S For uniformly deposited dose, a simple relation ties energy, fluence and absorbed ionizing dose derivatives: D = 1.610-5 the derivative of the absorbed dose in rad(material).s-1 the particle flux in the elementary abscissa in cm, projected along the particle track (flux vector) the ionizing energy in MeV transferred per dx mass density of the material in g.cm-3 In de , the Linear Energy Transfer (LET) in MeV.cm2.mg- can be easily recognized. From the tables of LET versus particles and energies, the following set of curves can be obtained III-7 (fig. 5). For practical use, one has to be careful to observe conditions of validity, i.e. sufficient number of particles and sufficiently far from interfaces between materials SO that secondary electrons clouds overlap and be considered as homogeneous. Integrating over time, it gives also the relation between dose and fluence. Particle Fluence for 1 rad, deposited in Silicon (cm-2) (MeV cm: 2 mg-1) neutrons Blendel-7 photons electrons protons alphas oxygen Particle Energy Particles Ionizing Power Hierarchy (particules/cm2/rad(Si)) D (rad) = 1.6 E-5 LET (MeV cm2 mg-1) (cm-2) Absorbed Dose Linear Energy Integrated Flux Transfer Figure 5. Relation between dose and fluence for homogeneous dose deposition (after [VanL-75], completed). RADIATIVE ENVIRONMENTS AND SIMULATION OF THESE ENVIRONMENTS Photon interactions are not a primary concern for satellites in the natural environment. However, photon interactions are important in hardness assurance testing of devices devoted to space equipment, since most laboratories use photon sources (low energy X-rays or high energy gamma rays) to simulate total-dose effects for space applications [Holm-93], [Adam-91]. This is well suited for simulation of military environments and the nuclear power industry [Shar-94], [Coen-95] where gamma photons are encountered [Glas-77], [Boud-93], which both result from nuclear energy. But the concern exists for the reproduction of space ionizing radiation, and for the recent concern of high energy physi