The three-body model with central two-body Yukawa interactions is appl
ied to the nuclei Li-11, Be-14 and 17B and a long-range effective pote
ntial is obtained using the equivalent two-body method for a three-bod
y system. It is first pointed out that the long-range effective potent
ial indicates the effect of the three-body correlation and leads to ne
utron haloes in these nuclei. Quite good agreement between theoretical
results and the experimental data is obtained.