Dear Sohrab Bin Noor ,

please have a look at the certificate of the SRM 1976c given in

https://tsapps.nist.gov/srmext/certificates/1976c.pdf

Please have a look at page 1 in the section 'Material Description'.

It is stated there:

"Given this, and the essential absence of crystallite sizebroadening, SRM 1976c can be used to obtain an approximation of the instrument profile function".

So, to my opinion, you do not need any further steps for evaluating your IB.

Take the FWHMs of around 0,2 to 0,3 as the IB (but smooth the glitch at around 77° to about 0,3; at that section there will be measurement errors due to the closely lying peaks).

There is only a weak 2theta dependence and its variation will be within the error margin of your FWHM evaluation. Thus you should only assign a single value to the IB.

There are only two peaks [ (104) at about 35°, 100% and (116) at 57,5°, 87%]*) which have significant peak heights and their FWHM evaluation will be quite reliable. So you should take the mean of their widths as the IB (~0,25?).

By the way; peak broadening of about 0,25° is due to 30 to 40 nm crystallite sizes...

*) see page 4, table 1 and 3.

Best regards

G.M.