Does Weeping Willow Tree Bark Have Pain Relieving Properties?

I have a question about willow tree bark and its pain relieving properties. Can any variety of willow be used for this? I have a weeping willow, and I was wondering if I could use its bark. Also, is there any specific part of the bark that you use, such as the inner bark or outer bark?

I worked on this for a long time and can't get to a definitive answer.
Regarding species, it seems that Salix fragilis and S. purpurea are actually used more often and have a higher salicin content than S. alba and S. nigra. But I can't find any medicinal references to weeping willow (S. babylonica).
Most of the texts say that the "bark" is used. Only one source said that the inner bark is used.