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National Centre For Free Radical Research (NCFRR)


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

 


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