An unexplained $>4\sigma$ discrepancy persists between “beam” and “bottle” measurements of the neutron lifetime. A new model proposed that conversions of neutrons $n$ into mirror neutrons $n^{\prime }$, part of a dark mirror sector, can increase the apparent neutron lifetime by 1% via a small mass splitting $\mathrm{\Delta }m$ between $n$ and $n^{\prime }$ inside the 4.6 T magnetic field of the National Institute of Standards and Technology Beam Lifetime experiment. A search for neutron conversions in a 6.6 T magnetic field was performed at the Spallation Neutron Source which excludes this explanation for the neutron lifetime discrepancy.

Conversions between neutrons n and dark matter candidate sterile neutrons n ′ have been proposed as a mechanism for baryon number B violation. In the case that there is a small mass difference Δ m between the n and the n ′ states, oscillations can be induced by compensating for Δ m with a magnetic field. A search for such neutron oscillations was performed at the Spallation Neutron Source by looking for anomalous neutron transmission through a strongly absorbing cadmium wafer inside of a 6.6 T magnet. The approach described here saw no regenerated neutrons above background, which provides an improved limit for neutron–sterile neutron transformations for a range of Δ m between 0.1 and 1000 neV. Published by the American Physical Society 2024

In this work, the previously unmeasured ${}^{232}\mathrm{Th}(d,5n){}^{229}\mathrm{Pa}$ reaction is reported at deuteron energies of 31.0, 35.2, 41.4, and 49.6 MeV. The irradiation took place at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron. The target processing and analysis were performed at Oak Ridge National Laboratory. The experiment used four thin foils $\left(\approx 17\mathrm{mg}/\mathrm{c}{\mathrm{m}}^2\right)$ of natural thorium metal in a stacked-target configuration, which were irradiated with a deuteron beam (1 µA) for approximately 11 continuous hours. Column chromatography techniques were implemented to directly assay ${}^{229}\mathrm{Pa}$ and its low intensity γ-ray emissions. The measured peak of the excitation function of ${}^{232}\mathrm{Th}\left(d,5n\right){}^{229}\mathrm{Pa}$ is $121.9\pm 12.7$ mb at $E_d=35.2\mathrm{MeV}$. In addition to ${}^{229}\mathrm{Pa}$, the production cross sections of the ${}^{232}\mathrm{Th}\left(d,xn\right){}^{234-x}\mathrm{Pa}$ reactions, where $x=1$, 2, 4, and 6, are also reported and compared to previous measurements. The experimental cross sections were compared with calculated cross sections using several reaction modeling codes including phits, talys, alice, coh, and empire as well as the evaluated nuclear reaction database TENDL.