I had lung xray, i think my semen was also exposed, is my sperm become dead? do i need to masturbate to remove dead sperm, how many times?

Unlikely.: I don't think so. One chest x-ray wouldn't cause such harm. At your age you can still be fertile . Get a sperm analysis to check condition of your sperms. Stay active and eat healthy.

Not a concern: There is essentially no appreciable gonadal radiation dose from a single chest x-ray. To learn more about radiation exposure please visit: http://www.Conciergeradiologist.Com/radiation-exposure.Html.