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X-Ray Glass

X-Ray Glass

Date posted: October 14, 2016 // Glass

Although widely studied, the first example of a practical application for so-called X-rays was demonstrated by the Rector of Würzburg University, Wilhelm Conrad Röntgen, in 1895. Just three days before Christmas, Röntgen produced an image on a photosensitive glass plate of his wife’s hand in which just the bones and her wedding ring were visible. This showed that while soft tissues were penetrated by this form of radiation, solids such as bone and metal were clearly not. Simultaneously investigating cathode rays and fluorescence, he observed that his newly-discovered phenomenon differed from cathode rays in that it was not distorted by a magnetic field. Within months, doctors were using modified incandescent light bulbs designed by Edison to locate bullets and to photograph fractured bones.

Only two years later and long before the invention of X-ray glass, did the dangers of excessive exposure begin to become apparent in the form of superficial burns and hair loss. During the decade that followed, three forms of radiation emanating from uranium and radium were shown to have similar penetrative properties that did not need to be produced artificially but which, instead, occurred spontaneously. Known as alpha, beta and gamma radiation, they too were found to be a danger to handlers, and this prompted the use of lead and concrete as a protective barrier.

Today, each of these forms of radiation is in frequent use with some acting as analytical and research tools, while one form in particular has become an invaluable diagnostic tool for which lead is no longer the sole form of shielding following the eventual development of the equally effective, but transparent material that we now label as X-ray glass.

The benefits of this material are obvious. It is no longer necessary for a patient to remain shielded from view by opaque concrete or lead. Instead, the radiographer is able to maintain a constant watch over the patient and the apparatus, without risking the potentially harmful effects of repeated exposure from the radiation. The same material is also impervious to other forms of radiation, and this means it is a good choice for the manufacture of the windows used in the radiation-proof cabinets designed for handling medical radioisotopes such as iodine 131. This has long been used in the treatment of an overactive thyroid and, more recently, it has become a first line treatment for cancer of the thyroid, rather than surgery. Another common application in which the visibility provided by X-ray glass can be of value, is seen in the gamma-ray sterilisation process that is applied to certain foods and disposable plastic items.

What is it, then, that makes this rather commonplace material that we use in our windows and to manufacture the vessels from which we like to sip wine that renders it impervious to such powerful radiations? Not surprisingly perhaps, the answer is lead. Lead oxide is introduced into the molten glass during the smelting process and the percentage added determines the so-called lead-equivalency of the finished product.

Schott, a leading manufacturer of specialised glass products, produces a high-density radiation shielding known as RD 50. Supplied and stocked  to hospitals, research labs and nuclear plants in South Africa by LIT Africa, it blocks X-rays and gamma radiation, yet is crystal clear.