Radiation poisoning is a condition caused by exposure to a large enough dose of radiation. Everyone is exposed to some radiation over a year, but this dose is almost never enough to cause radiation poisoning. Only a dose of 400 millisieverts or more has a significant chance of causing radiation poisoning if received in a short time, although other adverse effects, such as an increased cancer risk, have been clearly linked to a yearly dose of 100 millisieverts or more.
Ionising radiation is radiation which is capable of removing electrons from an atom. Certain types of radiation are more ionising than others; alpha particles (composed of two protons and two neutrons) are the most ionising, due to their relatively large electric charge of 2+ and "slow" speed of ~20,000,000 m/s, meaning that they interact with the electrons much more, and have a greater likelihood of displacing them from their position. Beta particles (high-energy electron/positron) are less ionising, as they have a lower electric charge of 1- and move faster, while gamma rays (very high-energy photons) are the least ionising of all, as they are chargeless and do not interact with the electron, and therefore must hit it directly in order to give it enough energy to promote it to a higher energy level and maybe remove it from the atom entirely. The ionising effect of radiation can lead to damage to DNA, and eventually cancer.
The symptoms of radiation poisoning include, among others, nausea, vomiting, hair loss, internal bleeding, diarrhoea and fatigue. In addition, high doses of radiation can also cause bone marrow suppression, also known as myelosuppression, where the bone marrow produces much less white blood cells, leading to immunosuppression and a decreased ability of the body to fight diseases. In very severe cases of radiation poisoning, the marrow can be sufficiently damaged to need to be replaced entirely, by means of a bone marrow transplant.
Radiation is most dangerous to cells which are dividing, tending to kill them first (these cells are the most radiosensitive). The same dose of radiation which kills a dividing cell is unlikely to kill a regular cell, but may still kill it. This property of cells helps to explain some of the symptoms; some the cells responsible for hair growth and intestinal cells are some of the most rapidly dividing, so hair loss and intestinal bleeding are easily explained by damage to these cells. This property of radiosensitivity can also be applied to cancer treatment. As cancer cells divide very rapidly, radiotherapy can be used to target these cells, with some of the side effects of radiation poisoning. In these treatments, the general goal is to optimise them such that the ratio of cancer cells killed to other cells is as high as possible, while also trying to avoid myelotoxicity.
In order to combat potential overexposure to radiation in the workplace, the UK, as well as other countries, has introduced dose limits in order to safeguard workers who work in an environment where they may be exposed to high levels of radiation. For workers over the age of 18, the maximum one-year dose for skin and extremities is 500 millisieverts, while the maximum dose for the lens of the eye is 20 millisieverts. The large difference between the two dose limits is due to the much greater risk of damage if the eye is exposed to a large dose of radiation, as opposed to the skin, where the outer layer is capable of stopping alpha radiation, and to some extent beta radiation, from reaching vital organs.
An example of just how rare deaths by radiation poisoning are is that only one death due to radiation was attributed by the Japanese Government to the Fukushima Daiichi nuclear disaster, while the earthquake and tsunami which caused the meltdown were cumulatively responsible for the deaths of at least 18,500 people. The one person who died worked at Fukushima plant at the time of the accident, and was therefore exposed to very high levels of radiation. Even though he was exposed to a high level of radiation, he died not of radiation poisoning, but of lung cancer caused by his exposure to radiation.
While acute radiation exposure today is known to cause severe health problems, in the past, the dangers were much less known. In the early 20th century, a craze for radioactive products, primarily containing radium, began across the whole of the west. Due to speculation, radiation was presumed to have a beneficial impact on human health, even though adverse effects had already been observed. In 1896, a man named William Levy volunteered to have an X-ray done of his head, in order to locate a bullet which had lodged there ten years prior. He underwent exposures for approximately 14 hours straight, with obvious implications. Within a day his entire head was blistered, the hair on the right side of his head had fallen out, and his right ear had swelled to twice of its usual size. The long term implications of this exposure are not known, but considering that the radiation was directed at his brain, and as it was electromagnetic radiation, was very penetrating, it is likely that he would have severe problems in future, with a higher probability of cancer. It is also clear that companies had enough information, due to many other incidents like the one above, to conclude that radiation exposure was detrimental to health, but nevertheless, continued making these products until well into the 1930s.
Particularly popular was a drink called Radiothor, advertised as "containing radium and mesothorium (thorium)". This was very dangerous if a person drunk enough over their lifetime, as radium, being a Group 2 element, resembled calcium enough that it accumulated in the bones, rather than being excreted, exposing the unfortunate person to high internal doses of radiation constantly, while also destroying their bone marrow. A well-publicised instance of this was of the athlete Eben Byers, who reportedly drunk a bottle of Radiothor every day, until 1930. In 1931, his health began to deteriorate, and the whole of his upper jaw and most of his lower jaw had to be removed. He died in 1932, of multiple cancers. This ultimately led to government action against the company which manufactured Radiothor, and was the beginning of the end for the radium craze.
Overall, people today are at much lower risk than previous generations of radiation poisoning, due to a better knowledge of the dangers of radiation, and stricter guidelines. In addition, nuclear waste disposal is more professional and safe than before, as since the London Convention of 1972, most countries no longer dump nuclear waste in the ocean, although some countries, notably India, have failed to sign. Due to modern regulations, people are now safer than ever from radiation poisoning.
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