Decay is also called "metamorphosis", which meansradioactive elementThe process of emitting particles and transforming them into another element, such asradiumreleaseAlpha particleLater becomesradon。[1]
UnstableNucleusAt emissionparticleAnd energy can become more stable, this process is called radioactive decay.These emitted particles or energy (the latter emitted in the form of electromagnetic waves) are collectively referred to as radiation.The radiation emitted by unstable atomic nuclei can beAlpha particle、Beta particle、Gamma rayorneutron。
RadionuclideIn the process of decay, thenuclideThe number of nuclei will gradually decrease.The time that the number of radionuclides decreases to half of the original due to attenuation is defined as the physical half-life T, or half life for short.[4]Each radionuclide has its specific half-life, which consists ofMicrosecondTo millions of years.
The phenomenon that an atomic nucleus becomes a new nucleus because it emits some particles.The nucleus is aquantumSystem, nuclear decay is the spontaneous change of atomic nucleus, which is a quantumtransitionProcess, which obeys quantumStatistical law. For any oneRadionuclideThe exact time of its decay is unpredictable, but as a whole, the law of decay is very clear.If the number of nuclear decays in the dt time interval is dN, it must be proportional to the number of atomic nuclei that exist at that time N, obviously also proportional to the time interval dt. Decay is not affected by any conditions, and is a unique property of matter.
OneAlpha particleWith aheliumThe nuclei are the same, and their mass number and nuclear charge number are the same.In essence, alpha decay is a process of quantum mechanical tunneling effect.AndBeta decayDifferent, it is composed ofStrong interactioncontrol.
The kinetic energy of alpha particles generated by decay is usually about 5MeV, and the speed is 30000 km/s,light speedOne tenth of.Because its mass is relatively largepositive charge, the speed is relatively slow (for other decay particles), so they are easy to interact with other atoms and lose energy.Therefore, they can be almost completely absorbed by a layer of air several centimeters thick.
The α decay process is expressed as:
formula
The difference between the static mass energy of parent nucleus and daughter nucleus is called decay energy E-decay:
Edecline= (Mx-MY-Ma)ctwo
The kinetic energy allocated to the nucleus and particle a (the particle speed in the decay process is far less than the speed of light, so the energy and momentum can be treated as non relativistic)
Generally, heavy elements undergo alpha decay, with A>>4, so Eα≈Edecline
The inference shows that each substance producing alpha radioactivity only emits alpha particles of single energy.But accurate measurement shows that the same kind of α radioactive material can emit several groups of particles with different energies, forming the fine structure of α energy spectrum, which reveals the separation of atomic nuclear level: like atoms, there are a series of discrete energy levels in atomic nuclei.In the process of alpha decay, the daughter nucleus and the parent nucleus (usually the parent nucleus) can be in different energy levels, so the emitted alpha particles can also have different energies.[2]
Beta decay
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Beta decayIs a kind ofradioactivityDecay.In the process, one nucleus releases oneBeta particle(electron or positron), divided into beta+decay (releasepositron）And beta decay (releasing electrons).
β decay in quantum mechanics
Beta decay,Weak interactionTo convert a neutron into a proton, an electron, and aAntielectronneutrino。Its essence isquarkBy releasing a W-BosonInto an upper quark.The W-boson then decays into an electron and an antielectron neutrino.
In β+decay, a proton absorbs energy and converts it into a neutron, a positron and an electronMicroenterpriseChild.Its essence isUpper quarkIt transforms into a lower quark by releasing a W+boson.The W+boson then decays into a positron and aElectron neutrino。
Unlike beta decay, beta+decay cannot occur alone because it must absorb energy.When all β+decay can occur, it is usually accompanied byElectron captureReaction.
Natural radioactive beta decay emits radiation, and there are two kinds of artificial radioactive decay: beta+decay and K electron capture.The three decay reaction formulas are as follows:[2]
