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Nuclear Physics: Elements, Isotopes, Nuclides, and Radioactive Decay, Lecture notes of Chemistry

Chemistry

A comprehensive overview of nuclear physics, covering fundamental concepts such as elements, isotopes, nuclides, and radioactive decay. It delves into the structure of the atom, the nucleus, and the forces that hold it together. The document also explores nuclear stability, radioactive decay processes, and the applications of nuclear physics in areas like nuclear power plants and transmutation. It is a valuable resource for students seeking a deeper understanding of nuclear physics.

Typology: Lecture notes

2022/2023

Uploaded on 04/07/2025

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bg1
ELEMENTS
- Elements can also be named as
Element Name-Given Mass Number:
Ba-138
ISOTOPES
- Has the same atomic number
(number of protons) but different
mass (neutrons)
Carbon has 3 isotopes.
THE NUCLEUS
- Contains most of atoms mass
- DENSITY (2x1014 g/cm3 or 9T) >
DENSITY of OSPIUM (Densest
element of 22.6 g/cm3)
- The densest region of the atom
- Contains the nucleons: protons and
neutrons
ATOM
- Types of atoms is defined by the
specific number of proton and
neutrons and is called nuclide.
NUCLIDES
- Can be characterized by their energy
states: HIGH ENERGY EXCITED
(METASTABLE) AND LOWER ENERGY
GROUND STATE
- Ex: TC-99 (43) has 2 types, and both
are different nuclides.
2 TYPES OF NUCLIDES
1. STABLE
- These are elements that have stable
nuclides and remains intact
indefinitely.
2. UNSTABLE
- Called RADIONUCLIDES
- Unstable nuclides undergo
SPONTANEOUS NUCLEAR
DISINTERGRATION where radioactive
decay happens
SPONTANEOUS NUCLEAR DISINTERGRATION
- A process in which a parent nuclide
produces a daughter nuclide (that
can be stable or radioactive)
accompanied by the emission of
small fragments (p, n , e, or etc.) or
electromagnetic radiation.
NUCLEAR EQUATION
Maps the difference of parent
and daughter nuclides and
indicates nature of decay.
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ELEMENTS

  • Elements can also be named as Element Name-Given Mass Number: Ba- ISOTOPES
  • Has the same atomic number (number of protons) but different mass (neutrons) Carbon has 3 isotopes. THE NUCLEUS
  • Contains most of atoms mass
  • DENSITY (2x10^14 g/cm^3 or 9T) > DENSITY of OSPIUM (Densest element of 22.6 g/cm^3 )
  • The densest region of the atom
  • Contains the nucleons: protons and neutrons ATOM
  • Types of atoms is defined by the specific number of proton and neutrons and is called nuclide. NUCLIDES
  • Can be characterized by their energy states: HIGH ENERGY EXCITED (METASTABLE) AND LOWER ENERGY GROUND STATE
  • Ex: TC-99 (43) has 2 types, and both are different nuclides. 2 TYPES OF NUCLIDES

1. STABLE

  • These are elements that have stable nuclides and remains intact indefinitely.
  1. UNSTABLE
  • Called RADIONUCLIDES
  • Unstable nuclides undergo SPONTANEOUS NUCLEAR DISINTERGRATION where radioactive decay happens SPONTANEOUS NUCLEAR DISINTERGRATION
  • A process in which a parent nuclide produces a daughter nuclide (that can be stable or radioactive) accompanied by the emission of small fragments (p, n , e, or etc.) or electromagnetic radiation. NUCLEAR EQUATION  Maps the difference of parent and daughter nuclides and indicates nature of decay.
  • When a nucleus undergoes this process, radioactive decay happens. RADIOACTIVE DECAY TYPES OF RADIOACTIVITY
  1. Alpha Decay
  • Has 2 proton and 2 neutrons
  • Penetration: Very low
  1. Beta Decay
  • 2 types:  Beta minus (carries negative charge): Emission of electron and n  p. P increase by 1 but N decrease by 1 so mass # remains the same.  Beta plus (positron):
  • Penetration: Blocked by lightweight materials
  1. Positron Decay
  • A B+. Converts p  n and emits positive charged particles called positron.
  • Positron is the antiparticle of electron it has the same mass of it but different charge, it is short lived because it collides quickly with e, they both go boom and release 511 keV.
  1. Neutron Decay
  • Ejection of neutron from a nucleus.
  • Happens spontaneously or from bombardment by gamma rays or particles
  • Penetration: Blocked by lightweight materials
  1. Gamma ray Decay
  • Occurs when excited DN decays to nuclear ground state.
  • Penetration: passes through most materials.
  1. X-rays/Radioactive (Electron capture)
  • Captures inner electron, converts p to n. So outer e drops to inner level to fill vacancy by emission of xray.

NUCLEONS AND NUCLEAR FORCES

  • Nucleons are held together by strong nuclear forces
  • It is determined by the balance of proton-proton repulsion and nucleon-nucleon attraction (neutrons attract each other and has no repulsion. WHAT HAPPENS WHEN P-P REPULSION OUTWEIGHS NUCLEAR FORCES?
  • Radioactive decay happens since nucleus disintegrates (repulse mean to move away) NUCLEAR STABILITY
  • A stable nuclei occupies the BELT or VALLEY OF STABILITY, a central region, determined by the number of P and N present in a nuclei. N TO P RATIO
  • Light nuclides: For a nucleus to be stable its N/P ratio must be equal or greater than
  • As atomic number increases beyond 20, more N is required to balance the P-P repulsion to be balanced:
  • Heavy nuclides: Since N-N is attraction, increase of N strengthen nuclear force, therefore more stable. This is N/P>
  • Radionuclides has higher N/P ratio so it goes under B- Decay so that N/P ratio decreases because it will yield a DN that has N/P ratio closer to stability belt.
  • Thus, lower N/P ratio must emit positrons or undergo electron capture to move closer to stability belt (because one converts p to n, and p and e produces n.) THE MOST STABLE ISOTOPES PAIRING
  • Inside the nucleus, proton-proton pair and neutrons-neutrons pair like how electrons-electrons pair outside the nucleus.
  • The most stable pairing is when both nucleons are even
  • DOUBLY MAGIC: Nuclei that has certain numbers or the magic numbers of P and N that is 2, 8, 20, 28, 50, 82 are more stable.
  • Nuclei with atomic numbers higher than 83 are radioactive, Bismuth-209 (83) has long half-life of 2x10^19 years.
  • All isotopes of Tc and Pm are radioactive.

MASS DEFECT

Δm = Σ (^ mass of proton , neutron , electron )− actual mass

Where mass of P= #P x 1.0073 amu N= #N x 1.0087 amu E= #E x 1.00055 amu

  • Energy released in this reaction is the reason for this difference or mass defect.
  • Convert this difference to kg/mol. Example: 0.0305 amu = 3.05 x10-5^ kg/mol MASS-ENERGY EQUIVALENCE

ΔE = Δm c

2 Where c= 2.998x10-8^ m/s

  • This is the energy released when nucleons bind together, it is equal to energy needed to break the formed nucleus (this is called nuclear binding energy)
  • So nuclear binding energy is the same as mass defect in terms of amount NUCLEAR BINDING ENERGY PER NUCLEUS
  • Divide MEE to Avogadro’s number= 6.022x10^23
  • Express it to electron volts by dividing it by 1.602x10-19^ J NUCLEAR BINDING ENERGY PER NUCLEON
  • Divide the energy in electron volts (eV) by the number of nucleon
  • Neutrons released by fission are fast neutrons, it moves through large nuclei without interacting with it. It loses energy or becomes slow/thermal energy when it collides with a similar-sized nuclei, these neutrons reach equilibrium
  • Fissile are fissionable nuclides that absorb thermal neutrons to undergo fission.
  • Some neutrons does not cause fissile to fission but when they do a process occurs called chain reaction.
  • Chain reactions are described by neutron generations. First generation starts the chain, the first fission will produce neutrons. Neutrons produced by the first gen fission if turned into thermal neutrons then will start another generation called second generation that will produce another neutron. The cycle repeats until there are no more neutrons produced.
  • If the average number of fission remains constant throughout the chain, energy is kept in constant. This only happens if neutron slows down before they leave the material. CRITICAL MASS
  • This is the minimum mass that will ensure that there is enough neutrons produces to keep the fission continuing.
  • Subcritical is the mass below the threshold of critical mass, means less neutrons.
  • Supercritical is the mass above the threshold of critical mass, means more neutrons.
  • This is calculated by the amount of neutrons produced in a fission in a generation divided by the amount of neutrons produced in a fission by the previous generation.
  • The above is denoted by k. If k<1 subcritical, k=1 critical mass, k>1 supercritical FISSION IN NUCLEAR POWERPLANT
  • The thermal energy released from fission allows electricity generation by using the concept of steam turbine. PARTS
  1. Nuclear fuel
  • The fuel of the nuclear is the fissile.
  1. Fission
  1. Helium Burning (Stars begin helium fusion)
  • A long reaction process where 2 He-4 combine to form Be-8 (highly unstable, endothermic, reversible reaction)
  • When He-4 accelerates, Be-8 becomes abundant and fuses with He-4 which produces C-12 that relaxes later on.
  1. Alpha Process (in massive stars)
  • Before supernova, a chain of fusion reaction is initiated by C-12 and He-4, process repeats with fusion with He-4 until it reaches Mg-24 until the sequence reaches Ni- 56 (has highest Binding Energy per Nucleon.
  • This happens to stabilize because the difference between the products and reactants result in lessened binding energy per nucleon needed.
  • Before supernova, heavier elements are produced by multiple neutron or proton capture. TRANSMUTATION
  • The conversion of one element into another via radioactive decay, fusion, and fission.
  • This is exampled by Rutherford when a N-14 was bombarded by alpha particle and produced a new proton and new nuclei (O-17)
  • Common bombarding particles: neutron and alpha particles
  • Element atomic number greater than 92 are called transuranium elements. They are common targets of transmutation experiments because they are entirely synthetic except Np and Pu (Neptium and Plutonium which are naturally produced in U decay chain series)
  • EXAMPLE:
    1. U-238 bombardment by neutrons create Np-239. Np-239 decays to Pu-239 by beta minus decay.
    2. Pu-239 hit with alpha particles yield Cm-242. Although alpha particles required greater kinetic energy to overcome electrostatic repulsion by positive charges of the nuclei. (Smaller nuclei has weaker electrostatic repulsion) PARTICLE ACCELERATORS IN A TRANSMUTATION
  • Used to impart desired speeds to charge nuclear particles.
  • Can be used also to bombard large nuclei. Example: Pb-208 bombarded with Zn- produced Cn-277. Cn-277 generated 13 transuranium elements through its decay chain ending to Bi-209.
  • TYPES:
  1. Multistage linear accelerator- long tube with many tubes lined up. These tubes are increasing in length as it alternates charge/polarities. For the charged particles to reach the end of the tube, an oscillating electrical potential is used to create alternating current by rapidly switching polarities (attract and repulse). This produces about 90% speed like light.
  2. Cyclotron- Alternate voltage accelerates the particle in a spiral path using electrodes and electromagnet.

Where GMC can be modified respond proportionally to energy of radiation so it can measure dose of different rays.