Archive for July, 2019

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.

Posted in FAQs, Karlsruhe Nuclide Chart | Comments (0)

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.

Posted in FAQs | Comments (0)

More from this blog