An HVEM for high resolution low-dose studies of biomacromolecules

A 1 MeV EM-7 TEM has been modified to investigate the possibility that low-dose studies of biomacromolecular crystals might be more effectively carried out in an HVEM. The modifications include a TV viewing system, a deflection-type minimum exposure system, a side-entry, -150 degrees C transfer cold-stage and improvement of the working resolution to 0.2 nm. The advantages of HVEM for this type of study include a possible reduction in radiation damage rate, greater depth of focus on tilted specimens, broader instrumental contrast transfer function and a reduction in dynamical effects on thicker samples. Disadvantages and possible solutions to them are also discussed. Preliminary results on radiation damage in catalase at 400, 600 and 800 kV and images of catalase and squaric acid are included.