Jorge Machado

K$_{\alpha , \beta}$ X-ray lines from photon excitation were measured in selected elements from Mg to Cu using a high-resolution double-crystal X-ray spectrometer with a proportional counter, and the K$_beta$/K$_\alpha$ intensity ratio for each element was obtained, after correcting for self-absorption, detection efficiency, and crystal reflectance. This intensity ratio increases rapidly from Mg to Ca but, in the 3d elements region, the increase becomes slower. This is related to the intensity of the Kβ line involving valence electrons. The slow increase of this ratio in the 3d elements region is thought to be due to the correlation between 3d and 4s electrons. Moreover, the chemical shifts, FWHM, asymmetry indices, and Kβ/Kα intensity ratios of the Cr compounds, due to different valences, were also investigated using the same double-crystal X-ray spectrometer. The chemical effects were clearly observed, and the Kβ/Kα intensity ratio was found to be compound-dependent for Cr.

The CREMA collaboration is pursuing a measurement of the ground-state hyperfine splitting (HFS) in muonic hydrogen (μp) with 1 ppm accuracy by means of pulsed laser spectroscopy to determine the two-photon-exchange contribution with 2×10-4 relative accuracy. In the proposed experiment, the μp atom undergoes a laser excitation from the singlet hyperfine state to the triplet hyperfine state, then is quenched back to the singlet state by an inelastic collision with a H2 molecule. The resulting increase of kinetic energy after the collisional deexcitation is used as a signature of a successful laser transition between hyperfine states. In this paper, we calculate the combined probability that a μp atom initially in the singlet hyperfine state undergoes a laser excitation to the triplet state followed by a collisional-induced deexcitation back to the singlet state. This combined probability has been computed using the optical Bloch equations including the inelastic and elastic collisions. Omitting the decoherence effects caused by the laser bandwidth and collisions would overestimate the transition probability by more than a factor of two in the experimental conditions. Moreover, we also account for Doppler effects and provide the matrix element, the saturation fluence, the elastic and inelastic collision rates for the singlet and triplet states, and the resonance linewidth. This calculation thus quantifies one of the key unknowns of the HFS experiment, leading to a precise definition of the requirements for the laser system and to an optimization of the hydrogen gas target where μp is formed and the laser spectroscopy will occur.

Phys. Rev. C 105, 014611 (2022). doi:10.1103/PhysRevC.105.014611

Radiation Physics and Chemistry, 194 (2022) 110048. doi:10.1016/j.radphyschem.2022.110048

The energy levels of hydrogen-like atomic systems can be calculated with great precision. Starting from their quantum mechanical solution, they have been refined over the years to include the electron spin, the relativistic and quantum field effects, and tiny energy shifts related to the complex structure of the nucleus. These energy shifts caused by the nuclear structure are vastly magnified in hydrogen-like systems formed by a negative muon and a nucleus, so spectroscopy of these muonic ions can be used to investigate the nuclear structure with high precision. Here we present the measurement of two 2S–2P transitions in the muonic helium-4 ion that yields a precise determination of the root-mean-square charge radius of the $\alpha$ particle of 1.67824(83) femtometres. This determination from atomic spectroscopy is in excellent agreement with the value from electron scattering1, but a factor of 4.8 more precise, providing a benchmark for few-nucleon theories, lattice quantum chromodynamics and electron scattering. This agreement also constrains several beyond-standard-model theories proposed to explain the proton-radius puzzle2–5, in line with recent determinations of the proton charge radius6–9, and establishes spectroscopy of light muonic atoms and ions as a precise tool for studies of nuclear properties. The 2S–2P transitions in muonic helium-4 ions are measured using laser spectroscopy and used to obtain an $\alpha$-particle charge-radius value five times more precise than that from electron scattering.

Ion beam analysis of fluorine has applications in research on teeth and bones, materials science, geochemistry and archaeometry. A novel PIGE (particle induced gamma-ray emission) standard free methodology for fluorine content determination for in-depth heterogeneous samples based on the excitation function of the 19F(p,p’$\gamma$)19F nuclear reaction is presented. New precise cross section measurements of this reaction in the proton energy range 2.1 to 4.1 MeV have been performed. In addition, the ERYA-Profiling code, a computer program specially developed for PIGE analysis of in-depth heterogeneous samples, employed this new excitation function in a case study where different fluorine simulated depth profiles probed the capability of insight into fluorine distributions in a given sample, showing the potential of PIGE analysis.

Nuclear Inst. and Methods in Physics Research, A, 1014 (2021) 165701. doi:10.1016/j.nima.2021.165701

Physics Letters B, 809 (2020) 135748. 10.1016/j.physletb.2020.135748

Physics Letters B, 795 (2019) 682–688. 10.1016/j.physletb.2019.06.069