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. Going from an opacity map to a density map requires therefore a model or more generally an “inversion technique” that provides the most probable mass distribution functions inside the target. The inverse problem needs to be constrained by the available “a priori” information but is also driven by the data quality which imposes strict requirements on the detector performance in terms of acceptance, resolution, stability in operation, duty cycle, etc.








is shown in Figure 8-bottom: the agreement between data and simulation is not better than 20% in average. Figure 9 shows the ratio 
















