Cosmic rays are extremely high-energy subatomic particles – mostly protons and atomic nuclei accompanied by many forms of electromagnetic emissions – that move through space, eventually bombarding the Earth’s surface. They travel at nearly the speed of light.
Cosmic rays are of two kinds: galactic and solar. Galactic cosmic radiation comes from the remnants of supernovas, which are powerful explosions during the last stages of existence of massive stars.
Solar cosmic radiation is composed of charged particles emitted by the Sun, predominantly electrons, protons and helium nuclei. Some of this radiation is continuously emitted from the Sun’s corona and known as ‘solar wind.’ The remainder comes from solar particle events – sudden and sporadic outbursts of electrically charged particles accompanied by electromagnetic emissions that occur when magnetic fields on the Sun’s surface stretch and twist. Like a rubber band, the Sun’s fields can snap, suddenly releasing enormous energy and presenting potential health concerns to astronauts in space. Although rare, strong solar flares can create radio blackouts and impact modern communication and navigation technology on ground.
The Earth is shielded by a magnetic field that makes the charged particles bounce from pole to pole, creating two gigantic donut-shaped belts populated by energetic electrons and protons. This field protects us from most of the cosmic rays. Passengers on aeroplane flights do receive higher doses of cosmic rays particularly at high altitude over the poles.
Ref: IAEA https://www.iaea.org/newscenter/news/cosmic-radiation-why-we-should-not-be-worried
The background radiation levels originating from rocks in the earth’s crust, vary considerably. There is increasing evidence that people who live on granite areas have evolved stronger repair mechanisms to cope with the higher radiation levels.
Radon gas is the most insidious of background radiation sources. The gas is breathed into the lungs. Radon concentrations can build up to elevated levels in basements and tunnels or even houses built of granite. Ventilation goes a long way to solving the problem.
Potassium 40 levels can be surprisingly high in many foodstuffs such as bananas and potatoes. No harm has been measured from these sources.
There are quite a few different units used when describing nuclear radiation/radioactivity. The table above shows many of these units. Throughout this series, I have chosen to use millisieverts. This unit has both weighting factors for the type of radiation and also uses weighting factors for the tissue affected when appropriate. This standardisation makes comparisons easier.
Most of Australia has low natural background levels at 1.5 mSv per year. Surprisingly high background levels occur in some parts of the world. Many can be as high as 20 mSv per year. Recent studies are showing little evidence of increased cancer levels in these zones. Our cells divide and divide at enormous rates every day of our lives. Errors can occur. These errors are detected during the process of mitosis at several points in the cell division process and corrected by our wonderful biochemistry. It has been estimated that over 10,000 cancer cells are generated in our bodies every day. Our immune systems detect these cells and destroy them with incredible efficiency.
Australians double their exposure to radioactivity using medical diagnostics. A CT scan of the chest or abdomen delivers about 10 mSv. The levels of radioactivity used during radiation therapy for cancer are extremely high but are carefully aimed at the troubled tissue. Methods of delivering radiation therapy are becoming more sophisticated and more targeted.
Much of our knowledge about high doses of radiation and its effects, come from detailed studies of the impact of the nuclear bombs on Hiroshima and Nagasaki. Standards set for acceptable levels of radiation are extremely conservative and evidence is building up that these standards are far too low. Instead of protecting the general public, the standards have caused unnecessary fear and inappropriate actions that led to mental health issues and other health issues.
Statistics from the US show a lifetime risk of having some form of medically diagnosed cancer as 1 in 3 (33%) and death from cancer as 1 in 5 (20%). An acute dose of 100mSv has a cancer risk of only 0.4%. An accumulated dose at this level would be lower still as the body has a chance to repair itself.
I have noted that radiation doses and their effects vary from source to source but they are not dissimilar and the slides shown above provide a reasonable concept.
Recently, five ex-Prime Ministers of Japan sent a letter to the EU claiming children in Fukushima province were still suffering from thyroid cancer because of contamination from the nuclear power plant following the 2011 tsunami. The Governor of Fukushima Province was irate over this and said the information was not based on science. The inflammatory letter was probably based on two viewpoints. Many children had all, or part of their thyroid glands removed because of a large screening exercise for thyroid abnormalities following the impact of the tsunami and now some will need thyroid hormone substitution all their lives. Six of these children are currently suing Tokyo Electric Power Company, the Daiichi Power station operators for damages.
The first signatory to the letter, Koizumi Junichiro, is an advisor to a private organization that promotes zero nuclear power and renewable energy.
The large screening exercise was undertaken on hundreds of thousands of children using a new advanced ultrasound technology capable of picking up a range of abnormalities not usually seen and panic set in. When control screening was undertaken on children in 3 prefectures far from any possible contamination, the same extent and types of abnormalities were found. They did not lead to thyroid cancer. It is sad that so many children were overtreated. A wait and see approach would have been better and not led to further illness.
Some references on thyroid cancers:
https://www3.nhk.or.jp/nhkworld/en/news/20220203_11/ – NHK WORLD-JAPAN is the international service of Japan’s public media organization NHK.
There is an optimum amount for most substances in biological beings. Too much is toxic, too little can often be harmful too. The optimum range is not the same from organism to organism and can be different at various times. For minerals, the optimum level ranges are often like those in the environment where the species evolved. Does this same concept apply to radiation?
My Blog has become My Nuclear Journey 