High-resolution neutron transmission and capture measurements of the nucleus ${}^{206}\mathrm{Pb}$

Neutron total and capture reaction cross-section measurements for ${}^{206}\mathrm{Pb}$ were performed at the GELINA neutron time-of-flight facility in the energy range from 1 to 620 keV. The resonance parameters corresponding to 304 excited nuclear levels in ${}^{207}\mathrm{Pb}$ were determined from the data using the R-matrix formalism. The results are compared to existing data. From the capture data photon strength functions have been deduced. No evidence has been found for a previously reported enhancement of the $M1$ transition strength, nor for a strong enhancement of the s-wave doorway state in the photon channel. The neutron capture cross section of ${}^{206}\mathrm{Pb}$ is of importance in stellar evolution calculations of the formation of the elements by neutron capture. Maxwellian-averaged neutron capture cross sections have been calculated at different stellar temperatures ranging up to 100 keV and compared with the results of previous work and evaluated data libraries.

Figure 1

Experimental arrangement for the transmission (above) and the capture (below) measurements performed at the GELINA neutron time-of-flight facility.

Figure 2

The neutron spectrum at the 58-m capture station, obtained from ${}^{10}\mathrm{B}$($n,\alpha$) and ${}^{235}\mathrm{U}$($n,f$) measurements, with the accelerator operating at 800 Hz.

Figure 3

The transmission factor for the 0.030-atoms/b-thick sample. The insert shows the result of an analysis with REFIT around the s-wave resonance at 66 keV.

Figure 4

The yield ($C_w/{\phi }_n$) as function of neutron energy together with the background contribution ($B_w/{\phi }_n$) and the contribution due to scattered neutrons ($Y_{\mathrm{bn}}$). The bottom figure shows the result of an analysis around the 27- and 35-keV resonances of ${}^{19}\mathrm{F}$ and ${}^{27}\mathrm{Al}$, respectively.

Figure 5

The ratio of the capture kernel obtained by Allen et al. [3] (left), Mizumoto et al. [4] (left), and Musgrove and Macklin [5] (right) relative to the area obtained in this work as a function of the resonance energy.

Figure 6

The measured and fitted ${\text{C}}_6$${\text{D}}_6$ pulse height spectra for the ${}^{206}\mathrm{Pb}$ resonances at 3.36 keV (left) and 16.4 keV (right). The latter ones are the sum of the contributions $Y_k=1,2,3$.

Figure 7

The experimental yield, $Y_{\exp }$ as a function of neutron energy is compared with the yield obtained using the ENDF/B-VI.8 parameters and the parameters deduced in this work.

Figure 8

The reduced neutron widths and the radiation widths for s-wave resonances in the ${}^{207}\mathrm{Pb}$ compound system as a function of the resonance energy.

Figure 9

The MAC cross section obtained in this work is compared with the one in Bao et al. [2] and the one deduced from the data in JENDL-3.3 and ENDF/B-VI.8.

Figure 10

The relative contribution to the MAC cross section of (1) the resonances listed in ENDF/B-VI.8, (2) the additional resonances for which the capture areas were deduced in this work and (3) the first term in Eq. (12).