"The Speck Of Matter God Had Not Welcomed At Creation..."

Today marks an anniversary of the Nagasaki atomic bomb, the so-called "Fat Man." Many forget that we dropped two kinds of atomic bombs in three days in 1945: The first, "Little Boy," contained all the laboriously accumulated U-235; its design was so simple that it didn't need testing: Fire one subcritical U-235 mass at another U-235 subcritical mass and blammo! --  the whole thing went nuclear.

The second was a plutonium bomb -- and its design was so radical that it had to be tested first, hence "Trinity" at Yucca Flats.

The bomb makers knew early on that U-235 would be the limiting factor: Only 1/140th of any natural uranium source was useable for a bomb -- the rest is the unusable U-238 isotope. But the eggheads (really a who's who of nuclear physicists and chemists) figured out that nuking the otherwise useless U-238 with cyclotron radiation would transmute that useless uranium isotope into heavier elements. Thus began a series of top secret experiments at Berkeley which extended the Periodic Table one element at a time.  That sort of work still continues.

First came element 93, the very first transuranic element, now known as neptunium, and synthesized by Edwin McMillan and Philip H. Abelson in 1940. That element proved unusable as a fissile material, so the search for the next heavier element continued. The work quickly became a rather a dirty job -- separating the toxic gemischt into identifiable components --and one more suited for chemists. Glenn T. Seaborg, and a graduate student, Arthur C. Wahl, did the yeoman's work. By early 1941, they knew that they had something new, but were unable to separate it from co-produced thorium.  Seaborg and Wahl pressed on, working in a cramped third floor laboratory in the chemistry department at Berkeley. Success followed and by early March 1941 Seaborg recorded:

With this final separation from thorium, it has been demonstrated that our alpha [particle] activity can be separated from all known elements and thus it is now clear that our alpha activity is due to the new element with atomic number 94. 

Within weeks, and after gathering enough material, tests showed that element 94 was fissile bomb material. They were already way ahead of anyone else. Because it was immediately apparent that chemical separation of elements was easier than isotopic separation, plutonium production became a second major project in the Manhattan Project, running in parallel to uranium isotope separation.

Richard Rhodes wrote in his incomparable "The Making Of The Atomic Bomb:"

Not until 1942 would they officially propose a name for the new element that fissioned like U-235 but could be chemically separated from uranium. But Seaborg already knew what he would call it. Consistent with Martin Klaproth's inspiration in 1789 to link his discovery of a new element [uranium] with the recent discovery of the planet Uranus and with McMillan's suggestion to extend the scheme to Neptune, Seaborg would name element 94 for Pluto, the ninth planet outward from the sun, discovered in 1930 and named for the Greek god of the underworld, a god of the earth's fertility but also the god of the dead: Plutonium. 

More notes on "The Disappearing Spoon"

[continuation in part]

I'm reading a book and posting comments about it. I'm on page 27:

Electron behavior drives the periodic table. But to really understand the elements, you can't ignore the part that makes up more than 99 percent of their mass---the nucleus. And whereas electrons obey the laws of the greatest scientist never to win the Nobel Prize, the nucleus obeys the dictates of probably the most unlikely Nobel laureate ever, a woman whose career was even more nomadic than Lewis's.

Maria Goeppert-Mayer. I blogged about her here. She was the poster girl for how badly science used to treat women. Kean tells a good story, but mischaracterizes one aspect which I'd like to correct and add to. At page 28, middle of the second paragraph:

After the Depression lifted, hundreds of her intellectual peers gathered for the Manhattan Project, perhaps the most vitalizing exchange of scientific ideas ever. Goeppert-Mayer received an invitation to participate, but peripherally, on a useless side project to separate uranium with flashing lights. No doubt she chafed in private, but she craved science enough to continue to work under such conditions.

I object to the characterization of "useless side project to separate uranium with flashing lights," or whatever that means. What Goeppert-Mayer was working on was the separation of uranium isotopes, under the direction of H.C. Urey at Columbia University. I suppose that work could be characterized as "useless" because ultimately gaseous diffusion solved the problem. But Goeppert-Mayer did make a valuable contribution to science during the war. The results were declassified and finally published in 1947 and became the seminal paper for the science of isotope effect chemistry.

Years ago, I corresponded with Jacob Bigeleisen, the doyen of that branch of science. He was her junior coworker at Columbia U on the Manhattan Project and was a coauthor of the 1947 paper I mentioned above. I happened to ask him about his role in isotope chemistry and he opened up, telling me a great story involving her which I already blogged on here. It's long, but well worth a read. I'm just going to re-post the part where he later told a reporter about the amazing moment when he was briefly overwhelmed by Goeppert-Mayer's brilliance. Bigeleisen had been struggling to derive an equation and to simplify it. Goeppert-Mayer glanced at his work and instantly finished it for him:

She looked at my work and asked 'why don't you finish it up by taking out the classical part?'  Without a pause, she wrote the simplified equation, saying 'Now you have it; it's all done.' I didn't immediately understand what she meant when she said to cut out the classical part. I went home. I worked on it, and eventually I got the same result. link

I suppose that those with an ax to grind could subtitle that moment in time "superior female intellect briefly overwhelms male dominance." I'm sure that she had other moments later on. But all the players are now dead and together somewhere, I suppose.

Rumford, Soddy, and The Crash

Frederick Soddy (1877-1956)

Despite years of formal education in chemistry, I'd never really heard of Frederick Soddy until I started reading about the early days of radioactivity. He wrote a book called The Interpretation Of Radium (1909) which is available free online here.  The book so influenced H.G. Wells that he dedicated his book, The World Set Free (1914), to Soddy.

Soddy seems to have had two careers--first as an accomplished physical scientist (Chemistry Nobel in 1921) and then as a sort of social scientist, but more accurately as a social activist during the Great Depression. In this way he was a prototype Linus Pauling, who won both a Chemistry Nobel and a Peace Nobel for his activism.

Soddy was a chemist by training but today he'd be called a radiochemist. He must have seen or heard firsthand many of the key discoveries in nuclear physics in the late 19th and early 20th century, first at Oxford and then as graduate student with Lord Rayleigh. Afterwards, Soddy moved to Canada around the same time Ernest Rutherford did and the two joined forces. Together they discovered the natural transmutation of elements. Soddy's Nobel Prize citation reads:

for his contributions to our knowledge of the chemistry of radioactive substances and his investigations into the origin and nature of isotopes.

His isotope work came later.

Recall that Count Rumford first paid attention to the heat given off boring cannon and thereby converted our notions of energy.  Like Rumford, Soddy first realized how much heat and energy radioactive decay gave off--orders of magnitude more energy than burning fossil fuels did and it was also seemingly inexhaustible. Soddy was so prescient regarding how much energy was locked inside uranium, radium, and thorium that he warned Britain's government about the dangers of "atomic" bombs during the First World War.

The notion of cheap and abundant atomic energy crested in 1954 with Lewis Strauss' famous too cheap to meter statement, though it appears that he was referring to hypothetical hydrogen fusion reactors.

Soddy died in 1956 in relative obscurity. This (from the Wiki bio) is intriguing:

In four books written from 1921 to 1934, Soddy carried on a 'quixotic campaign for a radical restructuring of global monetary relationships', offering a perspective on economics rooted in physics—the laws of thermodynamics, in particular—and was 'roundly dismissed as a crank'. While most of his proposals - 'to abandon the gold standard, let international exchange rates float, use federal surpluses and deficits as macroeconomic policy tools that could counter cyclical trends, and establish bureaus of economic statistics (including a consumer price index) in order to facilitate this effort' - are now conventional practice, his critique of fractional-reserve banking still 'remains outside the bounds of conventional wisdom'. Soddy wrote that financial debts grew exponentially at compound interest but the real economy was based on exhaustible stocks of fossil fuels. Energy obtained from the fossil fuels could not be used again. This criticism of economic growth is echoed by his intellectual heirs in the now emergent field of ecological economics.

Neutrons Made It Possible

Neutrons are everywhere, in everything, hiding in plain sight. Historically, they had to be imagined before they were detected because they were so hard to find. Rutherford had thought special "neutral pairs" of protons and electrons were inside atomic nuclei in order to explain why atomic weights varied and also to explain isotopes. To him, an alpha particle had four protons and two electrons instead of two protons and two neutrons and no electrons.

Certainly bearing a charge--being polarized--had made the earlier detection of electrons and protons easier because electromagnetic fields could deflect them. Their flight paths could be swayed. They could be attracted or repelled. Their charges gave them away and allowed them to be counted because they ionized things. Not so neutrons. Even today, neutrons are detected only indirectly via their effects on other signalling atoms.

At first, neutron radiation was confused with a more powerful type of gamma ray because it passed right through matter and with such ease--outdoing even gamma rays. But the new radiation did weird things to hydrogen-containing molecules like paraffin. And, they didn't do something that gamma rays did: they didn't spring electrons from metals like X-rays (the photoelectric effect). But the clincher was proving that the radiation had heft...mass. James Chadwick did that and won the Physics Nobel Prize the very next year.*

If neutrons have no polarity, no "handle," to steer them or deflect them, how are they channeled?  Mainly by projecting them through tunnels of neutron absorbing materials. Those that make it through have directional velocity. It sounds crude, but that's all there is.

At Los Alamos National Laboratory (LANL), there used to be an underground experimental station which resembled a spoked wheel. At the center, the hub, was a block of tungsten (I was told--of course I couldn't see it).  A proton beam impinged this target from above, creating a spallation of neutrons. Numerous tunnels led outwards from the hub like spokes on wheel. The tunnels were surrounded by paraffin and borax--materials with good neutron capture cross-sections. Each tunnel created a beam of neutrons terminated out at a "rim" of connected experimental stations.
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*The defining experiments are briefly described here.
Chadwick wrote in 1940 (after reviewing progress on the atomic bomb):

[I] realised that a nuclear bomb was not only possible, it was inevitable. I had to then take sleeping pills. It was the only remedy.

The Red Line Of Rubidium

original

The name rubidium derives from "deep red" in Latin. Robert Bunsen (yes, that Bunsen) named the element that after he and physicist Gustav Kirchoff discovered it burned reddish-purple in a flame. They also found caesium which lies below (rhymes with) rubidium and which burns bright blue. Burning elements is still important in fireworks and also in modern analytical chemistry techniques such as ICP-MS. Also, a fair number of elements are named after colors: chlorine, rubidium, caesium, chromium, rhodium, indium, iridium, iodine, etc.

The depiction above implies how weakly rubidum holds its outermost electron and why it so readily gives it up to become Rb⁺. Most anything can pluck it off. Here's a spectacular video of rubidium hitting water:

Naturally occurring rubidium has two isotopes: the stable ⁸⁵Rb (72.2%) and the radioactive ⁸⁷Rb (27.8%).  ⁸⁷Rb is considered only "slightly" radioactive--despite its abundance (it is naturally present in seawater)--because of its extremely long half-life of 10¹⁰ years.  Remember that something has to actually decay in order for it to emit radiation.

Radioactivity is not something which has occurred naturally in the previous 36 elements except in very trace amounts (though artificial isotopes of lighter elements of course exist). Radiochemistry is a fascinating topic unto itself and becomes increasingly important for heavier elements which pretty much means from here on out.

Imagine If You Will, Another Dimension of Atoms...

Cobalt and nickel are elements 27 and 28, respectively, but this wasn't always so. Older textbooks often put cobalt and nickel together because they weren't sure which came first. Though there were chemical reasons to believe that cobalt preceded nickel in the Periodic Table, no matter how carefully they measured it, nickel always came out lighter than cobalt, even though it should be heavier.

Scores of new elements were discovered in the 19th century and back then weight measurements were used to identify them and to place them in the table. T. W. Richards won the Chemistry Nobel in 1914 "in recognition of his exact determinations of the atomic weights of a large number of the chemical elements." But realize that while the Periodic Table originally sorted and arranged chemical elements according to their atomic weights, the table actually sorts the elements according to their atomic numbers. The notion of atomic number was unknown to 19th century chemists.

A hypothetical sample of cobalt, nickel, and copper** ions would give a mass spectrum looking something like this:

Natural cobalt is monoisotopic (⁵⁹Co), while nickel has five isotopes: ⁵⁸Ni, ⁶⁰Ni, ⁶¹Ni, ⁶²Ni, and ⁶⁴Ni, with the lightest being the most abundant. Note how ⁵⁸Ni precedes ⁵⁹Co.  Why cobalt likes neutrons more than nickel does is an interesting question for which I have no answer.

Henry Moseley first showed that cobalt and nickel were correctly ordered despite their anomalous weights. Around the same time, J.J. Thompson invented mass spectrometry which sorts ions according to mass as shown above. Thompson discovered that neon had two isotopes but the concept of isotopes wasn't fully understood until James Chadwick discovered the neutron in 1932.  Chadwick's discovery also enabled the subsequent syntheses of elements beyond uranium.
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*Tellurium (element 52) presents a similar weight anomaly because it is on average heavier than iodine (element 53).
**I wrote about copper isotopes back here and included it because it falls close to Ni and Co.

Let's take a closer look at those copper atoms

How small can we see? Pretty small, it turns out. We can see atoms (see above)--not with light but with electrons (light is too crude of a yardstick and can't "measure-down" to the job). In Scanning Electron Tunneling Microscopy (STM), a tiny metal wand just an atom or two thick approaches a surface. Electrons, dripping from the tip of the sweeping probe, jump to a surface below, feeding signal back and mapping the atomic topography:

original

Successive traces of electronic signals become a "photo" of the surface. The way STM works reminds me of the spark of life implied so long ago here. The technique is more fully explained here.

Suppose we could zoom a microscope down onto a pure copper surface to find out what's really there. I mean really there there. We'd find, even for ultra pure copper--heterogeneity. What looks the same is really different. No matter where we look, about one in three copper atoms has two "extra" neutrons because native copper comes in two isotopic flavors: ⁶³Cu and ⁶⁵Cu.

A while back, Michael Haz mentioned that pure copper native to Upper Michigan was distinguishable from pure copper native to South America. It's true. Copper sources have isotopic signatures. The natural ratio of the two copper isotopes varies slightly from place to place for various reasons. The reason(s) why they vary are complex and altogether unimportant here. The point is that they differ and they do so in a way that can be reliably measured--like fingerprints. A similar isotopic method has been used to trace the influx of South American silver into European coinage: link

Stability And Instability Juxtaposed

As the universe ages, more and more matter is converted into iron-56.

...binding energy is greatest for iron
...nuclei lighter than iron are produced by fusion in stars
...nuclei heavier than iron are made in shockwave of supernova implosion
...we are all recycled star dust Link

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Whatever iron has the most of, technetium lacks: all isotopes of technetium are unstable.

Whatever makes iron the most stable nucleus and all technetium so unstable is beyond my pay grade. Link  I do find their diagonal juxtaposition in the Periodic Table intriguing:

It's almost like opposites attract.

Word Verifications: Isotope and Allotrope

wv = "isotope": noun. The prefix iso is obvious and means the same in Greek.  Topos as in topography has the meaning of place. The word isotope was coined by a Greek-schooled physician named Margaret Todd to convey the notion of at the same place in the Periodic Table. Thus only chemical species with different numbers of protons get separate seats at the Table. Elements having different numbers of neutrons must share the same seat. This is also true for radioisotopes.

wv =  "allotrope": noun:  The prefix allo is related to the Greek allos meaning other. Trope is a confusing root and in my opinion is a vague word having several different meanings. The combination allotrope means a structurally different form of the same element ("Graphite and diamond are allotropes of carbon"). 

Phosphorus and especially sulfur are allotrope-rich. The concept of allotrope is akin to an elemental alias. Sulfur has several different aliases or allotropes. Yes, I like that.

The Great Wave Of Healing

Link to original

The beautiful blue coloration in the wood block print by Hokusai comes from a pigment known as Prussian Blue. The pigment has been used for centuries by artists. A lesser known use for Prussian blue is as an antidote for heavy metal poisoning, including cesium-137, a radioactive isotope which now threatens post-tsunami Japan.

I tweeted yesterday about how the simple inorganic salt potassium iodide (KI) works to displace the radioactive isotope of iodine which gathers in the thyroid. I hope that the people most affected are the first in line to get these ready-made treatments.

Conversations with Henry

[Continued from here]

At Henry's suggestion, I wrote to Jacob Bigeleisen. He replied:*

[Salutation]:

How did I get into isotope chemistry? In 1943 I worked at SAM Laboratory at Columbia U (Manhattan Project). My initial assignment was to look for isotope shifts in the electronic spectra of uranium compounds (principally uranyl ion). The purpose of this research was to examine the feasibility of a photochemical separation of the uranium isotopes for military purposes. It was a small project. It was here that I became acquainted with Maria Mayer. She worked on the theory of the spectra. I did experiments and consulted with her regularly about my results and her results. The project was reviewed in July 1943 by James B. Conant and Richard C. Tolman, two high officials in the war time science effort. They brought along as an advisor E.B. Wilson, Jr., the outstanding spectroscopist and quantum chemist from Harvard. The Committee found our work very interesting, but recommended that it be discontinued. The time schedule for any practical application of a photochemical process was inconsistent with the plans for the production of a weapon. People like Urey favored a small scale continuing effort as part of scientific intelligence. Was this a path the Germans could be following?

The dozen or so people working on the project were reassigned in September. I was assigned to write up the work of the project as a final report, which was issued under the name of H.C. Urey. Maria Mayer went to the hospital in October 1943 for gall bladder surgery. In late November an assistant of Urey's (one of his former graduate students) Isidor Kirschenbaum came to see me. He said 'you know all about spectra of uranium compounds.' I said I didn't know everything; what was known, I knew. He said: 'Here is this formula. Put in the information about all uranium compounds and give me the results. We are interested in the possible chemical separation of the uranium isotopes. What we would be particularly interested in would be a volatile compound, which dissociates in the vapor. We have reason to believe that this would be very favorable.'  I asked: 'How do you know this?'  He said he could not tell me. I looked at the formula he gave me. It was the Urey-Greiff equation. I told him that I was not familiar with that whole field and I would have to study it out before I put numbers into the equation. He then said: 'Don't you know there is a war on?' He reported to Urey that I was not a very cooperative person.

Well I studied out the Urey-Greiff equation. There are a lot of factors. For uranium compounds, I could see that we did not know some of the factors; for some of the factors the number was of the order +1.001; for some of the factors the number was -1.001. With the computing facilities available then (desktop mechanical calculators) one could get any final answer from +1.00x to -1.00x from the Urey-Greiff equation. So, I decided I would look into a different approach. In chemistry and most of physics, one does not measure absolute quantities. One measures differences. Would it be possible to calculate differences directly instead of absolute quantities and then subtract the two to get the isotope effect? I started on this approach and I completed the zero point energy and the Boltzmann excitation terms.

On Monday after Thanksgiving 1943 Maria Mayer returned to work. She asked me how I was coming along with the final report. I told her I was not working on it. 'What was I doing?' she asked. I explained the problem to her and showed her my progress. This was a general type of problem she was thoroughly familiar with. In collaboration with George E. Kimball and Walter Stockmayer, she had calculated the isotope effect in the reaction HD + H₂O = H₂ + HDO. This reaction was used to produce heavy water at a plant in Trail B.C. and in Norway.) She was also familiar with the general subject since she and her husband, Joe Mayer, had just written a book on statistical mechanics. I had studied this book as a graduate student. She found my approach very interesting, very sensible and very promising. She then volunteered by asking me whether she could join me in working on this project. I said sure, that would be great. So she did and by the end of the day we completed the derivation of the Bigeleisen-Mayer equation. [1] We then made a number of predictions of systems that would be hopeless for uranium isotope separation and pointed to potential interesting avenues. An experimental program was then organized under Clyde Hutchinson. I worked on that for about a half a year.

Urey was too occupied to look into what we had done. His deputies either did not understand or did not believe that a green Ph.D. new to the field could simplify the Urey-Greiff equation to the point where meaningful calculations could be made. There was a lot of secrecy and people were not told everything they needed to know to make the best progress. In April I became involved in determining the structure of UF₆ by spectroscopic means. I did the experiments at American Cyanamid in Stamford, Conn., where they had outstanding spectroscopic equipment. I worked on the analysis of the the spectra with Maria Mayer, who had tried two years earlier in collaboration with Edward Teller to predict the vibrational structure of UF₆ from first principles! I told Maria Mayer when I started on that project that it was an experimental project, not one for calculation. She asked me whether I could do it (determine the Raman spectrum). She took out of her drawer the infra-red spectrum which had been measured by John Turkevich at Princeton. Neither she, Turkevich nor Edward Teller were able to decipher the infra-red spectrum of UF₆. While Maria Mayer and I worked on the analysis of the spectra, from which we deduced unequivocally the regular octahedral structure, in contrast to the electron diffraction results of Simon Bauer, she told me that she had written a summary report of our work on the theory of isotope effects in equilibria and our calculations relevant to uranium isotope separation.

She prepared this report at the request of Martin Kilpatrick, Urey's deputy to whom we reported. The reason for this was that Edward Teller was to make one of his regular consulting visits from Los Alamos. Kilpatrick showed Teller Maria Mayer's report of our work. Teller had also worked on this problem (there is a 1938 paper by Herzfeld and Teller). He told Kilpatrick that the work was correct and first class. Kilpatrick reported to Maria Mayer that Teller approved of the work. Fine. That made her furious. She said to me: 'They trust Edward Teller and not me.'

Regards to Henry. Pass this message on to him.

Jacob Bigeleisen

__________________________________
* Bigeleisen wrote to me in longhand. I transcribed it here. I supplied the links as well in case anyone was interested.

[1] Bigeleisen later retold a reporter about this amazing moment when he was briefly overwhelmed by Maria Mayer's brilliance:

She looked at my work and asked 'why don't you finish it up by taking out the classical part?'  Without a pause, she wrote the simplified equation, saying 'Now you have it; it's all done.' I didn't immediately understand what she meant when she said to cut out the classical part. I went home. I worked on it, and eventually I got the same result.

Conversations with Henry: She Was A Piece Of Work

[continued from back here]


Henry: Jake didn't really discover kinetic isotope effects -- he just explained them first. Plus I think he had some help.


Me: From whom?

Henry: Maria Mayer. Boy she was piece of work. Smart as a whip. She was the poster girl for how badly science used to treat women.

Me: Really?


Henry: Yes. She won the Nobel Prize eventually. Not in Chemistry though, but Physics. She developed the shell structure model of atomic nuclei. She ended up down by you you know.


Me: You mean UCSD?


Henry: Yep. But she started out in Germany -- as Maria Goeppert. She was friends with all the big time physicists back then. You should look her up. Interesting story. But if you're interested in isotope effects, why don't you just write Jake -- he's a nice guy.  


Me: Thanks, I will. Can I mention you?


Henry: Please do and give him my regards.

I look at my cards and frown. I discard two and ask for two more.

[story continued here]

Conversations with Henry: I knew him you know

Henry: I saw your post about isotopes. I knew the guy who discovered kinetic isotope effects.

Me: You did?

Henry: Yes. Jacob Bigeleisen. We roomed together during graduate school at Berkeley. He wasn't famous then of course. That came later. He went to Columbia afterwards. That was early in the war, when the Manhattan Project was still in Manhattan.

Me: Wow! Tell me more about it!

[Henry shuffles the deck and deals us both five new cards]

Vitalism Lives!

[I was discussing vitalism back here and this sort of a continuation]

There is one non obvious way in which synthetically produced molecules may differ from naturally occurring ones: they may differ ever so slightly in how and how many neutrons are sprinkled amongst their constituent atoms.

Consider carbon first because carbon is the central atom of life. The majority of carbon exists as carbon-12, but there are also carbon-13 as well a carbon-14 isotopes to consider. Let's forget carbon-14 for the moment and focus just on carbon-12 and carbon-13. The heavier isotope makes up only about one percent of total carbon. But that one percent translates to thousands of trillions of carbon-13 atoms when we're talking about something like a spoonful of sugar where one mole has 12 x 10²³ number of atoms.  In other words, there is a measurable quantity of sugar in that spoonful having one (or more) extra neutrons (a carbon-13 atom) than an "identical" neighbor.

The useful part of this neutron (isotopic) labeling is that, depending on the complexity of the molecule, the label can occur at distinct carbons. To illustrate, consider the lowly propane molecule. Most will be CH₃CH₂CH₃ but there will be a smaller fraction of propanes having an extra neutron at one end, viz., *CH₃CH₂CH₃ and also a fraction of propanes having an extra neutron in the middle, viz., CH₃*CH₂CH₃, where the asterisk stands for a carbon-13 which differs from "normal" carbon by having one more neutron.

OK, so what? The upshot is that for most molecules, especially for ones more complex than propane, the relative amounts of label "at the end vs. in the middle" will depend on how that particular batch of molecules was made (and of course whether the method of making them is isotope sensitive). The reason for the latter is beyond the scope I can cover here and deals with kinetic isotope effects. The non-statistical distribution of isotopes is smaller than one might at first believe because kinetic isotope effects are small themselves. But suffice it to say that commercial companies have sprung up in recent years to analyze such batches of molecules. The technique has proven useful for distinguishing the source and origin of otherwise identical chemical entities. Wine producers, for example, have discovered that their appellation d’origine contrôlée products can be distinguished from fake products in this way. Also, drug manufactures can detect counterfeit (infringed) products and methods of making them in this way. Though I haven't seen it yet, drug manufacturers could deliberately "mark" their products by including a small but detectable amount of isotopic enrichment.

Isotopic labeling is an old trick in the chemical arts and so is the metaphorical term isotopic signature.

Fluorine Gave Uranium Wings*

Fluorospar or Fluorite

Fluorine gas is wretched stuff.  Nothing can tear-out valence electrons like elemental fluorine can. Watch it corrode solid brick here: link  There's another video link along the sidebar there of fluorine eating through a dead chicken. Fluorine was too hot to handle for WW I trench warfare, and even Fritz Haber had to settle for chlorine, the next lower (and less reactive) halogen. Fluorine is superlative in a number of other ways: Uberchemist Martyn Poliakoff explains here: link
[added: an updated video here: link]

The name came from the rock in which it was found, and that mineral, fluorspar, was so named because it helped molten metal flow, a property known since the Middle Ages. Calcium fluoride is still used in welding flux. Fluorospar also glows blue when heated, and that property gave us the term fluorescence.

Fluorine and its heavier halide brethren are the polar opposites of the alkaline earths: Li, Na, K, Cs, etc. Here's some raw video of two polar extremes going at it: link  making salt (halogen means salt-forming in Greek) and a bunch of energy.

Hydrofluoric acid (HF) burns are particularly nasty: a decent amount of it burns right through flesh, overpowering the natural buffering system, and it keeps burning through flesh until it finds bone because calcium is the natural bonding partner of fluorine (as in fluorospar). I once witnessed the aftermath of a grad student who suffered an HF burn: he had to be med-evaced to Denver.

During WW II, uranium hexafluoride (or "hex" as it was so aptly nicknamed) became the vehicle of choice for the gaseous diffusion of uranium isotopes. Consider that nearly every single atom of U-235 that went into "Little Boy" was first borne aloft by six little fluoride wings (as volatile UF₆) before the Enola Gay carried them aloft en mass for Hiroshima. Teflon (polytetrafluoroethylene) was used by chemists during WW II to enable the safe handling of UF₆ during isotope separation.
UF₆ was also of early interest to the Manhattan Project, as told to me by Jacob Bigeleisen: link
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*The title is my homage to Ludwig Mond who in the words of Lord Kelvin "gave metal wings," referring to Mond's discovery of nickel tetracarbonyl, Ni(CO)₄, a volatile compound so insidiously poisonous that it packs a double whammy if inhaled: it nickel plates your lungs while poisoning you with carbon monoxide.

A Few Words About Neutrons And Isotopes*

I learned this today from Wiki:

The term isotope was coined in 1913 by Margaret Todd, a Scottish doctor, during a conversation with Frederick Soddy. Soddy, a chemist at Glasgow University, explained that it appeared from his investigations as if several elements occupied each position in the periodic table. Todd suggested the Greek term meaning "at the same place" as a suitable name. Soddy adopted the term and went on to win the Nobel Prize for Chemistry in 1921 for his work on radioactive substances.

The concept of isotopes confounded the builders of the Periodic Table in Soddy's time. Things got even worse after J. J. Thompson showed that he could resolve purified neon into neon of two different masses, Ne-20 and Ne-22. It took the birth of quantum mechanics and Chadwick's neutron to put things back together again.

Today we know with confidence that different isotopes of the same element differ in number of neutrons within their atomic nuclei. Neutrons add heft and stability (or instability) to atomic nuclei, without changing the "place" of the element at the table; in other words, what fixes an element's place is the number of protons in its nucleus, not the sum of its protons and neutrons. Thus the concept "at the same place" makes perfect sense for different atomic mass versions of the same element. All naturally occurring elements have isotopes, for example, hydrogen, which has three isotopes so important that they're given quasi-chemical symbols of their own: H, D, and T, corresponding to protium, deuterium, and tritium, having 0, 1, and 2 neutrons respectively.

Our government (and others) have long been in the business of separating isotopes: uranium-235 was the fission fuel for the first atomic bomb, and plutonium-239 was the fission fuel for the second one. The first hydrogen bomb (code-named Ivy Mike) used liquefied deuterium-tritium gas as fusion fuel, i.e., hydrogen molecules consisting of the two heavier isotopes of hydrogen. Ivy Mike weighed around 62 tons, the bulk of which was dedicated to cooling the liquefied fusion fuel. Practical weaponization of the H-bomb was not achieved until lithium deuteride (which doesn't require cryogenics) became the fusion fuel of choice.

Iran is actively pursuing uranium isotope enrichment, ostensibly to collect enough U-235 for either peaceful electrical power generation or for a fission weapon. Less talked about is the concomitant accumulation of so-called depleted uranium (DU) which is the non-radioactive U-238 “waste” obtained during enrichment. DU is both an effective tank armor and a lethal component of bullets or rounds. While travelling at high velocity, DU or DU-coated shells burn into uranium oxide, literally forming a burning projectile. DU weapons and armor were fielded with spectacular results by the US in the First Gulf War: Iraqi tank shells literally bounced off the Abrams tanks equipped with DU armor. You can bet the Iranians were watching that with keen interest.

Isotopes also have many, many peaceful uses: think of radiochemical uses in medicine and biology and their use in determining the geologic age of materials (radiocarbon dating). Stable isotopes like deuterium and carbon-13 also find broad use as detectable labels which can also be introduced into controlled experiments and followed where they go and don't go. Moreover, subtle effects on the rates (speed) of chemical reactions gives insight into how the reactions proceed.

I once worked around neutrons as part of a scientific collaboration. Our endeavors were peaceful, despite occurring in part at Los Alamos National Laboratory. While determining the molecular structure of a certain substance, we needed the help of neutrons to locate hydrogen atoms using a technique called neutron diffraction which uses beams of free neutrons. To make a long story short, we solved the structure, but I went on to show how one could get the same essential information using more conventional instruments, but that’s another story. And that's the closest I ever want to get to loose neutrons.

*My creds include working with neutrons and co-writing a book chapter on isotopes in chemistry.