Si-PIN X-Ray Detectors

The XR-100CR was a breakthrough in X-ray detector technology, providing “off-the-shelf” performance previously available only from expensive cryogenically cooled systems. Although newer detector technologies are now available, including Amptek’s XR-100SDD and the FastSDD®, the XR-100CR is still the workhorse of the XRF industry because of the combination of good performance and low cost.

The heart of Amptek’s XR-100CR is a thermoelectrically cooled Si-PIN photodiode which senses the X-rays. The two stage thermoelectric cooler keeps the detector and its input JFET at approximately -55 °C, reducing electronic noise without cryogenic liquid nitrogen. This cooling is key to the XR-100CR since it permits high performance in a compact, convenient package.

The hermetic TO-8 package of the detector has a light tight, vacuum tight, thin Be window to enable soft X-ray detection. There is vacuum inside the enclosure for optimum cooling. The XR-100CR detector includes an internal multilayer collimator to minimize background and spectral artifacts. It has a reset-style preamplifier, using a unique method of resetting through the high voltage connection to minimize noise.

In the XR-100CR the preamplifier is enclosed in a metal box, 3.0 x 1.75 x 1.125 inches, with the detector on an extender (available lengths: no extender, 1.5″, 5″, and 9”). The XR-100CR with a 5” or 9” extender is suitable for vacuum measurements, using the optional CP75 vacuum flange. Alternate preamplifiers are available, recommended for OEMs or where space is limited.

X-rays interact with silicon atoms to create an average of one electron/hole pair for every 3.62 eV of energy lost in the silicon. Depending on the energy of the incoming radiation, this loss is dominated by either the Photoelectric Effect or Compton scattering. The probability or efficiency of the detector to “stop” an x-ray and create electron/hole pairs increases with the thickness of the silicon. For more information, please refer to the Efficiency Curves on the “Performance” tab.

In order to facilitate the electron/hole collection process, a 100-200 volt bias voltage is applied across the silicon depending on the detector thickness. This voltage is too high for operation at room temperature, as it will cause excessive leakage, and eventually breakdown. Since the detector in the XR-100CR is cooled, the leakage current is reduced considerably, thus permitting the high bias voltage. This higher voltage decreases the capacitance of the detector, which lowers system noise.

The thermoelectric cooler cools both the silicon detector and the input FET transistor to the charge sensitive preamplifier. Cooling the FET reduces its leakage current and increases the transconductance, both of which reduce the electronic noise of the system.

Since optical reset is not practical when the detector is a photodiode, the XR-100CR incorporates a novel feedback method for the reset to the charge sensitive preamplifier. The reset transistor, which is typically used in most other systems has been eliminated. Instead, the reset is done through the high voltage connection to the detector by injecting a precise charge pulse through the detector capacitance to the input FET. This method eliminates the noise contribution of the reset transistor and further improves the energy resolution of the system.

A temperature monitor diode chip is mounted on the cooled substrate to provide a direct reading of the temperature of the internal components, which will vary with room temperature. Below -20 °C, the performance of the XR-100CR will not change with a temperature variation of a few degrees. Hence, closed loop temperature control is not necessary when using the XR-100CR at normal room temperature. For OEM applications or hand held XRF instrumentation a closed loop temperature control is recommended. The Active Temperature Control is standard in Amptek electronics such as the PX5 and DP5/PC5.

Figure 1. Resolution vs. Peaking Time and Temperature for the 6, 13, and 25 mm² Si-PIN detectors.

Figure 3. Resolution vs. input count rate (ICR) for various peaking times. Taken with XR-100CR and PX5.

Figure 4. PX5 throughput for various peaking times.

Efficiency Curves

Figure 5 (linear). Shows the intrinsic full energy detection efficiency for the XR-100CR detectors. This efficiency corresponds to the probability that an X-ray will enter the front of the detector and deposit all of its energy inside the detector via the photoelectric effect.

Figure 6 (log). Shows the probability of a photon undergoing any interaction, along with the probability of a photoelectric interaction which results in total energy deposition. As shown, the photoelectric effect is dominant at low energies but at higher energies above about 40 keV the photons undergo Compton scattering, depositing less than the full energy in the detector.

Both figures above combine the effects of transmission through the Beryllium window (including the protective coating), and interaction in the silicon detector. The low energy portion of the curves is dominated by the thickness of the Beryllium window, while the high energy portion is dominated by the thickness of the active depth of the Si detector. Depending on the window chosen, 90% of the incident photons reach the detector at energies  ranging from 2 to 3 keV. Depending on the detector chosen, 90% of the photons are detected at energies up to 9 to 12 keV.

Efficiency Package: A ZIP file of coefficients and a FAQ about efficiency. This package is provided for general information. It should not be used as a basis for critical quantitative analysis.

Theoretical Resolution as a Function of Energy

Resolution at Common Characteristic X-ray Energies

Example: Find the ⁵⁵Fe row in the above table and locate the resolution of the detector (bold). The column with that resolution lists the resolutions of that detector for these common energies.

X-123 Specifications

System Performance

Detector and Preamplifier

Pulse Processor

MCA

Communications

Power

General and Environmental

Operating temperature	-30 °C to +80 °C
Warranty Period	1 Year
Typical Device Lifetime	5 to 10 years, depending on use
Storage and Shipping	Long term storage: 10+ years in dry environment Typical Storage and Shipping: -40 °C to +85 °C, 10 to 90% humidity noncondensing
Compliance	RoHS Compliant
	TUV Certification Certificate #: CU 72101153 01 Tested to: UL 61010-1: 2009 R10.08 CAN/CSA-C22.2 61010-1-04+GI1

Connectors

Interface Software

Use of Collimators

Most of Amptek’s detectors contain internal collimators to improve spectral quality. X-rays interacting near the edges of the active volume of the detector may produce small pulses due to partial charge collection. These pulses result in artifacts in the spectrum which, for some applications, obscure the signal of interest. The internal collimator restricts X-rays to the active volume, where clean signals are produced. Depending on the type of detector, collimators can

• improve peak to background (P/B)
• eliminate edge effects
• eliminate false peaks

Vacuum Operation

The X-123 can be operated in air or in vacuum down to 10^-8 Torr. The X-123 can be connected to the vacuum chamber through a standard Conflat compression O-ring port. Optional Model EXV5 (5 inch) or EXV9 (9 inch) vacuum detector extender is available for this application. See figure 5 above. Click here for more information on vacuum applications and options.

XR100 Specifications

General

Detector Type	Si-PIN
Detector Sizes	6 mm2 (collimated to 4.4 mm2) 13 mm2 (collimated to 11.1 mm2) 25 mm2 (collimated to 21.5 mm2)
Silicon Thickness	500 µm
Collimator	Multilayer
Energy Resolution @ 5.9 keV (55Fe)	139 eV FWHM to 230 eV FWHM depending on detector type and shaping time constant.
Background Counts	<5 x 10-3/s, 2 keV to 150 keV for 6 mm2/500 µm detector
Detector Be Window Thickness	1 mil (25 µm), or 0.5 mil (12.5 µm)
Charge Sensitive Preamplifier	Amptek custom design with reset through the H.V. connection
Gain Stability	<20 ppm/°C (typical)
Case Size	3.00 x 1.75 x 1.13 in (7.6 x 4.4 x 2.9 cm)
Weight	4.9 ounces (139 g)
Total Power	<1 Watt
Warranty Period	1 Year
Typical Device Lifetime	5 to 10 years, depending on use
Operation conditions	-35 °C to +80 °C
Storage and Shipping	Long term storage: 10+ years in dry environment Typical Storage and Shipping: -40 °C to +85 °C, 10 to 90% humidity non condensing
	TUV Certification Certificate #: CU 72072412 01 Tested to: UL 61010-1: 2004 R7 .05 CAN/CSA-C22.2 61010-1: 2004

Inputs

Outputs

Reset Output Waveform	The output of the XR100CR swings from +5 V to -5 V. The reset period will vary with detector type and count rate.
Preamplifier Sensitivity	1 mV/keV typical (may vary for different detectors)
Preamplifier Polarity	Negative signal output (1 kohm maximum load)
Preamplifier Feedback	Reset through the detector capacitance
Temperature Monitor Sensitivity (Diode)	770 mV = -50 °C For Amptek electronics direct reading in K through software.

XR-100CR Connectors

6-Pin LEMO Connector Pin Out

Vacuum Operation

The XR-100CR can be operated in air or in vacuum down to 10-8 Torr. There are two ways the XR-100CR can be operated in vacuum: 1) The entire XR-100CR detector and preamplifier box can be placed inside the chamber. In order to avoid overheating and dissipate the 1 Watt of power needed to operate the XR-100CR, good heat conduction to the chamber walls should be provided by using the four mounting holes. An optional Model 9DVF 9-Pin D vacuum feedthrough connector on a Conflat is available to connect the XR-100CR to the PX5 outside the vacuum chamber. 2) The XR-100CR can be located outside the vacuum chamber to detect X-Rays inside the chamber through a standard Conflat compression O-ring port. Optional Model EXV9 (9 inch) vacuum detector extender is available for this application. Click here for more information on vacuum applications and options.

XR-100CR Si-PIN Application Spectra

The most common applications of the XR-100CR are in the field of X-Ray fluorescence, or XRF. This is an analytical technique which determines the elements present in a sample, and does so non-destructively and very rapidly.

RoHS/WEEE Application
Alloy Analysis: XRF of SS316, XRF of Ag/Cu
XRF of lead (Pb)
Metal Plating
Process Control
XRF of a Saint Gaudens US $20 Gold Coin
XRF of a Various Jewelry
Glass Analysis
Paper Analysis
Mössbauer Spectroscopy
Multi-Element Fluorescence Sample
Low Z Element Fluorescence
²⁴¹Am Spectrum

RoHS/WEEE Application

The RoHS / WEEE [Restriction of Hazardous Substances / Waste from Electrical and Electronic Equipment] directive requires that the electronics industry certify that products comply with maximum concentration amounts of particular elements and compounds (Cr VI, Pb, Cd, Hg, Br PBB/PBDE) by July, 2006. The chart below shows the X-ray spectrum emitted by a combination of chromium (Cr), lead (Pb), and cadmium (Cd). The XR-100CR can be used to verify compliance with the RoHS/WEEE requirements as part of a quality assurance program, via XRF. It permits users to measure the concentration of the specified elements, quickly, accurately, and non-destructively. Companies can verify supplier compliance and demonstrate their own compliance.

Figure 8. Chromium (Cr), lead (Pb), and cadmium (Cd) XRF. The RoHS / WEEE directive requires that the electronics industry certify product to comply with maximum concentration amounts of particular elements and compounds (Cr VI, Pb, Cd, Hg, Br PBB/PBDE) by July, 2006.

XRF of SS316

XRF can be used to determine exactly the alloy of a particular piece of metal. Each alloy has a unique ratio of elements, and with XRF, one can non-destructively determine the ratio of elements from the ratio of the intensities of the peaks. The spectrum below shows the spectrum of X-rays emitted from a piece of stainless steel 316, when excited by ¹⁰⁹Cd. The strong Fe line indicates that this is based on iron, while the Cr, Mn, Ni, and Mo peaks can be used to identify the alloy. This can be very important in numerous applications, such as quality assurance (verifying a vendor used the correct alloy), process control, metal recycling, etc.

Figure 9. X-Ray Fluorescence (XRF) of SS316 from ¹⁰⁹Cd.

XRF of Silver (Ag) and Copper (Cu) Alloy

Figure 10. XRF of Silver (Ag) and Copper (Cu) Alloy.

XRF of lead (Pb)

A very important special case in the field of metals analysis is that of lead (Pb). Lead has been commonly used in many products for years, from paint to plumbing solders to electronic assemblies. XRF provides a non-destructive method to assess whether or not lead is present in an item, without damaging the item. The spectrum below shows the characteristic L X-rays emitted from a piece of pure lead, with a ¹⁰⁹Cd excitation source.

Figure 11. X-Ray Fluorescence (XRF) of lead (Pb) from ¹⁰⁹Cd.

Figure 12. Lead (Pb) Fluorescence showing both K and L lines.

Plating on a Steel Connector

The spectrum below show the plating on electronic connectors. Since Cd cannot be used in certain connector applications, it can be important to verify its presence or absence. This spectrum clearly demonstrate that Cd and Cr were both used in the plating on the steel connector.

Figure 13. Cadmium & chromium plated steel

Gold (Au) Plated on Nickel (Ni)

Figure 14. Gold plated on nickel

XRF of Galvanized Steel

Figure 15. Galvanized Steel: Zinc (Zn) plating on Iron (Fe).

Process Control: XRF of Smoke Stack in Steel Plant

Figure 16.

XRF of a Saint Gaudens US $20 Gold Coin

Figure 17. XRF analysis of a Saint Gaudens US $20 gold coin with 90% Gold (Au) and 10% Copper (Cu).

XRF of a Platinum (Pt) Ring

Figure 18. Analysis of a Platinum (Pt) ring containing Copper (Cu), traces of Nickel (Ni), and Palladium (Pd).

XRF of a 14k Gold/White Gold (Au) Chain

Figure 19. Analysis of a 14k Gold/White Gold (Au) chain containing Copper (Cu) and Nickel (Ni).

XRF of Glass

Figure 21.

XRF of Paper

Figure 22.

Mössbauer Spectroscopy

The XR-100CR 7 mm²/300 µm detector is an excellent detector for Mössbauer Spectroscopy. Since the thickness of the detector is only 300 µm, it is very efficient at 14.4 keV and very inefficient at 122 keV. The ⁵⁷Co spectrum shown here shows a detection efficiency ratio between 14.4 keV and 122 keV of about 1700/1. By using a thin Aluminum absorber between the detector and the source, the 6.4 keV and 7.1 keV peaks can also be eliminated, leaving the 14.4 keV as the only detectable energy peak.

Figure 24.

Multi-Element Fluorescence Sample

Figure 25. X-ray fluorescence (XRF) of multi-element sample from¹⁰⁹Cd.

Low Z Element Fluorescence

Figure 26. Low (Z) element x-ray fluorescence (XRF) with 6 mm²/500 µm detector.

²⁴¹Am Spectrum

Figure 27. ²⁴¹Am Spectrum.

Options and Accessories

•  Other Beryllium window thicknesses are available on special order (0.3 mil – 7.5 µm).
•  Collimator Kit for high flux applications.
•  Vacuum Accessories
•  OEM Applications
•  X-123 Configuration
•  MP1 XRF Mounting Plate
•  Experimenter’s XRF Kit

Figure 28a. The X-123 configuration, which includes the detector, preamplifier, digital processor, and power supplies all in one box.

Figure 28b. The detector/preamplifier is available in OEM configurations to fit the requirements of any system. Pictured is the detector with the PA-230 preamplifier and housing. See the OEM page for details.

Figure 29. XR-100CR Detector Extender Options.

Additional Information

•  Selection Guide
•  Si-PIN vs. CdTe
•  Efficiency Package (zip file)
•  PX5 DPP, MCA and Power Supply

Use of Collimators

All of Amptek’s Si-PIN detectors contain internal multilayer collimators to improve spectral quality. X-rays interacting near the edges of the active volume of the detector may produce small pulses due to partial charge collection. These pulses result in artifacts in the spectrum which, for some applications, obscure the signal of interest. The internal collimator restricts X-rays to the active volume, where clean signals are produced. Depending on the type of detector, collimators can improve peak to background (P/B), eliminate edge effects, eliminate false peaks.

The 6 mm²/13 mm²/25 mm² X 500 µm detectors exhibit “edge effects” due to partial charge collection at the edge of the detector which produce a secondary peak.

Figure 30. This plot shows a comparison between a collimated detector and a detector without a collimator.

Although a small effect, approximately 1% of the counts of the 5.9 keV peak, an internal multilayer (see below) collimator is used on all 6 mm²/13 mm²/25 mm² X 500 µm detectors in order to remove the secondary peak.

Multilayer Collimator (ML)

A multilayer collimator is made by progressively using lower Z materials. Each layer acts as an absorber to the fluorescence peaks of the previous layer. The final layer will be of the lowest Z material whose fluorescence peaks are of low enough energy to be outside the anticipated X-ray detection range.

Amptek has developed a state-of-the-art internal Multilayer Collimator (ML). The base metal is 100 µm of tungsten (W), the first layer is 35 µm of chromium (Cr), the second layer is 15 µm of titanium (Ti), and the last layer is 75 µm of aluminum (Al).

Application Notes, Tutorials and Resources

•  Art and Archaeology
•  X-Ray Fluorescence – A Description
•  X-Ray Emission Line Chart
•  Glossary PDF
•  Publications
•  History of XR-100 Resolution
•  Digital Pulse Processor FAQ PDF

1.5 Inch Extender (standard)

Figure 31. All dimensions in inches ±0.005.

XR-100 STP File

No Extender

Figure 32. All dimensions in inches ±0.005.

General AXR (T0-8) Mechanical Dimensions

Figure 33. All dimensions in inches ±0.005.

TO-8 STP File

Typical Detector Geometry

Figure 34. Typical Detector Geometry.

Right Angle Heat Sink Mechanical Dimensions (supplied with OEM components)

Figure 35. All dimensions in inches ±0.005.

Figure 36. Detector, PA210 or PA230 preamplifier, and heat sink assembly.

Figure 37. Detector, PA210 or PA230 preamplifier, and heat sink assembly.

Download the Detector with Heat Sink STP File