Quadrupole moment of 37K

The electric quadrupole coupling constant of the ground state of K37(Iπ=3/2+, T1/2=1.22s) in a tetragonal KH2PO4 single crystal was measured to be |eqQ/h|=2.99±0.07MHz using the β-ray detecting nuclear quadrupole resonance technique. The electric quadrupole moment of 37K was determined to be |Q(K37)|=10.6±0.4efm2, where the known electric quadrupole coupling constant of stable 39K in the KH2PO4 crystal was used as a reference. The present experimental result is larger than that predicted by shell-model calculations in the sd or the sd and fp model spaces. A possible variation of effective charges was explored to explain the discrepancy.