X-Ray Detector Selection Guide

FAST SDD®:  This is Amptek’s highest performance detector. The FAST SDD® is recommended for users needing the best performance. It can provide the best energy resolution (down to 122 eV FWHM at 5.895 keV), can measure the lowest energy X-rays (down to the Li Ka line at 52 eV), has the best peak to background ratios, can run at the highest count rates (> 1 Mcps), and is available at the largest areas (up to 70 mm2). The FAST SDD® is widely used in the most demanding XRF applications, in EDS and SEMs/TEMs, in synchrotrons, and other research systems.

Si-PIN: Recommended for applications requiring moderate energy resolution and count rate, where cost is most important. Si-PIN devices have a conventional planar structure, yielding more electronic noise than an SDD but are easier to fabricate. There are three different Si-PIN variations currently available, with areas of 6 mm2, 13 mm2, and 25 mm2. The 6 mm2 detectors provide an energy resolution of 140 eV FWHM at the 5.9 keV Mn Ka line at count rates up to 50k cps. The 13 mm2 and 25 mm2 detectors typically offer energy resolutions of 180 and 210 eV FWHM for the same count rates.

CdTe: Recommended for applications above 20-30 keV. CdTe has much higher stopping power than Si and can be made much thicker, so has high efficiency for all characteristic X-rays, even up to the K lines of U. The electronic noise of CdTe is worse than that of either Si detector (resolution typically 450 eV FWHM at the 5.9 keV Mn Ka line), making a Si detector a better choice for energies below 20 keV. But above 20 to 30 keV, the resolution is dominated by Fano broadening anyway so the difference becomes small, the characteristic X-ray lines are more widely spaced, and the efficiency of the Si detector falls off, making CdTe a better choice. The CdTe detectors is very well suited to measuring the spectrum from an X-ray tube, where efficiency is very important and energy resolution is less critical.  CdTe is also the best choice for Gamma-Ray applications.

Comparison between CdTe and Si-PIN detectors.

*All results are under full detector cooling; please Contact Us to discuss guaranteed performance under different operating conditions. The Peak to Background (P/B) Ratio is the ratio of counts from 5.9 keV to 2 keV for 13 and 25 mm2 Si-PIN, and 5.9 keV to 1 keV for all SDDs and 6 mm2 Si-PIN.

The user should not only consider resolution in selecting a detector, but also area, thickness, throughput, and peak to background.

Figure 4. Resolution vs. Peaking Time for Si-PIN and SDD Detectors. Peaking time is approximately 2.4 x shaping time.

Figure 5. Resolution vs. Peaking Time and Temperature for 6 mm², 13 mm², and 25 mm² Si-PIN detectors.

Figure 6. Resolution vs. Peaking Time and Temperature for the 25 mm² Standard and FAST SDD® detectors.

Figure 7. Resolution vs. Peaking Time and Temperature for the 70 mm² FAST SDD® detector.

All Amptek x-ray detector elements are available in the XR-100, X-123, or OEM configurations.

The XR-100 configuration includes the detector and preamplifier only and must be paired with the PX5 Digital Pulse Processor, MCA, and Power Supply to be a complete system (or the DP5/PC5 OEM processor and power supply). The XR-100/PX5 combination is the most flexible and is designed for laboratory and research use. The PX5 can be used with other detectors, including from other manufacturers.

The X-123 includes the detector, digital pulse processor, MCA, and power supply all in one box, and is a complete system. The X-123 configuration is ideal for OEM bench-top and custom applications where size, portability, and speed to market are considerations.

For hand-held and custom OEM applications, other configurations are available.

Figure 1. The XR-100/PX5 configuration.

Figure 2. The X-123 configuration.

Figure 3. OEM configuration.

Figure 4. XR100 and X-123 with 9 inch extender and vacuum feedthrough coupling.