Average neutron cross sections of ${}^{99}\mathrm{Tc}$

${}^{99}\mathrm{Tc}$ has been the subject of several experimental programs at the JRC-Geel since the late 1990s. This work presents new transmission data measured at the GELINA facility with the time-of-flight technique, whose simultaneous analysis with past transmission experiments provided a revised set of resonance parameters up to 5 keV. An iterative analysis between the resonance and “continuum” energy ranges leads to average resonance parameters $[S_0=0.51\left(3\right)$, $\langle {\mathrm{\Gamma }}_{{\gamma }_0}\rangle =137\left(7\right)$ meV, $D_0=12.8\left(2\right)$ eV] and theoretical average capture cross sections consistent with those reported in the literature. At $E=30$ keV, we obtain a capture cross section of 1076(45) mb and a Maxwellian-averaged cross section (MACS) of 1016(43) mb. The agreement with the recommended MACS value of 933(47) mb remains within the quoted uncertainties. This result demonstrates the performances of transmission experiments to provide reliable theoretical capture cross sections for long-lived fission products in the energy range of interest for $s$-process nucleosynthesis calculations.

Figure 1

${}^{99}\mathrm{Tc}$ capture cross section as a function of the incident neutron energy recommended in the JEFF-3.3 [8], ENDF/B-VIII [9], and JENDL-4.0 [10] evaluated neutron cross section libraries.

Figure 2

${}^{99}\mathrm{Tc}$ transmission data measured at the GELINA facility up to 1 keV with the IRMM, JRC, and TC99C samples. Sample characteristics and filter set-up are given in Table 1. Noisy structures observed around 132 eV are due to black resonance of Co. Arrows in the bottom plot locate the three first ${}^{238}\mathrm{U}$ resonances at 6.7 eV, 20.9 eV and 36.7 eV.

Figure 3

Comparison of transmission measurements performed with the TC99C sample well aligned to the neutron beam ($\mathrm{TC}99{\mathrm{C}}_1$) and slightly shifted from the central position ($\mathrm{TC}99{\mathrm{C}}_3$).

Figure 4

Examples of refit calculations (red solid line) compared to transmission data measured at the GELINA facility with the IRMM, JRC, and TC99C samples (Table 1). For the JRC and TC99C samples, only data measured with the boron antioverlap filter are displayed.

Figure 5

${}^{99}\mathrm{Tc}$ total cross section calculated with the ecis module of the talys code, compared to data reported by Foster and Glasgow [31] and those deduced from the transmission measured with the thick IRMM sample [12]. The shadow area represents the uncertainty band due to systematic uncertainties.

Figure 6

$s$-wave radiation widths obtained in this work and compared to those compiled by Mughaghab [36]. Only values below 200 eV are used to calculate the average radiation width.

Figure 7

Distribution of the s-wave average radiation width obtained from the Monte Carlo propagation of the resonance parameter uncertainties and correlations. The two first moments of the distribution provides the $\langle {\mathrm{\Gamma }}_{{\gamma }_0}\rangle$ value and its uncertainty.

Figure 8

Cumulative distribution function of the reduced neutron widths calculated between $E_{min}=5.6$ eV and $E_{max}=3$ keV.

Figure 9

Staircase plots of the $s$-wave reduced neutron widths (a) and of the cumulative number of $s$-wave resonances (b). The slope of the distributions provides the neutron strength function $S_0$ and the level density $1/D_0$, respectively. The shadow areas represent the uncertainty band.

Figure 10

Staircase plots of the $p$-wave reduced neutron widths (a) and of the cumulative number of $p$-wave resonances (b). The slope of the distributions should provide the neutron strength function $S_1$ and the level density $1/D_1$, respectively.

Figure 11

$l$-dependent phase shift calculated with the optical model parameters of Table 2 and with the square-well approximation [Eq. (5)].

Figure 12

${}^{99}\mathrm{Tc}$ capture cross section calculated with the talys code. The dashed lines show the $s$-wave ($l=0$), $p$-wave ($l=1$), and $d$-wave ($l=2$) contributions.

Figure 13

The top plot (a) shows the ${}^{99}\mathrm{Tc}$ capture cross section (in barns) calculated with the talys code. It is compared with data reported in the experimental library EXFOR [40]. The red open circle locates the value at $E=30$ keV compiled by Mughaghab in his Atlas of Neutron Resonances [36]. The bottom plot (b) shows the same capture cross section times the square root of the incident neutron energy. The shadow area represents the uncertainty band due to the model parameter uncertainties.