April 19, 2005

To: File

From: Roger Zimmermann

Subject: ACNET Detector Scaling

The purpose of this memo is to discuss radiation detector scale factors as used in the ACNET system.

The image below is a section of a typical D106 ACNET page showing a group of Chipmunks. For the purpose of this discussion, we will consider the MI-13 Chipmunk. As can be seen, the detector is reading back 31.2 mrem per hour. The readback is in the Common Units format.

The next image shows the same chipmunks but the page is displaying the unscaled Primary Units data.

The Primary Units data reads back in counts per minute format white the Common Units data reads back in mrem per hour format. A chipmunk sends out one pulse (or count) for each 2.5 microrem it sees. We can perform a check on the Common Units readback by doing the following calculation.

rem per hour = counts/minute * minutes/hour * rem/count

= 208 * 60 * 2.5x10^-6

= 1.25x10⁴ * 2.5x10^-6

= 3.12x10^-2 rem/hr or

= 31.2 mrem/hr

Thus, the Common Units Readback appears correct.

Here is the ACNET database information showing the reading parameters for the MI-13 chipmunk

The C1 transform index can be tested for accuracy as follows.

Common units transform = C1 * (Primary Units / C2) where C1 =0.15 & C2 = 1

= 0.15 * (208 / 1)

= 0.15 * 208

= 31.2 mrem/hr

Both methods of calculating the hourly dose rate arrive at the same result. Thus, they serve as a reality check that the ACNET readback algorithm is correct.

The C1 scale factor serves as a conversion from Primary Units (in counts per minute) to Common Units in mrem per hour.

C1 = minutes/hour * microrem /pulse * microrem/millirem

= 60 * 2.5x10^-6 * 1x10³

= 60 * 2.5x10^-3

= 0.15