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Is this a way to speed up the decay of an alpha emitter? Date: 1999/02/19
Say we have a radioactive substance which emits alpha particles with an average energy E. Accelerate a bunch of said radioactive substance and have it crash into a sea of liquid helium which is in the ground state. Say we accelerate the radioactive substance so that in the rest frame of the radioactive substance the helium atoms appear to go rushing past with an average energy E.
Question, will the following happen:
In the rest frame of the radioactive substance there are a lot of helium nuclei going in the same direction, so the probability for the radioactive substance to give up its alpha particle is enhanced by there being many helium nuclei in just the right state?
Re: Is this a way to speed up the decay of an alpha emitter? Date: 1999/02/21
I think I see a problem here ALE. Are all the helium nuclei in just the right state? We know that all the helium are in the ground state but what is that state. We know that liquid helium at near zero temperature has a finite density so even though all helium atoms "sing" in phase they still each must occupy a finite volume. So as the radioactive substance crashes into the liquid helium it only "senses" one helium nuclei at a time?
Feynman has a nice section about this on pages 4-1 to 4-4 on his three volume set, you might try reading it again? So while you may be able to stuff a zillion massless photons, all in the same state, into a small box you can't do the same for massive "pseudo" Bose particles like helium atoms, to bad kid, try again.
Asking this question conjured up images of the Mossbauer effect the similarities and differences in your problem.
Relativistic particle spin questions. Date: 1999/02/22
In article <35269aab.16498769@aklobs.org.nz> Date: 1998/03/27 rtomes@kcbbs.gen.nz (Ray Tomes) writes:
> I have heard that particles in accelerators tend to have their spin > lined up in the direction of motion. Is that correct? > > Is this just an expected relativistic effect due to contraction along > the axis of travel as seen by us?
I have had this question, think I have resolved it?
Consider a large number of letter O's scattered about near the origin of some rest frame. Let the letter O's also have a random distribution of orientations with respect to that rest frame such that if we form the vector sum of all the unit normals (normal to the plane that contains the letter O) then that vector sum would be approximately zero. Now consider how the letter O's appear in another frame that moves rapidly past the rest frame of the letter O's.
We will no longer see a completely random distribution of orientations for the letter O's. To the observer rushing past the letter O's the unit normals will be "rotated" in alignment with our direction of travel, and at ultra relativistic velocities the unit normals will either point with or against our direction of travel.
At this point one only need to consider the letter O's to be spinning in the plane that contains them and one recovers the fact that an ultra relativistic electron has its spin with or against it direction of travel?
Re: Relativistic particle spin questions. Author: Igor Ivanov <i.ivanov@fz-juelich.de> Date: 1999/02/23
> Consider a large number of letter O's scattered about near the origin > of some rest frame. Let the letter O's also have a random distribution > of orientations with respect to that rest frame such that if we form > the vector sum of all the unit normals (normal to the plane that > contains the letter O) then that vector sum would be approximately > zero. Now consider how the letter O's appear in another frame that > moves rapidly past the rest frame of the letter O's. > > We will no longer see a completely random distribution of orientations > for the letter O's. To the observer rushing past the letter O's the > unit normals will be "rotated" in alignment with our direction of > travel, and at ultra relativistic velocities the unit normals will > either point with or against our direction of travel. > > At this point one only need to consider the letter O's to be spinning > in the plane that contains them and one recoveres the fact that an > ultra relativistic electron has its spin with or against it direction > of travel? > > Where did I go wrong? Thanks for any help!
First of all, I guess that your letters O should correspond to VECTOR particles, not SPINOR particles like electrons. And in this case you have just perfectly described (at the hand-waving level, of course) the fact that ultra relativistic vector particle has not 3, but only two polarization states - with spin along and against travel direction (or in other words, helicity up and down).
However, there is a more fundamental and much deeper problem in your analogy. In QFT we actually deal with quantum FIELDS. Fields with spin. Even after quatization, we don't get PARTICLES. We get only certain plane (or other) waves and wavepackets.
What you were trying to describe was relativistic PARTICLE with spin. This is conceptually different from electrons, photons, or other things which will call "particles". -- Igor Ivanov
[Moderator's note: actually relativistic quantum particles with spin are not so different from relativistic quantum fields with spin: if you second-quantize the former you get the latter. In particular, relativistic massless vector particles have only 2 spin states. - jb]
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