Absorption in the Region of Soft X-Rays

Abstract

Energy of soft x-rays from a tungsten-coated nickel target as a function of potential from 40 to 610 v---Soft x-rays from the target were allowed to fall on a solid solution consisting of CaS${\mathrm{O}}_{4}$+2 percent MnS${\mathrm{O}}_{4}$. The square of the time of duration of the thermoluminescence produced was assumed to be proportional to the total energy of the x-rays. The results indicate that in the range 40-610 v., the total energy varies approximately as the square of the potential applied to the tube.Absorption of soft x-rays (40-610 v.) by thin celluloid films.---By interposing a thin celluloid film, about 25 m\ensuremath{\mu} thick, between the target and the thermoluminescent substance, the transmission of the film was measured for various values of the applied potential from 40 to 610 volts. The transmission varied from 0.0 percent at 40 volts (minimum wave-length 310A) to 57 percent at 610 volts (minimum wave-length 20A). The results are in general agreement with the hypothesis that the absorption varies as the cube of the wave-length, that K absorption discontinuities in celluloid occur between 300 and 600 volts and that the x-rays cover a wide spectral region. A photographic method of investigating absorption is also described. The results are fairly consistent with those obtained otherwise but the method suffers from the fact that the photographic plate is not equally sensitive to energy of different wave-lengths.Absorption of soft x-rays (300-600 v.) in air and ${\mathrm{H}}_{2}$.---Computation based on previous measurements give for air values of $\frac{\ensuremath{\mu}}{\ensuremath{\rho}}=6.0, 6.25, 7.0, 7.6\ifmmode\times\else\texttimes\fi{}{10}^{3}$ at 600, 500, 400, and 300 volts respectively. These figures agree fairly well with those given by Holweck in ${\mathrm{O}}_{2}$ and ${\mathrm{N}}_{2}$. For ${\mathrm{H}}_{2}$ the value of $\frac{\ensuremath{\mu}}{\ensuremath{\rho}}$ is calculated to be about 1.8\ifmmode\times\else\texttimes\fi{}${10}^{4}$ which is larger than the value given by Holweck and larger than is to be expected from the results for air.