Portal de Periódicos da CAPES

Multiple Coulomb scattering of 160 MeV protons

1993; Elsevier BV; Volume: 74; Issue: 4 Linguagem: Inglês

10.1016/0168-583x(93)95944-z

1872-9584

B. Gottschalk, Andreas Koehler, Robert J. Schneider, J. M. Sisterson, Miles Wagner,

Nuclear Physics and Applications

We have measured multiple Coulomb scattering of 158.6 MeV protons in fourteen materials from beryllium to uranium including brass and several plastics. Targets ranged from thin (negligible energy loss) to very thick (greater than the mean proton range). The angular distribution was measured by means of a single diode dosimeter scanned typically over two decades of dose falloff. Each data set was fitted with a Molière scattering distribution (using Bethe's tables) to extract a characteristic angle θM as well as a Gaussian distribution to extract a characteristic angle θ0. As expected in the small angle region, the Gaussian fits about as well as the Molière shape. The θM values were compared with Molière's predicted value (χcB2) including Fano's correction for scattering by atomic electrons and using Molière's formalism to account for energy loss and/or compound targets or mixtures. The distribution of the deviation from theory for 115 independent measurements is approximately normal, with a mean value − 0.5 ± 0.4% and an rms spread of 5%. The θ0 values were compared with Highland's formula and with an “improved Highland” formula of Lynch and Dahl, using our own generalization to thick targets. The overall accuracy of Highland's formula is slightly worse than that of Molière theory. The distribution of the deviation from theory for 115 independent measurements is normal, with a mean value − 2.6 ± 0.5% and an rms spread of 6%. The Lynch formula gives nearly the same average statistics though details of the fit are different. Some data were taken for very thick targets (thickness greater than 97% of the mean proton range) where only a fraction of the incident protons emerge. Here the characteristic angle appears to level off or even to fall slightly with target thickness perhaps due to the filtering out of large-angle protons. These measurements are presented but were excluded from the comparison with theory. We have reviewed six other published proton measurements, partially reanalyzing four whose authors claimed that Molière theory either did not apply (because of thick targets) or was incorrect. These experiments range from 1 MeV to 200 GeV incident energy. Averaging each measurement including our own over everything but target material we obtain 39 independent measurements of the deviation from theory whose distribution is normal with a mean value − 0.3 ± 0.5% and an rms spread of 3%. We conclude that Molière theory with the Fano correction is accurate to better than 1% on the average for protons. Systematic discrepancies on the order of a few percent with target thickness and/or target material cannot be ruled out at present. In particular there is some indication that the theory may be ≈ 4% high for the highest-Z materials.