Electronic personal neutron
dosemeters for high energies:
calculation of pulse height spectra
using the PHITS code
M. Luszik-Bhadra1, M. Nakhostin2, K. Niita3
1. Physikalisch-Technische Bundesanstalt, D-38116 Braunschweig, Germany
2. Cyclotron and Radioisotope Center, Tohoku University, Sendai, Japan
3. Research Organization for Information Science and Technology, Tokai, Japan
WRMISS 11, Oxford, 6 – 8. Sept. 2006
Overview
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The dosemeters DOS-2002, EPD-N2, ALOKA
Mono-energetic neutron response up to 60 MeV
Estimation of DOS-2002 response using PHITS
Measured and calculated pulse height spectra
Thin (6 µm Si) versus thick detector (40 µm Si)
Response for 100 MeV protons
Further needs
Dr. Marlies Luszik-Bhadra,
PTB-6.52
2
Electronic neutron dosemeters
Thermo Electron EPD-N2
3 silicon detectors (n,γ)
ALoka PDM-313
1 silicon detector (n)
PTB DOS-2002
1 silicon detector (n, γ)
Dr. Marlies Luszik-Bhadra,
PTB-6.52
3
Response obtained by unfolding
Dr. Marlies Luszik-Bhadra,
PTB-6.52
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PHITS code
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3D MonteCarlo code
Transport and collision of all particles
Neutron, Proton, Meson, Baryon, Electron, Photon,
Nucleus
With wide energy range (up to 200 GeV)
Developed in Japan (Niita et al.)
Used for calculations in space and at high-energy
accelerators
For neutrons similar to MCNPX
Dr. Marlies Luszik-Bhadra,
PTB-6.52
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DOS-2002 on ISO water phantom
ISO water phantom
no. = 1, x = 0.0000E+00
2
6
Detector holder and
boronated plastics
10
y [cm]
void
1
5
0
8
3
7
Si-detector (1 cm2 with
combined 6LiF/PE converter)
2
9
−2
−2
Dr. Marlies Luszik-Bhadra,
PTB-6.52
0
z [cm]
2
6
Special Parameters
• Planar circular source, diam. 10 to 100 cm2, normal
incidence
• Low values of emin to allow transport of all particles
• Cross section libraries from MCNPX
• In most cases 1.0e6/ cm2 incident particles used
Dr. Marlies Luszik-Bhadra,
PTB-6.52
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Comparison of measured and
calculated pulse height spectra
1E-3
Fluence Response /cm
-2
1.2 MeV, PHITS
1.2 MeV, EPI 40 µm, 10V
1E-4
1E-5
1E-6
0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0
Pulse height / MeV
Dr. Marlies Luszik-Bhadra,
PTB-6.52
8
Fluence Response /cm
-2
Comparison of measured and
calculated pulse height spectra
1E-3
2.5 MeV, PHITS
2.5 MeV, EPI 40 µm, 10 V
1E-4
1E-5
1E-6
0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0
Pulse height / MeV
Dr. Marlies Luszik-Bhadra,
PTB-6.52
9
Comparison of measured and
calculated pulse height spectra
1E-3
Fluence Response /cm
-2
5.0 MeV, PHITS
5.0 MeV, EPI 40 µm, 10V
1E-4
1E-5
1E-6
0,0
0,5
1,0
1,5
2,0
2,5
3,0
Pulse height / MeV
Dr. Marlies Luszik-Bhadra,
PTB-6.52
10
Comparison of measured and
calculated fluence response
En / MeV
DOS-2002, 40 µm Si,
1.13 -1.83 MeV
PHITS calculation
DOS-2002, 40 µm Si,
1.13 -1.83 MeV
Measurement
Rcalc/Rmeas.
0,144
1,2
2,5
5
2,40E-05
1,60E-05
2,61E-04
1,10E-04
3,72E-05
3,00E-05
1,97E-04
1,59E-04
0,65
0,53
1,32
0,69
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Agreement of absolute responses (no normalization used)
satisfactory
Dr. Marlies Luszik-Bhadra,
PTB-6.52
11
Response of Saphydose-n and DOS2005 (6 µm Si, 200 keV- 1.2 MeV)
Hp(10) Response
100
Saphydose-n, # 76670, 0°
Saphydose-n, # 76670, 60°
DOS-2005, #4, 0°
DOS-2005, #4, 60°
10
1
0,1
0,1
1
10
Neutron energy / MeV
Dr. Marlies Luszik-Bhadra,
PTB-6.52
12
Calculated pulse height spectra for
100 MeV neutrons and protons
2
10
1
10
0
PHITS, 100 MeV n, 40 µm Si
PHITS, 100 MeV p, 40 µm Si
Fluence response /cm
2
10
10
-1
10
-2
10
-3
10
-4
10
-5
10
-6
10
-2
-1
10
10
0
Pulse height / MeV
Similar response for neutrons and protons in the interval 1 to 2 MeV
Dr. Marlies Luszik-Bhadra,
PTB-6.52
13
Calculated pulse height spectra for
100 MeV neutrons and protons
2
10
1
10
0
Fluence response /cm
2
10
10
-1
10
-2
10
-3
10
-4
10
-5
10
-6
PHITS, 100 MeV n, 6 µm Si
PhiTS, 100 MeV p, 6 µm Si
10
-2
-1
10
Pulse height / MeV
10
0
Similar response for neutrons and protons in the interval 0.2 to 1 MeV
Dr. Marlies Luszik-Bhadra,
PTB-6.52
14
Dose equivalent response for neutrons
PHITS calculation
4
Dose equivalent response / mSv
-1
10
DOS-2002, 40 µm Si, 1.13 -1.83 MeV
DOS-2002, 6 µm Si, 0.22 -1.29 MeV
10
3
10
2
10
1
10
-1
10
0
10
1
10
2
Neutron energy / MeV
• improved for thin detector at 1.2 MeV
• no drastic increase of response at 100 MeV
Dr. Marlies Luszik-Bhadra,
PTB-6.52
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Summary
• Measured and calculated (PHITS) pulse height
spectra agree well for neutrons of 1.2 MeV, 2.5 MeV
and 5.0 MeV
• The calculations indicate that the neutron dose
equivalent response at 100 MeV is similar to that of
2.5 MeV
• The detector with 6 µm effective layer shows an
improved response at 1.2 MeV and otherwise no
big changes
• The proton response is comparable to the neutron
response for 100 MeV for normally incident
particles and the thresholds used for the DOS-2002
and the DOS-2005
Dr. Marlies Luszik-Bhadra,
PTB-6.52
16
Further needs
Further measurements with high-energy neutrons up to
200 MeV (iThemba)
Some measurements with protons with energies up to a
few hundred MeV
Agreement on conversion factors for high energy
neutrons and protons
Response measurements and calculations at angles (also
backward directions)
Folding energy and direction dependent responses with
spectra in space
Based upon these results decision whether the proton
response disturbs the neutron dose indication
Dr. Marlies Luszik-Bhadra,
PTB-6.52
17
Estimated dosemeter responses
Radiation field
CERF (Concrete)
CERF (Iron)
GSI (OC-11)
GSI (EM-21)
Hp,estim.(10)/ Hp,c(10)
DOS-2002
ALOKA
EPD-N2
6.6
1.8
6.3
2.0
4.0
2.1
4.1
6.0
6.2
1.7
5.8
3.2
Assumptions
Dosemeter response flat at energies above 60 MeV
Neutrons incident normally to the dosemeter surface
Dr. Marlies Luszik-Bhadra,
PTB-6.52
18