BEAM ALIGNMENT OF SCANNING MICROBEAM PIXE ANALYSISSYSTEM IN NIRS ELECTROSTATIC ACCELERATOR FACILITY
H. Imaseki, M. Yukawa, T. Ishikawa, H. Iso, and T. Hamano
National Institute of Radiological Sciences, Chiba, Japan
Abstract
The scanning microbeam PIXE (Particle Induced X-rayEmission) analysis allows identifying the several surface
elements and taking the high-resolution elemental mapsof the specimen at a time, by using the narrow beam
downed the size to 1 µ m and the maximum scanning areaof 2mm square. We are applying this system to theelements and the structure analysis for bio-cells andenvironmental specimens. The most important procedure
to obtain the high-resolution maps is increasing spatialresolution of the microbeam. We diagnose the resolution
by using Scanning Transmission Ion Microscopy (STIM)
and PIXE images of the 12.5µm pitch copper mesh. In
this workshop, we introduce our experiences of thealignment of the microbeam system.

1 INTRODUCTION
The National Institute of Radiological Science (NIRS)
was established in 1957 as a special research institute,attached to the Science and Technology Agency of Japan.
NIRS discarded the van de graff accelerator (ModelKM3000, High Voltage Engineering) in1997 that had
been operated as a device for pre-tumor therapy byneutron and PIXE analysis from 1961. In March 1999, an
electrostatic accelerator, of HVEE Tandetron, wasinstalled in the Electrostatic Accelerator Building for
PIXE (Particle Induced X-ray Emission) analysis. PIXE
analysis is a trace analytical method, which has anadvantage of simultaneous determination of elemental
concentrations in a small specimen without any chemical
separation by measuring characteristic X-rays of elements
induced by accelerated charged nuclear particles such asprotons.

2 SYSTEM SPECIFICATIONS
2.1 Electrostatic accelerator system
The installed accelerator for PIXE analysis is theTandetron (Model 4117MC) manufactured by HighVoltage Engineering Europe Co. The accelerating voltage
is 0.4 to 1.7MV, and the maximum beam current for
protons is 5 µ A at 3.4MeV. This system has three beamlines designed for different types of PIXE analysis:
conventional, in-He and scanning micro-beam. [1]Figure 1

2.2 Conventional PIXE analysis line
The beam port for normal PIXE can supply beams of0.5 - 2.0 mm square with currents of 10-100 nA. The
beam size can be regulated with a set of X-Y slits. Since
two types of X-ray detectors, Si (Li) and CdZnTedetectors, are available here, elements from Na (Z=11) toU (Z=92) are detectable. Fifteen samples can mount andanalysed semi-automatically using computer control.
Each sample is attached to the center of a hole of diameter
20mm on an aluminum plate of 25mm×35mm withappropriate backing film. Detector # 1 is a Si (Li) detector
and detector # 2 is a CdZnTe detector, and these are set at
135 degree with respect to the incident ion beam.

2.3 In-He PIXE analysis line
The in-He PIXE analysis system was commissioned inMarch 2001, and is connected to the second beam port.
The in-He beam line is used for irradiation of wet samples
using a proton beam of size approximately 2 mm φ. The
proton beam, which passes from the vacuum through
Kapton film, enters the analysis chamber filled withhelium gas at 1 atmosphere.

2.4 Scanning micro-beam PIXE analysis line
The layout of micro-beam scanning system (ModelOM2000, Oxford Micro beams, Ltd.) installed at NIRS isillustrated in Figure 1. A proton beam is focused to themicron level by passing the beam through a coarse 0.5
mm diameter object aperture, and two more precise setsof X-Y slits which serve as object and collimator
apertures. The beam is focused using a set of quadrupoletriplet magnets, and scanned over the sample using ascanning coil positioned before the lens system. Thissystem enables multi-elemental mapping over 2mm ×2mm areas with a spatial resolution of about 1 µ m.
Figure 2 shows the chamber for the scanning micro-beam.
Characteristics of the system are summarized in Table 1.
This apparatus is useful for a research into the elementaland structural analysis of small samples, for example acell. [2].

2.5 Scanning Transmission Ion Microscopy(STIM)The STIM system was attached to the micro-beamscanning line in March 2001. The function of thisapparatus is illustrated in Figure 2.

can observe simultaneously the structure of samples in thescanning area during PIXE analysis.

3 THE RESULTS OF BEAM RESOLUTIONTESTS
3.1 First step in the year of 2000
Figure 3 indicates the result of beam resolution tests
carried out in February 2000 during the systeminstallation. The beam size was estimated to be 0.4 × 0.6µm with 12.7 µ m meters repeat distance gold grid for
3MeV proton. The beam current was 50pA, the scan size
was 5µ m square and the irradiation time was 20min.

Scan Coils

Triplet Quadrupole
X-Y Slit

Object Slit(1.5mmΦ)1μm
Figure 3
Result of beam resolution test

3.2 Second step in the year of 2001: The
installation of Scanning Transmission Ion
Microscopy (STIM)

Figure 2
Schematic diagram of Scanning micro-PIXE line andMicro-PIXE chamber
An energy-loss spectrum of transmitted proton can beobtained using a surface barrier Si detector behind thesample. Since the energy-loss of transmitted protons
depends on thickness and density of the sample, byscanning the sample surface with proton beams, we canget the energy-loss map to image the structure of a thinsample (up to 30 µ m meters) with this system. Thus, weFigure 4 indicates the result in December 2001. The
estimated beam resolution is 100 × 200 nm, measured
using a 2.6 MeV proton beam scanned over a 12.5µ m
repeat distance copper grid.

3.3 Measuring objects and system condition
90%

Table 1 shows the analyzed samples and the systemcondition. Mainly we analyze biological andenvironmental samples.

10%

4 FUTURE RESEARCH PLAN: MICROBEAM IRRADIATION OF CELLS

0.63 μm

0.47 μm

The use of high-energy ion Microbeams is a new
avenue of radiation research especially in radiation
biology and radiation protection. For this purpose, wehave started the construction of a new microbeam
irradiation facility (named as SPICE) which will beconnected to our Tandem accelerator (3.4 MeV 2H1+ and
5.1 MeV 4He2+). For our primary goal, “irradiation of cellorganelles by a single high energy ion within a position
resolution of 2µ m in a reasonable irradiation time",
special features must be considered. Using a 90 degree
magnet, a vertical beam line will be branched from thepresent the micro-beam PIXE beam line. The focusing
system will be installed in a cradle which is hung on arigid frame structure. At the end of the vertical beam line
will be mounted a focusing triplet quadrupole -magnetsystem (Oxford Microbeams, Ltd.), an automated x-y
stage for cell dishes and a video microscope will bemounted.

6 REFERENCES
1μm

Figure 4
Highest resolution of this apparatus is estimated as 100
× 200 nm[1] M. Yukawa, H. Imaseki: International Journal ofPIXE, 10[1-2], 2000, P71-75.
[2] H. Imaseki, M. Yukawa: International Journal ofPIXE, 10[3-4], 2000, P77-90.

Table 1Sample

Beam LineSpecies

EnergyIntensity

Beam Size

Comment

Chestnuts of mouse
Ear stone of fish

Microbeam
Microbeam

ProtonProton2.6MeV
2.6MeV

20-100pA
30pA

Raster scan: 50um-2mm
Raster scan: 10um-2mm

Paste include Hg and AS
Fossilized wood
Blood of mouse
Hair
Yellow sandMicrobeam
Microbeam
Microbeam
Microbeam
Microbeam

ProtonProtonProtonProtonProton2.6MeV
2.6MeV
2.6MeV
2.6MeV
2.6MeV

20-100pA
20-100pA
20-100pA
20-100pA
20-100pA

Raster scan: 50um-2mm
Raster scan: 50um-2mm
Raster scan: 50um-2mm
Raster scan: 50um-2mm
Raster scan: 50um-2mm

Need to use absorber

Cells of organ
CR-39 film (track detector)

Microbeam
Microbeam

ProtonProton2.6MeV
2.6MeV

20-100pA< 1pA

Raster scan: 50um-2mm
Resolution: 0.5-1um
Raster scan: 50um-2mm

Less than 100cps

Ear stone of fish

Conventional

Proton2.6MeV

13nA

0.5mm x 0.5mm

Paste include Hg and AS
Plankton
Blood of mouse
Seawater filter
Paste of organ

Conventional
Conventional
Conventional
Conventional
Conventional

ProtonProtonProtonProtonProton2.6MeV
2.6MeV
2.6MeV
2.6MeV
2.6MeV

10nA
12nA
13nA
11-14nA
13nA

0.5mm x 0.5mm
0.5mm x 0.5mm
0.5mm x 0.5mm
0.5mm x 0.5mm
0.5mm x 0.5mm

Need to use absorber
Ratio of Ca is highDifficult to select afixativeNeed to use absorber
Ratio of Ca is high

Need to use absorber