# Do isomeric transitions have vector characteristics?

1. Jan 29, 2012

### xander77

When considering a single atom of Technetium 99m, or any other gamma emitter, does the emitted gamma ray have a vector?

In other words, suppose it were possible to have just one molecule of Tc99m, and it were to decay in the middle of a room. Next suppose that two people with perfectly efficient detectors are standing on opposite sides of the molecule.

If the gamma ray is emitted toward one detector, would the other detector observe the decay as well? What if the gamma ray were emitted orthogonally to each person/detector. Would either of them observe the gamma ray/photon?

Now, suppose we consider a photoelectric event. If a NaI crystal scintillates from a single Thallium molecule, does that photon have a specific vector? Or does it radiate in a all directions in a probability wave?

2. Jan 30, 2012

### kurros

I am not entirely sure what your general question is, but I have answers for your sub-questions:

No they will not. If a nucleus emits a single gamma ray, there is just the one gamma ray, so you cannot detect it in multiple places. If it was a β+ emitter, though, the positron would annihilate with a nearby electron, emitting two gamma rays back to back, in which case if one detector saw one photon, then so would the other (with your 100% efficiency assumption). This is the basis of positron emission tomography (PET).

I think I see the confusion. This is really a quantum mechanics questions? If there is one photon being emitted and equal probability for it to be emitted in any direction, then the wavefunction of the emitted photon will be spherically symmetric and travel out in all directions until some "measurement" occurs (the exact definition of which is something of a fundamental issue), at which point said wavefunction collapses and the photon will end up being detected in only one place or another.

There are some extra subtleties but I think we need not go into them. Although of course, there certainly need not be equal probability for the emitted photon to go in any direction in general, there are zillions of things that could alter the symmetry of the scenario. Also if you are actually asking about how scintillators in particular behave then I haven't really answered your question.

Last edited: Jan 30, 2012
3. Feb 2, 2012

### xander77

>I think I see the confusion. This is really a quantum mechanics questions?

Yes, actually, but I needed to set up some background, as I was only casually aware of Schrodinger's cat and actively studying gamma emitters in nuclear medicine.

Fundamentally, my question is: Does a gamma ray also exist in a probability wave, radiating outward spherically until detected. If not, why, as it is simply shorter wavelength of the same "stuff" as light. This is what I meant by asking about "vectors" initially. Does it radiate outward in a perfectly spherical wave function until detected, or does it initially leave with a specific vector.

My initial suspicion had been the later, but I can't reconcile that with the wave function stuff.

Again, specifically for alternate energies of photon, ie gamma and xray.

You've already helped immensely, because I had forgot that the collapse of a light photon's probability wave necessarily meant it couldn't be detected anywhere else, and this was a source of confusion for me, but I still wonder if all photon radiation, ie gamma and xray also behave probabilistically.

> There are some extra subtleties but I think we need not go into them.

Might be fun :)

>Although of course, there certainly need not be equal probability for the emitted photon to go in any direction in general, there are zillions of things that could alter the symmetry of the scenario.

One thing at a time, I think, ya?

>Also if you are actually asking about how scintillators in particular behave then I haven't really answered your question.

No, thank you. I think I have a pretty good grip on them, but before your response I had wondered if it were possible for two separate pmts to pick up one probability wave from a single scintillation. I think you did help to clarify that, to my great appreciation.

I seem to understand now that when the Thallium scintillates, the emitted photon is in fact a probability wave, until it interacts with some random portion of the nearby photocathodes, somehow not yet becoming an actual photon while flying through the collimator, where it there manifests itself as a light photon, and is consequently transmuted to an electron and multiplied by the dynodes of the pmt.

We've been taught that the scintillated photons have vectors, creating scatter, striking septa, or passing through collimator holes cleanly. My classmates and instructors haven't gotten into any quantum aspects of this science, but I've been markedly curious.

Thanks again!