High-resolution ${}^{100}$Mo${(}^3$He,${t)}^{100}$Tc charge-exchange experiment and the impact on double-$\beta$ decays and neutrino charged-current reactions

The Gamow-Teller (GT) strength distribution has been investigated in a high-resolution (${}^3$He,$t$) charge-exchange experiment on the double-beta ($\beta \beta$) decaying nucleus ${}^{100}$Mo. The experiment was carried out at the Osaka University Research Center for Nuclear Physics (RCNP) with a 420 MeV incident ${}^3$He beam and the Grand Raiden magnetic spectrometer. A final-state energy resolution of 33 keV was achieved. It was found that nearly the entire low-energy (up to $\approx 4$ MeV) ${\mathrm{GT}}^{-}$ strength is concentrated in the ground-state transition to ${}^{100}$Tc, which is interpreted as a result of the particular neutron and proton sub-shell occupancies. The impact on the matrix elements for the two-neutrino double-beta ($2\nu \beta \beta$) decay and the use of ${}^{100}$Mo as a neutrino detection material is discussed.

Figure 1

Schematic representation of the $\beta \beta$ decay of ${}^{100}$Mo to the ground state and the first excited $0^{+}$ state of ${}^{100}$Ru. The $\beta \beta$ decay $Q_{\beta \beta }$ value has been taken from Ref. [58]. In the $2\nu \beta \beta$ decay mode only the intermediate $1^{+}$ states contribute.

Figure 2

Excitation-energy spectra of the ${}^{100}$Mo(${}^3$He,$t$)${}^{100}$Tc reaction at 420 MeV. Three angular cuts have been stacked on top of each other to indicate the angular dependence of certain transitions. Forward-peaked transitions are likely of $\Delta L=0$ nature, whereas $\Delta L\ge 1$ transitions are more backward-peaked. The inset shows the isobaric analog state (IAS) identified at 11.085 MeV. Note the change of scales above 4 MeV.

Figure 3

Experimental angular distributions compared with DWBA model calculations (lines) for the ${}^{100}$Mo(${}^3$He,$t$)${}^{100}$Tc reaction for typical transitions. The different $\Delta L$ angular momentum transfer components indicated by broken lines have been added incoherently to the calculated cross sections (full lines). The error bars represent statistical errors.

Figure 4

Experimental $B$(GT) distribution up to $E_x=4$ MeV. Above 3 MeV the GT distribution is integrated over ($\Delta =500$ keV) intervals and evenly distributed into 33 keV energy bins, which is the experimental energy resolution (cf. axis label right). Error values appear in Table .