## What killed Madame Curie? (Part 2)

### Los Alamos, 1946

I should have sought Dr. Fermi right away, back when it was easy.  When Mademoiselle Curie gave me the lead, Enrico was a quiet university professor in Rome.  Since then, he’s got a lot harder to find, and it seems that the professor has government ties— secrets as big as the men who hide them.  I chanced upon a tip leading me to a project in Manhattan, and though I found Fermi on the books as a Columbia professor, I had just missed the man himself.  Asking an associate about where in the New World this Italian Navigator might be, he turned bright red and insisted that there was absolutely nothing in the basement.  Nothing at all.

Sometimes you just get lucky.  I asked one of his students to give me a tour of the basement, and was shown a room-sized apparatus for creating artificial radiation.  “Artificial radiation?”

“Radiation is just ordinary particles, accelerated to high speeds.  Naturally radioactive elements like radium spontaneously break off parts of themselves and shoot them at us, but we can accelerate them on our own with rapidly oscillating electric fields.”

“So this,” I asked, “is a sort of ‘particle-accelerator?'”

“I guess you could call it that.”

I was on the right track!  “What do you use it for?”

“Well, Dr. Fermi did a lot of experiments with neutron capture, but by far the most exciting was the splitting of uranium atoms by a neutron beam.  He disappeared soon after that.”

So Enrico wasn’t content to let atoms do all of the dirty work— this cat shoots back!

From there, the trail went cold.  After a few unsuccessful years of inquiries in the criminal underground, a newsreel was kind enough to point me to the University of Chicago.  I booked a train from the Big Apple to the Windy City at once.  Again I found the professor to be curiously absent.

In Chicago, or rather under it, I found a secret laboratory in a modified squash court below the school’s football stadium.  The room was two stories high with a kind of observation deck overlooking what seemed to be a Mayan temple.  A vat of acid was held above it by a single rope, and next to that, an axe.  But no Fermi.

A little investigation sent me back to the train station for another cross-country ticket— for years, the doctor has been frequenting an even larger military compound in the high New Mexico desert.  All of this, I’m told, was until recently a hush-hush operation, but it’s wide open now that some war’s over.  So I bought a ticket for Santa Fe, and from there hitched a ride to the Los Alamos compound.  The place was crawling with scientists.  My ride couldn’t get me past the soldier on guard, but told me about a little hole cut in the fence 71 feet from the gate, where I could kindly let myself in.

Once admitted, I had no trouble finding Enrico’s office— he was an important man.  I tried my luck with the direct method: finding him at work behind a stack of papers, I sat myself down on the other side of the desk and pulled out a little notebook.  It took him a moment to put his thoughts into words.  “Er— who are you?”  His accent was still rather thick.

“Just someone looking for answers,” I said, lighting a cigarette.  When I started trailing the good doctor, more than a decade ago, I had imagined an Italian don or Mafioso.  But this guy was Mickey Mouse.

I shot a glance through the open door and whispered, “Radiation!”

Fermi’s eyebrows raised as he whispered back, “Radiation?”

“That’s right.  I’m investigating a death.”

“What happened?”

“Did you know a Madame Marie Curie?”

“Yes, of course.”

“Well, she died.”

“Yes… ?”  He seemed unconcerned.  Suspicious— I mentally filed it away.  “That was many, many years ago.”

“And do you know what killed her?” I asked, flicking my lighter shut.

That left him dumbfounded for a moment, but then he asked, “Are you a student?”

“One might say that,” I responded, fishing out a pen for my notebook.  “Tell me everything you know about this radiation— I’ve got all day.”

“I’m sorry; we would talk about this, but just— not right now.”  He pointed to his papers— I could tell I was losing him.

“It has something to do with neutrinos, right?”

“Neutrinos?”  His ears perked, like I had brought up the name of a child.

“From what I hear, the dame was done in by neutrinos.”

“No no no no, neutrinos, they are little,” he indicated a speck with his thumb and finger.

“But they are radiation, aren’t they?”  Playing right into my hands.  “Particles travelling at high speeds? I’ve read your theory of nuclear beta decay.”

“Well, then you would have learned that neutrinos interact only weakly, only in weak interactions: they go right through you.  Just a little— look.”  He dropped his pen and picked up a piece of chalk.  Erasing a big patch of blackboard, he started to draw.

“There are four kinds of interactions, okay?”  He drew four boxes.  “Electromagnetism.  Gravity.  And two nuclear forces: here is the strong one, and here is the weak.  The strong nuclear force holds together the nuclei, the nuclei at the centers of atoms, and the weak force causes particles to change.”

“Change— how?”

“Well, neutrons turn into protons— they are like cousins, neutrons and protons.  They have about the same mass, they are both heavy, and protons have positive charge while neutrons are neutral.  They are both found in atomic nuclei.  Like that.”  (He tapped his exquisite drawing with the chalk.)  “But they decay.  When we take neutrons out of the nucleus, they decay into protons in about 15 minutes.  But not just protons: one neutron will become a proton, an electron, and a ‘neutrino.'”  He turned to face me.  “This neutrino, you must understand me, it is not a neutron, it is much, much lighter.  Probably it has no mass at all, like light itself.  It is because a ‘neutron’ in Italian sounds like a big thing, ‘neutrone'” (exaggerating the “-one” with a hand gesture), “and so when we found this little one, we called it a ‘neutrino.’  They don’t have anything to do with one another.  They are distant relatives, if at all.”

“So there’s four suspects we’re talking about here,” I summarized, “protons and neutrons, the big ones, found in the nuclei of atoms, held together by the nuclear strong force, and electrons and the little neutrinos.  Every 15 minutes, one of the neutrons just turns into a proton, an electron, and a neutrino?  Got it.”

With a curious bobbing of his head and hands, Dr, Fermi seemed to indicate that I’ve almost got it.  “Approximately 15 minutes, outside of an atomic nucleus.  In a nucleus, it can take a little longer.  Millions of years because of a potential the electron must escape.  But that is a complicated matter— you have the basic idea and that’s the important thing.”

“So which of them killed Curie?  The proton?  The electron?”

“Ah, well not the proton because the proton stays behind.  If a beta decay happens in a nucleus, as in natural beta decay, the proton sticks because it is attracted by all the other protons and neutrons.  Only the electron and the neutrino get away because they don’t feel the strong nuclear force.”

“And the neutrino, you said, was weakly interacting.  It goes right through us?”

“Like a ghost.”

“Wouldn’t that hurt?”

“Why?  Everything we experience happens by way of one of the four forces: we feel the earth by its gravitation, we feel hard objects by their electromagnetic interactions.  Nuclear forces can change our atomic nuclei, which have consequences later, but if the interaction is very weak, it will rarely happen and not much influence anything.”

“How can we be sure the neutrinos are harmless?”  I liked backing him into a corner.

“The neutrinos from the sun don’t bother you, do they?”

“From the sun?”

“Yes, nuclear reactions are always happening in the sun— that’s where its energy comes from.  Like this—” he wrote,

$4p + 2e \to {\rm He} + 2\nu$

and said, “four protons and two electrons combine in a series of collisions that result in a helium nucleus and two neutrinos.  The helium is really just two protons and two neutrons, so the important part of the reaction is:

$p + e \to n + \nu$

Which is almost nuclear beta decay in reverse, where a proton absorbs an electron and becomes a neutron.  The only difference is that the neutrino is on the other side of the reaction.  The sun is making neutrinos; they pass through the sun, and through you and me all of the time without trouble.  In fact, we can estimate how many.  Do you know how much heat the sun produces?”

“Why would I know how much heat the sun produces?”

“Perhaps because you’ve gone outside and felt its warmth.  The sun produces a lot of light and heat, but most of it doesn’t fall on you; most of it goes out into space and we never see it.  But the part that does fall on you is about as bright as a 100 Watt light bulb up close.  So say that the sun shines 100 Watts of light and heat on you.”  He waited for me to nod in response.

“I’m with you, doc.”

“This reaction” (he tapped the topmost equation) “releases 7 MeV of nuclear energy— er, that is an obscure unit.  7 MeV is about 1 trillionth of a Joule, okay?  Somehow, the sun has to collide enough protons to shine 100 Watts, or 100 Joules per second, on you.  How many collisions is that?”

“Uh… divide them?”

“Right, 100 trillion proton collisions have to collide to create enough light and warmth to shine on you for one second.  From each of those collisions, two neutrinos are created.  You receive the same fraction of neutrinos as you do the light, so 200 trillion neutrinos are passing through your body each second.”

I must have turned pale.  “I’m toast.”

“No, you seem to be doing very nicely.  The neutrinos don’t bother you.”

“Then they couldn’t have killed Madame Curie, either.”

“No, they could not.”

“If I remember correctly, that leaves only one suspect standing: the electrons.”

“Yes, high energy electrons are dangerous.  They escape the nucleus because they don’t feel the nuclear force, but they are electrically charged and can pull molecules apart.  That is not healthy.”

“Then we’ve solved the crime!”  I pounded the metal desk as I lept to my feet.  “Marie Curie was killed by electrons from radium!”

“Yes, after all these years!  Finally, to get to the bottom of the mystery!”

“Er, radium is an alpha emitter.”

“What was that?”

“Radium,” Fermi said carefully, “emits alpha particles— fast helium nuclei.  Not electrons, as in beta decay.”

I slumped back into the chair.  Thicker and thicker…

“Oh, for crying out loud!” came another voice, and some banging, from the closet. A few more rattles and the door was open, revealing a kid with a thick Brooklyn accent.  “That has nothin’ to do with it!  Alpha particles, beta particles: they’re all charged, and they’ll all kill ‘ya.”

“What are you doing in my closet?” asked Fermi meekly.

“That’s not gettin’ to the bottom of things!  Look, what you wanna know is why particles change type at all.  Not once did you ask how the neutron became a proton, electron, and a neutrino: you just took it on faith that they do, ’cause this smart guy said so.”

If Dr. Fermi was Mickey Mouse, this kid was Bugs Bunny.

“What are you doing in my closet?” Fermi asked again, a bit more forcefully.

“Pickin’ your safe.  Now where was I?  Oh yeah: do we even know what electrons and whatever are, apart from the fact that they’re not protons and neutrinos and the like?  No!  We just say, ‘this has electric charge, and no nuclear charge, so it must be an electron, ’cause that’s how they’re defined.'”

“Why were you picking my safe?  And what were you doing in my closet?  My safe is over there.”

“I heard you comin’ in— had to scoot.”

“Well scoot.  Scoot!”  Fermi pointed to the door.

Flabbergasted, Bugs relented and shuffled out into the hallway.  Fermi sat and rubbed his eyes.  When he opened them and found me still in his office, he said, “Keep an eye on him.  Something— someday— he is going to do something.”

A new lead!  Soon enough, I was on the trail…