Method for Determining Mössbauer Spectrometer Line Width

Bernard A. Goodman and Joseph W. Stucki

University of Illinois

1. Ideally, use a 7-μm-thick Fe foil. Obtain spectrum at room temperature at +/- 11 mm/s and at +/- 2 mm/s. Save these files with proper dates, etc.

2. Using Notepad or Wordpad, convert the raw data text file into two files; one containing channels 0 through 511, labeled LHS, and one containing channels 512 through 1023, labeled RHS

3. Open the Recoil fitting program; select start new project, start new analysis, Lorentzian analysis.

4. Open the raw data file for LHS (will need to change the file type to “all files” to see the text data file)

5. Treat each pair of peaks in the calibration file as a separate quadrupole doublet site, giving three sites for the +/- 11 mm/s spectrum.

6. Enter the beginning parameters (CS, QS, and w+) for the respective quadrupole sites, using the values from the “channels” columns in the table below:

Iron Foil Calibration Parameters

Peaks	CS = 0 (channels)		QS
Peaks	CS = 0 (channels)		+/- 11 mm/s (23.27273 channels/mm/s)		+/- 2 mm/s (128 channels/mm/s)
	LHS	RHS	mm/s	channels	mm/s	channels
1,6	255.5	766.5	10.6246	247.26	N/A	N/A
2,5	255.5	766.5	6.1520	143.17	N/A	N/A
3,4	255.5	766.5	1.6794	39.08	1.6794	214.96
Line Width (w+ in Recoil; same as HWHM)	N/A	N/A	0.097	2.257	0.097	12.416

7. Allow only the Area to float in each doublet site by checking the box beside this parameter and unchecking all other boxes for each site.

8. Select Analysis, Fit Spectrum; the resulting fit will not be exact, but should give a result without an error..

9. Now allow QS and w+ also to float by checking the respective boxes

10. Repeat step 8. The fit now should be pretty good. If not, check to be sure sensible values appear in the windows for each of the fitting parameters for each doublet.

11. Now allow CS also to float by checking the box beside this parameter for each site.

12. Repeat step 8. The fit now should be the best.

13. Save the results for Parameters, Fitted Spectrum, Report, and Project.

14. The w+ (HWHM) value for peaks 1,6 is used to determine the line width. It can be back converted from channels to mm/s using the above calibration value. A value less than 0.12 mm/s is the target.

15. If the drive is linear, values for CS should be the same for peaks 1,6, 2,5, and 3,4. The degree to which these differ is the indication of degree of non-linearity. Also compare line width given for each set of peaks.

16. Repeat steps 4 through 15 for the RHS file. The spectrum can be folded without line broadening if the following relations are true:

(w+)_LHS = (w+)_RHS

(QS)_LHS = (QS)_RHS

(511 - CS_LHS) = (CS_RHS - 512)

If these are true, the folding point is perfectly symmetrical and folding is a valid process to use. If these are untrue, fitting each side separately is the preferred procedure, treating a sextet as three quadrupole doublet sites.

17. Now determine the HWHM and drive linearity using the +/- 2 mm/s calibration file by repeating steps 4 through 16, except only one doublet site will be used and the channel numbers for CS, QS, and w+ corresponding to the +/- 2 mm/s spectrum in the table above. Again, the target value for HWHM is less than 0.12 mm/s.

18. It is sometimes desirable to use a well ordered hematite for calibration purposes. When this is desired, repeat the procedure described above, except use the parameters given in the table below.

Hematite Calibration Parameters

Peaks	CS = 0 (channels)		QS
Peaks	CS = 0 (channels)		+/- 11 mm/s (23.27273 channels/mm/s)		+/- 2 mm/s (128 channels/mm/s)
	LHS	RHS	mm/s	channels	mm/s	channels
1,6	255.5	766.5	17.62	410	N/A	N/A
2,5	255.5	766.5	10.18	237	N/A	N/A
3,4	255.5	766.5	2.84	66
Line Width (w+ in Recoil; same as HWHM)	N/A	N/A	0.097	2.257	0.097	12.416