Fluke Biomedical 660-6 - Manual (Page 13)

Operation
Operation
3
3-1
Section 3
Operation
3.1 Operation
The following considerations should be noted when using CT Probes and Phantoms:
• The phantom adaptor (built-up sleeve) is designed to provide mechanical protection for the ion
chamber and to properly place the probe’s sensitive volume in the phantom.
• The phantom adaptor should never be removed from the probe in the field; it should only be
removed when necessary and in the calibration laboratory (e.g., to verify probe sensitivity).
• The hole plugs supplied with the phantoms have small 1.5 mm holes through their midpoint. When
the phantom is properly centered in the CT beam, the holes will appear as small rectangles on the
CT scan.
• The ion chamber electrode is not guarded; therefore, after a collection voltage is applied, allow five
minutes for the insulators to polarize.
• If using the Model 660 readout, five minutes after the unit is turned on remove the plug button in the
probe preamp and adjust the zero (while in the Rate Mode).
The Model 660 does not read below zero;
therefore, adjust the zero from a positive reading
down to just zero. Otherwise, appreciable error may
be introduced due to negative leakage.
Use the above guidelines and following procedure to take data
1. Position the phantom, readout device, and cable.
2. Connect the probe to the readout device.
3. Turn on the readout device, applying a collection voltage.
4. Run a scan to check that the holes in the hole plugs are visible.
5. Place the probe in the phantom.
6. Place the probe readout in the integrate mode.
7. Wait one minute to be sure there is not excessive leakage.
8. Run scans and record data as required.
CAUTION