A. Sugimoto

Development of a Submilli-PIXE Camera

We developed a PIXE analysis system which provides spatial distribution images of elements in a region of several cm2 with a spatial resolution of < 0.5 mm. We call this system a submilli-PIXE camera. This system consists of a submilli-beam line, beam scanners and a data acquisition system in which the X-ray energy and the beam position are simultaneously measured. We demonstrate the usefulness of the submilli-PIXE camera by analyzing the surface of a shell and of granite.

Development of a Micro-PIXE Camera

We developed a system of μ-PIXE analysis at the division of Takasaki ion accelerator for advanced radiation application (TIARA) in Japan Atomic Energy Research Institute (JAERI), which consists of a microbeam apparatus, a multi-parameter data acquisition system and a personal computer. Elemental analysis in the region of 500 μm × 500 μm can be performed with a spatial resolution of < 0.3 μm and multi-elemental distributions are presented as images on a computer display even during measurement. We call this system a micro-PIXE camera.

APPLICATION OF MICRO-PIXE CAMERA TO ELEMENTAL ANALYSIS OF A SINGLE CELL

Since the cellular metabolism has not yet been fully elucidated, it is very useful to get the information of elemental distributions in a single cell. We applied a micro-PIXE camera to obtain a picture presented with density of an element in a cell. Our micro-PIXE camera is on the basis of PIXE analysis using micro ion beams with the spot size of less than 1 μ m and the samples can be analyzed in air, so the size and the state of samples are not limited. Here, we analyzed the spatial distributions of elements in a single cell of animal for a medical application. Bovine aortic endothelial cells(BAECs) were cultured in culture medium containing bromodeoxyuridine(BrdU) which is known to be used in the DNA synthesis. We could take the elemental maps of phosphorus, potassium and sulfur which present well a shape of cell and a position of nucleus in this cell. Moreover, we obtained the picture of Br, that is, BrdU. It was found that BrdU was locally concentrated in two or three regions in the nucleus.

NO DETERIORATION ELEMENTAL ANALYSIS WITH IN-AIR SUBMILLI-PIXE CAMERA

Elemental images of rice leaves with lesion parts were taken with an in-air submilli-PIXE camera at Tohoku University. The rice leaves were analyzed in vivo and it resulted that the elements of Ca and Mn are accumulated in the lesion parts. It was confirmed by checking the intactness of cells that the living leaves were not seriously damaged. The surface of japan bowls (the Edo period), Japanese vessels (Shigaraki wares, the Edo period) and wooden tablets (the Meiji period) were directly surveyed by submilli-beams (3 MeV protons). Japanese vessels and wooden tablets were not discolored by the beam irradiation. Shigaraki vessels were discolored first, but their color disappeared after 10 days from the irradiation. It is concluded that such samples are not seriously deteriorated in in-air PIXE analysis.

RADIATION DAMAGE OF PAPER SAMPLES IN IN-AIR PIXE ANALYSIS

Degradation of paper caused by beam irradiation was investigated from a viewpoint of discoloration in PIXE analysis and its application to the paper samples of archaeology. Two types of paper (Japanese paper and fine quality paper) were tested in in-air PIXE analysis with 3 MeV protons. The degree of discoloration was quantitatively measured by the use of a calorimeter. The degree of discoloration was different for each tested paper and corresponded to the radiation dose of ions. It is resulted that even the in-air PIXE analysis should be carefully applied to archaeological treasures. Because discoloration of all tested paper decreased gradually at first but then increased after a few weeks. However, this phenomenon can be used to develop a technique of funny coloration.

AN ATTEMPT TO DETERMINE POSITIONS OF AEROSOL SOURCE BY THE PIXE ANALYSIS

Aerosols were continuously collected for 2 or 3 hours during the periods of 4-27 August 1997 and of 23 March-2 April 1998 at a suburb of Sendai City (east 10 km from Sendai), and meteorological data such as wind directions, wind velocities, etc were measured at the same time. The collected aerosol samples were analyzed by the particle-induced X-ray emission (PIXE) method. Fourteen elements (S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Hg and Pb) were contained in these samples. The elemental concentrations increased in the daytime and decreased at night. It coincided with the time variation of people movement. The concentrations of Mn, Fe, Zn and Pb elements depended strongly on the direction of wind and their distributions for wind directions reflected to the position of aerosol sources. This result suggests that the position of aerosol source can be determined by measuring aerosols and wind directions at the many positions.

OBSERVATION OF INTERFERENCE BETWEEN ATOMIC BREMSSTRAHLUNG AND NUCLEAR BREMSSTRAHLUNG

An aluminum target was bombarded with 1.5 MeV protons and continuous x-rays were measured at the angles of 45°, 90° and 135° with respect to the beam direction. By investigating the shape of the x-ray energy spectrum, it was recognized that, the continuous x-rays below 12 keV are atomic bremsstrahlung (AB) and those of above 12 keV are nuclear bremsstrahlung (NB), and AB and NB are mingled in the energy region of around 12 keV The x-ray energy dependence of angular distributions presented well a change from the process of AB to that of NB in the continuous x-ray spectrum. Interference between AB and NB were discussed on the basis of PWBA theory. Continuous x-ray production cross sections were calculated on the basis of PWBA BEA and a semi-classical theory and compared with the experimental results. The theoretical prediction reproduced well the experimental cross sections over the wide range of 6 orders in magnitude and of 2 keV – 35 keV in the energy except for the energy region mingled with AB and NB. The ratio of the theoretical cross sections to the experimental ones showed an interference effect between AB and NB in their mingled region.

AN ATTEMPT TO SUPPRESS THE COMPTON SCATTERING BACKGROUND APPEARING IN THE PIXE SPECTRUM

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.

AN OPEN EXPERIMENT OF A SUBMILLI-PIXE CAMERA

We have annually held an open experiment of PIXE analysis since 1996 to get peoples understanding on nuclear technology and radiation science. Up to the present, more than 270 participants joined and enjoyed the open experiments. This year, we demonstrated performance of a submilli-PIXE camera and had sixty-nine participants in the open experiment of PIXE. Elemental spatial distribution images gave deep impression to the participants. Half of the participants were high school students since the open experiment of PIXE was held during the period of open campus of Tohoku University. About ten percents of the participants were junior high school students. Our open experiment of PIXE was very effective to arouse public interest in radiation science and nuclear technology.