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,
;