Uranium-238 emits alpha particles which are less penetrating than other forms of radiation, and weak gamma rays As long as it remains outside the body, uranium poses little health hazard (mainly from the gamma-rays).Beginning with naturally occurring uranium-238, this series includes the following elements: astatine, bismuth, lead, polonium, protactinium, radium, radon, thallium, and thorium.nThe peak happened I n 90,100,130 and 140

I would refer to the Lund Radioisotope Library that is the reference for radiation emission lines from radioisotopes... (http://nucleardata.nuclear.lu.se/toi/)

Especially consult the page for U-238 (http://nucleardata.nuclear.lu.se/toi/nuclide.asp?iZA=920238) we see that gamma rays at 49.5 keV and 113.5 keV have a really low intensity hence are difficult to detect with a spectrometer, same sroty for the x-rays emitted by U-238.

What it is often done is to detect emissions following the decay of the first daughter, 234Th (http://nucleardata.nuclear.lu.se/toi/nuclide.asp?iZA=900234

63 keV and 92.5 keV that is the sum of two lines at 92.3 and 92.8 keV). These lines might be difficult to quantify because of attenuatiopn/interferences in that part of the spectrum so you might need to use a correctly designed shield and some post-processing of the spectrum...

You may be interested in a recent paper we published, where we measured fission products gamma rays from uranium 238 (in photofission, not spontaneous fission, however). We computed the cumulative fission yields from prominent peaks: Article Measurement of cumulative photofission yields of 235 U and 2...

Spontaneous fission of natural uranium is low rate process, so concentrations of fission nuclei is very small. Much more gammas are coming from daughter of decay chain: https://physicsopenlab.org/2016/01/29/uranium-gamma-spectrometry/