Published online: 03.06.2019
Author: James M. Byrne

Sample Preparation

Sample preparation is crucial for ensuring good quality spectra are collected in a reasonable time frame. The sample must be fixed so as to enable recoilless absorption and emission of γ-radiation. In general, for measurement in transmission configuration, the sample must be thin and homogeneous and have sufficient 57Fe concentration to obtain a useable spectruma within 1 day. Longer measurement time may be required for environmental sciences. Outlined below are three different approaches for preparing Mössbauer samples for measurement in transmission.

  1. Filtration of wet sample.
  2. Dry powder in plexiglas cap.
  3. Viscous fluid frozen in cap.

1. Filtration of wet sample

We routinely use this method for measuring samples which require extraction from a reactor containing a solution. For example, microbial cultivation experiments or sediment slurries. The approach is relateively easy, however it typically results in longer measurement time because filters block easily, learing to unsatisfactory amounts of Fe in a sample.

Prior to taking samples, prepare the filter housing unit:

Sampling:

Notes
prep
Figure 1 - Filter houseing unit. A) All necessary parts of the filter housing unit; B) Completed filter housing unit compared against scale in cm; C) Example of kapton-filter-kapton sandwich containing a sample.

2. Dry powder in plexiglas cap

We routinely use this method for measuring samples which have been air dried and freeze dried. The holder is a custom design which was produced in our workshop, but in general it should be possible to make your own version.

Prepare the sample holder:

Sampling:

Notes

prep
Figure 2 - Completed plexiglas cap (1 cm2) containing a sample. The inner part is placed within the outer part

3. Viscous fluid frozen in cap.

We very rarely use this appraoch except for samples which cannot be filtered or dried. We have custom designed Teflon caps which were made in our workshop.

Prepare the sample holder:

Sampling:

Notes

prep
Figure 3 - Teflon cap for viscous samples