Jorge Machado

Light has long being used in medicine; however, the high scattering of biological tissues always hindered its use. The aim of this work is the development of methodologies to focus light inside biological tissues. Geant4/GAMOS Monte Carlo platform was used to simulate the possibility of parameterize the time delay of multiple sources of external light, offset in time, as a function of the interest region position in order to create constructive interferences in a breast sample. A computational model was implemented and the platform was configured in order to perform these simulations. Preliminary results using a single light source were performed. It was concluded that scattering in adipose tissue is very high which is consistent with previous studies.

In this paper, we present a theoretical study of the X-ray fluorescence emission after vacancy of K-shell due to electron impact ionization. In particular, we focus on the angular distributions of the characteristic Kα emission lines following this process. Rh was chosen for the analysis since it is a common element in X-ray tube anodes. In this analysis we also considered some elements along the period-4, i.e., Ni, Cu and Co as case-studies. In doing so, we studied the magnetic sub-level population of the ionized states, which is directly related to the angular distribution of the emission. A relative low angular distribution for the Kα emission of Rh of 0.5% was observed, which makes the assumption of isotropic emission correct for most studies. Moreover, a comparison with the respective angular emission for adjacent elements in the fourth period of the periodic table shows that this isotropy is attributed to a small total angular momentum of the resulting configurations after ionization, as well as to opposite angular distributions of the various transitions, which average to a maximum of 0.7% angular asymmetry in Ni.

Elemental content plays an important role in biological processes, and so, the multielemental analysis of human tissue samples is required in biomedical research. Still, the small amount of available biological samples and the adipose content of the samples can be major setbacks for the accurate determination of elemental content. In this study, we explored the potential of several analytical approaches combined with total reflection X-ray fluorescence spectrometry (TXRF) for multielemental analysis of human tissues with different adipose content (colon, heart, liver, lung, muscle, intestine, skin, stomach, uterus, bladder and aorta). The capabilities and limitations of different sample treatment procedures (suspension and acidic digestion) and two TXRF systems with different anode configurations (Mo and W X-ray tubes) have been evaluated for such purpose. Results showed that for tissues with a higher fat content (e.g., skin, and intestine) the best strategy was the acidic digestion of the sample before TXRF analysis. However, for other tissues, acceptable results were obtained by suspending 20 mg of powdered material in 1 mL of 2 M nitric acid. A further enhancement of the limits of detection and accuracy of the results was achieved if using Mo-TXRF systems, especially for the determination of low Z elements (e.g., K, and Ca) and of elements present at low concentrations (e.g., Cu) in the human tissues. Finally, results by TXRF analysis were compared with those obtained with μ-EDXRF and ICP-OES, and a good agreement was obtained.

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.

In this work, we present K- and L- shell fluorescence yield values of the full isonuclear sequence of Fe ions, using a state-of-the-art multiconfiguration Dirac–Fock approach. These results may be of importance for spectral fitting and plasma modeling, both in laboratory and astrophysical studies, where Fe is an important benchmark element. The K-shell fluorescence yields were found to be very similar up to the removal of 14 electrons.

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.

Journal of Analytical Atomic Spectrometry (2020), 35, 2920-2927, doi:10.1039/D0JA00307G

Journal of Trace Elements in Medicine and Biology, 68 (2021) 126837. doi:10.1016/j.jtemb.2021.126837