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Beryllium Free X-Ray Windows


New Be Free - Boron Carbide Windows

Amptek is announcing the introduction of Boron Carbide (B4C) windows for use with Amptek’s FAST SDD® and SiPIN detectors. The product offering is the result of a multi-year effort to provide end-users and OEM manufacturers with a high-performance window alternative to standard beryllium (Be) foils. 

Advantages

  • Comparable transmission efficiency to Be foils over a wide energy range, typical to hand-held and benchtop XRF applications
    • Results from an instrument will not be greatly affected when switching from Beryllium to B4C windows.
    • Can be used in most places where a beryllium window was previously used. 
  • Non-toxic material provides worry-free handling during installation and use
    • Concerns over the potential health hazards of beryllium and exposure are not an issue with these windows. 
  • Less thickness variation as compared to typical Be foils
    • The beryllium window forming process allows a fair amount of variation in window thickness.  The tightly controlled semiconductor fabrication process on the B4C windows produces a much more consistent window thickness.  
    • OEM's prefer this as they can expect similar transmission from detector to detector, even at lower energies.  
    • Allows for better modeling in quantitative calculations if the window thickness more closely matches the nominal values.

Applications

B4C windows have been designed to provide transmissions comparable to standard mil and ½ mil Be windows.  The initial product release utilizes a uniform 3.5 µm thick B4C layer, self-supported, without the need for an underlying grid.  An aluminum outer coating provides a grounded surface to help shield the detector from EMI. 

 

Consistent Thickness 

In comparison to beryllium (Be) window thickness, B4C window thickness is far more consistent due to the highly controllable semiconductor fabrication methods. The result is that B4C can provide more predictable transmission behavior, particularly at low energies.
  
  • Transmission for Low Z Elements +





    The figure above shows a magnesium K peak with the results from the new (B4C) Boron Carbide window overlaid on the results from a Beryllium window.  The boron carbide windows were designed to match the transmission of the Beryllium windows.  

    The figure above shows the transmission efficiency comparison of the B4C window and the Beryllium windows for 0 to 6keV x-ray energy.  


  • Specifications +


    General Specifications

     

    New Boron Carbide

    B4C

    compared to standard Be windows

     

    1/3 mil Be

    ½ mil Be

    Thickness

    3.5 µm

    7.6 µm

    .0003”

    12.7 µm

    .0005”

    Tolerance

    (-.3/+.3 µm)

    (-.0 µm/+5.1 µm)

    (-.0000”/+.0002”)

    (-.0 µm/+5.1 µm)

    (-.0000”/+.0002”)

    Diameter

    6.5 mm

    7 mm

    Grounded?

    Yes (Al coated)

     

    Additional coatings

    None

    Yes (Parylene)

    He Leak Rate

    </= 10e-13 mbar/s

    ???

    ???

    Operating Temperature

    -35 °C to +80° C

    -35 °C to +80° C

    Ruggedness

    80% survival from 4ft. drop test

     

  • Mechanicals +


    Mechanicals

    B4C windows are currently available and sized to match Amptek’s 25 mm2 FAST SDD® (illustrated) and 6, and 25 mm2 Si-PIN detectors.  Bevel covers are anticipated in Fall 2021. 

     

     

     

  • Are there any disadvantages to using B4C windows? +


    Above 1.5 keV the B4C windows offer slightly more attenuation (lower efficiency) than the Be windows. This difference is small for most elements. For example the B4C windows offer ~5% lower efficiency than Be around 3 keV. For X-rays above 6 keV the efficiency for the two windows is nearly identical.

    The B4C windows are made from the extremely hard material Boron Carbide and coated with aluminum. The characteristic X-rays from Al are observed in the spectrum. All Amptek detectors contain aluminum (e.g. the multilayer collimator is coated with aluminum) so this interference is always present. 

    The B4C windows may not survive as well in corrosive environments.  

  • Vacuum Usage +


    Yes, the B4C windows will hold vacuum. The detector hybrid has a vacuum inside, so the B4C windows usually hold 1 atmosphere of pressure. Used in a vacuum chamber, the pressure across the window is actually reduced.

    One must be careful when using these detectors in vacuum systems. It is common for debris from samples or from handling to exist inside the chamber of an XRF system. When one begins to pump or breaks vacuum, the pieces of debris can fly around inside the chamber and penetrate thin windows. Cleanliness is vital, but one must not touch the windows when cleaning the system.

    While best practice has typically been to allow at least two minutes to vent from vacuum to atmosphere, and that you vent to dry nitrogen (preferable) or air which has passed through desiccants and filters, we have found that reducing turbulent airflow in the chamber during venting, and locating the vent such that it doesn’t allow particulate to impact the window is most useful.