S.E. International Inspector EXP Specifications download pdf (Page 17)

Eciency Calibraon

The Inspector EXP can be used beyond simple detecon of contaminaon and can also be used to determine

the acvity of any beta- or alpha-eming isotopes present.

Eciency is the rao of events detected by the instrument to the number of decays of the parcular isotope.

The units are therefore counts per disintegraon of c/d. Since eciencies are generally somewhat less than

one, they are oen mulplied by 100 and expressed as a percentage. However, the Observer USB soware

requires that values not be entered as percentages. Since eciency varies based on the energy and abundance

of the parcular isotope being measured, it is best to determine eciency for the specic isotope(s) for which

the acvity is to be determined.

The eciency is also aected by the size of the source and the source to detector distance. To achieve

consistency, eciencies should be determined using a point source (which means a source with an area

signicantly smaller than the detector entrance window) at a xed distance from the detector face (which

must be specied, but 1 cm will be assumed to be the standard).

Requirements

You will need a PC running Observer USB, Calibraon sources, and a holder to keep constant-geometry to

maintain sources 1 cm from the detector entrance window)

Procedure (American Units)

1. Ensure the Inspector EXP is in Timed Count (Total/Timer) mode, displaying COUNTS.

2. Place the Inspector EXP in the locaon where the eciency calibraon will be performed and take a

count of at least 10 minutes. Divide the total number counts by the acquision me (in minutes) to

calculate the background counng rate (RB) in CPM. Record this value.

3. Center the source 1 cm from the end window of the Inspector EXP’s external probe (the small radiaon

symbol on the back of the probe marks the center of the detector) and take a count of at least 1 minute.

Divide the total number of counts by the counng me (in minutes) to calculate the gross count rate

(gcpm or RG).

4. Calculate the eciency using the following equaon:

Where

E is instrument eciency in counts per disintegraon

RG is the gross count rate in counts per minute (cpm)

RB is the background count rate in cpm

A is the acvity of the source in disintegraons per minute (dpm)

5. Repeat Steps 3 and 4 for addional radionuclides.

6. If you would like to record eciency values in the Inspector EXP’s memory for any of the supported

radionuclides (S-35, Sr/Y-90, Cs-137, P-32, C-14, I-131, Co-60, ALPHA), connue with the following steps.

7. Connect the Inspector EXP to the PC running Observer USB using the USB cable. An applicaon window

for the Inspector EXP should open within a few seconds.

8. Display the control panel by clicking View|Cal Panel.

9. Enter the updated eciencies in the appropriate elds.

10. If you would like the Inspector EXP to display in acvity units (i.e., DPM) for a specic source instead of

the count rate (CPM), select it from the Applied Isotope dropdown box. Otherwise, leave as None (cpm/

cps).

11. When all relevant values have been updated, click the Update Sengs buon. Aer a second or two

the Inspector EXP should beep twice to acknowledge receiving the updated sengs.

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S.E. International Inspector EXP Specifications Page 17