To end our discussion on modern physics and to end the entire course youll learn about nuclear physics. This topic of physics focuses on the subatomic characteristics; essentially this is the physics derived from splitting the atom. Scientists have found not only things like the forces between atoms that hold them together and the rate at which they decay, but have also developed processes to acquire vast amounts of energy. Well also step outside the tiny box and look at general laws of the universe and the forces that, together, affect everything. This is more of a conceptual topic than anything, with no general equation or law governing it. Once you have the concepts down you have successfully completed the AP physics 1 & 2 course!
Atoms are described by their atomic number (Z=# of protons), mass number (A=# of protons + neutrons), and their net charge.
Mass is a measure of how much energy an object contains, and can be calculated using E=mc^2.
The strong nuclear force holds the particles of the nucleus together. It is the strongest fundamental force, but only operates at very small distances.
When nucleons are combined to make a nucleus, some of the mass of the constituents is converted to energy to hold the nucleus together. This energy is known as the binding energy. The difference in mass is known as the mass defect.
The three main types of nuclear decay processes are alpha decay (emission of alpha particle), beta decay (emission of electron or positron), and gamma decay (emission of a gamma photon).
Fission is the splitting of a nucleus into two or more nuclei.
Fusion is the combining of two or more nuclei into a large nucleus.
The fundamental forces in the universe, from strongest to weakest, are the strong nuclear force, the electromagnetic force, the weak nuclear force, and the gravitational force.
Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.
Hi everyone and welcome back to Educator.com. 0000
I am Dan Fullerton and today we are going to talk about nuclear physics. 0003
Our objectives are going to be to identify the number of protons and neutrons in a nucleus from a chemical symbol, to determine the energy produced or required to complete a variety of nuclear reaction processes, identifying and analyzing three types of radioactive decay...0007
...explaining the process of fission and fusion given examples of each, and identifying the fundamental forces in the universe and order of strength. 0023
Einstein wrote a paradigm changing paper in 1905 titled "Does the Inertia of a Body Depend Upon Its Energy Content?" 0127
In it, he explains how mass is a measure of how much energy an object contains and he talks about this formula, E = mc2, a conversion ratio for mass and energy. 0136
That led us to adjusting our conservation laws.0147
Now if energy and mass are really different sides of the same coin, we have conservation of mass energy, not conservation of mass and conservation of energy, it is conservation of mass energy; they are two sides of the same coin -- conservation of charge, conservation of linear momentum, conservation of angular momentum. 0151
Let us talk about nuclear binding energy because there is some cool stuff you can do with this. 0175
The protons in a nucleus repel each other, so how does the nucleus stay together? 0179
Well, that strong nuclear force is what holds all of those particles together, all those nucleons or particles of the nucleus. 0183
It is extremely strong, but only works over very, very, very short distances, which is why it works in the nucleus, but nowhere else. 0190
Now combining nucleons to bake a nucleus takes energy. 0199
If you have positive charges and protons, you have to do a lot of work to get them together, to get to the point where the strong nuclear force is going to take over and hold them together. 0202
That energy is known as the binding energy of the nucleus and where does it come from? 0211
Well, a fraction of the mass of the nucleons themselves, gets converted in order to hold those together. 0217
So the mass of the individual constituents is greater than the mass of the combined nucleus and this difference in mass is what we call the mass defect, δm. 0223
Now one atomic mass unit -- if you completely convert it into energy will provide 931 mega-electron volts (MeV). 0236
That is the same thing as if we took one mass unit and used E = mc2 to determine the energy in joules and then converted that to electron volts, but that can save you a little bit of time knowing that one atomic mass unit, when converted to energy is 931 MeV. 0243
The binding energy then, is going to be the mass defect times the square of the speed of light, E = mc2 applied to that mass defect. 0261
Now, in the early 1900s, scientists started investigating radioactive materials and what they found were three different types of nuclear decay, of radioactive decay. 0271
Now in alpha decay, we have the emission of an alpha particle, a helium nucleus, so we start off with our elements symbol (X) with (Z) protons and an atomic mass of (A). 0282
It is going to split into a helium nucleus of 2 protons, 2 neutrons for an atomic mass of 4, so what you have left over is going to be a new element that has 2 fewer protons and 4 fewer protons and neutrons or 2 fewer neutrons from its original. 0293
Beta decay, which can be beta plus or beta minus decay, is the emission of an electron or a positron, where a positron is the anti-matter version of an electron, an anti-electron. 0310
A neutron decays into a proton and an electron. 0319
If we have our element symbol (X), (Z) protons, (A) mass number, and we give off an electron, we are going to take away as this neutron decays into a proton and an electron...0322
...we are going to take away 1 charge here, so we are going to have to have an extra proton because that neutron became a proton and we still have the same total mass number. 0334
Now gamma decay is the emission of a gamma photon. 0346
We have our initial element, we give off a gamma ray and we still have our initial element. 0349
As we talk about nuclear decay, first off, let us talk about half-life for just a second. 0356
Half-life is the amount of time for half of the material to decompose, which is pretty straightforward. 0361
I also want to talk about what happens -- now that we have mentioned an electron and an anti-electron are a positron -- what happens if they come in contact? 0368
If they come in contact, they will completely annihilate each other; they will completely convert their mass to energy. 0376
In so doing, they are going to release 2 photons traveling in opposite directions and each is going to have an energy of .511 MeV -- complete annihilation if you have a positron and an electron; they will annihilate each other. 0381
Well, let us assume that we are going to shoot a neutron at some Uranium-235, so let us give ourselves a little neutron and we will shoot it here to the right and we are going to hit some of our Uranium-235. 0419
When that neutron hits it, very briefly, it is going to become Uranium-236, an isotope, but an unstable isotope. 0439
Uranium is not happy being Uranium-236, so what it is going to do then, is it is going to split into Barium-141 and Krypton-92, and as it does that it is also going to give off three more neutrons, that can go hit other Uranium-235 atoms. 0448
Well what is the big 'whoop' you say? As we do this, as we are splitting this nucleus, we are going to get a bunch of energy released. 0472
We have a bunch of energy as the output here as well and three more neutrons to continue to cascade this effect. 0483
Fusion, on the other hand, is the process of combining two or more smaller nuclei into a larger nucleus. 0494
If fusion occurs with small nuclei, the product of the reaction can have a smaller mass than its precursors and therefore releases energy. 0500
This is what fuels suns, stars, and it is also the basis of the hydrogen bomb. 0508
Now it is a tremendous potential energy source for a clean source of power as it creates hydrogen precursor straight from water, but fusion releases much more energy than fission, has minimal radioactive by-products...0513
...but it is way too hot to run for long periods of time with our current technology, which is why you may hear about the search for cold fusion. 0525
In the universe, we have four fundamental forces and we are going to rank them from strongest to weakest. 0540
The strongest of course, is the strong nuclear force, what holds the nucleons together or the protons and the neutrons together in the nucleus. 0546
The electromagnetic force -- we have done a lot of study on that already. 0553
The electrical and magnetic attractive and repulsive forces; the weak nuclear force, which is responsible for radioactive beta decay and finally, the gravitational force, which is the weakest force -- that is the attractive force that we have between objects that have mass; it is the weakest of those four forces. 0558
All right. An example problem -- If we have a Deuterium nucleus, it has a mass of 1.53 × 10-3 atomic mass units less than its component, what is its binding energy? 0579
Well, if it has 1.53 × 10-3 atomic mass units less than its component, let us convert that into energy. 0590
That will be -- we want universal mass units or atomic mass units to go away and we will convert it to MeV's and we know that 1 U converts to 931 MeV's and universal mass units make a ratio of 1 and I end up with about 1.42 MeV. 0600
Another one with a particle accelerator -- In the first nuclear reaction using a particle accelerator, accelerated protons bombarded Lithium atoms, producing alpha particles in energy. 0625
The energy resulted from the conversion of mass into energy. 0636
The reaction could be written as Hydrogen plus Lithium, which gives you two Helium's plus energy. 0639
Determine the energy and MeV produced in the reaction. 0646
Let us see what the difference is in mass; how much of that mass was converted into energy?0649
Our total mass defect is going to be -- well we started off with a proton (1.00783) and a Lithium (7.01600 atomic mass units) and at the end we have two Helium's... 0654
...which is going to be 2 times 2 alpha particles (4.00260 atomic mass units). 0674
That comes out to be about .01863 atomic mass units, so let us convert that into energy. 0683
We want .01863 atomic mass units to go away and we want MeV and we know that 1 atomic mass unit is equal to 931 MeV...0692
...so again we are just multiplying by 1, our units are going to cancel out there, and we will be left with 931 × .01863 or about 17.39 MeV. 0703
A Tritium nucleus is formed by combining two neutrons and a proton. 0726
The mass of this nucleus is 9.106 × 10-3 atomic mass units less than the combined mass of the particles from which it is formed. 0730
How much energy is released when this nucleus is formed? 0739
That means that our mass defect (δm) is 9.106 × 10-3 U and all we have to do is convert that to energy. 0742
9.106 × 10-3 U times -- we want universal mass units to go away and we will convert to MeV and 1 universal mass unit is 931 MeV, and again we will cancel out our universal mass units and I come up with about 8.48 MeV. 0753
Let us take a look at an example involving beta decay. 0782
A radioactive Hafnium nucleus emits a positron and becomes what? 0786
Well, it is emitting a positron, so that is beta plus decay and when that happens we have a proton that is becoming a neutron and a positron, a beta plus. 0791
So let us start off with our Hafnium (Hf-72-178) and it is going to become -- well first off we have our beta plus particle and that is 0 + 1e. 0806
Now if we have 72 here, we must have 71 as our atomic number here and nothing is changed on the top, so 178 -- I have to look up what element atomic number 71 is and I did that and I found out that that was Lutetium. 0824
That is how you would deal with a positive beta decay sort of problem. 0849
Gamma decay -- a radioactive Hafnium nucleus now emits a gamma ray. 0855
The book features an effective, 5-step plan to guide your preparation program and help you build the skills, knowledge, and test-taking confidence you need to succeed. This fully revised edition covers the latest course syllabus and matches the new exam. It also includes access to McGraw-Hill Education’s AP Planner app, which will enable you to customize your own study schedule on your mobile device. It includes a full-length practice AP Physics 1 exam and 3 separate study plans to fit your learning style.
This book is written by our very own Professor Fullerton and features more than 600 worked-out problems with full solutions and deeper understanding questions. AP Physics 1 Essentials covers all major topics included in the AP Physics 1 course, including: kinematics, dynamics, momentum, impulse, gravity, uniform circular motion, rotation, work, energy, power, mechanical waves, sound, electrostatics, and circuits.