Particle Physics For All

    Table of contents  THE SURVIVAL  OF A  NEUTRON View my previous article here - Weak Interaction View the next article here - Cosmic Rays ----------------------------------------- (In this article, and in several others, u means up quark and d means down quark. Similarly, u with a bar on top means anti-up quark and d with a bar on top means anti-down quark.) Let us consider this puzzle: all of the atoms that make up the Universe (apart from hydrogen atoms) contain neutrons as well as protons in their nuclei. Yet free neutrons (that is, those not inside nuclei) undergo beta decay with a half-life of about 10 minutes. In the early Universe, soon after the Big Bang and before atoms formed, there are believed to have existed equal numbers of protons and neutrons. So why didn’t the neutrons all decay at that time, leaving a Universe made only of hydrogen? What do you think? 🤔 Apart from hydrogen, nuclei made solely of protons cannot exist . Neutrons are necessary...

  Table of contents  WEAK INTERACTION View my previous article here - Beta Decay View the next article here - The Survival of a Neutron ----------------------------------------- Weak interactions manifest themselves as reactions, or decays, in which some particles may disappear, while others appear. No structure is bound together by a ‘weak force’, but weak interactions are vital for understanding the world around us. Weak interactions were involved in most of the reactions in the very early Universe by which particles changed from one sort to another. They are therefore largely responsible for the overall mixture of particles from which the current Universe is made. The most common example of a weak interaction is beta-decay and, as you saw earlier, there are three related processes, each of which is a different type of beta-decay. In each of these three processes, the nucleus involved will change from one type of element to another, as a result of either increasing or decre...

      Table of contents  BETA DECAY View my previous article here - Strong Interaction View the next article here - Weak Interaction ----------------------------------------- (In this article, and in several others, u means up quark and d means down quark. Similarly, u with a bar on top means anti-up quark and d with a bar on top means anti-down quark.) A particular type of radioactivity is known as beta-decay, which occurs in three forms known as beta-minus decay, beta-plus decay and electron capture . In each form, protons convert into neutrons, or vice-versa.  For instance, in beta-minus decay, one of the neutrons in a nucleus is converted into a proton with the emission of an electron and an electron antineutrino . This process may be written as: As a neutron has the quark composition (udd) and a proton has the quark composition (uud), at the level of individual quarks, a beta-minus decay must involve a down quark converting into an up quark as follows: This...

  Table of contents  STRONG INTERACTION View my previous article here - Higgs Field with a Touch of Time Travel View the next article here - Beta Decay ----------------------------------------- As discussed earlier, the force that binds quarks together inside nucleons (i.e. neutrons and protons) is known as the strong interaction. This force has a very short range but is the strongest . It operates only within the size of a nucleon. When two up quarks and a down quark form a proton, or when two down quarks and an up quark form a neutron, the strong interaction has done its job, in much the same way that the electric interaction between a proton and an electron does its job by forming a hydrogen atom. In addition, there is a residual strong interaction between nucleons , which you can imagine as ‘leaking out' of the individual protons and neutrons. This is sufficient to bind them together in nuclei and is similar in nature to the residual electromagnetic interactions betw...