Counting Statistics

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# Counting Statistics - PowerPoint PPT Presentation

Counting Statistics. 31. 32. Statistical Accuracy. Factors that affect statistical accuracy :. Count rate Count time Background Equipment efficiency . Sample vol. Geometry Moisture absorption. Events. 33. Error Reduction. Peer Check STAR Procedure Use and Adherence.

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## PowerPoint Slideshow about 'Counting Statistics' - ordell

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Presentation Transcript

Counting Statistics

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Statistical Accuracy
• Factors that affect statistical accuracy:
• Count rate
• Count time
• Background
• Equipment efficiency
• Sample vol.
• Geometry
• Moisture absorption

Events

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Error Reduction
• Peer Check
• STAR
Accuracy and Precision

34

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Standard Deviation

Where’s the mean?

• Represented by the Greek symbol sigma 
• One  is the distance from the peak out to a vertical line enclosing 34.15% of the total area under the curve
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Frequency Distribution
• Data is plotted on a histogram
• Height of bar represents frequency of occurrence
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Poisson Distribution
• Probability of “success” is low
• Number of trials is high
Gaussian Distribution

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• One  includes 68.3% of area under curve

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Confidence Level

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1 = 68.3 % confidence level

2 = 95.4 % confidence level

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Minimum Detectable Count Rate
• Calculated using the equation:

MDC = 2.71 + 3.3 [B(tb+ts)/tb]1/2

where: MDC is the minimum dectectable counts;

B is the background counts;

tb is the background counting time, minutes;

ts is the sample counting time, minutes.

MDCR = MDC/ts

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MDCR Application
• If gross count rate is > (Bkd + MDCR):

It may be concluded with 95% confidence that radioactivity is present above natural background. Calculate results using normal processes.

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MDCR Application (cont’d)
• If gross count rate is < (Bkd + MDCR):

record as

"< MDA".

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Lower Limit of Detection
• Calculated using the equation:

LLD (Ci/cc) = 4.66 b

(2.22E6)(E)(V)(Y)(D)

where: V is the sample volume in cc;

E is the counter efficiency (cts/dis);

Y is the chemical yield if applicable;

D is the decay correction for delayed count on sample.

2.22E6 is a conversion factor - dpm per Ci

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Chi-Square Test
• Calculated using the equation:

x2 = (n-)2

where: n = the data for each count;

 = the average of the individual counts;

 = n/N

N = the number of observations (usually 21)

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Chi-Square Test