The jobs of a CRA and clinical research scientist are very different. Other than working in research, they have little in common.
Clinical research scientists are very knowledgable about the investigational product. They design protocols, pick end points, and ensure the study is scientifically sound. These people work in an office and only travel occasionally. Typically, they will become specialized in a certain therapeutic area.
CRAs are given the responsibility of protecting the rights, safety and welfare of human subjects. They also serve as a primary point of contact for physicians treating patients with everything from ensuring the protocol is carried out per the plan, coordinating supplies and troubleshooting problems. CRAs travel every week and can often switch between therapeutic areas.