Section 2 presentation

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)

Nuclear Hill Model

Assumptions in Bohr’s ModelThe 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

ExamplesThe 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 Coulomb's Law, two point charges of +1 C, placed one meter apart, would experience a repulsive force of 9×109 N, a force roughly equal to the weight of 920,000 metric tons of mass on the surface of the Earth.

Assumptions in Bohr’s ModelThe mass of a protons is 1.6726E-24 g. Or

1.0073amuThe mass of a neutron is 1.6749E-24 g. Or

1.0087amu

Assumptions in Bohr’s ModelThe 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 ModelThe 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 ScaleAtomic 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 12C atom. 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 the element’s isotopes.

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.

DEFINITIONSRadiation: 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

Electromagnetic Radiation

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.

The Photoelectric Effect

Atomic Mass ScaleOne 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 of Atoms

The Mole

Avogadro’s number—6.022 1415 1023—is the number of particles in exactly one mole of a pure substance.

Avogadro’s Number

A 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.

Relating Mass to Numbers of Atoms, continued

Molar Mass

The molar mass of an element is numerically equal to the atomic mass of the element in atomic mass units.

Molar mass is usually written in units of g/mol.

The mass of one mole of a pure substance is called the molar mass of that substance.


• Chemists use molar mass as a conversion factor in chemical calculations.

4.00 g He2.00 mol He = 8.00 g He

1 mol He

To find how many grams of helium there are in two moles of helium, multiply by the molar mass.

For example, the molar mass of helium is 4.00 g He/mol He.

Gram/Mole Conversions


• 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.

Conversions with Avogadro’s Number


What is the mass in grams of 3.50 mol of the element copper, Cu?


A chemist produced 11.9 g of aluminum, Al-26. How many atoms of aluminum were produced?


How many atoms of plutonium-239 are present in a bare-sphere critical mass of 10kg?

Energy and MassEinstein’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 JOr = 931.5 MeVSo 1 AMU of mass = 931.5 MeV of energy

BINDING ENERGYThere 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

Data

Where:Mp, The mass of a proton: 1.0072766 mMn, The mass of a neutron: 1.0086654 m Me, The mass of an electron: .0005486 mMatom, The mass of the bound atom (varies

by isotope)

ExampleFind 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 Total

8 p+ 1.0072766 8.0582128

9 no 1.0086654 9.0779886

8 e-1 .0005486 0.0043888

Total = 17.1405902

D= 17.1449790 - 16.999133 = 0.1414572 amu

0.145846 amu x 931.5 amu/ MeV = 131.77MeV

Or 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 NucleonThe 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 NumbersThe 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 originNucleus 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…IonizingNon-Ionizing

In this course we are concerned only with ionizing forms of radioactivity

What is Radiation

There are two major types of ionizing radiationParticulate RadiationElectromagnetic 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 radiationAlphaBetaNeutron

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

PZ

ADZ-2

A-4+ He

Regions of the Periodic Table

Parent Radionuclide

Alpha Decay

Decay Product

Alpha Particle

Alpha Decay

What is Radiation

Beta – Beta particles are made up of electrons “born” in the nucleus

They can have either a + or – chargeEven 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

p

p p

nn

p

Parent Radionuclide

Positron Decay

p

p n

nn

p

Decay Product

Positron

Neutrino

Positron Decay

p

p p

nn

p

Decay Product

Positron

Neutrino

Positron Decay

Positron Decay

Positron (β+)

Electron (e-)- an innocent bystander -

Positron Decay

Positron has given up all its kinetic energy.

Positron (β+)

Electron (e-)- an innocent bystander -

Positron Decay

Because of their opposite charges, the positron and electron are attracted to each other.

Positron (β+)

Electron (e-)

Positron Decay

Positron 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 captureA proton will be converted to a neutron

without the release of a positronThis will result in the release of an electron

neutrinoAs 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 cloudMonoenergitic

This acts as a beta particleAlso, 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


Gamma – Gamma rays are electromagnetic rays of pure energy

They have no mass and no chargeGamma 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

Parent Radionuclide

Gamma Ray Emission

Decay Product (Excited)

Alpha Particle

Gamma Ray Emission

Decay Product

Alpha Particle

Gamma Ray

Gamma Ray Emission

What is Radiation

Gamma, and X-rays are measured in KeV = 103 eV

Particulate Radiation is measured in MeV = 106 eV


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.

X-Ray Emitting Atom

Nucleus

X-ray

e-

e-

e-

e-

e-e-

What is Radiation

Energy can be described as the ability to do work.

Two kinds of energy:potential energyKinetic 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

UnitsRoentgen (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 not't 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 not't 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 RadionuclidesNaturally 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 Produced Radionuclides

Isotope Half Life Isotope Half life

10Be 2.7 E 9 y 36Cl 3.0 E 5 y14C 5.7 E 3 y 32Si 7.1 E 2 y

3H 12.5 y 22Na 2.6 y35S 87 d 7Be 53 d33P 25 d 32P 14 d

Naturally Occurring Radionuclides (not in decay 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 Springs

Spring 22Rn (pCi/l) 238U (pCi/l)

Warm Springs 63 oC

2900 0.09

Crystal Springs32 oC

18 1.5

Ash Springs36 oC

140 1.2

Bailey’s Hot Spring 42 oC

3560 3.5

VIDEO BY

Dr. Robert Holloway

Founder of NTA

Historical

1895, Roentgen discovered x-rays.

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 Model of the Atom

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

Historical1918, 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.

http://www.epa.gov/radiation/docs/402-k-07-006.pdf

GET THIS DOCUMENThttp://

www.epa.gov/radiation/docs/402-k-07-006.pdf




History of Nuclear FissionThe 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.

Documents

Section 2 presentation