Operating instructions for the X-Y scanner

B.Satyanarayana

Department of High Energy Physics,

Tata Institute of Fundamental Research,

Homi Bhabha Road, Colaba, Mumbai, 400005

This note provides basic operating instructions for the quality control testing of Outer Hadron Calorimeter detector modules (trays) using the X-Y scanner.

1. Radiation safety procedures

The X-Y scanner uses a 10mCi Cs-137 radioactive source. Though it is a strong source, it is well collimated and shielded using a lead and brass container. The radiation levels around the scanner have been surveyed by the Health Physics Division of BARC and certified to be safe for personnel working in the lab even for prolonged periods of time. However, it is still recommended that the following AERB safety procedures be followed by all the persons while working in the X-Y scanner lab.

1. Always wear your TLD badge at your chest level.

2. Don't allow any visitors inside the lab.

3. Never leave the lab without locking.

4. Don't lean over the radioactive source holder or go below the scanner. There is no source shielding in the vertically downward direction and the shielding in the vertically upward direction is inadequate for complete safety.

5. Always keep as much distance as possible from the moving source.

To sum up, it is totally safe to work in the X-Y scanner lab, but we should always aim at receiving As Low As Reasonably Achievable(ALARA) radiation doses. A radiation survey meter is made available in the lab for your use.

2. Mounting the detector tray

The detector tray is mounted on the aluminium mounting plate while it is being tested. Stoppers and alignment guides have been provided on the mounting plate for this purpose. The detector tray should be mounted such that the connector end of the tray along with its tray carrier are aligned with the L-shaped guide on the mounting plate.

There are two pairs of optical cables to carry light from the tray to the photomultiplier tube(PMT) assembly - one using 12 pin and the other using 18 pin connectors. In each pair, left and right connectors are labeled accordingly. Appropriate pair of cables should be connected to the pigtail connectors on the tray, while the other pair of cables are stored inside a black cloth bag provided for this purpose. Please wipe the connector surfaces with a dry tissue paper before connecting. Care must be taken to tighten both ends of the optical connectors evenly. Entire tray along with the optical cables and the PMT assembly should be covered with black cloth. Again care must be taken so that the cloth doesn't get entangled in the moving parts of the scanner.

Please handle the optical cables and fragile fibers with all the possible care.

3. Turning ON the PMT supply

The PMT is operated at a nominal voltage of 1457 volts. 457 volts is permanently set on the high voltage power supply using the vernier potentiometer and it should not be disturbed. 1000 volts is applied using the rotary switch, which sets 1000 volts per step. So, setting the PMT supply involves turning ON the high voltage supply and turning the rotary switch to the position marked '1'. Please allow about 20-30 minutes for the PMT supply to stabilise.

3. Taking the test run

The Current-to-Voltage converter's power supply as well as the stepper motors' power supply should be turned ON. The PC monitor should also be turned ON. The PC may have to be brought out of screensaver mode, if necessary.

Usually, one can use Norton Commander Menu to operate the PC for taking the test run etc. The menu option 'Execute XYSCANV6' brings up the X-Y scanner control and data acquisition program.

Use the control program option 'C: Change configuration' to set the tray identification number. The format for supplying this number is 'RrLlSsTt'. For example, you will enter R0L0S3T2, as the identification number for Ring 0, Layer 0, Sector 3 and Tray 2. This is the only configuration entry to be supplied with data. Accept defaults for all other entries by hitting a RETURN key.

The actual scan is taken by using the program option 'U: Run programmed scan'. The program moves the radioactive source in the predetermined route on the tray and records the data. The source position indicator and data collected at every point on the tray are displayed on the PC. One can use toggle key 'd' to switch between this and the screen showing the on-line graphical plot of the data. The data is automatically saved in a predetermined file under a directory.

Here is some related information:

It is adviceable to switch off all the lights in the lab so that light leaks can be minimised while the tray is being tested. Please use the table lamp for operating the PC and switch off the same just before you start the actaul scan.

3. Transferring test data

The test data can be transferred to HECR/EHEP machines by choosing appropriate menu options on the Norton Menu. Please enter the following commands thereafter:

username: Enter the username in the remote machine

password: Enter the password for the above account

ftp> asc Choose ASCII data transfer

ftp> cd .... Change directory in the remote machine, if necessary

ftp> mput xyRRRR.* Transfer data files of the run, RRRR

ftp> bye Terminate FTP session

3. Unwinding sequence

Please follow these steps for unwinding a tray testing session:

Put off the PC monitor after transferring the test data. Put OFF the PMT supply by turning the rotary switch of the high voltage supply to '0' position and turning OFF the supply. Switch off low voltage supply for the Current-to-voltage converter as well as the stepper motors' supplies. Remove the black cloth from the detector tray and disconnect the optical connectors carefully. Store the optical connectors back in the black cloth bag. And finally remove the tray from the X-Y scanner.

3. General information

Key for the X-Y scanner lab is kept in C-217. It should be returned back to same place after use. Please enter all the test details including name of the user etc. in the X-Y scanner log book kept in the lab. Please contact me for any help and myself or Prof Mondal in case of emergency.