ELSEVIER Nuclear Instruments and Methods in Physics Research A 362 (1995) 205-207 NUCLEAR zyxwvutsrqponml INSTRUMENTS 8 METHODS IN PMYSICS RESEARCH In-vacuum target transfer facility D. Kabiraj * , Samit Mandal, D.K. Avasthi zyxwvutsrqponmlkjihgfedcbaZYXW Nuclear Science Centre, Aruna Asaf Ali Marg, Post Box No. 10502, New Delhi 110067, India zyxwvutsrqponmlkjihgfedcba Abstract In order to transfer highly oxidizing and hygroscopic targets in-vacuum or in controlled atmosphere and to change the target ladder without affecting the chamber vacuum, an in-vacuum target transfer system has been designed, fabricated and installed. It consists of a transfer body, compatible flanges with gate valves at the bell jar and the chamber. Ca, being a highly oxidizing element, was taken as a test case to stress the utility of the in-vacuum target transfer system. Using the elastic recoil detection analysis (ERDA) technique, we could see that there was only 11.5% of 0, in the target when it was transferred from the bell jar to the scattering chamber using the in-vacuum target transfer facility. When the target was exposed to air for 35 min the 0, content rose to 63.5 at.% 1. Introduction Nuclear physics experiments often require targets which are very reactive to the atmosphere. Generally they react with oxygen to form oxides and/or absorb moisture. If so, an in-vacuum target transfer system [l] is normally used to protect the highly reactive targets from atmospheric gases. We have designed, fabricated and installed an in-vacuum target transfer system to transfer the reactive targets from the evaporator to the scattering chamber in vacuum or in controlled atmosphere. In some experiments, it was required to replace the target ladder inside the chamber during the experiments. It may be due to breaking of the target foil under heavy ion bombardment or due to the need of targets of different elements and specifications. If the chamber has to be vented to replace the target, normally it takes 4 to 5 hours to pump down to u 10m4 Pa because of the large size of the scattering chamber. The in-vacuum target transfer facil- ity installed at the 1.5 m diameter general purpose scatter- ing chamber (GPSC) [2] finds application in required procedures such as this. An elastic recoil detection analysis (ERDA) [3,4] experiment has been carried out to test the effectiveness of the transfer system. Ca, being a highly oxidizing element, was taken as the test case. 2. Design and operation of the in-vacuum target trans- fer system The in-vacuum target transfer system consists of a transfer body, an intermediate body, and compatible flanges l Corresponding author. Fax +91 11 689 3666, e-mail kabiraj@nsc.emet.in. with gate valves at the bell jar and the scattering chamber. A schematic diagram of the system is shown in Fig. 1. The transfer body can accommodate a target ladder which can fit six targets at a time. Before evaporating a readily oxidizing element (Ca in the present case), the target ladder was loaded with 10 pg/cm’ self-supporting carbon foils. The ladder was then attached to the stainless steel shaft using the screwing arrangement shown in Fig. 1 and then moved inside the transfer body. The assembly was coupled to the bell jar of the evaporator [5] having a port compatible with it. The bell jar was already at a pressure of N 10e4 Pa. Using a rotary pump, the intermediate body was first evacuated to 10’ Pa as measured by the pirani gauge. It was then connected to the transfer body and the valve V, was closed. At that time, the gate valve GV, was closed and GV, was open. Then by opening GV, the system was opened to the bell jar. The pressure of the bell jar rose to 10e3 Pa but within a few minutes it came down to 10v4 Pa. The ladder was then pushed inside the bell jar and Ca of 40 kg/cm’ thickness was evaporated on the self-supporting carbon foils. The vacuum during the evap- oration was _ 5 X 10m3 Pa. After evaporation, the ladder was taken back into the transfer body and valves GV, and GV, (the gate valve connected to the bell jar) were closed. After decoupling the transfer body from the bell jar, it was taken to the scattering chamber and connected to it. During this operation the vacuum in the transfer body was N 10-i Pa and the vacuum in the GPSC was 10e4 Pa. The same steps were followed before the gate valve GV, was opened to connect the transfer system to GPSC. The high vacuum valve of the diffusion pump connected to the scattering chamber was open and the pressure in the chamber raised to - 10e3 Pa during this operation. The chamber was restored to its original pressure within a few minutes. The shaft was used to mount the ladder in a mounting arrange- 0168~9002/95/$09.50 8 1995 Elsevier Science B.V. Ail rights reserved SSDI 0168-9002(95)00231-6 VI. EQUIPMENT OF TARGET PREPARATION