What is Neutron: Definition and 766 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. RobinBanks

    I Speeding up the half-life of plutonium

    I know that it is possible to speed up the half-life of plutonium with neutrons. Who can tell me more about this? Thoughts on harnessing this power to decay plutonium so it's unusable in nuclear weapons?
  2. D

    I How Does the Size of Neutron Stars Compare to Black Holes?

    In the following article it is stated: https://skyandtelescope.org/astronomy-news/measuring-neutron-stars-exactly/ "We're seeing the gas whipping around just outside the neutron star's surface," said Edward Cackett (University of Michigan), in a press release. "And since the inner part of the...
  3. eneacasucci

    I Negative Q-value for 7Li(alpha,n) reaction

    I see that the Q value for the reaction 7Li + α -> 10B + neutron is Q=-2789.909 keV, which is a negative value. I knew that Q<0 means that the reaction is not spontaneous. The "Glenn F. Knoll - Radiation detection and Measurement" says: "In particular, the 7Li (α, n) reaction with its highly...
  4. A

    How I can declare a spherical neutron source to calculate the thermal neutron flux in a cell?

    c Created on: Tuesday, September 05, 2023 at 11:26 1 1 -1.58 -1 2 0 -2 #1 3 0 -3 #1 #2 4 0 3 1 rpp -0.5 0.5 -0.5 0.5 0 0.1 2 so 10 3 so 15 mode n m1 15000. 0.12951 $matrix...
  5. Hamidul

    MCNP code for Neutron Spectroscopy

    Hello everyone , in my mcnp coding for finding neutron spectroscopy I used F2 tally across a surface. Is it correct or I should use f4 tally? Morever I need to transform the flux data into neutron fluence. How can I do that. Here I uploaded my code. Though my data from codes is way more...
  6. Hamidul

    Help with neutron spectroscopy experiments in MCNP code

    Hello everyone, currently I am doing a neutron spectroscopy experiments. I am doing it with the MCNP code. I designed my Geometry there, but facing problems in data cards, is there anyone who can help me in this sector?
  7. BWV

    B Would a solid neutron mass be stable?

    not asking about neutron stars, where gravity holds neutrons together, rather would the strong force hold individual neutrons together in a solid mass, preventing their decay if one could somehow put them together in a lab?
  8. Islam Nabil

    Thermal neutron detection using MCNP

    How can i detect the thermal neutron, E = 0.025 Ev, by MCNP using CUToff Or PHYS:N cards?
  9. gurbir_s

    A Solving this first-order differential equation for neutron abundance

    The time rate of change of neutron abundance ##X_n## is given by $$\frac{dX_n}{dt} = \lambda - (\lambda + \hat\lambda)X_n$$ where ##\lambda## is neutron production rate per proton and ##\hat\lambda## is neutron destruction rate per neutron. Given the values of ##\lambda## and ##\hat\lambda## at...
  10. Astronuc

    B Vulpecula, pulsars and neutron stars

    I was listening to a Star Date podcast regarding the constellation Vulpecula and learned about the discovery of pulsars and neutron stars. https://stardate.org/radio/program/2023-03-19 The first neutron star was discovered in Vulpecula in 1967. https://en.wikipedia.org/wiki/PSR_B1919+21 In...
  11. 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...
  12. gleem

    Rocket Lab's Neutron Rocket

    The Neutron is the rocket that Rocket Lab intends to compete with SpaceX's Falcon9. Still in development Rocket Lab is planning to use composites for tankage and airframe. Didn't SpaceX try this for the Falcon but abandoned it in favor of proprietary stainless steel...
  13. C

    A Has the merger of a neutron star and an anti-neutron star been modeled?

    If a neutron star and an anti neutron star collided, would they 1) completely annihilate each other, 2) form a black hole, or 3) partially annihilate each other with the remaining stars being pushed away from each other by the energy created?
  14. C

    I Is it possible to unbind a neutron star?

    Type 1a supernovas unbind a white dwarf. Is there some theoretically possible scenario in which a neutron star could be unbound and thus turned into degenerate matter or even regular matter? For example, by a high speed glancing collision with another neutron star or by tidal disruption by a...
  15. K

    I Primordial neutron star -- a new candidate for dark matter

    could this explains the 3rd peak of the CMB and dark matter cold Primordial neutron star High Energy Physics - Phenomenology [Submitted on 7 Sep 2022 (v1), last revised 12 Sep 2022 (this version, v2)] Primordial neutron star; a new candidate of dark matter M. Yoshimura Z-boson exchange...
  16. D

    B What Could Explain the Mysterious Beam of Plasma Seen in the Sky in 2017?

    Basically, after seeing a meteor transit our atmosphere below 30,000 feet altitude too fast for my eyes to register yet leaving what looked like a beam of plasma from hanging from 1 side of the sky to the other for 3 seconds which I realized was a trail of smashed atoms of the atmosphere that...
  17. K

    B Object Weight on Magnetar vs Neutron Star: Attract or Repel?

    Probably a misguided question, but would the intense magnetic field of a magnetar increase the overall pull an object would feel at the surface of the magnetar as compared to a regular neutron star? Or would it possibly lessen the amount of gravitational pull the object would feel at the...
  18. mark_bose

    I want to write my own Monte Carlo code for Neutron transport

    Hi, i would like to write my own MC code in order to simulate the transport of Neutrons in Nuclear reactors. I know the basics of MC and i have already written a code for homogeneus reactors, my problem is the generalization to more complex geometries made of different materials, such as fuel...
  19. evceteri

    Neutron scattering probability distribution

    Hi, I'm reading Chapter 2-II of of Duderstadt & Hamilton's "Nuclear Reactor analysis". In the section "Differential scattering cross sections with upscattering" it is discussed the situation in which neutrons suffers elastic scattering collisions in a hydrogen gas at finite temperature T and the...
  20. Grinkle

    B Maximum mass of a neutron star

    I read this - https://www.sciencedaily.com/releases/2018/01/180116093650.htm And I see this - "However, there are indications that a neutron star with a maximum mass would collapse to a black hole if even just a single neutron were added." And I think the maximum mass of a neutron star is...
  21. A

    B Mass transfer between neutron stars in a binary pair

    When we read about the mass transfer between neutron star pairs in a binary system, how is it that the one receiving the matter can increase its spin rate. Adding mass to a spinning object ought to slow due to conservation of momentum. Where does the energy come from?
  22. J O Linton

    B Doppler Shift of Neutron: Energy & Momentum

    When a photon emitted by a distant galaxy travels across space and is detected at a later time when the universe has expanded by a factor of 2, its wavelength, frequency, energy and momentum are all changed by a factor of 2. If a neutron is emitted with energy E and momentum p and is also...
  23. 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...
  24. P

    B Can a hydrogen atom become a neutron?

    I read this from Nasa's website: "Within the first second after the Big Bang, the temperature had fallen considerably, but was still very hot - about 100 billion Kelvin (1011 K). At this temperature, protons, electrons and neutrons had formed, but they moved with too much energy to form atoms...
  25. S

    I Nuclear knockout reactions - why does a proton knockout a neutron?

    I am studying the synthesis of FDG for a job interview. The process of creating the F-18 used in FDG involves the collision of O-18 with an accelerated proton -- the proton kicks out a neutron and everything adds up. I am just wondering why a neutron is specifically knocked out, why wouldn't...
  26. F

    Neutron quantity normalization in an eigenvalue computation

    Dear Community, I am having a question. I have developed a simple code to perform iteration power algorithm and find the keff value of a system. However, it is not still totally clear in my mind if I have to normalize all my scores by the eigenvalue, i.e. multiply by the keff (fluxes, power...
  27. A

    Fusion reactors are neutron sources AKA fission bomb factories?

    Assumptions: 1) Fusion reactors are easily obtainable. Every spacecraft or hover-car has one. 2) Fusion reactors are neutron sources. 3) Neutron sources are the "difficult bit" in the enrichment of uranium and plutonium. 4) Uranium and plutonium are "freely" available in asteroids or...
  28. P

    B Interested in Black Holes, Neutron Stars, and White Dwarf Stars

    How did you find PF?: duckduckGo search. My math is very weak and I don't like explanations done using math. I read books with very little math. I try to use reason based on what I've read. My understanding is time slows down in gravity and it will actually stop at the event horizon (see...
  29. B

    B Collapse of a neutron star - strong nuclear force vs gravity

    I understand that gravity causes a neutron star larger than about 10 solar masses to collapse into a black hole. I also understand that gravity is the weakest of the four forces. So I find this counterintuitive and I'm puzzled that why is it gravity that causes the collapse and NOT the strong...
  30. C

    Calculating Count Rate for Neutron Beam Detection

    Finding the neutrons per second. Uncluttering the question: ##P = 6 \times 10^{7} J/s, E_{1} = 149.7 MeV/event, A = 10^{-4} m^{2}, R = 5 m ##. Number of events per second = ##\frac{P}{E_{1}}## = escaping neutrons per second Area of ##5m## sphere around reactor = ## 4 \pi R^{2} ## Fraction of...
  31. D

    Help with neutron scattering in solid state physics

    Hello fellow physicists, I have a homework assignment which is to make a scientific essay (10-15 pages long) on neutron scattering in solid state physics. Our teacher is kind of the worse and he hasn't specified what he wants it on. He just said what I'm telling you: "An essay on neutron...
  32. Y

    I 9 y.o. question: will a spoon of neutron star matter explode?

    Greetings All, Well, this is the question from my 9 y.o. son: what will happen if a famous Everest heavy spoon of neutron star matter is actually removed from the star? I am inclining to his version that it will explode rather quickly, e.g. neutrons will quickly decay into protons-electrons...
  33. BenKlesc

    Does neutron embrittlement pose a real threat in this century?

    I've been reading up on neutron embrittlement lately. However I go onto the DOE's website, and they are now saying that there really is no technical limit to how long a reactor can stay operational. Eventually I believe in the next 100 years because of embrittlement, reactors will have to be...
  34. jedishrfu

    B There's Gold in Them Neutron Stars - or - Maybe Not

  35. jjson775

    Neutron Wavelength Calculation

    λ^2=h^2/m^2v^2 =h^2/2/(m^2v^2/2) =h^2/2/(Km) =h^2/2Km
  36. phinds

    I Discover the Rare Black Neutron Star

    This BBC article posts no references so I wonder if anyone has any idea how significant it is? https://www.bbc.com/news/science-environment-53151106
  37. A

    A Energy needed to convert a bound proton to a neutron?

    Hey everyone, I've got a question on converting bound protons into neutrons. a. What are some methods used to achieve the proton-to-neutron conversion in atomic nuclei? I'm familiar with particle scattering off a proton in the nucleus. I'm also aware of (n,p) reactions. Are there any other...
  38. O

    I Governing force and Neutron elastic scattering

    Hi, Which force does govern the neutron elastic scattering and capture reactions? It seems to me it is the strong nuclear force, but I am not sure about that.Thanks.
  39. T

    I What happens when a Neutron Star forms a Black Hole?

    Supposing the total mass of a stationary, non rotating Neutron Star is just one Kg below the mass required to form a black hole. Based on the wiki reference below the Schwarzschild radius must be just beneath the surface of the Neutron Star sphere. Now supposing an object with a mass of one Kg...
  40. A

    I Questions about neutron interactions

    So I am reading a book "Fundamentals of Nuclear reactor physics" by Elmer E. Lewis On page 37 it talks about neutron interactions. some sentences I feel are left a bit short so let me rephrase here and hopefully get a clear answer. We have a neutron with a given kinetic energy and bunch of...
  41. Leonardo Muzzi

    I Why the center of black holes should be different from neutron stars?

    Physically speaking, why the insides of the least massive black hole should be any different from the heaviest possible neutron star?
  42. T

    B What is the Cooling Time of a Neutron Star?

    Neutron stars have surface temperatures of 1,000,000 degrees K. Yet they are not creating energy like a normal star. They are just cooling off. How long does it take for such a star to cool to room temperature, 300 degrees K.?
  43. Attu

    B Neutron Star Paradox: Understanding Coulomb & Gravitational Forces

    For instance let's take that a neutron star mass is so high that the gravitational force is more than the coulumb force. If this happens then then the electrons will go down and alpha particle will be left . This is not observed in the star so how will the particle stay normal By the way I am...
  44. S

    Delayed neutron energy spectrum

    First: what precisely is the shape of delayed neutron energy spectrum for each single emitter, generally? Second: what are the delayed neutron energy parameters for the common isotopes producing them? The attested list seems to be: Br-87 55,65 s 2,52 % Cs-141 24,8 s 0,035 % I-137 24,13 s 7,14 %...
  45. B

    I The spin of the neutron is a quantized property

    In the brilliant.org website talking about quantum properties it is said that neutrons coming from a nuclear oven and passing through two permanent magnets of opposite polarity hit a surface only at the top and the bottom of it (there is no continuity) because the spin property is quantized and...
  46. A

    I Nucleus energy levels, neutron energy

    From what I read I see that for example a radioactive nucleus is a nucleus in an excited state and when it transitions back to it's stable state (changes from one element to another due to radioactive decay) one of the ways this happens is that the nucleus emits a energetic photon with a...
  47. K

    I Understanding Coherent Neutron Scattering in Hydrogen Molecules

    Hello! I am not sure I understand how neutron coherent scattering takes place. The case I am particularly talking about is neutron scattering off a hydrogen molecule. When thinking of Coulomb interaction, I would imagine this as if the incident particle (not a neutron, as the neutron doesn't...
  48. L

    B Colliding Neutron Stars Collapse into Black Holes

    Here is a presentation on the discovery of two colliding neutron stars and the resulting phenomena such as gravity waves, gamma ray bursts, and synthesis of high atomic number elements. The author is a theoretical physicist who is involved in the research. He says that the neutron stars most...
  49. C

    B Neutron Decay Outside of a Nucleus Near Absolute Zero

    Does neutron decay outside of the nucleus occur faster, slower, or at the same speed when the environment it is in is near absolute zero? Do any external factors affect the speed of a neutron decaying?
  50. B

    I What is the Minimum Neutron Energy Required for Lithium Fission?

    Whats the minimum kinetic energy a neutron must have in order to trigger the fission of for example a lithium core ?