The vast majority of nuclides are unstable. They will spontaneously undergo sharp changes and become another nuclide, while emitting various rays, which is called radioactive decay
Including α, β, γ and other decays
radioactivity
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NucleusSpontaneous emission of various rays is calledradioactivity。Study in magnetic fieldRadioactive rayIt is found that radioactive rays are mainly composed of α, β and γ rays.
Isotopes that can spontaneously emit various rays are called radioisotopes.Radioisotope emits various raysnuclear transmutationThe process of radioactive decay is called radioactive decay.The radioactive isotope before decay is called parent, and the new isotope produced during decay is calledRadiogenic isotope, or progeny.
In the process of radioactive decay, the number of atoms in the parent body decreases with timeAtomic numberIs increasing.If the radioactive parent is transformed into a stable daughter after one decay, it is called single decay.Sometimes, the radioactive parent can undergo several decays. The intermediate daughter formed by each decay is unstable, and will decay itself until a stable final daughter is produced. This decay is called continuous decay.By such aradioactivityFormed by parent body, several radioactive intermediate daughters and one final stable daughterDecay chainIt is called decay series.Most radioisotopes decay in such a way that one parent only transforms into another seed.A few radioisotopes can have two or more decay modes to form different daughters, that is, one parent can produce two daughters at the same time. Such decay is called branching decay.These types of decay exist in nature.
During radioactive decay, radioactivityparent isotope OfAtomic numberThe time required for attenuation to half of the original number is calledhalf life, recorded as T1/2。The average time that the radioactive parent isotope exists before decay is calledaverage life span, recorded as τ.The half-life is a main characteristic constant of radioactive isotope decay. It does not change with the change of external conditions, element state or mass. The half-life of radioactive isotopes varies greatly, from one millionth of a second to tens of billions of years. Isotopes with shorter half-life,radioactivityThe stronger.
NucleusSpontaneously emitAlpha particleThe process of transforming into another kind of nucleus is called alpha decay.For natural radioisotopes, onlyMass numberOnly heavy nuclei with A greater than 140 can produce alpha decay, especiallyAtomic numberRadioisotopes with Z greater than 82 and mass number A greater than 209 are dominated by alpha decay.The general formula of α decay is:
Beta particleThere are positive and negative electrons, which are releasedpositronIt is called beta decay, and it is called beta decay that emits negative electrons.The general formula of beta decay,
Gamma rayIt is an electromagnetic radiation emitted from the inside of atomic nucleus, often accompanied by α orBeta rayGenerate.The parent and daughter of gamma decay are isotopes of the same kind, but the internal energy state of the atomic nucleus is different.Gamma decay can also be called isomeric transition.
The process of heavy nuclei splitting into two or several fragments of medium mass and simultaneously emitting neutrons and energy is called nuclear fission.Spontaneous fissionIt is a nuclear fission that occurs spontaneously without the bombardment of foreign particles. It can also be usedhalf lifeTo measure the difficulty of fission.Spontaneous fission in nature can only be found in uranium and thorium isotopes.compareAlpha decay, spontaneous fission of uranium and thoriumBranching ratioVery small, almost negligible.
Induced fissionMeansNucleusFission caused by bombardment of foreign particles.With variousparticle(neutrons, protonsGamma rayBombardment of uranium and thorium isotopes can lead to induced fission.
As mentioned earlier, the decay and fission rate of radioisotopes is constant and independent of external conditions.But it is impossible to predict when a single atom will decay.For a large number ofradioactivityNucleus can statistically determine how its entire atomic number changes with time.
