210Pb-Test with alpha spectrometry

The so called 210Pb test for the authentication of metal artifacts is based on the disturbance of the radiochemical equilibrium of the 238U decay chain during the smelting process. Ores and minerals accompanying the ore usually contain small amounts of uranium. In the decay chain of uranium elements with different geochemical and metallurgical behavior are produced; among those is the radioactive nuclide 210Pb. While lithophile trace elements like U, Th and Ra remain in the slag, chalcophile and siderophile elements, like Bi and Pb, are taken up by the metal phase. Thus the short-lived radionuclide 210Pb (t1/2 = 22.3 y) is efficiently separated from its long-lived ancestors 238U (t1/2 = 4.4 * 109 y) and 226Ra (t1/2 =1600 y). The concentration of 210Pb in the metal depends on the geological setting of the ore and the manufacturing process, so that the range of the initial activity is large and, therefore, it cannot be used for dating. The 210Pb in the metal decays with its own half life of 22.3 years and as a result of the disrupted decay chain it cannot be renewed. This means that usually no radioactivity is measurable in metals older than about 110 years (~ five half-lives of 210Pb).

It should, however, be noted that the absence of 210Pb is no proof of authenticity, because in principle old metal could have been used to produce objects in modern times.

The measurement of 210Pb is carried out via determination of the alpha-emitting daughter nuclide 210Po (t1/2 = 138.4 d) by alpha-spectrometry. An alpha-spectrometer with eight ion-implanted silicon detectors is used for the measurements with very low background activity and an energy resolution of 20 keV full width at half maximum peak height (FWHM).

Your contact person:

Prof. Dr. Ernst Pernicka und Dipl.-Arch. Nicole Lockhoff