Measurement of the neutron capture cross section of the $s$-only isotope ${}^{204}\mathrm{Pb}$ from 1 eV to 440 keV

The neutron capture cross section of ${}^{204}\mathrm{Pb}$ has been measured at the CERN n_TOF installation with high resolution in the energy range from 1 eV to 440 keV. An R-matrix analysis of the resolved resonance region, between 1 eV and 100 keV, was carried out using the SAMMY code. In the interval between 100 keV and 440 keV we report the average capture cross section. The background in the entire neutron energy range was reliably determined from the measurement of a ${}^{208}\mathrm{Pb}$ sample. Other systematic effects in this measurement were investigated and precisely corrected by means of detailed Monte Carlo simulations. We obtain a Maxwellian average capture cross section for ${}^{204}\mathrm{Pb}$ at $\mathit{kT}=30$ keV of 79(3) mb, in agreement with previous experiments. However our cross section at $\mathit{kT}=5$ keV is about 35% larger than the values reported so far. The implications of the new cross section for the $s$-process abundance contributions in the Pb/Bi region are discussed.

Figure 1

${}^{204}\mathrm{Pb}$ capture yield and pointwise background in the neutron energy region between 54 and 74 keV.

Figure 2

Correction factor $f^{\mathrm{ms}}(E_n)$ due to self-absorption and multiple scattering calculated with the code SESH [21].

Figure 3

Maxwellian averaged cross section for ${}^{204}\mathrm{Pb}$ compared with data from Ref. [22].