Why can lead clothing block nuclear radiation?

Answer: Lead is the non-radioactive element with the largest atomic number in the periodic table of elements. It also has a very high density (11.33 g/cubic centimeter), so it can well shield nuclear radiation.

Lead clothing is a kind of clothing that can effectively shield radiation. When doing certain radioactive examinations, doctors may use lead clothing to protect non-examination parts to avoid damage to important organs.

There are three types of nuclear radiation: alpha rays, beta rays and gamma rays.

(1) The essence of alpha rays is the nucleus of helium atoms, which carries two units of positive charge and has a large mass, so it is easy to be shielded. A piece of white paper can completely block it.

(2) The essence of beta rays is electron flow, with a unit negative charge and a very small mass. Since conventional substances are composed of atomic nuclei and extranuclear electrons, beta rays are also easily shielded. A few centimeters of air or ordinary metal can completely block it.

(3) The essence of γ rays is high-energy photons, which are uncharged, have very small dynamic mass and extremely strong penetrating power.

Therefore, among these three types of nuclear radiation, gamma rays are the most dangerous and can cause serious and irreversible damage to human cells. In addition, neutron radiation is also fatal.

To shield gamma rays and neutron radiation, you need to use materials that can absorb rays. In essence, any material has a probability of absorbing rays, but the ability to absorb rays is very different.

For an atom, the larger the nucleus in the atom and the more electrons outside the nucleus, the easier it is to block the spread of gamma rays and neutron radiation at the same thickness. Lead is the non-radioactive atom with the largest atomic number. The element has a density as high as 11.33 g/cm3, so it can effectively absorb gamma rays and neutron radiation.

Uranium has a higher atomic number and higher density, and can better absorb gamma rays and neutron radiation. However, the uranium element itself decays, so it is not suitable for shielding nuclear radiation; some Precious elements, such as gold, platinum, etc., are also denser than lead, but their prices are too high and are not suitable for large-area radiation shielding.

Concrete is also an effective material for shielding gamma rays and neutron radiation. Therefore, in important military sites, buildings are wrapped in thick concrete, and important underground rooms are covered with dozens of meters of concrete. Protected.

Many things can block nuclear radiation, even a piece of paper. Not all nuclear radiation needs to be blocked by lead.

Lead is mainly used to block gamma rays (γ rays), which are high-energy rays that belong to the category of electromagnetic waves. When it comes into contact with atoms, it can easily cause the electrons of the atoms to gain energy and run away. , this process is called ionization. Lead has a high atomic density and a high atomic number (which means it has a lot of electrons), so lead becomes a good barrier to gamma rays and is very suitable for scattering gamma rays or X-rays. , to prevent them from harming the human body.

But gamma rays are not the only type of nuclear radiation. There are other types of nuclear radiation. Some of these nuclear radiations can be blocked with a piece of paper, but others need to be very thick. of cement rather than lead. Because lead doesn't work well at this time.

To understand why this is, we need to know more or less what nuclear radiation is. Then you need a little more patience to read the following words.

What exactly is nuclear radiation?

Illustration: Nuclear radiation occurs during the decay of atoms, when heavy elements spontaneously transform into relatively lighter elements.

Until about 100 years ago, physicists accidentally discovered that certain elements were unstable and magically changed from one element to another, which was like a scientific version of "alchemy." Of course it's not from brass to gold, on the contrary it's from "gold" to "brass"! The pattern of this change is always from heavier atoms of elements to atoms of lighter elements! That’s why I said this change is from gold to brass, because gold atoms are heavier than copper atoms. Of course, don’t worry about the gold bars, gold bricks, rings, and gold earrings at home. They are very stable and will not undergo this elemental change. Of course, no nuclear radiation harmful to humans will be released.

Nuclear radiation is the process of changing heavy elements into lighter elements, which releases energy and particles. These energy and particles constitute nuclear radiation.

Elements with this property are also called radioactive elements. The changes that occur in radioactive elements are called radioactive decay. The best example of this element is uranium, which is the heaviest naturally occurring radioactive element. All elements heavier than uranium are unstable and radioactive.

Radioactive decay is a natural process. Atoms of a radioactive isotope will spontaneously decay into another element through one of three common processes:

During this process, four different types of radiation are produced:

First, The natural decay of radioactive atoms is part of nature, so they are "natural", but all radioactive elements are potentially dangerous to living things. Alpha particles, beta particles, neutrons, and gamma rays are all called ionizing radiation. This is because when they collide with atoms, they can knock away the electrons surrounding the nucleus, and the electrons run away. This process is called Being ionized is like having your wife run away. This will mess up our cells, causing genetic mutations or direct death.

How to block nuclear radiation

Alpha particles are very large, and their essence is helium nuclei moving at high speed, which makes them easy to block. In fact, only a piece of paper is needed Just a few centimeters of air is enough to block it. If it loses its kinetic energy, it loses its ability to harm the human body. Therefore, nuclear radiation that only produces alpha particles has almost no effect on the human body as long as you stay a little away from it.

Illustration: Particles cannot penetrate even a piece of paper, nor can they penetrate several centimeters of air.

Image: It’s because this thing is very safe. Therefore, the most commonly used smoke alarm uses a radioactive isotope americium 241 that can only release alpha particles. The alpha particles it produces can ionize the air. These ionized air are attracted by the positive and negative electrodes and hit the positive and negative electrodes. A weak current is generated. If smoke enters the ionization chamber, it will neutralize the ionized air. If the current drops, the smoke alarm will start to sound an alarm.

But if you inhale or eat such radioactive elements, you are seeking death. At this time, high-speed alpha particles will directly attack you from the body, and you may suffer from cancer as a result. The most notorious element is radioactive radon, which is a gas. After inhaling it, the alpha particles it releases directly bombard your lung cells, which may cause lung cancer. For non-smokers who develop lung cancer, radon may be a potential cause of lung cancer. the culprit. But some places still use radioactive radon springs as a selling point to attract tourists and welcome everyone to take a bath. In my opinion, this is seeking death.

The essence of beta particles is high-energy electrons. They are much smaller than particles, so they are more penetrating. However, electrons are still physical subatomic particles after all, so use a piece of aluminum foil or resin to Glass is enough to block them. In fact, the old and traditional TV screens in the past were developed by bombarding phosphors with high-speed electrons, which is considered artificial nuclear radiation. However, apart from damaging eyesight, traditional TVs have no direct impact on human health. As for being made an idiot by TV advertisements, watching TV plus fried chicken and beer, and becoming a disaccharide patient, it has no direct relationship with high-speed electronics itself. But similarly, if you eat or inhale radioactive isotopes that release beta particles, you are really seeking death.

The ranges of gamma rays and X-rays overlap, but to put it simply they are high-energy X-rays, which are far more penetrating than alpha particles and beta particles. In this case, lead needs to be used to block them.

Illustration: Nuclear fission caused by neutrons is the principle behind the operation of atomic bombs and current nuclear power plants. During this process, the fissioning atoms will release more neutrons. If the conditions are right, the fission will continue continuously.

Since neutrons lack charge, high-speed neutrons are very penetrating. The best way to block high-speed neutrons is to block them with extremely thick layers of concrete or liquids such as water or fuel oil. Current nuclear power plants use neutrons to hit the nuclei of heavy elements to achieve nuclear fission and release energy. The only way to prevent these high-energy neutrons from causing biological hazards is to build layers of water, oil and thick concrete.

Illustration: Three options for blocking high-energy fast neutrons.

1. First block with cadmium board, then shield with lead, and finally use aqueous solution containing boric acid

2. First block with cadmium board, then shield with lead, and finally block with concrete

3. First block with water, and then block with cadmium board to solve the problem. This is the simplest and cheapest solution.

Illustration: China’s third-generation large-scale commercial pressurized water reactor nuclear power station, a nuclear reactor immersed in high-pressure water.

During the Cold War, the United States and the Soviet Union once thought about developing neutron bombs (a small, low-yield hydrogen bomb). This nuclear bomb relied on a large number of high-speed neutrons and gamma rays to kill armed personnel in armor. It is the best choice for large-scale destruction of tanks and armored fighting vehicle groups.

Illustration: Neutron bomb test

The lethal range of neutron bombs far exceeds that of other weapons. Additionally, neutrons interact with armor and can render it so radioactive that it becomes temporarily unusable (usually 24-48 hours). For example, the M-1 tank armor includes depleted uranium, which can undergo rapid fission and become highly radioactive after being bombarded with neutrons.

Illustration: A slogan from the anti-nuclear war movement, opposing the development of a new nuclear weapon, the neutron bomb. The first neutron bomb was added to the U.S. arsenal in 1974.

All energy in the world is expressed through electromagnetic waves. Nuclear radiation is also a kind of electromagnetic wave. It is produced by the nuclear change of atoms and mainly includes three types of rays: α, β, and γ.

How can we block these rays?

In fact, any object can be used, but the blocking ability is different. For example, the shielding effect of a 1mm lead plate is equal to that of a 6mm iron plate, which is also equal to that of a 12cm thick solid brick.

The outer radiation shield of the nuclear power plant is not made of lead, but only concrete. As long as it is thick enough, any rays will be blocked no matter how strong their penetrating ability is.

Why are the rays blocked?

All matter is composed of atoms. When photons representing radiation energy pass through the "atomic array" of matter, they will be absorbed by these atoms. This process has three effects: photoelectric effect, CommScope Dayton effect, electron pair effect.

Briefly explain these three effects:

Photoelectric effect: Photons transfer energy to electrons outside the nucleus and disappear themselves;

Compton effect: When a photon collides with an electron, part of the energy is transferred to the electron, causing it to become a recoil electron, and the energy and propagation direction of the photon itself will change;

Electron pair effect: When the photon passes through an atom, it is absorbed by the nucleus Attracted by the Coulomb force, it was converted into a positron and a negative electron, and were quickly annihilated.

So why lead?

Because the density of lead is high, that is, the number of protons and electrons in the atoms inside lead is dense enough, making it more difficult to pass through.

Then why not other denser substances?

Other high-density substances are either very difficult to obtain or very precious (such as gold). In comparison, lead is already the most ideal choice.

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Lead shielding refers to the use of lead as a form of radiation protection to reduce the effective dose to a person or object. Because of its high density and atomic number, lead can effectively attenuate certain types of radiation. In principle, it is effective in shielding gamma rays and x-rays.

Lead's high density results from a combination of its high atomic mass and the relatively small size of its bond lengths and atomic radii. A high atomic mass means more electrons are needed to maintain a neutral charge and a small atomic radius combined with a small length means that many atoms can be assembled into a specific lead structure. Because of lead's density and large number of electrons, it is ideal for scattering x-rays and gamma rays. These rays form photons, a type of boson that are given strong penetrating properties when they come into contact with electrons. Without lead shielding, electrons in the body are affected, which can damage the body's DNA and cause cancer. When radiation tries to pass through the lead, the lead's electrons absorb and scatter the energy. Eventually, however, lead degrades from the energy to which it is exposed. However, lead is not effective against all types of radiation. High-energy electrons (including neutron radiation) may cause Bremsstrahlung radiation, which is potentially more dangerous to tissues than raw radiation.

Additionally, lead is not a particularly effective absorber of neutron radiation.

Lead is used in shielding for X-ray machines, nuclear power plants, nuclear laboratories, military equipment and other places where radiation may be encountered. There are many types of shielding that are used both to protect people and to shield equipment and experiments. Personal protection includes lead clothing (such as X-ray protective clothing used during dental procedures), protective shields, and lead gloves. Laboratory equipment also has various shielding devices, including structures composed of lead blocks and thick containers used to store and transport radioactive samples.

It is suspected that it will be blocked! Is it because he was detained? This science is rigorous enough