Assumptions in Bohr‘s Model The two forces acting in the nucleus are: A Coulomb force of repulsion between the positively charged protons The strong nuclear force that holds protons and neutrons together. o The combined effects of these two forces enable only certain neutron to proton ratios to be stable. (magic numbers)
Assumptions in Bohr‘s Model The nucleus contains positively charged protons (each 1.6E-19 C) and neutrally charged neutrons. What is a Coulomb? The coulomb (symbol: C) is the SI derived unit of electric charge. It is defined as the charge transported by a steady current of one ampere in one second: 1C = 1A x 1s Examples The charges in static electricity from rubbing materials together are typically a few microcoulombs. The amount of charge that travels through a lightning bolt is typically around 15 C, although large bolts can be up to 350 C. The amount of charge that travels through a typical alkaline AA battery is about 5 kC = 5000 C = 1400 mAh. After that charge has flowed, the battery must be discarded or recharged. According to Coulombs Law, two point charges of +1
Assumptions in Bohr‘s Model The mass of a protons is 1.6726E-24 g. Or 1.0073amu The mass of a neutron is 1.6749E-24 g. Or 1.0087amu
Assumptions in Bohr‘s Model The majority of an atom’s mass is contained within a small, dense nucleus (on the order of 10 million tons / cm3).
Assumptions in Bohr‘s Model The number of extranuclear electrons equals the number of protons within the nucleus. Each electron carries an electrical charge of - 1.6E-19 C Thus, the net charge of an atom is zero. Electrons have a mass around 9.11E-34 g. Electrons orbit nuclei in fixed energy shells (quantized orbits); with each shell having a characteristic binding energy for a given element.
Atomic Mass Scale Atomic mass units (amu) is its mass ―relative‖ to 12C unbound, at rest, and in its ground state. By definition 12C has 12 amu; 1 amu equals the mass in 1/12 of a 12Catom. The actual mass of one amu is based on the 6 protons, 6 neutrons, and 6 electrons in one 12C atom. 1 amu = 1.66E-24 g. An atom‘s ―atomic weight‖ is its ―amu number‖; which is its mass ―relative‖ to 12C or: atomic weight = 12 x (mass a / mass c 12) The atomic weight of an ―element‖ is a weighted average, accounting for the natural abundance of all
Radiation & Radioactivity Definitions Radioactivity: the spontaneous process by which unstable atoms emit or radiate excess energy from their nuclei, and thus, change or decay to atoms of a different element or to a lower energy state of the same element. Radionuclide: unstable atomic species which spontaneously “decay” and emit radiation.
DEFINITIONS Radiation: high energy particles and electromagnetic rays emitted from atomic nuclei during radioactive disintegration. However, the term ―radiation” is also often used instead of the longer term “electromagnetic radiation” (aka electromagnetic rays or photons), whether or not they originate in the nucleus. There are two broad categories of electromagnetic radiation (ionizing and non- ionizing). For example, x-rays originate outside of nuclei and typically have sufficient energy to ionize atoms.
Electromagnetic Radiation Another term for ―photon‖ which is an electromagnetic ―particle‖ that always travel in waves at a velocity of 3E8 m/s in a vacuum. Each particle has zero rest mass, no electric charge, and an indefinitely long lifetime. The energy of a photon is inversely proportional to its wavelength. E = hn
Ionizing Electromagnetic Radiation Ionizing electromagnetic radiation consists of photons possessing enough energy to completely free electrons from atoms, thereby producing ions. An ion is an atom which has lost or gained one or more electrons, making it negatively or positively charged.
Non-Ionizing Electromagnetic Radiation Non-ionizing electromagnetic radiation consists of photons that do not possess sufficient energy to ionize atoms. However, non-ionizing electromagnetic radiation may have enough energy to excite electrons, that is cause them to move to a higher energy state. Examples include near ultraviolet rays, visible light, infrared light, microwaves, and radio waves.
Atomic Mass Scale One mole = atomic weight-g and contains Avogadro’s no. of particles. Avogadro’s number = 6.0221415x1023 atoms (or molecules). Since one mole of an element is its atomic weight in grams and will contain 6.0221415x1023 atoms, the number of atoms in any given mass can readily be computed. For example, since 12-g of 12C contains 6.0221415x1023 atoms as does 235-g of 235U: 100 g of 235U contains 100/235 x 6.0221415x1023 = 2.56E23 atoms, 100 g of 12C, 100/12 x 6.0221415x1023 = 50.18E23 atoms.
Relating Mass to Numbers ofAtoms The MoleA mole (abbreviated mol) is the amount of a substance that contains as many particles as there are atoms in exactly 12 g of carbon-12.Avogadro‘s NumberAvogadro‘s number—6.022 1415 1023—is the number of particles in exactly one mole of a pure substance.
Relating Mass to Numbers ofAtoms, continued Molar MassThe mass of one mole of a pure substance is called the molar mass of that substance.Molar mass is usually written in units of g/mol.The molar mass of an element is numerically equal to the atomic mass of the element in atomic mass units.
Relating Mass to Numbers ofAtoms, continuedGram/Mole Conversions• Chemists use molar mass as a conversion factor in chemical calculations.For example, the molar mass of helium is 4.00 g He/mol He.To find how many grams of helium there are in two moles of helium, multiply by the molar mass. 4.00 g He 2.00 mol He = 8.00 g He 1 mol He
Relating Mass to Numbers ofAtoms, continuedConversions with Avogadro‘s Number• Avogadro‘s number can be used to find the number of atoms of an element from the amount in moles or to find the amount of an element in moles from the number of atoms.In these calculations, Avogadro‘s number is expressed in units of atoms per mole.
Relating Mass to Numbers of Atoms,continuedWhat is the mass in grams of 3.50 mol of theelement copper, Cu?
Relating Mass to Numbers ofAtoms, continuedA chemist produced 11.9 g of aluminum, Al-26.How many atoms of aluminum were produced?
Relating Mass to Numbers ofAtoms, continuedHow many atoms of plutonium-239 are present ina bare-sphere critical mass of 10kg?
Energy and Mass Einstein‘s famous E = mC2 equation shows the relationship between mass and energy. For 1 m, E = 1.66 x10-27kg *2.998 x 108 m/s2 = 1.492 x 10-10 J Or = 931.5 MeV So 1 AMU of mass = 931.5 MeV of energy
BINDING ENERGY There is a complication, the whole does not equal the sum of the parts. If you add the masses of all the protons, neutrons and electrons in an atom the predicted mass is ALWAYS more than the measured mass. This is the MASS DEFECT, D D =ZMp + NMn + ZMe - Matom
DataWhere: Mp, The mass of a proton: 1.0072766 m Mn, The mass of a neutron: 1.0086654 m Me, The mass of an electron: .0005486 m Matom, The mass of the bound atom (varies by isotope)
Example Find the mass defect,D, and binding energy, Q, for an 17O nuclide. It has 8 protons, 9 neutrons, and an atomic weight of 16.999133 amu
Oxygen 17# Particles Mass each Total8 p+ 1.0072766 8.05821289 no 1.0086654 9.07798868 e-1 .0005486 0.0043888 Total = 17.1405902D= 17.1449790 - 16.999133 = 0.1414572 amu 0.145846 amu x 931.5 amu/ MeV = 131.77MeVOr 135.85 / 17 = 7.75 MeV / nucleon
Mass Defect The missing mass is believed to be converted to energy that holds the nucleus together. It is called binding energy, BE. The Coulomb force of repulsion must be overcome to allow so many p+ particles in the nucleus. This Strong Nuclear Force accomplishes this but it‘s range is only ~10-13 m
BE per Nucleon The binding energy per nucleon can be calculated for each isotope by dividing the total BE by the number of nucleons. The stability of a nucleus is a function of this BE/nucleon A plot of BE/nucleon vs atomic number shows the most stable isotopes
Magic Numbers The ratio of odd to even numbers of protons and neutrons show surprising trends Even N, Even Z.........159 stable nuclides. Odd N, Even Z......... 53 stable nuclides. Even N, Odd Z......... 50 stable nuclides. Odd N, Odd Z......... 5 stable nuclides.
What is Radiation Radionuclides undergo a process referred to as decay (also known as transformation or transition) During decay, a radionuclide changes its ratio of protons and neutrons to a more stable combination – it becomes a different nuclide In the process some of it‘s mass is converted to energy and is carried off by the radiation
What is Radiation The physical characteristics of radiations include; mass, charge, point of origin (where it‘s found) There are two possible points of origin Nucleus Electron Cloud Most radiations originating outside the nucleus are not in the scope of this course, these including…visible light, radio, etc.
What is Radiation Radiations also can be characterized by their effects on matter When atoms are exposed to radiation they are either created into ions or not, therefore we classify radiation as either… Ionizing Non-Ionizing In this course we are concerned only with ionizing forms of radioactivity
What is Radiation There are two major types of ionizing radiation Particulate Radiation Electromagnetic Radiation Particulate Radiation is solid matter, consists of particles, therefore has mass or substance Electromagnetic Radiation is made up of waves of pure energy, therefore having no mass
What is Radiation There are three types of particulate radiation Alpha Beta Neutron Alpha radiation is made of 2 protons and 2 neutrons, therefore having an atomic mass of 4 (ionized helium nucleus) Alpha radiation has a charge of +2 and as it travels through air it ―ionizes‖ atoms
What is Radiation The majority of alpha particles are emitted from the nuclei of large atoms ~ 83 protons and up The reason large atoms give off ―large‖ particles i.e. alpha particles is because they are very unstable therefore need to give off large amounts of mass A A-4 Z P Z-2 D + He
What is Radiation Beta – Beta particles are made up of electrons ―born‖ in the nucleus They can have either a + or – charge Even though positive electrons are not supposed to exist, under some circumstances they can be produced in the nuclei of atoms These positive electrons (positrons) are more commonly known as antimatter
What is Radiation Beta particles are a result of protons and neutrons changing identity When a neutron changes to a proton (neutron conversion) a negative electron is emitted When a proton changes to a neutron (positron emission) a positive electron is emitted
What is Radiation Every time a positron is produced, two 511 keV (kiloelectronvolt) photons will also be produced. When the positron has given up all, or almost all, of its kinetic energy, it will combine with an electron The electron and positron annihilate each other – their mass is completely converted into energy
Positron Decay p n n p p p Parent Radionuclide
Positron Decay p Positron n n n p p Decay Product Neutrino
Positron Decay Positron p n n p p p Decay Product Neutrino
Positron Decay Electron (e-) - an innocent bystander -Positron (β+)
Positron DecayPositron has given up all its kinetic energy. Positron (β+) Electron (e-) - an innocent bystander -
Positron DecayBecause of their opposite charges, the positron andelectron are attracted to each other. Positron (β+) Electron (e-)
Positron DecayPositron and electron annihilate each other. 511 keV photon 511 keV photon
Electron Capture Sometimes when a nucleus will absorb an orbiting electron This is known as electron capture A proton will be converted to a neutron without the release of a positron This will result in the release of an electron neutrino As outer electrons fill the lower energy level, x- rays are produced
Internal Conversion As the nucleus undergoes de-excitation in inner electron can be kicked out of the electron cloud Monoenergitic This acts as a beta particle Also, X-Rays are produced
What is Radiation Neutrons are the last type of particulate radiation that we will discuss Neutrons have a mass of 1 AMU and ø charge They are produced most commonly in nuclear reactors from when atoms fission
What is Radiation Now that we have looked at the types of particulate radiation, we will now look at the types of electromagnetic radiation Remember electromagnetic radiation is waves of pure energy for example; light, x-rays and all other members of the electromagnetic spectrum
Electromagnetic Radiation Gamma – Gamma rays are electromagnetic rays of pure energy They have no mass and no charge Gamma rays are produced as a result of the de- excitation of the nucleus of atoms that have given off either an alpha or a beta particle The gamma is actually emitted from the product of the decay, but is attributed to the parent nuclide
Gamma Ray Emission Alpha Particle Decay Product (Excited)
Gamma Ray Emission Alpha Particle Gamma Ray Decay Product
What is Radiation Gamma, and X-rays are measured in KeV = 103 eV Particulate Radiation is measured in MeV = 106 eV
Electromagnetic Radiation Only a specific number of electrons is allowed in each shell (energy level). The number of electrons in the various shells determines the chemical properties of the atom. Electrons (like all particles) ―want‖ to occupy the lowest possible energy level. When an electron moves (undergoes a transition) to a lower energy level, it must release energy.
What is Radiation When an electron fills a vacancy in an inner shell (moves to a lower energy level), this energy might take the form of an x-ray. X-rays (and gamma rays) have a high enough energy to ionize atoms (remove electrons from atoms) and are therefore considered a type of ionizing radiation.
What is Radiation Energy can be described as the ability to do work. Two kinds of energy: potential energy Kinetic energy Kinetic energy is the energy of motion (1/2mv2) Basic unit: joule (J) Special unit: electron volt (eV) 1 eV = 1.6 x 10-19 J
Units Roentgen (R) The roentgen is a unit used to measure a quantity called exposure. This can only be used to describe an amount of gamma and X-rays, and only in air. One roentgen is equal to depositing in dry air enough energy to cause 2.58x10-4 coulombs per kg. It is a measure of the ionizations of the molecules in a mass of air. The main advantage of this unit is that it is easy to measure directly, but it is limited because it is only for deposition in air, and only for gamma and x rays.
Curie (Ci) The curie is a unit used to measure radioactivity. One curie is the quantity of a radioactive material that will have 37,000,000,000 transformations in one second. Often radioactivity is expressed in smaller units like: thousandths (mCi), one millionths (uCi) or even billionths (nCi) of a curie. The relationship between becquerels and curies is: 3.7 x 1010 Bq in one curie.
Rad (radiation absorbed dose) The rad is a unit used to measure a quantity called absorbed dose. This relates to the amount of energy actually absorbed in some material, and is used for any type of radiation and any material. One rad is defined as the absorption of 100 ergs per gram of material. The unit rad can be used for any type of radiation, but it does nott describe the biological effects of the different radiations.
Rem (roentgen equivalent man) The rem is a unit used to derive a quantity called equivalent dose. This relates the absorbed dose in human tissue to the effective biological damage of the radiation. Not all radiation has the same biological effect, even for the same amount of absorbed dose. Equivalent dose is often expressed in terms of thousandths of a rem, or mrem. To determine equivalent dose (rem), you multiply absorbed dose (rad) by a quality factor (Q) that is unique to the type of incident radiation.
Becquerel (Bq) The Becquerel is a unit used to measure a radioactivity. One Becquerel is that quantity of a radioactive material that will have 1 transformations in one second. Often radioactivity is expressed in larger units like: thousands (kBq), one millions (MBq) or even billions (GBq) of a becquerels. As a result of having one Becquerel being equal to one transformation per second, there are 3.7 x 1010 Bq in one curie.
Gray (Gy) The gray is a unit used to measure a quantity called absorbed dose. This relates to the amount of energy actually absorbed in some material, and is used for any type of radiation and any material. One gray is equal to one joule of energy deposited in one kg of a material. The unit gray can be used for any type of radiation, but it does nott describe the biological effects of the different radiations. Absorbed dose is often expressed in terms of hundredths of a gray, or centi-grays. One gray is equivalent to 100 rads.
Sievert (Sv) The sievert is a unit used to derive a quantity called equivalent dose. This relates the absorbed dose in human tissue to the effective biological damage of the radiation. Not all radiation has the same biological effect, even for the same amount of absorbed dose. Equivalent dose is often expressed in terms of millionths of a sievert, or micro-sievert. To determine equivalent dose (Sv), you multiply absorbed dose (Gy) by a quality factor (Q) that is unique to the type of incident radiation. One sievert is equivalent to 100 rem.
Naturally Occurring Radionuclides Naturally Occurring Radionuclides, NORM, are present everywhere on earth. Their sources are: Primordial radionuclides were contained in the matter that condensed to form the earth. Cosmic Rays very high energy radiation and particles that come from space. Cosmogenic radionuclides are formed by nuclear reactions in the atmosphere.
Cosmic Ray ProducedRadionuclidesIsotope Half Life Isotope Half life10Be 2.7 E 9 y 36Cl 3.0 E 5 y14C 5.7 E 3 y 32Si 7.1 E 2 y3H 12.5 y 22Na 2.6 y35S 87 d 7Be 53 d33P 25 d 32P 14 d
Naturally Occurring Radionuclides (not indecay chains) 244 Pu, Progenitor of 238 U, t ½ 80 E 6 y (now extinct) 129 I, Parent of 129 Xe, t ½ 16 E 6 y (now extinct) 40K, Parent of 40Ar & 40Ca, t ½ 1.3 E 9 y (40Ar = 1% atmosphere) 87Rb, Parent of 87Kr, t ½ 48 E 9 y
Radon in Nevada Hot SpringsSpring 22Rn (pCi/l) 238U (pCi/l)Warm Springs 2900 0.0963 oCCrystal Springs 18 1.532 oCAsh Springs 140 1.236 oCBailey‘s Hot 3560 3.5Spring 42 oC
Historical 1896, Henri Becquerel Discovered Penetrating Radiation from Uranium Salts.
Historical 1898, Marie and Pierre Curie isolated Radium and Polonium from Pitchblende.
Historical 1903, Rutherford and Soddy developed the basic radioactive decay equations. 1911, Rutherford proved the atom has a very tiny nucleus. 1913, Fajans and Soddy demonstrated the existence of isotopes.
Rutherford‘s a Scattering Experiment This experiment showed that about 1 in every 20,000 a particles ―bounced back‖ Since a ‗s were much heavier than electrons the uniform positive matrix Thomson proposed was wrong. (This is how we know the nucleus is so small. )
Historical 1897, J.J. Thomson measured the charge/mass ratio of the electron. 1926, G. P. Thomson received the Nobel Prize for discovering the electron, like light, had both particle and wave nature.
Historical1911 Millikan Measures the Charge of an electron
Other History Radioactivity of Rain 1902, Wilson found rain contained short lived radionuclides. 1906, Rain from thunderstorms was found to be very radioactive. 1908, 214Pb and 214Bi were identified in rain. (today we know these are decay products of 222Rn)
Other History Radioactivity of Hot Springs 1906, Boltwood found Radon 222 in water at Hot Springs, AR. Many spring, hot or cold, contain Rn and its daughter isotopes. The hot salt water, brine, produced with oil often contains Radium and Radon
Historical 1918, Max Planck derives the constant, h. 1932, Chadwick discovered the neutron. 1938, Hahn and Strassman discovered nuclear fission. 1940, Seaborg discovered Plutonium. 1941, First man made nuclear chain reaction.
Historical 1949, Libby develops the Carbon 14 nuclear chronometer. 1956, Kuroda predicts a natural nuclear reactor occurred somewhere on the earth. 1972, Natural ancient nuclear reactor discovered in Africa.
GET THIS DOCUMENT http://www.epa.gov/radiation/docs/402-k-07- 006.pdf http://www.epa.gov/radiation/docs/402-k- 07-006.pdf
History of Nuclear Fission The history of the discovery of nuclear fission is fascinating. All the great players in nuclear physics and chemistry were involved. The account of how the information was secreted out of Germany to this country, Einstein‘s letter to President Franklin D. Roosevelt, the self imposed secrecy of the scientists in Chicago, and the extent of Japan‘s nuclear research is better than any action thriller you can find today.