[AndroidNeox (OP)]

I've wondered if you could make a good air purifier (sterilize & ionize) by passing the air past a gamma ray emitter. Maybe a box with a “U” shaped air path. It would need to be very tough to ensure the radioisotope was contained. I don’t know if steel is good at blocking gamma rays, or whether the box would need to be lined.

[CliffordK]

It likely would work as lower energy UV has also been used.  Gamma rays have been used for preserving foods, and one could likely find a gamma concentration that would be lethal to airborne microbes. 

This article discusses use of Gamma for sterilization including sterilization of gases and pharmaceuticals.

There are a few limitations.

• Gamma sterilization is time and dose dependent.  So, it may be effective in a low flow air input, but ineffective with in a high flow HVAC system.
• Different organisms, or stages have varying susceptibilities to gamma radiation.  While it will kill viruses and spores, they take a much higher dose than most other organisms.
• Gamma would provide no benefit to filtering non-biologic particles, such as vehicle exhaust fumes
• Assuming high dose radiation, the device would need to be heavily shielded, isolated from people, and would probably be inappropriate for home-consumer use.

Personally I'm not a big fan of sterilizing anything beyond what is absolutely necessary.  Our bodies are designed to deal with low dose dust and etc.  In fact, Asthma is supposed to have lower incidence in rural settings than urban settings. with the rural settings presumably bringing greater exposure to dust, but possibly of a significantly different makeup than urban contaminants.

[Mike Ortan]

Hello!
A gamma-ray air purifier is used to sterilize instruments in the medical field. But if you want to use the air purifier in the home for cleaning dust from the table or anyplace then use a desk air purifier because it is best for home use.

[alancalverd]

The interaction of gamma radiation with air and airborne particulates is very inefficient. Ultraviolet is a better steriliser and any radiation that is not absorbed on a first pass (i.e. most of it) can be reflected several times in a polished steel channel. Field ionisation is even more efficient if that is what you want to do, and it can also generate a lot of ozone which is a chemical sterilant. Alpha radiation is also used to ionise air.

[evan_au]

If you think of photons:
- Photons of Visible/Infra-Red (IR) light don't have enough energy to tear an electron off an organic molecule, so they are not useful for sterilisation
- Photons of Ultra-Violet (UV) light do have enough energy to tear off outer electrons and disrupt organic molecules; they are very good at producing certain mutations in RNA/DNA
- X-Ray photons can rip out inner electrons from atoms. But because the energy of each photon is higher, you get a much lower number of photons for a certain level of input power, so it can sterilize a lower volume of air. X-Ray tubes operate at high voltages (complex power supply) and get very hot. The source also needs shielding.
- Gamma rays can disturb the nucleus of an atom. But because the energy of each photon is much higher than that of X-Rays, you get far fewer of them, so it can sterilize an even lower volume of air. Gamma ray sources are radioactive, which creates problems in manufacture, shielding during use and disposal, as well as risks of accident or terrorism.

So the wavelength which produces the most sterilizing photons for a given energy input is UV light.
- Recent developments of UV-emitting LEDs should allow a cheap, safe, reliable source, with a simple power supply.
- Older UV sources like mercury vapor lamps require higher voltages, and we would prefer to have less mercury in our environment.