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From earth to space: What’s your risk from ionising radiation?

Two manikin torsos, referred to by NASA as phantoms, will join a mannikin named Moonikin Campos aboard the Artemis I mission, which will take the Orion spacecraft on a 42-day, 1.3 million-mile, uncrewed mission as far as 280,000 miles from Earth.

The role of the torsos, named Helga and Zohra, is to conduct radiation detection and measurement to better understand the levels that astronauts on future missions may encounter and assess how effective a protective vest would be for any future human mission. The torsos are made of materials that imitate female bones, soft tissue and organs, and one torso will wear the vest while the other won’t.

Astronauts are exposed to large amounts of ionising radiation, specifically space radiation, when they travel beyond Earth’s atmosphere. As NASA has noted, exposure to space radiation in the form of galactic cosmic rays and solar particle events places astronauts at risk of cancer and degenerative diseases.

A 2021 report from the National Academies of Sciences, Engineering, and Medicine advised that astronauts should not be exposed to more than around 600 millisieverts (mSv) in the course of their career. By way of comparison, Australians are exposed to 1.5 mSv each year from natural sources, excluding occupational exposure.

What we do, our jobs and where we live affects our radiation exposure. Flying exposes you to different doses of radiation by virtue of being closer to the edge of the atmosphere, and that exposure will vary depending on the altitude at which you’re flying. As an example, a flight from Perth to Darwin would expose you to 16 microsieverts (μSv), a microsievert being 0.001 mSv, and it would take 62 flights from Perth to Darwin for that exposure to reach 1 mSv. Studies have been carried out into the health of pilots and aircrew and have not found an increased risk of cancer associated with radiation exposure.

Terrestrial radiation also varies depending on where you live. Granite, for example, can give off small amounts of beta and gamma radiation, but that doesn’t mean you should move because there’s granite rock or granite buildings where you live, since the level emitted is negligible.

In a 2014 video, science communicator Derek Muller visited the most radioactive places on Earth. Hiroshima, the site of the world’s first nuclear bomb attack, is only 0.3 μSv per hour more than 70 years after the deadly explosion. That is higher than in Australian cities but still well within what would be considered safe levels.

The mine in the Czech Republic where uranium was discovered records 1.7 μSv per hour while Marie Curie’s office still has a few radioactive spots – a doorknob and the back of her chair. The site of the world’s first nuclear bomb, the Trinity bomb test site in New Mexico, is only about 0.8 mSv an hour. Chornobyl, meanwhile, registers around 5 μSv an hour, which Muller says over an hour would expose you to a similar dose of radiation to what you would get with a dental x-ray. The reason for the perhaps lower-than expected level of radiation is due to the fact that the top layer of soil was removed after the explosion.

Fukushima, on the other hand, still registered much higher levels of radiation (5 to 10 μSv per hour) when Muller made his video in 2014, which was just three years after the accident. The most radioactive place Muller visited was the basement which contains the suits of the firemen who responded to the Chernobyl disaster, with a reading of 1,500 μSv per hour. Even that is less than the radiation from a CT scan, which is around 7,000 μSv.

Here in WA, we have our own radiation hotspot, the Montebello Islands, which were the site of the UK’s first nuclear tests 70 years ago. Researchers are currently working to find out the type and how much radioactive material still exists in the sediment on the ocean floor. For now, tourists are advised not to spend more than an hour at Trimouille and Alpha islands due to what the Department of Biodiversity, Conservation and Attractions refers to as “slightly elevated radiation levels.”

None of these exposure sites or even astronauts come close to the level of radiation absorbed by one group of people: smokers. On average a smoker’s lungs receive 160,000 μSv of radiation per year, Muller explains. As some of have said, Muller’s video perhaps should be used in anti-smoking campaigns.

What does all of this mean for the Artemis 1 mission, the space suits and for astronauts? The report calling for space travel limits are one element of the broader effort to improve safety for astronauts, which are the most at-risk profession. The space vests are another. Scientists will assess how well the vest protected Zohar’s body compared to Helga, who won’t be wearing the vest. Until the mission takes off – currently planned for mid-November – both mannikins remain safely on Earth.

 

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