The metal cake in the picture is an alloy of uranium and zirconium, molybdenum and other metals. Uranium is known to be radioactive and can make nuclear fuel. In everyone's impression, exposure to this radioactive nuclear material requires wearing protective clothing and arming the whole body to the teeth to avoid being injured by radiation. However, it is this radioactive substance that knowledgeable experts dare to hold directly in their hands, even if they do not wear gloves, but they need to wash their hands after contact.
Is there really no danger in doing so?
Unlike chemical bombs, the explosive energy of a nuclear bomb comes from two types of nuclear reactions, nuclear fusion and nuclear fission (the difference between nuclear reactions and chemical reactions is that nuclear reactions occur at the nuclear level and can change the type of elements). Taking the atomic bomb as an example, the nuclear material filled inside its projectile body is enriched uranium with a purity of more than 90%, which can release huge energy when the uranium is chain-fissioned.
Nuclear weapons are extremely powerful, and when they explode, they can release extremely strong nuclear radiation, which is released after the fission of a large number of uranium nuclei.
When it comes to radiation, many people think it's scary, but when you have the right understanding of radiation, you will have a new perspective.
Radiation is a phenomenon in which energy diffuses to the outside world with electromagnetic waves or particles, which can be divided into ionizing radiation and non-ionizing radiation, usually only ionizing radiation can produce greater harm in a short period of time. However, non-ionizing radiation is not so terrible, sunlight is the electromagnetic radiation emitted by the sun, any temperature above absolute zero (minus 273.15 ° C) will continue to radiate infrared to the outside world, we are always receiving these electromagnetic radiation irradiation, but nothing.
Microscopic particles have wave-particle duality, ionizing radiation refers to radiation with a wavelength of less than 100 nanometers, and nuclear radiation belongs to ionizing radiation. Nuclear radiation is released during fusion or fission, as well as during the decay of radioactive elements (decay is a phenomenon in which the nucleus of an unstable element is transformed into a nucleus of a stable element by releasing rays or particles transforming into a stable element).
There are many types of nuclear radiation, including alpha rays (helium nuclei), beta rays (electrons), gamma rays (photons), neutrons, positrons, neutrinos, and so on. Among them, alpha rays can be blocked by a thin piece of paper, and the penetration is very weak; beta rays have a slightly stronger penetration and can be blocked with aluminum foil; the strongest penetration is gamma rays, which require thick lead plates to block; as for neutron rays, its penetration ability is stronger than gamma rays. When the atomic bomb explodes, it releases a large number of gamma rays and neutron rays.
Uranium (U), atomic number 92, that is, there are 92 protons in the nucleus, which naturally exist in nature three isotopes (isotopes are the elements with the same number of protons in the nucleus and different neutron numbers), namely uranium 238, uranium 235, uranium 234, and their abundance in nature is 99.28%, 0.71% and 0.006%, respectively, all three of which are radioactive. Uranium-238 was discovered in 1789 by Martin Heinrich Claprote, while uranium-235 was discovered in 1935 by Canadian scientist Dun shida.
Although uranium-238 is highly abundant and can also undergo fission, it cannot continue to carry out spontaneous chain reactions, so uranium-238 is also called depleted uranium. However, uranium-235 can, but its abundance in nature is very low, and it usually coexists with uranium-238, so it needs to be separated to purify uranium-235, so that its purity reaches more than 90%, before it can be used to make atomic bombs. High-purity uranium-235 can be obtained by gas diffusion method, gas centrifugation method, etc., but the process is not simple, only 1 kg of weapons-grade uranium-235 requires 200 tons of uranium ore.
(The picture shows the intermediate product in the process of uranium ore processing and refining: ammonium diuranate powder)
The nuclear material loaded in the atomic bomb is nuclear-grade uranium-235. Uranium-235 is usually used in fusion power plants, but the purity of that enriched uranium is only about 3%, which is far less pure than the enriched uranium of nuclear weapons.
Many people are under the impression that radioactive materials are very dangerous, let alone nuclear-grade uranium-235. But researchers dare to hold it with their bare hands, not because they are not afraid of death, but because they are really harmless.
Radioactive elements spontaneously emit nuclear radiation, but the natural isotopes of the three uranium mentioned above decay only emit alpha rays that cannot penetrate even your skin. The outermost layer of skin on the surface of our bodies is a layer of dead skin, like a thin layer of armor, which radiates impenetrable.
And the half-lives of these three isotopes (half-life refers to the time it takes for a certain number of nuclei to decay halfway) are super long, with a half-life of about 4.5 billion years for uranium-238, a half-life of about 700 million years for uranium-235, and a half-life of about 250,000 years for uranium-234.
In short, direct contact with nuclear-grade uranium with bare hands in a short period of time will indeed not cause any harm to the body. As for natural uranium ore, its radiation is even lower. However, it should be noted that although direct contact is not harmful, it is still harmful if uranium enters the human body, after all, it is still radioactive and still heavy metals.
Once the uranium is put into the reactor for reaction, the amount of radiation is large, it is very dangerous, even if you wear protective clothing, you can not directly contact, you need to use robots.
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