Measurement of the half-life and gamma-ray branching ratio of ⁹¹Y

Half-lives and gamma-ray intensities are critical to accurate quantification of ⁹¹Y in several applications, including nuclear medicine, toxicology studies, and nuclear forensics. The last evaluation of the A = 91 mass chain was completed in 2013 [1], and the ⁹¹Y half-life measurement given there was taken from a 1971 publication (Ref. [2]), which appears to have been chosen by merit of being the most recent measurement and having the smallest error bars; the published value is 58.51(6) days. The gamma-ray branching ratio of the 1204-keV gamma ray in the last evaluation was taken to be 0.26(4)%, which was determined by taking the unweighted average of two disagreeing measurements: 0.22(1)% in Ref. [3] and 0.30(5)% in Ref. [4]. Recently, an additional branching ratio value was published by Gilligan et al. from Ref. [5], which determined a value of 0.2297(39)% but did not use an isotopically pure sample.



A chemically separated, isotopically pure fraction of ⁹¹Y was measured using a multi-particle coincident spectrometer dubbed the Gamma Alpha Beta Radio-Isotope EvaLuator (GABRIEL) detector [6,7]. The sample was measured using traditional singles gamma, beta-gamma, gamma-gamma, and beta-gamma-gamma coincidence over a period of eight months. These data sets were used to determine the half-life of ⁹¹Y and the branching ratio for the 1204-keV gamma-ray emission. The gamma-gamma and beta-gamma-gamma measurement results were used to validate the absence of possible contaminants such as ⁸⁸Y. A half-life for the ⁹¹Y beta decay and a branching ratio for the 1204-keV gamma ray will be presented.



[1] C. Baglin, Nucl. Data Sheets 114 (2013) 1293–1495.

[2] S. Baba, H. Baba, H. Natsume, J. Inorg. Nucl. Chem. 33 (2) (1971) 589–595.

[3] B. Kahn, W. S. Lyon, Phys. Rev. 98 (1955) 58–59.

[4] M. E. Bunker, J. P. Mize, J. W. Starner, Phys. Rev. 94 (1954) 1694–1697.

[5] C. Gilligan et al. Appl. Radiat. Isot. 205 (2024) 111172.

[6] B.D. Pierson et al. J Radioanal Nucl Chem 331 (2022) 5453–5467.

[7] S.M. Collins et al. Appl. Radiat. Isot. 182 (2022) 110140.