HZE cosmic rays in space. Is it possible that they are not the major radiation hazard?

The majority of hadrons in space are protons. Galactic cosmic rays have a small component of high energy heavy ions (HZE) which can be highly effective in initiating biological damage. That component is frequently assigned a large quality factor. Earlier risk analyses have indicated that individual heavy ions could be as much as 10,000 times more likely to induce cancer than protons. Although such large values are somewhat unusual and have been called into question, heavy ions do have the potential for being a major source of radiation risks to personnel in space. Nevertheless, estimates of such risk have large uncertainties associated with them. Previous procedures for establishing risk estimates are examined in the light of recently published microdosimetric spectra for heavy ions and protons. We conclude that higher quality factors appear to be unwarranted at this time. In fact, it is suggested that the present data do not exclude the possibility that biological risks from the direct ionisation density of primary galactic heavy ions may be less than that from protons when secondary delta rays, neutrons, mesons, heavy ions, and recoils from the protons and HZE particles are taken into account. Relatively straightforward ground based experiments are proposed to aid in addressing the issue.