The Australian Nuclear Science and Technology Organisation (ANSTO) is experiencing unprecedented demand for its silicon irradiation services.
While ANSTO’s HIFAR (High Flux Australian Reactor) research reactor at Lucas Heights is best known for producing radiopharmaceuticals for the diagnosis and treatment of cancer and other diseases, ANSTO is also one of the world’s big players in the silicon irradiation business.
Demand for these services from Japanese and European electronics companies is expected to continue, with more efficient irradiation facilities earmarked for the replacement research reactor.
Following a surge in demand, HIFAR is irradiating silicon at full capacity - around one tonne of silicon each month - and orders are continuing to rise. Silicon irradiation, or Neutron Transmutation Doping (NTD), changes the properties of silicon, making it more conductive of electricity. Large single crystals of pure silicon are grown in Japan and air freighted to ANSTO for irradiation inside the HIFAR reactor.
Irradiation involves bombarding the ingots with neutrons for precise periods. One in each billion silicon atoms in each ingot is changed to phosphorous. This uniformly doped silicon is used in video cameras, fax machines, air conditioning control units, and in computer DRAM (Dynamic Random Access Memory).
It is also used in electrical components such as high power transistors, diodes, thyristors and Silicon Controlled Rectifiers for power transmission.
Silicon ingots are lowered into the reactor’s graphite reflector facilities, just outside its heavy water tank, for irradiation. Depending on the size of the ingot (they vary from 77mm in diameter to 205mm) and the electrical properties required by the client, irradiation can take anywhere from half an hour to five days or, sometimes, even weeks.
ANSTO has an edge over the other major players in that HIFAR is the only reactor that can accommodate 205mm crystals. Though the majority of ingots irradiated in HIFAR are just 127mm in diameter, demand for larger diameters is expected to increase.