The atoms of metals such as radium and uranium are decaying spontaneously with α-particle emission, β-particle and gamma-radiation. this phenomenon is known as spontaneous disintegration radioactivity. Nuclear radiation occurs in other forms, including protons or neutrons emission or spontaneous fission of a massive core.
Radioactive decay change a core product to another if the core has a higher binding energy than the initial nucleus nuclear decay. The difference in the binding energy (comparing the states before and after) determines which decays are energetically possible and which are not. The link appears excess energy as kinetic energy or energy of the rest mass of the decay products.
Charter nuclides, part of which is shown above, both natural known graphical representation of nuclei by the number of protons, Z, and the number of neutrons, N. All cores stable and radioactive nuclei as manmade, are shown in this letter, along with their decay properties. Nuclei with an excess of protons or neutrons compared to stable nuclei decay into stable nuclei changing protons into neutrons into protons or neutrons, or by the shedding of neutrons or protons individually or in combination. The nuclei are unstable also be nervous, that is, not in their lowest energy states. In this case, the core may fail to get rid of his excess energy without changing Z or N by emitting a gamma ray.
nuclear decay processes must meet various conservation laws, which means that the value of the amount retained after decomposition, considering all decay products, must be equal to the same quantity evaluated for core before decomposition . conserved quantities include the total energy (including ground), electrical, linear load and angular momentum, number of nucleons, and the number of leptons (sum of the number of electrons, neutrinos and antineutrinos, the antiparticles positrons-which are counted - 1).
Alpha decay
An alpha particle is identical to a helium nucleus consisting of two protons and two neutrons together.
Initially it escapes from the core atom thereof matrix invariably one of the heaviest elements, processes of quantum mechanics and is repelled more from it by electromagnetism, since both the alpha particle and the core are positively charged.
The process changes the original atom of the alpha particle is emitted in a different element.
Its mass number decreases by four atomic number two. For example, uranium-238 decay to thorium-234.
Sometimes, one of these children also radioactive nuclides will usually decomposed further by one of the other methods described below.
Beta decay
own beta decay comes in two types: β + and β-.
β- emission occurs by the transformation of one of the neutrons in the nucleus into a proton, an electron and an antineutrino. The byproducts of fission nuclear reactors often suffer β- decay, as they are likely to have an excess of neutrons.
β + decay is a similar process, but involves a proton to a neutron change, a positron and a neutrino.
gamma decay
After a nucleus undergoes decomposition alpha or beta, it is often left in an excited state with excess energy.
As an electron can move to a lower energy state by emitting a photon somewhere in the ultraviolet to infrared range, an atomic nucleus loses energy by emitting a gamma ray.
Gamma radiation is the most penetrating of the three, and will travel through several centimeters of lead.
Beta particles are absorbed by a few millimeters of aluminum, while the alpha particles will be stopped in their tracks are a few centimeters of air, or a piece of paper - but this type of radiation causes the most damage to the material arrives .
lifetimes and probability
Radioactive decay is determined by quantum mechanics - that is inherently probabilistic.
So it's impossible to work out where any particular atom will decay, but we can make predictions based on the statistical behavior of a large number of atoms.
The half-life of a radioactive isotope is the time after that, on average, will have disintegrated through the original material. After two half-lives, half of which have fallen back and one fourth of the original material remain, and so on.
Uranium and plutonium are only weakly radioactive, but have very long half-life - in the case of uranium-238, about four billion years, roughly the same as the current age of the Earth, or the remaining lifetime So Sol estimated half of the uranium-238 at all times will still be here when the sun dies.
Iodine-131 has a half-life of eight days, so that, once the fission is stopped, less than 1% of iodine-131 produced in a nuclear reactor is maintained after about eight weeks. Other iodine radioisotopes are even shorter duration.
Cesium-137, however, stick around longer. It has a half life of about 30 years, and, because of this and because it breaks through the process more dangerous beta, is believed to be the greatest risk to health if leaked into the environment.
Although some radioactive materials are artificially produced, many naturally occurring and result in the existence of a certain amount of radiation in the environment all the time - the "background radiation".
Deeply
There is a natural level of radiation around us, which comes from several sources.
Part of gamma radiation coming from space as cosmic rays. Other radiation from sources in the atmosphere, such as radon gas and some of its decay products.
There are also natural radioactive materials in the soil - and as well as the obvious elements like uranium radioactive isotopes are also common substances such as potassium and carbon.
To understand the amount of background radiation is about, which helps to distinguish between the effects on normal matter and the human body.
The amount of radiation absorbed by the non-biological material is measured in gray, equivalent to one joule of energy per kilogram of mass unit. To a biological tissue, a dose equivalent measured in sievert (Sv), depending on the type of radiation involved and the amount of damage that radiation makes particular cells affected.
The equivalent dose is the dose in Sieverts gray multiplied by a "quality factor" for the type of tissue irradiated and the type of radiation - for electrons or gamma rays, 1; for alpha particles, such as that it emerges from the radioactive decay of uranium, 20.
The average amount of radiation received from reference sources in the UK is around 2-2.5 mSv per year. Due to the preponderance of granite, which contains higher than average levels of uranium in areas such as Cornwall or Aberdeenshire may be twice that level - have not high enough to cause any concern, but high enough that facilities nuclear can not be built there as the background level and exceeds the maximum allowed limit of radiation. In some parts of the world, such as northern Iran, the background radiation is as high as 50 mSv per year.There a variety of other artificial and natural causes routine low-dose X-ray radiation.A Dental will give you a dose less than 1 mSv; A CT scan of the whole body 10 mSv.As fewer cosmic rays are stopped by the atmosphere as higher you go, the crew of a passenger plane flying between the US and Japan once a week for a year would receive an additional dose of about 9 mSv.Under normal conditions, the dose limit for nuclear industry workers is 50 mSv per year.
The effects on human health
There are two main effects on health caused by radiation, which act in the short and long term as well as shorter and longer distances.
Radiation causes health problems by killing cells in the body, and the amount and type of damage done depends on the radiation dose and the time during which the dose is spread out.
The dose limits for emergency workers in case of a nuclear accident are 100 mSv if the protection of property or 250 mSv in a salvage operation.
Between the upper and 1 Sv received in a single day, exposure can cause some symptoms of radiation poisoning, such as nausea and damage to organs including the bone marrow and lymph nodes. Up to 3 Sv these same effects are more severe with a chance of getting infections due to reduced number of white blood cells in the body - with treatment, survival is likely but will not guaranteed.Larger dose plus the above symptoms, cause bleeding, infertility and skin peeling; a dose is not more than 3.5 Sv will be fatal, and it is expected that death even with treatment doses of more than 6 Sv.The level of radiation decreases with the square of the distance from its source, so someone twice as far from an external source source will receive a quarter of the radiation.Receiving a high dose in a shorter time usually causes a more serious injury, and that higher doses kill more cells, while the body you may have had time to repair some damage over time has elapsed between doses.
However radioactive material that spread to a wider area may cause effects on the long-term health by prolonged exposure, especially if they enter the food chain or by inhalation, ingestion directly.Taking radioactive materials in the body also it presents the greatest danger of atoms that undergo alpha decay, such as alpha particles are not very penetrating and are easily absorbed by a few centimeters of air. It was alpha emitter polonium-210 that was used to murder Alexander Litvinenko in 2006.Radioactive iodine isotopes that undergo beta decay, it can accumulate in the thyroid gland and can cause thyroid cancer. Attempts to prevent this involves the distribution of pads including no radioactive iodine-127 and flooding the thyroid, which prevents the absorption of radioactive iodine.For once doses, such as medical analysis, later risk of developing cancer is estimated at about 1 20 000 mSv received.Absorbing a cumulative dose of 1 Sv for a longer time period is estimated to cause cancer finally 5% there people.However disagreement over whether very small doses comparable to the level of background radiation actually contribute to health effects.
