SOFT-X-RAY DAMAGE TO BIOLOGICAL SAMPLES

X-ray damage to biological samples was investigated in the wavelength region of 2.7-5 nm, which overlaps the so-called 'water window', the w avelength range of 2.4-4.3 nm usually used in X-ray microscopy. Yeast cells and myofibrils were chosen as representatives of whole cell samp les and motile protein systems, respectively, The samples were exposed to X-rays using an apparatus composed mainly of a laser-plasma X-ray source, a Welter mirror condenser, and a sample cell, The yeast cells lost their dye exclusion ability when the X-ray flux was higher than 1 x 10(6) photons mu m(-2), while the myofibrils lost contractility whe n the X-ray nux was higher than 4 x 10(5) photons mu m(-2). These X-ra y fluxes are lower than the nux required for the X-ray microscope obse rvation of biological samples at a resolution higher than that of ligh t microscopes.