Hardware and Software
for Scan Test with Radioactive Source
The Limited Stream Tubes (LSTs) that will be used to replace the BaBar muon chamber will be put through rigorous quality control tests at OSU. One test involves radioactive sources being scanned over the tubes while under high voltage with their outputs monitored. Details and criteria for the test are given in point 8 of LST QC/QA Procedures and Test Part II. The hardware consists of a table on which the tubes will be placed, the scanning apparatus that will hold and maneuver the radioactive sources, the system for controlling the flow of gas through the tubes, and the electronics for monitoring and controlling all other hardware.
The table is approximately 3' 2" H x 13' L x 3' 2" W. It is constructed primarily of unistrut beams and can hold a maximum of four tubes. The top has been constructed out of two layers of medium-density fiberboard (MDF) with a flat aluminum plate on top. Two of the long vertical beams on one of the long sides of the table will support horizontal arms.
The two unistruts at the sides of the table carry an aluminum I-beam (the one at center does not provide any support) from which the source cart will be hung. The source cart can hold three 137Cs sources. Each of the two unistrut has a stepper motor, a threaded rod and a Thomson rod. The stepper motor turns the threaded rod which drives the I-beam along the Thomson rod. The I-beam moves perpendicularly to the unistruts.
The source cart rides along the I-beam on a drive belt. A stepper motor drives the belt via gears and coupling belt. The cart will move at 10 cm/s during scanning.
Each tube is divided into eight cells with a square cross section. To scan the tubes for defects, the carriage will be moved along the entire length of the beam; it will effectively scan three cells at a time. Then the I-beam will be moved so that the carriage can scan three new cells. This process will be repeated until all four tubes have been scanned. A computer will monitor the current produced by the tubes; specifically it will look for unacceptable spikes in current as described in point 8 of LST QC/QA Procedures and Test Part II.
A nice presentation of the mechanics written by Professor Kass can be found here.
Both of the stepper motors will be controlled by a Rabbit 3200 Microprocessor acting as a server. A client program will communicate with the Rabbit via Ethernet connection. Server and client software are currently in the final development phase.
The schematics of the stepper motor driver circuit can be found here.
In order to gauge the accuracy of the LSTs, one of the radioactive sources used in testing was placed near a Geiger counter that was covered with a piece of PVC identical in thickness to the walls of the tube. The results are shown in the "Uniform Comparison" plot in the spreadsheet here.
Photos and Drawings (Click to enlarge)
Last Updated: 2-4-2004
By: Quincy Wong (Email: wong.244@osu.edu)
