Duration of the Solar Radio Spike Radiation at Decimetric Waves and Milliseconds

The duration of the solar radio millisecond spike radiation is shortened with the increase in the frequency,which has been a puzzling problem for a long time.In this paper,according to the electron cyclotron maser excited by the electron beams of the hollow beam distribution associated with the type Ⅲ bursts,the relation between the duration of the spike radiation and the characteristic frequency ratio(i.e.the parameter ξ=ω_P/ω_B) with the wave growth rate is discussed in detail.Finally,it is concluded that at the different wavelengths of the decimetric wave,the spike radiations are the different frequency harmonic waves and the correlative decrease of the duration appears with the increase in the frequency