Archive for the ‘FAQs’ Category

Gamma Spectrum Generator – spectrum cut-off at 2500 keV?

March 31st, 2021

Qu.) JTE, BfS, Berlin
Dear Nucleonica Team,
I created a mixture of U-233 and U-232 and tried to obtain the gamma spectra using the Gamma Spectrum Generator.
I noticed that the spectrum was cut off at 2500 keV. Is this a build-in restriction? I am interested in the U-232 daughters Tl-208 which has a peak at 2600 keV.

(Ans. Nucleonica Team)
The cutoff at 2500 keV is due to the choice of the configuration. You probably have used the HPGE with rel. eff. 50% (this is the default).
To increase the range you need to go into the drop down menu for the Current configuration. Then choose Edit from the list of options. Then check the box “Show more settings”.
There you will see that the Channel to energy conversion factor is 0.3 keV per channel. You can change this to 0.35 or some other number to increase the range.
Then return the calculation and you’ll see the 2500 keV peak (see the image below).
This configuration can be saved under a new name if you intend to do more calculations.Tl208at2600keV

Hope this helps

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Possible issue(s) with “inclusion of short-lived daughter radionuclides”

February 23rd, 2021

Qu.) TvD, RIVM, Netherlands
Dear Nucleonica Team,
We are using Nucleonica and we have a question about the following App: Photon Dose Rate Constants++. This app offers the option to include short-lived daughter nuclides.
For Th-232, we get the following results:
Th-232 daughtersThis result occurs for the following two Data sets: 8th ToRI and the JEFF-3.1 (other data sets do not contain short-lived daughters). What is extremely puzzling is the BR product of 2.780E-12 for daughter products Tl-208, Hg-206 and Tl-206. If we look in the help section of this specific app, the following is mentioned under the inclusion of short-lived daughters:
For the calculation of the dose rate constants, some nuclides are considered to be in equilibrium with daughter products. This is the case when a single radioactive decay chain in which radionuclides are present in their naturally occurring proportions, and in which no daughter nuclide has a half-life either longer than 10 days or longer than that of the parent nuclide, shall be considered as a single radionuclide. Such nuclides are denoted with an asterisk in the Nuclide Summary tab e.g. Cs-137*.
In the case of radioactive decay chains in which any daughter nuclide has a half-life either longer than 10 days or greater than that of the parent nuclide, the parent and such daughter nuclides shall be considered as mixtures of different nuclides.

Our issues/questions are as follows:
If the chain is assumed to be in secular equilibrium, the BR product for Tl-208 (we assume this stands for the product of branching ratios, i.e., the compound branching ratio) should actually amount to 0.36, or better: 0.3593.
Why are other gamma-emitting nuclides missing, such as: Ra-228 (it has a half life of 5.75 y, but it should be taken into account as well due to the “either-or” formulation above), Ac-228, Th-228, Ra-224, Rn-220, Po-216, Pb-212, and Bi-212?
These are all preceding daughters (with photon emissions) in equilibrium as well.
Under the same description for included daughters (see above, highlighted text in italics), why does U-238 not have any short-lived daughters? All nuclides could be included as no other daughters have a half life larger than that of the head-of-chain parent radionuclide U-238. Anyhow, I would at least expect the ‘actual’ short-lived nuclides to be included: Th-234 and Pa-234 and Pa-234m.
What are Hg-206 and Tl-206 doing in this chain?

(Ans. Nucleonica Team)
We have now looked into your question in more detail.
Let’ start with …
Issue 4: Where does Hg-206 and Tl206 come from?
Hg206 and Tl206 come from cluster emission (CE) of the parent Th232. This is a very rare decay mode. They are included in the calculation for completeness although they have no effect on the results. If you look into the Datasheets (JEFF-3.1) for Th-232 you will see the cluster emission involves the emission of the nuclei Hg-206 and Hg-208. The nuclide Tl-208 arises through the decay of the cluster emitted Hg-208. (The Tl-208 is somewhat confusing since it arises both through cluster emission CE and from the Po-212 in the Th-232 decay chain. So the three nuclides shown in your table 1, Tl-208, Hg-206 and Tl206, all arise from CE and as such are not important.
Th-232 CE

Regarding the rules in italics…
– Th-232 (alpha) Ra-228: T/2(Ra-228) = 5.75 y > 10 d: not a short lived nuclide and thus no further short nuclides

– Th-232 (2ß) U-232: T/2(U-232) = 69.8 y > 10 d: not a short lived nuclide and thus no further short nuclides

– Th-232 (Ne-26) Hg-206: T/2(Hg-206) = 8.15 min < 10 d < T/2(Th-232) = 1.405e10 y: Hg-206 is a short lived nuclide,

Hg-206 (ß-) Tl-206: T/2(Tl-206) = 4.202 min < 10 d < T/2(Hg-206): Tl-206 is a short lived nuclide

Tl-206 (ß-) Pb-206 stable

– Th-232 (Ne-24) Hg-208: T/2(Hg-208) = 42 min < 10 d < T/2(Th-232): Hg-208 is a short lived nuclide, but has no radiations in JEFF-3.1;

Hg-208 (ß-) Tl-208: T/2(Tl-208) = 3.053 min < 10 d < T/2(Th-232): Tl-208 is a short lived nuclide

Tl-208 (ß-) Pb-208 stable

Issue-1: Here it is sufficient to say that the Th-232 is NOT in secular equilibrium with the (normal) daughters, only the CE daughters.

Issue-2: I think there is a misunderstanding of the rule in italics here. Ra-228 has a half-life of 5.75y and as such >10 days. So it should not be included in the calculation.

Additionally the italics text is not “either or”. The half-life must be less than 10 days AND less than the half-life of the parent nuclide. (this is the IAEA rule). In other words…In fact one follows the decay chains only as long as daughter nuclides having a half-life shorter than 10 days and shorter than that of the parent nuclide are found.

Issue-3: U-238 : the first daughter is Th-234 with a half-life 24.09 days.(i.e >10days). For this reason th228 and all daughters are not included.

I hope this manages to answer the questions you raise.

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Decay Engine – Daughter activities zero?

June 23rd, 2020

Qu.) PB, CERN, Switzerland
Dear Nucleonica Team,
I wanted to make a quick test to validate a part of a code one colleague developed, by decaying 1 Bq of Fm-257 during 1 second. please find below the result:
Fm257 Decay We were surprised to see that for many daughter radionuclide, activity calculated is zero. We found on our side very low activities (1.192E-6 for Cf-253 / 8.818E-13 for Cm-249 / 6.172E-13 for Es-253 / <1E-18 for the other).

I was wondering if you applied like a cut of, meaning if the activity is below a certain value, you show 0? If yes, what is this cut off?

(Ans. Nucleonica Team)
We do indeed we apply a threshold: when the number of atoms for a nuclide is less than 0.5 and also if its activity is less than 1% from the total activity the number of atoms for this nuclide is set to 0. In the Decay Tree tab (a section is shown below) the cut off is not applied so you can see the calculated number of atoms.
DecayTree-Fm257 To avoid the problem of zero activites, you have always the possibility to use a higher starting quantity e.g. 1 GBq or 1 Tbq. We are currently considering suppressing the cut-off, in which case the results in the main tab will be similar to those in the Decay Tree tab.

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Confusing use of prefixes with half-lives

March 11th, 2020

Qu.) RB, MINDEF, Netherlands
Dear Nucleonica Team,
I would like to report a confusing use of prefixes in Nucleonica concerning the halflife-values of radionuclides. In the paper version of the KNC, as well as in the online KNCO, the values are in powers of ten (T½ U-238 = 4.5E9). But in the “Universal Nuclide Chart” and the “Dosimetry and Shielding++” the unit is in years with prefixes, like mega-years (My) and giga-years (Gy). Especially that last one is really confusing, since Gy also stands for Gray. Why the use of these prefixes, which are not only unusual, but also confusing? Note; the very high halflife-values are in powers of ten, as I expect it to be, e.g. Bi-209.

(Ans. Nucleonica Team)
You are correct, the display of the half-lives is indeed not consistent in the Apps, KNCO and UNC. In particular the Gy for gigayears is really confusing. Every time we give a Nucleonica training course this always comes up. Users do think this is Gray! We have now initiated an update procedure where the use of hte units is consistent throughout Nucleonica. First results can already be seen in the UNC and other apps.

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“Short-lived decay products included” Option in Nuclide Mixtures

November 29th, 2019

(Qu.) FB, INE KIT Karlsruhe
Dear Nucleonica Team,
We face the problem that the “Short-lived decay products included” option yields results for some nuclei twice – the ones which are already in the input (from calculation results from another program) and the ones which are calculated by the short-lived decay products option in Nucleonica.
Is there any way to avoid this?

(Ans. Nucleonica Team)
For mixtures it is sometimes a problem to known if the short-lived daughters have to be included or not. To avoid counting such nuclides twice, we will de-activate the option include short-lived daughters for mixtures in the radiological converter.
This is already the case in the Dosimetry and Shielding H*(10) application. When single nuclides are selected, the option include short-lived daughters is again set by default for single nuclides.

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Gamma Spectrum Generator for large nuclide inventories?

October 15th, 2019

(Qu.) AM, Linköping University, Sweden
Dear Nucleonica Team,
We work with a mixture of about 900 radionuclides. We would like to generate corresponding gamma spectra using the Gamma Spectrum Generator++, but the generator allows to work with no more than 20 nuclides in the mixture. Is there a way how to increase this number? Would a standalone application help? It would be a bit laborious to split the 900 nuclides to 45 groups, process each group individually and then combine the results.

(Ans. Nucleonica Team)
Depending on your requirements, it may not be necessary to use the Gamma Spectrum Generator, GSG (which is as you say restricted to 20 nuclides). A spectrum can be obtained using the Gamma Dosimetry & Shielding, D&S H*(10) application. This line spectrum is obtained using the activities, emission probabilities and the energies of the emitted radiation. This may be sufficient for your purposes. It does not include peak broadening, Compton scattering and background scattering as in the GSG. The advantage of using the D&S H*(10) is that it is can handle 900 nuclides with a reasonable calculation time (typically a few seconds).
If you require the full GSG spectrum with line broadening, Compton scattering etc. You will need to use one of our test servers for this purpose. There a GSG spectrum for approx. 900 nuclides (with around 28000 gamma lines) will require a calculation time of approx. 20 mins. The Nucleonica Team can provide more information on our test servers.

Once you have the GSG spectrum for the 900 nuclides, you can save this in XML format. This xml file can then be uploaded into the webGraph application. Using the xml files in webGraph provides therefore an “Active” graph which can be used for later viewing and examination. With the Active graph the user can zoom in and out and use the mouse cursor to identify the underlying nuclides.

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Some questions concerning Shielding calculations in Nucleonica using Cm244 and W

September 16th, 2019

(Qu.) LH JRC, Karlsurhe, Germany
Dear Nucleonica Team,
May I ask you some question about shielding calculation using Nucleonica?
I want to shield a Cm244 source using Tungsten. Unfortunately I get some strange results, using both the older Dosimetry & Shielding calculation and the newer Dosimetry & Shielding H*(10) apps. The Tenth value shield thickness of these 2 methods do not match: They are a factor 10 different, which I consider far too much.

(Ans. Nucleonica Team)
Please note that the newer D&S H(10) includes the high energy prompt gammas.
The older D&S does not. You can see this in the graph at the bottom of the page. The D&S H(10) contains groups of gammas in the range 1-10 MeV. You can also see this is more detail in the datasheets.
Cm244Although the BR for SF is low (1e-6), the emission probabilities for the low energy gammas is also low. Hence these high energy gammas need to be accounted for in the calculations.

Note also that the high energy gammas are included only in the JEFF3.1 database. Other databases (e.g. ENDF/B) do not have these high energy gammas. The database can be changed in the D&S H(10) Options menu.
The contribution of individual gamma energies can be investigated using the “photons/s” in the source strength drop-down menu. There one can see that it is the higher energy gammas which make the difference.

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Build up factor interpolation

August 21st, 2019

(Qu.) SG SCK-CEN, Belgium
Dear Nucleonica Team,
As shown below is the buildup factor equal to 1 at a distance of 15 m in air for gammas with an energy of 1 MeV.
My assumption would be that for a number of mean free paths of 0 the buildup factor would be 1. If this is the case, the buildup factor at 15 meters (mfp = 0.1107) should be interpolated between 1 (the buildup factor at mfp=0) and 1.47 (the buildup factor at mfp=0.5). If I do this I get a buildup factor of 1.104.
Am I wrong in my assumption or does Nucleonica interpolate differently? (Logarithmic or spline interpolation instead of linear interpolation what is shown in the help menu).

Buildup factor interpolation

(Ans. Nucleonica Team)
Until now the buildup factor was extrapolated for a given energy from the two last tabulated values µd=0.5 and µd = 1 when µd < 0.5. But since BU = 1 for µd = 0 interpolating between µd = 0 and µd = 0.5 is a better approach and will be realised by the next deployment. Thanks again for your observations.

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Metastable states in the Karslruhe Nuclide Chart

July 24th, 2019

Qu. (from M. R. KTE Karlsruhe, Germany):
Dear Nucleonica Team,
I have always wondered what the criteria are to show the metastable state of a nuclide on the chart. The first guess would be the half life of the state. But I found for example the nuclide Rn-214 which shows a metastable state of only 0,69 ns. Is there an arbitrary threshold just below that number where you show the state on the chart if it is above? If the threshold depends on the half life, is there a scientific reason for that threshold? Are all states shown that are above that threshold?
Rn214Ans. (Nucleonica Team)
Metastable states, which do not undergo alpha or beta decays or spontaneous fission, i.e. decay only by isomeric transition are shown (usually) only if their half-life is larger than 1 s (to save space).

Rn 214 excited states Rn 214m and Rn 214n have been observed, both with alpha decay to Po 210. Although their half-lives are less than 1s they are shown in KNC. In this way the users of KNC can know that the alpha emission is not from the ground state of Rn 214 and can have higher energy than the Q-value of ground state to ground state decay.
In some particular cases when the metastable state has an important role in a decay chain or in nuclear physics theory, it is presented even it decays only with isomeric transition and has a half-life shorter than 1s.
There is an interesting article on wikipedia.

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How can I find the spontaneous fission yields used in the Decay Engine++?

July 18th, 2019

This question is only relevant if at least the parent nuclide or one of its daughter nuclides decays by spontaneous fission.
In the results data grid (in the Decay Engine tab) the decay modes of the nuclides are shown with the corresponding branching ratios. For spontaneous fission only the total branching ratio for all fission products is given.

In the Decay Tree tab in turn each produced nuclide is shown in the decay tree with the half-life, the number of atoms, the number of disintegrations and the branching ratio from the parent nuclide to the considered nuclide. If the nuclide is a fission product this branching ratio is calculated as the branching ratio of the SF decay mode from the parent nuclide times the independent fission yield of the fission product.

In the databases JEFF and ENDF databases used inside Nucleonica the spontaneous fission yields are reported for three nuclides Cm-242, Cm-244 and Cf-252. Many other nuclides however decay by SF in which case the yields of Cm-244 are used.

For example, consider the decay Cm-248 and the fission daughter nuclide Mo-104. In the Decay Tree tab, this nuclide can be highlighted. The decay tree can be collapsed to show only the branches leading to the nuclide of interest Mo-104 as shown below.
Cm248 Decay TreeFig.1: The collapsed decay tree computed by the Decay Engine++ showing the decay branches leading to the highlighted nuclide of interest Mo-104.

In the above figure, the first occurrence of Mo-104 is as a fission product of Pu-244. The SF branching ratio of Pu-244 can be found in the results grid as 0.00125 whereas the BR of Mo-104 is given in the above figure as 6.95e-5. It follows that the independent fission yield of Mo-144 (from parent Cm-244 since no date for Pu-244 is available) will be:
Yind(Mo-104) = BR(Mo-104) / BRsf(Pu-244) = 6.95e-5 / 0.00125 = 5.56%
This is exactly the Ind. Yield given in the Fission Yields app for the parent Cm-244.

The second occurrence of Mo-104 in figure 1 is as a fission product of Cm248. From the results grid BRsf(Cm-248) = 0.0839. Again
Yind(Mo-104) = BR(Mo-104) / BRsf(Cm-248) = 4.67e-3 / 0.0839 = 5.57%
This independent fission yield can be found in the Fission Yields app from the Cm-244 parent nuclide (because neither Pu-244 nor Cm-248 are in the database), using the JEFF-3.1 library and the spontaneous fission type for the given nuclide.

In the tree structure in fig. 1, further occurrences of Mo-104 as a daughter of fission products are shown.

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