Overview
EN ISO 16526-3:2020 - “Non‑destructive testing - Measurement and evaluation of the X‑ray tube voltage - Part 3: Spectrometric method” is the CEN-adopted version of ISO 16526-3:2011. It defines a non‑invasive spectrometric method for checking the X‑ray tube voltage by analysing the energy spectrum of emitted X‑rays. The standard covers the voltage range 10 kV to 500 kV and is intended to verify that the actual maximum X‑ray energy corresponds to the voltage indicated on the X‑ray unit control panel. The procedure applies to tank‑type and constant‑potential X‑ray units.
Key topics and requirements
- Purpose: Measure the maximum X‑ray energy (not the full spectral composition) to assess correspondence with the nominal tube voltage.
- Voltage range: 10 kV – 500 kV.
- Detector: Use an energy‑dispersive photon detector (e.g., Ge‑based) with:
- Energy range ≥ 20% above the expected maximum energy.
- Energy resolution approx. 1 keV FWHM.
- Multichannel analyser (MCA):
- Channel width calibrated to 0.23–0.27 keV per channel.
- Total energy range ≥ 20% above expected maximum.
- Calibration recommended using characteristic lines from radioisotopes (Ir‑192, Am‑241, Ba‑133).
- Filters and shielding:
- Use filters (Al, Fe, Cu, Pb, W) to attenuate soft radiation; minimum permitted filter material voltages are specified (e.g., Al ≥ 10 kV, Fe ≥ 15 kV, Cu ≥ 20 kV, W ≥ 140 kV, Pb ≥ 180 kV).
- When using lead filters, place 1 mm tin in front of the detector window to reduce secondary radiation.
- Annex A provides recommended filter thicknesses by voltage (e.g., 1 mm Al at 20 kV; 3 mm Fe at 80 kV; larger Fe thicknesses for higher voltages).
- Measurement practice:
- Collimated direct beam geometry with careful shielding to avoid scatter.
- Avoid pile‑up (too high count rate); choose filter thickness, beam diameter and distance accordingly.
- Minimum counting statistics: 1 000 pulses per keV.
- The maximum energy is determined where the decaying slope of the spectrum intersects the energy axis; 1 keV = 1 kV equivalence for tube voltage.
- Electronics: pulse shaping, amplifier linearity and impedance‑matched cabling are required.
Applications and users
- Practical use: routine verification, acceptance testing, maintenance checks and compliance assessments of X‑ray units in medical imaging, industrial radiography and NDT facilities.
- Typical users: NDT technicians, radiation safety officers, equipment maintenance engineers, calibration laboratories and regulatory inspectors who need a non‑invasive means to validate X‑ray tube voltage.
Related standards
- EN ISO 16526‑1: Voltage divider method (direct absolute measurement).
- EN ISO 16526‑2: Thick filter method (constancy checks).
- EN ISO 16526‑3 is the recommended spectrometric method when a voltage divider cannot be applied (e.g., tank units).
This standard is essential for accurate, traceable X‑ray tube voltage measurement, ensuring image quality, safety and regulatory compliance in non‑destructive testing and radiography.
