Backscattering Study of Electrons from 0.1 to 3.4 MeV

TL;DR

The paper addresses uncertainties in modeling electron backscattering in matter for energies from 0.1 to 3.4 MeV by measuring backscattering probabilities with a 2×2π calorimeter surrounding YAP:Ce scintillators and a 6He beta source. It combines a detailed experimental setup, background subtraction, and a robust Geant4-based simulation framework comparing six electromagnetic physics lists, focusing on Option4, Livermore, and Penelope. The results show that these lists reproduce both the overall backscattering probability (within about 3.5%) and the energy tail distributions across large incidence angles, significantly improving confidence in low-energy electron transport simulations. This work provides a concrete benchmark dataset to reduce systematic uncertainties in beta-decay and related applications, and highlights the importance of using appropriate EM physics lists for accurate backscattering modeling.

Abstract

Benchmarking simulation codes for electron transport and scattering in matter is a crucial step for estimating uncertainties in many applications. However, experimental data for electron energies of a few MeV is scarce to make such comparisons. We report here the measurement and the quantitative analysis of backscattering probabilities of electrons in the energy range 0.1 to 3.4~MeV impinging on YAP:Ce scintillator. The setup consists of a $2\times 2π$ calorimeter which enables, in particular, the inclusion of large incidence angles. The results are used to benchmark various scattering models incorporated in Geant4, showing relative deviations smaller than 5% between experiment and simulations. They demonstrate the current rather high reliability of the simulations when employing appropriate electromagnetic Physics Lists.

Figures (15)

• Figure 1: Sectional views of the detection setup for respectively (a) the implantation and, (b) the detection configurations. The labels indicate the $^6$He$^+$ beam (1), the Ø 4 mm collimator (2), the two YAP scintillators (3,4) and the beam implantation region (5).
• Figure 2: Sectional view of the detector assembly in the measuring configuration. The red and purple arrows indicate the scintillation light distributed between the two detectors. The $f_{ij}$ coefficient inside an arrow corresponds to the fraction of light collected by PMT $i$ and originating from YAP crystal $j$.
• Figure 3: 2D histogram registered during the first half of the decay window showing the energy collected in Det. 2 ($Q_2$) versus the energy collected in Det. 1 ($Q_1$), after background subtraction and a crude energy calibration.
• Figure 4: 2D histogram collected during the first half of the decay window, after background subtraction, calibration and optical crosstalk correction.
• Figure 5: Backscattering probability $R_{\rm sim1}$ obtained from Geant4 simulations as a function of the total deposited energy, for five Physics Lists. The energy bin width is 100 keV. The error bars are only statistical, at $1\sigma$, and are visible at the extremes of the spectrum.