IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
VI.11. Indigenous Development of X-ray Imaging Plate
Based on Photostimulated Luminescence Phosphor
For over 100 years, X-ray
radiography has relied on film
as the image detection and
display medium. Recently,
photographic films are being
gradually replaced by imaging
plates (IP) based on photo
stimulated luminescence (PSL)
storage phosphors, mainly,
BaFBr:Eu 2+ . These are superior
to conventional X-ray film due
to high detective quantum
efficiency, wide dynamic range
and reusability. IPs made of
BaFBr:Eu 2+ are used worldwide
in hospitals and in several other
applications such as X-ray
diffraction, auto radiography,
transmission electron
microscopy etc. Computed
Radiography (CR) using PSL
technique allows the
radiological community to go
digital. By image processing of
the actually acquired data,
superior image quality can be
obtained. Hence multiple
exposures are not needed.
Comparatively, the non-linear
film response implies that X-ray
exposures must be chosen quite
carefully to avoid over or under
exposures. Further benefit of
CR is that the digital data can
be easily transmitted to other
places to seek specialist's
opinion.
With the aim of indigenously
developing an X-ray imaging
plate, high sensitive BaFBr:Eu 2+
storage phosphor has been
successfully synthesized recently
using high temperature solid
state diffusion route in a
reducing atmosphere. The PSL
spectra of the BaFBr:Eu 2+
synthesised are comparable to
that of commercial IP (Fuji)
after irradiation. A broad
stimulation spectrum in 480 -
650 nm region corresponding
to the depopulation of the
electrons trapped at F(Br-)
centers is observed. Fluorineexcess
non-stoichiometric,
BaF 1.015 Br 0.985 :Eu 2+ showed
maximum PSL with 590 nm
light stimulation. The
stimulated luminescence
process in this phosphor can be
explained on the basis of the
presence of interstitial fluorine
ions (F I-
) and bromine ion
vacancies prior to X-irradiation
(during crystal growth) in nonstoichiometric
materials as
shown in Fig. 1a. On X-
irradiation, electrons dislodged
Ba 2+ F -
Br -
Ba 2+ F - Br -
Ba 2+ F - Br -
Ba 2+ F -
F I
-
Eu 2+ F -
Br -
Ba 2+ Br -
F 2
-
Eu 2+ F - e -
Ba 2+ F 2
-
(300 nm)
Br -
Eu 2+ F - e -
(a) Before irradiation (b) On X-irradiation (c) On photo stimulatiion
(~400nm)
Fig.1 Proposed model of PSL process in BaF 1.015 Br 0.985 : Eu 2+
164 BASIC RESEARCH