What technique could Becquerel and others have used to determine that a rays are positively charged, b

Question:

What technique could Becquerel and others have used to determine that a rays are positively charged, b rays negatively charged, and g rays uncharged? Explain how they could find that a rays have a charge-to-mass ratio half that of the H+ ion, and β rays have the same chargeto-mass ratio as "cathode rays" (electrons). (See Chapter 19 for some ideas.)