JAEA-Conf 2011-002 - 日本原子力研究開発機構

JAEA-Conf 2011-002
constructing the decay schemes[1][2] of short-lived nuclides on the basis of the high-resolution
-ray measurements. When the -feeding to the highly excited states are overlooked, the
E value is underestimated and the E value becomes too large. Recently, TAGS was
successfully applied to measure some of the most important FP nuclides in the decay-heat
calculation for Pu-239. This series of the new TAGS measurement was initiated by a
European group, and a part of their novel result was published very recently [3]. We plan to
include these new TAGS data eventually into JENDL (Japanese Evaluated Nuclear Data
Library). This procedure needs not only the average energies but also the energy spectra of
the -rays and the-particles. But the TAGS data consist only of the -feeding rates into
energy-bins of the excited stats of the daughter with finite width. So we have to estimate the
energy spectra with the aid of theoretical consideration along with the TAGS results. On
this context, the present study aimes at establishing a way to estimate the energy spectra
with combined knowledge of the TAGS -feedings and the -decay and the-decay
theories.
2 . Comparison of European TAGS and Current Data
On the long-range point of view over decades of years, introducing the Gross theory into
the FP decay heat calculations[4] was thought to be a provisional treatment. It was expected
that the theoretical values of E and E for important FPs would gradually be replaced by
the data firmly based on some certain and reliable measurements which would be free from
the pandemonium problem. Having this long-standing anticipation as a background, they
stated the TAGS measurement led by a group of Valencia[5]. This measurement is able to
detect all the -feedings into the whole range of daughter’s excitation energy up to the Q -value itself. Their results are shown in Figs. 1 ~ 7 along with the current data.
The -feeding from Tc-104 to Ru-104 are compared between the TAGS and Table of
Isotopes[1] in Fig. 3 among others. The TAGS data provide us only with the -feedings into
energy-bins representing the excitation energies of the daughter, or Ru-104. In this case, the
TAGS supports the presence of the structures in the -feedings, which the current data
vaguely indicates. Further, the TAGS data provide us with the feedings up to much higher
in the exciting energy, where the current decay scheme gives us no information. So, we
adopt the data as it is in the energy range where the current level schemes say nothing.
3. Gamma energy spectrum calculation
When we introduce the decay data into the JENDL decay data file, we need not only the
average energies of the -rays and the -particles but also the -feeding rate and the
energy spectra of the radiations. Figure 8 shows the calculated -ray spectra starting from
the TAGS -feeding to the whole energy range from 0 (ground sate) to Q (the highest