X射線點解又分軟X射線和硬X射線?

Soft and Hard X-rays are classified according to their energies.

Generally, X-rays with lower energies can only penetrate little on human skin. This soft X-ray brings much radiation dose to the skin and serves not much useful purpose in medical diagnosis.

Examples are those from some radionuclides such as Americium-241 (used in ionization chamber smoke detectors in Hong Kong), which gives off 60 keV X-rays.

Other example include mammography X-rays (X-ray used in diagnosis of breast cancer in women), which employs X-ray energy of around 40~50 keV.


More penetrating X-rays (hard X-ray) can penetrate deep into the body or even passes through the body with little attenuation. This kind of X-ray is used in widely medical diagnosis and imaging.

Examples like chest X-ray (70~80 keV) and X-ray examination of other body organs (X-ray of about 100~150 keV)

More high energy X-rays (ultra-hard X-rays) is used in medical therapy in curing cancer.

Therapeutic X-rays can be as high as 10~15 MeV.