Archive for the ‘FAQs’ Category

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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Nuclide ID in ZZAAA (or ZAID) format possible?

June 26th, 2019

Qu. (from F. B. KIT-INE Karlsruhe, Germany):
Dear Nucleonica Team,
To import .csv files to Nuclide Mixtures ++ we have to give the Nuclide ID as e.g.
PU241, Pu-241 or Pu 241. However many programs use the ZZAAA notation (or ZAID notation): 94241. Hence it would be great to have the ZZAAA notation as .csv input accepted too. It this possible?

Further info: The MCNP6 suggestion for representing metastable isotopes seems to be a good idea: adjust the AAA value using the following convention:
AAA’=(AAA+300)+(m × 100), where m is the metastable level and m=1, 2, 3, or 4.
For naturally occurring elements, AAA=000 is suggested, for example 008000 represents the element oxygen.

Ans. (Nucleonica Team)
We now have the ZAID format working in the nuclide mixtures..

For example, you can upload a file with the data…
Nuclide, Activity(Bq)
95241, 1e6

This will then be interpreted as Am-241.
Further format options are shown in the figure below. The notation 92238 represents U-238.
Mixtures-formatsMore info…
ZAID format
Allowed file formats

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Application loading and running times

June 12th, 2019

Working with Nucleonica the user may notice differences in the loading times not only between different applications but also for the same application loaded at different times. Analogously the execution time of a given application and for the same calculation may vary over time.

In particular, after a maintenance or new deployment operation on the server the different memory caches are empty and the first call to an application may take significantly longer than a second or further calls to that application issued from the same or another user. The same is true for calculations involving intensive database operations such as gamma spectrum modelling or calculation of a large decay trees with lots of fission products.

Clearly different applications use more or less data generally retrieved from the underlying databases. The CPU time needed to prepare the data depends on the activity level on the server but can generally be neglected except when extensive calculations are involved. The transmission time over the net is proportional to the data amount to be transmitted and depends on many factors like the location of the client, the quality of the connection or the time of day. The time needed to load the data from the database in turn depends on whether the data are read from the disk or retrieved from the memory cache which is much faster than a disk operation.

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Uploading Nuclides with Metastable States in Nucleonica

June 5th, 2019

Qu. (from M. R. KTE-Karlsruhe, Germany):
Dear Nucleonica Team,
We are expanding the usage of the decay engine in Nucleonica into more and more groups to make time corrections to nuclide mixtures. While doing so we encountered a difficulty that you might be able to help us with:
When uploading a mixture with many different nuclides, we sometimes get the data from our database „KADABRA“. For mostly historical reasons in this database the nuclides are written in a slightly different way than is common in Nucleonica. So we are having problems with the writing of the metastable nuclides such as „Am-242m“ or „Nb-93m“ which are written in big letters „AM-242M“ and „NB-93M“. When we upload these nuclides, the „M“ for the metastable state is ignored and the nuclides would be read as „Am-242“ and „Nb-93“. We just thought it might be possible on your side to accept also big letters for the metastable states in the code or throw an error message when that happens. This way it would be easier to identify the mistake, because otherwise we don’t see it and continue working with wrong mixtures.
Do you think it is possible to accept the big letters for metastable states in the code?

Ans. (Nucleonica Team)
This problem has now been resolved. The nuclide mixtures app now accepts capital letters.

The image below shows the Nuclide Mixtures upload tab with the nuclide names in capital letters.
TestM

More info…
Nuclide Mixtures wiki page

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Ra-226 irradiations now possilbe with webKORIGEN

March 22nd, 2019

Qu. (from D. B. Garching, Germany):
Dear Nucleonica Team, if I let Ra-226 irradiate in a certain flux for a certain time, why I do not get nuclides with mass numbers higher than 226?

Ans. (Nucleonica Team)
This problem has now been resolved.

Results are shown below for an irradiation of Ra-226 (2g) in a dedicated facility with a thermal neutron flux of 2e14 neutrons per cm2 per s for a period of 100 days.
Ra226 Irrad

More info…
– webKORIGEN++ neutron activation wiki page

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Problem with using mixtures in DELNuS++

February 25th, 2019

Some of our users have reported that the results of a decay calculation using DELNuS++ for a mixture does not give the same result as the sum of the results for the single nuclide calculations.
As an example, the activity of Cs137 or Kr85 produced from a mixture of Cf252 and Cf250 is almost a factor two higher that from the sum of the results using the single nuclides Cf252 and then Cf250.
The problem has now been identified and resolved.
The results obtained using DELNuS++ for the mixture are now consistent with the sum of the results for the individual component nuclides. The results also agree with those obtained using the Decay Engine++ (which can also account for fission products).

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Ambient dose rates caused by different types of radiation

February 8th, 2019

Ambient dose equivalent H*(d) is the normal monitoring (area monitoring) quantity for X, gamma and neutron radiation where d is the depth at which the dose applies. International convention in radiation protection is to use the ambient dose equivalent at 10 mm depth i.e. H*(10). The ambient dose gives a conservative estimate of the effective dose a person would receive when staying at the point of the monitoring instrument (NPL).
In Nucleonica applications, the photon (X+gamma), beta, and neutron doses are calculated separately using analytical and semi-analytical formulae. To obtain the (total) ambient dose H*(d), these individual doses must be added. Following Otto, the ambient dose from a radionuclide can be represented as a sum of components caused by different radiation types, i.e.
ADR_Radiations3This is the notation which will be used in various Nucleonica applications for ambient doses and dose rates i.e.
ADR_Radiations4
For control of doses to skin and lens of eye, the directional dose equivalent is used. The directional dose equivalent denoted by H′(d) is intended for use with less penetrating radiation such a beta particles. Its main use is for skin dose at a depth of 0.07 mm. For beta radiation and electrons, for example, this is denoted as i.e. H'(0.07)e.
ADR_Radiations6

More info…
– T. Otto, Personal Dose-Equivalent Conversion Coefficients for 1252 Radionuclides, Radiation Protection Dosimetry (2016), Vol. 168, No .1, pp1-70. Link
NPL: Measurement of dose rate
Operational quantities (Wikipedia)

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