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  • one of the big surprises of the whole Periodic Video project for me,

  • was my actually seeing a sample of Technetium.

  • Before I tell you how I saw it, let me explain why I was surprised.

  • Technetium is one of four elements that were predicted by Mendeleev,

  • to exist in the Periodic Table, but had not yet been discovered.

  • He predicted it first to have an atomic weight of a 100 which he then revised to 99,

  • which was pretty accurate.

  • So, Technetium is element 43 and obviously between Molybdenum which is 42 and Ruthenium which is 44.

  • The real discovery came when two Italians, Emilio Segrè and Carlo Perrier in Palermo in Sicily,

  • were sent a sample of Molybdenum

  • that had been radiated in the cyclotron in Berkeley.

  • It had been radiated with a mix of neutrons and deuterons.

  • Deuterons are the nucleus of Deuterium, one proton one neutron.

  • And so, Segrè and Perrier were dissolving up this piece of Molybdenum which is highly radioactive,

  • so they let it sit for a bit so some of the radioactivity decayed just to find what was in it.

  • By carefully precipitating and seeing where the radioactive went,

  • they isolated the first sample of Technetium.

  • But it was too small to see, but by its behavior and the fact that it precipitated together with rhenium,

  • they could tell that it must be in the same group.

  • I think it was just sent to them because they were interested,

  • nobody thought or expected Technetium to be in it,

  • and the Technetium was therefore the first element that had ever been made synthetically.

  • Chemists who were looking at the structure of Periodic Table felt that synthetic elements were somehow cheating,

  • so it should not be put on the Periodic Table.

  • Can you imagine that the paper was published in 1937 and nothing happened to the Second World War.

  • Then, in the Second World War, there was the Manhattan Project, the development of nuclear weapon,

  • and lots of new synthetic elements were discovered,

  • particularly Plutonium which had never been discovered before.

  • And after the war, 1947, very shortly before I was born,

  • there was a historic paper published in the journal "Nature" by the German chemist, Paneth,

  • who during Nazis time had moved to the UK and was working at the University of Durham.

  • He laid down the grant rules which exist to this day for the naming of elements.

  • number 1, the right to name an element should go to first (presumably group or person),

  • to give definite proof of the existence of one of its isotopes.

  • Second point, in discussing the priority of the discovery,

  • there should be no discrimination between naturally occurring and artificially produced isotope.

  • And the third point, and this is very important,

  • If a claim to such a discovery has been accepted in the past,

  • but is refuted, that means, contradicted , by later research,

  • the name should be deleted and replaced by one chosen by the real discoverer.

  • And those rules applied till these days.

  • And it was Technetium that really precipitated this.

  • So what happened then, was that the names of six new elements including plutonium were accepted,

  • and Segrè and Perrier were invited to name their element,

  • and they chose the name, Technetium, in the same journal,

  • in a really short paper from the Greek word which means synthetic.

  • So, it is embodied in its name that it was the first synthetic element.

  • In the early 1960s, with improvement of instrumentation, people discovered that in uranium minerals,

  • because of the radioactive decay of the uranium, you can detect tiny tiny traces of technetium.

  • And therefore, it is natural after all.

  • So, the name isn't quite right.

  • And then in 1972, there was an extraordinary discovery by geologists in Gabon in Africa,

  • where they discovered that in a uranium deposit underground about a million years ago,

  • a natural nuclear reactor had started.

  • There was a high enough concentration of uranium for nuclear reaction to take place,

  • and because of this nuclear reaction, there were in fact traces of technetium found under the ground.

  • Because of all the nuclear research that was done during the Manhattan Project,

  • there was an abundant supply of technetium become available after the Second World War,

  • and people started studying the chemistry and you can get a wide range of compounds.

  • And as you might expect,

  • the chemistry is perhaps a little closer to rhenium than to manganese

  • because heavier element tends to be more similar.

  • One of the most interesting applications turns out to be medicine.

  • The application is in diagnosis.

  • When people have cancer, it is often quite hard to see the tumors,

  • or particularly the secondary tumors that spread across somebody's body,

  • because they're small and they're not easily imaged.

  • But turns out, if you take radioactive molybdenum, molybdenum-99,

  • it decays by emission of electron to make technetium.

  • But very unusually and something which we never talked about before,

  • the technetium is formed with a nucleus in an excited state,

  • that is with higher energy than it might have otherwise.

  • And the excited state is symbolized by the letter 'm' which stands for metastable,

  • which means it's stable for a short time but not very long.

  • And so what happens is this metastable technetium decays to the stable isotope,

  • or stable state but with the same mass,

  • and gives out a gamma ray which can penetrate a large distance through, for example, human flesh.

  • And then much more slowly, the technetium-99 decays to the ruthenium.

  • So what happens is that if you do your chemistry very quickly,

  • you can isolate this technetium-99m and before it decays,

  • you can react with another chemical which will complex, that's bind round the technetium,

  • and you choose this binding chemical so that it will also bind to the tumor cells.

  • Selectively, it will bind to the tumor but not to ordinary organs.

  • So, quickly you inject it into the patient, it goes round the body,

  • and is localized at the tumors.

  • Then, if you put the patient into a suitable detector or array of detectors,

  • you can measure the gamma rays coming out,

  • and the gamma rays will come out much more strongly from where the tumors are,

  • and because the technetium decays rapidly,

  • you can get a good signal to do your imaging

  • without giving your patient a big overall dose of radioactivity.

  • So now this brings me back to how I saw technetium.

  • Some years ago, I went to Zurich University and met a professor, Roger Alberto,

  • who is one of the world's experts in technetium chemistry.

  • During the coffee break, Roger came up to me and pulled out of his pocket a little metal vial,

  • and unscrewed the lid, and took out a glass container,

  • and inside was a piece of metal coated with technetium.

  • I was amazed! I never thought i would be able to see this.

  • So I immediately asked him, how he could get hold of this stuff.

  • And he explained that one of his co-workers had used electrolysis,

  • that's passing electric current through a solution,

  • to deposit a thin layer of technetium onto a piece of copper.

  • Now, you don't need very much metal,

  • only a few nanometers to see the metal looks like because light doesn't go through it.

  • And in fact, this particular sample I think had probably a couple of milligrams of technetium on it,

  • so it looked just the same as a large block of technetium would look.

  • But i felt really excited because here was an element which i'd seen sort of in brackets on the Periodic Table,

  • and I never thought I would actually hold a sample in my hand,

  • where I held the glass bottle.

  • And because technetium decays by beta emission, that's emitting electrons,

  • and these electrons don't penetrate through material very easily,

  • even a small glass vial is quite enough to protect people at least for short time.

  • So I could safely hold it and in triumph,

  • I held it against my tie next to the symbol of technetium and I felt,

  • I'd really made the discovery.

  • Hi there, thanks for watching this video.

  • Of course, we've made video's on every element on the periodic table.

  • On the screen now, I will put links to a playlist

  • So you can watch, well all 118 in order if you want.

  • some of them are quite old but we are updating them with new video's all the time,

  • like this one to make bigger and better videos about each element.

  • You can support the process, as well, on Patreon,

  • if you do that, there is a chance for you to adopt an element on our periodic videos webpage.

  • You can have your name there, under that particular element.

  • Check it out at Patreon.com/periodicvideos

  • But as always, the best thing you can do is keep watching here on youtube,

  • stay subscribed to the channel, switch on the notifications so you know everytime we upload a new video.

  • And we will see you again, very soon.

one of the big surprises of the whole Periodic Video project for me,

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テクネチウム - 動画の周期表 (Technetium - Periodic Table of Videos)

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    林宜悉 に公開 2021 年 01 月 14 日
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