# Units of Electron Volts (AMeV)

1. Nov 18, 2009

### GreenLRan

Hi,
I have been viewing some publications related to space weather and have noticed that in many graphs and in the articles, the units AMeV appear very often. I am wondering what the A is for?

My best guess is that means atomic, ie relating energies of ions rather than single electrons. Does anyone know for certain. If so, can you provide proof or documentation?

Thank you!

2. Nov 18, 2009

### Norman

A is the mass number of a nucleus. So if a Carbon nuclei has 1 A MeV, it has a total energy of 12 MeV since A=12 for Carbon.

3. Nov 19, 2009

### sophiecentaur

That's weird. If an eV is the energy of a single electronic charge which has been accelerated across 1V PD then it will be the same for all singly charged objects. If the atom is multiply ionised then the energy would be higher, natch, but would it not relate to the Atomic (Proton) Number, rather than the Mass Number? (The Neutrons are not accelerated by the V, after all)
All this is only applicable under pretty extreme generating conditions, I guess.

4. Nov 20, 2009

### Rajini

hi Norman,
is there any book explain it. because i notice in particle physics journal many author ref it as AMev or AMeV, without a space between A/A and MeV. I also just curious about this unit confusion..
thanks

5. Nov 20, 2009

### Redbelly98

Staff Emeritus
I think the rational for AMeV units is that it gives the energy-per-nucleon, an important quantity to know for nuclear reactions. For example a 12 MeV C-12 nucleus is comparable to a 56 MeV Fe-56 nucleus. Different total energies, but each has the same 1 AMeV.

6. Nov 21, 2009

### Norman

I don't know of any books off hand that cover the subject (there might be some older nuclear physics books that I am not familiar with that look at it). Much of your confusion is simply sloppy notation which is very common the physics literature and which I am often guilty of. Typically there is no space between the A and MeV. And whether A is italicized or not is likely due to whether the author is using italic letters to denote variables or not.

7. Nov 21, 2009

### uart

So does that mean that this unit have been better expressed as MeV/A ?