A technique to measure the positions of sense wires in low mass drift chambers

Drift chambers are now among the most important detector elements in present day high energy physics experimental detectors . Resolution of 100-200 win per measurement can be obtained without great difficulty . Higher resolution can be achieved by pressurizing the chamber [1]. To achieve good position resolution of tracks, the position of the sense wires must be known accurately . There are several ways to measure the wire positions. If the wires can be seen directly, one method is to survey the wire using an optical telescope . If the wires are not visible, one can use X-rays to obtain a picture of the wires and measure their position on the film . The optical telescope has limited usage since the sense wires must be exposed, and perhaps exposed for a long period of time if a large number of wires is involved . The X-ray technique has also the drawback of having to scan and to measure each wire on film, which can be very time consuming. Both methods require extensive human intervention . In this paper, we discuss a technique to measure the wire position using a collimated 90Sr source . This method is relatively easy to implement as shown below and fast enough to measure a large number of wires with minimum human intervention . Although this technique was developed to measure the sense wire position inside a straw tube, it can be applied to other types of low mass chambers . There have been several drift chambers constructed with straw tubes [2] . One of the main applications of such chambers m the future is in the SSC (Superconducting Super Collider) detectors [3] . Since the expected number of sense wires is between 100000 to 200 000 for a SSC tracking detector, an easy way to measure and to check sense wire position will be necessary during and after the construction . This paper is organized as follows. In the second section, the experimental setup is presented. In the third section, a detail discussion of the data taking and analysis is presented. In the final section we summarize our results .