Alpha and omega: Physics in the Bragg family windows??

This is the central panel of the three wonderful windows that Melvyn Bragg put in to Wigton Parish Church. The letters are the capitals for alpha and omega, the first and last letters of the Greek alphabet. Like most Greek letters, they have some Physics pedigree. Back in the day, most physicists had a classical education and were proficient in both Latin and Greek. So if you found three types of radioactivity, it was obvious to call them alpha, beta and gamma. The raises a question that had never before occurred to me: in what order were the three types isolated? Is it in the order they are listed? A capital omega is used to denote the unit Ohms. You couldn't abbreviate 10Ohms as 10O for obvious reasons. Hence the recourse to Greek.