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Dose Measurement for 110 keV Electron Beam
H. Seito a) , S. Matsui b) , T. Hakoda a) , M. Ishikawa b) , H. Hanaya a) , Y. Haruyama a) ,
H. Kaneko a) , J. Kimura b) and T. Kojima a)
a) Department of Advanced Radiation Technology, TARRI, JAEA,
b) Hamamatsu Photonics K. K.
An electron beam (EB) generator of a few tens of keV is
frequently used to hardening of printing ink and addition of
the hydrophily for various materials. Thin radiochromic
film dosimeters such as FWT-60, GAF and B3 are mainly
1)
used in low energy EB industrial processing . These
dosimeters are calibrated for high energy EB or cobalt-60
gamma-rays 2) . Consistency in dose evaluation for a few
MeV electron and ten-hundred keV electron is still under
discussion 3) . This work aims to reveal consistency in dose
response of film dosimeter between low and high energy EB.
The dosimetry study for 110 keV electron beams was
performed at the EB generative machine called
EB-ENGINE (Hamamatsu Photonics K. K). The machine
is composed of electron source (filament), vacuum tube and
irradiation chamber. Accelerated electrons traverse air
through beryllium accelerator window. The distance from
the window to the surface of film dosimeter was 40 mm as
shown in Fig. 1. The dosimeters (FWT-60) were calibrated
for 2-MeV electron and dose distribution in 110 keV
electron beam irradiation field was evaluated by both the
film dosimetry and Monte Carlo calculation code:
PENELOPE. The absorbed dose distributions given by
measurement and the calculation are compared in Fig. 2.
The difference in dose between the measurement and
calculation was found to be within ± 6 kGy. Such a
difference is small, considering geometrical deviation in
setting of film dosimeter. This fact suggests that
calibration curve of FWT-60 film dosimeter for 2 MeV EB
would be valid also for 110 keV EB. These results show
that dose responses of FWT-60 film dosimeters are
independent on electron energy.
As the next step, calorimetry was tested to check the film
dosimetry results. A calorimeter with an aluminum
absorber was designed. The calorimeter consists of mainly
three parts; an absorber disk, a temperature sensitive sensor
and an aluminum stage with three polycarbonate props to
sustain the absorber disk. A cross section of the
calorimeter is shown in Fig. 3. Energy fluence values
measured by the calorimeter were slightly smaller than those
estimated by the PENELOPE code calculation. The factor
of this difference is under consideration. Application of
calorimetry to 110 keV EB dosimetry needs to be discussed
further.
References
1) ISO/ASTM 51275, 2004. Standard Practice for Use of a
Radiochromic Film Dosimetry System. ASTM
International, 100 Barr Harbor Drive, West
Conshohocken, PA 19428-2959, USA.
JAEA-Review 2010-065
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2) ISO/ASTM 51261, 2002. Standard Guide for Selection
and Calibration of Dosimetry System for Radiation
Processing. ASTM International, 100 Barr Harbor Drive,
West Conshohocken, PA 19428-2959, USA.
3) J. Helt-Hansen et al., Radiat. Phys. Chem. 74 (2005)
341.
Filament
Accelerator window
Film dosimeter
H.V. Generator Controller
Fig. 1 Geometry of the irradiation set-up.
250
200
150
Vacuum tube
40 mm
Fig. 2 Comparison of the dose distribution given by
FWT-60 film dosimeter with that by PENELOPE
calculation.
Thermistor sensor
1 mm
25 mm
20 mm
Fig. 3 Schematic drawing of the calorimeter.
○ Film dosimeter
◇ PENELOPE
100
50
0
-5 -4 -3 -2 -1 0 1 2 3 4 5
Absorber disk
Polycarbonate prop
Aluminum stage