IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
Fig.2 Skull phantom image using Kodak IP (14) and IGCAR IP (13)
-
from F I get trapped at bromine
ion vacancies thereby forming
F(Br-) centers. The interstitial
fluorine atoms thus formed
combine with the lattice fluorine
-
ions to form molecular ions, F 2
(H type center), whose presence
on x-irradiation was detected by
ESR (Fig. 1b). In the proposed
model, F I-
ions act as hole traps
and bromine vacancies act as
electron centers. On photo
stimulation, the electrons
released from F(Br-) centers
recombine with holes trapped
at F 2 - centers, which results in
intrinsic (self-trapped exciton)
emission (~300 nm) which is
characteristic of the BaFBr host
(Fig. 1c). This radiatively excites
the Eu 2+ ions thereby causing
PSL emission around 400 nm.
The merits of the proposed
mechanism are: it explains why
only fluorine excess compounds
cause intense PSL, it provides a
charge compensation
mechanism arising out of the
presence of bromine vacancies,
it supports the experimentally
-
observed F 2 centers on X-
irradiation in fluorine excess
BaFBr, and above all it brings
the material back to its initial
state on photo stimulation.
An imaging plate has been
made with the help of M/s
Kiran X-ray screens Ltd,
Mumbai using the indigenously
synthesized storage phosphor. A
comparative skull phantom
image was recorded using a
commercial scanner and a
commercial Kodak IP as well as
the IP made from the storage
phosphor synthesized at IGCAR
at the same X-ray exposure
parameters (Fig. 2). All the
salient features of the image
are seen in the IP made from
our phosphor. The sensitivity is
comparatively good but the
contrast needs improvement.
The grain morphology is
uneven and higher than the
desired value, which causes
uneven light scattering that
reduces the image contrast.
Modified synthesis techniques
and grinding procedure of the
phosphor developed recently
have improved the grain
morphology (grain size ~ 20
µm). Recent efforts in preparing
the phosphor in large scale with
a simple and cost effective
technique using the local make
chemicals have been
successful. Manufacturing more
number of test IPs and
comparative studies with
commercial IPs are in progress.
BASIC RESEARCH 165