Shulou(Shulou.com)11/24 Report--

After Japan discharged nuclear sewage into the sea, people not only grabbed salt, but also grabbed Geiger counters. The Geiger counter is a nuclear detector that can detect different types of nuclear radiation, such as alpha particles, beta particles, gamma radiation and, in some cases, neutrons. The principle on which this Geiger counter is based is very interesting, but before we go any further, let's discuss the structure of this counter.

As shown in the figure above, this is the general structure of a Geiger counter. The structure is mainly composed of a Geiger tube, which is actually a hollow metal cylinder and contains some kind of gas medium. The gas medium usually consists of some inert gas (such as argon) and other alcohols.

Now, this metal cylinder is connected to the negative pole of a very high voltage battery, so it acts as a cathode. Through the center of the cylinder, there is a metal electrode made of tungsten, which is connected to the load resistance and again to the positive pole of the same battery. The load resistor is also connected to an electronic device that can detect the voltage drop occurring on the resistor and count it.

So how does the device count nuclear radiation? When nuclear radiation enters the gas medium in the Geiger tube, it causes ionization. What is ionization? When some external nuclear particles, such as alpha particles, enter the material medium, it collides with the molecule of the material and transfers energy to it. The outermost electrons of these molecules or atoms absorb some energy, and if the energy is large enough, these electrons will escape, producing a positive ion and a free electron.

We can see that the central tungsten rod acts as the anode and the metal cylinder acts as the cathode. When connected to a high-voltage battery, a strong electric field is generated between them. When these positive ions and free electrons are produced by some external nuclear particles, they are affected by the external electric field: the electrons accelerate to the anode and the positive ions accelerate to the cathode.

What is happening now is that once the electron is accelerated to a very high speed, it will also collide with gaseous molecules located in other locations, and the electron can further induce secondary ionization. Therefore, we will get a free electron induced by nuclear particles and an electron produced by the secondary ionization of the electron. But things don't end like this, and they continue to induce ionization, eventually creating a chain reaction or avalanche effect that causes a lot of ionization along the path before reaching the central electrode, a phenomenon known as the Townsend avalanche.

Once all these electrons reach the center, they will be absorbed by the anode, and then they will move along the circuit and cause a voltage drop on the load. The electronic devices on the load will be detected and counted. Now that these electrons have completed their mission, they will continue to move along the circuit and combine with the positive ions gathered on the metal surface to produce neutral molecules, thus restoring the entire device to its original state. Therefore, the whole process caused by the existence of a nuclear particle will produce a count.

From the ionization caused by nuclear particles to the Townsend avalanche to the recombination of electrons with positive ions, this process takes some time. In the process, the nuclear detector cannot detect more external particles, so during this time, the detector crashes a bit. As long as this process is not completed, it cannot detect other nuclear particles, so this period of time is called dead time. The dead time of a Geiger tube is usually about 200 to 400 microseconds.

In addition, this process may lead to photon emission when electrons complete the circuit and recombine with positive ions. The energy of this photon may be high enough to cause another avalanche effect. We don't want that to happen, because the count is done, and we only want the count related to the external nuclear particles.

Therefore, in order to prevent this from happening, some measures need to be taken, which are called quenching. One of the methods is chemical quenching, in which we mix the gaseous medium with some other organic compounds, such as alcohol. In this case, we have 90% argon and 10% alcohol. The role of alcohol is that whenever electrons recombine with positive ions, instead of emitting excess energy in the form of photons, excess energy is usually released to nearby alcohol absorption in the form of vibration or rotation.

This article comes from the official account of Wechat: Vientiane experience (ID:UR4351), author: Eugene Wang

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.