I'm a radiation oncology physicist at a smaller centre (two linear accelerators) that's a satellite of a larger centre affiliated with a university. Most of my time involves:
1. Running a quality assurance program for our linacs and CT simulator. This means designing and maintaining the program, conduction the measurements, supervising a physics assistant who does some of the more regular measurements, following up on trends that are pressing the tolerance threshold and making decisions about whether the equipment is safe for clinical use.
2. Quality control in treatment planning. This involve regular checks of plans that come though prior to any radiation actually being delivered, consulting in particularly problematic plans, administration of the treatment planning system, following up on errors, training dosimetrists (the people who do the regular planning), etc.
3. Commissioning new devices or new technologies. For any new technology that comes into the clinic, we have to make sure that it's doing what it is supposed to be doing and we have to figure out how to modify our current processes and procedures to incorporated. This involves everything from making measurements to designing procedures. As a concrete example, we're soon going to be upgrading our treatment planning system, so this means going through all the documentation on the new system, testing it in known situations to prove it's performance is acceptable, working through bugs, setting up the algorithms so they perform as we expect, etc.
4. Clinical investigations. This involves a lot of "problem solving" as inevitably, we run into scenarios where it's necessary to treat someone in a way that hasn't quite been done before or trying to get a better understanding of the consequences when faced with treatment decisions that push established limits. Right now, for example we're doing some work measuring errors that occur in pacemakers under irradiation by hooking them up to a circuit that we've designed that emulates a heart. Another example might be figuring out how to plan using only a conebeam CT image, and what the restrictions to that kind of practice might be in our clinic, given the resources available to us.
5. Beyond that, I spend a fair amount of my time doing research and academics. I remotely teach at least one course per year in our graduate program, supervise graduate students, and try to move my own research forward. Much of my research is done in collaboration with other universities. For example I've recently done some work with a local radiation biologist and a neuroscientist who are interested in the bystander effects of radiation and scatter radiation on cognition.
What I would say is that medical physics is definitely an "applied physics" field.
For a more general description:
http://www.aapm.org/medical_physicist/
