J. Inoue

Development of a fast multi-parameter data acquisition system for microbeam analyses

Abstract A commercially available Personal Computer (PC)-based multi-parameter data acquisition system has been developed for ion microbeam analyses. The PC is equipped with a recent fast processor, a large volume of memory and a general multi-channel Analogue to Digital Converter (ADC) interface board. When a signal from an X-ray detector (PIXE), from a particle detector (RBS)or from others triggers this ADC for data acquisition. X-Y beam scanning control signals which indicate the beam position are also digitized at the same time. These data are addressed to the 3D matrices in the memory space, that consist of 1024 channels for the energy spectra and 150 × 150 pixels for corresponding the beam scan area. Real time data processing can be done in addition to this data acquisition by the fast processor with the large memory. Simultaneous PIXE and RBS elemental mapping and ion beam induced charge (IBIC) imaging on fine structure diodes have been demonstrated with this system.

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.

Preparation of Thin Polycarbonate Film and Its Application to PIXE Analysis of Anionic Elements in Water Samples

A polycarbonate film of thin and uniform thickness was prepared. A casting solution for film-formation was made up by diluting a solution of poly (bisphenol A carbonate) in chloroform by a factor of two to three with benzene. A uniform film was created by dropping 0.2-0.3 cm3 of the casting solution slowly on a water surface within an aperture (20 mm diameter) of Mylar target frame floating on 50 wt% sucrose aqueous solution. Films of 0.14-0.27 mg/cm2 thickness thus prepared offer a good combination of mechanical strength and low continuum backgrounds. To test PIXE analysis of anionic species in water, targets containing SO42-, Cr2O72-, AsO43-, and Ga3+-internal standard were prepared by depositing 100 μl of the test solutions onto the polycarbonate film, and irradiated in vacuum by 3 MeV proton beams. The difference between the nominal and the analyzed concentrations seldom exceeded ± 15 % in the range from 10 to 2000 ppb.

Determination of Heavy-Metal Concentrations in Water by PIXE Analysis Using Zr as an Internal Standard

A metal-preconcentration procedure, which consists of a combination of chelation by dibenzyldithiocarbamate ions with subsequent condensation into dibenzylidene-D-sorbitol gels, has been reformed by using Zr as an internal standard. The colloidal gels formed in solutions were collected on a nuclepore filter for direct irradiation by 3 MeV proton beams in a system of vertical beam type in-air PIXE. The methodology was tested for simultaneous determination of the concentrations of seven metals (Fe, Co, Ni, Cu, Cd, Hg, Pb) in 25 ml of an aqueous sample. A good linear relationship was obtained between the nominal concentration and the elemental X-ray yields normalized with Zr-Kα ones. Absolute values of concentration in the sample solutions can be determined with an experimental error less than ±14 % in the 5-100 ppb range by employing published data pertinent to the inner shell ionization and subsequent X-ray emission of the heavy metals.

FACILITY OF PIXE ANALYSIS AT TOHOKU UNIVERSITY

PIXE research at the 4.5-MV Dynamitron laboratory of the Faculty of Engineering, Tohoku University started as a joint project between Cyclotron and Radioisotope Center(CYRIC), Tohoku University, and the Dynamitron laboratory. The PIXE equipments including vertical beam in air PIXE system called ViaPIXE was installed at a vacant beam course of the Dynamitron laboratory. Some PIXE experiments conducted at this facility as well future PIXE research in this laboratory are briefly described.

A PRECONCENTRATION TECHNIQUE FOR WATER ANALYSIS BY PIXE

The enrichment procedure of heavy metals (Fe3+, Co2+, and Hg2+) in water was examined in conjunction with in-air PIXE. The preconcentration step consisted of adsorption of dibenzyldithiocarbamate complexes of the metal ions onto dibenzylidene-D-sorbitol gels. The colloidal gels in solutions were then collected on a nuclepore membrane for direct irradiation by proton beams in a system of vertical beam type in-air PIXE. The amounts of the chemicals used in the enrichment were minimized to prepare thin target specimens with the homogeneous composition. The metal-recovery in the preconcentration step was confirmed to be quantitative in a wide range of the concentrations. The reproducibility and detection limit were shown and discussed for the present setup of PIXE analysis in our laboratory.

An endurance test of Kapton foil in in-air PIXE system

We have tested endurance of Kapton foil for beam irradiation, which is used as an exit window of in-air PIXE system. Kapton foil is strong enough to withstand the pressure differential, thin enough to transmit the proton beam with minimal energy loss and does not contain heavier elements. However, little is known about the relation between its lifetime until breakdown and beam parameters such as beam current, beam diameter and energy loss. Endurance tests were made by an in-air PIXE system at Tohoku university. Irradiation was performed by proton beam with 2 or 3 MeV until the foil was broken for various beam parameters. The total charge until breakdown of the Kapton foil was analyzed in consideration of beam current, diameter and energy loss. Total charge until breakdown decrease with increase in the beam current density in case of the beam current density higher than 100 nA/mm2. On the other hand, total charge until breakdown does not decrease so much in the beam current density up to 100 nA/mm2. The li...

SYSTEM OF PATTERN ANALYSIS IN PIXE SPECTRA

We have developed a software system based on the pattern analysis method in order to realize the automatic and quick PIXE spectra analysis. The software system was applied to some PIXE spectra to test the present method. Through the tests, important knowledge was obtained and some notions were adopted to the system.

USE OF Si-PIN PHOTODIODE X-RAY DETECTOR FOR PIXE

Si-PIN photodiode type detector is one of the X-ray detectors which have recently shown significant improvement in resolution of FWHM of 250 eV at 5.9 keV which is worse only by 130 eV than that of a conventional type Si(Li) detector. The remarkable advantages of the SPINP detector are high operability with the thermoelectric cooling system and low voltage bias, and small volume including the preamplifier system. It is found that SPINP detector is applicable to the X-ray spectrometry and also PIXE in the X-ray energy range below about 15 keV with a reasonable efficiency. The pattern analysis method is feasible to analysis such bad resolution spectra obtained with this detector. Some techniques related to the Si-PIN photodiode type detector in Bio-PIXE are discussed.

AN OPEN EXPERIMENT OF PIXE ANALYSIS

PIXE analysis opened to public was conducted as an event of an open school of the Atomic Energy Society of Japan, which is semiannually held in order to arouse public interest in the science of radiation and nuclear power. The experiment was performed using a vertical in air (Via) PIXE system at Tohoku university. Forty-seven people participated and enjoyed this open experiment.