External scanning micro-PIXE for the characterization of a polycapillary lens: Measurement of the collected X-ray intensity distribution

• Published in: Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms Beam interactions with materials and atoms, 2010-06, Vol.268 (11), p.1945-1948
• Main Authors: Grassi, N., Guazzoni, C., Alberti, R., Klatka, T., Bjeoumikhov, A.
• Format: Article
• Language: English
• Subjects: Collection; Detectors; Lenses; Microorganisms; Proton beams; Scanning; Scanning micro -PIXE; Silicon Drift Detector; X-ray polycapillary optics; X-rays
• ISSN: 0168-583X; 1872-9584
• DOI: 10.1016/j.nimb.2010.02.100

We developed a PIXE detection system for the analysis of medium-light elements which exploits a weakly focusing polycapillary lens for the transmission of the X-rays emitted from the target material to a Silicon Drift Detector. The polycapillary lens efficiently collects X-rays, while prevents back-scattered protons from impinging on the detector chip, thus avoiding electronics perturbation and consequent quality loss of PIXE spectra. The system is optimized for the detection of X-rays in the energy range 1–10 keV, when the emission from the target is induced by MeV proton beams with size of the order of a few hundreds of micrometers. This work reports the results of the lens characterization in terms of X-ray collection spot, i.e. the area of the sample actually “seen” by the lens, and its dependence on the X-ray energy. The lens properties have been measured using the external scanning microbeam facility of the Tandetron accelerator at LABEC-INFN in Florence. The detection system was used to detect X-rays from a set of pure elemental standards with an incident 3 MeV proton beam focused to a size of about 30 μm scanning an area of 1.9 × 1.6 mm 2. By measuring the spatial distribution of characteristic X-rays from each given material, the collection profile of the lens at the corresponding X-ray energy was obtained. Using several standards, the behaviour throughout the range 1–10 keV was examined. The sensitivity of the lens collection profile on the lens-sample out-of-focus distance was also investigated.