Abstract. An isomeric state in the proton drip-line nucleus 26 P has been observed by the γ-ray spectroscopy. The γ-ray energy and the half-life are 164.4 ± 0.1 keV and 120 ± 9 ns, respectively. For the isomeric transition of the mirror nucleus 26 Na, the γ-ray energy of 82.40 ± 0.04 keV and the half-life of 4.35 ± 0.16 µs are also revised. Comparing the experimental reduced transition probabilities of 26 Na and 26 P with theoretical ones calculated by the shell model with the USDA interaction, the spin-parity (J π ) of the isomeric state in 26 P is most likely to be 1 + .

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