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Hard x-rays are the highest energy \(x\)-rays, while the lower energy \(x\)-rays are referred to as soft \(X\)-rays. The distinction between hard and soft \(x\)-rays is not well defined. Hard x-rays are typically those with energies greater than around \(10 keV\). More relevant to the distinction are the instruments required to observe them and the physical conditions under which the \(x\)-rays are produced.