Quasi-Elastic Sample Thickness Estimate

Usage notes:

To calculate the sample thickness that you need for your the desired percent scattering (usually 10%) enter the compound and the mass density and click "Calculate". The first calculation will take the longest because the program has to download all of the data tables of neutron scattering lengths, but it should be faster after that is performed.

It is not necessary to enter a number into the wavelength field. The wavelength is used to calculate the absorption cross section. The default wavelength is 1.8 Angstroms. If a value is entered into this field the absorption cross section will be scaled as wavelength/1.8 since the cross section data is given for 1.8 Angstrom (2200 m/s, 0.0253 eV, thermal) neutrons.

Specific isotopes are specified by putting the mass number in parenthesis after the symbol.

Element Symbols are case sensitive.

Only integer stoichiometry is supported at this time. If there is sufficient interest I will add non-integer stoichiometry. Until it is added you can use factors of 10 to do non-integer stoichiometry. For instance if you wanted to calculate Pd_1.3Si you can enter it as Pd13Si10, and as long as the density is correct it will calculate it correctly.

Examples of how to format the compound name:

• SiO2 (silicon dioxide)
• H20 (water)
• H(2)2O (heavy water), can also be written as D2O
• A 50% mixture of H2O and D2O can be calculated as follows: The mass densities of H20 and D2O are 1.0 and 1.1 g/cm^3, respectively. A 50-50 mixture of the two would then have a mass density of 1.05 g/cm^3. Write this mixture of H2O and D2O as H2OD2O or more simply as HDO. Other compositions can be calculated as well, for example a 70-30 mixture of H2O/D2O can be written as H14O7D6O3 or more simply H7D3O5 (i.e. 7 hydrogens, 3 deuteriums, and 5 oxygens) and the mass density calculated based on the percentages of H and D.
• C(13)6H(2)12O(18)6 (6 Carbon-13 atoms, 12 deuterium atoms, and 6 Oxygen-18 atoms)

To see what isotopes can be included in these calculations look at Neutron Scattering Lengths and Cross Sections on the web. All of the isotopes contained in that site are included in this calculator.

Report errors or make inquiries to Alan Munter, <[email protected]>