What is the difference between hard x-rays and soft x-rays? I mainly need to know what soft-rays are used for. :) (Can't find the right topic for this question)

X-rays with high photon energies (above 5–10keV, below 0.2–0.1nm wavelength) are called hard X-rays, while those with lower energy (and longer wavelength) are called soft X-rays. Due to their penetrating ability, hard X-rays are widely used to image the inside of objects, e.g., in medical radiography and airport security. By contrast, soft X-rays are easily absorbed in air; the attenuation length of 600 eV (~2nm) X-rays in water is less than 1 micrometer.

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the skeletons of most mammals reach a certain size and then stop growing. however, many animals, including some mammals, keep growing throughout their lives. kangaroos, for example, just keep growing and growing until they die. also, the longer an animal lives the greater the chance it might catch some deadly disease.