Phi Book 2 Mod 3

Front 1

Five general types of errors that occur when analyzing radioactive samples

Back 1

1-self-absorption

2-backscatter

3-resolving time

4-geometry

5-Random disintegration of radioactive atoms (statistical variations)

Front 2

Self-absorption

Back 2

When A sample has an abnormally large amount of material on the sample media, it could introduce a counting error due to self absorption, which is the absorption of the emitted radiation by the sample material itself. Self-absorption could occur for:

1-liquid samples with a high solid content

2-Air samples from a high dust area

3-use of improper filter paper or sometimes using the wrong side of the filter paper, may introduce a type of self absorption, Especially in Alpha counting (absorption by the media or filter)

Front 3

Backscatter

Back 3

Accounting errors that are the result of backscatter occur when the emitted radiation traveling away from the detector is reflected, or scattered back, to the detector by the material behind the sample.

Front 4

Backscatter factor (BF)

Back 4

BF=counts with reflector/counts without reflector.

Front 5

Resolving time

Back 5

Resolving time is the time interval that must elapse after detector pulse is counted and before another full-size pulse can be counted.

Front 6

Geometry

Back 6

Geometry related accounting errors result from the positioning of the sample in relation to the detector.

Front 7

Poisson distribution

Back 7

a simplified version of binomial distribution is POISSON distribution, which is valid when the probability of success, P(X) , is small

Front 8

Gaussian distribution

Back 8

Also called the normal distribution, the Gaussian distribution is a further simplification that is applicable if the average number of successes is relatively large but the probability of success is still low

The Gaussian, or normal, distribution is apply to counting applications with a mean success is expected to be greater than 20. It is used for accounting system calibrations and operational checks, as well as for normal samples containing activity

Front 9

State the two purposes for statistical analysis of count room operations

Back 9

1-predict the inherent statistical uncertainty associated with a single measurement, thus allowing us to estimate the Percision associated with the measurement

2-serve as a check on the normal function of nuclear counting equipment

Front 10

Mode

Back 10

An individual data point that is repeated the most in a particular data set

Front 11

Median

Back 11

The center value in a data set arranged in ascending order

Front 12

Mean

Back 12

The average value of all the values in a data set

Front 13

Variance

Back 13

Variance- distance from the mean. The amount of scatter of data points around the mean is defined as the sample variance. In other words it tells how much the data varies from the mean

Front 14

Standard deviation

Back 14

Standard deviation is the estimated dispersion of a set of measurements. Mathematically, in a normal distribution, it is the square root of the variance. It is represented by The symbol sigma

Front 15

One standard deviation

Back 15

68.2% of the time that observe success (or counts) will be within the plus minus 1 standard deviation of the mean

Front 16

Two standard deviation

Back 16

95.4% of the time we observe success (or counts) will be within plus minus 2 standard deviation of the mean

Front 17

Three standard deviation

Back 17

99.97% of the time we observe success or council will be within plus or minus 3 standard deviation of the mean

Front 18

Chi (pronounced KI)-squared test

Back 18

The CHI square test is used to determine the precision of a

counting system.

The CHI square test is often referred to as a goodness of fit test

Precision is a measure of exactly how a result is determined without regard to its accuracy. It is a measure of the reproducibility of a result or in other words how often that result can be repeated or how often a success can be obtained

*for 20 one-minute counts at 95% confidence, the satisfactory range (for P=10% through 90%) is 12 to 27

Front 19

Goodness of fit test

Back 19

Also known as the CHI square test. It answers the question; how well does this data fit a POISSON distribution curve? If it does not fit a curve indicating sufficient randomness, then the counting instrument maybe malfunctioning

Front 20

State the Criteria for acceptable CHI squared values in the industry

Back 20

12-27

Within certain facilities concerned with their quality control measures in the industry, 20 one-minute counts are performed to a desired confidence level of 95% for CHI square testing to ensure operability for fixed counting systems

Front 21

State the purpose of creating quality control (QC) documentation

Back 21

Quality control documentation should be maintained in the area of the radioactivity counting system such that they will be readily accessible to those who operate the system. This documentation can then be used by RCTs to determine if routine, periodic checks (typically daily) have been completed before system use

Front 22

Warning limits

Back 22

Counts outside the warning limits indicate that something may be wrong

Plus or minus 2 standard deviations

Front 23

Control limit

Back 23

The values outside of plus or minus 3 sigma indicate unacceptable performance even though values maybe statistically valid

Front 24

State the purpose of determining efficiencies and correction factors

Back 24

The reason for determining efficiency is to determine the actual activity of a sample.

Correction factor is the inverse of the efficiency. Using the correction factor you can more easily find out what the activity in the sample is.

Front 25

State the meaning of counting data reported as X plus or minus Y

Back 25

Since nuclear laboratories prefer to be right more than they are wrong, counting results are usually reported any range that would be correct 95% of the time or at a 95% confidence level

X +or- y (K sigma)

X= measured activity in units of DPM, CI, BQ

Y= associated potential (or possible) error in the measurement

K= multiple of correcting error

Sigma= Standard deviation atstated confidence level (CL)

Front 26

State the purpose of determining background

Back 26

The contribution of the background will produce an error in radioactivity measurements unless the background count rate is determined by separate operation and subtracted from the total activity. Typically the lower the system background the more reliable the analysis of the sample will be.

Front 27

State the method and requirements for determining background for counting systems in the industry

Back 27

1-Performance check should be performing daily or prior to operation

2-After the last step a complete accounting of a swipe, filter, or source, it should be removed from the planchet

3-The source should be placed in the center of the planchet

4-all sample accounts must be for a minimum of one minute unless facility/project specific time is established

5-all background counts must be for a minimum of 10 minutes unless facility/project specific time is established. And exception is after a counter is relocated and is portable, such as Ludlum 3030. Then they should be checked for operability by performing a background check after being moved. The background count must be for a minimum of one minute

6-all source response counts must be for a minimum of one minute unless facility/project specific time is established

7-The Alpha background counts should remain consistent with the one established prior to the move.

8-The beta background counts need not be consistent with the one established prior to the move

Front 28

State the purpose of performing planchet maintenance

Back 28

Planchet and carriers should be inspected, cleaned and counted on a routine basis. All in use planchets and carriers must read less than established facility limits. Planchets exceeding these limits should be decontaminated and re-counted as necessary.

Front 29

State the method and requirement for performing planchet maintenance for accounting systems in the industry

Back 29

Planchet maintenance is performed during background checks and periodically through counting cycles. Planchets to be contaminated are decontaminated or discarded.

Front 30

Define detection limit

Back 30

The detection limit of a measurement system refers to the statistically determined quantity of radioactive material (or radiation) that can be measured (or detected) at a preselected confidence level. This limit is a factor of both the instrumentation and technique/procedure being used.

Front 31

Critical detection level

Back 31

The response level at which the detector output can be considered above background

Front 32

Minimum significant activity level

Back 32

The activity level that can be seen with a detector with a fixed level of certainty

Front 33

Cross talk

Back 33

Crosstalk is a phenomenon that occurs on proportional accounting systems such as TENNELEC, that employee electronic pulse site discrimination, thereby allowing the simultaneous analysis for alpha and beta activity. Discrimination is accomplished by establishing two thresholds, or windows, which can be set in accordance With the radiation energies of the isotopes of concern

Front 34

State the criteria for acceptable values of crosstalk for accounting systems in the industry

Back 34

Crosstalk is also called spill over. Calibration procedure is for most of the counting instruments used in the industry specify that spillover must be less than 1% for beta to Alpha and less than 3% alpha to beta. The specific criteria when listed, will be in the calibration procedure for the instrument

Front 35

State the purpose of performing a voltage plateau

Back 35

Voltage plateau is a graph that indicates a detectors response to a Radion nuclide with variations of high voltage. The X-axis is the high-voltage and the Y-axis is the response (counts). The resulting curve Gives an indication of detector quality. The curve can also be used to determine the optimal operating high voltage for the system