The measurement of the absolute transport efficiency for recoils from heavy ion reactions with He-JET systems

Abstract

The complex problems involved in the transport of reaction recoils with He-jet systems have been investigated. The recoils 149,150,151Dy produced in the reactions 141Pr( 14N; 6, 5, 4n) were stopped in He gas and transported with the He flow through teflon, stainless steel, and glass capillaries. From the recoils knocked out of the target, 65% were transported through a 0.86 mm i.d. teflon capillary of 5 m length, 75% through a 2.25 m stainless steel capillary. The dependence of the transport efficiency on various parameters was investigated. The transport efficiency was increased by a small amount of carbon tetrachloride injected into the target chamber. In order to transport the reaction products from the high pressure region necessary to stop the recoils into a low pressure region where in future experiments an ion source can be operated, various glass-capillary-skimmer systems and also a double vacuum chamber evacuated by booster jet pumps have been tested. With the glass-capillary-skimmer system and using differential pumping with mechanical pumps only, about 30% of the recoils were brought into a region with a 3 × 10 3 times smaller pressure. Using two booster pumps and the double vacuum chamber with one 1.5 mm brass skimmer, 46% of all the recoils were introduced into the second vacuum chamber where the pressure is 10 6 times smaller than in the target chamber. The opening angle of the cone into which the recoils from the He-jet are emitted has been measured by radiograms to be 3°. The double vacuum chamber was put on high potential during the operation without the occurrence of a gas discharge.