Cross section for the neutron radiative capture on ${}^{173}\mathrm{Lu}$ nuclei

We report the measurement of a neutron radiative cross section on a target with a high gamma activity, at the Los Alamos DANCE detector (Detector for Advanced Neutron Capture Experiments) for the first time. The $(n,\gamma )$ reaction properties of the unstable ${}^{173}\mathrm{Lu}$ isotope were studied. Two experimental campaigns were needed to determine the ${}^{173}\mathrm{Lu}(n,\gamma )$ cross section. They were performed at the Los Alamos Neutron Science Center (LANSCE) spallation neutron source facility. To this end, two targets were produced from an Hf sample using successively proton irradiation and chemical separations. They were composed of ${}^{173}\mathrm{Lu},{}^{174}\mathrm{Lu}$, and ${}^{175}\mathrm{Lu}$ isotopes. The two measurements were conducted at two-year intervals, taking advantage of the difference of the isotopic decay lifetimes in order to identify resonances from the ${}^{173}\mathrm{Lu}(n,\gamma )$ and ${}^{174}\mathrm{Lu}(n,\gamma )$ reactions. Just over one hundred new resonances were observed, the majority of which come from the ${}^{173}\mathrm{Lu}(n,\gamma )$ reaction. Only a few of them were assigned to the ${}^{174}\mathrm{Lu}(n,\gamma )$ reaction. As regards the ${}^{173}\mathrm{Lu}(n,\gamma )$ reaction, the radiative neutron capture cross section was determined over the energy range from thermal neutron up to 200 eV. The parameters of resonances in the resolved resonance region were extracted with the sammy code while calculations with talys determined the capture cross section in the unresolved resonances region. At the keV region, we performed standard talys calculations as well as other microscopic investigations by substituting the standard talys photon strength function by another one from QRPA models.

Figure 1

Production pathways for the main isotopes in the target.

Figure 2

636 and 1241 keV $\gamma$ rays used for energy calibration from the energy spectrum of the ${\mathrm{BaF}}_2$ crystal no. 8.

Figure 3

Neutron energy spectrum with (black line) and without (red line) raw data reduction cuts. We can notice that for the raw data the resonances are totally drowned in the background but they become apparent with cut selections.

Figure 4

Detection efficiency from evita DANCE-geant4 simulations for both ${}^{173}\mathrm{Lu}(n,\gamma )$ and ${}^{175}\mathrm{Lu}(n,\gamma )$ reactions.

Figure 5

Total capture yield with $3<M_{\gamma }<8$ and $4<E_{\mathrm{sum}}<7$ MeV cut selections measured in December 2011 according to the incident neutron energy [(a)–(c)].

Figure 6

Total capture yields from 2 to 30 eV [(a)–(c)] measured in 2011 (red line) and 2014 (black line). All resonances were assigned to the ${}^{175}\mathrm{Lu}(n,\gamma )$, the ${}^{173}\mathrm{Lu}(n,\gamma )$, or the ${}^{174}\mathrm{Lu}(n,\gamma )$ reactions (circles, arrows, and dashed arrows respectively).

Figure 7

(a) Resonance integrals ratio between 2014 and 2011 for ${}^{173–175}\mathrm{Lu}(n,\gamma )$ reactions measured in December 2014 according to the decay of the different Lu isotopes. (b) Resonance integrals ratio between 2014 and 2011 for ${}^{173–175}\mathrm{Lu}(n,\gamma )$ reactions according to the incident neutron energy.

Figure 8

Experimental data are represented by a red line while theoretical distributions are displayed in black. (a) Reduced $\gamma$-width measured distributions compared to a ${\chi }^2$ law $\left(\nu =100\right)$. (b) ${\mathrm{\Gamma }}_n$ width compared to a Porter-Thomas distribution. (c) Resonance spacings and Wigner distribution comparison.

Figure 9

${}^{173}\mathrm{Lu}(n,\gamma )$ reaction neutron cross section from the sammy-7.0 code over the resonance domain.

Figure 10

Orbital momentum assignment of resonances.

Figure 11

Number of observed resonances with neutron widths larger than a threshold fitted by Eq. (3).

Figure 12

(a) Cumulative sum of the reduced neutron widths as a function of the neutron energy. (b) Neutron strength function versus neutron energy.

Figure 13

Radiative capture cross section for ${}^{175}\mathrm{Lu}(n,\gamma )$ reaction. Data from Wisshak [23] are plotted in pink, data from Beer [27] are in green, and data from Macklin [26] are in blue. The standard talys calculation normalized in the region is in black. The calculation computed with $E1,M1$ PSFs from QRPA models is in red.

Figure 14

Radiative capture cross section for the ${}^{173}\mathrm{Lu}(n,\gamma )$ reaction. Standard talys normalized calculations are in black for ${}^{175}\mathrm{Lu}$ normalization $\left(G_{\mathrm{norm}}=2.3\right)$ and in grey for normalization based on experimental data from this work $({\mathrm{\Gamma }}_{\gamma }=73$ meV). The calculation computed with $E1,M1$ PSFs from the QRPA formalism is in red.