Yes, IONIZATION is a Scrabble word!

Letter values in Scrabble US: I 1, O 1, N 1, I 1, Z 10, A 1, T 1, I 1, O 1, N 1.

Is it a valid word?

IONIZATION is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

the condition of being dissociated into ions (as by heat or radiation or chemical reaction or electrical discharge)
the process of ionizing; the formation of ions by separating atoms or molecules or radicals or by adding or subtracting electrons from atoms by strong electric fields in a gas

Not playable in Scrabble US: IONISATION.