95 really massive kinds of expenditures in shielding, In this type of accelerator there, a helf value there for the mass neutrons being produced, the fast neutron. components can be eighteen inches of londed concreta, Eighteen inches of loaded concrete can re=present an investment of many thousands of dollars for an adequate shield. , Next slide, please? This shows a picture taken at the State Univereity of Iowa, where the CO, Ionization Chamber and Tissue Equivalent Chamberis being used to evaluate not the neutron hazard but simply the back electron current in a Van de Grasf accelerator. The levels here were reasonably high, It was simply a question of determine ing what they were. Next slide, please? Again, if you have a portable, if one ig dealing with a direot current machine, it is desirable to make use of . portable equipment, ;