- There are quite a lot of videos
about how Roentgen discovered the X-ray,
but most of them really skimp on the physics.
What was he doing?
Why was he doing it?
How did he discover the medical X-ray?
And how did he discover that X-rays
are really high energy invisible light?
Ready for the real story?
Let's go.
♪ Electricity ♪
According to Roentgen it all started
because he'd been interested in the researches
on the cathode ray
especially those of his friend Heinrich Hertz,
and Hertz's assistant Phillip Lenard.
Actually the cathode ray had been discovered
26 years previously, and are invisible rays
that emanate from the negative electrode of a vacuum tube
and can make glass and phosphors glow.
In 1892, Heinrich Hertz discovered
that cathode rays could go through thin pieces of aluminum.
And two years after that, his assistant Phillip Lenard
made a tube with an aluminum window
that let the cathode rays escape the tube entirely.
Lenard found he could get his phosphors plate
to glow a few inches from his tube
and he could even see electrical effects
up to 30 centimeters away.
What Lenard didn't know was that cathode rays
are a beam of electrons,
which is why the cathode ray can be moved with a magnet
and bombarding the solid with fast moving electrons
can produce X-rays.
In fact, the electrical effects 30 centimeters away
were from X-rays, not the cathode ray.
However, Lenard was using a phosphor
made of calcium sulfide,
which is made of calcium atomic number 20,
meaning it has 20 protons in the nucleus,
and sulfur, atomic number 16.
Atomic number is so low that they're nearly transparent
to small amounts of x-rays,
which is why Lenard didn't notice X-rays
with his phosphors screen.
In addition, it is important to note
that in order to study his phosphor screen
Lenard studied his screen in a dark room
and covered the tube in light tight cardboard.
Thus Lenard made the first cathode ray tube
slash X-ray machine that you covered
and studied from the outside.
Now Roentgen had a different phosphorous
that he was thinking of using with Lenard's tube.
Roentgen used a barium Plantinocyanide
that had barium, atomic number 56
and platinum, atomic number 78
which according to an article published in physics this day
was quote, approximately a hundred times more efficient
for the detection of X-rays
than Lenard's low-atomic-number screen.
This is not to imply that Roentgen thought
a heavier element would discover a new type of ray.
It's more that he had a new type of phosphor
and wanted to see what would happen.
In October of 1895, Roentgen began to buy and build
a variety of different vacuum tubes.
This brings us to the fateful night of November 8th, 1895.
Like Lenard, Roentgen covered a tube with thick cardboard,
turned off the lights and excited his vacuum tube.
As he reached for the screen on the side of his tube
he noticed out of the corner of his eye
a glimmer of light on the screen,
quote, the effect was one with could only be produced
by the passage of light
but no light could come from the tube
because the shield which covered it was impervious
to any light note.
The importance that Roentgen noticed the ray
on the side of the tube, should not be understated.
Cathode rays, i.e. beams of electrons
can make it through thin pieces of metal,
but are easily blocked by insulators like cardboard.
So Roentgen was expecting to see fluorescence
past the aluminum face,
but he knew that the cardboard blocked any cathode rays
as well as all visible and ultraviolet light.
So wasn't expecting anything out of the side.
So what was happening?
Roentgen recalled quote,
it seemed at first a new kind of invisible light,
it was clearly something new, something unrecorded.
For weeks, he secretly studied these rays
which he named X-rays, X for unknown,
to distinguish it from any other kind of ray.
Roentgen then found that all of his tubes would make X-rays
whether the cathode ray hit aluminum or glass.
By the way,
it wasn't until after Roentgen's first publication
that many people including Roentgen
found out that hitting low mass materials
like aluminum and glass produces far less x-rays
than the hitting high mass materials like platinum.
For this reason within months of Roentgen's publication
X-ray machines were made.
They used to focus cathode on a piece of platinum.
However, that was not what Roentgen used in 1895.
Roentgen also knows that X-rays have quote,
a penetrative power, two degree hitherto unknown.
Roentgen started to hold up
various items in front of his screen,
from a thousand page book, a pack of cards,
rubber and metal plates.
Roentgen wrote quote,
we soon discovered that all bodies are transparent
to this agent, though in very different degrees.
He then determined that the density of the object
was the decisive feature for its transparency to X-rays.
In fact, we now know that Roentgen rays
interacted with matter, do the photo electric effect,
which depends approximately to the fourth power
of their atomic number.
This is why medical X-rays work so well.
The calcium in the bones, atomic number 20,
give bones around 10 times more X-ray absorption
than the tissue, a mix of atomic numbers,
but mostly hydrogen one, carbon six, and oxygen eight
which makes it easy to make a shadow image
where the bones around 10 times darker
than the surrounding tissue.
So how did Roentgen discover the medical X-ray?
Well, one day while he was studying
lead's transparency to X-rays
he held a small led disc in front of a plate with his hand
he then noticed not only the shadow from the disc
but also the bones in his own hand.
He dryly noted in his paper that quote,
the darker shadow of the bones
is seen within the slightly dark shadow image
of the hand itself.
Roentgen was an amateur photographer.
So he decided to see if the X-rays would develop the film.
And he was delighted to find that they did.
Therefore to validate his experiments,
Roentgen noted that quote, wherever it has been possible,
I've photographed every important observation
which I've made with the eye
by means of the fluorescent screen.
It was for that reason on December 22nd, 1895
Roentgen asked his wife Bertha
if she would come to the laboratory
and hold her hand on a photographic plate for 15 minutes.
They made a ghostly photo
that showed the bones in her hand
and a large ring on her finger.
This was the world's first medical X-ray.
When Bertha saw this picture she supposedly exclaimed,
"I have seen my own death."
Remember before X-rays the only time you saw bones
was in a skeleton.
But what were these new rays?
Well, they were noticed that the first
on the side of the tube,
but they were far brighter on the face, and quote,
if one deviates cathode rays within the two,
by means if a magnet,
it's seen that the x-rays proceed from a new point,
again, from the end of the cathode ray.
Roentgen thus correctly concluded
that X-rays are created when the cathode ray
hit the solid.
Roentgen also found that the X-rays
like ultraviolet invisible light are not moved by a magnet.
So he concluded that X-rays are an electromagnetic wave
and not a form of cathode rays
which is what we think is correct today.
On December 8th, 1895,
Roentgen turned in his paper on a new kind of ray,
and it was ignored for a mere eight days
until suddenly everyone was talking about it.
And there was a whole X-ray crates,
how X-rays changed the society, our medicine,
and our physics, and destroyed Roentgen's life
is next time on The lightning Tamers.
♪ Electricity ♪
Thanks for watching my video.
Please give it a thumbs up.
If you're interested in more
about the different vacuum tubes,
I have plenty of videos about that
and the story about how X-ray took over the world
is a pretty great one.
So check that out.
Okay, have a good day.
Well, one day while he was discovered (growls)
So how did Roentgen discover the medical X-ray?
Well, one day while he was studying, studying!
Studying.