在α衰变的习题中有下述这样一道题:题目云室处在磁感应强度为B的匀强磁场中,一静止的质量为M的原子核在云室中发生一次α衰变,α粒子的质量为m,电荷量为q,其运动轨迹在与磁场垂直的平面内.现测得α粒子运动的轨迹半径为R,试求在衰变过程中的质量亏损. In the problem of α-decay, there is a problem like this: In a uniform magnetic field with a magnetic induction of B, a static atomic mass of M undergoes α-decay in the cloud chamber. The mass of α-particle is m, the amount of charge is q, and its trajectory is in the plane perpendicular to the magnetic field.It is found that the trajectory radius of α particle movement is R, so as to seek the mass loss in the decay process.