Tables for
Volume C
Mathematical, physical and chemical tables
Edited by E. Prince

International Tables for Crystallography (2006). Vol. C, ch. 4.2, pp. 195-196

Section Radioactive X-ray sources

U. W. Arndta Radioactive X-ray sources

| top | pdf |

Radioactive sources of X-rays are mainly of interest to crystallographers for the calibration of X-ray detectors where they have the great advantage of being completely stable with time, or at least of having an accurately known decay rate. For some purposes, spectral purity of the radiation is important; radionuclides that decay wholly by electron capture are particularly useful as they produce little or no β or other radiation. In this type of decay, the atomic number of the daughter nucleus is one less than that of the decaying isotope, and the emitted X-rays are characteristic of the daughter nucleus. In some cases, the probability of electron capture taking place from some shell other than the K shell is very small and most of the photons emitted are K photons. The number of photons emitted into a solid angle of 4π, uncorrected for absorption, is given by the strength of the source in Curies (1 Curie = 3.7 × 1010 disintegrations s−1), since each disintegration produces one photon. A list of these nuclei (after Dyson, 1973[link]) is given in Table[link].

Table| top | pdf |
Radionuclides decaying wholly by electron capture, and yielding little or no γ-radiation

Element[K{\alpha_1}] (keV)
37Ar 35 d Cl 2.622
51Cr 27.8 d V 4.952 γ at 320 keV
55Fe 2.6 a Mn 5.898
71Ge 11.4 d Ga 9.251
103Pd 17 d Rh 20.214 Several γ's; all weak
109Cd 453 d Ag 22.16 γ at 88 keV
125I 60 d Te 27.47 γ at 35.4 keV
131Cs 10 d Xe 29.80
145Pm 17.7 a Nd 37.36 γ's at 67 and 72 keV
145Sm 340 d Pm 38.65 γ's at 61 keV; weak γ at 485 keV
179Ta 600 d Hf 55.76
181W 140 d Ta 57.52 γ at 6.5 keV; weak γ's at 136, 153 keV
205Pb 5 × 107 a Tl L only (Lα1 = 10.27 keV)

Useful radioactive sources are also made by mixing a pure β-emitter with a target material. These sources produce a continuous spectrum in addition to the characteristic line spectrum. The nuclide most commonly used for this purpose is tritium which emits β particles with an energy up to 18 keV and which has a half-life of 12.4 a.

Radioactive X-ray sources have been reviewed by Dyson (1973[link]).


Dyson, N. A. (1973). X-rays in atomic and nuclear physics. London: Longman.

to end of page
to top of page