Experimental and theoretical results for stopping power of protons in Hafnium

C.C. MONTANARI, A. MENDEZ, D. MITNIK , J. MIRAGLIA, P.A. MIRANDA, M. AGUILERA, J. WACHTER, R. CORREA , E. ALVES, N. CATARINO, AND R.C. DA SILVA; D.M. MITNIK

Antibes

Conferencia; 24th International Conference on Ion Beam Analysis; 2019

Société Française du Vide

Stopping power cross sections of Hafnium for 0.3 to 2.5 MeV protons have been measuredusing the transmission method [1]. The measurements were made at 2.5 MV Van de Graffaccelerator of the Laboratory of Accelerators and X-Ray Diffraction in Lisbon, Portugal.The overall energy resolution of the detection system was about 15 keV relative to 5.486MeV alpha particles from a 241Am source. The stopping material was a Hafnium foil withnominal thickness of 1.0 μm and 99.95% purity. A precise thickness value was determinedto be 0.920±0.046 μm.The theoretical description involved the calculation of the relativistic wave functions andbinding energies of Hf, which proved to be different from the non-relativistic ones, even forthe outer shells. We considered 4 electrons per atom in the free electron gas (FEG), andrs=2.14 a.u. The shell-wise local plasma approximation (SLPA) [2] was employed todescribe the energy transferred to the bound 1s-4f electrons, and two different models for theFEG: the screened potential with cusp condition (SPCC) [3] for energies below that of theplasmon excitation, and the dielectric formalism, for energies around the stopping maximumand above.The experimental-theoretical comparison is shown in Figure 1, with the previous data [4],and the SRIM curve [5] too. Our curve combines the two models, the non-perturbative one(dotted lines) up to 35 keV (approximately the starting energy for plasmon excitations [3]),and the perturbative one (solid line) for higher energies. Present calculations describe wellthe new data, and also that by Sirotonin [4], except the point at 80 keV. Our curve clearlydiffers from SRIM below the stopping maximum. Future experiments for impact energiesbelow 100 keV would be important to complete this study.