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Author Topic: Can an electron convert a proton to a neutron?  (Read 5477 times)

Offline syhprum

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Can an electron convert a proton to a neutron?
« on: 26/04/2015 22:05:18 »
As a boy we were taught that the nucleus of an atom consisted of protons and electrons, Neutrons like radar were military secrets we did not want the Germans to know about.
After the war we were told that this was nonsense and the nucleus consisted of Protons and Neutrons, with the discovery of Neutron stars it was postulated that Electrons could be forced into Protons by gravitational pressure so the first theory was not that far out.
how does this happen Protons and Electrons and are of different classes of particle I would have thought that any union would be impossible.   
« Last Edit: 27/04/2015 08:57:57 by chris »


 

Offline PmbPhy

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Re: How does an electron convert a proton to a nuetron
« Reply #1 on: 26/04/2015 22:36:08 »
As a boy we were taught that the nucleus of an atom consisted of protons and electrons, Neutrons like radar were military secrets we did not want the Germans to know about.
After the war we were told that this was nonsense and the nucleus consisted of Protons and Neutrons, with the discovery of Neutron stars it was postulated that Electrons could be forced into Protons by gravitational pressure so the first theory was not that far out.
how does this happen Protons and Electrons and are of different classes of particle I would have thought that any union would be impossible.
Not at all. Since the transformation

n + e -> p

is possible then that's all that one can say about it. I have no idea what the mechanism is. I'm not sure anyone is.
 

Offline chiralSPO

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Re: How does an electron convert a proton to a nuetron
« Reply #2 on: 26/04/2015 22:58:01 »
To the best of my knowledge, I'm not sure that we have observed electron + proton → neutron. However, there have been many observations, and indeed much data on the reverse reaction: the decomposition of a free neutron into a proton an electron and a neutrino. There are also nuclei that undergo beta decay, whereby the neutron count is decreased by one, the proton count is increased by one, and an electron (beta particle) is ejected. I'm not sure if how much we can say about "which" nucleon changed in the nucleus, but the overall reaction is well studied. Interestingly, nuclei with too many protons can eject an antielectron and increase the neutron count at the expense of the proton count.

All interesting stuff. I assume the nuclear physicists have a better idea about this than I do.
 

Offline alancalverd

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Re: How does an electron convert a proton to a nuetron
« Reply #3 on: 26/04/2015 23:22:53 »
As a boy we were taught that the nucleus of an atom consisted of protons and electrons, Neutrons like radar were military secrets we did not want the Germans to know about.


Which war? Chadwick was awarded the Nobel Prize in 1935 for discovering the neutron 3 years earlier - hardly the best way to keep a secret.
 

Offline PmbPhy

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Re: How does an electron convert a proton to a nuetron
« Reply #4 on: 27/04/2015 00:44:25 »
Quote from: chiralSPO
However, there have been many observations, and indeed much data on the reverse reaction: the decomposition of a free neutron into a proton an electron and a neutrino.
Good point. I forgot about he neutrino. Thanks for mentioning that.
 

Offline chiralSPO

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Re: How does an electron convert a proton to a nuetron
« Reply #5 on: 27/04/2015 02:42:07 »
Sure thing! Those sneaky little particles...
 

Offline PmbPhy

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Re: How does an electron convert a proton to a nuetron
« Reply #6 on: 27/04/2015 05:01:20 »
Sure thing! Those sneaky little particles...
Let's back up a bit. The reaction you were speaking of is really

n -> p + e- + v'e

where v'e is an electron antineutrino (I'm using a prime to denote the antiparticle). There is a general principle in particle physics calledcrossing symmetry. See: http://hyperphysics.phy-astr.gsu.edu/hbase/particles/parint2.html

Essentially this moves a particle to the other side of the particle reaction equation and change it to its antiparticle. Thus, if you were to start with the reaction

A + B -> C + D

then crossing symmetry means that the three following reactions are possible

A -> B' + C + D
A + C' -> B' + D
C' + D' -> A' + B'

In our case

n -> p + e- + v'e

so

p -> n + e+ + ve

which is the reaction we're looking for.

Suggestion: Don't forget the principle of crossing symmetry. It's an important principle and it will come in handy for you someday. :)
 

Offline PmbPhy

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Re: How does an electron convert a proton to a nuetron
« Reply #7 on: 27/04/2015 05:19:23 »
Quote from: alancalverd
Which war? Chadwick was awarded the Nobel Prize in 1935 for discovering the neutron 3 years earlier - hardly the best way to keep a secret.
I think that he's confused the fact that data on neutron capture was kept secret until 1955 with the discovery of the neutron being kept secret.

See http://periodic.lanl.gov/100.shtml
Quote
The discovery of the new elements, and the new data on neutron capture, was kept secret on the orders of the U.S. Military until 1955 due to Cold War tensions
The discovery of a particle has never been kept a secret. In the case of the neutron, James Chadwick published his findings in the journal, Nature, on February 27, 1932. The article was called The possible Existence of a Neutron. You can read the article online at: http://www.mabra.it/clil/phase4/chadwick.pdf

What I found odd in this article is that Chadwick speaks of the neutron as if it already existed. He never really defined the term neutron, he just uses it.

But clearly the neutron was never a secret as this article demonstrates. The entire world has always had access to this journal.
 

Offline alancalverd

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Re: How does an electron convert a proton to a nuetron
« Reply #8 on: 27/04/2015 06:58:07 »
Quote
What I found odd in this article is that Chadwick speaks of the neutron as if it already existed. He never really defined the term neutron, he just uses it.

Chadwick and others had postulated and named the neutron several years earlier as an explanation of the existence of isotopes, but as with all good science, the crucial point is an experimental demonstration, which was the basis of the paper and the Nobel. 
 

Offline syhprum

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Re: How does an electron convert a proton to a nuetron
« Reply #9 on: 27/04/2015 07:16:32 »
During the 1939/1945 there was a deal of censorship radar was supposed be a secret British invention and publications such as Wireless World could not publish details, surprisingly just after the war a great deal was published about the design and construction of atom bombs some of which quickly became secret again.
I know of course that Neutrons had been discovered three years earlier but our school textbooks were seriously out of date.
 
« Last Edit: 27/04/2015 07:30:59 by syhprum »
 

Offline evan_au

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Re: Can an electron convert a proton to a neutron?
« Reply #10 on: 27/04/2015 12:26:35 »
Quote from: PmbPhy
where v'e is an electron antineutrino (I'm using a prime to denote the antiparticle). There is a general principle in particle physics called crossing symmetry.

It is still an open question in physics: is ν'e = νe? (ie is the neutrino its own antiparticle?)

It is hard enough to get the the ghostly neutrino to interact with ordinary matter, let alone get them to annihilate with each other!
 

Offline syhprum

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Re: Can an electron convert a proton to a neutron?
« Reply #11 on: 27/04/2015 14:30:01 »
Another strange thing about the Neutron decay to a Proton is the vast amount of time it takes when nuclear reaction times are normally measured in femto seconds rather as though gravity was playing a part rather than the normal nuclear forces
 

Offline chiralSPO

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Re: Can an electron convert a proton to a neutron?
« Reply #12 on: 27/04/2015 15:10:28 »
I'm not sure I would call 15 minutes vast, when there are several radioactive isotopes that have half lives >109 years (for instance: 238U at 4.47x109 years, 109Pt at 6.9x1011 years, and even 50V at 6.0x1015 years!)

http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/nuclidet.html
 

Offline PmbPhy

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Re: Can an electron convert a proton to a neutron?
« Reply #13 on: 27/04/2015 15:37:02 »
I'm not sure I would call 15 minutes vast, when there are several radioactive isotopes that have half lives >109 years (for instance: 238U at 4.47x109 years, 109Pt at 6.9x1011 years, and even 50V at 6.0x1015 years!)

http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/nuclidet.html
In particle physics 15 minutes is forever. In fact if a particle has a lifetime greater than 10-10 s (?), particle physicists think of them as being stable.
 

Offline syhprum

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Re: Can an electron convert a proton to a neutron?
« Reply #14 on: 27/04/2015 15:40:42 »
The answers to most of the questions asked here are in the Wiki article "Quark"
 

Offline chiralSPO

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Re: Can an electron convert a proton to a neutron?
« Reply #15 on: 27/04/2015 16:35:57 »
I'm not sure I would call 15 minutes vast, when there are several radioactive isotopes that have half lives >109 years (for instance: 238U at 4.47x109 years, 109Pt at 6.9x1011 years, and even 50V at 6.0x1015 years!)

http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/nuclidet.html
In particle physics 15 minutes is forever. In fact if a particle has a lifetime greater than 10-10 s (?), particle physicists think of them as being stable.

Fair enough. I guess "stability" really can only get a useful definition when given a context. Neutrons are "stable" in the context of a nuclear reactor (even star-sized), but not "stable" in the context of a nebula...
 

Offline alancalverd

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Re: Can an electron convert a proton to a neutron?
« Reply #16 on: 27/04/2015 17:32:24 »
The half life of a free neutron is just short enough to shower the earth with pions and protons from the sun.
 

Offline jeffreyH

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Re: Can an electron convert a proton to a neutron?
« Reply #17 on: 27/04/2015 23:38:04 »
Another strange thing about the Neutron decay to a Proton is the vast amount of time it takes when nuclear reaction times are normally measured in femto seconds rather as though gravity was playing a part rather than the normal nuclear forces

Surely it depends upon how the electron is bound to the proton. A tiny amount of leakage of color charge could bind the electron without any need for an interaction with gravity. This could result in a confined orbital that exists entirely outside the proton but the charge of the electron is neutralized by the leak of color charge.
 

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Re: Can an electron convert a proton to a neutron?
« Reply #17 on: 27/04/2015 23:38:04 »

 

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