| 摘要 |
PROBLEM TO BE SOLVED: To provide a freezer for MRI capable of removing impurities in the coolant sufficiently. SOLUTION: When the temperature of a cold head 6 is lowered by the operation of a helium freezer 100 for MRI, the hydrogen vapor pressure in a hydrogen vapor pressure thermometer is lowered a pressure relief valve 13 apeus, a pressure relief valve 15 closes, and gaseous helium flows into a catridge 20. And the impurities in the gaseous helium not removed by separators 2, 3 or an adsorber 4 are adsorbed and removed in a charcoal plate 24 cooled to about -170 deg.C by a cooling coil through which liquid helium boil-off gas flows. Therefore, the impurities in gaseous helium can be removed by a trap device 10 just before the intake part HP on the high pressure side of the cold head 6, and the cost can be reduced without using expensive gaseous helium with high purity. Since the liquid helium boil-off gas is used for cooling the charcoal plate 24 at the trap device 10, extra cost is not required and also the impurities generated in a flexible hose 5 can be removed. |
