Re: GM Counters in High Backgrounds

["Tom O'Dou" <tom_dixie@email.msn.com>]

In answer to your question:


>Scenario:  Eberline E-140 with an HP-210 probe set up in a shielded
>configuration in lower levels of a PWR Containment during     Outage.
>The meter/probe combination is 10% efficient. The background is still
>1000cpm/probe area.

Background = 1000 cpm

Gross count rate = 1500 cpm

Net count rate (on smear) = Gross count rate - Background count rate
1500 cpm  - 1000 cpm = 500 cpm

>
>Question:  If a disk smear with a 100cm2 smeared area reads 1500cpm/scan in
>the shielded configuration as mentioned above,     what would the smear
>actually read if the smear was moved to a low background area (e.g., 50cpm
>background) and     counted with the same type of instrument/probe
>setup?

If moved into a lower background area (50 cpm), the gross count rate
observed
would be:

Gross count rate (low background) = 50 cpm + 500 cpm = 550 cpm.

The net count rate on the smear would not change.

The sensitivity of the instrument changes because of the lower background
count rate.

The efficiency stays the same.

The activity on the smear is 500 cpm/ 0.1 c/d = 5000 dpm

Tom O'Dou
tom_dixie@msn.com




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