Misassigned neutron resonances of ${}^{142}\mathrm{Nd}$ and stellar neutron capture cross sections

Time-of-flight spectra of the neutron capture events of ${}^{142}\mathrm{Nd}$ were measured using a spallation neutron source at the Japan Proton Accelerator Research Complex. The first six resonances of ${}^{142}\mathrm{Nd}$ reported in a previous work were not observed. The experimental results and cross-search of resonance energies in nuclear data libraries suggested that resonances of the impurity nuclide ${}^{141}\mathrm{Pr}$ have been mistakenly assigned as ${}^{142}\mathrm{Nd}$ in the previous experiment. To investigate the impact of the nonexistence of the resonances on the $s$-process nucleosynthesis model, the Maxwellian averaged neutron capture cross sections with and without the misassigned resonances were compared.

Figure 1

TOF spectrum of the ${}^{142}\mathrm{Nd}$ sample. The TOF time bin is 1 $\mu \mathrm{s}$. The TOF position of the first nine resonances of ${}^{142}\mathrm{Nd}$ in Ref. [12] are indicated by arrows.

Figure 2

Close-up of the TOF spectrum of the ${}^{142}\mathrm{Nd}$ sample. The TOF time bin is 100 ns. The TOF position of resonances of ${}^{142}\mathrm{Nd}$ in Ref. [12] are indicated by arrows. Resonances identified as ${}^{142}\mathrm{Nd}$ and impurity ${}^{143}\mathrm{Nd}$ are marked with the red full and blue open points, respectively. Each resonance has doublet peaks due to the double-bunched pulse beam.

Figure 3

Estimated capture yield TOF spectra under the present experimental conditions. Resonance parameters of JENDL-4.0 were used in the estimation. The TOF bin width is 1 $\mu \mathrm{s}$. The $1/E$ incident neutron spectrum was assumed. (a) Nd isotope impurities in the sample (Table 1) and statistically fluctuating background are included in the calculation. (b) Contribution of ${}^{142}\mathrm{Nd}$ to the calculation is shown and the red vertical lines indicate the TOF positions of the ${}^{142}\mathrm{Nd}$ resonances in the low-energy region.

Figure 4

TOF spectrum of the ${}^{141}\mathrm{Pr}$ sample. The TOF time bin is 1 $\mu \mathrm{s}$. The TOF position of the first six resonances of ${}^{142}\mathrm{Nd}$ in Ref. [12] are indicated by arrows.

Figure 5

Estimated transmission TOF spectra under the experimental condition of Ref. [2] for (a) a ${}^{141}\mathrm{Pr}$ and (b) a ${}^{142}\mathrm{Nd}$ sample with an isotope composition in Ref. [2]. The resonance parameters in JENDL-4.0 were used in the calculation. The ${}^{142}\mathrm{Nd}$ sample has Nd isotope impurities. The vertical lines indicate the TOF positions of the first six resonances of ${}^{142}\mathrm{Nd}$ reported in Ref. [2].

Figure 6

Close-up of the estimated transmission TOF spectra for the same calculation inputs as Fig. 5 (black solid line) and for assuming that 0.35% ${}^{141}\mathrm{Pr}$ impurity exists in the sample and the first six ${}^{142}\mathrm{Nd}$ resonances reported in Ref. [2] do not exist (red dashed line).

Figure 7

Estimated capture yield TOF spectra under the present experimental condition assuming that the first six ${}^{142}\mathrm{Nd}$ resonances in Ref. [2] do not exist and ${}^{141}\mathrm{Pr}$ impurity exists in the sample. The TOF spectra were calculated for ${}^{141}\mathrm{Pr}$ impurities of 0.3% (red solid), 0.15% (blue dashed), and 0% (black solid). Except for the removed ${}^{142}\mathrm{Nd}$ resonances and the additional ${}^{141}\mathrm{Pr}$ impurity, the calculation parameters are the same as those for Fig. 3.

Figure 8

Calculations of the Maxwellian averaged neutron capture cross section of ${}^{142}\mathrm{Nd}$. Evaluated data in JENDL-4.0 were used for the calculations. Calculations with the original JENDL-4.0 (open circle) and without the first six resonances (triangle) are compared.