Narrow Results

A physical method of quantitative analysis for in-air PIXE has been established. Among the three parameters required for performing physical analysis, X-ray production cross sections were recalculated by using the effective energy of the proton beam after losing its energy through a Kapton foil and in air. Detection efficiencies of the Si(Li) detector have been determined according to our method established for in vacuum system, where effects of absorption of X-rays in air are incorporated into the detection efficiencies. As a result, it is confirmed that the present method gives us accurate results in the analyses of standard samples as well as actual samples such as soil and ash. It becomes possible to perform quantitative analysis of various samples by optimizing the measuring conditions depending on the samples.

A simultaneous measuring system of two different targets by in-vacuum and in-air PIXE has been developed in order to improve efficiency of analyses in the limited machine time. The proton beam passes through a thin target in vacuum and it allows us to perform in-vacuum PIXE, and the beam is further transported to the in-air PIXE system for analyzing another target. The beam intensity for in-air PIXE while performing in-vacuum PIXE is 1.5 nA, which is almost sufficient. The effect of slight changes in the beam transport parameters on the background X-rays for both in-vacuum and in-air PIXE has been found to be negligible. As a result, it is confirmed that accuracy and sensitivity of analysis for many kinds of sample, such as various samples in earth, environmental sciences and in bio-medicine, are almost unchanged for the both systems, and a four-detector-simultaneous measuring system has been completed. It is expected that the system will work miracle for solving the problem of deficient machine time in our laboratory.

Standard-free method for untreated hair samples in in-air PIXE has been developed. It is confirmed that the method gives us good sensitivity and accuracy within several minutes' measurement if more than twenty hairs are attached onto the target. Even in the case where the number of hairs is less than eight, which is regular for usual in-vacuum PIXE, 10-15 minutes measurement is found to be sufficient to achieve almost satisfactory sensitivity and accuracy for elements from Cl to Pb. As the present method allows us to carry out analyses without labor in target preparation, it is expected to be quite helpful in the studies on human exposure to toxic elements. Its availability will more and more increase when the method is combined with the method of simultaneous measurement of in-vacuum and in-air PIXE we have just developed.

A standard-free method for living plants in in-air PIXE has been developed in order to clarify the mechanism of elemental transportation and movement in farm products. The components of the continuous X-rays originated from air and a backing film can be exactly subtracted using a blank spectrum after normalization by the yields of Ar Kα X-rays. It is found by observing the yield of continuous X-rays with passage of time that water content is continuously decreasing during irradiation with a proton beam in a case of pinched leaves. In contrary, it is kept almost constant during irradiation for the living plants to which water is continuously provided through the roots. Stability of the yield of continuous X-rays is a required condition for a standard-free method, which makes use of the yield of continuous X-rays mainly emitted from water content. It is confirmed that potassium concentration shows no large position dependence on a leaf, and it keeps almost constant during irradiation, which also indicates that regular metabolism is going on. As potassium is always contained in all kinds of plants in large amount, it is designated as an index element. As a result, it is found that the potassium concentration obtained by the present standard-free method shows quite consistent values with those obtained by the internal-standard method. The present method is confirmed to be quite useful for investigating movement of not only toxic elements but also essential elements reflecting metabolism in plants.

The method, which was developed by our group, enables us to perform quantitative analysis of living plants. It has been applied to investigate the transport of heavy elements such as germanium, gallium, bromine and arsenic in plants. These heavy elements are transported to the leaf through vascular vessel, and changes of their concentration with elapsed time after absorption could be clearly observed. It was confirmed that the movement depends on elements, on the manner of absorption and on the states of plant growth. In addition to the movement of supplied elements, some elements in the plant show interesting changes in response to proton irradiation. It was found that the method is quite effective for examining elemental movement in living plants.

In this paper, a two-detector measuring system in in-air PIXE system composed of two Si(Li) detectors has been developed for simultaneous measurement of low- and high-Z elements. In order to improve detection sensitivity of the detector for low energy region, a new device which is attached at the tip of the detector has been designed. It is made of acryl and has a thin end on which a 1.5 μm-thick Mylar film is stuck. As a result, it exhibited a miraculous effect in improving detection sensitivity at low energies and it became possible to detect K X-rays of aluminium. In order to perform quantitative analysis in in-air system, we have measured detection efficiencies for the two Si(Li) detectors including the effect of X-ray absorption in air on the basis of the method that we developed. Concerning the beam energy at the target and corresponding X-ray production cross-sections, the same values as were reported in the previous paper were applicable since conditions of irradiating system were unchanged. It was confirmed that the new method allows us to quantitatively analyze all the elements heavier than aluminum and to obtain mostly the same results as those by in-vacuum PIXE for various kinds of samples. Accuracy of analysis was also confirmed by using a standard material.

The two methods, which enable us to observe changes in concentration of heavy elements in living plants and to perform quantitative analysis of all elements heavier than aluminum in in-air PIXE with two detectors, simultaneously, were successfully applied to studies on movement of light elements in plants. It was found that light elements including silicone, phosphorus and sulfur in leaves of living plants can be quantitatively analyzed. Accuracy of the method for light elements could be confirmed by comparing the results with those obtained by an internal-standard method. It was also confirmed that changes in elemental concentration with elapsed time after starting irradiation could be observed for silicone, phosphorus, sulfur and chlorine together with heavier elements at the same time. Interesting changes in elemental concentration with elapsed time were observed for phosphorus and sulfur together with heavier elements such as potassium, calcium and manganese. Moreover, quite interesting changes of concentration of some light elements were clearly observed after supplying water-soluble manure containing phosphorus acid and potassium to the plant.

A microbeam system at the Wakasa Wan Energy Research Center is presented. A magnetic quadrupole doublet is used for the focusing of ion beams from a 5 MV tandem accelerator. Micro-PIXE and micro-PIGE measurements both in the vacuum and air are applicable with this system. Examples of the measurements for tooth and tea leaves are also presented.

In the present study, we used a silicon drift detector (SDD) for the quantitative analysis of in-air PIXE. First, we examined the basic performances of the detector. We found that the shift of the peak position was less than 0.45 eV, and the energy resolution was 130–136 eV at 5.98 keV. We then used the SDD for a quantitative analysis. Physical parameters, such as the X-ray production cross-sections, values of the transmission of X-rays through absorbers and the detection efficiencies, which are required for quantification, were obtained theoretically and experimentally. We confirmed that many elements, from magnesium to barium, were able to be detected without using any special device. The results of the quantitative analyses of a few standard materials showed good agreement with the certified values. This method was also used to analyze practical samples, including bio-medical samples, and the results were in good agreement with the results obtained with in-vacuum PIXE.