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CHAPTERS: 0:00 Become dangerously interesting 1:29 Atomic components \u0026 Forces 3:55 What is an isotopes 4:10 What is Nuclear Decay 5:45 What is Radioactivity - Alpha Decay 6:31 Natural radioactivity - Beta \u0026 Gamma decay 9:03 What is half-life? 9:41 Nuclear fission 10:48 Nuclear fusion
SUMMARY In this video, I summarize All Nuclear Physics in about 10 minutes. Atoms are made of a positively charged nucleus surrounded by negatively charged electrons. The nuclei of atoms are made up of protons and neutrons. These are called nucleons. Because all protons have the same charge, they repel. And force can be calculated using coulombs law. Two protons separated by the width of a neutron repel with a force of 60 Newtons, or 12 lbs!
But what keeps them from flying apart is an even stronger force the strong nuclear force. It’s about 100X stronger than electromagnetism. But this force only operates at very small distances, about the width of a proton. And it only operates within and between nucleons. Electrons, photons, and neutrinos are not affected by it. It’s like Velcro. Nucleon stick together when really close, but have no affect when far apart.
The number of protons in an element is solely responsible for its chemical and physical properties. A given element or atom can have the same number of protons, but different numbers of neutrons. These are called isotopes of the element. They have exactly the same chemical properties and differ only in mass.
Stable nuclei consist of roughly the same number of protons and neutrons. The neutrons serve to provide additional strong force needed to keep the nucleus stable. Without neutrons, not even two protons can be held together against their repulsion.
Free protons are stable, but free neutrons are not stable. Lone neutrons decay into a proton, an electron, and an antineutrino within 15 minutes. But inside a nucleus they remain stable because it is energetically unfavorable for them to decay.
If a nucleus is very large, or has an excess number of protons or neutrons, this causes alpha decay, which is a helium nucleus consisting of 2 protons and two neutrons. This is what we call radioactivity.
There are three forms of natural radioactivity, alpha, beta and gamma-decay. A beta-particle is a high-energy electron. This occurs in very large nuclei when a neutron decays even though it is in the presence of protons. This gives off an electron and an antineutrino. This electron is the beta-particle.
A gamma-particle is a high-energy photon. Gamma-rays are usually emitted by excited nuclei that have been created after either an alpha or beta decay. These nuclear processes release high energy photons is because they involve the strong force with is very energetic.
Alpha-particles can be stopped by a thin piece of paper. Beta-particles can penetrate your skin, but can be stopped by a sheet of aluminum foil. But gamma-rays can penetrate through an inch of lead.
A radioactive nucleus is characterized by its “half-life.” What this means is that if I have a 16 atoms, with a half-life of 1 week, then one week later I will have ½ or 8 atoms remaining. In 2 weeks, I will have 4 and so on. The half-life is a statistical concept, and we can’t predict in advance which specific atoms will decay.
If a large nucleus, like some isotopes of uranium is hit by a particle, usually a neutron, then it will split into two smaller nuclei. This is called nuclear fission. If the total mass of the two smaller nuclei is less than that of the uranium before it was hit, the missing mass is turned into energy via E = mc2. This is called fission.
If there is enough fissionable nuclei in high enough concentration, then it is possible for the thrown off neutrons to, in turn, fission more nuclei, creating a chain reaction. This is the mechanism behind an atomic bomb. #nuclearphysics Fusion happens when two small nuclei such as hydrogen, which consists of only a single proton, can be brought close enough together that they fuse into a single nucleus. Fusion is very difficult to achieve, because the protons strongly repel each other. Only gases heated to millions of degrees Celsius have atoms moving fast enough to fuse. In the sun this process is easier because of the assistance of gravitational pressure in the core. Quantum tunneling also plays a role.
Content
0 -> before I begin let me clarify that I'm
2.52 -> not claiming you'll become a nuclear
4.56 -> physicist in 10 minutes most of you
6.24 -> probably don't want to do that anyway it
7.919 -> is not for everyone but if you want to
10.5 -> understand what I believe are the most
12.36 -> important and essential Concepts in
14.28 -> nuclear physics then stick around
15.96 -> because I'm about to make you
18.02 -> dangerously interesting at your next
20.52 -> dinner party and that's about to happen
23.22 -> right now
25.63 -> [Music]
27.779 -> before we start I want to acknowledge
29.519 -> the inspiration for this video which
31.019 -> comes courtesy of today's sponsor
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34.739 -> documentary called North Korea versus
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54.18 -> thinking about nuclear physics in
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84.18 -> thank you enough for that now back to
86.4 -> the show
90.14 -> atoms are made of a positively charged
92.759 -> nucleus surrounded by negatively charged
94.799 -> electrons the nuclei of atoms are made
97.259 -> up of protons and neutrons these are
99.36 -> called nucleons
100.619 -> because all the protons have the same
102.659 -> charge and like charges repel force can
106.02 -> be calculated using the classical
107.7 -> Coulomb's law equation here you can see
110.46 -> that the force between charged particles
112.38 -> is inversely proportional to the
114.479 -> distance between them r
116.46 -> because positively charged protons are
118.799 -> in such close proximity to each other in
120.96 -> the nucleus the electrostatic repulsive
123.24 -> force between them is enormous two
125.82 -> protons typically separated by the width
127.86 -> of a neutron is on the order of 60
131.099 -> newtons or 12 pounds
133.92 -> but what keeps them together against
136.02 -> this tremendous repulsion is an even
138.599 -> stronger Force called the strong nuclear
140.7 -> force which is about a hundred times
142.86 -> stronger than electromagnetism this
145.5 -> Force comes from one of the four
146.94 -> fundamental forces in the universe a
149.16 -> strong force but this Force unlike
151.56 -> gravity and electromagnetism operates at
154.379 -> very small distances only about the
156.84 -> width of a proton and it only operates
159.66 -> within and between protons and neutrons
162.56 -> electrons photons and neutrinos are not
165.54 -> affected by it you can think of the
167.819 -> strong force like velcro when two
169.98 -> objects carrying the strong force are
171.66 -> very close they stick to each other like
173.64 -> glue but if they're far apart they are
176.16 -> unaffected this means that a nucleus can
179.22 -> only grow so large the reason is that
182.58 -> the two opposing forces electromagnetism
185.04 -> and the strong force operate differently
187.92 -> the strong force only acts at Short
190.56 -> distances so a given proton or Neutron's
193.319 -> attractive effect diminishes rapidly as
196.26 -> the nucleus grows larger but since
198.319 -> electromagnetism has an infinite range
201 -> its Force accumulates as more and more
203.76 -> protons are added together so all the
206.22 -> protons in the nucleus participate in
208.379 -> repelling each other this repulsion
210.659 -> quickly overwhelms the attractive effect
213.12 -> of the strong force as more protons are
215.7 -> added disrupting the stability of the
218.04 -> nucleus so the heaviest stable element
220.26 -> is lead which has 82 protons the number
223.92 -> of protons in an element is important
225.959 -> because it is solely responsible for its
229.14 -> Atomic properties this proton number
231.62 -> corresponds to the position of the
233.76 -> element on the periodic table a given
236.58 -> element or atom can have the same number
238.62 -> of protons but different numbers of
241.319 -> neutrons these are called isotopes of
243.78 -> the element they have exactly the same
246.06 -> physical and chemical properties but
247.86 -> differ in Mass
252.42 -> stable nuclei consists of roughly the
255.42 -> same number of protons and neutrons the
258.12 -> neutrons serve to provide additional
261.06 -> strong force needed to keep the nucleus
263.34 -> stable without neutrons not even two
266.1 -> protons can be held together against the
268.44 -> repulsion free protons are stable but
271.68 -> free neutrons are not stable
273.96 -> low neutrons Decay into a proton an
277.68 -> electron and an antineutrino within
280.02 -> about 15 minutes
281.46 -> but inside the nucleus they remain
283.62 -> stable because it is energetically
286.32 -> unfavorable for them to decay in other
288.54 -> words the energy gained from a neutron
290.639 -> decaying to a proton is lower than the
293.4 -> increased energy required to keep an
295.56 -> additional proton in the nucleus if
297.54 -> there are plenty of other protons around
299.88 -> but this type of neutron decay in the
301.979 -> nucleus is not impossible and can happen
304.32 -> in very neutron-rich isotopes of a given
307.32 -> element
308.04 -> but a nucleus cannot have too few
310.5 -> neutrons or the nucleus will not be
312.78 -> stable it also cannot have too many
315.54 -> neutrons because eventually the strong
317.52 -> force can no longer keep them from
319.74 -> decaying into a proton and forming a
322.02 -> different element
322.979 -> protons and neutrons just like all
325.08 -> Quantum objects are subject to the laws
327.479 -> of quantum mechanics one consequence of
330 -> this is that Quantum particles have a
333.12 -> very small but non-zero probability of
336.12 -> appearing anywhere in the universe
338.34 -> the reason I mention this is because it
340.979 -> is tied to a certain kind of natural
343.139 -> radioactivity called alpha decay if a
346.38 -> nucleus is very large or has an excess
348.539 -> number of protons and neutrons and the
350.699 -> strong force can barely hold it together
352.82 -> Quantum objects have a higher
355.199 -> probability of appearing on the other
356.94 -> side of an energy barrier if the barrier
359.58 -> is not very high in the case of very
361.919 -> large nuclei such as uranium The energy
365.16 -> needed to liberate protons and neutrons
367.38 -> is small enough that sooner or later an
370.259 -> alpha particle which is essentially a
372 -> helium nucleus consisting of two protons
374.16 -> and two neutrons can Quantum
376.199 -> mechanically tunnel through the strong
378.84 -> force barrier and appear outside the
381.419 -> nucleus then they speed away very fast
383.819 -> this is what we call radioactivity if
387.36 -> you want to learn more about Quantum
388.74 -> tunneling I have a video on that right
390.36 -> up here
394.16 -> there are three forms of natural
396.18 -> radioactivity alpha beta and gamma Decay
399.72 -> an alpha particle consists of two
402.06 -> protons and two neutrons this type of
404.22 -> radiation happens via the mechanism I
406.74 -> just described the beta particle is a
409.62 -> high energy electron in some very large
411.96 -> nuclei that might be barely bound
414.06 -> together a second fundamental Force
416.58 -> called the weak force can compete with
419.28 -> the strong force and cause a neutron to
421.68 -> Decay even though it's in the presence
424.02 -> of protons
425.4 -> as I said before when a neutron Decatur
427.919 -> proton it gives off an electron and an
430.68 -> antineutrino this electron that it gives
433.139 -> off is the beta particle a gamma
435.9 -> particle is a high energy Photon also
438.3 -> called a gamma ray gamma rays are
441 -> usually emitted by excited nuclei that
443.099 -> have been created after either an alpha
445.68 -> or beta Decay The Reason these processes
448.979 -> release such high energy photons is
451.319 -> because they involve nuclear processes
453.479 -> which are due to the strong force and
456.66 -> since the strong force is so much
458.639 -> stronger than for example the next
461.22 -> strongest force electromagnetism
462.78 -> whenever there's a shift to lower energy
465.78 -> levels within the nucleus an enormous
468.18 -> amount of energy is released and this
470.34 -> high energy is in the form of gamma rays
472.62 -> the three forms of radioactivity have
474.96 -> very different abilities to penetrate
477.12 -> matter alpha particles can be stopped by
480.24 -> a thin piece of paper
481.8 -> beta particles can penetrate your skin
483.96 -> but can be stopped by a thin sheet of
486.419 -> metal like aluminum foil but gamma rays
489.419 -> are very difficult to stop and can
491.22 -> penetrate through even an inch of lead
493.819 -> why is this the case
496.139 -> alpha particles consisting of two
497.94 -> protons and two neutrons are relatively
500.22 -> big heavy and thus slow because of their
503.039 -> large size they can be easily blocked
505.34 -> beta particles travel much faster and
508.199 -> can penetrate matter more easily because
510.599 -> of their higher velocity and smaller
512.339 -> size
513.12 -> gamma rays have no charge and they're
515.159 -> moving at the speed of light these
516.779 -> photons pretty much have to hit a
518.279 -> nucleus directly to be stopped Alpha and
521.459 -> beta Decay change the atomic identity of
524.52 -> the decaying nucleus because they change
526.32 -> the number of protons alpha decay
528.6 -> subtracts two protons so the element
530.58 -> moves down two notches on the periodic
532.86 -> table beta Decay changes in Neutron into
535.5 -> a proton or vice versa so it changes the
537.839 -> type of element either up or down a
540.42 -> radioactive nucleus is characterized by
542.459 -> something called its Half-Life what this
544.86 -> means is that if I have a certain number
547.08 -> of radioactive atoms let's say 16 atoms
549.66 -> and its Half-Life is one week then one
553.08 -> week later I'll have half of this or
555.42 -> eight atoms remaining and in two weeks
557.82 -> I'll have half of that or four of the
560.22 -> original atoms left and this goes on
562.339 -> Half-Life is a statistical concept if
565.32 -> you're holding the 16 atoms you'll not
567.24 -> be able to determine which of the atoms
569.82 -> will Decay one week from now or a
571.8 -> billion weeks from now you can only say
574.019 -> that any given atom has a 50 50 chance
576.779 -> of doing so in the time of one week
581.04 -> foreign
582.6 -> if a large nucleus like some isotopes of
585.6 -> uranium like u-235 is hit by a particle
588.779 -> usually a neutron then it will be split
591.12 -> into two smaller nuclei this is called
593.88 -> nuclear fission a if the total mass of
596.64 -> the two smaller nuclei is less than that
599.339 -> of the uranium before it was hit the
601.62 -> missing mass is turned into energy via
604.38 -> the equation E equals m c squared in the
606.899 -> case of certain isotopes of uranium and
608.94 -> plutonium such as u-235 and
612.38 -> plutonium-239 when these are hit by a
615.3 -> neutron they split into two lower Mass
617.339 -> nuclei and three neutrons are also
619.98 -> thrown off if there's enough fissionable
622.38 -> nuclei in high enough concentrations
624.6 -> then it is possible for the three thrown
628.019 -> off neutrons to in turn fission three
631.08 -> more nuclei which in turn fission 9 more
634.5 -> nuclei which in turn fission 27 more
637.2 -> nuclei creating what's called a chain
639.18 -> reaction this is the mechanism behind
641.88 -> the atomic bombs dropped on Hiroshima
644.94 -> and Nagasaki during World War II
649.74 -> a kind of opposite of fission is Fusion
651.959 -> this happens when two small nuclei such
653.94 -> as hydrogen which consists of only a
656.04 -> single proton can be brought close
658.56 -> enough together that they fuse into a
660.6 -> single nucleus
661.92 -> Fusion is very difficult to achieve
663.779 -> because the protons strongly repel each
666.36 -> other only gases heated to millions of
668.94 -> degrees Celsius have atoms moving fast
672.3 -> enough so that they can approach each
674.16 -> other close enough to achieve Fusion
676.56 -> Quantum tunneling also plays a role here
678.839 -> a hydrogen bomb achieves very high
681.06 -> levels of energy release by using the
683.279 -> heat of a fission bomb to trigger
685.32 -> hydrogen Fusion I have a video on how a
688.079 -> hydrogen bomb works if you want to learn
689.519 -> more about it the sun is powered by
692.16 -> hydrogen Fusion but its mechanism is
694.8 -> quite different than that of a hydrogen
696.54 -> bond it does not need nearly as high a
699.36 -> temperature because its mass creates
701.399 -> tremendous pressure in its core pushing
703.8 -> hydrogen nuclei together
705.42 -> the sun has such a huge amount of
707.459 -> hydrogen atoms that the low probability
709.92 -> of fusion still amounts to a very high
712.86 -> number of nuclei fusing together
715.14 -> now if you've seen this whole video I
717.72 -> officially crowned you a dangerously
720 -> interesting Nuclear Physics aficionado
723.12 -> please use your newfound powers for good
