X-ray fluorescence (XRF) is a powerful technique for elemental analysis used in a variety of industries, from mining to electronics manufacturing. XRF is the emission of characteristic “secondary” (or fluorescent) X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays. The phenomenon is widely used for elemental analysis and chemical analysis, particularly in the investigation of metals, and for research in geochemistry, forensic science, archaeology and art objects such as paintings and murals. To generate the X-rays used in XRF, an X-ray tube is used. There are two main types of X-ray tubes used in XRF applications: side window tubes and end window tubes.
X-RAY FLOURESCENCE THEORY OF OPERATION
When materials are exposed to short-wavelength X-rays or to gamma rays, ionization of their component atoms may take place. Ionization consists of the ejection of one or more electrons from the atom and may occur if the atom is exposed to radiation with an energy greater than its ionization potential. X-rays and gamma rays can be energetic enough to expel tightly held electrons from the inner orbitals of the atom. The removal of an electron in this way makes the electronic structure of the atom unstable, and electrons in higher orbitals “fall” into the lower orbital to fill the hole left behind. In falling, energy is released in the form of a photon, the energy of which is equal to the energy difference between the two orbitals involved. Thus, the material emits radiation, which has energy characteristic of the atoms present. The term fluorescence is applied to phenomena in which the absorption of radiation of a specific energy results in the re-emission of radiation of a different energy (generally lower).
XRF is an analytical strategy, non-destructive in nature, used to discover the elemental makeup of materials. A sample is assessed using XRF analyzers by measuring the secondary, or fluorescent, x-ray emitted from it once it becomes excited from a primary x-ray source. A sample is comprised of numerous elements, each of which produces its own signature fingerprint or unique set of fluorescent x-rays. Discovering these signatures is why the X-ray Fluorescence XRF is useful technology-based machinery for both qualitative and quantitative analysis of the composition of various materials.
END WINDOW XRF TUBES
The Lightbright end window tube has a cone angle of 75° degrees, while the Minifocus side-window tube has a cone angle of 22°-26° (depending on the model). The cone angle refers to the angle of the radiation cone which is emitted from the X-ray tube. A larger cone angle means that more of the X-ray flux generated exits the tube and is available to be used in the XRF measurement. Therefore, the Lightbright tube provides a higher X-ray flux and more focused beam than the Minifocus tube. This results in faster measurement times and lower ppm detectability compared to the Minifocus tube.
One advantage of end window tubes is that they enable close tube/detector/source geometry, which maximizes the use of available flux. More flux from the tube, plus optimized geometry, means faster measurement times. However, the form factor of end window tubes does not work in app applications.
SIDE WINDOW XRF TUBES
Side window tubes minimize the distance from the window to the back of the tube’s package, which can allow for smaller form factor benchtop machines. In addition, for applications which do not require light element analysis, side window tubes can provide adequate flux in many XRF applications.
XRF FOR ROHS ANALYSIS
When it comes to RoHS analysis, both side window and end window tubes are suitable for use in He purge and vacuum environments. Both have o-ring grooves, which allows them to be compatible with vacuum or He purge measurement chambers. The Lightbright end window tube provides much more beam current at lower excitation voltages (up to 11mA!), allowing faster measurement and lower ppm detectability of light elements compared to the Minifocus tube. The Lightbright tube also has a thinner Be window (50μm) compared to the Minifocus tube (127-256μm), which can be advantageous for certain light element detection applications.
WHY MICRO X-RAY IS BETTER
Benchtop XRF machines are designed to have a small footprint with minimal wasted space inside. Our tubes incorporate a Mammoflex ® cable allowing for tight bend radius in tight spaces. Some applications require continuous x-ray operation – both our Lightbright and Minifocus tubes are designed to operate at full power continuously, while efficiently transferring internal heat to the outside. Typical XRF tubes use a high voltage well to connect the high voltage cable. This is a common cause of arcing. Micro X-Ray has eliminated the high voltage well, and thereby reduce failures due to arcing.
Another common failure mode in packaged X-ray tubes is contamination of the oil inside the package. Our Minifocus tubes use dielectric oil conditioned with a proprietary process, eliminating internal arcing and external oil leakage. For the most demanding applications, our Lightbright tubes are 100% oil-free.
And of course, all our products come with our industry-leading, Micro X-Ray standard six week lead time.
SIDE WINDOW VS END WINDOW
So which is better, the Lightbright or the Minifocus? The Lightbright end window tube offers a wider cone angle and faster measurement times, but may not fit in all existing machines. Side window Minifocus tubes offer a compact package, but lack the low energy flux of the Lightbright. The choice between side window and end window X-ray tubes ultimately depends on the specific application and requirements.
End Window X-ray Tubes
The LightBright 50W is an end window X-Ray tube designed for customers that require maximum flux, short FOD and a wide beam angle. The large heat sink coupled with the nickel plated bronze body provides efficient heat transfer enabling high power operation, all the way down to 4kV.
Mini Focus Packaged X-Ray Tubes
These x-ray tubes have bronze packaging that provides both isolation and excellent thermal properties that enable continuous operation without compromise.
We are always happy to help or advise on your specific x-ray requirements—from general to technical questions we are happy to help.