Neutrons are small subatomic particles that, along with protons, make up the nucleus of one corn.
While the number of protons determines the element of an atom, the number of neutrons in the nucleus can vary, resulting in different isotopes of an element. For example, normal hydrogen has one proton and no neutrons, but hydrogen isotopes deuterium and tritium have one and two neutrons respectively besides the proton.
Neutrons are composite particles made up of three smaller elementary particles called neutrons subatomic particleswhich was brought together by Sheer force. Specifically, a neutron has one “up” and two “down” quarks. Particles made up of three quarks are called baryons, and thus baryons contribute to all “visible” baryonic matter in Universe.
Related: What is the theory of everything?
Who discovered neutrons?
After, after Ernest Rutherford (With help from Ernest Marsden And the Hans GeigerThe gold leaf experiment) discovered in 1911 that atoms have a nucleus, then nine years later discovered that atomic nuclei are made, at least in part, by protons, and the discovery of the neutron in 1932 by James Chadwick followed normally.
The idea that there is something else in the nucleus of an atom came from the fact that the number of protons does not match the atomic weight of the atom. For example, an oxygen atom has 8 protons, but its atomic weight is 16, which indicates that it contains 8 more particles. However, these fuzzy particles must be electrically neutral, because atoms usually do not have an overall electric charge (the negative charge of electrons cancels out the positive charge of protons).
At that time, many scientists were experimenting alpha particles, which is another name for a helium nucleus, bombarding a material made of the element beryllium with an alpha particle current. When the alpha particles collided with the beryllium atoms, they produced fuzzy particles that seemed to originate from within the beryllium atoms. Chadwick took these experiments a step further and saw that when the fuzzy particles hit a target made of paraffin wax, they would release loose protons with high energy. In order to do this, Chadwick calculated, the mystery particle would have to have roughly the same mass as a proton. Chadwick declared this mysterious particle to be the neutron, and in 1935 he won the Nobel Prize for its discovery.
Neutrons: mass and charge
Neutrons, as their name suggests, are electrically neutral, so they have no charge. Its mass is 1.008 times that of a proton — in other words, it’s about 0.1% heavier.
Neutrons do not like to exist on their own outside the nucleus. The strong force binding energy between it and the protons in the nucleus keeps it stable, but when it comes out on its own it undergoes beta decay After about 15 minutes, it turns into a proton, an electron, and an antineutrino.
Albert Einstein, in his famous equation E=mc2, he said that mass and energy are equivalent. Although the masses of a neutron and a proton are slightly different, this slight difference means that a neutron has more mass, and therefore more energy, than the mass of a proton and electron combined. For this reason, when a neutron decays, it produces a proton and an electron.
Isotopes and radioactivity
An isotope is a variation of an element that has a higher number of neutrons. For example, at the top of this article, we gave an example of hydrogen isotopes, deuterium and tritium, which have 1 and 2 extra neutrons, respectively. Some isotopes are stable like deuterium. Others are unstable and inevitably undergo radioactive decay. Tritium is unstable – it has a half-life of about 12 years (the half-life is the time it takes on average for half of a given amount of an isotope such as tritium to decay), but other isotopes decay much more quickly, in a matter of minutes, seconds, or even parts from the second.
Neutrons are also essential tools in nuclear reactions, particularly when triggering a chain reaction. Neutrons absorbed by atomic nuclei create unstable isotopes that then undergo nuclear fission (It is divided into two smaller daughter nuclei of other elements). For example, when uranium absorbs an additional 235 neutrons, it becomes unstable and decays, releasing energy in the process.
Neutrons are also instrumental in the creation of heavy elements in massive stars, through a mechanism known as the r process, where “r” means “rapid.” This process was first detailed in the famous Nobel Prize-winning B2FH paper before Margaret And the Jeffrey BurbidgeAnd the William Fowler And the Fred Howell which described the origins of the elements through stellar nucleosynthesis – the formation of elements by stars.
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stars Such as the sun Elements can be produced from oxygen, nitrogen and carbon through Nuclear fusion Interactions. more huge stars It can go on and create shells of increasingly heavier elements all the way down to Iron 56 in the star’s core. At this point, the reactions require more energy to be put into them to fuse elements heavier than iron than are already produced from those reactions, so these reactions stop, energy production stops and the core of the star collapses, leading to Supernova. In an extremely violent supernova explosion, conditions can become severe enough to release many free neutrons in a short period of time.
In a supernova explosion, the atomic nuclei are then able to sweep away all of these free neutrons before they all decay (which is why they are called fast), inducing r nucleosynthesis. Once the nuclei are filled with neutrons they become unstable and undergo beta decay, converting those excess neutrons into protons. Adding these protons changes the type of element the nucleus represents, hence it is a method Create new heavy elements Like gold, platinum and other precious metals. The gold in your jewelry was made billions of years ago by the rapid capture of neutrons in a supernova!
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As we’ve seen, neutrons can survive outside atomic nuclei only in the most extreme conditions, and there are very few places in the universe more extreme than Neutron stars. As their name suggests, these are objects made almost entirely of neutrons.
Neutron stars are what remains of a star’s core after its core collapsed and exploded as a supernova. The explosion may have carried away the outer layers of the star, but the shrinking core is still intact.
With no nuclear reactions to generate energy to counteract gravity, the core’s mass is so great that it undergoes a catastrophic gravitational collapse in which the gravitational pressure is great enough that protons and electrons can overcome the electrostatic force between them and smash together, fusing to form neutrons in a type of reverse beta decay. . Almost all of the atoms in the core turn into neutrons, which is why we call the result a neutron star. It’s small, only 6-12 miles (10-20 km) across, yet it packs in the entire mass of a dead star’s core.
The most massive neutron star ever found has mass 2.35 times Bigger than our Sun, all crammed into a tiny volume. If you could take a spoonful of material from the surface of a neutron star, that spoon would weigh as much as a mountain on Earth!
The mergers of binary neutron stars, which can be detected as kilonovas and via their gravitational waves, are also sites of nucleosynthesis in the prolific r process. The kilonova From two merging binary stars, a gravitational wave burst was launched GW 170,817 16,000 times the mass of Earth was produced in the form of heavy elements by the r process, including the equivalent of ten Earth masses gold and platinumwhich is extraordinary!
Learn more about neutrons with US Department of Energy (Opens in a new tab). Find out how neutrons are used in experiments studying condensed matter UK Science Technology Facilities Council (Opens in a new tab). Read the The famous B2FH paper (Opens in a new tab) On the formation of elements inside stars with the help of neutron capture.
Particle Physics, by Brian R Martin (2011, One World Publications) (Opens in a new tab)
The Cambridge Encyclopedia of Stars, by James R. calr (2006, Cambridge University Press) (Opens in a new tab):
Collins Online Associated Dictionary of Physics (2007, Collins) (Opens in a new tab)
This month in the history of physics. American Physical Society Websites, APS News, Volume 16, Issue 5. Accessed December 1, 2022, from https://www.aps.org/publications/apsnews/200705/physicshistory.cfm (Opens in a new tab)
neutron decay. direct science. Accessed December 1, 2022, from https://www.sciencedirect.com/topics/physics-and-astronomy/neutron-decay (Opens in a new tab)
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