Miscellaneous

Does Angle correct for true coincidence effects?

No. We consider true coincidence corrections (TCS) a part of spectroscopy (spectrum elaboration, including peak area corrections for various spectroscopic effects), thus a preliminary issue to Angle application.

However, Angle can be helpful to TCS, since many approaches combine the decay scheme (which is generally known) and efficiency (calculated by Angle). Of course, whenever possible, coincidence free gamma-lines and/or large source-to detector separations should be employed for analytical purposes. This is especially valid for constructing the Angle reference efficiency curve, since the uncertainty on the latter is subsequently fully propagated to all Angle results.

We are developing software to study the impact of the source density for detection efficiency. Can we somehow automate the process of generating Angle input files, or we have to make all changes/variation of input parameters and calculations manually in Angle?

Yes, you can automate the process. All files in Angle 4 are based on the XML format. You can modify or create them from your software. You can run them manually or automatically, using the command line parameters.

The easiest way, in your case, is to create one set of calculation parameters file in Angle, load it in your software and then just change the parameter(s) you want.

I would like to use a preview image from Angle in my paper. There are four different formats to choose from. How to choose between them?

That depends on your needs. Most probably you would like to choose one of the vector formats for your paper, since they look better on paper. You can scale them without losing any quality and consume much less space on disk. You can even import them to vector graphics applications such as Adobe Illustrator or CorelDRAW and edit them freely.

Raster images may look better on screen and other low resolution devices, and are ideal choice for the web. The BMP format is lossless, but the resulting file is much bigger than JPEG.

I tried to save the preview image in the BMP/JPEG format, but the resulting image is too small/big. What should I do?

Raster images are saved using the current zoom factor, so the more you zoom it, the larger the resulting image will be. To adjust the size of your resulting image simply zoom it in/out until you reach the required level of details, and then save the image.

I tried to send the reference energy curve/output file/saved file... in an email as an attachment, but I cannot find it. Thus, I can use it in Angle, but cannot manage to attach it.

Angle 4 saves, by default, all files in the “ANGLE” folder located in your Documents folder. You can see the location (and even change it) in the configuration dialog box.

You can also use a simple trick – when you see the list of files in Angle (for example when you click “Load curve from file” button), right-click on the file you want to share and select “Copy”. Then you simply paste it to some other location temporarily (e.g. on the Desktop) and attach it from there.

How does Angle compare to the relative method used for the determination of sample activities?

Angle is a semi-empirical method for detection efficiency calculations; from detection efficiencies there is a single straightforward step (involving gamma-peak areas) to determining activities of the radionuclides present in the sample. Angle thus combines the advantages of both the absolute method (flexibility in application) and the relative method (high accuracy), while minimizing their drawbacks. When care is taken to ensure that the actual and calibration counting arrangements do not differ too much, the “quasi-relative” conditions are met and accuracies comparable to the relative method can be achieved.

Why do I need software at all for efficiency calculations? I have plenty of standards in my lab and I am happy with them.

The relative method, based on a simple comparison of samples to standards under the same counting conditions is the spectrometry “classic” – the method of choice. It is simple to apply, results are easy to calculate and, most importantly of all, the resulting accuracies are the best possible. For a while this will satisfy the user’s needs, but sooner or later it will be realized this approach is extremely rigid, requiring ever more standards (never enough), and eventually limiting laboratory performance. Just small differences in counting conditions between the sample and the standard (e.g. different source matrix, or a slight difference in the source container) will introduce systematic errors which cannot be accounted for. Also, any “new” gamma-line in the sample, not present in the standard, will be impossible to quantify.

Whatever valuable source of reliable fundamental information, the standards are not easy to handle (e.g. dilute), they are not cheap either, their activities are continually decreasing and hence have a limited working life, after which have to be disposed of. In addition, they have to be under regulatory control during their whole “cradle-to-the-grave” lifetime.

This rigid inflexibility is the main drawback of the relative method, and forms the main advantage of Angle, which is free of it altogether. In addition, there are many other advantages.

I learned Angle can be used in “quasi-relative” mode. What is that actually?

Angle is based on the efficiency transfer (ET) principle: from known detection efficiency (reference efficiency curve, REC), an unknown efficiency is calculated. In principle this works for any two counting arrangements (with the same detector, of course). There are uncertainties in input parameters (unavoidable), though, which are propagated to the final result (calculated efficiency). Error propagation factors tend to be smaller if the two counting arrangements are similar to each other. For instance, it is more favorable to calculate efficiency for a one liter Marinelli source having a REC of 0.5 liter Marinelli, than from a point source counted at 30 cm distance from the detector. This happens because uncertainties in such cases tend to compensate for this issue (error reduction/compensation effect). Extrapolating the error reduction effect to its limits, we arrive at the “quasi-relative” method, when both the known and unknown efficiencies differ only a little. The difference is large enough that a proper relative method cannot be used, but small enough to enable Angle calculations to produce comparably good results (to the relative method); without doubt the relative method is the one which yields the most accurate results in quantitative gamma-spectrometry and the quasi-relative method is just behind it.

What is the error propagation factor?

In any gamma-spectrometric method (absolute, relative, semi-empirical...) there are input parameters needed for obtaining the final result – activities of radionuclides present in the sample. These parameters include numerous characteristics of the detector, source (incl. its container), and counting geometry. Uncertainties in the values of these parameters, as in any physical quantity, are unavoidable. One way or another, these uncertainties are propagated to the final result. The proportionality factor with which this propagation is made for a given counting arrangement is called the error propagation factor. Note that the term “error” here is not exact – it refers to the uncertainty, not an error in its proper sense.

What is the error propagation function?

The term error propagation function represents the variation of an error propagation factor with changes of some of its input parameters. In Angle, we speak of the error propagation function of calculated detection efficiency vs. changes in, for instance, detector crystal dead layer.

What is the difference between “detector efficiency” and “detection efficiency”?

Detection efficiency is a characteristic of the counting arrangement. It is the probability that a photon (in this context: gamma or X-ray) emitted from the sample will be detected by the detector (and recorded by the accompanying equipment, e.g. multi-channel analyzer); apparently it depends on photon energy, detector and source characteristics, absorbing layers photon encounters, counting geometry, etc. Being a probability, it is a dimensionless quantity, fraction of 1.

Detector efficiency, also called relative efficiency, is a characteristic of the detector. It is defined as detection efficiency at 1332 keV of a Co-60 point source counted at 25 cm distance from the given detector, as compared to (the same with) 3 × 3" NaI detector. It is thus expressed in %.

Detection efficiency is, thus, a broader, more complex term than detector efficiency.

How do you see spectroscopy vs. spectrometry? In this context, what does Angle address and what doesn’t it?

In the Angle context, gamma-spectroscopy is a qualitative analysis, a means of determining which radionuclides are present in the sample.

Gamma-spectrometry is quantitative analysis, it means determining the quantity/concentration/activity of radionuclides present in the sample

Gamma-spectrometry can, thus, be regarded as the quantification of spectroscopic results. Logically, spectroscopy precedes spectrometry.