Question about ionization process

[kelvin490]

we know that particles produced in radioactive decay process, such as alpha and belta particles, can produce "ion pairs" along their paths. Does the "ion pairs" means "positive ion and election pairs" or "positive ion and negative ion pairs" ? I am not sure whether negative ions can be produced by bombarding an alpha particle to air (or other gases) molecules?

 

[Astronuc]

Ionization pairs implies free-electrons and corresponding + ions. Some free electrons may be picked up by a molecule to briefly form a - ion.

Ultimately, the electrons cascade back to neutralize the + ions.

 

[kelvin490]

Ionization pairs implies free-electrons and corresponding + ions. Some free electrons may be picked up by a molecule to briefly form a - ion.

Ultimately, the electrons cascade back to neutralize the + ions.

Thanks. But why sometimes neutral molecules can pick up free electrons to form -ve ion?

 

[Astronuc]

Thanks. But why sometimes neutral molecules can pick up free electrons to form -ve ion?

Because the molecule has some affinity for electrons. Some atoms readily give up electrons, e.g., the alkali metals like Cs, K, Na, Li, while other atoms, e.g. halides more readily accept electrons.

There are cations and anions.

 

[Bob S]

Thanks. But why sometimes neutral molecules can pick up free electrons to form -ve ion?

This article describes the design of a negative hydrogen ion beam source.

http://docs.google.com/viewer?a=v&q...cLUFct&sig=AHIEtbTVOYlzweasDlXP2W9iJ2SfJDI98g

The negative hydrogen ion is a single hydrogen atom with one proton and two bound electrons. The "second" electron is bound by about 0.75 eV (electron volts). The negative hydrogen ion is easily accelerated in particle accelerators, and one or both electrons are easily stripped off by a laser or by a thin foil.

Bob S

 

[Bob S]

In a gas, a charged particle (alpha, beta decay or cosmic ray) can ionize the gas, producing a positive ion and a free electron. It usually takes 25 to 35 eV energy loss to create an electron-ion pair in a gas. Electrically-charged plates in ionization chambers can collect these electron pairs, creating a current proportional to the number of electron-ion pairs per second. See section on gas ionization chambers in

http://beamdocs.fnal.gov/DocDB/0010/001068/001/A%20tutorial%20on%20beam%20loss%20monitoring.pdf

Bob S