Role of electric and magnetic dipole strength functions in the ${}^{114}\mathrm{Cd}\left(\gamma ,{\gamma }^{\prime }\right)$ and ${}^{113}\mathrm{Cd}\left(n,\gamma \right)$ reactions

The distribution of the electromagnetic dipole strength below the neutron separation energy and its influence on the photon distribution after neutron capture were investigated in two experiments for the compound nucleus ${}^{114}\mathrm{Cd}$. By measuring the photoabsorption cross section at the bremsstrahlung facility $\gamma \mathrm{ELBE}$ at Helmholtz-Zentrum Dresden-Rossendorf it was possible to deduce the distribution of dipole strength below the neutron separation energy. The de-excitation spectrum after cold-neutron capture in ${}^{113}\mathrm{Cd}$ was measured at the Budapest Neutron Center. In a combined analysis, the experimentally deduced spectra after photon scattering on ${}^{114}\mathrm{Cd}$ and the neutron capture in ${}^{113}\mathrm{Cd}$ were analyzed in terms of electric and magnetic strength functions and nuclear level density with the help of the statistical code $\gamma$dex.

Figure 1

Overview of the spin and parity of the states, which are mainly excited in neutron capture and nuclear resonance fluorescence experiments.

Figure 2

Spectral bremsstrahlung fluence at the target deduced from transitions in ${}^{11}\mathrm{B}$ (black circles). The solid black line shows the calculated fluence distribution using the Schiff distribution [15], and the dashed lines show the uncertainty of the photon fluence.

Figure 3

Measured spectrum in the different analysis steps for the detector pair under $127{}^{\circ }$. The spectrum corrected for natural background (black), the spectrum unfolded for detector response (red [gray]), the simulated atomic background (green [light gray]), and the subtracted spectrum (blue [dark gray]).

Figure 4

Photo-absorption cross section deduced at ELBE (black points) in combination with the prediction of the TLO model (red [gray] line) and the RIPL3 prediction with two Lorentzian functions (green [light gray] line). In addition, the outputs for the electric dipole strength function during the iterations of the analysis (brown [dark gray] lines) and the first few data points (pink [very light gray]) of the $\left(\gamma ,n\right)$ experiment [12] are shown.

Figure 5

Comparison of the strength functions deduced from the present measurement and different models. The symbols are the same as in Fig. 4. In addition the strength function of ${}^{112}\mathrm{Cd}$ deduced from ${}^3\mathrm{He}$ scattering [29] (blue [dark gray] triangles) is shown. The magnetic dipole strength functions from RIPL3 (green [light gray] dashed line) and for the three Gaussian models (red [gray] dashed lines) are also plotted. The inset shows the region close to the neutron separation energy in detail.

Figure 6

Comparison of different simulation calculations with the measured and response corrected $\gamma$-ray spectrum (black diamonds) after neutron capture. The temperature parameter used in $\gamma$dex was varied from 570 (dashed violet [dark gray]) to 770 keV (solid red [gray]). Both simulations were performed with the TLO model for electric dipole strength and with the triple Gaussian model for magnetic dipole strength and should show for one pair of strength function how the nuclear level density can change the shape of the de-excitation spectrum. The uncertainties for the experimental data are $10\%$ at higher energies and are increasing towards $25\%$ at 1 MeV excitation energy.

Figure 7

Comparison of the measured and response-corrected $\gamma$-ray spectrum (black diamonds) after neutron capture with different simulation results. Various combinations of strength functions were used in each data set, while the temperature value was fixed to $T=670$ keV. The red (gray) lines show that the TLO model was used as input in the simulation, and the blue (dark gray) ones stand for the usage of the $E1$ strength function determined at ELBE. The solid lines indicate the usage of the three-Gaussian model as $M1$ strength function whereas the dashed lines stand for the RIPL3 parametrization of the magnetic dipole strength.

Figure 8

Reduced ${\chi }^2$ value for the comparison between the simulation outputs and the experimental spectrum for photon energies between 2 and 7 MeV. Different models are used as simulation input: the triple-Lorentzian model (black) and the iteratively experimental deduced electric strength function (red [gray]) for the electric dipole strength and the RIPL3 parametrization (open diamonds) and the Gaussian model (filled squares) for the magnetic strength. The experimental deduced dipole strength is retrieved separately for each temperature value.