Published online: 12.06.2019
Author: James M. Byrne

#### Ideal Thickness Calculator

One of the challenges of preparing Mössbauer samples is knowing exactly how much material is needed to produce a decent spectrum with a good signal to noise ratio. Ultimately it comes down to having a suitable amount of Fe in your sample and the capacity of your sample holder. Below, we describe three methods for calculating the amount of sample you need for sample preparation:

### 1. Stoichiometric formula

Based on the approximation suggested by Rancourt 1993, you can calculate the ideal thickness of your sample by entering the molecular formula, e.g. Fe3O4 and hitting Calculate below. The calculation uses mass absorption coefficients for each element at 14.4 keV taken from Gütlich et al. 2010.

This means that if you have a sample holder of 1 cm2, you should take the "Ideal thickness" as the mass you need to add to your sample holder. For our example of magnetite Fe3O4, the ideal thickness is 21.31 mg/cm2 so you shoud add 21 mg of sample into a holder with area 1 cm2. In case you cannot create a nice homogenous thin layer when using such a small amount you can mix your sample with an Fe free unreactive compound such as glucose. For an example of a holder design, see our preparation page.

### 2. Fe wt%

In some cases, the exact composition of the sample is unknown. This is not advisable because it suggests you have little idea about what is present within the sample which is a common mistake people make when trying to apply Mössbauer spectroscopy. A rough approximation can be made for how much sample is required based on the relative mass of Fe in the sample (i.e. wt%). Simply enter the Fe wt% (e.g. type 30 for 30 Fe wt%) in the box below and press Calculate.

Fe: wt%
Thickness: mg/cm2

Caution: This calculation does not take into account the influence of other absorber atoms which might be present and can cause significant deviations from the calculated amount.

### 3. Fe Concentration

Finally, lets assume you have a liquid and are preparing a sample through the filtration method described on the preparation page. Now, we need to think in terms of the concentration of Fe present in your solution. The tool below will take that concentration (in mM) and make an approximation for the total volume of solution you need to use in order to prepare an "ideal" sample.

Concentration: mM
Volume: ml

Caution: The filtration method is not perfect and it is not always possible to use the desired volume. If filters block easily, for example if you have a lot of organic matter, you should consider preparing several and making a stack. However, if you use too many filters, then your sample will deviate from the ideal thickness estimation so do not use more thana 3 stacked filters. Furthermore, this calculation does not take into account the influence of other absorber atoms which might be present and can cause significant deviations from the calculated amount.

### References

• Rancourt D. G., McDonald A. M., Lalonde A. E., Ping J. Y., Mössbauer absorber thickness for accurate side populations in Fe-bearing minerals, 1993, American Mineralogist, Volume 78,
• Gütlich, P., et al., Mössbauer spectroscopy and transition metal chemistry: fundamentals and applications. 2010, Springer Science and Business Media