0 Members and 1 Guest are viewing this topic.
yes. for instance, see here: socrates.berkeley.edu/~phylabs/adv/ReprintsPDF/BRA%20Reprints/03%20-%20Beta%20Decay.pdf
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.
Quote from: theThinkerCan anyone give an exact name of scientist/experimentI think you are trying to erect artificial barriers so you don't have to deal with the facts.
Quoteand 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).
QuoteIn 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).
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.
I'll like to know if anyone has ever measured directly the speed with which electrons are ejected from natural beta-decay.
Quote from: theThinkerI'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 know all that. v = E/B which is not a direct measure of velocity. I am talking of speed = distance / time.
Quote from: theThinker on 05/10/2016 04:28:07I 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].
Do you know about this sort of thing? newbielink:https://www.ncnr.nist.gov/staff/hammouda/distance_learning/chapter_12.pdf [nonactive]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)
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
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.QuoteIf someone really want to do a direct measure of speed with which electron's are ejected from beta decay, a way may be foundAnd 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.
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?