Free radicals
are reactive chemical species with odd unpaired electron. Since their
discovery by Moses Goomberg about 100 years ago, these species are
implicated in various chemical and biological reactions. These species have
usually lifetimes ranging from a few hundred femto seconds (10-15) to
milliseconds (10-3) and for their detection and monitoring some special fast
reaction techniques are required. The free radicals are involved in various
processes, some of which are listed below:
-
Organic
reaction mechanisms
-
High-energy
radiation induced processes
-
Photochemical processes
-
Processes in
photosynthesis and vision
-
Action of
antioxidants
-
Polymerization processes
-
Homogeneous
catal
-
Lipid
peroxidation processes
-
Health
disorders like diabetes, arthritis
Pulse radiolysis is an excellent technique to
generate both oxidizing and reducing radicals of choice in known yields in
dilute aqueous solutions - the usual solubility limit of organic and
biomolecules- can be easily employed. Thus, this technique is ideally suited
to investigate the kinetics and absorption spectra of the transients. The
pulse radiolysis facility at BARC has
significantly contributed to radiation chemistry and has acquired both
national and international recognition. In order to give an impetus to
research in this area and to cater to the needs of researchers from the
Universities, BARC and other national
institutes, NCFRR was established at the University of Pune campus on an
initiative from Professor B. S. M. Rao with a copious financial grant from
BRNS-DAE, Government of India. During
the first phase of the programme, a pulse radiolysis facility has been
installed. Currently the facility is operational in the time domain of
nanoseconds (10-9) to milliseconds. The facility is open to users from
various University Departments, National Institutions, and other
laboratories. Hon'ble Shri Prithviraj Chavan, Minister of State in
PMO, Government of India, inaugurated
NCFRR on 26th June 2005.
|
Parameters |
Specifications |
|
Electron beam energy |
7 ± 0.5 MeV |
|
Peak beam current @ 10 ns |
≥1 A at 10 ns |
|
Peak beam current @ 3 μs |
0.115 A |
|
Beam diameter at exit window |
2 ± 0.5 mm |
|
Jitter in pulse |
± 200ps |
|
Pulse rate (Mains locked option) |
50 to 200 pps in 12.5 pps steps |
|
Dose due to dark current |
< 1 % of beam current |
|
Pulse to pulse reproducibility |
± 1 % |
|
Energy spread |
± 0.5 MeV |
|
Exit window material |
Titanium |
|
Modes of Operation
a. Single shot
b. Multishots
c. Preset beam pulses |
50 to 200 pps |
|
Pulse width – 10 ns to 3 μs |
10 to 250 pulses in steps of 10 pulses |
|
Pre-trigger delay |
10, 20, 50, 100, 200, 400 ns & 3 μs |
|
Sequential delay generator |
10 μs, 100 μs, 1 ms. Delay for Shutter & Oscilloscope |
The above figure
shows Linear Accelerator (LINAC)
system. In the LINAC electrons emitted by electron gun (left)
are accelerated in the wave-guide to 7 MeV, which exit from
window (extreme right). The detailed specifications of the LINAC
are given in the table above. The interaction of electron beam
with matrix creates free radicals, which are monitored by their
optical absorption in the spectral region 220-800 nm. The
detection system mLFP-111 from
Luzchem,
Canada. is used for this purpose.
|
Parameters |
Specifications |
|
1. Lamp |
Cermax 175W parallel lamp
Spectral range 200 – 1600 nm |
|
2. Monochromator |
CVI 110mm, Ruled gratings, 1200lines/mm
Spectral range 200 – 750 nm |
|
3. PMT |
Hamamatsu R-7400U - 04
Spectral range 185 – 850 nm
Rise time : 0.78 nsec
Programmable, -1000V. |
|
4. PMT Power supply |
TDS 3032B |
|
5. Digitizer |
Bandwidth: 300 MHz Sampling rate 2.5 Gs/sec |
|
6. Software |
Software is supplied as an executable code in the form
of compiled Lab VIEW application. The spectrometer
software allows for full computer controlled data
acquisition with PMT including single shot & multi-shot
Kinetics, time resolved Spectra. Off-line Analysis
software allows extraction of Kinetic and Spectral
information |
Time Resolved Fluorescence
Spectrometer:
Recently Jobin-Yvon- IBH time
resolved fluorescence spectrometer has been installed in the centre.
This spectrometer uses nanosecond LED' s (Currently 389, 452 and 584
nm). The fluorescence lifetimes are measured by time correlated
single photon counting method. Lifetimes in the time scales of 500
picoseconds to 1 microsecond are measured.
For further information, please
contact:
Dr. Avinash S. Kumbhar,
Project Coordinator,
NCFRR, Department of Chemistry,
University of Pune,
Pune-411007.
e-mail:
askum@chem.unipune.ac.in
Mobile:9890607871
Fax: 91-020-25691728
