Saturday, September 19, 2015

Scott Kelly radiation exposure for 1 year in space.

I was curious of the exposure of the astronaut Scott Kelly would receive with this one year in space.
NASA Astronaut Scott Kelly reached the halfway point of his historic ‪#‎YearInSpace‬mission on the International Space Station. On Sept. 15, he completed 2,736 orbits around the world traveling 72 million miles. By the end of his mission, Scott will have circumnavigated the globe 5,472 times. He captured this video and wrote 'Come full circle with me, and fly one full orbit of our beautiful planet.'
I was said that he would receive 5250 times more radiation that what we receive from a flight from Los Angeles to New york.

Using this web site, we can get the number of microSievert received:

So 20.19 uSv * 5250 = 105,997.5 uSv or rounded to 106 mSv.

How does this compare to other radiation exposure?
  • The effective dose limits for a nuclear energy worker is set at 50 mSv in any one year
    • So 106 is more than double the limit imposed for nuclear energy workers.
  • The background radiation in Quebec is maximum of 0.5 uSv/hr, so in 1 year, this is around 4.4 mSv.
    • So 106 is 24x the normal radiation you would receive from home in Quebec
  • In April 2011, the Fukushima radiation zone was measured and the red zone was in the range of 19-91 uSv/hr.  So taking the average 55 uSv/hr, this gives us around 482 mSv per year.
    • So he would be exposed to around 2/9th the radiation of Fukushima exclusion zone a few weeks after the disaster. 
  • The most recent Fukushima survey I found was from this greenpeace web site. I took the most recent readings from 2014 and took the high red point closest to the failed power station.  This gives us an exposure of 0.83uSv/hr at 1 meter above ground, which is close to the average height of an adult.  
    • So this 0.83uSv/hr is around 7.3 mSv for 1 year exposure.
    • Thus Scott would be exposed to 14.5x more radiation than the worst measured point near the power station inside the Fukushima exclusion zone.
  • Another point of comparison is the region of Ramsar Iran where we have a yearly exposure of around 260 mSv
    • In this case, the population of Ramsar Iran is exposed in average at a level of 2.45x what Scott Kelly will be exposed in space. According to the study linked above...
Inhabitants of Ramsar have lived for many generations in these high background areas. Cytogenetic studies show no significant differences between people in the high background compared to people in normal background areas.

Here's a table showing the different levels:

Exposure type uSv/hr
Background radiation 0.30
Fukushima 2014 exclusion "red zone" 3 years after 0.83
Nuclear power worker average max allowed 5.71
1 year average for Astronaut Scott Kelly exposure 12.10
Ramsar Iran average exposure of population 29.68
Fukushima 2011 "red zone" avg 2 months after event 55.00

The source used was natural Uranium:
Natural uranium (NU, Unat) refers to uranium with the same isotopic ratio as found in nature. It contains 0.7% uranium-235, 99.3% uranium-238, and a trace of uranium-234 by weight (0.0055%). In terms of the amount of radioactivity, approximately 2.2% comes from uranium-235, 48.6% uranium-238, and 49.2% uranium-234.

The decay chain of Uranium 238 is:
 Which consist mostly of Alpha and Beta emitters.  Thus explain why the piece of wood blocks most of it.

Astronauts would be exposed to mostly cosmic gamma rays, which penetrates almost everything and is very hard to be shielded from.

Update: From

Here's a good graph to put radiation level in perspective:

Monday, August 17, 2015

Discovery Science explains radiation exposure in planes

I was watching discovery channel... this section I found interesting about exposure limits and wanted to double check the numbers...

From :
The effective dose limits for a nuclear energy worker is set at 50 mSv in any one year
So this is 50 milli Sievert per year... or 50/365 = 137 micro Sievert / day or 137/24 = 5 uSv/hr.

Normal background around my place in Quebec, north of Montreal is 0.50 uSv/hr.

So this limit is 10x the normal background I get.

But to compare with what you get in a plane... let's take as an example the short trip to Toronto I took...

While cruising at 35,000 feet you get exposed to 3.5uSv/hr or 7x the background.

So to get to 50,000 uSv (50mSv), you would need to spend 595 days in the air at the elevation.

So the numbers 321 days is a bit low, but that depends on the background, elevation and which regulation they used to calculate.  The more elevation you get, the higher the radiation dose you get.

Bottom line, flying is safer than working in a nuclear power plant (if exposed to the limit, which never happens)