  The electric quadrupole coupling constant of the ground state of 37K(3/2+,
1.22 s) in a tetragonal KH2PO4 single crystal was measured to be |eqQ/h| = 2.99
+- 0.07 MHz using the beta-ray detecting nuclear quadrupole resonance
technique. The electric quadrupole moment of 37K was determined to be |Q(37K)|
= 10.6 +- 0.4 efm2, 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.
