Radiation Resistance – What does it mean and how do optimised lenses maintain throughput?

Radiation resistant, radiation hard or non-browning lenses are all terms used to refer to a lens designed for use in a radioactive environment.

When exposed to Gamma or X-ray radiation the majority of optical materials will change colour, typically dark brown, resulting in almost total loss of transmission. There are a few optical materials available that are naturally non-browning, such as fused silica and quartz. However, there are simply not enough of these materials available to provide the variety required for a good lens.

Fortunately, standard optical glass can be stabilized against the transmittance loss caused by ionizing radiation by adding cerium to the composition. The added cerium changes the intrinsic colour of the glass from white to a yellowish tint. The goal of creating a cerium-doped glass, is to optimize the cerium content in order to achieve high stability against radiation while keeping the tint colouring to a minimum.

Cerium doped glasses are designed to maintain transmission when exposed to very high levels of gamma or x-ray radiation. These glasses will initially change colour slightly and then they will stabilise and maintain a high level of transmission.

While Resolve Optics has extensive experience of supplying fixed focus and zoom radiation resistant lenses for applications in nuclear reprocessing and power generation – today our expertise is helping organisations operating in a growing number of different and interesting applications.

In medical research – our radiation resistant lenses form targeting elements in synchrotron radiation therapy machines and also in commercial x-ray instrumentation. In outer space all instrumentation, sensors and cameras are subject to constant bombardment by radiation that will quickly degrade and make inoperative standard optical components. Space borne applications present a challenging environment, subject to radiation, where camera lens servicing or replacement is highly undesirable. Recently several satellite manufacturers and an international space agency selected Resolve Optics to supply them with a selection of high performance, radiation tolerant zoom lenses because of our expertise in this area and willingness to work with them on adapting our standard non- browning zoom lens designs to be ‘space ready’.