Chapter 19: The Nucleus: A Chemist’s View – Radioactivity, Fission, and Fusion

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Welcome to the Deep Dive.

You know, this is where we take those complex topics and really try to break them down, give you those aha moments.

And today, we're definitely doing that.

We usually think chemistry, we think electrons, right, those tiny things whizzing around the outside, doing all the bonding stuff.

But today, we're going way deeper into something, well, smaller but way, way more powerful, the atomic nucleus.

Okay, let's unpack this then.

We're talking about the absolute core of the atom, a place that's just incredibly dense and packed with energy.

To give you a sense of scale,

imagine the nucleus of a hydrogen atom is like a ping -pong ball.

It's electron.

It would be orbiting on average about half a kilometer away.

That's quite the distance.

And the density, well, if you had a ping pong ball made of nuclear material, it would weigh something like 2 .5 billion tons.

Yeah, it's almost impossible to wrap your head around, isn't it?

Exactly.

And the energies involved here are millions of times greater than, you know, your standard chemical reaction.

So our mission today is to really demystify this nucleus.

We want to understand what makes it stable, how it changes, why it holds so much power, and how all that affects everything from medicine to energy.

Really make it clear without needing diagrams in front of you.

It's amazing how our picture of the atom changed.

You know, atom meant indivisible for ages.

Right, until people like Rutherford came along early last century and showed, nope, there's a dense bit in the middle.

And now we know that bit, the nucleus, is made of primarily two particles,

protons and neutrons.

And collectively, they're just called nucleons.

Keeps it simple.

Nucleons, okay.

So when we talk about a specific atom, we use the atomic number, right?

Z.

Yeah, Z.

That's just the number of protons is what defines the element.

Six protons, always carbon.

Got it.

And the mass number, A, is protons plus neutrons.

Exactly.

So you can have atoms of the same element, same number of protons, but with different numbers of neutrons.

Those are isotopes.

Like carbon -12 and carbon -14.

Both carbon, different neutrons.

Precisely.

And any specific combination like carbon -14, we call that a nuclide.

And what's really fascinating here, going back to that ping pong ball, is just the sheer power locked inside those kind of structures.

Like you said, the energy scale for nuclear stuff is just, it's millions of times bigger than chemical reactions.

Right.

And that fundamental difference is why nuclear chemistry is so important, you know, for energy, for medicine.

We're tapping into something huge.

Right, that immense power.

And it kind of begs the question, you know, what actually makes nucleus stable?

Because they don't all just sit there peacefully, do they?

Not at all.

There's thermodynamic stability, sort of its energy compared to its parts, and kinetic stability.

Kinetic stability is about whether it's actually likely to fall apart to decay.

And many are unstable.

They're radioactive.

Meaning they spontaneously change into something more stable by spitting out particles.

That's radioactive decay.

Like your carbon -14 example, turning into nitrogen -14 and kicking out an electron.

Exactly.

And a key thing here is conservation.

In these nuclear reactions, the total mass number A and the total atomic number Z, they have to balance out before and after.

Okay, so the books have to balance, basically.

Pretty much.

And if you actually plot out the stable nuclides, neutrons versus protons, you see this pattern.

Scientists call it the zone of stability.

Not just a straight line, then?

No, not at all.

For light elements, it's roughly one neutron per proton, 1 .1.

But as you get heavier, you need more neutrons than protons to stay stable.

That ratio climbs.

Interesting.

And there's a hard limit, it seems.

Anything with 84 or more protons?

Unstable, period.

Also, having even numbers of protons and neutrons tends to make a nucleus more stable.

It's a noticeable trend.

And then there are these magic numbers, 2, 8, 20, 50, 82, 126 nucleons that grant extra stability.

Sort of like electron shells, but for the nucleus.

Magic numbers.

So these unstable nuclei are always trying to get to that zone of stability?

That's the driving force.

That quest for stability powers so much naturally and in technology.

So if they're trying to get stable, what are the different ways they do it?

What kinds of things get emitted?

Good question.

There are several main strategies, you could say.

If a nucleus is really heavy, it might just shed a chunk.

That's alpha decay.

It spits out an alpha particle, which is basically a helium nucleus, two protons, two neutrons.

So gets lighter and changes element, like uranium -238 becoming thorium -234.

Exactly.

Very heavy nuclides often do this.

Or even more drastically, some just split into that spontaneous fission.

Okay.

What if it has too many neutrons for its protons?

Then it can use beta decay.

A neutron inside the nucleus transforms into a proton and it emits an electron, a beta particle, to balance the charge.

So the mass number stays the same, but the atomic number goes up by one, like thorium -234 becoming prutectinium -234.

Precisely.

It shifts towards that stability zone.

Now you mentioned something fascinating earlier about that electron.

It's not actually in the nucleus.

Ah, yeah.

This is one of those mind -bending quantum things.

The electron doesn't exist before the decay.

When the neutron changes to a proton, energy is converted into matter that electron is created right then and there.

Wow.

Okay.

Like words being formed as you speak them.

Kind of.

It's a real manifestation of obsidian.

So what about the opposite problem?

Too many protons.

Two main ways to handle that.

One is positron production.

A proton changes into a neutron and it emits a positron plus one E, which is like an electron but with a positive charge.

It's antimatter.

Antimatter.

So sodium -22

decaying to neon -22 would do that.

It could, yes.

The other way is electron capture.

The nucleus actually grabs one of its own inner orbital electrons, pulls it in, and combines it with a proton to make a neutron.

So again, a proton becomes a neutron like mercury -201 turning into gold -201.

Right.

The alchemists dream, almost, but not very efficient.

And both positron emission and electron capture often release extra energy as gamma rays.

Gamma rays are just high energy light.

Right.

Exactly.

High energy photons.

They often accompany other decay types when the nucleus is left in an excited state and needs to settle down.

And sometimes it takes multiple steps.

A whole chain reaction.

Yes.

A decay series.

Especially for the very heavy elements.

They might undergo alpha decay, then beta, then alpha again.

Maybe multiple times.

Step by step until they finally land on a stable nuclide.

Uranium -238 eventually ends up as lead -206 after a long series.

That variety really shows how they're navigating towards that stable zone.

It does.

And this naturally leads to the question,

how fast does all this happen?

Can we predict it?

Yeah, it seems so random for one atom, but is it predictable for like a whole bunch of them?

It is.

Remarkably so.

While we can't predict which atom will decay next, the overall rate for a large sample is very predictable.

Radioactive decay falls first order kinetics.

Meaning the rate just depends on how many radioactive atoms you have left.

Exactly.

The more you have, the faster the decay rate overall.

And this leads to the concept of half -life.

$212.

Ah, half -life.

The time it takes for half the sample to decay.

Right.

And the crucial thing is, it's a constant for a specific nuclide.

It doesn't matter if you start with a gram or a ton, the time for half of it to decay is always the same.

Like technetium -99 meters used in medicine has a half -life of about six hours.

So after six hours, half is gone.

After 12 hours, three -quarters is gone.

Half of the remaining half.

After 18 hours, seven -eighths, and so on.

And that half -life really matters in the real world, doesn't it?

Absolutely.

It dictates how long something remains radioactive and potentially hazardous, or how useful it is for certain applications.

Take strontium -90.

It's a fission product, has a half -life of about 29 years.

Right.

Chemically, it's like calcium.

So it gets into the environment, into the food chain.

You can get incorporated into our bones and sit there irradiating tissues for decades.

That's a serious health hazard.

Right.

Long half -life, chemically active, bad combo.

Yeah.

But half -lives range incredibly widely.

Some are fractions of a second, like polonium -214.

Others are billions of years, like uranium -238, which is around 4 .5 billion years.

Billions.

That's why it's still around from the Earth's formation.

Exactly.

And that huge range is what makes radioactive isotopes useful for everything from fast medical scans to dating ancient rocks.

Dating rocks.

Okay, but humans didn't just watch this happen, right?

We figured out how to cause nuclear changes.

We did.

Rutherford, again, back in 1919.

He didn't just discover the nucleus.

He was the first to achieve artificial nuclear transformation.

That's changing one element into another on purpose.

Yes.

He bombarded nitrogen gas with alpha particles and detected oxygen.

Nitrogen -14 turned into oxygen -17.

That must have been revolutionary.

How do we do it now?

With bigger machines, I assume.

Oh, yeah.

We use particle accelerators, like cyclotrons or linear accelerators.

These machines use electric and alpha particles,

moving incredibly fast.

Fast enough to overcome the positive charge repulsion of the target nucleus and slam into it, causing a reaction.

Smashing atoms together, basically.

Pretty much.

Another key technique is using neutrons.

Ah, because they don't have a charge.

Exactly.

No electrostatic repulsion.

So even slow neutrons can just wander into a nucleus and be absorbed, transforming it.

This neutron bombardment has been crucial for creating transuranium elements.

Elements heavier than uranium, Z greater than 92.

Right.

Uranium was the heaviest known element naturally occurring in significant amounts.

But starting in 1940, scientists began synthesizing elements 93, neptunium and 94 plutonium, and onwards.

Creating brand new elements.

Yeah, often through incredibly complex experiments involving international collaboration, like creating element 117 tennessine.

That involved firing calcium -48 ions at a target of

249 for months in a specialized facility, really pushing the frontiers.

It's amazing we can make them, even if they vanish quickly.

But how do we even know they're there?

How do we detect radioactivity?

Good point.

We can't see or feel it directly.

Usually.

We need instruments.

The classic one is the Geiger -Miller counter, or Geiger counter.

The clicky thing from old movies.

That's the one.

It basically has a tube filled with a gas, like argon.

When radiation passes through, it knocks electrons off the gas.

Atoms ionizes them.

This creates a little pulse of electricity, which the counter detects.

Off it is a click, or a reading.

Okay.

Any other ways.

Yeah.

Centilation counters are also very common.

They use materials that actually emit a flash of light they scintillate when struck by radiation.

Sensitive detectors pick up these light flashes and count them.

Okay.

So we can detect it.

And you mentioned dating things.

How does that work?

Radiocarbon dating.

Right.

Radiocarbon dating is maybe the most famous application.

Willard -Louis won a Nobel Prize for it.

It uses carbon -14, which is an isotope of carbon.

It's radioactive with a half -life of 5 ,730 years.

And how does it get into things?

It's constantly being made in the upper atmosphere.

Cosmic rays hit nitrogen atoms, nitrogen -14, and turn them into carbon -14.

This C -14 gets incorporated into carbon dioxide, just like normal C -12.

And plants breathe that CO2.

Exactly.

Plants take it up.

Animals eat the plants.

So all living things maintain roughly the same ratio of C -14 to C -12 as the atmosphere.

But when they die?

They stop taking in new carbon.

The C -12 just sits there stable.

But the C -14 starts to decay away, following its half -life.

Ah.

So by measuring the remaining C -14 -C -12 ratio in something organic like wood or bone or cloth, you can figure out how long ago it died.

Precisely.

It's effective for dating things back maybe 50 ,000 or 55 ,000 years.

Were there limitations?

Yeah, a couple.

You have to assume the atmospheric C -14 level was constant, which isn't quite true, but we can correct for that using tree ring data.

And obviously it only works for organic materials and only up to a certain age.

So for really old stuff like rocks?

You need isotopes with much longer half -lives.

Uranium lead dating is a key one.

Uranium -238 decays eventually to lead -206 with that 4 .5 billion year half -life.

By measuring the ratio of U -238 to Pb -206 in certain minerals within rocks, geologists can date incredibly old formations, even estimate the age of the Earth.

Amazing stuff.

And what about the medical side?

You mentioned radiotracers.

Yes.

Radiotracers are hugely important in medicine.

These are radioactive nuclides attached to the molecules that the body uses.

You introduce a tiny safe amount into the patient, and because it's radioactive, you can track where it goes using detectors outside the body.

So you can see how organs are functioning.

Exactly.

Iodine -131, for instance, naturally goes to the thyroid gland, so you can use it to see if the thyroid is overactive, underactive, or has abnormal growths.

Clever.

Thallium -201, or technetium -99m, can be used to image blood flow in the heart, looking for damage after a heart attack.

And researchers like Rosalyn Yalow and Solomon Burson developed radioimmunoassay, RIA.

What's that?

It uses radioactive tags to measure incredibly tiny amounts of substances in the body, like hormones.

It revolutionized endocrinology and diagnostics.

So these aren't just about imaging, but also about measuring things precisely.

Right.

Non -invasive ways to diagnose, monitor treatments, understand how drugs work.

It's had a massive impact on healthcare.

Incredible applications.

But let's go back to the source of all this energy.

You mentioned stability.

How does MCFROT fit in?

Ah, yes.

Thermodynamic stability again.

It all comes down to mass defect.

Mass defect?

Sounds like something's missing.

In a way, it is.

If you take the mass of all the individual protons and neutrons that make up a nucleus,

and compare it to the mass of the actual assembled nucleus, you find the nucleus is slightly lighter.

Lighter than its parts.

How?

Because when those nucleons bind together to form the nucleus, a huge amount of energy is released.

That's the binding energy.

And according to Einstein's EMSU Visser, energy and mass are equivalent.

So releasing that energy means the nucleus loses a tiny bit of mass.

The lost mass is the binding energy converted.

Precisely.

That mass defect multiplied by c squared equals the energy holding the nucleus together.

Wow.

Okay.

And how do we compare stability between different nuclei?

We look at the binding energy per nucleon.

You take the total binding energy and divide by the number of protons and neutrons.

The higher that number, the more stable the nucleus is, the more energy it took to form it or would take to break it apart.

And is there a peak?

A most stable nucleus?

Yes, there is.

The curve of binding energy per nucleon peaks around mass number 60.

The champion is iron 56.

Iron 56.

So elements lighter and heavier than iron are technically less stable.

In terms of binding energy per nucleon, yes.

And that difference is the key to releasing nuclear energy.

Okay.

So if iron 56 is the of stability,

how do we get energy from other nuclei?

Two main ways.

Based on which side of iron you're on.

If you have very heavy nuclei like uranium 235, they are less stable than medium weight nuclei.

So if you can split them into smaller, more stable pieces, energy is released.

That's fission.

Splitting the atom.

Right.

And the energy release is enormous.

Like you mentioned, uranium 235 fission gives off millions of times more energy than burning fossil fuels per atom.

Fission releases neutrons too, right?

Which can cause more fission.

Exactly.

That's the chain reaction.

One fission triggers others.

If you have enough fissionable material together, the critical mass, the reaction could become self -sustaining or even accelerate rapidly like in a bomb.

But in a nuclear reactor, you control it.

Yes.

Nuclear reactors use controlled fission to generate heat, usually to boil water and drive turbines for electricity.

They use fuel, like enriched uranium, a moderator like water to slow the neutrons down so they're more likely to cause fission, and control rods, often cadmium or boron, that absorb neutrons to speed up or slow down the reaction rate.

But there are challenges.

Accidents, waste.

Definitely.

Accidents like Chernobyl and Fukushima highlight the potential dangers.

And managing the highly radioactive waste with its very long half -lives is a major, major challenge requiring long -term geological solutions.

Okay, that's splitting heavy nuclei.

What about the other side of iron?

The light elements.

Right.

Very light nuclei like hydrogen isotopes are also less stable than things closer to iron.

So you can force them to combine to fuse together into a heavier, more stable nucleus like helium.

Energy is also released.

That's fusion.

Like what happens in the sun.

Exactly.

The sun fuses hydrogen into helium, releasing the energy that sustains life on earth.

So why aren't we all using fusion power?

Sounds great light elements, lots of energy.

The catch is getting it started.

Remember, nuclei are positively charged.

They repel each other strongly.

Like trying to push two strong magnets together the wrong way.

Kind of, but much stronger.

To overcome that repulsion and get them close enough to fuse, you need incredible temperatures and pressures.

We're talking tens of millions, even hundreds of millions of degrees Celsius.

Hotter than the core of the sun.

Wow.

How do you even contain something that hot?

That's the multi -billion dollar question.

Researchers are using powerful magnetic fields in devices called tokamaks or stellarators or intense lasers to try and confine the superheated plasma and trigger fusion.

It's incredibly difficult, but the potential payoff clean, abundant energy from readily available fuels like deuterium from water is immense.

Immense potential, but also we need to talk about the What are the actual effects of radiation on us?

It's a critical question.

Basically the high energy particles or rays from radioactive decay can act like tiny bullets crashing into molecules in our cells.

They can break chemical bonds, create reactive ions and damage crucial molecules like DNA.

And that damage can cause problems.

Yes.

We talk about somatic damage, which affects the individual organism directly.

This can range from radiation sickness at high doses to an increased risk of cancer later in life, even at lower doses.

And genetic damage.

That's damage to the DNA and sperm or egg cells.

Yeah.

It doesn't harm the individual exposed, but it can cause mutations that are passed on to their offspring.

What determines how much damage radiation does?

Is all radiation equal?

No, definitely not.

Several factors matter.

One is the energy of the radiation.

Higher energy particles generally do more damage.

We measured the absorbed energy dose in rads.

Okay.

Two is the penetrating ability.

Gamma rays go right through you.

Beta particles penetrate skin and tissue, maybe a centimeter.

Alpha particles are stopped by the outer layer of skin.

So alpha isn't dangerous from the outside?

Not usually, but factor three ionizing ability.

Alpha particles, despite their short range, are very effective at causing intense damage along their short track.

So if you ingest or inhale an alpha emitter, like radon gas decaying in your lungs, it can be extremely harmful.

Ah, so internal exposure is key for alphas.

Yes.

And factor four is the chemical properties of the source.

Does it stay in the body?

Where does it go?

Strontium -90 stays in bones for years.

Krypton -85 is an inert gas.

You breathe it in and out quickly.

Same type of radiation, very different long -term risk.

So we need a measure that accounts for the biological effect, not just energy.

Exactly.

That's the rem Bromchin equivalent for man.

It multiplies the rad dose by a factor, RBE, that reflects the biological effectiveness of that specific type of radiation.

One rem of alpha damage is biologically much worse than one rem of gamma damage, even if the energy deposited is the same.

And what about low levels?

Is there a safe threshold?

That's debated.

The linear model assumes any radiation exposure increases risk proportionally.

The threshold model suggests there's a level below which the body's repair mechanisms can handle the damage.

For safety regulations, scientists usually default to the more cautious linear model.

Assume any dose carries some risk.

Which makes sense when dealing with things like nuclear waste.

Absolutely.

The long -term accumulation and safe handling of radioactive materials remains a huge societal and scientific challenge.

Balancing the benefits and risks is crucial.

What a journey.

We've gone from the incredibly tiny nucleus, explored its stability, its transformations,

seen how we measure it, use it for dating, for medicine,

unpacked the immense energy in fission and fusion, and considered the very real risks of radiation.

It really shows how understanding these fundamental nuclear processes is vital, you know, for making informed decisions about energy, health, and our future.

It really does.

And it makes you think, doesn't it?

Considering that ongoing debate about nuclear energy, what specific breakthrough, maybe in waste disposal or perhaps finally achieving practical fusion, do you think could genuinely change the game for public acceptance?

And maybe more importantly for our listeners, what role could bright students like you studying chemistry today play in making that future happen?

That's the ongoing challenge.

A huge challenge and a fascinating one.

The future really could hinge on answers to those questions.

Well, thank you for joining us on this deep dive into the atomic nucleus.

We hope you feel a little more well -informed.

Maybe you sparked some curiosity.

From the Deep Dive team, thank you for listening.