Because type-1100 aluminum is only 99.0% pure, it has some impurities that can give a HVL value which is 7.5% lower than those measured with pure aluminum. When doing HVL measurements with a mammography unit, it is recommended that the highest purity aluminum be used. This set of six attenuators satisfies this recommendation, because they are 99.9% pure (type-1145). 07 434
