What is Neutrons: Definition and 225 Discussions

The neutron is a subatomic particle, symbol n or n0, which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave similarly within the nucleus, and each has a mass of approximately one atomic mass unit, they are both referred to as nucleons. Their properties and interactions are described by nuclear physics.
The chemical properties of an atom are mostly determined by the configuration of electrons that orbit the atom's heavy nucleus. The electron configuration is determined by the charge of the nucleus, which is determined by the number of protons, or atomic number. The number of neutrons is the neutron number. Neutrons do not affect the electron configuration, but the sum of atomic and neutron numbers is the mass of the nucleus.
Atoms of a chemical element that differ only in neutron number are called isotopes. For example, carbon, with atomic number 6, has an abundant isotope carbon-12 with 6 neutrons and a rare isotope carbon-13 with 7 neutrons. Some elements occur in nature with only one stable isotope, such as fluorine. Other elements occur with many stable isotopes, such as tin with ten stable isotopes.
The properties of an atomic nucleus depend on both atomic and neutron numbers. With their positive charge, the protons within the nucleus are repelled by the long-range electromagnetic force, but the much stronger, but short-range, nuclear force binds the nucleons closely together. Neutrons are required for the stability of nuclei, with the exception of the single-proton hydrogen nucleus. Neutrons are produced copiously in nuclear fission and fusion. They are a primary contributor to the nucleosynthesis of chemical elements within stars through fission, fusion, and neutron capture processes.
The neutron is essential to the production of nuclear power. In the decade after the neutron was discovered by James Chadwick in 1932, neutrons were used to induce many different types of nuclear transmutations. With the discovery of nuclear fission in 1938, it was quickly realized that, if a fission event produced neutrons, each of these neutrons might cause further fission events, in a cascade known as a nuclear chain reaction. These events and findings led to the first self-sustaining nuclear reactor (Chicago Pile-1, 1942) and the first nuclear weapon (Trinity, 1945).
Free neutrons, while not directly ionizing atoms, cause ionizing radiation. So they can be a biological hazard, depending on dose. A small natural "neutron background" flux of free neutrons exists on Earth, caused by cosmic ray showers, and by the natural radioactivity of spontaneously fissionable elements in the Earth's crust. Dedicated neutron sources like neutron generators, research reactors and spallation sources produce free neutrons for use in irradiation and in neutron scattering experiments.

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  1. S

    Equation for neutrons in a nuclear reactor

    I am trying to solve a problem from Thorne and Blandford: Modern classical physics, chapter 3, problem 21: Neutron diffusion in nuclear reactor. I am struggling with how the equation, from which this should be calculated, should look like. I watched some videos where they did the derivation a...
  2. Phil App

    Termination of a nuclear reaction

    I have long pondered the question of whether it is possible to extinguish an ongoing atomic explosion. From a practical standpoint, it is certainly possible that currently it is a supernatural, if not impossible, task. However, from a theoretical standpoint, I cannot stop thinking about all...
  3. Hak

    I Impossibility of constructing a particle consisting of only neutrons and proton-neutron interaction

    Why can't we construct a particle consisting of only neutrons? Why are there nuclei of ##_2^3He## (2 protons and 1 neutron) and ##_2^4He## (2 protons and 2 neutrons) but there is no ##_2^{50}He##? Maybe a first approach might be that neutrons and protons interact with each other not through the...
  4. M

    FLUKA: Why Does Neutron Flux Increase When Passing Through a Moderator?

    I have been banging my head against this for a few weeks now; tweaking the simulation, adjusting my calculations, and searching around the web to try to find an answer. I can't post questions on CERN's Fluka help forum so this seemed like the best option. I really appreciate any help you can...
  5. J

    B What Are the Key Safety Concerns When Building a Fusor for Nuclear Fusion?

    Hi PF, I am new here. I'm trying to perform a risk assessment to enumerate, and then take steps to mitigate, the risks posed by building a fusor and performing nuclear fusion. The risks as I see it are: 1. Electrical hazards posed by the high voltage equipment 2. Potential fuel-air explosion...
  6. jianggong

    14MeV neutrons in MCNP interact with carbon without producing alpha

    14MeV neutrons in MCNP interact with carbon without producing alpha particles and protons, yes Questions about my cross section data? I've tried ENDFB8/B7.1, JEFF3.3, JENDL5, CENDL3.2 without any results, but if you use phys:n model, it looks like alpha particles will be produced, but it doesn't...
  7. S

    I Does antineutrino capture preferentially form neutrons?

    Besides the energetic preference (lower threshold, and more phase space above)? Antineutrino capture is a weak process, so it can and does change quark flavour. p+ν=n+e+ is actually uud+ν=udd+e+ that is u+ν=d+e+ But given enough energy (like cosmic ray neutrinos), do antineutrinos also get...
  8. F

    B Why don't neutrons bind into large out of control masses?

    I'm trying to understand why neutrons don't just continually bind into large masses. As I understand it proton binding in a nucleus is governed mostly by the strong nuclear force which attracts at close distance and electromagnet force that repels. So for protons to bind, they must have enough...
  9. Astronuc

    I Four neutrons form a transient isolated entity - a tetraneutron?

    I was reading another article when this headline from June 22 caught my attention. Collisions hint that four neutrons form a transient isolated entity https://www.nature.com/articles/d41586-022-01634-x An experiment firing helium-8 nuclei at a proton target has generated evidence that four...
  10. S

    I Magnetar Mystery: How Do Neutrons Generate a Magnetic Field?

    If a magnetar is a neutron star, how do the neutrons composing the star generate a magnetic field? A neutron has zero charge, so it generates no magnetic field.
  11. W

    I Can you tell the difference between two neutrons in an alpha particle?

    Can you tell the difference between two neutrons in an alpha particle? In one alpha particle, we know that the sum of the spins of two neutrons is zero. Can a neutron with upspin and a neutron with downspin be distinguished from each other? Or can't you tell because it's superimposed?
  12. elua0105

    How can I model both photons and neutrons with MCNP?

    Hello, I am a student who started studying MCNP. I'm not used to writing in English, so I'd appreciate it if you could understand even if there were grammatical errors in my thread. I want to check the energy of gamma rays from neutrons reacting with matter. So, I wrote this in the content of...
  13. j2mhall

    B Fusing Neutrons: Can It Lead to Cold Fusion?

    Hi Is it possible to get two neutrons to fuse together to form helium? If so, would it not make cold fusion possible?
  14. Mayan Fung

    A Interaction between neutrons and nuclei during scattering

    When we learn about the scattering of a particle, the context is usually a charge shooting towards a Coulomb potential. With some assumptions, we can derive the scattering cross-section pretty reasonably. Therefore, the scattering cross-section of different elements in X-ray spectroscopy is...
  15. A

    Creating stationary neutrons by colliding protons and electrons

    Lets say, in zero gravity space, you have an incredibly precise collider that slams protons and electrons into each other as perfectly as possible such that all momentum is canceled out and the resulting neutron has no velocity relative to the observer. As protons and electrons continue to...
  16. S

    How many neutrons are produced in nuclear fission?

    The nuclear fission reaction is: ##U_{92}^{235} + n^{1}_{0} \to Ba_{56}^{141} +Kr_{36}^{92} + 3 ~n^{1}_{0} ## I am not sure about the number of neutrons produced. Is it 2 or 3? 2 is from the number of neutrons on the RHS - number of neutron on LHS 3 is from the number of neutrons on RHS only...
  17. DrChinese

    Physicists Discover Neutrinos Just Little Italian Neutrons

    https://www.theonion.com/physicists-hail-major-breakthrough-after-discovering-ne-1844363984 "Confirming the search for the mysterious Godfather particle was finally over, physicists at the University of Chicago hailed what they call a major breakthrough Monday after discovering neutrinos are...
  18. F

    B Neutrons, fertile, fissile and fissioning

    How do you turn fertile material to fissile without fissioning when they are afterwards are hit with neutrons again?
  19. S

    B Gravity & Neutrons: Could They be Connected?

    Could the mysterious force of gravity be the force of neutrons being attracted to each other? (There is nothing to suggest this it was a random thought that occurred to me this morning.)
  20. J

    I Neutrons, fusion and efficiency

    Regarding electricity generation from a fusion reactor: I can't seem to find any discussion about the percentage of fusion product neutrons that can be realistically caught in the thermal blanket to utilise the energy they carry from the fusion reaction. The neutrons from fusion have to be...
  21. B

    I Neutrons and neutron interactions

    Does one neutron or more than one make different when they interact with the nuclei? what is the result that could happen if one neutron or neutrons hit the nuclei? I'm not sure but I think the neutrons are the most confusing particles to deal with. I wish you guys can help me Thanks
  22. S

    I Interaction of Neutrons with Matter

    For Elastic neutron interactions with matter, they mentioned that the neutron will collide with atomic nucleus and the recoil nuclei quickly become ion pairs and loose energy through excitation and ionization. How does this nuclei become ion pair? It is when the neutron interact with it and...
  23. J

    Fusion power generation: percentage of neutrons expected to be caught?

    Surely the real efficiency of Fusion power is the percentage of neutrons that can be caught to extract kinetic energy from. I am assuming it is the neutron that is carrying the nuclear energy that can be recovered from the fusion reaction. Now I'm pretty sure neutrons cannot be focused, so the...
  24. B

    I Why is there a limit to the number of neutrons in a nucleus?

    Hello! Why can't we have as many neutrons as we want inside a nucleus? I understand that for protons you have the Coulomb repulsion, but what leads to an increase of energy when adding more neutrons (which in turns lead to beta decay or fission)?
  25. Javier Lopez

    I Why there is a general lack of neutrons in the Earth?

    I where looking for elements that can absorpt neutrons without generating radioactive materials, and I found that most of them in Earth are suitable. I found that could work: C, O, Si, S, N, H The most common isotopes can receive one or two neutrons being stable, but if a neutron would be...
  26. R

    A Need help with the reaction of neutrons and electrons

    Please let me know if the following reaction is possible for high energy electrons colliding with neutrons or neutron-rich nuclei: n+e^{-}\to \Delta^{-}+\nu_e.\tag{1} If it is forbidden for some conservation law or for some other reason, please give me an explanation why. This reaction is...
  27. maxd23

    A Nuclear Reaction: Determining the velocity of neutrons

    Homework Statement Fission, the process that supplies energy in nuclear power plants, occurs when a heavy nucleus is split into two medium-sized nuclei. One such reaction occurs when a neutron colliding with a 235U (uranium) nucleus splits that nucleus into a 141Ba (barium) nucleus and a 92Kr...
  28. J

    I If we teleport 1mm^3 of a neutron star outside it what hapens?

    if we teleport a small amount of millimeter cube of a neutron star outside it, will it remain still as a very dense heavy neutron clump or will it revert back into its components (iron) or will the neutron destabilize and turn into cosmic radiation of neutrons which then turn back into hydrogen?
  29. T

    Calculations based on Neutrons in a Gravitational field

    Hello everybody! I am TanX. I was reading about neutrons in a gravitational field, which was based on the Grenoble experiment ( Institute Laue - Langevin ) conducted in 2002. I have put a link down here to the research papers below ( Refer to page number 17 in the booklet for the important...
  30. O

    I Number of fission neutrons in ENSDF

    I use ENSDF to get information about gamma energies and emission abundances for various nuclides. Now I need to know data about Cf-252, in particular the abundance of spontaneous fission and the average number of emitted neutrons per fission. Where can I find this information there? Just as a...
  31. Bikash Kumar Das

    B Meson particles emitted from neutrons and protons

    Neutron and proton are themselves not composed of mesons, then how do they emit these particles inside the nucleus?
  32. Gene Naden

    I Pion decaying to two neutrons demonstrates odd parity

    Does anyone have a reference to a good explanation of this experiment. I am looking at https://quantummechanics.ucsd.edu/ph130a/130_notes/node323.html I am unable to comprehend the reasoning by which it determines the parity of the two neutrons in the final state. Particularly when it says the...
  33. Pickled_Gorilla

    Neutrons Falling on a Detector

    Homework Statement A collection of neutrons, nominally at rest, are confined in a region 1.0 nm wide on the x-axis at a height of 50 cm above a neutron detector. The neutrons are released and fall under the influence of gravity towards the detector which records the horizontal position of the...
  34. P

    Calculate the temperature of neutrons emerging from a reactor

    Homework Statement A collimated beam of thermal neutrons emerges from a nuclear reactor and passes through a speed selector into a detector. The number of neutrons detected in a second with speeds in the range 4000 to 4010 m s−1 is twice as large as the number per second detected with speeds in...
  35. F

    What is the Velocity of Thermal Neutrons at 25 Degrees Celcius?

    Homework Statement Estimate the velocity of thermal neutrons at 25 degrees celcius Homework EquationsThe Attempt at a Solution I attempted to use KE=0.5mv^2 but I realized that I didn't know the Kinetic energy
  36. axer

    How to find an isotope given mass number and neutrons?

    Homework Statement An isotope of which element has a mass number of 111 and has 5 more neutrons A- Antimonu B- Cadmium C- Iodine D- Tin E- Xenon Homework EquationsThe Attempt at a Solution I don't know where to start
  37. O

    Resonance absorbtion of neutrons

    Hi, As you may know, the following equation gives the number of neutrons absorbed per cm3/sec in a resonance region. Fa=Φav∫∑a(E) dE So, it is said in Lamarsh, introduction to nuclear engineering, that Φav depends on temperature. I do not get this because I know that the flux is something we...
  38. P

    B How do Neutrons and U235 Nuclei get out of the fuel rod

    I understand that there are fuel rods, water control rods. I also understand that fuel rods are metal tubes filled with special U235 pellets. Finally, I understand that water slows the neutrons down enough to collide. How do the neutrons and U235 nuclei get out of the metal encased fuel rod...
  39. Quantum Velocity

    B Where do neutrons in the sun come from?

    If star start from a big ball of hidrogen and the all the neutron to make helium. Thx for help!
  40. C

    I Do Neutrons Have Different Masses in Different Isotopes?

    My physics is not good, please kindly don't judge my physics. In some molecular weight calculator to get mono-isotope neutral mass for atoms listed below. In FTICR, we could find these difference. For example, m/z 101.960035, ^1H^35Cl^16O3^18O m/z 101.952838, ^1H^37Cl^16O4 Here is my question...
  41. O

    I Neutrons and strong interaction

    Is there any type interaction between neutron and matter other than strong interaction? When a neutron elastically or inelastically scattered, does the strong interaction still govern the whole process? Thank you!
  42. S

    What is the resulting product when Si28 is irradiated with fast neutrons?

    When a target material is irradiated with neutrons, a number of nuclear reactions are possible. For the slow neutron activation of 28Si, 29Si is created. Determine what is created if 28Si is irradiated with fast neutrons. Then, consult the National Nuclear Data Centre...
  43. Lacplesis

    Prompt neutrons, delayed neutrons, chain reaction control

    Hello, I am reading about this and I have a question , so let me explain how I understood this and please correct where I am wrong. I will ask about nuclear reactors because obviously in bombs only prompt neutrons matter since there is no need for any control only an exponential increase in...
  44. O

    Moderating Neutrons: Strong Interaction Involved?

    Hi, As we know, neutron does not have charge so it can not interact with any other particle with coulombic force. But in the reactor core fast neutrons can be slowed down. Does strong interaction govern this slowing down process?Thank you.
  45. F

    I Fission of 238U with high energy neutrons & other questions

    Hi, I have a question related to 238U. I know of course that it can fission with neutrons above 1 MeV, but there is a elevated risk it would absorb the neutron and produce 239Pu instead. Let's assume you have a ram of metallic 238U, with perhaps 0,7% 235U, and that you collide it very very...
  46. Mary curie

    B How Does Cadmium Absorb Neutrons?

    Hello guys ! How are you ? So, I am a senior student and we're studying nuclear transformations. Well long story short our teacher tell us that in a nuclear reactor we make a surface with cadium to absorb the neutrons ! And than a problem was created in my head ! Please help ! I don't...
  47. B

    Quantum mechanics: one thousand neutrons in an infinite well

    I apologize in advance for not being familiar with LaTex. 1. Homework Statement One thousand neutrons are in an infinite square well, with walls x=0 and x=L. The state of the particle at t=0 is : ψ(x,0)=Ax(x-L) How many particles are in the interval (0,L/2) at t=3? How many particles have...
  48. A

    I Weak force - only free neutrons decay?

    Reading this article - http://hyperphysics.phy-astr.gsu.edu/hbase/particles/proton.html#c4 there is a statement - "A free neutron will decay with a half-life of about 10.3 minutes but it is stable if combined into a nucleus." So is it only free neutrons that decay into protons? In...
  49. gennarakis

    I Quantum Kinetic Energy of Neutrons, Protons and Electrons

    Hi there, I have a problem to solve in Cosmology which says: "Write the formulas for the quantum kinetic energy of neutrons, protons and electrons as well as the formula for the gravitational energy for a neutron star that is comprised of free neutrons, protons and electrons in a ratio of Nn ...
  50. Zoey

    Does an Atom's Type dictate the Protons and Neutrons?

    Hi, Does an Atom's Type have to do with the number of protons and neutrons it has? Or are they completely unrelated? Just curious. Thanks :)