RESEARCH ACTIVITIES USING

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• RESEARCH ACTIVITIES USING
• MICROTRON FACILITY
• GANESH SANJEEV

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Microtron at Mangalore University

• An indigenously developed variable energy
  Microtron, designed and developed at RRCAT
  Indore, has been set up at Mangalore University
  to strengthen the teaching and research programs
  in the areas of Radiation Physics and allied
  sciences
• The first of its kind electron accelerator in the
  country is capable of delivering energetic
  electrons of energy 8/12 MeV, intense
  bremsstrahlung photons of peak energy 8/12MeV and
  also neutrons of reasonably high flux for variety
  of applications
• A birds eye view of this unique facility and the
  RD programs with some sample results are
  presented

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Microtron Features

• Beam Energy 8/12 MeV (Variable)
• Pulse Current 50 mA (max)
• No. of Electron Orbits 14
• Beam Size 3 mm X 5 mm
• Pulse Duration 2.5 ?sec
• Pulse Repetition Rate 250 Hz (max)
• Average Beam Power 375 W (max)
• Magnet Field Strength 1927.5 G
• Magnetron Power 2 MW
• Operation Frequency 2998 MHz

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8/12 MeV MICROTRON
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Electron Dose Distribution
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LABORATORY INFRASTRUCTURE

• Deep Level Transient Spectrometry (DLTS) system
  for defect characterization in semiconductor
  devices
• Keithley I-V measurement set with trigger
  controller unit for electrical characteristics
  of the semiconductor materials and devices with 2
  or 3 terminals
• A UV-Vis Spectrometer (Secomam) for dosimetry
  studies
• TLD Reader for analysing glow curves of various
  irradiated TL materials
• Fission chamber and SSNTD facility
• Research Microscope with relevant softwares
• Laminar flow for radiobiological studies
• Bacteriological grade Incubator
• Ag wrapped GM tubes for Neutron detection
• 41.2 relative efficiency HpGe Detector

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Research Acitivities

• Radiation Dosimetry Studies
• Chemical Dosimeters - Fricke, FBX, Alanine
  Glutamine
• TL dosimeter - CaSO4Dy
• Semiconductor Irradiation Studies
• Power Diodes, Schottky diodes, Transistors,
  MOSFETs, Solar Cells etc.
• Photofission Studies
• Cross-section, Angular Distribution of fission
  fragments
• Radiation Biophysics
• Chromosome Aberration, Micronucleus Induction in
  human blood lymphocytes, Cell Survival and Gene
  Conversion, Relative Biological Effectiveness
• Radiation Processing
• Coffee seed, Onion, Potato, Spices, Seeds of
  non-conventional legumes canavalia, Vanilla
  beans, Bakery items, ayurvedic medicines (powder)
• Irradiation studies on Polymer, Hydrogel, Thin
  films, Nano particles, ferroelectric materials,
  Crystals NLO, TGS and other organic crystals
• Neutron based studies - Activation Experiments

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Semiconductor Irradiation Effects

• Semiconductor materials/devices are highly
  susceptible to radiation damage. Radiation
  induces transient and permanent changes in the
  electrical properties of semiconductor devices.
  The changes in the properties can be desirable or
  undesirable depending on the dose imparted. Such
  changes can also cause an electronic device to
  fail.
• A clear understanding of the degradation
  mechanism of the semiconductor and semiconductor
  devices are therefore necessary to improve the
  device performance against irradiation by
  discovering the ways for minimizing the effects.
• It is also necessary to check whether the devices
  will withstand the harsh radiation environments
  encountered

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Power Diode Ut Qrr Trade-off
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Power Diode Reverse Characteristics
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NPN TRANSISTOR Characteristics
NPN Transistors were exposed to 8 MeV electrons
from 0.2 kGy to 51 kGy of total dose in
laboratory temperature with biasing. There is a
significant decrease in the current gain with
the increase of total dose.
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Schottky Diode Irradiation Effects

• SS/CdTe/Au Schottky diodes were irradiated with 8
  MeV electrons for various doses
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• Effect of irradiation is more pronounced at
  higher voltages than at lower voltages.
• The main effect of irradiation is a reduction in
  forward current with increasing dose.
• The nature of the I-V characteristics indicates
  that the resistivity of the material has
  increased after irradiation.

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Schottky Variation of parameters with dose
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Schottky Variation of capacitance with dose

• Upon irradiation the capacitance values are found
  to decrease.

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Silicon photodetector I - V Characteristics

• The semi logarithmic plot of dark forward I-V
  characteristics Si photo-detector at room
  temperature and reverse I-V characteristics at
  various doses

It can be seen that both the reverse and forward
currents increase systematically with dose.
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Silicon photodector Variation of parameters
with dose
The increase in I01 can be interpreted as
resulting from a decrease of the minority carrier
diffusion length in the base region. The minority
carrier diffusion length change is due to a
change in the minority carrier lifetime. It can
also be seen that the saturation current I02 is
not affected significantly by irradiation. From
the table it can also be seen that the series
resistance Rs increases with electron dose while
the shunt resistance Rsh decreases with dose. The
recombination centers induced by electron
irradiation might have influenced the series
resistance, increasing it with dose.
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Silicon Photodetector CV Plot

• Capacitancevoltage characteristics of Si
  photo-detector at various temperatures a)
  unirradiated and b) irradiated with electrons of
  dose 350 kGy

No considerable number of deep levels is not
formed in the device even after irradiation
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Irradiation Studies on Solar Cell

• The shunt resistance is determined from the slope
  of the reverse current in a linear scale. The
  device series resistance in the dark and under
  illumination was determined from the inverse of
  the slope of I-V characteristics in the high
  forward bias region

Increase in the series resistance and decrease in
the shunt resistance can be seen only after a
dose of 10 kGy
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Solar Cell in Radiation Environment

• Capacitance of unirradiated and electron
  irradiated CdTe/CdS solar cells at various
  frequencies

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Solar Cell in Radiation Environment

• Illuminated I-V characteristics of CdTe/CdS solar
  cell at various doses of 8 MeV electrons.

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DLTS System (Lab-Equip)
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Sample DLTS Spectrum(NPN Transistor at
Base-Collector junction)
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Studies on Relative Biological Effectiveness

• Radiation Biophysics studies are being carried
  out to work out all possible physical and
  biological parameters for electron beam from the
  microtron
• The main objective of the study are
• to investigate radiation dose rate effects on
  survival and gene conversion responses of yeast
  and bacteria
• Chromosome aberration as well as micronucleus
  induction in human peripheral lymphocytes with an
  emphasis on physical and biophysical modifying
  factors like irradiation, dose rate and exposure
  time.

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Radiobiological Studies
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Radiobiological Studies
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Theoretical approach -Bremsstrahlung from Tantalum
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Bremsstrahlung Spectrum
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Photofission Studies

• Studies on photofission using bremsstrahlung
  radiation in the sub-threshold region are being
  carried out
• to study the anisotropy in the angular
  distribution in even-even nuclei, energy
  dependence of the fission cross-sections that
  reflects the shape of the fission barrier and
• to investigate the nuclear structure of the
  fissioning nuclei at the saddle (transition
  state) configuration

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Photofission Studies
Anisotropy decreases with increasing energy and
this is due to contribution of K?0 channels in
addition to K0. The anisotropy observed at the
fission barrier is due to the non-uniformity of
the distribution of K, which is also to the
direction of the fission fragments, the latter
will be isotropic if the distribution of K is
uniform
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Microtron based Neutron Converter

• Accelerator based pulsed neutron sources can
  provide neutrons of thermal energies (0.025eV) up
  to several tens of MeV
• Applications such as radiography which were
  thought to be viable only using high flux are now
  possible with fluxes which are several orders
  less magnitude.
• The advantages of accelerator based neutron
  sources are that there will not be any
  radioactive waste, wide and easy accessibility
  and availability of variable broad energy
  spectrum of neutrons.

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Neutron Converter

• The bremsstrahlung photons from the Microtron are
  made to fall on cylindrical beryllium discs of
  appropriate dimension to get fast neutrons. The
  fast neutrons would be thermalised using high
  density polyethylene (HDPE), borated wood and
  borated rubber.
• Beryllium has been selected for the purpose as it
  has a low reaction threshold (1.67 MeV) for
  neutron production.
• Neutron converter design and MCNP simulation have
  been carried out to get optimum neutron yield.
  The simulation was carried out for various
  thicknesses of beryllium target.
• A neutron yield of 1010 n/sec was obtained
  theoretically for beryllium thickness of 6cm at
  250 Hz PRR

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Neutron Converter
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Experimental and MCNP simulation estimated yield
for 8.7 MeV Electrons
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Microtron based Research Projects

• DST Sponsored Research Project
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• RD Using Variable Energy Microtron
  Establishment of a National facility
• Budget Rs. 91,00,000
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• DAE-BRNS Research Project
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• Basic and Applied Research using Microtron
  facility
• Budget Rs. 98,00,000
• Microtron based BRNS sponsored Research Project
  to Users 30

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• THANK YOU