What is Neutron decay: Definition and 20 Discussions

Outside the nucleus, free neutrons are unstable and have a mean lifetime of 879.6±0.8 s (about 14 minutes, 39.6 seconds). Therefore, the half-life for this process (which differs from the mean lifetime by a factor of ln(2) ≈ 0.693) is 611±1 s (about 10 minutes, 11 seconds). The beta decay of the neutron, described above, can be denoted as follows:
n0 → p+ + e− + νeThis decay, like any flavor-changing process, occurs through operation of the weak force. It involves the emission of a W− boson from one of the down quarks within the neutron, thereby converting the down quark into an up quark and the neutron into a proton; the W− then decays into the electron and the antineutrino. The following equations denote the same process as the first equation above, but also include the short-lived W− and describe the process on both the nucleon and the quark level:

n0 → p+ + W− → p+ + e− + νeudd → uud + W− → uud + e− + νeFor the free neutron, the decay energy for this process (based on the rest masses of the neutron, proton and electron) is 0.782343 MeV. That is the difference between the rest mass of the neutron and the sum of the rest masses of the products. That difference has to be carried away as kinetic energy. The maximal energy of the beta decay electron (in the process wherein the neutrino receives a vanishingly small amount of kinetic energy) has been measured at 0.782 ± .013 MeV. The latter number is not well-enough measured to determine the comparatively tiny rest mass of the neutrino (which must in theory be subtracted from the maximal electron kinetic energy); furthermore, neutrino mass is constrained by many other methods.
A small fraction (about one in 1000) of free neutrons decay with the same products, but add an extra particle in the form of an emitted gamma ray:

n0 → p+ + e− + νe + γThis gamma ray may be thought of as a sort of "internal bremsstrahlung" that arises as the emitted beta particle (electron) interacts with the charge of the proton in an electromagnetic way. In this process, some of the decay energy is carried away as photon energy. Internal bremsstrahlung gamma ray production is also a minor feature of beta decays of bound neutrons, that is, those within a nucleus.
A very small minority of neutron decays (about four per million) are so-called "two-body (neutron) decays", in which a proton, electron and antineutrino are produced as usual, but the electron fails to gain the 13.6 eV necessary energy to escape the proton (the ionization energy of hydrogen), and therefore simply remains bound to it, as a neutral hydrogen atom (one of the "two bodies"). In this type of free neutron decay, in essence all of the neutron decay energy is carried off by the antineutrino (the other "body").
The transformation of a free proton to a neutron (plus a positron and a neutrino) is energetically impossible, since a free neutron has a greater mass than a free proton. However, see proton decay.

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  1. 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?
  2. D

    A Neutron Decay: Questions & Answers

    Hi, I have questions on the neutron decay What prevent the neutron to decay in udc or udt except mass/energy consideration ? If we do the assumption that (udc) and (udt) have the same mass than the proton (yes I know, this doesn't make sense) the three decay (p, udc, udt) woulld have the same...
  3. W

    Recoil Proton Momentum Spectrum in Neutron Decay

    I wish to draw the proton momentum spectrum by transforming the energy spectrum of recoil protons. I have calculated the energy spectrum using Nachtmann's spectrum: wp=g1[T]+a*g2[T] Where: g1[T]=(1 - x2/σ[T])2 * Sqrt[1 - σ[T]] * (4*(1 + x2/σ[T]) - (4/3*(σ[T] - x2)/σ[T])*(1 - σ[T])); g2[T]=(1 -...
  4. A

    B What is the equation for proton emission after muon capture in heavy nuclei?

    Can anyone tell me what is proton emission equation after muon capture for heavy nuclei?is it same with neutron emission equation??
  5. 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...
  6. O

    A Conservation of Information: Neutron Formation and Decay

    Has anyone analyzed the process of Neutron formation and decay from the perspective of "information conservation"? Does anyone have any thoughts on what the results of such an analysis would be? What is the status of the observed evidence of reality in respect of whether one should conclude...
  7. T

    About neutron decay in neutron stars

    Hi, I was reading about free neutron beta decay the other day and it came to me the idea of neutron stars. As I understand, neutron stars are held together by gravity instead of strong force interaction (which I think is the mechanism that gives stability to neutron in common nuclei). So one...
  8. anorlunda

    Free neutron vs bound neutron decay

    I was curious as to the difference in free neutron decay and the lack of decay when bound in a nucleus. I found the following statement here http://en.m.wikipedia.org/wiki/Neutron#Free_neutron_decay I don't understand that. Is the wave function of the neutron different when free or bound...
  9. Mordred

    Neutron Decay in Neutron Stars: Gravity or Half-Life?

    On decays I have only a preliminary understanding. I was looking up the half life of a neutron for another reason. The value I found for neutron decay for a free neutron was 10.3 seconds. Hope that's reasonably accurate. Anyways knowing that neutrons are stable in a nucleus held together...
  10. B

    Exploring Neutron Decay in the Early Universe: The Mystery Unraveled!

    In the early universe electrons and protons would combine to form neutrons and few, if any, protons would remain. If the mass difference were greater than the binding energies of nuclei, neutrons inside nuclei would decay leaving no nuclei behind. Does anyone know why the above...
  11. H

    Neutron Decay and the Weak Force

    I believe the neutron decays with a half life around 12 minutes via the weak mechanism. I'm wondering what causes a particular neutron to decay. At the moment the neutron decays, has it encountered (run into) a stray weak field? Or ... does the neutron decay just because of internal forces...
  12. J

    Neutron Decay Rate: Calculating Width & Lifetime

    How do we calculate the decay width or the mean lifetime of neutron/
  13. J

    Neutron decay - is my answer unrealistic?

    Hi, here's the problem: "a neutron at rest decays into a proton with a decay energy of 0.78MeV. What is the maximum kinetic energy of the proton left behind?" here's what I've tried: In this decay, I assumed that although it's not mentioned, there would be something negatively charged...
  14. gmax137

    Free Neutron Decay: Is It True?

    I was reading a blog where someone stated that the decay of a free neutron is characterized by a 'mean lifetime' but not by a half-life. They went on to indicate that the decay time is not random (in the sense that leads to a true half life) but rather most decay at the mean lifetime (said to...
  15. B

    Maximum Helium Fraction: Neutron Decay Time & Rest Mass Difference

    Suppose the neutron decay time n was 89 sec. AND the difference in rest mass between neutron to proton, Qn, was 0.129 MeV. What would the maximum Helium fraction, Yp, be?
  16. J

    Neutron Decay Into Proton: Hawking's New Book

    can a neutron decay into a proton? i certainly didnt think so, but i am reading hawking's new little book "breifer history of time", and he states that in there while talking about the early universe. thanks.
  17. R

    Neutron decay products: n → p + e + ν + DC-photon?

    This is one of those old-high school questions that never got answered (And the search mechanism here doesn't narrow on quotemarks)-- A neutron decays to a proton, electron, antineutrino ... But the highspeed escaping electron is a charge moving relative to (away from) the proton opposite...
  18. K

    Charge Conservation in Neutron Decay

    A neutron can decay into a proton, a positron, and a neutrino. A proton is made up of two up quarks and a down quark. A neutron is made up of one up quark and two down quarks. An up quark has a charge of +2/3, and a down quark has a charge of -1/3. Given the statements above, can someone...
  19. E

    Understanding Neutron Decay in Elementary Particle Physics

    In ‘Introduction to Elementary Particles’, David Griffiths makes the following two statements: a neutron decays into a proton, an electron, and an antineutrino (1.8) And later: but the following decay is not observed an antineutrino plus a neutron decay into a proton and an electron...
  20. M

    Calculating Proton & Electron Kinetic Energies from Neutron Decay

    A neutron at rest in the laboratory spontaneously decays into a proton, an electron, and a small essentially massless particle called a neutrino. Calculate the kinetic energy of the proton and the electron in each of the following cases: a) the neutrino has no kinetic energy b) the neutrino...