Reactor Decay Heat in ${}^{239}\mathrm{Pu}$: Solving the $\gamma$ Discrepancy in the 4–3000-s Cooling Period

The $\beta$ feeding probability of ${}^{102,104,105,106,107}\mathrm{Tc}$, ${}^{105}\mathrm{Mo}$, and ${}^{101}\mathrm{Nb}$ nuclei, which are important contributors to the decay heat in nuclear reactors, has been measured using the total absorption technique. We have coupled for the first time a total absorption spectrometer to a Penning trap in order to obtain sources of very high isobaric purity. Our results solve a significant part of a long-standing discrepancy in the $\gamma$ component of the decay heat for ${}^{239}\mathrm{Pu}$ in the 4–3000 s range.

Figure 1

Upper panel: Comparison of the reconstructed spectrum from our analysis (gray) with the measured spectrum (black dots) for the decay of ${}^{104}\mathrm{Tc}$ (practically undistinguishable). The dotted line represents the contribution of contaminants. Lower panel: Deduced feeding from the current analysis (black dots) compared with previously known feeding from high resolution measurements (gray histogram lines) [13].

Figure 2

Comparison of the calculated electromagnetic decay-heat component for ${}^{239}\mathrm{Pu}$ before and after the inclusion of our measurements with the data of Tobias et al. [16], which is considered the standard of the field.