Do gamma rays leave "partice" tracks?


by billb@eskimo.com
Tags: gamma, partice, rays, tracks
billb@eskimo.com
#1
Dec14-07, 05:00 AM
P: n/a
In cloud chambers (or bubble/spark/crystal detectors,) do MeV photons
leave trajectory-tracks like particles do?

I've been arguing with myself about the details of laser
amplification, and it doesn't make sense to me that stimulated
emission produces photons with a "trajectory" the same as the
stimulating light: atoms should produce dipole radiation. But even
sphere-wave dipole radiation from the pumped atoms in a laser medium
would interfere with the stimulating beam and create a large anti-node
in the "downstream" direction. It's sort of like a trajectory.
Vaguely. And if this narrow chain of antinodes is absorbed by atoms
downstream in the beam, the energy gets localized then re-emitted,
perhaps producing an EM phenomenon like a narrow trajectory.

Therefore I ask if gamma-ray photons are seen to behave like
particles; producing ion trails when sensed by detectors which can
image the tracks of alphas/betas/etc.? (Can *EM waves* produce
tracks?)

Associated question/musing: if such a "photon localized trajectory"
effect exists, do rod-like pulse lasers amplify better than expected
when operated without mirrors?


((((((((((((((((((((((( ( ( (o) ) ) )))))))))))))))))))))))
William J. Beaty Research Engineer
beaty a chem washington edu UW Chem Dept, Bagley Hall RM74
billb a eskimo com Box 351700, Seattle, WA 98195-1700
ph425-222-5066 http://staff.washington.edu/wbeaty/

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Murray Arnow
#2
Dec14-07, 05:00 AM
P: n/a
billb wrote:
>In cloud chambers (or bubble/spark/crystal detectors,) do MeV photons
>leave trajectory-tracks like particles do?
>
>I've been arguing with myself about the details of laser
>amplification, and it doesn't make sense to me that stimulated
>emission produces photons with a "trajectory" the same as the
>stimulating light: atoms should produce dipole radiation. But even
>sphere-wave dipole radiation from the pumped atoms in a laser medium
>would interfere with the stimulating beam and create a large anti-node
>in the "downstream" direction. It's sort of like a trajectory.
>Vaguely. And if this narrow chain of antinodes is absorbed by atoms
>downstream in the beam, the energy gets localized then re-emitted,
>perhaps producing an EM phenomenon like a narrow trajectory.
>
>Therefore I ask if gamma-ray photons are seen to behave like
>particles; producing ion trails when sensed by detectors which can
>image the tracks of alphas/betas/etc.? (Can *EM waves* produce
>tracks?)
>


Gammas don't produce ion trails. What usually happens in bubble chambers
is the gamma converts to one or more electron-positron pairs. It's the
trajectory of these pairs that provides the information about the gamma.
Lower energy photons, like those to which you refer, do not have enough
energy to produce e-p pairs (you need at least 1 Mev photons to start).

The cloud chamber gammas can also ionize the gas in the chamber
producing secondary electrons call delta rays. The delta rays can be
analyzed for information about the primary ionizing agent. This is a bit
more difficult than analyzing e-p pairs (this scenario is complicated by
the myriad of possibilities that occur when you have charged particles
banging a round in a cloud chamber). Again, the gamma has to give up all
its energy to the charged particle. So a gamma ray trajectory still
isn't seen. But delta rays can be produced by gamma energies well below
1 Mev.

Considering everything available to detecting low energy photons, bubble
chambers are probably the poorest choice.

Uncle Al
#3
Dec15-07, 05:00 AM
P: n/a
billb@eskimo.com wrote:
>
> In cloud chambers (or bubble/spark/crystal detectors,) do MeV photons
> leave trajectory-tracks like particles do?


No tracks. Electron mass is 0.511 Mev. A fat gamma photon plus a
heavy nucleus could give you pair formation. Compton scattering at
lowwer energies. Overall, even high energy photons are invisible
absent high-Z element detectors (scintillation crystals). At lower
energies scattering is visible in cloudy media.

> I've been arguing with myself about the details of laser
> amplification, and it doesn't make sense to me that stimulated
> emission produces photons with a "trajectory" the same as the
> stimulating light: atoms should produce dipole radiation.


Crack a book. The quantum numbers of the stimulating photons are the
quantum numbers of the emitted photons. Photons are bosons Their
energy levels don't stack when populated.

> But even
> sphere-wave dipole radiation from the pumped atoms in a laser medium
> would interfere with the stimulating beam and create a large anti-node
> in the "downstream" direction. It's sort of like a trajectory.
> Vaguely. And if this narrow chain of antinodes is absorbed by atoms
> downstream in the beam, the energy gets localized then re-emitted,
> perhaps producing an EM phenomenon like a narrow trajectory.

[snip]

OK. Lasers don't work. Now convince my CD/DvD computer drive and
laser pointer.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/lajos.htm#a2


Tom Roberts
#4
Dec15-07, 05:00 AM
P: n/a

Do gamma rays leave "partice" tracks?


billb@eskimo.com wrote:
> In cloud chambers (or bubble/spark/crystal detectors,) do MeV photons
> leave trajectory-tracks like particles do?


No.

Charged particles lose energy continuously when traversing a material,
by ionizing atoms of the material close to their trajectory. This occurs
because the transient electric field of the traveling particle is strong
enough to overcome the Coulomb barrier of the atom and "kick" an
electron out. A few-MeV (or higher) charged particle can ionize millions
of atoms per centimeter in some materials (a few tens of MeV energy loss
per meter). The detectors you name are specifically designed to be
exquisitely sensitive to such a tiny deposition of energy into their
material.

A photon (gamma ray), on the other hand, is neutral and does not affect
atoms near to its trajectory at all. It can interact with a single atom,
but that obviously cannot leave a track. Its interaction can, however,
either liberate an electron from the atom (photoelectric effect) or
produce an e+e- pair (pair production), and these charged particles can
then leave tracks.


> I've been arguing with myself about the details of laser
> amplification, and it doesn't make sense to me that stimulated
> emission produces photons with a "trajectory" the same as the
> stimulating light: atoms should produce dipole radiation.


The details work out so the stimulated emission is precisely parallel to
the original radiation.


> Therefore I ask if gamma-ray photons are seen to behave like
> particles;


In some ways they do, but not in leaving tracks in a bubble or cloud
chamber. MeV photons do interact with a single charged particle giving a
very precise location of their interaction (this is in some sense
"particle like"). So, for instance, detectors designed for such photons
always register an integral number of photons.


> Associated question/musing: if such a "photon localized trajectory"
> effect exists, do rod-like pulse lasers amplify better than expected
> when operated without mirrors?


Remember that visible-light lasers are using photons in the fractional
eV range, not the MeV range. These optical photons behave rather
differently from the higher energy ones. In particular, it is MUCH more
difficult to construct a single-photon detector (but it can be done:
google "visible light photon counter" -- they must be cooled to 10K or
so to keep the noise down).

The mirrors in a He-Ne laser are to provide a longer path through the
lasing material. The necessary condition is that the gain through the
lasing material be greater than 1. Some lasers, such as the free
electron laser, have gains greater than 1 in a single pass without
mirrors. I believe some semiconductor lasers also work without mirrors.
A He-Ne tube many meters long would presumably work without mirrors.

The mirrors also provide beam-forming, and act as a
Fabry-Perot interferometer to give much narrower line
widths in laboratory lasers.


Tom Roberts

Oh No
#5
Dec16-07, 05:00 AM
P: n/a
Thus spake billb@eskimo.com
>In cloud chambers (or bubble/spark/crystal detectors,) do MeV photons
>leave trajectory-tracks like particles do?
>
>

As posters have said no tracks are left by uncharged particles. We do
see events (e.g pair creation) triggered by high energy photons,
separate from the original scattering event.

Regards

--
Charles Francis
moderator sci.physics.foundations.
charles (dot) e (dot) h (dot) francis (at) googlemail.com (remove spaces and
braces)

billb@eskimo.com
#6
Dec16-07, 05:00 AM
P: n/a
On Dec 13, 11:00 pm, ar...@iname.com (Murray Arnow) wrote:

> Gammas don't produce ion trails.


Thanks!



> The delta rays can be analyzed for information about the primary ionizing agent.


That's more like the idea I was after. I imagine that the trajectory
of the
resulting deltas would be mostly unrelated to the direction of the
incoming
gammas which produced them. Otherwise we could provide an electron
lens and end up with a gammaray telescope.


((((((((((((((((((((((( ( ( (o) ) ) )))))))))))))))))))))))
William J. Beaty Research Engineer
beaty a chem washington edu UW Chem Dept, Bagley Hall RM74
billb a eskimo com Box 351700, Seattle, WA 98195-1700
ph425-222-5066 http://staff.washington.edu/wbeaty/

tarbag
tarbag is offline
#7
Dec16-07, 10:08 AM
P: 20
In cloud chambers (or bubble/spark/crystal detectors,) do MeV photons
leave trajectory-tracks like particles do?
The photon is a concept, a mental construction, made by the men to explain the interactions between the electromagnetic radiations and the matter. One can thus speak about photon only at the time of the interaction. Apart from any interaction, one does not know - and one cannot know which "form" has this radiation. One can imagine that the photon would be a concentration which would be formed only at the time of the interaction, then would be spread out, and would be reformed at the time of another interaction. One cannot thus speak about "localization" nor of "trajectory" of the photon.
Dan Riley
#8
Dec17-07, 05:00 AM
P: n/a
billb@eskimo.com writes:
> > The delta rays can be analyzed for information about the primary
> > ionizing agent.

>
> That's more like the idea I was after. I imagine that the
> trajectory of the resulting deltas would be mostly unrelated to the
> direction of the incoming gammas which produced them. Otherwise we
> could provide an electron lens and end up with a gammaray telescope.


As Murray also said,

What usually happens in bubble chambers is the gamma converts to one
or more electron-positron pairs. It's the trajectory of these pairs
that provides the information about the gamma.

For gammas well above the pair production threshold, tracking the
primary electron-positron pair does provide the basis of a gamma
telescope--see for example GLAST, the Gamma-ray Large Area Space
Telescope.

-dan

Tom Roberts
#9
Dec17-07, 05:00 AM
P: n/a
billb@eskimo.com wrote:
> On Dec 13, 11:00 pm, ar...@iname.com (Murray Arnow) wrote:
>> Gammas don't produce ion trails. [...] The delta rays can be
>> analyzed for information about the primary ionizing agent.

>
> That's more like the idea I was after. I imagine that the trajectory
> of the resulting deltas would be mostly unrelated to the direction
> of the incoming gammas which produced them.


No. For a charged particle traversing matter, the delta rays are emitted
in a direction very close to the direction of the charged particle.
Note, however, that they are very low energy and multiple scatter a lot
(which changes their direction), and don't have much range.

Note: "delta ray" is an old-fashioned term for a low-energy
electron kicked out of a material (typically they have a few
keV energy, but can occasionally be up to an MeV or so); the
term is not normally applied to higher energy electrons.

But a gamma can produce only a single electron (the term "delta ray" is
not normally used for this) or an electron-positron pair. A gamma with
several MeV energy would produce a several MeV electron, which would
immediately shower.


Tom Roberts

Richard Saam
#10
Dec19-07, 05:00 AM
P: n/a
Tom Roberts wrote:
> billb@eskimo.com wrote:
>
>> On Dec 13, 11:00 pm, ar...@iname.com (Murray Arnow) wrote:
>>
>>> Gammas don't produce ion trails. [...] The delta rays can be analyzed
>>> for information about the primary ionizing agent.

>>
>>
>> That's more like the idea I was after. I imagine that the trajectory
>> of the resulting deltas would be mostly unrelated to the direction of
>> the incoming gammas which produced them.

>
>
> No. For a charged particle traversing matter, the delta rays are emitted
> in a direction very close to the direction of the charged particle.
> Note, however, that they are very low energy and multiple scatter a lot
> (which changes their direction), and don't have much range.
>
> Note: "delta ray" is an old-fashioned term for a low-energy
> electron kicked out of a material (typically they have a few
> keV energy, but can occasionally be up to an MeV or so); the
> term is not normally applied to higher energy electrons.
>
> But a gamma can produce only a single electron (the term "delta ray" is
> not normally used for this) or an electron-positron pair. A gamma with
> several MeV energy would produce a several MeV electron, which would
> immediately shower.
>
>
> Tom Roberts
>


An indication of the extremely high optical 'X-ray laser' energies
(intensity 10^22 watt/cm^2 and electric field 10^17 volt/cm )
required for 'Schwinger' pair production
are indicated:
http://arxiv.org/abs/nucl-th/0511085

The latest powerful lasers (XFEL) are enlisted to study such
EM pair production effects.

Richard D. Saam



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