Silicon Drift Detector response function for PIXE spectra ﬁtting G. Calzolai a , S. Tapinassi b , M. Chiari a,⇑ , M. Giannoni a,b , S. Nava a , G. Pazzi b , F. Lucarelli a,b a INFN-Florence, via G. Sansone 1, I-50019 Sesto Fiorentino, Italy b Department of Physics and Astronomy, University of Florence, via G. Sansone 1, I-50019 Sesto Fiorentino, Italy article info Article history: Received 7 May 2017 Received in revised form 3 August 2017 Accepted 12 September 2017 Available online xxxx Keywords: PIXE SDD Detector response function Spectra ﬁtting abstract The correct determination of the X-ray peak areas in PIXE spectra by ﬁtting with a computer program depends crucially on accurate parameterization of the detector peak response function. In the Guelph PIXE software package, GUPIXWin, one of the most used PIXE spectra analysis code, the response of a semiconductor detector to monochromatic X-ray radiation is described by a linear combination of several analytical functions: a Gaussian proﬁle for the X-ray line itself, and additional tail contributions (expo- nential tails and step functions) on the low-energy side of the X-ray line to describe incomplete charge collection effects. The literature on the spectral response of silicon X-ray detectors for PIXE applications is rather scarce, in particular data for Silicon Drift Detectors (SDD) and for a large range of X-ray energies are missing. Using a set of analytical functions, the SDD response functions were satisfactorily reproduced for the X-ray energy range 1–15 keV. The behaviour of the parameters involved in the SDD tailing func- tions with X-ray energy is described by simple polynomial functions, which permit an easy implementa- tion in PIXE spectra ﬁtting codes. Ó 2017 Published by Elsevier B.V. 1. Introduction An accurate parametrization of the detector response function is required for the correct determination of the peak areas in X- ray spectra by ﬁtting with a computer program. In the software package, GUPIXWin [1], one of the most used analysis code for par- ticle induced X-ray emission (PIXE) spectra, the response of a semi- conductor detector to monochromatic X-ray radiation is described by a combination of several analytical functions: Gaussian for the X-ray peak itself, and additional tail contributions (exponential tails, long and short step functions) on the low-energy side of the X-ray peak to account for incomplete charge collection effects. The physical processes responsible for deviations from the Gaus- sian proﬁle of the X-ray peak are basic electron transport processes [2–3], including, for instance, the escape of Auger electrons and photo-electrons that are created near the front surface through that surface (responsible of a long step, ﬂat shelf function that extends to near zero energy) and the escape of thermalized ioniza- tion electrons due to diffusion out of the front surface (responsible of exponential or short step, truncated ﬂat shelf functions). The principal component of the peak is a Gaussian function, G (i), described in terms of the channel number i: GðiÞ¼ H g Á e ÀðiÀcÞ 2 2r 2 ð1Þ where c is the peak centroid (in channels), r is the Gaussian standard deviation (in channel), and H g is the Gaussian height. Depending on the particular detector, the tail contribution on the low energy side of the X-ray peak due to incomplete charge collection effects can be described by a linear combination of various appropriate analytical functions; those implemented in GUPIXWin to reproduce the detector response function are: DðiÞ¼ 0:5H d Á e ðiÀcÞ b Á erfc i À c ﬃﬃﬃ 2 p r þ r ﬃﬃﬃ 2 p b   ð2Þ T ðiÞ¼ 0:5H t Á erfc i À c ﬃﬃﬃ 2 p r   ð3Þ TSðiÞ¼ 0:5H ts Á erfc i À c ﬃﬃﬃ 2 p r   erfc i À i t ﬃﬃﬃ 2 p r     ð4Þ where D(i) is an exponential function descending leftward from the peak centroid c with height H d and inverse slope b, T(i) is a ﬂat shelf starting at the peak centroid c and extending leftward down to zero energy with height H t , and TS(i) is a step function, a truncated ﬂat shelf starting as well at the peak centroid c but extending leftward up the channel i t , with height H ts . Each function is further convoluted with a unit-area Gaussian function. https://doi.org/10.1016/j.nimb.2017.09.010 0168-583X/Ó 2017 Published by Elsevier B.V. ⇑ Corresponding author at: INFN Florence, Sezione di Firenze, via G. Sansone 1, 50019 Sesto Fiorentino, Firenze, Italy. E-mail address: chiari@ﬁ.infn.it (M. Chiari). Nuclear Instruments and Methods in Physics Research B xxx (2017) xxx–xxx Contents lists available at ScienceDirect Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb Please cite this article in press as: G. Calzolai et al., Silicon Drift Detector response function for PIXE spectra ﬁtting, Nucl. Instr. Meth. B (2017), https://doi. org/10.1016/j.nimb.2017.09.010