A stationary ball of radius R is irradiated by a parallel
stream of particles whose radius is r. Assuming the collision of
a particle and the ball to be elastic, find:
(a) the deflection angle 0 of a particle as a function of its aiming
parameter b;
(b) the fraction of particles which after a collision with the ball
are scattered into the angular interval between 0 and 0 + d0;
(c) the probability of a particle to be deflected, after a collision
with the ball, into the front hemisphere (0 <