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TOSCA è uno spettrometro inelastico di neutroni a geometria indiretta ottimizzato per spettroscopia vibrazionale ad alta risoluzione. Nella sua forma attuale, lo strumento è operativo da quasi due decenni e in quel periodo ha fissato lo standard per la spettroscopia chimica ad ampio spettro con i neutroni. Nel 2013, nel corso di una revisione internazionale degli strumenti, si è concluso che per TOSCA sarebbe stato altamente vantaggioso incrementare di flusso di neutroni incidenti mediante una guida di neutroni, affinché lo strumento fosse in grado di partecipare ad aree di ricerca strategiche. Questo importante aggiornamento è stato implementato e ha richiesto la riprogettazione completa dello spettrometro primario, così da alloggiare una guida di neutroni all'avanguardia. La nuova configurazione è stata testata per avere una migliore idea dell'influenza della guida sul flusso incidente, il profilo del fascio, la risoluzione spettrale e il background. Lo studio mostra un buon profilo del fascio sul campione e i nostri sforzi per il design teorico della guida hanno garantito un profilo di fascio omogeneo. Grazie alla guida, il flusso di neutroni alla posizione del campione è stato significativamente aumentato. Il guadagno sperimentale medio è stato di un ordine di grandezza sul flusso. Un ulteriore aggiornamento richiede la riprogettazione dello spettrometro secondario TOSCA e il loro effetto combinato sarà quello di migliorare notevolmente l'efficienza di utilizzo della sorgente di neutroni. L'analizzatore piano attualmente utilizzato su TOSCA ha area ridotta ed è posizionato ad un angolo di riflessione di 45° e a una distanza media di 320 mm rispetto al campione. Esso è realizzato in grafite pirolitica ad alta orientazione, questo materiale è particolarmente adatto per la riflessione specifica dei neutroni sub-termici grazie all'elevata riflettività e ai picchi di diffrazione netti. Gli attuali banchi inelastici sono anche dotati di un filtro in beri, TOSCA is an indirect-geometry inelastic neutron spectrometer optimised for high resolution vibrational spectroscopy. In its current form the instrument is operational for almost two decades and during that time has set the standard for broadband chemical spectroscopy with neutrons. In 2013 as part of the international beamline review it was concluded that for TOSCA to be able to participate in strategic research areas, an increase in the incident neutron flux via the provision of a neutron guide was highly beneficial. This major upgrade has been implemented and has required the complete redesign of the TOSCA primary spectrometer to house a state-of-the-art neutron guide to boost its incident flux. We have tested the new setup to have better idea about the influence of the guide inside the shutter on the neutron flux, beam profile, spectral resolution and background. The data overall show a good beam profile across the TOSCA sample thanks to our efforts on the theoretical guide design to ensure that the chain of reflections had minimal beam profile patterns. As a result of the guide being installed on TOSCA the neutron flux at the sample position has been significantly increased. The experimental gain in incident neutron flux is an order-of-magnitude on average. A further upgrade required the redesign of the TOSCA secondary spectrometer, and their combined effect will be to highly improve the utilization efficiency of the neutron source. The flat analyzer currently used on TOSCA can be approximate with a square shape with a limited area, and the centre of the analyzer is placed at a 45° glazing angle and at an average distance of 320 mm with respect to the sample. The analyzer is made of highly oriented pyrolythic graphite, this material is particularly suitable for the specific reflection of sub-thermal neutrons thanks to its high reflectivity and sharp diffraction peaks. The current inelastic banks are also equipped with a beryllium-cadmium filter to cut the higher

High-resolution inelastic neutron scattering and extensive first-principles calculations have been used to explore the low-temperature phase of the hybrid solar-cell material methylammonium lead iodide up to the well-known phase transition to the tetragonal phase at ca. 160 K. Contrary to original expectation, we find that the Pnma structure for this phase can only provide a qualitative description of the geometry and underlying motions of the organic cation. A substantial lowering of the local symmetry inside the perovskite cage leads to an improved atomistic model that can account for all available spectroscopic and thermodynamic data, both at low temperatures and in the vicinity of the aforementioned phase transition. Further and detailed analysis of the first-principles calculations reveals that large-amplitude distortions of the inorganic framework are driven by both zero-point-energy fluctuations and thermally activated cation motions. These effects are significant down to liquid-helium temperatures. For this important class of technological materials, this work brings to the fore the pressing need to bridge the gap between the long-range order seen by crystallographic methods and the local environment around the organic cation probed by neutron spectroscopy.

We describe and assess the performance of a detailed computational description of the high-resolution TOSCA spectrometer at ISIS using neutron-transport Monte Carlo simulations. Extensive calculations using the McStas software package have been performed using the present instrument geometry and compared with available experimental data. The agreement between expected and measured performance is satisfactory in terms of the incident flux spectrum, associated time structure, and spectroscopic resolution. Encouraged by these results, we also consider the upgrade of the primary spectrometer with a tapered high-m guide. This instrument development offers the exciting prospects of providing order-of-magnitude gains in detected neutron flux over the energy-transfer range of the instrument whilst preserving its outstanding spectroscopic capabilities.

TOSCA is a high-resolution neutron spectrometer at the ISIS Pulsed Neutron and Muon Source. The instrument is optimised for broadband vibrational spectroscopy in the 0-4000 cm-1 region and it has been operational since 2000. This paper describes how the instrument has been progressively upgraded in the intervening years to enable new science. Future upgrades are outlined.