neutron

Examples of neutron in the following topics:

• Nuclear Reactors

  • A portion of these neutrons may later be absorbed by other fissile atoms and trigger further fission events, which release more neutrons, and so on.
  • This chain reaction can be controlled using neutron poisons and neutron moderators to change the portion of neutrons that can cause more fissions.
  • In a nuclear reactor, the neutron population at any instant is a function of the rate of neutron production and the rate of neutron loss.
  • Another neutron leaves the system without being absorbed.
  • However, one neutron does collide with an atom of uranium-235, which then splits and releases two neutrons and more binding energy.

• Nuclear Stability

  • In nuclear physics, stability of an atom's nucleus depends on the number of protons and neutrons it contains.
  • This force is offset by the nuclear force, which attracts protons and neutrons.
  • To an extent, nuclei become more stable with increasing neutron number.
  • An example is nickel-48, which has 28 protons and 20 neutrons, both of which are magic numbers.
  • Stability of isotopes is shown as a function of proton and neutron numbers.

• Nuclear Fission

  • Nuclear fission occurs when an atom splits into two or more smaller atoms, most often the as the result of neutron bombardment.
  • In order to initiate fission, a high-energy neutron is directed towards a nucleus, such as 235U.
  • While nuclear fission can occur without this neutron bombardment, in what would be termed spontaneous fission, this is a rare occurrence; most fission reactions, especially those utilized for energy and weaponry, occur via neutron bombardment.
  • If an element can be induced to undergo fission via neutron bombardment, it is said to be fissile .
  • There are also ways to modulate the chain reaction by soaking up the neutrons.

• Atomic Number and Mass Number

  • The atomic number is the number of protons in an element, while the mass number is the number of protons plus the number of neutrons.
  • The number of neutrons can vary to produce isotopes, which are atoms of the same element that have different numbers of neutrons.
  • An element's mass number (A) is the sum of the number of protons and the number of neutrons.
  • Protons and neutrons both weigh about one atomic mass unit or amu.
  • For example, the atomic mass of chlorine (Cl) is 35.45 amu because chlorine is composed of several isotopes, some (the majority) with an atomic mass of 35 amu (17 protons and 18 neutrons) and some with an atomic mass of 37 amu (17 protons and 20 neutrons).

• Isotopes of Hydrogen

  • The nucleus consists of a proton and four neutrons.
  • One tritium nucleus captures two neutrons from the other, becoming a nucleus with one proton and four neutrons.
  • It consists of one proton and five neutrons.
  • 7H consists of one proton and six neutrons.
  • Unique among all stable isotopes, it has no neutrons.

• Average Atomic Mass

  • Atoms of the same element can, however, have differing numbers of neutrons in their nucleus.
  • This is because each proton and each neutron weigh one atomic mass unit (amu).
  • Chlorine consists of two major isotopes, one with 18 neutrons (75.77 percent of natural chlorine atoms) and one with 20 neutrons (24.23 percent of natural chlorine atoms).
  • Stylized lithium-7 atom: 3 protons (red), 4 neutrons (blue), and 3 electrons (black).
  • (Lithium also has another, rarer isotope with only 2 neutrons. )

• Overview of Atomic Structure

  • Atoms consist of three basic particles: protons, electrons, and neutrons.
  • The hydrogen atom (H) contains only one proton, one electron, and no neutrons.
  • Protons and neutrons have approximately the same mass, about 1.67 × 10-24 grams.
  • Both protons and neutrons have a mass of 1 amu and are found in the nucleus.
  • However, protons have a charge of +1, and neutrons are uncharged.

• Isotopes

  • Isotopes are various forms of an element that have the same number of protons, but a different number of neutrons.
  • Isotopes are various forms of an element that have the same number of protons but a different number of neutrons.
  • Isotopes are defined first by their element and then by the sum of the protons and neutrons present.
  • Carbon-12 (or 12C) contains six protons, six neutrons, and six electrons; therefore, it has a mass number of 12 amu (six protons and six neutrons).
  • Carbon-14 (or 14C) contains six protons, eight neutrons, and six electrons; its atomic mass is 14 amu (six protons and eight neutrons).

• The Atomic Bomb

  • When a free neutron hits the nucleus of a fissile atom like uranium-235 (235U), the uranium splits into two smaller atoms called fission fragments, plus more neutrons.
  • Fission can be self-sustaining because it produces more neutrons with the speed required to cause new fissions.
  • The inherent radioactivity of uranium will then release a neutron, which will bombard another atom of 235U to produce the unstable uranium-236, which undergoes fission, releases further neutrons, and continues the process.The uranium atom can split any one of dozens of different ways, as long as the atomic weights add up to 236 (uranium plus the extra neutron).
  • The following equation shows one possible split, namely into strontium-95 (95Sr), xenon-139 (139Xe), and two neutrons (n), plus energy:

• Nuclear Binding Energy and Mass Defect

  • Nuclear binding energy is the energy required to split a nucleus of an atom into its component parts: protons and neutrons, or, collectively, the nucleons.
  • The binding energy of nuclei is always a positive number, since all nuclei require net energy to separate them into individual protons and neutrons.
  • The actual mass is always less than the sum of the individual masses of the constituent protons and neutrons because energy is removed when when the nucleus is formed.
  • The strong force is what holds protons and neutrons together at short distances.
  • U-235 has 92 protons, 143 neutrons, and has an observed mass of 235.04393 amu.