Beta ray: high-speedElectron flowe，Strong penetration ability,IonizationWeak, there is no left and right in the physical world, but there are left and right in beta rays.Beta particles are beta particles, which means that whenRadioactive materialhappenBeta decayThe high energy electrons released can reach 99% of the speed of light.In the process of beta decay,radioactivityNucleusBy emissionElectronicsandneutrinoThe electrons in the product are calledBeta particle。In the positive beta decay, a proton in the nucleus changes into aneutron, release one at the same timepositronIn the "negative beta decay", a neutron in the nucleus is converted into a proton, and an electron is released at the same time, that is, a beta particle.
Due to electronicmass ratioProtons and neutrons are much lighter. When a beta particle passes through an electric field, if it is a negative electron, its path will twist towards the positive pole.When passing through the magnetic field, if the direction of the magnetic field is from inside to outside, its particles willcounter-clockwise directionTwist, the path is curved.It can penetrate several mm thick aluminum plate.
There are two types of beta rays emitted by atomic nuclei: beta-Radiation and beta+Ray.β-Rays are ordinary electrons with one unitnegative charge, with the symbol e-The negative electron is stable.β+A ray is a positron with one unitpositive charge, with the symbol e+express.[1]
Interaction
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(1) Ionization and excitation
Ionization: the specific ionization value of β particles is higher than that of β particles with the same energyAlpha particleMuch smaller,charged particleWhen passing through matter, there will be a lot ofion pairThe number of ion pairs produced by the ray per unit distance is called specific ionization orIonization density。For single energy fast electrons, the specific ionization value in the air is related to the speed of the electron. The higher the speed, the smaller the specific ionization value, and the smaller the (- dE/dx), and the stronger the penetration ability.
Material atomic ionization (inner layerElectron ionizationElectron vacancy filling in the rear outer layer)X-ray: The fast electrons knock the shell electrons out of the atom, and the shell creates a vacancy. When the outer electrons transition to the inner layer, the energy difference between the two shells is emitted in the form of X-ray, which has a certain energy.
Excitation: emitted after the material atom is excited (the inner layer electron is stimulated to transition backward)visible lightandultraviolet raysWhen fast electrons interact with matter, they will alsovalence electronExcited to higher levels, and they returnground stateWill emit visible light and ultraviolet lightSecondary radiationIt is generally called fluorescence.
(2) Scattering and absorption
Scattering: beta particles andTarget substanceNucleusCoulomb fieldWhen acting, only changeDirection of movement, without changingRadiant energyThis process is calledelastic scattering 。Because of the small mass of the electronScattering angleThe degree can be large (compared withAlpha particleIn contrast, the scattering of beta particles is much larger), andMultiple scatteringAnd finally deviate from the original direction of motion.At the same time, the lower the incident electron energy, and theAtomic numberThe greater the scattering, the greater the scattering.The final scattering angle of β particle after multiple scattering in the material can be greater than 90 °, and this scattering isBackscattering。
Absorption: β particles in someBinding energyLargerTarget materialAs the energy is limited, when the energy is exhausted, it may be bound by the target atoms and thus absorbed. It is called a member of the electrons outside the nucleus of the medium.Its penetration distance (usually called range, recorded as R) and incidenceParticle energySize.
BremsstrahlungWhen the electron passes near the atomic nucleus, it will radiate when accelerated by the Coulomb fieldelectromagnetic wave, called bremsstrahlung.radiationLoss rateIt is proportional to the square of the atomic number, that is, the electron hitsHeavy elementBremsstrahlung is easy to occur.Heavy charged particles have similar radiation when penetrating the mediumenergy loss , but it is ignored because of its high quality.
Cerenkov radiation: When the electron passes through the medium, the atom will be temporarily polarizedDepolarizationIt emits electromagnetic waves with a wavelength in the visible light range, which is called Cherenkov radiation.（LuchtineProfessor explanation)
Another solution: when the electron is in the mediumMovement speedV exceeds thepropagation velocityWhen v>c/n (n is the mediumRefractive index）, will emit electromagnetic waves in a specific direction, called Cherenkov radiation.（Yang Fu's FamilyAcademician explanation)
(4) Positron annihilation
In addition to a series of effects of negative electron energy,positronIs moderated toQuiescent stateThe annihilation of positive and negative electrons will also occur, and two annihilation photons will be emitted in the opposite direction. The energy of both photons is 0.511Mev.
harm
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Beta ray is a charged, high-speedRadioactive decayThe particles released from the.Human beings are exposed to β - rays from man-made or natural sources (tritium, C-14, etc.), β - ray ratioAlpha rayMorePenetrability, but it will cause less damage when passing the same distance.Some beta rays can penetrate the skin, causingradioactivityhurt.But once it enters the body, it will cause more harm.Beta particles can be eliminated and blocked by external clothes or a piece of aluminum foil with a thickness of several millimeters can be completely blocked.
ionizing radiationIt is a kind of radiation with enough energy to make electrons leave atoms.Hereinafter referred to as radiation.One kind of radiation comes from some unstable atomsradioactivityAtoms ofRadionuclideorradio isotope）In order to become more stable, the atomic nucleus releases secondary and high energyLight quanta(Gamma ray)。The above process is called radioactive decay.For example, the natural nuclides radium, radon, uranium and thorium exist in nature.In addition, it exists inhuman activity(e.g. innuclear reactorAnd natural activities, they also release ionizing radiation.In the process of decay, the main products of radiation are alpha, beta and gamma rays.X-rayIt is another kind of radiation caused by the outer electrons of the nucleus.
Encyclopedia x confusion: illustration of nuclear radiation
Ionizing radiation can causeCytochemistryChanges in balance, some changes will causecanceration。Ionizing radiation can causegenetic materialDNAThis effect may even spread to the next generation, leading to the new generation of malformations, congenitalleukemia... Under the irradiation of a large amount of radiation, it can cause pathological changes or death in a few hours or days.[2]
Protective factors
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stayradiation protectionThere are three main factors in: time, distance and shielding.
time
When you areradiation sourceIn the vicinity, you must stay as little as possible to reduce the radiation.Suppose we go to the seaside for vacation. You stay on the beach all the time, that is, you are exposed to the sun, and finally you areSunburn。If you spend less time in the sun and more time in the shade, you won't get sunburnt.
distance
The farther away from the radiation source, the less radiation is received.If we go to an open-air concert, you may sit in front of the singer, or sit 50 meters away from the stage, or sit on the grass in the park across the street, and your ears will hear different sounds.If you sit in front of performers, your ears will be damaged.At 50 meters, the sound is about the same;Sitting on the park lawn, you may not hear music at all.As in the above example, the closer you are to the radiation source, the more likely you are to be burned by the radiation, and the farther away you are, the less harmful you will be.
Beta particles generally have a strong penetration ability, and can walk several meters in the air, that is, they can pass through aluminum sheets several millimeters thick.
shield
If you add shielding around the radiation source, you will receive less radiation.It's like in a rainy day, if you don't hold an umbrella, you will get wet.But it won't be like this with an umbrella.[3]
