**Definition:**

The observed and calculated linear attenuation coefficient, \m, in units of inverse millimetres. Note that this quantity is sometimes referred to as the mass absorption coefficient; however, this term accounts for other potentially significant losses of incident radiation, for example incoherent scattering of neutrons. The calculated \m will be obtained from the atomic content of the cell, the average density (allowing for specimen packing) and the radiation wavelength. The observed \m will be determined by a transmission measurement. Note that _pd_char_atten_coef_mu_calc will differ from _exptl_absorpt_coefficient_mu if the packing density is not unity.

The permitted range is 0.0 -> infinity

**Type:** numb

**Category:** pd_char

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