Femtosecond photoelectron and photoion spectrometer with vacuum ultraviolet probe pulses

We describe a setup to study ultrafast dynamics in gas-phase molecules using time-resolved photoelectron and photoion spectroscopy. The vacuum ultraviolet (VUV) probe pulses are generated via strong field high-order harmonic generation from infrared femtosecond laser pulses. The band pass characteristic in transmission of thin indium (In) metal foil is exploited to isolate the $9^{\text{th}}$ harmonic of the 800 nm fundamental (H9, 14 eV, 89 nm) from all other high harmonics. The $9^{\text{th}}$ harmonic is obtained with high conversion efficiencies and has sufficient photon energy to access the complete set of valence electron levels in most molecules. The setup also allows for direct comparison of VUV single-photon probe with 800 nm multi-photon probe without influencing the delay of excitation and probe pulse or the beam geometry. We use a magnetic bottle spectrometer with high collection efficiency for electrons, serving at the same time as a time of flight spectrometer for ions. Characterization measurements on Xe reveal the spectral width of H9 to be $190\pm60$ meV and a photon flux of $\sim1\cdot10^{7}$ photons/pulse after spectral filtering. As a first application, we investigate the S$_1$ excitation of perylene using time-resolved ion spectra obtained with multi-photon probing and time-resolved electron spectra from VUV single-photon probing. The time resolution extracted from cross-correlation measurements is $65\pm10$ fs for both probing schemes and the pulse duration of H9 is found to be $35\pm8$ fs

Proton and alpha radiation-induced mutational profiles in human cells

Ionizing radiation is known to be DNA damaging and mutagenic, however less is known about which mutational footprints result from exposures of human cells to different types of radiation. We were interested in the mutagenic effects of particle radiation exposures on genomes of various human cell types, in order to gauge the genotoxic risks of galactic cosmic radiation, and of certain types of tumor radiotherapy. To this end, we exposed cultured cell lines from the human blood, breast and lung to fractionated proton and alpha particle (helium nuclei) beams at doses sufficient to considerably affect cell viability. Whole-genome sequencing revealed that mutation rates were not overall markedly increased upon proton and alpha exposures. However, there were modest changes in mutation spectra and distributions, such as the increases in clustered mutations and of certain types of indels and structural variants. The spectrum of mutagenic effects of particle beams may be cell-type and/or genetic background specific. Overall, the mutational effects of repeated exposures to proton and alpha radiation on human cells in culture appear subtle, however further work is warranted to understand effects of long-term exposures on various human tissues.© 2023. The Author(s)

An ultra-thin diamond membrane as a transmission particle detector and vacuum window for external microbeams

Several applications of external microbeam techniques demand a very accurate and controlled dose delivery. To satisfy these requirements when post-sample ion detection is not feasible, we constructed a transmission single-ion detector based on an ultra-thin diamond membrane. The negligible intrinsic noise provides an excellent signal-to-noise ratio and enables a hit-detection efficiency of close to 100%, even for energetic protons, while the small thickness of the membrane limits beam spreading. Moreover, because of the superb mechanical stiffness of diamond, this membrane can simultaneously serve as a vacuum window and allow the extraction of an ion microbeam into the atmosphere

Commissioning of an ultra-high dose rate pulsed electron beam medical LINAC for FLASH RT preclinical animal experiments and future clinical human protocols.

To present the acceptance and the commissioning, to define the reference dose, and to prepare the reference data for a quality assessment (QA) program of an ultra-high dose rate (UHDR) electron device in order to validate it for preclinical animal FLASH radiotherapy (FLASH RT) experiments and for FLASH RT clinical human protocols. The Mobetron <sup>®</sup> device was evaluated with electron beams of 9 MeV in conventional (CONV) mode and of 6 and 9 MeV in UHDR mode (nominal energy). The acceptance was performed according to the acceptance protocol of the company. The commissioning consisted of determining the short- and long-term stability of the device, the measurement of percent depth dose curves (PDDs) and profiles at two different positions (with two different dose per pulse regimen) and for different collimator sizes, and the evaluation of the variability of these parameters when changing the pulse width and pulse repetition frequency. Measurements were performed using a redundant and validated dosimetric strategy with alanine and radiochromic films, as well as Advanced Markus ionization chamber for some measurements. The acceptance tests were all within the tolerances of the company's acceptance protocol. The linearity with pulse width was within 1.5% in all cases. The pulse repetition frequency did not affect the delivered dose more than 2% in all cases but 90 Hz, for which the larger difference was 3.8%. The reference dosimetry showed a good agreement within the alanine and films with variations of 2.2% or less. The short-term (resp. long-term) stability was less than 1.0% (resp. 1.8%) and was the same in both CONV and UHDR modes. PDDs, profiles, and reference dosimetry were measured at two positions, providing data for two specific dose rates (about 9 Gy/pulse and 3 Gy/pulse). Maximal beam size was 4 and 6 cm at 90% isodose in the two positions tested. There was no difference between CONV and UHDR mode in the beam characteristics tested. The device is commissioned for FLASH RT preclinical biological experiments as well as FLASH RT clinical human protocols

Mapping the Local Spatial Charge in Defective Diamond by Means of N- v Sensors - A Self-Diagnostic Concept

Electrically active defects have a significant impact on the performance of electronic devices based on wide-band-gap materials. This issue is ubiquitous in diamond science and technology, since the presence of charge traps in the active regions of different classes of diamond-based devices (detectors, power diodes, transistors) can significantly affect their performance, due to the formation of space charge, memory effects, and the degradation of the electronic response associated with radiation-induced damage. Among the most common defects in diamond, the nitrogen-vacancy (N-V) center possesses unique spin properties that enable high-sensitivity field sensing at the nanoscale. Here, we demonstrate that N-V ensembles can be successfully exploited to perform direct local mapping of the internal electric-field distribution of a graphite-diamond-graphite junction exhibiting electrical properties dominated by trap- and space-charge-related conduction mechanisms. By means of optically detected magnetic resonance measurements, we performed both point-by-point readout and spatial mapping of the electric field in the active region at different bias voltages. In this novel “self-diagnostic” approach, defect complexes represent not only the source of detrimental space-charge effects but also a unique tool for their direct investigation, by providing an insight on the conduction mechanisms that could not be inferred in previous studies on the basis of conventional electrical and optical characterization techniques

Harmonium: A pulse preserving source of monochromatic extreme ultraviolet (30–110 eV) radiation for ultrafast photoelectron spectroscopy of liquids

A tuneable repetition rate extreme ultraviolet source (Harmonium) for time resolved photoelectron spectroscopy of liquids is presented. High harmonic generation produces 30-110 eV photons, with fluxes ranging from similar to 2 x 10(11) photons/s at 36 eV to similar to 2 x 10(8) photons/s at 100 eV. Four different gratings in a time-preserving grating monochromator provide either high energy resolution (0.2 eV) or high temporal resolution (40 fs) between 30 and 110 eV. Laser assisted photoemission was used to measure the temporal response of the system. Vibrational progressions in gas phase water were measured demonstrating the similar to 0.2 eV energy resolution. (C) 2015 Author(s)

Study of interstrip gap effects and efficiency for full energy detection of Double Sided Silicon Strip Detectors

In this work is reported a study on the response of double sided silicon strip detectors. In order to investigate the effect of the electrode segmentation on the detector response, two experiments were performed aimed to measure the efficiency for full energy detection. Results show that the efficiency for full energy detection, that is directly related to effective width of the inter-strip region, varies with both detected ion energy and bias voltage. The experimental results are qualitatively reproduced by a simplified model based on the Shockley-Ramo-Gunn framework