Paul Scherrer Institute

About: Paul Scherrer Institute is a facility organization based out in Villigen, Switzerland. It is known for research contribution in the topics: Neutron & Large Hadron Collider. The organization has 9248 authors who have published 23984 publications receiving 890129 citations. The organization is also known as: PSI.

Secondary neutron dose during proton therapy using spot scanning

Abstract: Purpose: During proton radiotherapy, secondary neutrons are produced by nuclear interactions in the material in the beam line before and after entering the patient. The dose equivalent deposited by these neutrons is usually not considered in routine treatment planning. In this study, we estimated the neutron dose in patients from a spot scanning beam line by performing measurements and Monte Carlo simulations. Methods and Materials: Measurements of the secondary neutron dose were performed during irradiation of a water phantom with 177-MeV protons using a Bonner sphere and CR39 etch detectors. Additionally, Monte Carlo simulations were performed using the FLUKA code. Results: A comparison of our measurements with measurements taken at a beam line using the scatter foil technique shows a dose advantage of at least 10 for the spot scanning technique. In the region of the Bragg peak, the neutron dose equivalent can reach for a medium-sized target volume approximately 1% of the treatment dose. Neutron doses expected in healthy tissues of the patient (in the not-treated volume) are for large and medium target volumes, approximately 0.004 Sv and 0.002 Sv per treatment Gy, respectively. Conclusions: We conclude from the measurements and simulations that the dose deposited by secondary neutrons during proton radiotherapy using the spot scanning technique can be neglected in the treatment region. In the healthy tissue, the dose coming from neutrons (0.002 Sv per treatment Gy) is approximately a factor of two larger than during photon treatment (0.001 Sv). These contributions to the integral dose from neutrons are still very low when compared to the dose sparing that can be achieved by using a proton beam instead of photons.

Standard Model Higgs-Boson Branching Ratios with Uncertainties

Abstract: We present an update of the branching ratios for Higgs-boson decays in the Standard Model. We list results for all relevant branching ratios together with corresponding uncertainties resulting from input parameters and missing higher-order corrections. As sources of parametric uncertainties we include the masses of the charm, bottom, and top quarks as well as the QCD coupling constant. We compare our results with other predictions in the literature.

Model of vector leptoquarks in view of the B -physics anomalies

Abstract: Lepton number as a fourth color is an intriguing theoretical idea which is combined with a possible left-right symmetry within the famous Pati-Salam (PS) model. In the conventional PS model, a spontaneous breaking of the PS gauge group down to the SM, one can only take place at very high scales (above the PeV scale) due to the stringent bounds from ${K}_{L}\ensuremath{\rightarrow}\ensuremath{\mu}e$ and $K\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\mu}e$ induced by the resulting vector leptoquarks. In this paper, we show that these constraints can be avoided once additional vectorlike fermions are introduced and, thus, a breaking at the TeV scale is possible. We consider the flavor phenomenology of this model in the context of the intriguing hints for new physics in semileptonic $B$ decays. The necessary violation of lepton flavor universality is induced by mixing SM and vectorlike fermions. Concerning $R(D)$ and $R({D}^{*})$, we find that sizable effects are possible while respecting the bounds from other flavor observables but predicting a large enhancement of ${B}_{s}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$. Furthermore, also in $b\ensuremath{\rightarrow}s{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ transitions, the observed deviations from the SM predictions [including $R(K)$ and $R({K}^{*})$] can be explained with natural values for the free parameters of the model without any fine-tuning, predicting sizable decay rates for $b\ensuremath{\rightarrow}s\ensuremath{\tau}\ensuremath{\mu}$. Finally, the anomaly in the anomalous magnetic moment of the muon can be accounted for by a loop contribution involving the vector leptoquark and vectorlike leptons.

Skyrmion-based artificial synapses for neuromorphic computing

Abstract: Magnetic skyrmions are topologically protected spin textures that have nanoscale dimensions and can be manipulated by an electric current. These properties make the structures potential information carriers in data storage, processing and transmission devices. However, the development of functional all-electrical electronic devices based on skyrmions remains challenging. Here we show that the current-induced creation, motion, detection and deletion of skyrmions at room temperature can be used to mimic the potentiation and depression behaviours of biological synapses. In particular, the accumulation and dissipation of magnetic skyrmions in ferrimagnetic multilayers can be controlled with electrical pulses to represent the variations in the synaptic weights. Using chip-level simulations, we demonstrate that such artificial synapses based on magnetic skyrmions could be used for neuromorphic computing tasks such as pattern recognition. For a handwritten pattern dataset, our system achieves a recognition accuracy of ~89%, which is comparable to the accuracy achieved with software-based ideal training (~93%). The electrical current-induced creation, motion, detection and deletion of skyrmions in ferrimagnetic multilayers can be used to mimic the behaviour of biological synapses, providing devices that could be used for neuromorphic computing tasks such as pattern recognition.

Near-Synchronous Interhemispheric Termination of the Last Glacial Maximum in Mid-Latitudes

Abstract: Isotopic records from polar ice cores imply globally asynchronous warming at the end of the last glaciation However, 10Be exposure dates show that large-scale retreat of mid-latitude Last Glacial Maximum glaciers commenced at about the same time in both hemispheres The timing of retreat is consistent with the onset of temperature and atmospheric CO2 increases in Antarctic ice cores We suggest that a global trend of rising summer temperatures at the end of the Last Glacial Maximum was obscured in North Atlantic regions by hypercold winters associated with unusually extensive winter sea ice