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Author Topic: Has electron speed from beta-decay ever been measured? How fast is it?  (Read 948 times)

Offline theThinker

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I'll like to know if anyone has ever measured directly the speed with which electrons are ejected from natural beta-decay.
« Last Edit: 06/10/2016 00:19:43 by chris »


 

Offline chiralSPO

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Offline theThinker

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Re: Has electron speed from beta-decay ever measured?
« Reply #2 on: 04/10/2016 18:47:16 »
yes. for instance, see here: socrates.berkeley.edu/~phylabs/adv/ReprintsPDF/BRA%20Reprints/03%20-%20Beta%20Decay.pdf

I don't think so.

Can anyone give an exact name of scientist/experiment and what range of speed were found. In the early days of beta-decay they don't have the technology to measure electron speed.
 

Offline alancalverd

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Re: Has electron speed from beta-decay ever measured?
« Reply #3 on: 04/10/2016 20:52:25 »
It's always been possible to measure the energy of a beta particle, so you can apply the standard relativistic equations for kinetic energy (since we know the rest mass of an electron) to  derive its speed. Or you can measure its path in a magnetic field. This is all classical physics that has been well documented since the 1920s.
 

Offline evan_au

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Re: Has electron speed from beta-decay ever measured?
« Reply #4 on: 04/10/2016 21:26:21 »
Quote from: theThinker
Can anyone give an exact name of scientist/experiment
I think you are trying to erect artificial barriers so you don't have to deal with the facts.

Quote
and what range of speed were found.
The reprint from Berkely has a large number of graphs of Beta particle energy, ranging from 0 up to some maximum which is in the MeV range (depending on which kind of nucleus emits it).

Given that the electron at rest has a mass of around 0.5MeV/c2, you could say that the fastest electrons are traveling at close to the speed of light, c.

So the range is pretty much 0 to c (but they don't quite reach c).

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In the early days of beta-decay they don't have the technology to measure electron speed.
The Cloud Chamber was developed by Charles Wilson in 1911, for which he received a Nobel Prize. A cloud chamber was used to study cosmic rays, and resulted in the first detection and measurement of a positron in 1936.

1911 is not long after the Curies were discovering radioactive elements, so I would say it was still "early days".

The Bubble Chamber was invented in 1952 by Donald Glaser, for which he received a Nobel Prize in 1960.

From the spirals in the Bubble Chamber, physicists can calculate the velocity of the electron - and even determine how its velocity changes over time as it interacts with matter in the bubble chamber (the radius of the spiral decreases over time).
 

Offline theThinker

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Re: Has electron speed from beta-decay ever measured?
« Reply #5 on: 05/10/2016 04:28:07 »
Quote from: theThinker
Can anyone give an exact name of scientist/experiment
I think you are trying to erect artificial barriers so you don't have to deal with the facts.

It is no artificial barrier. Common to have names of first person/experiment etc..

Quote
Quote
and what range of speed were found.
The reprint from Berkely has a large number of graphs of Beta particle energy, ranging from 0 up to some maximum which is in the MeV range (depending on which kind of nucleus emits it).

Given that the electron at rest has a mass of around 0.5MeV/c2, you could say that the fastest electrons are traveling at close to the speed of light, c.

So the range is pretty much 0 to c (but they don't quite reach c).

I know all that. v = E/B which is not a direct measure of velocity. I am talking of
speed = distance / time.
 
Quote
Quote
In the early days of beta-decay they don't have the technology to measure electron speed.
The Cloud Chamber was developed by Charles Wilson in 1911, for which he received a Nobel Prize. A cloud chamber was used to study cosmic rays, and resulted in the first detection and measurement of a positron in 1936.

1911 is not long after the Curies were discovering radioactive elements, so I would say it was still "early days".

The Bubble Chamber was invented in 1952 by Donald Glaser, for which he received a Nobel Prize in 1960.

From the spirals in the Bubble Chamber, physicists can calculate the velocity of the electron - and even determine how its velocity changes over time as it interacts with matter in the bubble chamber (the radius of the spiral decreases over time).

This chamber does not measure velocity. It estimates. I'll accept the statement that "they did estimate the speed of electrons from beta-decay". It probably is good enough for all purposes and nothing much more need be said.
 
 

Offline theThinker

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Re: Has electron speed from beta-decay ever measured?
« Reply #6 on: 05/10/2016 04:39:29 »
It's always been possible to measure the energy of a beta particle, so you can apply the standard relativistic equations for kinetic energy (since we know the rest mass of an electron) to  derive its speed. Or you can measure its path in a magnetic field. This is all classical physics that has been well documented since the 1920s.

Notwithstanding, William Bertozzi in 1966 measured his electron's speed by doing a : distance/time.
 

Offline PmbPhy

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Re: Has electron speed from beta-decay ever measured?
« Reply #7 on: 05/10/2016 07:45:58 »
Quote from: theThinker
I'll like to know if anyone has ever measured directly the speed with which electrons are ejected from natural beta-decay.
I don't believe those kinds of measurements have been made. In fact most of the information that has amassed from experiments has not been obtained in the way that you appear to have in mind. It's simply far too difficult to make those kinds of measurements. But I don't really see any benefit of doing the kind of measurements that you have in mind. There's simply no need for it. It would be a waste of time, effort and funding to do that kind of thing. In fact I don't really see any strong justification to use the term "directly." In fact, what you might think of as a "direct measurement" of an object is something that has never been done. Consider how one might "directly" measure the speed of a car on the highway. In order to "directly" measure the speed of a car you'd have to know where the car was at the beginning of the measurement and where it is at the end of the measurement. You'd have to have a clock to determine the time it took for the car to travel a given distance. Now, how do we measure the location of the car at the begining of the measurement and where it was at the end. But think about how we do something like that. Do we look to see where the car was? Do we have an apparatus to tell us that. If we look then we're using our eyesight to accomplish this task. So is that really a "direct" measurement or are we really making an indirect measurement based on our knowledge of light and our sense organs.

My point here is that what you may have thought of as a "direct measurement" never rally was what you thought it was. It's very easy to miss points like this since we rarely think about how we do certain things." However physicists take such things into account.

Why is it so important that you have the need to do a literature search to find it anyway?
« Last Edit: 05/10/2016 08:12:37 by PmbPhy »
 

Offline theThinker

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Re: Has electron speed from beta-decay ever measured?
« Reply #8 on: 05/10/2016 10:49:45 »
Quote from: theThinker
I'll like to know if anyone has ever measured directly the speed with which electrons are ejected from natural beta-decay.
I don't believe those kinds of measurements have been made. In fact most of the information that has amassed from experiments has not been obtained in the way that you appear to have in mind. It's simply far too difficult to make those kinds of measurements. But I don't really see any benefit of doing the kind of measurements that you have in mind. There's simply no need for it. It would be a waste of time, effort and funding to do that kind of thing. In fact I don't really see any strong justification to use the term "directly." In fact, what you might think of as a "direct measurement" of an object is something that has never been done. Consider how one might "directly" measure the speed of a car on the highway. In order to "directly" measure the speed of a car you'd have to know where the car was at the beginning of the measurement and where it is at the end of the measurement. You'd have to have a clock to determine the time it took for the car to travel a given distance. Now, how do we measure the location of the car at the begining of the measurement and where it was at the end. But think about how we do something like that. Do we look to see where the car was? Do we have an apparatus to tell us that. If we look then we're using our eyesight to accomplish this task. So is that really a "direct" measurement or are we really making an indirect measurement based on our knowledge of light and our sense organs.

My point here is that what you may have thought of as a "direct measurement" never rally was what you thought it was. It's very easy to miss points like this since we rarely think about how we do certain things." However physicists take such things into account.

Why is it so important that you have the need to do a literature search to find it anyway?
I think it is correct that it has not been done directly. At the time, they would not have the technology yet. It would not be a trivial feat to separate and select electrons that span a full energy range, 0 - 1.16 MeV.

The closest to direct is of course distance/time. Nowadays, I think there is the technology. It seems to be applied in mass spectrometry.   

 

Offline Bored chemist

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Do you know about this sort of thing?
https://www.ncnr.nist.gov/staff/hammouda/distance_learning/chapter_12.pdf
it's more often used for neutrons (because there are easier ways to do charged particles) but there's no reason why it couldn't be used for electrons (from any source)
 

Offline chiralSPO

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beta decay is a stochastic process (ie it happens randomly), and there isn't (as far as I know) a way to induce a nucleus to decay and release a beta particle (electron). So even if we can quantify the distance from the sample to the detector and the time that the electron was detected, we don't know the precise time it was emitted, so distance/time measurement isn't feasible. It is, however, fairly easy to measure the kinetic energy of an electron, or the magnitude of its interaction with a magnetic field of precisely known strength. Why should it be "better" to measure the velocity of the electron by another means?

What are you actually after?
 

Offline alancalverd

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Re: Has electron speed from beta-decay ever measured?
« Reply #11 on: 06/10/2016 17:57:38 »


I know all that. v = E/B which is not a direct measure of velocity. I am talking of
speed = distance / time.
 


If you want to do that, you need some means of knowing when a single electron passes a reference point, and when it reaches another reference point, without imparting any energy to it or removing any energy from it. Heisenberg pointed out that this is not possible. But dimensional analysis of E/B will show you that it is indeed [L]/[T].   
 

Offline theThinker

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Re: Has electron speed from beta-decay ever measured?
« Reply #12 on: 06/10/2016 18:28:17 »


I know all that. v = E/B which is not a direct measure of velocity. I am talking of
speed = distance / time.
 


If you want to do that, you need some means of knowing when a single electron passes a reference point, and when it reaches another reference point, without imparting any energy to it or removing any energy from it. Heisenberg pointed out that this is not possible. But dimensional analysis of E/B will show you that it is indeed [L]/[T].   
If something is impossible, we just have to accept it as a limitation of nature. If it involves a problem to solve at hand, then we have to just seek the next best solution.   
 

Offline theThinker

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Do you know about this sort of thing?
https://www.ncnr.nist.gov/staff/hammouda/distance_learning/chapter_12.pdf [nofollow]
it's more often used for neutrons (because there are easier ways to do charged particles) but there's no reason why it couldn't be used for electrons (from any source)
I don't really know much. But I think the experimental physicists of today is capable of playing gods with physics experimentations. If someone really want to do a direct measure of speed with which electron's  are ejected from beta decay, a way may be found, unless of course if there really is some natural obstacles making it impossible.

 

Offline chiralSPO

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As alancalverd pointed out, it really is impossible to know exactly where an electron is and its exact velocity (due to Heisenberg uncertainty), and there is no work around, according to the laws of physics as we know them. But this isn't really a problem for determining the velocity as long as we don't try to determine where the particle is too.

And as PmbPhy pointed out, what you are calling "direct" is really not any more direct than the other methods that are used.

Quote
If someone really want to do a direct measure of speed with which electron's  are ejected from beta decay, a way may be found

And why would someone really want to do this "direct" measurement if there is already a cheaper, easier and more precise way to do it? There is no physical law that prevents me from constructing a sandwich one atom at a time, but why would I bother?
 

Offline theThinker

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As alancalverd pointed out, it really is impossible to know exactly where an electron is and its exact velocity (due to Heisenberg uncertainty), and there is no work around, according to the laws of physics as we know them. But this isn't really a problem for determining the velocity as long as we don't try to determine where the particle is too.

And as PmbPhy pointed out, what you are calling "direct" is really not any more direct than the other methods that are used.

Quote
If someone really want to do a direct measure of speed with which electron's  are ejected from beta decay, a way may be found

And why would someone really want to do this "direct" measurement if there is already a cheaper, easier and more precise way to do it? There is no physical law that prevents me from constructing a sandwich one atom at a time, but why would I bother?
I think Heisenberg's principle does not apply to a classical free electron. As an example, we could have a single electron trapped in equilibrium in Millikan's oil drop experiment.   
 

Offline chiralSPO

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I think Heisenberg's principle does not apply to a classical free electron. As an example, we could have a single electron trapped in equilibrium in Millikan's oil drop experiment.

That is incorrect, and I don't see what Millikan's oil drop experiment has do to with anything (those droplets were comparatively very large and barely moving).
 

Offline Bored chemist

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beta decay is a stochastic process (ie it happens randomly), and there isn't (as far as I know) a way to induce a nucleus to decay and release a beta particle (electron). So even if we can quantify the distance from the sample to the detector and the time that the electron was detected, we don't know the precise time it was emitted, so distance/time measurement isn't feasible. It is, however, fairly easy to measure the kinetic energy of an electron, or the magnitude of its interaction with a magnetic field of precisely known strength. Why should it be "better" to measure the velocity of the electron by another means?

What are you actually after?

Did you read the link I posted?
 

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