Cosmos and cancer
doi:10.1038/nindia.2010.77 Published online 14 June 2010
A big indigenously built machine sits in the campus of the Variable Energy Cyclotron Centre (VECC) in Kolkata. It hums into action occasionally prying open many secrets of the universe with its energetic radioactive ion beams (RIB).
Alongside cracking puzzles like how chemical elements were born in the fiery cauldron of stars, the RIB technology also generates energetic particles to selectively kill unruly cancer cells.
Researchers at VECC have designed the radio frequency quadrupole (RFQ) accelerator that accelerates low energy heavy ions. "It is a three-in-one accelerator — it accelerates, bunches and focuses the ion beam," says Alok Chakrabarti of VECC.
The VECC team has created the facility in collaboration with Durgapur-based Central Mechanical Engineering Research Institute, the UGC-DAE Consortium for Scientific Research, Kolkata and the Society for Applied Microwave Electronics and Engineering, Mumbai for the research.
The novelty of RFQ lies in its power to accelerate very low energy and high current beams. One potential application of RFQ is its use as an injector in the accelerator-driven subcritical system — an accelerator driven nuclear power reactor. Such reactors are touted to be the next generation of reactors to address the problem of radioactive waste disposal.
In the RIB facility, radioactive isotopes are produced first via nuclear reactions in a target by bombarding them with stable ion beams from a primary accelerator (cyclotron). Reaction products created in the target quickly pick up electrons from the surroundings and give rise to radioactive atoms.
These radioactive atoms are made to diffuse out of the target and are transported to Electron Cyclotron Resonance (ECR), an ion source where radioactive atoms are ionised. From ECR, the low energy beam reaches an isotope separator, where a special magnet purifies the beam selecting the desired one.
The pure radioactive beam is finally accelerated in the RFQ to 100A kilo electron volt (A is the total number of protons and neutrons in the nucleus of an ion). After exit from RFQ, the beam is passed through a chain of linear accelerators (Linac) to reach a final beam energy of 1.3A million electron volts.
The researchers plan to install six Linacs. For the moment, they have tested the efficacy of the RFQ accelerator using stable oxygen beam. Beam transmission efficiency of about 90 per cent was measured for oxygen beam in the RFQ.
In addition to oxygen beam, the researchers have accelerated nitrogen, carbon, argon, helium and iron beams. They have used iron beams from the RFQ to study ZnO, which is a semiconductor material that acquires a unique storage capacity once proper level of magnetisation is introduced. Magnetisation makes ZnO suitable for a wide range of potential applications. "We have observed 300 times higher room temperature ferromagnetism in iron implanted ZnO, which is significant," Chakrabarti says.