S.E. International Inspector EXP Spécifications télécharger pdf (Page 19)

Exposure Rate Calibraon

An exposure rate calibraon correlates the number of counts in a given me to the exposure rate present in

that eld. This is in many ways similar to eciency but we refer to it in this case as gamma sensivity. Although

it is possible to express this value in several dierent units, the Inspector EXP uses a formula of CPM/mR/hr

(counts per minute per milliroentgen per hour).

The instrument is placed in gamma radiaon elds of dierent (but known) intensies that span the working

range of the instrument, and the sengs are adjusted (if needed) such that all measurements are within ±10%

of the true value. The relevant sengs include both the sensivity and the dead me.

The gamma eld is usually generated by a relavely strong Cs-137 source. Exposure rates are calculated to the

center of the detector’s volume.

Requirements

You will need a PC running Observer USB and a Gamma calibraon range

Procedure

1. Power on the instrument.

2. Connect the instrument to the PC running Observer USB using the USB cable. An applicaon window for

the aached instrument should open within a few seconds.

3. Display the calibraon panel by clicking View|Cal Panel.

4. Record the displayed values for Dead Time and Sensivity.

5. Begin checking the instrument’s Sensivity. Place the instrument in a relavely low eld, approximately 5

mR/hr, and allow it 30 seconds or so to stabilize.

6. If the indicated response is o by more than 3% at this level, adjust the Sensivity to a lower value if the

instrument is reading too low, or to a higher value if the instrument is reading too high. Aer changing

the value on the Calibraon Panel, click the Update Sengs buon. Aer a second or two the instrument

will beep to indicate that the new value has been received.

7. Repeat Step 5 as needed to bring the instrument indicaon as close as possible to the true value.

8. Next, expose the instrument to a eld near the top of its range of 100 mR/hr. Allow the reading to

stabilize for at least 30 seconds. In the preferences tab, you can adjust the me in the gird to show a

selected average count.

9. If the indicated response is o by more than 10%, adjust the Dead Time to a lower value if the instrument

reading is too low, or to a higher value if the instrument reading is too high. Aer changing the value on

the Calibraon Panel, click the Update Sengs buon. Aer a second or two the instrument will beep

twice to indicate that the new value has been received.

10. Repeat step 9 as needed to bring the instrument’s indicaon within ±10% of the true value.

11. Once the values for Sensivity and Dead Time have been veried to be correct, expose the instrument

to a series of values spanning the range of the instrument. All indicaons should be within ±10% of the

true value.

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S.E. International Inspector EXP Spécifications Page 19