The high-energy Sun - probing the origins of particle acceleration on our nearest star

As a frequent and energetic particle accelerator, our Sun provides us with an excellent astrophysical laboratory for understanding the fundamental process of particle acceleration. The exploitation of radiative diagnostics from electrons has shown that acceleration operates on sub-second time scales in a complex magnetic environment, where direct electric fields, wave turbulence, and shock waves all must contribute, although precise details are severely lacking. Ions were assumed to be accelerated in a similar manner to electrons, but γ-ray imaging confirmed that emission sources are spatially separated from X-ray sources, suggesting distinctly different acceleration mechanisms. Current X-ray and γ-ray spectroscopy provides only a basic understanding of accelerated particle spectra and the total energy budgets are therefore poorly constrained. Additionally, the recent detection of relativistic ion signatures lasting many hours, without an electron counterpart, is an enigma. We propose a single platform to directly measure the physical conditions present in the energy release sites and the environment in which the particles propagate and deposit their energy. To address this fundamental issue, we set out a suite of dedicated instruments that will probe both electrons and ions simultaneously to observe; high (seconds) temporal resolution photon spectra (4 keV – 150 MeV) with simultaneous imaging (1 keV – 30 MeV), polarization measurements (5–1000 keV) and high spatial and temporal resolution imaging spectroscopy in the UV/EUV/SXR (soft X-ray) regimes. These instruments will observe the broad range of radiative signatures produced in the solar atmosphere by accelerated particles.

Serpent 2 Validation for Radiation Shielding Applications

This paper contributes to the validation of Serpent's photon transport and coupled neutron-photon transport routines. Two benhmarks presenting measurements of neutron and photon flux through different sized iron and lead spheres have been calculated using a development version of Serpent and MCNP6.2. The Serpent results were compared to the measurement results and the MCNP6.2 calculations. Additionally, the development version has been compared to the currently distributed Serpent version 2.1.31. In all cases, the Serpent calculated neutron and photon spectra followed the measured spectra fairly well. For the iron spheres, differences between Serpent and MCNP6.2 calculated neutron spectra were mostly below 2 % at neutron energies below 4 MeV. Differences between photon spectra through the iron spheres were mostly below 3 %. For the lead spheres, differences in the calculated neutron spectra were mostly below 1.5 % in the energy range 0.04-4.0 MeV. Differences between photon spectra through the 10 cm lead sphere were mostly below 5 % and for the larger spheres below 10 % except at higher photon energies above 6.5 MeV. Differences between the development version and the Serpent version 2.1.31 of the order of 3 % were observed in the photon spectra through the largest lead spheres with radius 20 and 30 cm when Gaussian Energy Broadening was not applied. These are probably related to the coupled neutron-photon transport routines in the different versions.

Spectral characterization of SPDC-based single-photon sources for quantum key distribution

In our laboratory, we employ two biphoton sources for quantum key distribution. The first is based on cw parametric down-conversion of photons at 404 nm in PPKTP waveguide chips, while the second is based on the pulsed parametric down-conversion of 775 nm photons in PPLN waveguides. The spectral characterization is important for the determination of certain side-channel attacks. A Hong-Ou-Mandel experiment employing the first photon source revealed a complex structure of the common Hong-Ou-Mandel dip. By measuring the spectra of the single photons at 808 nm, we were able to associate these structures to the superposition of different transverse modes of the pump photons in our waveguide chips. The pulsed source was characterized by means of single-photon spectra measured by a sensitive spectrum analyzer as well as dispersion-based measurements. Finally, we also describe Hong-Ou-Mandel experiments using the photons from the second source.

Coupling light to a nuclear spin gas with a two-photon linewidth of five millihertz

Nuclear spins of noble gases feature extremely long coherence times but are inaccessible to optical photons. Here, we realize a coherent interface between light and noble-gas spins that is mediated by alkali atoms. We demonstrate the optical excitation of the noble-gas spins and observe the coherent back action on the light in the form of high-contrast two-photon spectra. We report on a record two-photon linewidth of 5 ± 0.7 mHz above room temperature, corresponding to a 1-min coherence time. This experiment provides a demonstration of coherent bidirectional coupling between light and noble-gas spins, rendering their long-lived spin coherence accessible for manipulations in the optical domain.

Extension of the Stoichiometric Calibration of CT Hounsfield values to Metallic Materials

Nowadays, patients with metallic implants undergoing radiotherapy may suffer from inaccuracy in the treatment plan caused by the implant. To ensure a precise plan an accurate relation between Hounsfield values of the computer tomographic (CT) images and the electron density of the elements and material mixtures is indispensable. In order to extend the stoichiometric calibration approach known for tissues to the regime of metallic materials, the basic physical equations as well as approximations in the parametrization and fitting are carefully reviewed. CT images of a standard calibration phantom and pure metallic samples up to the atomic number Z = 29 were acquired for various energies. Hounsfield values were determined on an extended Hounsfield scale which allows the mapping of material having high atomic number Z. It is found that from basic physics an empirical factorization of the cross-sections into a function of Z and a function of photon energy E is not allowed over a wide range of Z. Specifically, the parameterization for tissue like materials cannot be prolonged to materials with high-Z. Thus, the calibration is subdivided into regions of materials and its accuracy is quantified in each region. It depends, among others, on the knowledge of the X-ray photon spectra, the segmentation of the material samples and the empirical parameterization of the linear-attenuation coefficient.

Scaling properties of direct photon yields in heavy ion collisions

A recent analysis from the PHENIX collaboration of available direct photon measurement results in collisions of various systems such as Au+Au, Cu+Cu, and Pb+Pb, at different beam energies ranging from 39 to 2760 GeV, has shown a universal, within experimental uncertainties, multiplicity scaling, in which direct photon $$p_{T}$$pT-spectra for transverse momenta up to 2 GeV/c are scaled with charged hadron pseudorapidity density at midrapidity raised to power $$\alpha =1.25$$α=1.25. On the other hand, those direct photon $$p_{T}$$pT-spectra also exhibit geometrical scaling in the similar $$p_{T}$$pT range. Assuming power-law dependence of the scaled photon spectra for both scaling laws, we formulate two independent conditions for the power $$\alpha $$α, which overshoot experimental data by $$\sim 10\%$$∼10% on average. We discuss possible sources that might improve this estimate.

Assessment of Radio-Induced Damage in Endothelial Cells Irradiated with 40 kVp, 220 kVp, and 4 MV X-rays by Means of Micro and Nanodosimetric Calculations

The objective of this work was to study the differences in terms of early biological effects that might exist between different X-rays energies by using a mechanistic approach. To this end, radiobiological experiments exposing cell monolayers to three X-ray energies were performed in order to assess the yields of early DNA damage, in particular of double-strand breaks (DSBs). The simulation of these irradiations was set in order to understand the differences in the obtained experimental results. Hence, simulated results in terms of microdosimetric spectra and early DSB induction were analyzed and compared to the experimental data. Human umbilical vein endothelial cells (HUVECs) were irradiated with 40, 220 kVp, and 4 MV X-rays. The Geant4 Monte Carlo simulation toolkit and its extension Geant4-DNA were used for the simulations. Microdosimetric calculations aiming to determine possible differences in the variability of the energy absorbed by the irradiated cell population for those photon spectra were performed on 10,000 endothelial cell nuclei representing a cell monolayer. Nanodosimetric simulations were also carried out using a computation chain that allowed the simulation of physical, physico-chemical, and chemical stages on a single realistic endothelial cell nucleus model including both heterochromatin and euchromatin. DNA damage was scored in terms of yields of prompt DSBs per Gray (Gy) and per giga (109) base pair (Gbp) and DSB complexity was derived in order to be compared to experimental data expressed as numbers of histone variant H2AX (γ-H2AX) foci per cell. The calculated microdosimetric spread in the irradiated cell population was similar when comparing between 40 and 220 kVp X-rays and higher when comparing with 4 MV X-rays. Simulated yields of induced DSB/Gy/Gbp were found to be equivalent to those for 40 and 220 kVp but larger than those for 4 MV, resulting in a relative biological effectiveness (RBE) of 1.3. Additionally, DSB complexity was similar between the considered photon spectra. Simulated results were in good agreement with experimental data obtained by IRSN (Institut de radioprotection et de sûreté nucléaire) radiobiologists. Despite differences in photon energy, few differences were observed when comparing between 40 and 220 kVp X-rays in microdosimetric and nanodosimetric calculations. Nevertheless, variations were observed when comparing between 40/220 kVp and 4 MV X-rays. Thanks to the simulation results, these variations were able to be explained by the differences in the production of secondary electrons with energies below 10 keV.