With expansion and deepening of investigations into the NPL lasing mechanism, as well as the specific features of onset and development of optical inhomogeneities in them, the question of how to determine the share of fission energy which is transmitted directly to the gas became increasingly more critical. Despite some differences in approaches, all of the calculation and theoretical work yields similar quantitative results. But in experimental investigations, lower values of efficiencies є were obtained, in comparison with calculations. And the results of different authors differed markedly from one another [27—33]. The greatest discrepancy between experiment and calculation (by roughly double) was obtained in studies [30, 31]. If such a great difference did indeed occur, it could lead to the need for adjustment of the efficiency values, and possibly the kinetic models of the NPL (see Chap. 5). Therefore, analysis of the causes of the spread of the experimental results on the efficiency of the energy deposition by fission fragments and their discrep­ancy from the calculated values is very important. Apart from that, this parameter plays a significant role in calculations of the energy and mass-dimension properties of reactor-laser facilities.