Invariance of solution of transport equations in closed subregion on surface sources of specific class

Invariance of solution of heterogeneous transport equation inside a closed subregion using a surface source set on its boundary with arbitrary change in the subregion properties was proved. Beyond the subregion solution equals the difference of the initial and subsidiary problems. The theorem proved is illustrated by numerical and analytical examples. The field of its application is heterogeneous regions of protection and subcritical systems with sources. 7 refs.; 2 figs.; 2 tabs