International Journal of PIXE

Total cross sections for the positronium formation in the ground (n=1) and excited (n=2) states in e⁺ - Na and e⁺ - K scattering have been studied within the framework of a distorted wave approximation. The present results have been compared with other theoretical and experimental findings.

The energy-loss effect of the projectile for direct inner-shell ionization cross sections by charged-particle impact has been examined. The relativistic and nonrelativistic calculations for K-shell ionization with and without the energy-loss effect are made in the plane-wave Born approximation and compared with the Brandt-Lapicki theory for the corrections of the relativistic and energy-loss effect. It is demonstrated that the Brandt-Lapicki method gives a good approximation to both relativistic and nonrelativistic cross sections, which implicitly take into account the energy-loss effect. However, the use of the Brandt-Lapicki relativistic correction method in the nonrelativistic theory with the exact integration limits for energy and momentum transfer overestimates the relativistic calculations for low-energy projectiles. This indicates that the Brandt-Lapicki method for correction of the electronic relativistic effect should be used only with their energy-loss correction method.

Partial M-x-ray production cross sections, which have not been well investigated up to the present, were measured in detail for six heavy lanthanides; Dy, Ho, Er, Tm, Yb and Lu. As a result, it is found that intensities of Mα,β lines, which are dominant among all the M-x-rays, and (M1-N2, M1-N3, M2-N4) lines agree well with those predicted by theory. However, clear discrepancy is found for Mζ and Mγ x-rays. Although it was pointed out by a PIXE analysis with a high-resolution crystal spectrometer that special attention must be paid for an analysis of Mζ and Mγ lines, it is found from the present work that it is possible to perform quantitative analysis using Mα,β lines.

Partial L- and M-x-ray production cross sections for Dy, Er and Lu have been systematically measured over the wide projectile-energy range of 3-40 MeV/amu for proton and ³He-ion impact, and values of partial x-ray production cross sections were compared with those predicted by the ECPSSR theory. As the result, it is confirmed that the ECPSSR theory gives consistent ionization cross sections for each subshell in L- and M-shells. It is also found that values of x-ray transition rate are correct for Mα,β and Lα₁₂ lines which are predominant in M and L x-ray spectra, respectively. However, it is pointed out that some of the values of x-ray transition rates must be revised, and improved values were obtained experimentally for the first time.

The analysis of copper, iron, calcium, and other elements in livers of Long-Evans Cinnamon(LEC) rats by PIXE determination is described. The copper contents in the livers of LEC rats which were supplemented with 1g/100g, in the food of calcium chloride dihydrate and iron(II) chloride n-hydrate, respectively, for 5 weeks were determined before and after supplement by PIXE.

The experimental results showed that after supplement of the calcium- and iron-fortified food the copper content in the livers of LEC rats decreased with the supplement. The present data suggest that supplement of iron or calcium can be responsible for copper homeostasis in livers of LEC rats, and that the excessive accumulation of copper in livers of LEC rats can readily remove when high load of iron or calcium are supplemented.

Cerebral vasospasm is a characteristic complication after subarachnoid hemorrhage (SAH), and the onset of vasospasm is a very important factor to decide the patient's outcome. Though various causal factors have been proposed for cerebral vasospasm after SAH, none of them explain the whole pathomechanism of vasospasm. To evaluate the role of trace elements in vasospasm, we have examined the sequential change in element concentration in the cerebrospinal fluid (CSF) after SAH by PIXE, and have investigated the relation between trace elements and vasospasm. We obtained the CSF samples from cisternal drainage of 17 patients with SAH who underwent radical surgery within 48 hours from the onset. The drainage was placed into basal cisterns at the end of the operation. Three sampling times (3-5, 7-9 and 12-14 days from the onset) were scheduled, because vasospasm is likely to occur from day 4 through day 14 after the onset. Cerebral angiograms were performed to classify vasospasm on day 1 and 7 after the onset. We measured 29 elements in the CSF and focused on Ca and Mg levels in this study, since Ca-influx into the smooth muscle cells is a principal mechanism of muscle contraction, and the competition between Ca and Mg is closely related to the muscle contraction. We found a significantly lower levels of Mg in the CSF of patients with vasospasm on days 7-9 after the onset. These results suggest that Mg in the CSF possibly ameliorate vasoconstriction due to Ca in the pathomechanism of vasospasm.

The background due to the Compton scattering of γ-rays in a Si(Li) X-ray detector was measured with the coincidence system which consists of a Si(Li) X-ray detector and NaI(Tl) scintillation detector. The Si(Li) X-ray detector is a through type to detect γ-rays of the Compton scattering into the forward direction. The energy spectra of the Si(Li) detector were measured for γ-rays of 662 keV from a ¹³⁷Cs source. The contribution of recoiled electrons to the PIXE spectrum in the energy region of 0~100 keV was ~20 % of its background spectrum. It was not enough to suppress the Compton scattering background by using the present system.