BBC Knowledge Asia Edition - December 2014

HOW DO WE KNOW?

images. That’s because the film

in the shadow of the bones is less

exposed to the radiation.

Röntgen submitted his work to the

journal of his university’s physical-

medical society on 28 December 1895.

The abundance of Crookes tubes in

researchers’ laboratories meant that other

researchers immediately set about doing

their own experiments.

News that there was a technique

allowing us to see into the body set the

world’s telegraph system alight. On 16

January 1896 The New York Times

published an article about this new form

of photography, predicting it would

transform surgery by guiding surgeons

to the location of foreign bodies. Within

weeks of Röntgen’s announcement, it

had been put to medical use. A German

doctor used X-rays to diagnose bone

cancer in the leg of a young boy, and

there are various tales of finding bullets

and other metal objects with X-rays. In

the UK, Birmingham physician John

Hall-Edwards was the first to use X-ray

images to guide surgery in February 1896.

X-ray imaging was particularly useful for

the military, and bullets were found in

the forearms of two soldiers in May 1896.

The image of Bertha’s hand captured

the public imagination, and X-rays were

soon being used to make ‘bone portraits’

for nothing more than intrigue, inspiring

poems, songs, cartoons and even lead-

lined ‘X-ray proof’ underwear.

THE KEY

DISCOVERY

Wilhelm Röntgen was the first to realise that something else is emitted by a Crookes tube

other than cathode rays, a discovery that would transform medicine in the years to come

But almost as quickly, the dangers

of X-rays became apparent. The

understandably gung-ho approach that

many had taken with the invisible rays

led to reports of burns, sores and hair loss,

and later tumours. Some experimenters,

including Hall-Edwards, had their

arms amputated after developing X-ray

dermatitis or cancer. In addition, early

X-ray images were far from crisp. If

X-rays were going to achieve their

immense potential, things were going to

have to change.

To produce an X-ray image, you

need a source of X-rays and a way of

capturing the image. Both of these

components would be transformed

from Röntgen’s Crookes tube and

Wilhelm Röntgen, who discovered a new form of electromagnetic radiation, at the University of Würzburg in Germany

Röntgen had been studying electricity and

gases for just a month when he unwittingly

performed his key experiment. He was using

a Crookes tube to generate streams of

electrons called cathode rays. The glass

Crookes tube contained a small amount of

gas with an electrode at either end.

When a voltage was applied,

electrons were released from the

negatively charged electrode

(the cathode) and directed towards the

positively charged anode.

In the darkened room was a screen painted

with a chemical called barium platinocyanide,

which releases light (fluoresces) when

exposed to electromagnetic radiation. He had

covered the Crookes tube in black

cardboard so that visible light would not

interfere with his observations. From

the corner of his eye he saw a faint

glow from the screen, suggesting that

something invisible was emerging from the

tube and making it fluoresce. The screen was

further away than the distance that cathode

rays were known to travel, and the effect was

still there when he placed books between the

tube and screen. Later, it is thought that when

he placed his hand between the tube and the

screen, he saw the ghostly image of his

fleshless bones.

PHOTO: GETTY X4, SCIENCE & SOCIETY, SCIENCE PHOTO LIBRARY