X-ray fluorescence from the element with atomic number Z=120.

An atomic clock based on x-ray fluorescence yields has been used to estimate the mean characteristic time for fusion followed by fission in reactions 238U + 64Ni at 6.6 MeV/A. Inner shell vacancies are created during the collisions in the electronic structure of the possibly formed Z=120 compound nuclei. The filling of these vacancies accompanied by a x-ray emission with energies characteristic of Z=120 can take place only if the atomic transitions occur before nuclear fission. Therefore, the x-ray yield characteristic of the united atom with 120 protons is strongly related to the fission time and to the vacancy lifetimes. K x rays from the element with Z=120 have been unambiguously identified from a coupled analysis of the involved nuclear reaction mechanisms and of the measured photon spectra. A minimum mean fission time τ(f)=2.5×10(-18) s has been deduced for Z=120 from the measured x-ray multiplicity.

The influence of technical factors on sonoelastographic assessment of solid breast nodules.

PURPOSE: The aim of the study was to assess the influence of technical factors and/or lesion characteristics on the final elastographic score in solid breast nodules. MATERIALS AND METHODS: Patients with solid breast masses examined between May 2007 and May 2008 in the Radiology Department of Cluj District University Hospital were included in the study. All lesions were examined with conventional ultrasound, Doppler ultrasound and sonoelastography, according to a preset protocol. The influence of the following factors on the elastographic score was evaluated: type of section (sagittal versus transverse); size of region of interest (small versus large); amplitude and frequency of movement; initial compression (light versus strong); angulation (perpendicular versus angulated transducer); characteristics of the lesion (size and location). The reference diagnosis was the histopathology diagnosis and, in twenty cases, short-term follow-up. RESULTS: Ninety-two patients with a mean age of 48.11 years and 101 breast nodules were included in the study. The overall sensitivity and specificity for elastography were 79 % [68-88 %] and 79 % [65 - 89 %], respectively, with a negative predictive value of 74 % [60-85 %] and a positive predictive value of 84 % [72-91 %]. The following factors did not influence the elastographic score: type of section (scores on transverse and longitudinal section, Z = -0.641, p = 0.552); the amplitude and frequency of movements during the elastographic examination (Cochran's Q concordance = 0.706, p = 0.872); strong initial compression in the case of benign nodules (Z = 0.000, p = 1.000); size of the lesions. Of the elastographically benign nodules, 9 were false negative and of the 46 elastographically malignant nodules, 12 were false positive. The following factors influenced the elastographic scores: size of the region of interest (the scores were significantly different when small or large region of interest was used, Z = -0.671, p < 0.0001); transducer angulation (Z = -5.42, p < 0.0001); strong initial compression in the case of malignant nodules (Z = -6.044, p < 0.0001) and the location of the mass in the vicinity of the chest wall. CONCLUSION: The most important factors that influence the final elastographic score, leading to false negative results, are the size of the region of interest, the initial compression and angulation of the transducer, while the frequency and amplitude of movement during the examination proved to be of no importance as long as the images were obtained within a range of assessment usefulness. Changing the scanning parameters never led to false positive results in the case of malignant breast masses.

Standardless PIXE analysis of thick biomineral structures.

The particle-induced X-ray emission (PIXE) of thick biomineral targets provides pertinent surface analysis, but if good reference materials are missing then complementary approaches are required to handle the matrix effects. This is illustrated by our results from qualitative and semiquantitative analysis of biomaterials and calcified tissues in which PIXE usually detected up to 20 elements with Z > 14 per sample, many at trace levels. Relative concentrations allow the classification of dental composites according to the mean Z and by multivariate statistics. In femur bones from streptozotocin-induced diabetic rats, trace element changes showed high individual variability but correlated to each other, and multivariate statistics improved discrimination of abnormal pathology. Changes on the in vitro demineralization of dental enamel suggested that a dissolution of Ca compounds in the outermost layer results in the uncovering of deeper layers containing higher trace element levels. Thus, in spite of significant limitations, standardless PIXE analysis of thick biomineral samples together with proper additional procedures can provide relevant information in biomedical research.