Technical note
A simulation study of the DQE of a linear plastic scintillating fiber array for
hard gamma-rays
Shi-Biao Tang
a,b
, Qing-Li Ma
c,
, Ze-Jie Yin
b
a
College of Electronic and Information Engineering, Ningbo University of Technology, Ningbo, Zhejiang 315016, China
b
Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
c
Electronics Department, Electronic Engineering Institute, Hefei, Anhui 230038, China
article info
Article history:
Received 21 November 2007
Received in revised form
7 July 2008
Accepted 4 September 2008
PACS:
29.40.m
Keywords:
Gamma-ray
Modulation transfer function
Detector quantum efficiency
abstract
The detector quantum efficiency (DQE) of a linear plastic scintillating fiber (PSF) array coup led with a
charge-coupled device (CCD) for hard
g
-ray imaging is studied using a Monte Carlo simulation. The
focus is on the energy from a few MeV to about 12 MeV. The excellent characteristic of PSF offers a
method to balance the detection efficiency and spatial resolution. Our simulation results indicate that
the modulation transfer function (MTF) for different energies become almost the same below the
certain frequency and the DQE should be better at lower frequency for imaging lower incident energy.
These characteristics suggest that the PSF may be useful for detecting high energy
g
-rays.
& 2008 Elsevier Ltd. All rights reserved.
1. Introduction
As an important diagnostic and characterization tool,
g
-ray
imaging has been increasingly used in many fields such as
medicine, biology, security, industrial testing and evaluations
(Kroning et.al., 2002). Currently, the most commonly used digital
g
-ray imaging detectors rely on scintillation technologies which
convert gamma photons into visible light through scintillation
materials and then detect the visible light using an imaging device
such as a CCD imager (Gruner et al., 2002). To increase the
efficiency or the sensitivity, a thicker scintillation material usually
is desired. However, an increased thickness of the scintillator
would result in a larger isotropic spreading of light generated in
the scintillation materials, and, thus, reduce the spatial resolution
of the imager. An alternative approach in constructing a
g
-ray
digital imager is to use scintillating optical fibers to build an array
plate that is directly coupled with a CCD (Ikhlef et al., 2000; Ikhlef
and Skowronek, 1998; Zanella and Zannoni, 1990). Early results
indicate that as the energy of the incident beam increases,
the resolution and sensitivity deteriorates quite rapidly, due to
insufficient absorption of
g
-ray and cross talk between adjacent
fibers (Tang et al., 2007, 2008a, b). However, the use of a lead
coating may be useful to achieve better performance but this has
not been done here.
The capability of the plastic scintillating fiber as a
g
-ray
imaging detector has been proved and some important para-
meters of the detector have been extracted experimentally
(Nasseri et al., 2004a). In this work, we used Monte Carlo
simulation to evaluate the detector quantum efficiency (DQE) of
such a linear scintillation fiber detector for imaging hard
g
-rays
with energy higher than a few hundred keV.
2. Theory and method
The modulation transfer function (MTF) (Smith, 2000; Levi,
1980) is a measurement of the spatial frequency response. One
method in achieving this measurement is through the edge-
spread function (ESF) method. The ESF can be obtained using
knife-edge imaging which is the response of the imaging system
to an edge. The ESF can be then differentiated with respect to
position from the edge to obtain the line-spread function (LSF)
(Tzannes and Mooney, 1995). By definition we can get the
MTF through the calculation of the Fourier transform of LSF
(Levi, 1980).
MTFðf Þ¼
1
ffiffiffiffiffiffi
2
p
p
Z
1
1
LSFðxÞ e
2
p
ifx
dx
(1)
ARTICLE IN PRESS
Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/apradiso
Applied Radiation and Isotopes
0969-8043/$ - see front matter & 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.apradiso.2008.09.004
Corresponding author. Tel.: +86 5513601169.
E-mail address: qinglima@gmail.com (Q.L. Ma).
Applied Radiation and Isotopes 67 (2009) 277–280