Background: Plasma stealth is one of the most important branches of the electromagnetic stealth technology. ?-ray could ionize the air and excite the plasma. Under certain conditions

the plasma has stealth effect to the radar wave. Purpose: The aim is mainly to investigate the plasma stealth excited by 90Sr/90Y. Methods: We calculated the density distribution of the plasma excited by 90Sr/90Y with different radioactivity through configuring the weighting factor based on the decay energy spectrum of 90Sr/90Y with the electron diffusion and recombination in the air taken into consideration

and obtained the reflectivity of the plasma that was excited by infinite metal plate coated with 90Sr/90Y to electromagnetic waves with different incident angles and frequencies using the WKB (Wentzel-Kramers-Brillouin) method. Results: The reflectivity of the plasma with the radioactivity being 3.7×1010Bq?cm?2 and 3.7×1011Bq?cm?2 to the vertically incident electromagnetic wave of 1.5 GHz could reach ?2.2dB and ?7.45dB respectively. Conclusion: In the range of 1–100GHz

the reflectivity increases monotonically with the frequency

while decreases monotonically with the increase of incident angle. The stealth effect of the plasma excited by 90Sr/90Y with a certain radioactivity is of significance.Cited