Measurements of short-lived cosmic-ray-produced radionuclides in rainwater

Cosmic-ray-produced (CP) nuclides with half-lives shorter than 21 h were measured in rainwater by ultra-low-background gamma spectrometry at Ogoya Underground Laboratory. As levels of CP nuclides are extremely low and their half-lives are very short, quick sampling methods for a large volume of rainwater and rapid chemical separations by ion exchange method were developed. The nuclides measured were short-lived 24Na, 28Mg, 38S, 38Cl, 39Cl, as well as nuclides with longer half-lives 7Be and 22Na. The number of atoms of CP nuclides in rainwater were evaluated to range from 30 to 1500 L−1 for 24Na (n = 16, mean; 520 [6.7 mBq L−1]), 80 to 600 L−1 for 28Mg (n = 13, mean; 260 [2.4 mBq L−1]), 400 to 1900 L−1 for 39Cl (n = 6, mean; 1200 [250 mBq L−1]), 1 × 106 to 4 × 107 L−1 for 7Be (n = 16, mean; 7 × 106 [1.05 Bq L−1]) and 2 × 103 to 1 × 105 L−1 for 22Na (n = 9, mean; 2 × 104 [0.2 mBq L−1]).