Krypton Kr 81m
Kr 81m

Krypton, isotope of mass 81 (metastable).
Krypton, isotope of mass 81 (metastable) [15678-91-8].
» Krypton Kr 81m is a gas suitable only for inhalation in diagnostic studies, and is obtained from a generator that contains rubidium 81 adsorbed on an immobilized suitable column support. Rubidium 81 decays with a half-life of 4.58 hours and forms its radioactive daughter 81mKr, which is eluted from the generator by passage of humidified oxygen or air through the column. Rubidium 81 is produced in an accelerator by proton bombardment of Kr 82. Other radioisotopes of rubidium are produced and are present on the generator column. These other radioisotopes do not decay to 81mKr. The column contains not less than 90.0 percent and not more than 110.0 percent of the labeled amount of Rb 81 at the date and time indicated in the labeling, and on elution yields not less than 80.0 percent of 81mKr.
Packaging and storage— The generator column is enclosed in a lead container. The unit is stored at room temperature.
Labeling— The labeling indicates the name and address of the manufacturer, the name of the generator, the quantity of 81Rb at the date and time of calibration, and the statement, “Caution—Radioactive Material.” The labeling indicates that in making dosage calculations, correction is to be made for radioactive decay, and also indicates that the radioactive half-life of 81mKr is 13.1 seconds.
note—Perform the following tests and Assay quickly, because of the rapid decay of the 81mKr.
Radionuclide identification (see Radioactivity 821) The gamma-ray spectrum of eluted 81mKr exhibits a monoenergetic gamma ray at a mean energy of 191 KeV.
Radionuclidic purity— Using a suitable counting assembly (see Selection of a Counting Assembly under Radioactivity 821), determine the radioactivity of each radionuclide present in a specimen of Kr 81m gas obtained from eluting the generator by use of a calibrated system as directed under Radioactivity 821. Not less than 99.9% of the radioactivity in the specimen eluted from the generator is present as 81mKr.
Assay for radioactivity— Using a suitable counting assembly (see Radioactivity 821), determine the quantity, in MBq (mCi), of Kr 81m contained in an elution of the generator. Decay correct the result to the time of generator elution, and calculate the quantity of 81Rb present in the column at the time of elution. The quantity of 81mKr eluted is not less than 80.0 percent of the labeled MBq (mCi) of 81Rb present on the column at time of elution.
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Topic/Question Contact Expert Committee
Monograph Ian DeVeau, Ph.D.
Director, Veterinary Drugs and Radiopharmaceuticals
(RMI05) Radiopharmaceuticals and Medical Imaging Agents 05
USP32–NF27 Page 2742