cosmic radiation change with altitude

[Broomstick Flier]

Cosmic radiation exposure and air travel

The Canadians have published this study:

Cosmic Radiation Exposure and Air Travel - Environmental and Workplace Health - Health Canada

and I quote:

The chance of a cancer occurring is generally believed to be proportional to the level of radiation exposure: the lower the exposure, the lower the risk. For example, the chance of a fatal cancer occurring would be approximately 1% following 30 years of flying, at 1000 hours per year.