The story of decaying particles and immortal (!) Protons

 

The fundamental particles of the Standard Model are the building blocks of nature. Our entire world is made up of them. They combine with each other to create all kinds of things we know and don't know, seen and unseen. The whole thing is a lot like building all kinds of fun things with the small pieces of a toy Lego set. But such a model of the formation of the universe can be said to be more or less true only for up quarks, down quarks and electrons. Such a model does not work at all for the rest of the elementary particles. Because, they don't have enough time to make something big by pairing up like this. Before that they decay. That is, they exist for a very short time. Retention times may vary from particle to particle.

Take top quarks. They decay after only 0.000000000000000000001 seconds (10-25). On the other hand, free neutrons can survive for about 882 seconds. However, this length of particle lifetime does not apply equally to every particle. This is actually the average value. That is, if you observe many free neutrons simultaneously for 882 seconds, you will see that not all of them decay. About two-thirds of the corrosion process will occur. And the rest will remain in good health. It is impossible to say precisely when and which particle will undergo the decay process.

Before going deeper into the discussion, let's clear up a confusion first. What does particle decay actually mean? Many people mean to break down or break down. An example of this is the spontaneous fission of the nucleus of a radioactive uranium atom into two smaller nuclei. Again, the process of breaking up the nuclei by hitting them with something from outside is often referred to as erosion. But this is not the definition of decay process for particle physicists. For them the decay process is actually a form of transformation. In this one particle is completely transformed into another particle. Considering the decay process simply as a breakdown leaves a good deal of trouble with the decay of elementary particles. Because elementary particles are the smallest unit of nature. Nothing is gained by breaking them. As a result, it is not possible to decay them in the traditional sense. So it is more logical to call the decay process a form of transformation. As the top quark decays through the weak interaction, they transform into bottom quarks and W bosons.

Various conditions

But why do particles decay? Have you ever thought? If we make fun of the answer, then we have to say, it happens because of the inertia of the particles. Particles are not interested in pruning at all. Therefore, if they can release the potential energy stored in themselves, they can survive. The less potential energy a particle has, the more balanced it is. For this reason, as soon as they get a chance, they release energy and try to reach a balanced state. And it is during this time that they transform or decay. That is, trying to achieve a balanced state by shaking the main lever behind the erosion process.

The corrosion process does not happen randomly. A number of conditions are met. As new particles are formed after the decay process, their mass must be less than the original particle. Any mass that is less available is converted into energy. They manifest themselves as the kinetic energy of newly created particles. Another important condition of the decay process is the conservation of quantum numbers. That is, the sum of quantum numbers must remain the same before and after the decay process.

Let's give an example of how conditions work. As we know, neutrons or protons are not elementary particles. They are made up of up quarks and down quarks. Neutrons have one up quark and two down quarks. Protons, on the other hand, are composed of two up quarks and one down quark. Neutrons can be converted into protons through the decay process. At this time, a down quark between them becomes an up quark through the weak interaction. An electron and an antineutrino are additionally produced in the decay process.

At the end of the neutron decay process, the resulting protons, electrons and antineutrinos have a combined mass less than the original particle neutron. They are released with kinetic energy equal to the lost mass. That is, the first condition is fully satisfied. There is no scope for complaining about the second condition either. All quantum numbers are conserved in this process. Take the case of electrocution. The elementary particle neutron has zero charge. On the other hand, the charges of proton, electron and antineutrino are +1, -1 and 0 respectively. That is, their combined charge is also equal to that of the original particle. As a result, the charge is completely preserved before and after the corrosion process. The same happens for the rest of the quantum numbers. Provided all conditions are met, both free neutrons and bound neutrons inside the atom can participate in this decay process.

Immortal protons and a new type of star

Although the decay of neutrons is not blocked by the boundary conditions, the decay process of free protons is correctly detected. Free neutrons can easily convert to protons, but not vice versa. That is, neutrons cannot be obtained from free protons. Subject to the conditions described above. For protons to convert to neutrons, an up quark must become a down quark. But the problem is, the down quark has slightly more mass than the up quark. Therefore, the decay process violates the condition of obtaining particles of relatively lighter mass than the original particles. In fact protons are the least massive baryon particles (composite particles made of at least three quarks). They contain the lowest potential energy. As a result, they are in the highest equilibrium state among baryon particles. So the free protons have no chance to transform into other particles through the decay process. They remain unaltered forever.

However, many physicists believe that protons also decay. But its speed is unimaginably slow. A single proton particle can take about 1034 years to decay. How big this number is, surely does not need to be re-stated. The current age of our universe is only around 1.38×1010 years. That is, not even half of the lifetime of protons in the universe has passed yet. However, no one has yet found conclusive evidence for the decay process of protons. So for the time being, assuming them as immortals will not be much wrong.

If protons are truly immortal, then in the distant future a whole new type of star will appear in the universe. Its name is iron star. Just by hearing the name, you can understand that all of them will be made of iron. Not only will iron-made stars appear, but in an unimaginably slow process, all the elements in the universe will be transformed into iron at once. Why? As I said earlier, at the root of the erosion process is achieving balance. Iron is the most balanced element in nature. Therefore, if protons do not decay, all elements will be transformed into iron at some point in the evolution of time. Elements that are more massive than iron will transform through nuclear fission and alpha decay processes. On the other hand, elements less massive than iron will undergo cold fusion.

A strange process is this cold fusion. Let's give a light idea. In the process of fusion basically two smaller nuclei are joined together to form one larger nucleus. At this time, a lot of energy is released. Smaller nuclei must first be brought closer together for fusion to occur. This task is not easy at all. Because protons in nuclei repel each other. However, due to the high temperature and pressure in the center of the star, there is an opportunity for these nuclei to overcome the repulsive force. Fusion may occur as a result. This kind of fusion is called thermonuclear fusion.

In cold fusion the whole thing is completely different. It does not suffer from extreme temperatures or pressures. With the touch of a 'magic wand', the nuclei come together at normal temperature and pressure, fusion takes place. In scientific terms, this magic wand is called quantum tunneling. The probability of quantum tunneling occurring is very low but not absolutely zero. So it would take an incredible amount of time for the small nuclei to turn into iron step by step through cold fusion. Its numerical value is 103200 years. However, scientists do not know for sure whether cold fusion will actually happen. As they are not sure about proton's immortality. However, all stars in the universe will eventually become iron stars through cold fusion. At that time they will not emit any kind of light or radioactive rays. They can only be found by detecting the effect of gravity. Iron stars below the Chandrashekhar limit will become neutron stars after about 1010^26 years. And stars above this limit will directly turn into black holes. It is likely that all iron stars will eventually become black holes after 1010^76 years. Those who will eventually be destroyed by Hawking radiation radiation. Supermassive black holes also take only 10,100 years to decay through Hawking radiation. Therefore, iron stars will rule the universe for a time. And this will be possible only if the immortality of protons is ensured.

So what is the positive beta decay process?

Hearing about Immortal Protons surely raises a question in many people's minds. Especially those who know a bit about nuclear physics. The question is, if protons cannot participate in the decay process, then how does the positive beta decay process take place in the nucleus of an atom? We have already talked about this process several times. In this process a neutron, positron and neutrino are obtained from a proton.

In fact, the protons in the nucleus of the atom can actually participate in the decay process. Only free protons cannot. The binding energy or binding energy of the nucleus of the atom plays the main role behind this. It's a bit complicated. However, let's try to explain.

The attraction between the electromagnetic force and the strong nuclear force in the nucleus of an atom goes on forever. Positively charged protons tend to push each other away through the electromagnetic repulsion force. On the other hand, strong forces want to bind them together. In a balanced nucleus the two forces repel each other. As a result stability is maintained. If somehow a proton in the nucleus decays into a neutron, the effective electromagnetic repulsion force will decrease. As a result, less energy will be required to hold the protons and neutrons of the nucleus together. It is this energy that survives that allows the protons to participate in the decay process by being converted into mass according to the mass-energy equation. As a result, the first condition for the corrosion process mentioned above will no longer be violated. In the case of free protons, there is no such possibility of gaining mass. Hence they cannot participate in the decay process.

Author: Ishtiaq Hossain Chowdhury, Assistant Manager, Nuclear Power Plant Company Bangladesh Limited (NPCBL)

Source: Based on Quarky Quarky: A Cartoon Guide to the Fascinating Realm of Physics by Benjamin Varr, Boris Lamar and Rina Piccolo