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Dilution refrigerator system
Continuous f l o w cryostat On show at the International Cryogenics Exhibition in Brighton was the Oxford Instruments' new CF 100 continuous flow cryostat. This instrument was designed for research facilities where up to now low temperature installations have been technically difficult. It is especially useful for optical research where it can be used with a spectrophotometer and different models are available for UV and Raman, x-ray, and Mossbauer applications. Custombuilt units can be designed for any other applications. The cryostat for x-ray studies is shown in the photograph below. It can be used in any orientation and this combined with its small size make it suitable for horizontal axis goniometers. The upper part contains the co-axial refrigerant input and exit tubes, vacuum vent valves, sample block, and radiation shield - this is the standard refrigeration u n i t - and the lower part consists of a demountable vacuum shroud. The refrigerant is circulated via a micrometer valve by a rotary pump. The exhaust gas cools the radiation shield thus no secondary refrigerant is required. By varying the gas flow by means of an adjusting collar and needle valve on the vacuum console, the temperature can be varied from 3 - 3 0 0 K. During tests temperatures approaching 2 K have been achieved. The additional entry post can
be used for injecting liquid or gaseous samples onto the cold point or using warm gases for rapid warm-up. The CF 100 is only 45 cm high with 6 cm shroud outer diameter and weighs 1"5 kg. It has a temperature stability of 0 " I K at 3 - 1 0 K , 0 " 5 K at 7 - 7 0 K , and 1 K at 7 0 - 3 0 0 K. Cool-down time from 300-4"2 K is approximately 10 minutes and refrigeration capacity at 4"2 K is 360 mW. Other advantages are that it is free from vibrations, has a safe low operating pressure - outer case vacuum 10 -5 torr (10 -3 N m -2) with LN2 refrigerant, and allows easy sample changes. Shrouds fitted with a variety of radial and axial windows for different spectral ranges can be supplied. Oxford Instruments has also introduced a new model of their Md4A Modular Dewar. This new model has 99 possible combinations of tails and variable temperature inserts. Also it has an increased liquid helium capacity which allows overnight operations to be carried out. Constructed from all stainless steel with copper welding, it covers a temperature range of 210 mK to 300 K and is fully guaranteed for 12 months. (Oxford Instruments Co Ltd, Oxney Mead, Oxford, UK)
Steel for liquefied gas containers The Armco Steel Corp has developed a process which produces a notch-tough alloy steel with 5% nickel content for use in the transportation, storage, and processing of liquefied gases. Known as Cryonic 5 this material is suitable for temperatures down to - 1 7 0 C. Cryonic 5 is heat treated by austenitizing, quenching, temperizing, quenching, and reversion annealing at a minimum temperature of 620 C. The first step, conventional austenitizing and quenching, produces a martensitic structure. The second treatment develops a lamellar pattern of martensite and ferrite with some retained austenite, while the third treatment refines the ferritic substructure, increases the amount of retained austenite, and causes precipitation of carbides. Welding characteristics are similar to those of 9% nickel steel; pre-heating is unnecessary except for welding joints in heavy or highly restrained members. Toughness of Cryonic 5 is tested by the Charpy V-notch impact test and the drop weight test. Steel is available in plates in thicknesses varying from ~/16 in (4"8 mm) to 1½ in (38 mm) and also in bars, billets, and various other structural shapes. (Armco Steel Corp, Middletown, Ohio, USA)
Dilution refrigerator system
O x f o r d Instruments' CF 100 continuous d i f f r a c t i o n studies
CRYOGENICS
. A U G U S T 1971
f l o w cryostat f o r x-ray
Cryogenic Associates Dilution Refrigerator is a complete modular system which can produce continuous refrigeration at externally measured temperatures as low as 0"02 K. Based upon London's He 3/He 4 method of refrigeration proposed in 1951, the refrigerator consists of four units external dewar, insert cryostat, dilution unit, and control, monitoring, and gas handling systems. The external dewar is a standard SD-13 nitrogen shielded dewar. This acts as a reservoir. The insert cryostat 331
is an all stainless steel system consisting of a 1 K condensation bath, a pumping tube, and provision for running temperature probes to the dilution unit. The dilution unit is constructed from OFHC copper and stainless steel. The heat exchangers are sintered copper and the mixing chamber bottom is detachable to enable easy sample mounting. The control, monitoring, and gas handling unit includes vacuum pumps, valves, pressure gauges, storage tanks, impurity traps, and electrical interlocks, all of which provide routine operation of the cryostat and dilution unit. The refrigerator has a heat extraction capacity of 1 000 ergss -l ( l e r g s -~ = 10 - T w ) a t 0 ' l K , o r 120ergss -1 at 0"04 K. Its simple, rugged construction allows operation in unfavourable environments. Possible experimental applications include Mossbauer spectroscopy, polarized targets for nuclear or elementary particle physics, quantum fluids, superconductivity, Kondo effect, thermal transport properties of solids, and nuclear demagnetization. A variety of optional equipment is available and the cryostat can be supplied as a standard immersion dewar or as a tail section dewar system. (Cryogenic Associates Inc, 1718 North Luett Avenue, Indianapolis, Ind 46222, USA)
of the apparatus was sub-contracted to the Essex Manufacturing Company of St Louis, Missouri. Air is either liquefied in a refrigerating unit, manufactured by US Philips Corporation, or liquid air is purchased from the Linde Division of Union Carbide Corporation. This is stored in a 10 litre vacuum stainless steel container with a built-in heat exchanger. The rest of the apparatus consists of valving arrangement, which provides great ease in ventilation, leakage protection, and a hose attached to the nasal face-piece, which is similar to the respirator more commonly used. Cleaning, checking, and refilling is carried out on the surface, and the operator transports the unit in an out of the mine on a personal carrier or by bus. The breathing apparatus are at present being used in the US Steel Corporation's Gary District No 2 Mine in McDowell County, West Virginia. (US Steel Corporation, 525 William Penn Place, Pittsburgh, Pa 15230, USA)
Disposable cataract e x t r a c t o r
A new type of breathing apparatus for coal miners which provides clinically pure air by means of a cryogenic process has been developed by Firewell Co Inc, and Mine Ventilation Systems Inc, for the US Steel Corporation. The device was first designed in 1965 by Firewell Co Inc, a subsidiary of Aro Corporation of New York, for mine rescue services. After assessing the merit of this instrument US Steel asked the Mine Ventilation Systems Inc, to develop a prototype unit for use by continuous mining machine operators. This was completed in April 1966 but in the next few years various other methods of delivering clean air were explored before it was finally decided in January 1969 to go ahead with this unit. The manufacture
A disposable cryosurgical instrument for cataract surgery is the latest development from Frigitronics Inc. The instrument known as the F - 2 0 / 2 0 disposable cryo-extractor is shown below complete with an 8 cm 3 canister which is supplied with it. This is sufficient to run the cryo-extractor for 4 minutes. When the canister is inserted in the cryo-extractor, the freezing process is activated by pressing and rotating the rear cap. Freon 12 is then conducted internally to the tip of the probe where it expands through a small expansion valve inside the silver tip. The resulting evaporation causes freezing, and the evaporated liquid then passes out the exhaust in the rear of the probe. The freezing process can be stopped and the probe defrosted by pressing the lever on the top of the probe handle. This action causes a small expansion valve inside of the probe tip to open and consequently the tip is flooded with liquid refrigerant. At the same time the exhaust from the inside of the probe tip is closed by another valve. The
US Steel Corporation's breathing apparatus at present undergoing field tests in their Gary District No 2 Mine
Frigitronics F - 2 0 / 2 0 disposable cateract extractor
L o w t e m p e r a t u r e process for breathing apparatus
CRYOGENICS
. AUGUST
1971
333
be used for injecting liquid or gaseous samples onto the cold point or using warm gases for rapid warm-up. The CF 100 is only 45 cm high with 6 cm shroud outer diameter and weighs 1"5 kg. It has a temperature stability of 0 " I K at 3 - 1 0 K , 0 " 5 K at 7 - 7 0 K , and 1 K at 7 0 - 3 0 0 K. Cool-down time from 300-4"2 K is approximately 10 minutes and refrigeration capacity at 4"2 K is 360 mW. Other advantages are that it is free from vibrations, has a safe low operating pressure - outer case vacuum 10 -5 torr (10 -3 N m -2) with LN2 refrigerant, and allows easy sample changes. Shrouds fitted with a variety of radial and axial windows for different spectral ranges can be supplied. Oxford Instruments has also introduced a new model of their Md4A Modular Dewar. This new model has 99 possible combinations of tails and variable temperature inserts. Also it has an increased liquid helium capacity which allows overnight operations to be carried out. Constructed from all stainless steel with copper welding, it covers a temperature range of 210 mK to 300 K and is fully guaranteed for 12 months. (Oxford Instruments Co Ltd, Oxney Mead, Oxford, UK)
Steel for liquefied gas containers The Armco Steel Corp has developed a process which produces a notch-tough alloy steel with 5% nickel content for use in the transportation, storage, and processing of liquefied gases. Known as Cryonic 5 this material is suitable for temperatures down to - 1 7 0 C. Cryonic 5 is heat treated by austenitizing, quenching, temperizing, quenching, and reversion annealing at a minimum temperature of 620 C. The first step, conventional austenitizing and quenching, produces a martensitic structure. The second treatment develops a lamellar pattern of martensite and ferrite with some retained austenite, while the third treatment refines the ferritic substructure, increases the amount of retained austenite, and causes precipitation of carbides. Welding characteristics are similar to those of 9% nickel steel; pre-heating is unnecessary except for welding joints in heavy or highly restrained members. Toughness of Cryonic 5 is tested by the Charpy V-notch impact test and the drop weight test. Steel is available in plates in thicknesses varying from ~/16 in (4"8 mm) to 1½ in (38 mm) and also in bars, billets, and various other structural shapes. (Armco Steel Corp, Middletown, Ohio, USA)
Dilution refrigerator system
O x f o r d Instruments' CF 100 continuous d i f f r a c t i o n studies
CRYOGENICS
. A U G U S T 1971
f l o w cryostat f o r x-ray
Cryogenic Associates Dilution Refrigerator is a complete modular system which can produce continuous refrigeration at externally measured temperatures as low as 0"02 K. Based upon London's He 3/He 4 method of refrigeration proposed in 1951, the refrigerator consists of four units external dewar, insert cryostat, dilution unit, and control, monitoring, and gas handling systems. The external dewar is a standard SD-13 nitrogen shielded dewar. This acts as a reservoir. The insert cryostat 331
is an all stainless steel system consisting of a 1 K condensation bath, a pumping tube, and provision for running temperature probes to the dilution unit. The dilution unit is constructed from OFHC copper and stainless steel. The heat exchangers are sintered copper and the mixing chamber bottom is detachable to enable easy sample mounting. The control, monitoring, and gas handling unit includes vacuum pumps, valves, pressure gauges, storage tanks, impurity traps, and electrical interlocks, all of which provide routine operation of the cryostat and dilution unit. The refrigerator has a heat extraction capacity of 1 000 ergss -l ( l e r g s -~ = 10 - T w ) a t 0 ' l K , o r 120ergss -1 at 0"04 K. Its simple, rugged construction allows operation in unfavourable environments. Possible experimental applications include Mossbauer spectroscopy, polarized targets for nuclear or elementary particle physics, quantum fluids, superconductivity, Kondo effect, thermal transport properties of solids, and nuclear demagnetization. A variety of optional equipment is available and the cryostat can be supplied as a standard immersion dewar or as a tail section dewar system. (Cryogenic Associates Inc, 1718 North Luett Avenue, Indianapolis, Ind 46222, USA)
of the apparatus was sub-contracted to the Essex Manufacturing Company of St Louis, Missouri. Air is either liquefied in a refrigerating unit, manufactured by US Philips Corporation, or liquid air is purchased from the Linde Division of Union Carbide Corporation. This is stored in a 10 litre vacuum stainless steel container with a built-in heat exchanger. The rest of the apparatus consists of valving arrangement, which provides great ease in ventilation, leakage protection, and a hose attached to the nasal face-piece, which is similar to the respirator more commonly used. Cleaning, checking, and refilling is carried out on the surface, and the operator transports the unit in an out of the mine on a personal carrier or by bus. The breathing apparatus are at present being used in the US Steel Corporation's Gary District No 2 Mine in McDowell County, West Virginia. (US Steel Corporation, 525 William Penn Place, Pittsburgh, Pa 15230, USA)
Disposable cataract e x t r a c t o r
A new type of breathing apparatus for coal miners which provides clinically pure air by means of a cryogenic process has been developed by Firewell Co Inc, and Mine Ventilation Systems Inc, for the US Steel Corporation. The device was first designed in 1965 by Firewell Co Inc, a subsidiary of Aro Corporation of New York, for mine rescue services. After assessing the merit of this instrument US Steel asked the Mine Ventilation Systems Inc, to develop a prototype unit for use by continuous mining machine operators. This was completed in April 1966 but in the next few years various other methods of delivering clean air were explored before it was finally decided in January 1969 to go ahead with this unit. The manufacture
A disposable cryosurgical instrument for cataract surgery is the latest development from Frigitronics Inc. The instrument known as the F - 2 0 / 2 0 disposable cryo-extractor is shown below complete with an 8 cm 3 canister which is supplied with it. This is sufficient to run the cryo-extractor for 4 minutes. When the canister is inserted in the cryo-extractor, the freezing process is activated by pressing and rotating the rear cap. Freon 12 is then conducted internally to the tip of the probe where it expands through a small expansion valve inside the silver tip. The resulting evaporation causes freezing, and the evaporated liquid then passes out the exhaust in the rear of the probe. The freezing process can be stopped and the probe defrosted by pressing the lever on the top of the probe handle. This action causes a small expansion valve inside of the probe tip to open and consequently the tip is flooded with liquid refrigerant. At the same time the exhaust from the inside of the probe tip is closed by another valve. The
US Steel Corporation's breathing apparatus at present undergoing field tests in their Gary District No 2 Mine
Frigitronics F - 2 0 / 2 0 disposable cateract extractor
L o w t e m p e r a t u r e process for breathing apparatus
CRYOGENICS
. AUGUST
1971
333