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Mo/Rh/W target-filter spectra & characteristic peaks

An x-ray energy spectrum for mammography. Relative photon fluence is plotted against photon energy in keV. A molybdenum target produces two sharp characteristic peaks at about 17.5 keV (K-alpha) and 19.6 keV (K-beta) sitting on a low bremsstrahlung continuum. A matched molybdenum filter removes the low-energy bremsstrahlung on the left and, at its K-edge near 20 keV, sharply cuts higher-energy photons, leaving a narrow quasi-monochromatic window between roughly 17 and 20 keV that maximises soft-tissue contrast at low dose. A rhodium filter K-edge near 23.2 keV is shown as the harder-beam alternative for denser breasts.

Molybdenum target and matched filter mammography spectrum An x-ray energy spectrum for mammography. Relative photon fluence is plotted against photon energy in keV. A molybdenum target produces two sharp characteristic peaks at about 17.5 keV (K-alpha) and 19.6 keV (K-beta) sitting on a low bremsstrahlung continuum. A matched molybdenum filter removes the low-energy bremsstrahlung on the left and, at its K-edge near 20 keV, sharply cuts higher-energy photons, leaving a narrow quasi-monochromatic window between roughly 17 and 20 keV that maximises soft-tissue contrast at low dose. A rhodium filter K-edge near 23.2 keV is shown as the harder-beam alternative for denser breasts. Mammography: molybdenum target with a matched molybdenum filter 0 5 10 15 20 25 30 photon energy (keV) relative photon fluence Kα 17.5 keV Kβ 19.6 keV Mo filter K‑edge ≈ 20 keV removes higher‑energy photons Rh K‑edge ≈ 23.2 keV (harder beam) low‑energy photons removed by filter bremsstrahlung continuum teal band: quasi‑monochromatic ~17–20 keV window — high soft‑tissue contrast at low dose Characteristic peaks dominate; the filter trims low‑ and high‑energy photons, cutting dose. A rhodium filter (K‑edge ~23.2 keV) hardens the beam for thicker, denser breasts.
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