Chapter 24: Nuclear Reactions and Their Applications

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Hey there, learner.

Welcome back to the Deep Dive.

We're here to unpack complex ideas, you know, strip away the jargon and give you the essential insights.

Today we're diving into something really fundamental,

powerful, and honestly a little mysterious.

The atom's core, nuclear reactions.

Think of this as your shortcut to understanding that key chapter in chemistry, the one dealing with the very heart of matter.

That's right.

Up until now, your chemistry journey has probably focused mostly on electrons, right?

How they form chemical bonds.

But today we're looking inward to the atom's tiny, incredibly dense nucleus.

This is the realm of the strongest force in the universe.

And our mission is simple.

Guide you step by step through the main ideas, the laws,

and well, the really mind -bending applications of nuclear chemistry.

Yeah, and we'll swap out those complex diagrams for clear descriptions, maybe some analogies, connecting the science to things like ancient artifacts, even the energy -powering stars.

So let's explore how elements themselves can actually change and why that's so important.

Okay, let's start with a basic contrast.

You know chemical reactions, right?

They involve electrons, atoms get rearranged into new compounds,

but the elements, they stay the same.

Think about burning wood.

Carbon atoms are still carbon atoms, just in different molecules, and the energy changes are, well, relatively small.

But nuclear reactions are, wow, they're dramatically different, fundamentally different.

Here, the nuclei themselves change.

They almost always form entirely different elements.

It's like real alchemy and the energy involved.

It's

so massive, actually, that you see measurable changes in mass.

You just don't get that in everyday chemistry.

What I find really fascinating here is how independent these nuclear reactions are.

They're basically unaffected by things like temperature, pressure, catalysts.

Exactly, which is a huge contrast to chemical reactions, which are super sensitive to those conditions.

And this independence really highlights the immense forces at play inside the nucleus.

I mean, despite its tiny size, like 10 to the minus five times the atomic radius, so incredibly small, it holds practically all the atom's mass that makes it unbelievably dense.

Imagine a sugar cube weighing billions of tons.

That's the kind of density we're talking about.

It's staggering.

Right, so to talk about this tiny, powerful world, we need some key terms.

It's like learning the language for this new area.

Absolutely.

So the basic particles in the nucleus, protons, and neutrons together, we call them nucleons.

Simple enough.

Each specific combination of protons and neutrons makes up a unique nuclide.

You already know about isotopes, right?

Atoms of the same element, so same number of protons, but different numbers of neutrons.

And we use a specific notation to keep track.

The element symbol, let's say X.

Then the mass number, A, that's total nucleons, goes top left as a superscript.

And the atomic number, Z, the protons, goes bottom left as a subscript.

So chlorine 35 would be 35 over 17, then Cl.

Thus you have 17 protons and 35 minus 17, 18 neutrons.

The whole story of nuclear chemistry really got going with some, well, accidental discoveries.

Back in 1896, a French physicist, Antoine Henri Becquerel, he just happened to find that uranium minerals gave off this penetrating radiation.

It could expose photographic plates even through black paper.

Apparently he just left some uranium salt on a plate in a drawer.

Pure chance.

Yeah, building on that, in 1898, Marie Sklodowska -Curie started her amazing work.

She found the intensity of this radiation was directly tied to the amount of the element, not the compound it was in.

That was a huge clue.

She actually coined the term radioactivity for these emissions.

And she confirmed they weren't affected by external conditions.

Her work led to discovering polonium and radium.

Earned her two Nobel prizes, incredibly.

And here's where it really gets wild.

In 1902, Ernest Rutherford and Sadi proposed something radical for the time.

They suggested that radioactivity actually causes one element to change into another.

People initially thought it sounded like, you know, medieval alchemy, but they were absolutely right.

So when an unstable nucleolide decays, it spits out radiation.

There are three main types, each with different properties.

Okay, first up, alpha particles.

Symbol.

Think of them as relatively heavy chunks, positively charged, basically a helium nucleus.

Second, beta particles.

Symbol minus.

These are just high -speed electrons.

Much lighter, negatively charged.

And third, gamma rays.

Simple.

Not really particles.

More like pure energy.

Very high -energy photons.

No mass, no charge.

Right.

And you can visualize the difference if you imagine them passing through an electric field.

The positive alpha particles bend a bit towards the negative plate.

The much lighter negative beta particles, they get yanked much more sharply toward the positive plate.

And the gamma rays.

Uncharged, so they just go straight through.

Unaffected.

Tells you a lot about them.

So these unstable nuclei, the parent nuclates, they decay into more stable daughter nuclates.

And the key rule for balancing these nuclear equations is pretty straightforward, but crucial.

Total mass number A and total atomic number C have to be the same on both sides.

Conserved.

Exactly.

Conservation is key.

Let's quickly run through the common ways they decay.

Alpha decay.

Mostly for heavy nuclei.

The parent loses an alpha particle, so mass number drops by 4, atomic number drops by 2, radium -2 -2 -2 is turning into radon -2 -22 is a good example.

Beta minus decay.

Here, a neutron inside the nucleus turns into a proton, and it kicks out a high -speed electron, that's the beta particle.

Mass number stays the same, but the atomic number goes up by 1.

Carbon -14 decaying to nitrogen -14, that's beta decay.

Crucial for carbon dating.

Then there's positron emission, or electron capture.

Both are ways for proton -rich nucleus to fix itself.

A proton basically turns into a neutron.

Positron emission spits out a positron like an anti -electron.

Electron capture grabs an electron from an inner shell, both cases.

Mass number's unchanged, atomic number drops by 1.

And finally, gamma emission.

An excited nucleus just releases extra energy as a high -energy photon, a gamma ray.

Doesn't change the element A and Z stay the same, it often happens alongside other decays.

Okay, so many ways to decay.

What actually determines if a nucleus is stable or not?

And, you know, how does it choose which way to decay?

Ah, big question.

Well, if you plot all the stable nuclides, neutrons versus protons, they fall into a narrow region called the band of stability.

For lighter elements, stability often means roughly equal numbers of protons and neutrons.

N equals Z, basically.

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

The N -Z ratio increases, neutrons provide extra glue, you could say, without adding more proton, proton repulsion.

Right, so if a nuclide has too many neutrons for its proton count, its neutron -rich, it's above the band, it'll likely undergo beta minus decay, right?

Turn a neutron into a proton,

moving it closer to the band.

Precisely.

And if it has too few neutrons or too many protons, proton -rich below the band, it'll probably go for positron emission or electron capture.

Turn a proton into a neutron, again shifting towards stability.

It's all about getting back to that stable ratio.

Interesting.

Is there anything else that influences stability?

Oh, yes.

There's a fascinating pattern with even and odd numbers.

Nuclides with both an even number of protons and an even number of neutrons, they tend to be exceptionally stable.

Lots of them exist.

Conversely, nuclides with both odd protons and odd neutrons are very rare among stable isotopes.

Only four exist naturally, like nitrogen -14.

It suggests pairing energy matters within the nucleus.

And you mentioned magic numbers, like stable electron shells and atoms.

Exactly like that.

Certain numbers of protons, or neutrons 2, 8, 20, 28, 50, 82, and 126, just for neutrons, seem to correspond to filled energy levels within the nucleus.

Nuclides with these magic numbers are unusually stable.

Tin, with Z50, is a great example.

It has more stable isotopes than any other element.

And what about the really, really heavy elements way out at the end of the periodic table?

Good point.

Beyond Bismuth, element 83,

all known nuclides are unstable.

They're just too big to hold together indefinitely.

They typically undergo alpha decay to reduce their size.

And often, it's not just one decay.

They go through a whole decay series, a sequence of alpha and beta decays eventually landing on a stable isotope, usually of lead, like uranium -238 decaying through many steps down to lead -206.

Okay, so nuclei are decaying, spitting out particles.

How do we actually detect this stuff?

We can't see it.

Right.

We detect the effects of the radiation.

The key effect is ionization.

When these emissions hit surrounding matter, they have enough energy to knock electrons off atoms or molecules, creating ions.

Like with a Geiger -Muller counter.

I think most people have heard of those, the clicking sound.

Exactly.

The radiation enters a tube filled with gas, ionizes the gas, and creates a little avalanche of electrons.

That causes a pulse of current, which makes the click.

Each click is basically one detection event.

What about other methods?

Another common one is the scintillation counter.

Here, the radiation hits a material that scintillates, gives off a tiny flash of light.

That light is then detected and amplified, usually by something called a photomultiplier tube.

Liquid scintillation counters are often used for biological samples, especially for low -energy beta emitters like carbon -14 or tritium.

So individual decays are random, but a whole bunch of radioactive atoms decay predictably.

That's the key.

A large population decays at a measurable rate, or activity.

And this rate is directly proportional to the number of radioactive nuclei present at that moment.

This makes radioactive decay a classic first -order process in kinetics.

How do we measure that rate, the activity?

The official SI unit is the becquerel, Bq, which is just one disintegration per second.

Very small.

More commonly, you'll see the curie, CI, named after Marie Curie, of course.

One curie is 3 .7 times 10 to the 10 disintegrations per second, a much larger unit, originally based on a gram of radium.

But probably the most intuitive concept for decay rate is half -life, T12.

Right.

The time it takes for half of the sample to decay.

Exactly.

It's a constant value for any specific radioisotope.

It doesn't matter how much you start with.

After one half -life, half of it is gone.

Wait another half -life, half of what's left

and so on.

Carbon -14, for instance, has a half -life of about 5 ,730 years.

So you start with, say, 10 grams of C14.

After 5 ,730 years, you have 5 grams.

After another 5 ,730 years, you'd have 2 .5 grams.

Precisely.

This constant predictable decay is what makes radioisotopic dating possible.

It's an incredible tool.

This is where we figure out the age of things, right?

Like ancient artifacts or even the earth.

Yes.

The most famous is probably radiocarbon dating, developed by Willard Libby.

He won a Nobel for it.

Here's how it works, basically.

Cosmic rays hit the upper atmosphere, constantly producing radioactive carbon -14 from nitrogen -14.

The C14 mixes into the atmosphere as carbon dioxide.

Living things, plants taking in CO2, animals eating plants, constantly exchange carbon with the environment.

So while alive, they maintain the same ratio of C14 to stable C12 as the atmosphere.

Okay, so they have a steady level of C14 while they're alive.

But when the organism dies, it stops taking in carbon.

The exchange stops.

From that point on, the C14 it already contains just decays away with its 5 ,730 -year half -life.

The stable C12 doesn't change.

So by measuring the remaining C14 activity, or the C14 -C12 ratio, in a sample like wood, bone, cloth, we can calculate how long ago it died.

Wow.

Like with the Shroud of Turin.

That was dated using C14, wasn't it?

It was.

They dated a small piece of the linen.

The results indicated the flax used to make it grew somewhere between 80, 1260, and 1390.

A very significant finding, whatever you believe about the shroud itself.

Of course, C14 dating is only good for things up to maybe 50 ,000 years old.

For older things, like rocks or meteorites, we need isotopes with much longer half -lives.

Things like uranium -238 decaying to lead -206.

That half -life is billions of years.

That's how we've estimated the age of the Earth and the solar system to be around 4 .7 billion years.

Amazing stuff.

Okay, so elements can change on their own through decay, but you also mentioned we can make them change, like Rutherford did.

Exactly.

That was the first artificial nuclear transmutation.

Bombarding nitrogen with alpha particles made oxygen and a proton.

We actually have a shorthand notation for this.

Target, bombarding particle, ejected particle product.

So Rutherford's experiment was 14N, 17O.

And interestingly, follow -up experiments trying similar things led James Chadwick to discover the neutron in 1932.

Hitting beryllium with alphas produced a neutral particle with mass similar to a proton.

It was the missing piece of the nucleus.

And we can create new radioactive isotopes this way too.

Yes.

Shortly after the neutron's discovery, Irene and Frederick Joliot -Curie, Marie Curie's daughter and son -in -law, bombarded aluminum with alphas and made the first artificial radioisotope phosphorus -30.

Today, most of the known radioisotopes are actually man -made, produced through transmutation.

But hitting a positive nucleus with a positive alpha particle,

they'd repel each other, right?

You must need a lot of energy.

You do.

Especially if you want to use heavier bombarding particles or hit heavier targets.

That's where particle accelerators come in.

They're needed to overcome that electrostatic repulsion.

Early types included the linear accelerator, using electric fields and stages to speed up particles in a straight line.

Then came the cyclotron, using magnets to bend the path into a spiral, allowing them to be accelerated repeatedly in a relatively compact space.

And today we have things like the Large Hadron Collider, LHC, near Geneva.

Right.

Incredible machines.

The LHC can accelerate protons to enormous energies, 13 Tera electron volts and speeds incredibly close to the speed of light, like 99 .99%.

Physicists use these collisions to study fundamental particles and forces.

But for chemists, what's the main use?

A key application is creating transuranium elements.

Elements heavier than uranium, Z92.

Accelerators let us smash heavy nuclei together with smaller ones, forcing them to fuse, at least briefly, into new super -heavy elements.

Pushing the boundaries of the periodic table, making things like fluorovium, element 114.

Okay, let's shift gears slightly.

We've talked about radiation, detecting it, using it for dating.

What about its effects on living things, both good and bad?

The fundamental interaction is still ionization.

That's the key to both the dangers and the benefits.

When radiation passes through tissue, it knocks electrons off molecules, creating ions and highly reactive species.

We hear a lot about the dangers, obviously.

Chernobyl comes to mind.

What determines how risky it is?

It really depends on three main things.

The type of radiation, its half -life, how long it sticks around, and, crucially, how the body handles the specific radioactive if it gets inside you.

For instance, consider penetrating power.

Alpha particles are stopped by skin.

Beta particles go a bit deeper.

Gamma rays go right through.

So an external source of alpha isn't too bad.

But if you ingest an alpha emitter, like the radium dial painters who lick their brushes, the alpha particles deposit all their energy in a very small area, causing intense local damage inside the body.

That's extremely dangerous.

Scrantium -90, a beta emitter from nuclear fallout, is dangerous because chemically, like calcium, it gets incorporated into bones, irradiating marrow.

Polonium -210, an alpha emitter, was used in an infamous poison case, injected.

It caused death in weeks.

Shows the internal hazard.

And this damage happens at the molecular level?

Yes.

The ionization creates free radicals molecules with unpaired electrons, making them super reactive.

These radicals can attack anything nearby.

Water, liquids in cell membranes, proteins, and especially DNA.

Damaged DNA can lead to cell replication, cancer, or genetic mutations passed to offspring.

We're exposed to radiation all the time though, aren't we?

Background radiation.

Yeah, constantly.

About half comes from natural sources.

Cosmic rays from space, radioactive elements in rocks and soil, like uranium decaying to radon gas, which can seep into basements.

Even potassium -40 naturally present in our own bodies.

The other half, roughly, comes from artificial sources.

And the biggest chunk of that is actually medical diagnostics.

X -rays, CT scans, nuclear medicine procedures.

Radon gas alone is thought to be a major contributor to lung cancer deaths, second only to smoking.

So it's definitely a double -edged sword.

What about the benefits?

How do we use radioisotopes constructively?

Oh, the applications are vast.

One really powerful technique is using radioactive tracers.

You take a tiny amount of a radioisotope, mix it with the stable version of the element, and use it as a sort of chemical spy or beacon.

You can follow it through a complex process.

Like tracking how a drug moves through the body.

Exactly.

Or how nutrients are absorbed by plants.

Melvin Kelvin used carbon -14 tracers to map out the entire process of photosynthesis.

Incredible work.

Won him a Nobel Prize.

Industry uses them, too, to track fluid flow in pipes, detect leaks, study engine wear, things like that.

What else?

There's neutron activation analysis, NAA.

You bombard a sample with neutrons, making some of its atoms radioactive.

Each element emits characteristic gamma rays as it decays, like a fingerprint.

By analyzing these gamma rays, you can tell exactly what elements are present, even in tiny amounts.

It's non -destructive, which is great.

Art historians use it to analyze pigments in paintings to spot fakes.

Forensic scientists use it to analyze gunshot residue, or maybe arsenic in hair samples from long ago.

And medicine seems to be a huge area.

Absolutely the largest use.

Medical diagnosis relies heavily on short -lived tracers.

Things like iodine -131 to image the thyroid gland, or technetium -99 meter, which is incredibly versatile for scans of the heart, lungs, liver, bones.

It lets doctors see how organs are functioning, not just their structure.

What about peat scans?

Those sound pretty advanced.

Positron emission tomography, yes.

Very powerful.

You synthesize a biologically important molecule, like glucose, with an isotope that emits positrons, like fluorine -18.

You inject this into the patient.

Where the molecule goes, positrons are emitted.

They immediately meet an electron and annihilate each other, producing two gamma photons that fly off in opposite directions.

Detectors pinpoint these photon pairs, allowing a computer to reconstruct a 3D image of where the tracer concentrated.

Since cancer cells often use more glucose, PE scans are great for finding tumors, also used for heart function, brain activity studies.

So diagnosis, what else?

Therapy, food.

Yep.

Radiation therapy uses targeted radiation, often from cobalt -60 to kill cancer cells.

Food irradiation uses gamma rays to kill bacteria, molds, and insects, extending shelf life, even controlling insect populations by sterilizing males with radiation and releasing them.

And way out there, literally, radioisotope heater units, RHUs, often using plutonium -238, provide heat to keep instruments working on spacecraft going to the outer solar system, where sunlight is too weak for solar panels.

Incredible range of uses.

Okay, let's connect this back to the energy.

You said nuclear reactions involve huge energy changes linked to mass changes.

Zero.

Einstein's, Eves -C, and Poitier.

Precisely.

That equation is the heart of it.

Energy and mass are interchangeable.

In chemical reactions, the mass change is absolutely minuscule, effectively zero for practical purposes.

But in nuclear reactions, it's significant.

Measurable.

How does that work?

Mass just disappears.

Not disappears.

It's converted into energy.

Take a carbon -12 nucleus.

If you weigh the six protons and six neutrons separately,

their total mass is more than the mass of the assembled carbon -12 nucleus.

That difference in mass, the mass defect, has been converted into the energy holding the nucleus together.

We call that the nuclear binding energy.

So the energy needed to break the nucleus apart into its individual nucleons.

Exactly.

And these binding energies are enormous, millions of times greater than chemical bond energies.

Now, if you calculate the binding energy per nucleon, per proton or neutron, and plot that against the mass number for all the elements, you see something really important.

What's that?

The curve goes up steeply for light elements, peaks around mass number 60 near iron 56, and then gradually slopes downward for heavier elements.

Iron 56 is basically the most stable nucleus in terms of binding energy per nucleon.

Okay, so what does that peak tell us?

It tells us there are two ways to release nuclear energy by moving towards that peak stability.

One, take very heavy nuclei, like uranium, way past the peak, and split them into smaller, lighter nuclei that are closer to the peak.

That's fission.

Two, take very light nuclei, like hydrogen isotopes, way before the peak, and combine them to form heavier, more stable nuclei, also moving up towards the peak.

That's fusion.

Both processes release the extra binding energy.

Let's talk fission first.

That's splitting heavy atoms.

Right.

Discovered in the late 1930s, scientists like Hahn, Strossman, and Meitner figured out that hitting uranium with neutrons could cause its nucleus to split into smaller fragments, like barium and krypton.

And critically, this splitting released a huge amount of energy and more neutrons.

More neutrons, which could then hit other uranium atoms.

Exactly.

That's the basis of a chain reaction.

One fission triggers more fissions, which trigger even more.

If you have enough fissionable material together, what's called the critical mass, the reaction can become self -sustaining, potentially escalating very rapidly.

Which leads to bomb.

Uncontrolled fission is the principle of the atomic bomb.

You quickly bring together two or more subcritical masses to form a super critical mass, triggering an explosive chain reaction.

The Manhattan Project during WWII developed this technology.

But we also use fission for power, right?

Yes, that's how nuclear power plants work.

You sustain a controlled chain reaction to generate heat.

Inside a reactor core, you have fuel rods, typically containing uranium dioxide, often enriched in uranium -235.

Control rods, made of materials like cadmium or boron that absorb neutrons, are moved in or out to regulate the rate of fission, keeping the chain reaction steady, not run away.

A moderator, like water or heavy water, slows down the fast neutrons produced by fission, making them more likely to cause further fission in U -235.

And a coolant, often the water moderator itself, carries the heat away, usually to boil water in a separate loop, creating steam to drive turbines and generate electricity.

Sounds straightforward, but obviously there are challenges.

Accidents.

Yes.

Major accidents like Three Mile Island, Chernobyl, and Fukushima highlight the potential dangers if control is lost or systems fail.

There's also thermal pollution releasing warm water used for cooling can affect aquatic ecosystems, but the biggest long -term challenge is nuclear waste disposal.

Many fission products are highly radioactive with very long half -lives.

Finding safe, secure, permanent storage for waste that remains dangerous for thousands, even hundreds of thousands of years, is a huge scientific and political problem.

Okay, so that's fission.

What about the other side, fusion, combining light atoms?

Ah, nuclear fusion.

That's the process powering the sun and stars, the ultimate energy source, really.

You take very light nuclei isotopes of hydrogen like deuterium H2 and tritium H3 and force them together under extreme conditions to form a heavier nucleus like helium -4.

The key DT fusion reaction releases even more energy per mass than fission, and importantly, its main products, helium and a neutron, are not long -lived radioactive waste.

Much cleaner in that sense.

Sounds amazing.

What's the catch?

Why don't we have fusion power plants everywhere?

The catch is the conditions required.

To overcome the massive electrostatic repulsion between positively charged nuclei, you need incredibly high temperatures, we're talking around 100 million Kelvin,

hotter than the core of the sun.

You also need sufficient density and confinement time for the reactions to occur frequently enough.

How are scientists trying to achieve that?

Two main approaches dominate fusion research.

One is magnetic confinement.

You use powerful, complex magnetic fields to contain the superheated fuel, now a plasma, a gas of ions and electrons, in a specific shape, usually a donut shape called a tokamak.

The International Eiger Project in France is a massive tokamak experiment under construction.

The other approach is inertial confinement.

You take a tiny pellet of fusion fuel and blast it from all sides with incredibly powerful lasers.

The laser energy rapidly heats and compresses the pellet, hopefully triggering before it blows itself apart.

Both approaches have made huge progress, but achieving sustained fusion that produces more energy than it consumes ignition and net energy gain is still probably decades away for commercial power.

The scientific and engineering challenges are immense, but the potential payoff is enormous.

Wow.

So to wrap this up, what does this deep dive into the nucleus mean for us, for the listener?

Well, on really fundamental level, almost everything you see, everything you are made of that's heavier than hydrogen and helium.

It was forged inside stars through nuclear fusion processes, stellar nucleus synthesis,

stars live, fuse elements, and then often die in spectacular supernova explosions, scattering those newly created heavier elements across the cosmos.

Those elements then became part of the next generation of stars, planets, and eventually us.

So many of the atoms in your body, the carbon, the oxygen, the iron, are literally stardust older than the earth itself.

That's a pretty incredible thought to end on.

We've covered so much today from the basic difference between chemical and nuclear changes to radioactivity, half -lives, dating, then transmutation, accelerators, making new elements.

Yeah.

And the double -edged sword of radiation, it's dangerous through ionization, but also its amazing uses in tracers, medicine, analysis, even space power.

And finally, understanding the sheer energy from EMCPA, driving both fission with its power and problems and fusion, the long term hope for clean energy born in the stars.

It really brings home the power locked inside the atom.

And it raises that ongoing question, doesn't it?

How do we keep balancing the incredible benefits of nuclear science with its undeniable risks, especially as we look for future energy solutions?

It's a question humanity will be grappling with for a long time.

We hope this is giving you a solid understanding of the fundamentals, the key ideas in nuclear chemistry.

We definitely hope this deep dive helped make sense of nuclear reactions and their applications.

Keep questioning, keep exploring.

From all of us at the Deep Dive in the Last Minute Lecture Team, thanks for learning with us.