MODELING THE SOFT X-RAY BACKGROUND WITH MULTIPLE SUPERNOVAE by RANDALL K. SMITH A dissertation submitted in partial ful llment of the requirements for the degree of Doctor of Philosophy (Physics) at the UNIVERSITY OF WISCONSIN | MADISON 1996 i ABSTRACT The existence and isotropy of the soft X-raybackground is discussed, and explored, using a one-dimensional hydrocode with non-equilibrium cooling, multiple explosions, and dust. Analytical results derived from thermal conduction and Kahn cooling are compared