95-021.

JAERI-Conf

3a2-1
X-RAY LEAKAGE
AROUND 1. 7 MV TANDETRON ACCELERATOR
Nobuyuki SUGIURA, Toshio KAWANISHI, and Toshiso KOSAKO
Research Center for Nuclear Science and Technology, the University of Tokyo,
Yayoi 2-11-16, Bunkyo-ku, Tokyo 113, JapanAbstract
For the purpose of offering fundamental
information on radiation protection of an accelerator,
the dose rates around 1. 7 MV tandetron accelerator
were measured in various operating condition. The
dose rates except around the ion source weregenerally kept low enough. The peak energy ofX -ray detected around the ion source was about 25
keV, which could be easily shielded by 1 mm thickuon.
1. Introduction
The installation of small accelerator isexpected for the research of ion beam science. The
1.7 MV tandetron accelerator was newly installed at
Research Center for Nuclear Science andTechnology ofthe University of Tokyo in 1994. For
the purpose of offering fundamental information onradiation protection of an accelerator, the dose rates
around the accelerator (ion source, magnetic inflector,
high voltage power supply, acceleration tube,
switching magnet, and end station) were measured invarious operating conditions (ion source, terminal
voltage, and beam current).
2. Outline ofTandetron Accelerator System
The 1. 7 MV tandetron accelerator system ismainly consisted of ion source, magnetic inflector,
high voltage power supply, acceleration tube,switching magnet, and end stations. For applications,
Particle induced X-ray emission (PIXE), Rutherford
backscattering spectroscopy (RBS), and ion
implantation system are prepared. The system wasbackscattering(Rutherford
RAPID
named
spectrometry Analyzer with Particle induced X-rayemission and-Ion implantatiOn Devices). Thesystem was supplied by HVEE (High Voltage
Engineering Europe B.V.). The system layout isshown in Fig. 1.
Two types of ion(1) Ion source and injector:
source are equipped for the system: one is aduoplasmatron (model 358), the other is a Cs spatter
They are mounted
ion source (model 860A).
simultaneously on the dual leg injector system. It
provides the flexibility to produce a large variety ofions and the quick changeover from heavy ions to HlOllS.

(2) Accelerator system: Model 4117-HC is used foran accelerator system. High voltage power supplysystem is a Cockroft-Walton type one. The terminalThe mainvoltage range is 0.1 - 1. 7 MV.
specifications of ion source and beam current are
shown in Table 1. The control of whole accelerator
system is done by the computer control. It allows
for unattended start-up and operation of the entire
accelerator system.
and IonRBS
PIXE,(3) End station:
Implantation system are prepared for the application.
- PIXE: 3 axis and 2 translations sample
manipulator, Si(Li) detector with 8192 chPHA

high voltage power supply ·PIXE chamber

E0/:'@r.---:c--_,.J~--~ =~~~

ion source!I~~~~~~~~~t!lD•II ALL

acceleration tube magnetic inflector

Fig.1 The system layout of 1. 7 MV tandetron accelerator system and dose rate measuring points.
A: ion source, B: magnetic inflector, C: low energy acceleration tube, D: center of acceleration tube, E: highenergy acceleration tube, F: end of acceleration tube, G: switching magnet, H: ion implantation target-416-JAERI-Conf 95-021

Table 1 Ion species and beam current
ion species
H+He2+s?+Cu2+
N2+Au2+

beam current
25 J.L A
2.4 J.L A
140 J.L A20 J.L A
20 J.L A
80 J.L A(3.4 MeV)(5.1 MeV)(5.1 MeV)(5.1 MeV)(5.1 MeV)(5.1 MeV)- RBS: 3 axis and 1 translation sample
manipulator, silicon surface barrier detector- Ion implantation: implantation angle 7• , 10
samples within 32 mm cf>, heatable andcoolable target holder(4) Control cabinet
The control cabinet is situated out of theaccelerator room. The door interlock system was
not prepared for the convenience of access. The datatransmission from the accelerator is done by the
optical fiber cable for the reduction ofelectro-magnetic noise.
3. Method
3.1 Radiation detectors
The ionizing chamber type survey meter(AE-133L, Applied Engineering Inc.) was used forthe dose rate measurement.
The spectrum
measurement around the ion source was done byusing Nai(Tl) scintillation detector with Be window(Ohyo Koken Kogyo Co.).
3.2 Measuring points
Measuring points are 8 as shown in Fig. 1
and, the measuring height was 1215 mm from thefloor, which is the same height of beam line.

3.3 Measuring operation condition
The ion species of H+, He2+, N 2+, S?+, Cu 2+,
2and Au + were measured. Terminal voltage wasaround 1.7 MV except W (1.5 MV). As for Si2+,
terminal voltages and beam currents were changed
as a standard case.
4. Results and Discussions
4.1 Dose rate
The results of dose rate measurements wereshown in Table 2.
High dose rates were detected around the ion
source in case of accelerating Cu2 + and Au2+ beam.
In case of Si2+, the high dose appears irregularly.
This X-ray generation has no reappearance. Thismay be caused by the difference of geometry
between a sputter electrode and an ion source holder.
Further measurements were done for this X-raygeneration.
The results was described in theparagraph 4.2.
The accelerating energy of H and He perparticle is rather high because of those small mass
numbers. Therefore, the dose rates around ion
implantation target become rather high in case ofaccelerating H+ and He2+.
In spite of the almost same operating
condition, the dose rates in case of accelerating N+
were slightly high as a whole. This was caused by
the way of accelerating N+. Nitrogen ion source wasprepared as No-. No- was accelerated from ion
source to stripper canal at the center of acceleration
tube. Then, oxygen was stripped with a charge
exchange.
Compared with the dose rate around the lowenergy. tube and around the high energy tube, theformer were generally high.
There were more
complex structures in the high energy tube than inTable 2 Dose rates around 1. 7 MV tandetron accelerator system ( J.L Sv/hr)
ion source
terminal voltage (MV)

1.53

1.70

1.74

1.73

1.71

1.72

beam current" 1 ( J.L A)

112.4

26

180

41130

ion source
ion injector
low energy acceleration tube
center of acceleration tube
high energy acceleration tube
end of acceleration tube
inflection magnet
ion implantation target

0.06
0.11
0.10
0.09
0.05
0.05
0.10
4.0

0.14
0.15
0.26
0.32
0.15
0.08
0.31
2.4

2.7
2.3
2.0
1.2
1.5
0.1
0.05
0.05

0.33
0.17
0.46
0.71
0.22
0.15
0.07
0.05

15 (0.45)"2
0.75
0.85
0.62
0.40
0.12
0.12
0.15

35 (0.8}"2
1.6
1.7
1.5
0.7
0.1
0.05
0.05

*1 at faraday cup of ion implantation, *2 after shielding of 1 mm thick iron, background dose rate: 0.05 ( J.L Sv/hr)-417-

JAERI-Confthe low one. Therefore, the shielding effect from thisstructure could be expected.

4.2 X-ray around ion source
The spectrum of X-ray around the ion
source in case of accelerating Au 2+ beam was shownin Fig. 2. The photopeak energy was 25.8 keV. The
photopeak energies were almost same in caseofaccelerating Cu2+and se+. This low energy X-ray
was easily shielded by 1 mm thick iron. The doserates were decreased from 15 fJ. Sv/hr under noshielding condition to 0.45 fJ. Sv/hr under the 1 mm
iron shield (Cu 2+), from 35 fJ. Sv/hr to 0.8 fJ. Sv/hr(Au 2+).

95-021

below 1.4 MV. The dose rates were relatively low
and the reading error of dose meter might be large.
Above 1.4 MV, the X·ray production at the centertube and the high voltage tube increased drastically.
X JQ-13
<(>
.._5>

U)

'-'~::Ju-- *--

low energy tube,,.. .........

center of tube
high energy tube
end of tube

II·-- - -.. ····---~........

....

10.,
C>~"§.,"'

050
0.8

1.0

1.2

1.4

1.6

1.8

"0000terminal voltage (MV):::::::.

....,"'

Fig. 3 Relationship of terminal voltage
and dose rate per voltage· current

c::J00--+-

15ion source: Si2 •c:0"' 10 3 •'/20'-..

225. 8keV----.--

25

1Q2

5. Conclusion
The measured dose rates around 1. 7 MV
tandetron accelerator were obtained, which will be
useful as a fundamental data for radiation protectionof this type accelerator.

energy (keV)

Fig. 2 Pulse height spectrum of X-ray
around the ion source

Reference
4.3 Relationship of voltage, current and dose rate
In the acceleration tube, the remaining air isionized by ion beam. In this process, the produced
As a result, theelectron is also accelerated.
bremsstrahlung X-ray is generated. Figure 3 shows
the relationship of terminal voltage and dose rate pervoltage· current around the acceleration tube in caseof accelerating sf+ beam.
No significant tendency was recognized

1. F. Nishiyama et al., Bremsstrahlung X rays
produced by operating 2.5 MV Van de Graff
Accelerator, Research report of faculty ofengineering, Hiroshima univ., 33, 97-102 (1984).
2. High Voltage Engineering Europe B.A., TechnicalPamphlet of Tandetron Accelerator Systems, Model
4110,4117, 4125,4130, (1993).

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