Normalized x-ray dose depends on the target effective thickness. 

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... the Monte-Carlo code EGS4 [8]. The electron beam parameters are obtained from DRAGON-I LIA as following: the electron current 2.5 kA, the electron energy $ 19 MeV , and the beam pulse width $ 70 ns . The normalized x-ray dose near 0 forward scattering dependence on the tantalum target thickness is shown in Fig. 1. The figure shows that the x-ray dose exceeds 90% of the maximal dose when the target thickness is larger than 0.4 mm. Above this value, small dose variations occur for relatively large thickness changes. Accordingly, we can conclude that the x-ray dose will satisfy the request of the x-ray machine for single electron pulse or multipulse operation if the target effective thickness is not less than 0.4 mm. We proposed a multipulse converter design which uses 1.2 mm thick tantalum foils evenly distributed over 1 cm. The design aims are to decrease the energy deposi- tion density in the converter target and reduce destruction of target material in order to satisfy the multipulse demand [9]. The configuration drawing of the distributed target is described in Fig. 2. We simulated the normalized angle distribution, and measured the x-ray doses and spots of two kinds of converter targets, standard and distributed target, for a single electron pulse, respectively. Figure 3 shows the comparison of normalized angle distribution for numerical simulation and the experiment measurement, respectively. The x-ray spots of different experiments are given in Table I. The electron beam is produced from DRAGON-I LIA. Figure 3 and Table I show that the distributed target can generate the similar dose after interaction with single pulse electron beam, and the x-ray spots are also stable and satisfy the demand of the single pulse electron beam ...