# Do H- annihilation spectra vary with element?

1. Jun 26, 2011

### danR

Do $\bar{H}$ annihilation spectra vary with element?

If $\bar{H}$ collides (slowly, at 10 Kelvin for example) with H, Beryllium, Lead, does it make a difference?

Last edited: Jun 27, 2011
2. Jun 27, 2011

Staff Emeritus
I don't understand what you are talking about. The H- ion has no excited states, so it doesn't really have a spectrum.

3. Jun 27, 2011

### danR

I could have been less lazy and written antihydrogen, or $\bar{H}$.

For further clarification, annihilation-spectra refers not to ions, but matter-antimatter collision debris.

Can anyone else take a shot at it?

4. Jun 27, 2011

### Bill_K

An interesting possibility is that the antiproton briefly orbits the nucleus in place of an electron, forming what has been called an atomcule. See 'Antiprotonic Helium' article on Wikipedia.

5. Jun 27, 2011

### danR

But what about the debris-spectra on annihilation? Does it vary with different materials? There's a reason behind this question pertaining to detection. If I coat the top and bottom of a chamber containing ant-H with different materials, each having a different spectrum of annihilation photons, then I don't have to 'image' and detect for both top and bottom collisions. Just examine the spectra.

6. Jun 28, 2011

Staff Emeritus
could --> should. H- means something very different than an antiproton.

If I fire an antiproton into a nucleus 10 times, I'll get 10 different outcomes. Sometimes a few pions, sometimes many, sometimes mostly charged, sometimes mostly neutral. So the concept of a "debris spectrum" isn't really relevant.

There is a small effect based on the target Z. For large Z the nuclear electric field is stronger than for small Z, so pi+''s will be more energetic on average (because they are being repelled by the nucleus) and pi-'s will be less energetic on average (because they are being attracted by the nucleus).

7. Jun 28, 2011

### danR

Yes, my furtive substitution of modals entails a moral indiscretion. Soon I'll be making spelling errors. William Safire will weigh in.

By 'collision' I should clarify this is at or below 10 Kelvin (to keep them slow, the slower the better).

Here is a lengthy description of my setup:

I have a small (evacuated) chamber with beryllium and the bottom and lead at the top. (I don't really have this, and my university probably wouldn't let me near their shop; I'm lying through my teeth). antihydrogen atoms (not protons) are introduced.

They are not fired (which suggests quite some velocity; I should have avoided the term collided), better to say: come in contact with either the top or bottom. The positron/antiproton interacts with either a high-mass atom (surface-lattice, to be precise) at the top, or with a low mass atom at the bottom.

From what you say about proton-antiproton differences, is it reasonable to think there will be a statistical difference in the distribution of debris-species spectra with respect to antihydrogen proper?

If I run my experiment long enough, I will see whether anti-H falls or rises without having to train separate detectors on the bottom and top of the vessel. Naturally, the thing must be shielded from stray radiation, confounding fields, and the like.

Over a long run I'm thinking there should/could be peaks in the spectrum of debris showing a bias for top or bottom.

8. Jun 28, 2011