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Thorium- and Uranium-activity standards

Thorium-activity standars in the form of powder

The material used for the preparation of thorium-activity standards in the form of powder is pure thorium oxide (ThO2) produced before 1950. The daughter products of Th-232 (Ra-228, Ac-228, Th-228,...) in the activity standards are, therefore, almost in radioactive equilibrium (within 1 %). In addition, the standards contain Th-230 of the uranium-radium series with a mass fraction in the order of 10-6. The activity fraction of Th-230 was determined by alpha-particle spectrometry. It amounts to 0.151 ± 0.024, related to the activity of Th-232.

Thorium-activity standards in the form of powders are made available as thorium oxide filled into tablet tubes (content: 10 g).

Thorium activity standards in the form of solution

The material used for the preparation of thorium-activity standards in the form of solutions is thorium nitrate dissolved in nitric acid. The thorium was separated in 1906. The daughter products of Th-232 (Ra-228, Ac-228, Th-228,...) in the activity standards are, therefore, almost in radioactive equilibrium. In addition, the standards contain Th-230 of the uranium-radium series with a mass fraction of the order of 10-6. The activity fraction of Th-230 was determined by alpha spectrometry. It amounts to 0.16 ± 0.04, related to the activity of Th-232.

The activity standards are delivered in the form of solutions filled into sealed glass ampoules (see 3.1) as HNO3 solution (1 mol/L) with a thorium content of 0.2 mg or with 2 mg of thorium per gramme of solution.

Uranium-activity standards

The material used for the preparation of uranium-activity standards is pure triuranium octoxide (U3O8) in "natural isotopic composition". The isotopic fractions obtained by mass spectrometry are: 0.006 % of U-234, 0,713 % of U-235 and 99.28 % of U-238. From alpha-spectrometric measurements it can be concluded that U-234 and U-238 are in equilibrium with U-238 within 2 %.

The following standards are available:

  1. Activity standards of triuranium octoxide, pulverised, filled into tablet tubes (content: 10 g);
  2. Activity standards in the form of solutions, filled into sealed glass ampoules (see 3.1) as HNO3 solution (1 mol/L) with a uranium content of 0.2 mg of uranium per gramme of solution;
  3. Activity standards in the form of solutions, filled into sealed glass ampoules (see 3.1) as HNO3 solution (1 mol/L) with a uranium content of 2 mg of uranium per gramme of solution.

Availability: ex stock.