WO2006010772A1

WO2006010772A1 - Cryogenic cooling device

Info

Publication number: WO2006010772A1
Application number: PCT/EP2005/053707
Authority: WO
Inventors: Jürgen Stein; Guntram Pausch
Original assignee: Target Systemelectronic GmbH
Current assignee: Target Systemelectronic GmbH
Priority date: 2004-07-28
Filing date: 2005-07-28
Publication date: 2006-02-02
Anticipated expiration: 2007-01-28
Also published as: US20080092556A1

Abstract

The present invention relates to a cryo temperature cooling device (1) comprising 5 a tank (2), being filled up at least in part with a coolant (3), and a heat conducting element (4), whereas the heat conducting element (4) can be brought into thermal contact with the coolant (3), so that the coolant has a phase transition occurring below a temperature of -100°C, so that the cryogenic cooling device more or less consumes no coolant during operation.

Description

Cryogenic Cooling Device

The invention refers to a cryogenic cooling device, a device, comprising a com¬ ponent to be cooled, which is cooled by a cryogenic cooling device, as well as to a cooling element for the cooling of the cryogenic cooling device.

From the prior art, a multitude of cooling devices are known, being used in order to cool down, for example, sensors, electric circuits or detectors and others. The cooling of radiation detectors is of specific importance, as the measured spectra are imprecise if there is no appropriate cooling, as especially the energy and time resolution of the measured values are strongly dependent from the temperature.

Just among radiation detectors, using semiconductor crystals, for example germa- nium, a good cooling of mostly below - 100⁰C is of essential importance.

It is known in addition that different cooling temperatures are necessary for dif¬ ferent detectors. Germanium or silicon detectors for the detection of x-ray or gamma-radiation for example do need a cooling to about 95 K to 130 K in order to achieve sufficiently good measurement results.

In order to achieve such cooling temperatures, especially in order to achieve a cooling down to a cryogenic temperature, that is below -100 ⁰C, the prior art is using liquid nitrogen, helium or other liquefied gas. It is also known to use a stir- ling cooling, a Peltier transition, the Joule-Thomson-effect or others. Those known cooling systems do, nevertheless, need large space, are heavy and there¬ fore not or only very limited suitable for the cooling of handheld devices. Comparably large and heavy, but, nevertheless, portable radiation detectors for the measurement of gamma radiation are, according to the prior art, cooled me¬ chanically, whereby accumulator cells, for example NiCd accumulators, are used for the operation of the cooling devices.

From UCRL-JC- 118973 and UCRL-JC- 119679, an electro mechanical cooling mechanism is known, used for a portable germanium detector. As with all me¬ chanical cooling devices, the cooling device described here has the disadvantage that mechanical vibrations affect the quality of the measurement. The detector system with the cooling device has a power consumption of 37 to 97 Watt, there¬ fore requiring big and heavy batteries. The complete system described, consisting of detector, cryo cooler and battery, weights 18.2 kg, therefore being not well suited for the mobile use in the field already because of its weight and its size.

In IEEE Transactions on Nuclear Science, Vol. 40, No. 4, August 2003, page 1043-1047, a portable germanium detector is described, which is cooled by the use of a Stirling cooler on the basis of electricity also. The cooling described therein also leads to a reduced resolution because of vibrations. In addition, the necessary cooling power could be upheld for two hours only by using 6 AH NiMH accumulators.

All mentioned cooling systems, receiving the energy from battery powered power sources, do not provide enough power in order to cool down a semiconductor crystal to its operating temperature sufficiently fast. Only when the cooling occurs fast enough, the cryo pump, being part of the detector, comprising regularly acti¬ vated charcoal, is activated, thereby improving the vacuum inside the detector. When the cooling process is slow, no activation occurs, which again leads, be¬ cause of the additional impurities remaining in the crystal, to a deterioration of the resolution. Known cooling systems in the form of cooling accumulators, which do not show those disadvantages and which would be suitable for portable use, for example cooling accumulators for the cooling of beverages or for the treatment of swell¬ ings, which for example make use of eutectic cooling, cannot provide a cryo tem- perature, being necessary for the operation of the semiconductor detectors. Never¬ theless, only when using cooled semiconductor crystals, energy resolutions better than 1 % at 662 keV can be achieved.

Portable radiation detectors, which could be easily used mobile, especially for the measurement of gamma radiation, do therefore make use only of crystals and ma¬ terials, which may be practically used in the respective surrounding temperature field, that is preferably in a temperature area between - 25⁰C to + 5O⁰C, offering a sufficient resolution in that temperature area. Regularly, NaI or CsI crystals are used here, but also plastic scintillators as well as so called room temperature semiconductor crystals (CdZnTe), which, nevertheless, by far do not achieve the measurement accuracy, which can be achieved with cooled semiconductor crystal detectors.

The problem underlying the present invention is therefore to provide a cryo tem- perature cooling device, being suitable for the cryo cooling of portable devices, avoiding the described disadvantages. This problem is, according to the invention, solved by a cryo temperature cooling device with the features according to claim 1. Preferred embodiments of the cryo temperature cooling device as described in the invention are provided in the dependent claims.

The cryo temperature cooling device according to the invention comprises a hold¬ ing tank, being filled up at least in part with a coolant, and a heat conducting ele¬ ment, whereas the heat conducting element is in thermal contact with the coolant. The coolant serves as a heat sink during operation, that is in other words as a "cooling accumulator". It can take particularly more heat, if there is a phase change within the temperature area of interest, preferably providing a high phase - A -

transition energy, which is when looking at a phase transition solid-liquid, a pref¬ erably high latent heat of fusion. Nevertheless, a coolant without a phase transi¬ tion in the temperature area of interest is also providing good results, as long as the cooling device is sufficiently insulated.

According to the invention, the coolant preferably provides for a phase transition from the group solid-solid, solid-fluid, and fluid-fluid, occurring below a tempera¬ ture of - 100⁰C, so that the cryogenic cooling device more or less uses or con¬ sumes no coolant during operation, as the volumes of the various phases can be kept constant, being the reason that mainly no coolant has to be sent to the sur¬ rounding, that is to be consumed. The constant volumes are achieved by either providing a sufficiently solid pressure tank, being pressure resistant and able to surround the coolant in the complete area of temperatures during operation of up to about 55⁰C, and/or by selecting suitable coolants, their vapor pressure being low in the complete temperature field during operation, preferably not being lar¬ ger than the surrounding air pressure.

According to a preferred embodiment, the coolant comprises an organic com¬ pound, comprising a heat of fusion of less than -100⁰C. Said coolant preferably comprises one or more of the following compounds: vinyl bromide (brome ethyl¬ ene), ethyl bromide (brome ethane), butane, butene-2-cis, ethyl acetylene, butene- 1 and isobutene. The suitable compounds are known in principle and can be found in respective tables, for example from the CRC Handbook of Chemistry and Phys¬ ics.

Vinyl bromide (C₂H₃Br) is of especial advantage as a coolant, as it has a melting point of -138 ⁰C (=135.2 K), a heat of fusion of about 15.7 ⁰C as well as a vapor pressure of 1.20 bar at room temperature (21 ⁰C). An additional advantage is the high density of 1.5 kg/dm³ of vinyl bromide. Therefore, the volume of the coolant, necessary for a sufficient cooling, is reduced, thus reducing the volume of the in¬ ventive device and at the same time increasing its portability. The energy radiation and therefore the thermal loss during storage and operation of the inventive device is nearly proportional to the difference of the 4 th power of the coolant temperature and the 4 Λh power of the surrounding temperature (Law of Stefan-Bolzmann). As the cooling temperature of -138 ⁰C of vinyl bromide is suf¬ ficient for the cooling of semiconductor detectors, especially of germanium detec¬ tors, the energy loss by thermal radiation is much smaller compared to a cooling with liquid nitrogen. This is increasing the effective cooling time even with re¬ spect to conventional nitrogen cooling substantially.

Using vinyl bromide as a coolant, the inventive cryo temperature cooling device can be kept at a nearly constant temperature of substantially lower than -100 ⁰C , more specifically of -138 ⁰C , for a time period of at least eight hours with 0.5 to 1.0 liter of coolant only. At the same time, the cooling temperature is reached fast enough in order to activate a cryo pump within a germanium detector, comprising activated charcoal on a regular basis, serving for improving the vacuum within the detector crystal.

The cryo temperature cooling device may also use butane, butene-2-cis, ethyl ace- tylene, butene-1, isobutene or ethyl bromide as a coolant, as those substances do show similar properties than vinyl bromide. Also a mixture of various coolants may be used.

Preferably, the cryo temperature cooling device provides a coolant with a phase transition temperature (T_p) below - 14O⁰C, whereby it has proved a specific ad¬ vantage, if the coolant provides a boiling temperature Tsi higher than 2O⁰C, pref¬ erably higher than 5O⁰C.

Furthermore, it has proved to be of advantage if the coolant has a phase transition energy of at least 35 kJ/ltr, preferably a phase transition energy of at least 50 kJ/ltr and especially preferred of at least 80 kJ/ltr. It furthermore is an advantage if the coolant is selected in such a way that the va¬ por pressure of the coolant at room temperature (21⁰C) is preferably below 3 bar, especially preferable 1.5 bar, where the vapor pressure is not increasing substan- tially at the maximum operation temperature. It is especially an advantage if the vapor pressure of the coolant at 2O⁰C, preferably even at 5O⁰C, does not exceed a value of 1 bar.

Especially during practical use it has been proven that it is an advantage to select the coolant in such a way that the product of the volume, being available for the coolant within the tank, and the vapor pressure of the coolant at room tempera¬ ture, is lower than 30 bar ltr, preferably lower than 20 bar ltr and especially pref¬ erable lower than 10 bar ltr.

This is especially of advantage with regard to the tank, as this should be exposed preferably only to low strain in order to provide for a long durability with regard to the cryo temperature cooling device. In addition, when only providing limited stress to the tank, cost effective materials could be used. Furthermore, the safety requirements, especially in more sensitive areas, for example in aviation, are much less strict when using tanks with a low pressure only, which additionally increases the field of operation of the device according to the invention. Finally, materials with a lower mass are sufficient for the making of the tank, when the maximum vapor pressure is low only, preferably being only inessentially higher than the pressure of the surrounding. This leads to lighter tanks, therefore lower- ing the complete weight of the device according to the invention, thus further in¬ creasing their portability.

It is an advantage, when the heat conducting element is situated in the device and protruding to the outside, whereas the device preferably comprises a recess, being suitable to house the heat conducting element, whereas the recess is made in such a way that it allows for a thermal contact between the heat conducting element on one side and the coolant within the device on the other side. Preferably, the heat conducting element of the cryo temperature cooling device is formed as a cooling finger.

Preferably, the phase transition temperature T_P of the coolant matches roughly the temperature, to which an object should be cooled by using the cryo temperature cooling device.

In order to further increase the thermal transfer between the coolant and the heat conducting element within the device, further substances are added to the coolant, increasing the heat conductivity according to a further preferred embodiment of the invention.

For a specific application it can be vice-versa necessary to lower the heat conduc- tion. In that case, substances are mixed to the coolant, which lower the thermal transfer.

The tank of the cryo temperature cooling device preferably comprises an inner wall and an outer wall, having a distance from the inner wall. In order to provide a good isolation of the cryo temperature cooling device between the inner wall and the outer wall of the pressure resistant tank, an intermediate area is provided, comprising, according to a preferred embodiment of the invention, a vacuum and/or a heat isolating material, for example styrofoam.

The cryo temperature cooling device preferably is set up as a mainly closed cool¬ ing accumulator, which can be cooled again with a cooling device, for example with a compression refrigerating machine, preferably at least down to the tem¬ perature of the phase transition.

Furthermore, the heat conducting element, which is designed to be within the tank of the cryo temperature cooling device, is preferably adapted in order to be con- nected thermally to an object to be cooled, especially to a detector, preferably a semiconductor detector for the measurement of ionizing radiation.

It is possible to combine the heat conducting element with the tank in such a way, that it protrudes out of this tank at the same time being in thermal contact to the coolant in the inside. For example, the semiconductor detector to be cooled then is connected to the heat conducting element, for example plugged to it. Vice-versa, the heat conducting element can also be connected to the detector, maybe even fixed to the detector. The tank then preferably provides a recession, with which the heat conducting element can be connected to, for example by plugging, the recess. The recess then is made up in such a way that it allows for thermal contact between the coolant and the heat conducting element. Preferably, the heat con¬ ducting element is formed as a cooling finger.

This adoption can be made in such a way at the same time so that it can act as a fixation of the cryo temperature cooling device to an object to be cooled, when the object to be cooled provides a respective plug for the heat conducting element. Thereby, the tank of the cryo temperature cooling device may provide additional devices in order to fix the cryo temperature cooling device to the object to be cooled. Preferably, the heat conducting element itself is fixed to the tank also.

Furthermore, the cryo temperature cooling device preferably comprises a protec¬ tive cap, which is detachably fixed to that part of the heat conducting element, especially the cooling finger, protruding from the tank. It is made shape congruent to the cooling finger, whereby the protective cap preferably comprises a thermal isolating material. The protective cap preferably is plugged to that part of the cooling finger, protruding from the pressure tank, as long as the device according to the invention is not in operation mode, that is used for cooling, for example as long as it is not coupled to a detector in order to cool it. In order to activate the cooling function, the protective cap is removed from the cooling finger. According to a further aspect of the present invention, a device is provided, com¬ prising an element to be cooled and a cryo temperature cooling device. This cryo temperature cooling device comprises a tank, being filled at least partly with cool¬ ant. It is further comprising a heat conducting element, whereas the heat conduct- ing element can be brought into thermal contact with the coolant.

Thereby the device preferably comprises the following features: it is designed as handheld device, the element to be cooled is brought to an intended temperature below -100⁰C, preferably below -14O⁰C, the cooling is effected by the cryo tem- perature cooling device, whereas the coolant is working as a low temperature res¬ ervoir, respectively as a heat sink, the coolant not being consumed or sent to the environment during operation, but remaining mainly within the tank. The cryo temperature cooling device is re-loadable with the help of a charge station, which may be designed stationary or portable, by removing sufficiently enough heat from the coolant so that the following operation of the device is possible for a sufficient period of time, preferably at least one hour, especially preferred at least eight hours and even more preferred at least 24 hours.

Also provided is a measurement device, comprising a detector and a cryo tem- perature cooling device according to the invention, comprising at least one of the following features: the measurement device is set up as a portable handheld de¬ vice , the measurement device is set up as a spectrometer, the detector comprises a semiconductor detector, preferably using germanium, for the measurement of ion¬ izing radiation, and at least one cooling finger of the cryo temperature cooling device is in thermal contact to the detector.

Preferably, the coolant used within the device comprises at least one phase transi¬ tion from the group solid- solid, solid-fluid and fluid- fluid, occurring below a tem¬ perature of -100⁰C. It has been proven to be of further advantage, if the cryo temperature cooling de¬ vice is detachable from the device, so that the reload of the cryo temperature cool¬ ing device can occur when separated.

The element to be cooled within the device may be an electronic element, whose essential characteristics depend from its temperature when used correctly, espe¬ cially its operational ability, noise and amplification, mainly becoming worse with rising temperature. The electronic device thereby may be a sensor or a detector for the detection of radiation, especially electro magnetic and/or ionizing radiation, for example microwaves, infrared, visible or ultra violet light, or of x-ray or gamma-rays.

The term electronic device as used here has to be interpreted very broadly and especially includes all devices, making use of electro magnetic effects in the wid- est sense, that is especially also detectors and detector crystals, but also a detector crystal together with at least the first part of the signal amplifiers of said detector.

The detector described preferably comprises a semiconductor crystal, preferably comprising germanium or silicon. In addition, it is an advantage if the detector comprises evaluation electronics so that the measured radiation can be identified mainly within the detector, whereas the detector preferably is set-up portable as multi-purpose handheld Radio isotope Identifier Device (RID). Such RIDs pref¬ erably comply with the relevant norms of the International Atomic Energy Or¬ ganization in Vienna (IAEO), especially with the classification "Techni- cal/Functional Specification for Border Radiation Monitoring Equipment" as it has been ratified within the Coordinated Research Project "Improvement of Tech¬ nical Measures to Detect and Respond to Illicit Trafficking of Nuclear and other Radioactive Materials", Research Coordination and Technical Meeting (M2-RC- 927), December 1 - 5, 2003, IAEA Headquarters, Vienna. A second cryo temperature cooling device may be provided, allowing for a larger cooling capacity. Said second cooling device may be used stationary, whereas the detector preferably is connected to this second cryo temperature cooling device when it is not used in mobile mission. It, therefore, suits especially for the long- term cooling of the detector between various missions. Such a pre-cooling has the advantage that the limited cooling capacity of the cooling accumulator according to the invention must not be used first for the cooling down to the operation tem¬ perature, so that the mission time of the system is extended.

After the cryo temperature cooling device has been warmed up or at least used part of the cooling capacity, it can be reloaded in such a cooling device used as a charging device, that is it can be cooled down to a temperature preferably below the phase transition of the coolant. Instead of coupling the coolant to the object to be cooled, for example the semiconductor detector, the coolant within the, op- tional pressure -resistant, tank is coupled to the cooling device, whereby the cool¬ ing device preferably is a conventional cooling device, for example making use of electro mechanical cooling, for example of a compression refrigerating machine, or of liquid gases like nitrogen or helium.

The cryo temperature cooling device according to the invention may comprise also a second thermal coupling. The cryo temperature cooling device may there¬ fore be connected with the object to be cooled, for example a circuit or a detector, the one side and on the other side with the cooling device or a cooling device with a higher capacity. In such a way, the complete system including the object to be cooled can be cooled down so that the complete system may be used for opera¬ tional purposes immediately, at the same time allowing for the maximum cooling capacity at the beginning of the mission.

Furthermore, a cooling device for the cooling of the above described cryo tem- perature cooling device is claimed, whereby the cooling device may be coupled thermally to the cryo temperature cooling device and whereby the cooling mainly occurs via the thermal connection and mainly without a mass exchange between the cooling device and the cryo temperature cooling device to be cooled. This includes a cooling by using a flow of gas and/or a flow of liquids, as long as the coolant of the cryo temperature cooling device mainly remains within the cryo temperature cooling device. The cooling device itself may be cooled by using liq¬ uid gases, preferably with liquid nitrogen and/or liquid helium and/or by using electric and/or mechanical cooling devices, for example a compression refrigerat¬ ing machine.

According to the invention, a compound, showing a phase transition temperature of below -100⁰C, is used as a coolant in the cryo temperature cooling device. The compound may be, according to one aspect of this invention, an organic com¬ pound, for example vinyl bromide, butane, butene-2-cis, ethyl acetylene, butene- 1, isobutene or ethyl bromide.

According to even another aspect of the invention, the coolant has a vapor pres¬ sure at room temperature (21⁰C) of preferably below 3 bar, especially preferred of lower than 1.5 bar, whereas it is explicitly an advantage if the vapor pressure of the coolant at 2O⁰C, especially preferred at 5O⁰C, does not exceed a value of 1 bar.

In the following, the invention is described by using a specific embodiment in the light of the enclosed figures.

The figures show:

Fig.l a cross sectional view through the cryo temperature cooling device accord¬ ing to the invention; Fig. 2 a cross sectional view through the measurement device according to the invention; Fig. 3 a top view to a portable measurement device according to the invention; Fig. 4 a further embodiment with a cooling device integrated in the detector; and Fig. 5 an embodiment with separate radiator coil.

Fig. 1 is a cross sectional view through the cryo temperature cooling device 1 ac¬ cording to the invention. The tank 2 is preferably made from pressure resistant material so that it can withstand the vapor pressure of the coolant 3 both at room temperature as well as at the maximum operation or storage temperature of the cryo temperature cooling device. A tank 2 in addition is made in such a way that it comprises an inner wall 5 and an outer wall 6, having a distance from the inner wall 5 via an intermediate area 7. The intermediate area 7 is filled with heat insu- lating layers so that tank 2 respectively the cryo temperature cooling device 1 separates the coolant sufficiently from the surrounding temperature and that it remains in the frozen state for a long term of time.

Within the tank 2 the coolant 3 is provided. The substances, coming into question as a coolant for the cryo temperature cooling device 1, stand out by a low phase transition temperature, for example a low melting temperature, being roughly the temperature to which an object is to be cooled, a preferably high heat of fusion, preferably high boiling temperature and a preferably low vapor pressure at the maximum operation/storage temperature. Some of the substances to be considered and their relevant properties are listed in the following, not completed Table 1 :

Table 1:

Melting Heat of Boiling Point Fusion Tempera¬ ture

T₈ Tsi

Coolant Formula [⁰C] PcM] [⁰C]

Pentaborane (11) B5-H11 -122,0 65,0

Phosphorotioc bromide difluoride PSBrF2 -136,9 35,5

Trichlorosilane SiHCB -128,2 33,0

Sulfur dichloride SC12 -122,0 59,6 1 ,2,2-Trichloro- 1 , 1 -difluoroethane C2-H-C13-F2 -140,0 71,9

1 ,2,2-Trichloro- 1 ,2- difluoroethane C2-H-C13-F2 -174,0 72,5

1 , 1 -Dichloroethene C2-H2-C12 -122,6 81,5 31,6

Bromoethene, Bromoethylene, C2-H3-Br -139,5 71,8 15,8 Vinyl bromide

Acetaldehyde C2-H4-O -123,4 41,1 20,1

Ethyl bromide, Bromo ethane C2-H5-Br -118,7 54,1 38,4

Ethane thiol C2-H6-S -147,9 66,7 35,1

1-Chloropropane C3-H7-C1 -122,9 62,8 46,5

1-Propanol C3-H8-O -124,4 71,5 97,2

2-Propanethiol C3-H8-S -130,5 61,4 52,6

Butane C4-H10 -138,0 81,2 -0,5

Butene-2 cis C4-H8 -139,0 130,2 3,7

Ethyl acetylene C4-H6 -125,7 111,5 8,1

Butene-1 C4-H8 -185,4 68,6 -6,3

Isobutene C4-H8 -140,0 105,7 -6,9 cis-l,3-Pentadiene C5-H8 -140,8 57,2 44,1

1,4-Pentadiene C5-H8 -148,2 59,4 26,0

2-Methyl- 1 , 3 -butadiene C5-H8 -145,9 49,2 34,0

Cyclopentene C5-H8 -135,0 38,1 44,2

1-Pentene C5-H10 -165,1 54,3 30,0 cis-2-Pentene C5-H10 -151,4 66,5 36,9 trans-2-Pentene C5-H10 -140,2 76,6 36,3

2-Methyl- 1 -butene C5-H10 -137,5 73,4 31,2

3 -Methyl- 1 -butene C5-H10 -168,4 47,5 20,1

2-Methyl-2-butene C5-H10 -133,7 71,8 38,6 trans- 1 ,2-Dimethylcyclopropane C5-H10 -149,6 28,2

Ethylcyclopropane C5-H10 -149,2 35,9

Methylcyclobutane C5-H10 -161,5 36,3

Pentane C5-H12 -129,7 72,9 36,1 Isopentane C5-H12 -159,8 44,3 27,9

2-Pentanethiol C5-H12-S -169,0 112,9

Diethylmethylamine C5-H13-N -196,0 66,0

4-Methylcyclopentene C6-H10 -160,8 65,7

1,5-Hexadiene C6-H10 -140,7 59,4

1-Hexene C6-H12 -139,8 74,3 63,5 cis-2-Hexene C6-H12 -141,1 72,0 68,8

Methylcyclopentane C6-H12 -142,4 61,7 71,8

2,3-Dimethyl- 1 -butene C6-H12 -157,3 55,6

Ethylcyclobutane C6-H12 -142,9 70,8 cis-2-Hexene C6-H12 -141,1 68,8

3 -Methyl- 1 -pentene C6-H12 -153,0 54,2

4-Methyl- 1 -pentene C6-H12 -153,6 53,9

4-Methyl-trans-2-pentene C6-H12 -140,8 58,6

2-Methylpentane C6-H14 -153,6 47,3 60,3

3-Methylpentane C6-H14 -162,9 40,6 63,3

2,3-Dimethylbutane C6-H14 -128,1 6,1 57,9

2-Hexanethiol C6-H14-S -147,0 142,0

Triethylsilane C6-H16-Si -159,0 109,0

1-Heptene C7-H14 -118,9 88,1 93,6

Methylcyclohexane C7-H14 -126,6 52,9 100,9

4-Methy- 1 -hexene C7-H14 -141,5 86,7 trans-2-Methyl3-hexene C7-H14 -141,6 85,9

2,2-Dimethylpentane C7-H16 -123,7 39,1 79,2

3,3-Dimethylpentane C7-H16 -134,4 47,4 86,1

1 -Ethyl- 1 -methylcyclopentane C8-H16 -143,8 121,6

3-Methylheptane C8-H18 -120,5 71,8 118,9

4-Methylheptane C8-H18 -121,0 66,6 117,7

It is to be understood that Table 1 does not list all coolants to be used according to the invention, but only a selection. Especially, this selection is mainly limited to substances with a boiling temperature Tsi > 2O⁰C and a melting temperature Ts < - 12O⁰C. Only butane, butene-2 cis, ethyl acetylene, butene-1 and isobutene have been mentioned in addition, even if their boiling temperature Ts₁ is lower than 2O⁰C. Suitable as coolants are propane and propene also, but they do have a vapor pressure of 8.7 and 10.3 bar at 21⁰C, therefore requiring higher standards with regard to the pressure resistance of the tank 2.

As a comparison, liquid nitrogen has a boiling temperature of - 196⁰C and a heat of fusion of about 161 kJ/ltr. Suitable as coolants are also substances like propane and propene, which nevertheless do have a vapor pressure of already 8.7 respec- tively 10.3 bar at 21⁰C and therefore having to meet higher demands when it comes to the pressure stability of the tank.

Furthermore, a heat conducting element 4 in the form of a cooling finger, protrud¬ ing from tank 2 through an opening 14 through the inner wall 5 and the outer wall 6, is seen in the cryo temperature cooling device 1. The cooling finger 4 is sur¬ rounded nearly completely from the coolant 3 within the tank 5. Mounted to the part of the cooling finger 4, protruding from the cryo temperature cooling device 1, is heat insulating protective cap 8. So, the complete cryo temperature cooling device 1 is isolated from the surrounding temperature as long as it is not in opera- tion respectively not used for the cooling of an object, therefore, being able to be stored. The cooling finger 4 preferably also comprises material, providing for a good heat transfer and at the same time for the thermal connection between cool¬ ant and the object to be cooled. It may for example be made from copper. In order to further improve the heat transfer of the coolant 3 to the cooling finger, further substances could be added to the coolant 3 in order to promote this property.

The cryo temperature cooling device is used as follows: the cryo temperature cooling device 1 is charged by bringing the cooling finger 4 to a temperature be¬ low the melting point of the coolant. When using vinyl-bromide, this would, for example, be a temperature below -138⁰C (135.2 K). This cooling process contin¬ ues until the coolant is mainly frozen. The cooling, respectively the charging of the cryo temperature cooling device 1, is conducted with a charging device, for example a compression refrigerating machine or with liquid nitrogen.

Afterwards, in order to store the cryo temperature cooling device 1 until it is used for operational purposes, the protecting cap 8 is mounted to the cooling finger 4. Therefore, a good heat insulation of the cryo temperature cooling device 1 with regard to the outside is achieved and the frozen state of the coolant 3 can be kept fairly long.

When the cryo temperature cooling device 1 should be used for cooling purposes, for example of a detector, the protective cap 8 is removed from the cooling finger 4 and the cooling finger 4 is connected to the object to be cooled or included therein.

Fig. 2 shows a cross section at view of a cryo temperature cooling device 1 ac¬ cording to the invention, which might be coupled to a detector 10, comprising a detector support 15, a detector crystal 16, being connected to a preamplifier, also mounted on the detector support 15 and therefore cooled also, as well as an outer wall 20. The outer wall in the embodiment is comprising a window, being mainly transparent for the radiation to be measured, namely a radiation entry window 21.

The cooling finger 4 of the detector 10 is thermally mounted to the detector sup¬ port 15, supporting also the detector crystal 16, for example a germanium crystal. There are, nevertheless, other detector crystals suitable in order to be cooled by the inventive cryo temperature cooling device 1, for example silicon crystal detec¬ tors, CdTe-detectors and others. Preferably, the preamplifier is thermally con¬ nected to the detector support 15 also so that this is cooled, too. When the meas¬ urement respectively the operation time of the detector 10 has ended, the cryo temperature cooling device 1 can be removed from the detector 10 again in order to be recharged for a further measurement. As the size of the cryo temperature cooling device 1 is small, it is especially suit¬ able for the operation in combination with a measurement device in the form of a handheld device 11, which is shown schematically in a top view in Fig. 3.

Because of its low weight and volume this handheld device 11 is especially suit¬ able for mobile missions, for example as gamma ray detector for luggage control at airports, borders or at big events. The handheld device 11 is touched at its han¬ dle 17 and hold thereon during the measurement. Input keys 12 allow the selection for example of various functions or are designed to start and end the measurement operation. Measurement results may be metered either acoustically, for example when excessing the detected limits, or via reading the display 13.

Fig. 4 shows a further embodiment in which, according to the invention, the cryo temperature cooling device is integrated to the detector, forming one measurement device 9. Thereby the detector, comprising a detector support 15 and a detector crystal 16 including pre-amplifier, the heat conducting element 4 and the inner tank 5 together with the coolant 3 are forming a fixed mounted device. Thereby, the heat conducting element 4 and the detector support 15 can be made from one piece. The inner tank 5 is made to withstand pressure in this embodiment, so that it can withstand the vapor pressure of the used coolant at the maximum operating temperature.

Via a connection 18, which may be protected and isolated by a removable heat insulating cap 8, it is possible - after removal of cap 8 - to "load" the cryo tem- perature cooling device as described above, that is it could be cooled, by keeping the heat conducting contact of the connection 18 at a temperature T until the de¬ tector is cooled and the coolant is mainly frozen. For the temperature T it is true that T < Tp, whereby Tp is the phase transition temperature of the coolant used according to the invention. After removing the charging device from the connec- tion 18 and attaching the protection cap 8, the detector is kept cooled for several hours ready for operation. Fig. 5 shows another embodiment, at which the "charging" occurs not via the heat conducting element 4, but via a cooling coil 19 mounted within the inner tank 5. Instead of the heat conducting element 4, the cooling coil 19 is led to the connec- tion 18, so that during the "charging process" the coolant 3 is cooled via the cool¬ ing coil 19.

The use of cooling coil 19 for the charging of the cryo temperature cooling device 1 is especially an advantage when cooled (liquefied) gases, for example nitrogen or helium or others, liquid coolants are available for the cooling process. Those cooled (liquefied) gases or coolants could then be piped directly through the inner part of the cooling coil, which allows for a higher heat transport so that the cool¬ ing can take place faster. Furthermore, the connections 18 of the cooling coil, be¬ ing directed to the outside, may consist of materials, being bad heat conductors, so that the heat insulation of the cryo temperature cooling device with regard to the surrounding is improved, so that the operation time can even be improved with regard to the device shown in Fig. 4.

In addition to the use for the cooling of detectors, the cryo temperature cooling device according to the invention can be used in any devices where cryo tempera¬ tures are necessary or wanted. This is especially true for, but not limited to further measurement applications, not the least for such applications, using superconduc¬ tors, especially high Tc superconductors. One has to think firsthand to electronics, here especially to noise sensitive preamplifiers, to IR sensors, night vision de- vices, to SQUIDs or to applications for radar. List of references

1 cryo temperature cooling device

2 tank 3 coolant

4 heat conducting element

5 inner wall (inner tank)

6 outer wall (outer tank)

7 intermediate space 8 protecting cap

9 measurement device

10 detector

11 handheld device

12 input key 13 display

14 opening

15 detector support

16 detector crystal, eventually with preamplifier

17 handle 18 connection

19 cooling coil

20 outer wall of the detector

21 radiation entry window

Claims

Applicant July 28, 2005Target Systemelectronic GmbH Our ref : T50448PC MSClaims

1. Cryo temperature cooling device (1) comprising a tank (2), being filled up at least in part with a coolant (3), and a heat conducting element (4), whereas the heat conducting element (4) can be brought into thermal con¬ tact with the coolant (3), characterized in that the coolant has a phase tran¬ sition occurring below a temperature Of -IOO⁰C, so that the cryogenic cool- ing device more or less consumes no coolant during operation.

2. Cryo temperature cooling device (1) according to claim 1, characterized in that the tank (2) is pressure resistant.

3. Cryo temperature cooling device (1) according to one of the preceding claims, characterized in that the coolant comprises an organic compound, comprising a heat of fusion of less than -100⁰C.

4. Cryo temperature cooling device (1) according to claim 1, characterized in that the coolant (3) comprises one or more of the following compounds:

• vinyl bromide,

• ethyl bromide,

• butane,

• butene-2 cis, • ethyl acetylene,

• butene-1,

• isobutene.

5. Cryo temperature cooling device (1) according to one of the preceding claims, characterized in that the coolant provides a phase transition from the group solid- solid, solid-fluid, and fluid-fluid.

6. Cryo temperature cooling device (1) according to one of the previous claims, characterized in that the coolant (3) has a phase transition tempera¬ ture (T_p) below -14O⁰C.

7. Cryo temperature cooling device (1) according to one of the previous claims, characterized in that the coolant (3) provides a boiling temperature

Tsi of higher than 2O⁰C.

8. Cryo temperature cooling device (1) according to the previous claim, char¬ acterized in that the coolant (3) provides a boiling temperature Ts₁ of higher than 5O⁰C.

9. Cryo temperature cooling device (1) according to one of the previous claims, characterized in that the coolant (3) provides a phase transition en¬ ergy of at least 35 kJ/liter, preferably a phase transition energy of at least 50 kJ/liter and especially preferred of at least 80 kJ/liter.

10. Cryo temperature cooling device (1) according to one of the previous claims, characterized in that the coolant (3) provides a low vapor pressure at room temperature (21⁰C), preferably below 3 bar, especially preferable below 1.5 bar, whereby the vapor pressure is not increasing substantially at the maximum operation temperature.

11. Cryo temperature cooling device (1) according to one of the previous claims, characterized in that the coolant (3) is selected so that the vapor pressure of the coolant at 2O⁰C does not exceed a value of 1 bar.

12. Cryo temperature cooling device (1) according to one of the previous claims, characterized in that the coolant (3) is selected so that the vapor pressure of the coolant at 5O⁰C does not exceed a value of 1 bar.

13. Cryo temperature cooling device (1) according to one of the previous claims, characterized in that the coolant (3) is selected so that the product of the volume, being available for the coolant within the tank (2), and the vapor pressure of the coolant (3) at room temperature is lower than 30 bar liter, preferably lower than 20 bar liter and especially preferable lower than 10 bar liter.

14. Cryo temperature cooling device (1) according to one of the previous claims, characterized in that the heat conducting element (4) is located in the device (2), protruding to the outside.

15. Cryo temperature cooling device (1) according to the previous claim, char¬ acterized in that the tank (2) comprises a recess, being suitable to house the heat conducting element (4), whereas the recess is made in such a way that it allows for a thermal contact between the heat conducting element on one side and the coolant (3) within the device (2) on the other side.

16. Cryo temperature cooling device (1) according to one of the previous claims, characterized in that the heat conducting element (4) is a cooling finger.

17. Cryo temperature cooling device (1) according to one of the previous claims, characterized in that the phase transition temperature (Tp) of the coolant (3) matches roughly the temperature, to which an object is to be cooled by the cryo temperature cooling device (1).

18. Cryo temperature cooling device (1) according to one of the previous claims, characterized in that there are further substances within the tank (2), increasing the heat transfer between the coolant (3) and the heat con¬ ducting element (4).

19. Cryo temperature cooling device (1) according to one of the previous claims, characterized in that the tank (2) comprises an inner wall (5) and an outer wall (6), having a distance from the inner wall (5) preferably meeting at least one of the following conditions: • the intermediate area (7) between the inner wall (5) and the outer wall

(6) of the pressure resistant tank (2) comprises a vacuum, • the intermediate area (7) between the inner wall (5) and the outer wall (6) of the pressure resistant tank (2) comprises heat isolating material.

20. Cryo temperature cooling device (1) according to one of the previous claims, being set up as a mainly closed cooling accumulator, being coolable again with a cooling device, preferably a compression refrigerat¬ ing machine, preferably at least down to the temperature of the phase tran¬ sition.

21. Cryo temperature cooling device (1) according to one of the previous claims, where the heat conducting element (4) is adapted in order to be connected thermally to an object to be cooled, especially to an electronic circuit, for example a pre- amplifier, or to a detector, especially to a semi- conductor detector for the measurement of ionizing radiation.

22. Cryo temperature cooling device (1) according to one of the previous claims, where the tank (2) comprises additional devices in order to fix the cryo temperature cooling device (1) to the object to be cooled.

23. Cryo temperature cooling device (1) according to one of the previous claims, where the heat conducting element (4) is fixed within the tank (2).

24. Cryo temperature cooling device (1) according to claim 14, further com- prising a protective cap (8), being detachably fixed to that part of the heat conducting element (4) protruding from the tank (2) and being shape con¬ gruent to it, whereby the protective cap (8) preferably comprises a ther¬ mally isolating material.

25. Cryo temperature cooling device (1) according to claim 15, further com¬ prising a protective cap (8), being detachably fixed to the recess of the tank (2) and being shape congruent to it, whereby the protective cap (8) pref¬ erably comprises a thermally isolating material.

26. Measurement device (9), comprising a detector (10) and a cryo tempera¬ ture cooling device (1) according to one of the preceding claims 1 to 25 for cooling the detector (10), comprising at least one of the following features:

• the measurement device (9) is set up as a portable handheld device

(H), • the measurement device (9) is set up as a spectrometer,

• the detector (10) comprises a semiconductor detector, preferably using germanium, for the measurement of ionizing radiation,

• at least one cooling finger (4) of the cryo temperature cooling device (1) is in thermal contact to the detector (10).

27. Device (9) according to the previous claim where the cryo temperature cooling device (1) is re-loadable with the help of a charge station, being designed stationary or portable, by removing sufficiently enough heat from the coolant so that the following intended operation of the device is possi- ble for a sufficient period of time, preferably at least one hour, especially preferred at least eight hours and even more preferred at least 24 hours.

28. Device according to one of the preceding claims 26 or 27, where the cool¬ ant (3) has at least one phase transition from the group solid-solid, solid- fluid and fluid- fluid, occurring below a temperature Of -IOO⁰C.

29. Device according to one of the claims 26 to 28, whereby the cryo tempera¬ ture cooling device (1) is detachable from the device, so that the re-loading of the cryo temperature cooling device (1) can occur in a separated state.

30. Device according to one of the claims 26 to 29, whereby the component to be cooled is an electronic element, whose essential characteristics for its intended use, especially its operational ability, noise and amplification, de¬ pend from its temperature, mainly becoming worse with rising tempera¬ ture.

31. Device according to the previous claim, whereby the electronic element is a sensor.

32. Device according to one of the claims 26 to 31, whereby the component to be cooled is a detector for the detection of electro magnetic and/or ionizing radiation.

33. Device according to the previous claim, whereby the at least the first part of the signal amplifier of the detector is cooled also.

34. Device according to one of the claims 32 or 33, whereby the detector com¬ prises a semiconductor crystal, preferably comprising germanium or sili¬ con.

35. Device according to one of the claims 32 to 34, whereby the detector com¬ prises evaluation electronics so that the measured radiation can be mainly identified within the detector, whereas the detector preferably is designed as a handheld device and set-up as Multi Purpose Handheld Radio Isotope Identifier Device (RID).

36. Use of a compound as coolant (3) in a device according to one of the pre¬ vious claims, whereas the coolant comprises a phase transition temperature Tp of below -100⁰C.

37. Use of an compound as coolant (3) according to the preceding claim, where the compound is an organic compound.

38. Use of a compound as coolant (3) according to the preceding claim, where the compound comprises vinyl bromide.

39. Use of a compound as coolant (3) according to claim 37, where the com¬ pound comprises butane, butene-2 cis, ethyl acetylene, butene-1, isobutene or ethyl bromide.

40. Use of a compound as a coolant (3) in a device according to one of claims 1 to 25, whereby the coolant provides a vapor pressure at room tempera¬ ture (21⁰C) of less than 3 bar, preferably a vapor pressure of less than 1.5 bar.

41. Use of a compound as coolant (3) in a device according to the previous claim, characterized in that a coolant (3) is selected, whose vapor pressure at 2O⁰C, especially preferred at 5O⁰C, does not exceed a value of 1 bar.

42. Cooling device for the cooling down of a cryo temperature cooling device (1) according to one of claims 1 to 25, characterized in that the cooling de- vice for the cooling down of the cryo temperature cooling device (1) can be connected thermally with said cryo temperature cooling device (1) and where the cooling down is provided mainly via said thermal connection and mainly without material exchange between cooling device and the cryo temperature cooling device (1) to be cooled down.

43. Cooling device according to the previous claim, characterized in that the cooling device is cooled with liquefied gases, preferably with liquid nitro¬ gen and/or liquid helium.

44. Cooling device according to claim 42, characterized in that the cooling device is cooled with a compression refrigeration machine.