She S. In terms of diameters, then there’s a 15-fold difference between 20 and 300 nm. The scattering is roughly proportional to d^6 (Rayleigh) and thus is approximately 11.4 million times as much scattering from a 300 nm particle as from a 15 nm particle. Did you mix them in approximate 1:10 million dilution to get equal peaks? Even in the region where equal volumes scatter with equal intensities (Mie), then you’d still need them in 15^3 proportion. The scattering from the 300 nm particles swamps that from the 20 nm particles.

She S. Also take a look at:

https://www.materials-talks.com/intensity-volume-number-which-size-is-correct/

Now consider 2 particles - one of 20 units and one of 300 units. Which one do you prefer? On a number basis they have equal validity (weighting). Imagine they're particles of gold, which one would you like? The volume and mass of the 300 unit one is over 1000 times (3375 to be precise) that of the 20 unit one. That's over 3000 times the value... Most materials are sold on the basis of mass or volume. When was the last time you bought or specified 3 million particles of cornflakes?

She S. BTW, with what research group are you associated? Take a look at:

https://help.researchgate.net/hc/en-us/articles/14292743587601-Your-institution-and-department

and the 'Use your real identity' on the Community Guidelines section:

https://www.researchgate.net/community-guidelines

Thank you Alan for your answer.