I s s u e n o . 2 7 3 O c t o b e r 2 0 0 68
DEVELOPMENT OF NEUTRON AND X-RAY DETECTORS
AND NEUTRON RADIOGRAPHY
AT BARC
A.M. Shaikh
Solid State Physics Division
Bhabha Atomic Research Centre
The author is the recipient of the DAE Technical ExcellenceAward for the year 2004.
A b s t r a c t
Design and development of neutron and X-ray detectors and R&D work in Neutron Radiography (NR) for non-
destructive evaluation are the important parts of the neutron beam and allied research programme of the
Solid State Physics Division (SSPD) of BARC. The detectors fabricated in the division not only meet the in-house
requirement of neutron spectrometers but also the need of other divisions in BARC, DAE units and some
universities and research institutes in India and abroad for a variety of applications. The NR facility set up by
SSPD at Apsara reactor has been used for a variety of applications in nuclear, aerospace, defense and
metallurgical industries. The work done in development of neutron and X-ray detectors and Neutron
Radiography since 1992 is reported in this article.
Neutron and X-ray Detectors
Radiation detectors play an important role in
medicine, biology, materials science and high-energy
physics for monitoring and imaging applications. Gas
filled detector, semiconductor detector and scintillation
detector are widely used in flux measurement, area
monitoring and scattering experiment applications with
each of them having their own advantages and
limitations. The detector technology is rapidly evolving
by making use of recent developments in material
processing, new detector designs, data acquisition and
analysis systems [1]. In case of neutron scattering
experiments the neutron beam intensities are low due to
collimation, monochromatisation and scattering.
Efficient neutron detection or imaging is therefore
essential to use the neutron beam time judicially. Demand
for neutron detectors with higher count rates, larger
scanning angles and finer position resolutions, is ever
increasing.
Among the various types of detectors, gas-filled detectors
are widely used especially by the neutron scattering
communities around the world. Gas-filled position
sensitive detectors [2] are conveniently used in various
spectrometers to scan large angles as these detectors
can be fabricated with large size and show high detection
efficiency. They have the advantages of
9 I s s u e n o . 2 7 3 O c t o b e r 2 0 0 6
†Detector type nomenclature: the number before alphabet indicates length of detectorin inches and A, B, C, D and E indicate cathode diameter of 0.4”, 0.5”, 1”, 1.5” and 2”
respectively. The anode is made of tungsten wire of 25 mm diameter.Cathode material: brass.
low gamma sensitivity, high neutron efficiency, very high
noiseless internal amplification, no radiation damage,
flexibility of size and fill gas pressure and need simple
counting and pulse processing electronics. Large area
position sensitive detectors with multiwire geometry
developed in 1970s have become widely popular for
many applications [3]. At Solid State Physics Division,
we are involved in indigenous development of gas filled
signal detectors and position sensitive detectors (PSDs)
for X-rays and neutrons for various applications at BARC
and other laboratories in India. These detectors are widely
used as low sensitivity monitor counters to very high
sensitivity signal detectors. Continuous efforts are put in
towards modification of detection techniques to carry
out the experiments efficiently. Various types of detectors
developed are 3He and BF3 filled detectors for neutrons,
linear 1-D single anode PSD, 1-D and 2-D multiwire PSDs,
curvilinear PSD and a microstrip based PSD for both
neutrons and X-rays[4-11]. These detectors show excellent
operational characteristics and stability over the long
periods. Various types of neutron proportional counters
fabricated in our laboratory are listed in Table 1 along
with their specifications and applications. Fig.1 shows
some of these detectors.
Table 2 gives photographs and salient features and
applications of various types of position sensitive detectors
designed, developed and successfully tested in our
laboratory. Many of the 1-D position sensitive neutron
detectors are mounted on the neutron spectrometers at
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Dhruva and working over the years satisfactorily.
The gas filled neutron proportional counters are
extensively used in BARC over a wide range of application
such as flux and area monitoring, spent fuel activity
measurement, study of nuclear reactions, measurement
residual activity of nuclear waste, measurement
of cosmic neutron radiations and
Fig.1: Some of the neutron proportional counters mentioned in Table 1
Table 2: Various types of Position Sensitive Detectors for Neutron and X-rays developed
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material studies using neutron scattering techniques.
The detectors are also supplied to atomic energy
establishments of other countries like Bangladesh,
Vietnam and Austria ( IAEA). Table 3 gives the statistics
about different types of detectors designed, fabricated
and supplied to various users in BARC and outside
institutions. Users other than BARC can procure these
detectors through the Technolgy Transfer & Collaboration
Division of BARC.
Neutron Radiography Facility and
Applications
The property of thermal neutrons, which makes them
valuable for studying industrial components is their high
penetration through widely used industrial materials such
Table 2 contd...
Table 2 contd...
Table 2 contd...
13 I s s u e n o . 2 7 3 O c t o b e r 2 0 0 6
as steel, aluminium or zirconium. Neutrons are efficiently
attenuated by only a few specific elements such as
hydrogen, boron, cadmium, samarium and gadolinium.
For example, organic materials or water attenuate
neutrons because of their high hydrogen content, while
many structural materials such as aluminium or steel are
nearly transparent. Neutron Radiography (NR) is a non-
destructive imaging technique for material testing. It is
similar to X-ray and gamma radiography and has some
special advantages in Nuclear, Aerospace, Ordnance and
rubber and plastic industries. Information is obtained on
the structure and inner processes of the object under
investigation by means of transmission. At BARC, neutron
radiography has been actively pursued by the Solid State
Physics Division for various applications, using the 400kW
swimming pool type reactor, Apsara as the neutron
source. In this facility the thermal neutrons from the
reactor are collimated by a divergent, cadmium lined
aluminum collimator with a length/inner diameter (L/D)
ratio of 90. A cadmium shutter facilitates the opening
and closing of the beam. The specimen can be mounted
about 60 cm from the collimator followed by a cassette
containing neutron converter and X-ray film. The whole
setup is properly shielded to avoid any radiation exposure
to the operator. Table 4 gives the important parameters
of the facility, which is schematically shown in Fig. 2.
Table 3 : Statistics of Neutron & X-ray Detectors Fabricated and Supplied
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The NR facility of Apsara has been used for a variety of
applications in nuclear, aerospace, defense and
metallurgical industries[12]. The facility has been
extensively used for recording neutron radiographs of
. experimental fuel elements,
. water contamination in marker shell loaded with
phosphorous,
. electric detonators,
Fig. 2 : Schematic of NR Facility at Apsara Reactor
15 I s s u e n o . 2 7 3 O c t o b e r 2 0 0 6
. satellite cable cutters and pyro valves,
. boron-aluminium composites,
. hydride blisters in irradiated zircaloy pressure
tubes,
. variety of hydrogenous and non hydrogenous
materials and
. two phase flows in metallic pipes.
While some of the radiographs are shown in Fig.3, the
most recent work on NR is described in the following
paragraphs.
Assessment of hydriding on
Zircaloy-2/Zr-Nb2.5% pressure tube
material using Neutron
Radiography
One of the most important applications of NR in the
nuclear field is the post irradiation examination of pressure
tube (PT) to check formation of hydride blisters if any. To
ascertain the detection of hydride blisters in zircaloy
pressure tubes, detectability limit of hydride was first
established[13]. For this purpose hydride blisters were
Fig. 3 : Neutron Radiographs of various objects taken with Apsara NR facility.
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created in the laboratory on hydrogen charged Zircaloy
pressure tubes under thermal gradient are examined using
neutron radiography. It was established that a zirconium
hydride blister of nearly 0.25% of job thickness could be
detected using neutron radiography. The theoretical
detectability was also analyzed and found to be in good
agreement with the experimental results. This work served
as reference to examine an irradiated pressure tube from
a power reactor[14,15,16]. Neutron radiographs of an
irradiated pressure tube [Rajasthan Atomic Power Station
(RAPS#2, K-7 position, 8.25 EFPY) sample were recorded
using Apsara NR facility after modifying it for handling
the radioactive zircaloy-2 pressure tube coupons. The PT
sample of size 59mm x 29mm x 4.2mm was radiographed
using transfer technique with 100m thick Dysprosium
converter screen. A PT strip containing four laboratory
generated hydride blisters were also mounted on the
same converter screen cassette to act as a reference.
Fig.4(a) shows neutron radiographs of laboratory
generated hydride blisters in zircaloy-2 and Zr-2.5% Nb
pressure tube coupons where as Fig. 4(b) shows hydride
blister streaks in the zircaloy-2 coupon of the pressure
tube from power reactor RAPS#2. Enlarged view of one
of the blisters is also shown to the right of the figure.
Neutron radiography was also used to study size and
shape of the zirconium hydride blister in the zircaloy-2
pressure tube. Figs. 5(a) and (b) show neutron
radiographs of a pressure tube with three laboratory
generated hydride blisters and with neutron beam incident
parallel and normal to the plane of the blisters
respectively. Fig.5 (a) shows lenticular shape of the blister
with nearly 2/3 of the blister embedded in the wall of
the tube. In the present photograph maximum width of
the blister corresponds to 1.5 mm in 4 mm thick wall of
the pressure tube. However, the smallest blister grown
in the laboratory was found to be mainly on the outer
surface of the pressure tube with almost no penetration
in the wall of pressure tube.
Fig. 4(a) : Hydride blisters in zircaloy-2(L)and Zr-Nb(R) PT coupons (Lab. Generated)
Fig. 4(b) : Hydride blister streak in zircaloy-2 PTcoupon (L) from a power reactor. Enlarged view
of the blister shown in (R)
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Recently characterization of hydride blisters in burst tested
Zr-2.5% Nb pressure tube was done using Apsara NR
facility [17]. Hydride blisters were grown in a 16.5 cm
long Zr-2.5% Nb pressure tube piece in RED, BARC. The
tube was subjected to burst testing. The tube failed axially
in brittle manner during testing. The axial crack passed
through two hydride blisters which was also seen in the
neutron radiograph (Fig. 6).
HYSEN radiography technique with
NR facility at Apsara reactor
The technique, referred as Hydrogen Sensitive Epithermal
Neutron (HYSEN) radiography technique was first
developed for imaging small amounts of hydrogenous
materials encapsulated within high thermal neutron
absorbers, and found to be useful in study of hydride-
induced embrittlement of metals. The HYSEN imaging
system consists of a converter screen (In) and a neutron
beam filter ( In + Cd ) with the object placed between
the screen and filter. For neutrons, In has a resonance
peak at 1.49 eV. Combination of Cd foil with In foil
almost completely cuts off neutrons with energy lower
than 1.49 eV. Incident neutrons with energy higher than
1.49 eV, which pass through, are scattered elastically by
hydrogen atoms present in the object. The neutrons that
are slowed down to the vicinity of 1.49 eV by this
scattering are absorbed by the second In foil placed
behind the sample. Since the image is induced by the
scattered neutrons, the resolution and the sensitivity of
the technique are highly dependent on the object
dimensions and object to screen distance. Hydrogen
concentrations as low as 50 ppm ( 0.020 mg H /cm2 ) in
0.62 mm zircaloy coupons have been reported. The
detection limit of standard NR techniques is about 0.66
mg H/cm2. Thus the sensitivity of this method was found
to be about 30 times better than the normal NR
techniques.
Setting up of HYSEN radiography technique with existing
NR facility at Apsara reactor was undertaken as a part of
coordinated research project of IAEA[15,18]. The imaging
Fig. 5 : NR of zircaloy-2 PT coupons withneutrons incident parallel (a)
and perpendicular(b) tothe plane of blisters
Fig. 6 : Neutron radiograph of Zr-2.5%Nbpressure tube piece containing laboratory
generated hydride blisters(B).The axial crack isseen passing through two blisters
at position 4 on the tube.
(a) (b)
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system (Fig.7) consisted of a 250 mm indium converter
screen and a neutron beam filter comprised of 1 mm
cadmium and 1 mm indium foils, with the object being
placed between the filter and screen. The system was
exposed to neutron beam of the NR facility. Neutron
radiograph of 1-, 2-, 3-, 4- layers of cellophane adhesive
tape as object was recorded. The gradation of hydrogen
concentration in successive layers of adhesive tapes was
clearly seen in the radiograph (Fig.8). At present the
experimental set up is suitable for recording HYSEN
photographs of very thin hydrogenous samples. The
results of preliminary measurements are regarded as
encouraging, considering the very simple system that
was used (Fig. 9). The work on improvement over the
neutron images on a video monitor. This method is
especially attractive for the high-throughput inspection
of parts requiring instant feedback of information.
Unfortunately, it has limitations in its applications. It
cannot be used for inspection of the irradiated specimens
because of its sensitivity to gamma radiation. Typically,
an electronic imaging method utilizes a fluorescent
converter screen to produce a light signal that is suitably
Fig. 7 : Schematic of basic HYSENRadiography system
Fig. 8 : Neutron radiograph of 1-, 2-,3-, 4- layers of cellophane adhesive tape
as an object
Fig. 9 : Sensitivity of 8 mg/cm2 correspondingto 1mg/cm2 of hydrogen
existing set up with different neutron detector and filter
foils and use of electronic imaging camera for recording
the radiograph is in progress.
Digital Neutron Imaging
One of the important radiography methods is Electronic
Imaging or Real Time Radiography, which produces
19 I s s u e n o . 2 7 3 O c t o b e r 2 0 0 6
amplified and fed into video equipment for viewing.
The video output is digitized using frame grabber card
and processed using an onboard processor. Image
acquisition software performs operations like online
thresholding, contrast stretching, integration, averaging
etc. Trained human eye can distinguish 50 to 100 gray
levels between black and white.
Digital imaging accelerates this
probing dramatically, up to 4096
gray levels are differentiated. Use of
planar detectors like low light
cameras (e.g. CCD, C-CCD…) in
combination with fluorescent screens
is made to record the radiographs.
An electronic imaging system
(Figs. 10 and 11) based on
commercially available image
intensifier tube and low cost CCD
camera has been developed and
tested [19]. The neutron beam
transmitted through the sample is
absorbed in a NE-426 scintillator
screen. The light produced by the
screen is reflected by 90° and focused
onto the input fibre optic face of an
image intensifier tube. The output
image is focused onto a CCD camera
using, an F#1.4 lens. The CCD
camera used has 756(H) x 581(V)
pixel array and image intensifier used
has 30 lp/mm resolution with gain
of 105 Cd/m2/lx.The video output of
CCD is digitised using a frame grabber card and processed
using onboard processor. Various types of assemblies
and components were scanned using the imaging system.
Neutron images were instantly seen on the video monitor
indicating that flux at Apsara NR facility was adequate
for real time imaging work. Fig.12 shows images of some
of the objects scanned using the imaging system.
For Neutron Tomography the sample to be imaged is
placed on a platform, which is rotated using a stepper
motor. The stepper motor is controlled using a PC based
controller card. The sample rotation, image acquisition
and processing have been interfaced together within a
single control program. The images were recorded in
various angles and used in reconstruction program based
on Convolution Back Program method for obtaining CT
Fig. 10 : Schematic diagram of electronicimaging setup at Apsara
Fig. 11 : Photograph of an electronic imaging system usedat Apsara for real time neutron radiography
I s s u e n o . 2 7 3 O c t o b e r 2 0 0 620
scans at various slices. Several sets of samples were
fabricated to assess the quality of tomography system
[19,20]. One such sample is a cylindrical brass rod of 40
mm diameter with holes ranging from 1 mm to 5 mm,
some of them filled with wax, air and Indium wire, is
shown in Fig.13. Fig.14 shows the CT scan of this
sample. All the holes either wax or air filled, are visible in
the image.
Visualisation and analysis of water/air,
water/vapour two phase flow inside
metallic pipes under high temperature
and pressure condition is of
considerable importance in thermal
hydraulic design of nuclear reactors.
It is important to know under what
condition bubbly to slug or slug to
annular flow transitions occur. Ideally,
one would like to have method where
one not only determines such
transitions quantitatively but also
visualize the flow pattern. Neutrons
provide this facility. Most of the
cladding metals such as aluminum or steel are transparent
to neutrons whereas hydrogenous materials such as water
are relatively opaque. This makes neutrons a unique tool
for study of flow of water inside metallic pipes. Such
two phase flow visualization is done using electronic
imaging technique [21]. The prototype electronic
imaging system developed by us has been used for
Fig.12 : Neutron images of (1) carburettor, (2) spark plug,(3) INSAT cable cutter & U-tube filled with wax recorded
using electronic imaging system at Apsara
Fig.13 : Schematic diagram of a sample made ofsolid brass (40 mm φ) with holes of 1mm to 5 mm filled
with wax, air and indium wire
21 I s s u e n o . 2 7 3 O c t o b e r 2 0 0 6
visualization of two phase flow (water/air) inside metallic
pipes. Simulation of bubbly, slug and annular flow was
done using various combinations of flow rates of water
and air using the experimental arrangement shown in
Fig.15. The transition from one flow regime to other has
been visualized (Fig.16). Aluminum pipes of diameter
from 12 mm to 25 mm and wall thickness of 1.5 mm to
2 mm, and steel pipe of 12 mm diameter and 1.5 mm
wall thickness have been used for visualization purpose.
Acknowledgement
I thank my colleagues Mrs. S. S. Desai, Mr. A.K. Patra,
Mr. J.N. Joshi, late Mr. N.D. Kalikar, Mrs. M. Padalakshmi,
Mr. A.G. Temkar and Mr. S.M. Patkar for their sincere,
valuable assistance and hard work in fabrication and
testing of neutron and X-ray detectors. Thanks are also
due to Prof. K. Rajanna, Indian Institute of Science,
Bangalore for collaboration in microstrip detector work.
The work in Neutron Radiography was performed in
association with various research groups in BARC. I thank
Mr. B.K. Shah and Dr. P.R. Vaidya (AFD), Mr. K.C. Sahoo,
Mr.D.N. Sah, Mr. S. Gangotra (PIED) for their interest in
investigations of zirconium hydride
Fig.14 : Neutron computed tomographicimage of sample shown above
Fig. 15 : Experimental setup for two phase flow study at Apsara reactor NR Facility
I s s u e n o . 2 7 3 O c t o b e r 2 0 0 622
2. Position Sensitive Detection for Thermal Neutrons,
Edited by P. Convert and J.B., Forsyth Academy
press London.
3. G. Charpak, R.Bouclier, T. Bressani, J. Favier and C.
Zupanicic, Nucl. Instru. and Meth. 62(1968) 262.
4. Neutron Detection Techniques in Neutron Scattering
and Radiography Experiments, A.M. Shaikh, Bulletin
of Indian Association of Nuclear Chemists and Allied
Scientists Vol.1, No.3 , 66-71, 2002 .
5. Development of Gas Filled Radiation Detectors for
X-rays and Neutrons at SSPD, BARC, S.S. Desai and
A.M. Shaikh, Proceedings of DAE-BRNS National
Symposium on Compact Nuclear Instruments and
Radiation Detectors-2005, 495-502, 2005.
6. Two dimensional position sensitive neutron detector,
A.M. Shaikh, S.S. Desai, and A.K. Patra, Pramana-J
of Physics, 63(2), 465-470 (2004).
7. Development of a microstrip gas chamber to study
the effect of drift gap on its performance,
Fig.16 : Single frame image of water/air flow inside aluminium pipe at twodifferent instants
blisters and Dr. Amar Sinha (HPPD) for the work on
electronic imaging. My thanks are due to Dr. K.R. Rao
(Ex-Director, Solid State and Spectroscopy Group, BARC)
for his interest, suggestions and many useful discussions
in development of neutron detectors and neutron
radiography. I acknowledge support of Dr. A. Sequiera
and Dr. M. Ramanadham (Ex- Heads of SSPD) and Dr.
S.L. Chaplot, Head, SSPD and for their keen interest in
the work. I am indebted to Dr. Anil Kakodkar, Chairman
AEC and Dr. Srikumar Banerjee, Director BARC for the
recognition of my work with DAE award for Technical
Excellence for the year 2004.
References
1. Knoll G. F. Knoll, Radiation Detection and
Measurement, 2nd edition John Wiley and Sons,
1989.
23 I s s u e n o . 2 7 3 O c t o b e r 2 0 0 6
V. Radhakrishna, K. Rajanna, S.S. Desai and A.M.
Shaikh, Rev. Sci. Instr., 72( 2 ), 1361, 2001.
8. Development and Studies on Microstrip detector, V.
Radhakrishna, S.S. Desai, A.M. Shaikh and K.
Rajanna, Current Science (2003) vol. 84, No.10,
2003, pp 1327.
9. Study on meandering resistive strip for microstrip
position sensitive detector using charge division
method, V. Radhakrishna, K. Rajanna, S.S. Desai and
A.M. Shaikh, Rev. Sci. Instr.,74(10), 4263-
4267(2003).
10. Development of a microstrip based neutron detector,
S.S. Desai, and A.M. Shaikh, V. Radhakrishna and
K. Rajanna, Pramana-J of Physics, Vol. 63(2), 465-
470 (2004).
11. A Curvilinear Position Sensitive Neutron Detector,
S.S. Desai and A.M. Shaikh, Solid State Physics (India)
Vol. 50, 315(2005).
12. Y.D. Dande et al, Ind. J. Pure and Appl. Phys.,
29(1991)721.
13. Detection of zirconium hydride blister in zircaloy
tubes using neutron radiography, A.M. Shaikh, P.R.
Vaidya, B.K. Shah and P.G. Kulkarni, International
Seminar on Developments on Enhancement of
Research Reactor Utilization, IAEA-SR-198/26, 1996.
14. Neutron Radiography of contact location of
irradiated zircaloy-2 pressure tube from RAPS#2, S.
Gangotra, P.M. Ouseph, A.M. Shaikh and K.C.
Sahoo, in Trends in NDE science and Technology,
proceedings of the 14th WCNDT, Vol. 3, 1453-1456,
1996.
15. Bulk Hydrogen Analysis using Neutrons, A.M. Shaikh
et al, IAEA-CRP Report F1-RC-655.3, 2003.
16. Application of Neutron Radiography and Neutron
Diffraction techniques in study of zirconium hydride
blisters in zirconium based pressure tube materials”,
A.M. Shaikh, P.R. Vaidya, B.K. Shah, S. Gangotra
and K.C. Sahoo, J. of Non Destructive Testing and
Evaluation, Vol.2(3), 9-12, 2003.
17. Study of hydride blisters grown on Zr-2.5Nb pressure
tube spool piece under stimulated condition of in-
reactor pressure and temperature, S.K. Sinha, D.N.
Shah, Suparna Banerjee, V.K. Suri, K. Gurumurthy,
A.M. Shaikh and R.K. Sinha, BARC Report, 2006.
18. Bulk Hydrogen analysis using Neutrons: Hydrogen
Sensitive Epithermal Neutron Radiography Technique
(HYSEN), A.M. Shaikh, Proceedings of National
Seminar on Non-Destructive Evaluation, 155-157,
2003.
19. Development of CCD/Image intensifier based 2D/
3D tomography system and its application in neutron
and gamma tomography, Amar Sinha, A.M. Shaikh,
A. Shyam , Nuclear Instruments and Methods in
Physics Research B142, 425-431(1998).
20. Development of CCD/Image intensifier based 2D/
3D tomography system and its application in
neutron and gamma tomography, Amar Sinha, A.M.
Shaikh, A. Shyam and L.V. Kulkarni, Proceedings
of Twelfth National Symposium on Radiation
Physics, 142-144(1998).
21. Use of neutrons for visualization of water/air flow
inside metallic pipes, Amar Sinha, A.M. Shaikh, A.
Shyam and L.V. Kulkarni, Proceedings of Twelfth
National Symposium on Radiation Physics, 243-
245(1998).
I s s u e n o . 2 7 3 O c t o b e r 2 0 0 624
Dr. A.M. Shaikh joined BARC in 1992.
His areas of specialization are neutron
& X-ray detectors, neutron
radiography, high temperature X-ray
crystallography and instrumentation.
A Ph.D. from IISc, Bangalore, he was a
postdoctoral fellow at the University of
Washington Seattle, USA and has worked
as faculty member at IISc, Bangalore and
University of Kuwait. Dr. Shaikh has been associated with IAEA in
programmes related to Neutron Radiography and worked as an
IAEA expert in this field. He has about 90 research papers in national
and international journals and conference proceedings to his credit.
Dr. Shaikh is on the Board of Studies and Board of Ph.D. Examiners
of many universities and research institutions in India. Dr. Shaikh is
the recipient of DAE-Technical Excellence Award-2004 and also the
ISNT National Award-2003.