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This manuscript reports on the direct observation of a $\beta$-delayed two-neutron emission in a study of ${}^{134}\mathrm{In}$at the ISOLDE Decay Station using neutron spectroscopy. We also report on the first measurement in ${\beta }^{-}$decay of the long-sought $13/2^{+}$excited state in ${}^{133}\mathrm{Sn}$, attributed to be the neutron single-particle $i_{13/2}$orbital. The observation of sequential neutron emission is used to extract the relative population of the $i_{13/2}$state, which was found to be much smaller than the predictions of the statistical model. The experiment was possible because of the innovative use of a neutron array with neutron discrimination and interaction tracking capabilities. This is the first study of the details of the two-neutron emission for a nucleus, which belongs to the $r$-process path. Understanding $\beta$-delayed two-neutron emission probabilities is essential to validate models used in astrophysical $r$-process nucleosynthesis calculations. Observing two-neutron emissions in ${\beta }^{-}$decay paves the way for new experiments to study energy and angular correlations for $\beta$-delayed multineutron emitters. 

Abstract We report the detection of 21 cm emission at an average redshift $\overline{z}=2.3$in the cross-correlation of data from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) with measurements of the Lyαforest from eBOSS. Data collected by CHIME over 88 days in the 400–500 MHz frequency band (1.8 <z< 2.5) are formed into maps of the sky and high-pass delay filtered to suppress the foreground power, corresponding to removing cosmological scales withk_∥≲ 0.13 Mpc⁻¹at the average redshift. Line-of-sight spectra to the eBOSS background quasar locations are extracted from the CHIME maps and combined with the Lyαforest flux transmission spectra to estimate the 21 cm–Lyαcross-correlation function. Fitting a simulation-derived template function to this measurement results in a 9σdetection significance. The coherent accumulation of the signal through cross-correlation is sufficient to enable a detection despite excess variance from foreground residuals ∼6–10 times brighter than the expected thermal noise level in the correlation function. These results are the highest-redshift measurement of 21 cm emission to date, and they set the stage for future 21 cm intensity mapping analyses atz> 1.8. 

Abstract Localizing fast radio bursts (FRBs) to their host galaxies is an essential step to better understanding their origins and using them as cosmic probes. The Canadian Hydrogen Intensity Mapping Experiment (CHIME)/FRB Outriggers program aims to add very long baseline interferometry localization capabilities to CHIME, such that FRBs may be localized to tens of milliarcsecond precision at the time of their discovery, more than sufficient for host galaxy identification. The first-built outrigger telescope is theOutrigger (KKO), located 66 km west of CHIME. Cross-correlating KKO with CHIME can achieve arcsecond precision along the baseline axis while avoiding the worst effects of the ionosphere. Since the CHIME–KKO baseline is mostly east/west, this improvement is mostly in right ascension. This paper presents measurements of KKO’s performance throughout its commissioning phase, as well as a summary of its design and function. We demonstrate KKO’s capabilities as a standalone instrument by producing full-sky images, mapping the angular and frequency structure of the primary beam, and measuring feed positions. To demonstrate the localization capabilities of the CHIME–KKO baseline, we collected five separate observations each, for a set of 20 bright pulsars, and aimed to measure their positions to within 5″. All of these pulses were successfully localized to within this specification. The next two outriggers are expected to be commissioned in 2024 and will enable subarcsecond localizations for approximately hundreds of FRBs each year.