic bath. The sensor may comprise an electronic measurement system such as a thermometer or a mechanical system such as a float.

In an alternative embodiment the cryogen storage reservoir comprises a sealed container with a tube running through the sealed lid of the reservoir with one end of the tube terminating below the level of the liquid cryogen in the reservoir and the other end terminates in the cryogenic bath. A heating element such as a resistor positioned below the level of the liquid cryogen in the reservoir. When the sensor detects that the liquid cryogen has fallen below a threshold level current is passed through the resistor causing it to heat up. This causes increased boiling off of the liquid cryogen and increases the internal pressure of gas in the sealed reservoir and forcing the liquid cryogen through the tube into the cryogenic bath.

A computer program may be configured to provide any of the above described methods. The computer program may be provided on a computer readable medium. The computer program may be a computer program product. The product may comprise a non-transitory computer usable storage medium.

The computer program product may have computer-readable program code embodied in the medium configured to perform the method. The computer program product may be configured to cause at least one processor to perform some or all of the method.