How to get the namespace of the referenced project in c#

I have 2 projects:
Project_1
Project_2
Project_1 is referenced to Project_2, because it need to call some classes in Project_2.
I want to get all namespaces in Project_2 so that I can use Activator to dynamically instance the class.
Use AppDomain.CurrentDomain can get the Project_1 namespace but can not get the Project_2 namespace.
How can i get all namespaces in Project_2?