原子核ppt课件教学教程电子教案

1、The NucleusSome nuclear propertiesStructure of the nucleusThe nuclear forceThe masses of the nuclidesThe binding energyNuclear reactionAlpha, beta and gamma radiationRadioactive decayFissionFusion2022/7/261Some wordsNucleus, NucleiNuclide (核素)Binding energyNuclear reactionAlpha, beta and gamma radia

2、tionRadioactive decayFissionFusionIsotopemass spectrographprotons, neutronsQuakeMass defect2022/7/262The composition of the nucleusThere are two types of nuclear particles (nucleons) known to exist within the nucleus.Protons: mp=1.6726E-27kg, positive charge,Neutrons: mn=1.6749E-27kg, neutral,The nu

3、mber of protons present in any nucleus is called the atomic number and is denoted by Z. Elements in the periodic table are simply arranged in ascending order of atomic number. The total number of protons and neutrons is referred to as the atomic mass number A. The symbol of a nucleus is given by: ZM

4、A or AZM.2022/7/263Isotopes Isotopes: Nuclei with the same value of Z but with different values of A are referred to as isotopes. Or they have the same number of protons, but a different number of neutrons. For example: 126C(98.9%), 137C(1.10%)Mass spectrograph (质谱仪): An instrument used to measure t

5、he nuclear mass. It is based on the principle of deflecting positive ions in a magnetic field and inferring the mass of the nucleus from the radius of curvature of the track.2022/7/264QuakesThe nucleons are also composites, and contain objects called quakes.Hadrons (强子) are particles that interact w

6、ith each other via the strong nuclear forces.Mesons （介子）, particles with integer spins,Baryons（重子）, particles with half-integer spins2022/7/265Strong nuclear forcesStrong nuclear forces are short ranged and become zero at distances greater than a few femtometers (10-15 m).Nuclear forces are much str

7、onger than electrical forces. The nuclear force is attractive at the average inter-nucleon separation. Nuclear forces do not depend on the electrical charge. p-p, p-n, n-n,For a nucleus to be stable, the electrostatic repulsion between the protons must be balance by the attraction between the neucle

8、ons due to the strong nuclear force.2022/7/266Binding energyEinstein showed that the mass and energy are equivalent and are related by the simple equation: E=mc2The mass of a nucleus is less than the sum of the masses of its nucleons. Also, if a given nucleus were to be separated into its nucleons,

9、energy would have to be supplied equivalent to the missing mass.The missing mass is referred to as the mass defect and the energy equivalent to this is called the binding energy. 2022/7/267The bonding energy per nucleon is defined by the binding energy divided by the mass number, BE/A. It is a measu

10、re of the stability of a nucleus.The intermediate-size nuclei have the greater binding energy per nucleon than light and heavy nuclei.2022/7/268Nuclear reactionNuclear reactions involve the nuclei of atoms. They can undergo changes either as a result of radioactive decay or as a result of being bomb

11、arded with particles.In nuclear reactions, the total mass number (A) and the total atomic number (Z) must be the same on both sides of the equation. Meanwhile, the sum of the masses of all products is not equal to the sum of the masses of the reacting particles. This lost mass is converted to energy

12、 according to Einsteins theory.2022/7/269Q value of a nuclear reactionThe Q value of the nuclear reaction A+BC+D, is defined as the difference between the rest energies of A & B and the rest energies of C & D.Q=(mA+mB)-(mC+mD)c2.If Q is positive, energy is given off by the reaction. If Q is negative

13、, enough energy must be supplied by the reacting particles.2022/7/2610Three types of radioactivityThe spontaneous disintegration of unstable nuclei is called radioactivity. In the process, certain kinds of particles are released. Alpha-radiation (decay), Alpha particles are positively charged with t

14、wo positive charges and having a mass of 4u. AZXA-4Z-2Y + 42HeBeta-radiation (decay), Beta particles carry a negative charge and have a 1/1800 mass of the proton. AZXAZ+1Y + e-Gamma-radiation (decay), The neutral gamma rays with the energy greater than that of X rays. It penetrates furthest in matte

15、r. AZX* AZX + 2022/7/2611Radioactive decayIt is a process of continuous disintegration undergone by the nuclei of radioactive elements. The law of radioactive decay:Where is called the decay constant.N: undecayed nuclei,A nuclear decay is characterized by a half-life T, the time required for one-hal

16、f the nuclei to decay. Depending on the nucleus, T may vary from a fraction of a second to billions of years. T=ln2/2022/7/2612Application of radioactivityMeasuring the thickness: Radiation is absorbed in a certain way when passing through material, a precise indication of the thickness can be deter

17、mined by monitoring the intensity after passing through the material.Radiation therapy: Gamma rays are used to kill cancer cells with in tumor. It can also be used for general sterilization of food and equipment.Geology makes use of many isotopes to provide an estimate of the age of rocks and indeed

18、 the age of the earth itself, known as geological dating.2022/7/2613Induced nuclear reactionsA stable nucleus can be disintegrated by being struck with other particles. A nuclear reaction can be induced.For example, when an alpha particle strikes a nitrogen nucleus, and oxygen nucleus and a proton a

19、re produced. It can be represented by a shorthand form: 147N(,p)178O.2022/7/2614Nuclear fissionA heavy nucleus breaks up into two or more intermediate-size nuclei with the emission of two or three neutrons. It is accompanied by the release of energy .Spontaneous fission, induced fissionThe fission p

20、rocess occurs easily in the case of the isotope U235 which requires only the absorption of a low-energy neutron. The fission process releases a great deal of energy (roughly 200MeV) which is mainly in the form of kinetic energy of the fission fragments and released neutrons.2022/7/2615Nuclear fissio

21、n2022/7/2616Nuclear fusionTwo or more light nuclei are combined to produce heavier nuclei with the release of a large amount of energy. To bring the two nuclei together, it needs high temperature to take place and is also called a thermonuclear reaction, 1M degree Celsius. Uncontrolled fusion has al

22、ready been achieved in the form of hydrogen bomb in which the temperatures necessary for the thermonuclear reaction are generated by a primary fission bomb using uranium. 21H (deuterium) + 31H (tritium)42He+10n2022/7/2617Fusion and FissionThe fusion is better than the fission as an energy source.A fusion gives off more energy than a fis