I use True BASIC routinely, and that is indeed what this code is. It is a very powerful, flexible, and easy to use language. When my last employer required everything to be done in Matlab, I would first get it running in True BASIC, and then convert to Matlab, a great waste of effort, but easier for me than working in Matlab.
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The main program is the first 10 lines, down to the END statement. There are three external subroutines called INITIALIZE, CALCULATE, AND DISPLAY. The calling arguments for each are shown in the main program, and they correspond one-to-one to the lists in the subroutine declarations, even through the names are different. Thus, the first calling argument in the call to INITIALIZE is n_uraniaum which was previously dimensioned 100 in the main program. In the subroutine, the first argument is NUCLEI() where the parenthese tell the code to exxpect a one dimensional array.
The easiest way to run this code is to download the free trial version of True BASIC Bronze edition from TrueBASIC.com.