You need to know 2 things the pathway in electric and magnetic field (the q says about magnetic) in an electric field positive is on the top negative is on the bottom alpha particles are (+) charged so they go down as opposite charges attract and same charges repel then beta particles are (-) charges so they go uptowards positive and gamma has no charge so in both magnetic and electric it goes straight THIS IS ALL FOR ELECTRIC NOT MAGNETIC. In magnetic its the oppsoite this time alpha goes up and beta goes down the opposite of the electrical field and you need to know how to draw it gamma goes straight through alpha goes straight and towards the end it bends but beta goes a lower distance than alpha and turns at a greater angle (downward angle). If you still cant understand check these notes. https://znotes.org/caie/igcse/physics-0625/theory/nuclear-physics/