Partial Periodic Table
AlkaliMetals
1A
6C
12.01Carbon
AtomicChemical
AtomicName of
NumberSymbolMassElement
Noble Gases0
1H
1.01Hydrogen
AlkalineEarth
MetalsIIA IIIA IVA VA VIA VIIA
2He
4.00Helium
3Li
6.94Lithium
4Be
9.01Beryllium
5B
10.81Boron
6C
12.01Carbon
7N
14.01Nitrogen
8O
16.00Oxygen
9F
19.00Flourine
10Ne
20.18Neon
The Periodic Table provides the atomic number (Z), the chemical symbol, atomic mass, and element name. It also groups the elements based on their electron structure (I.e., how they react chemically).
Structure of the Atom
Nucleus
Orbiting Electrons
The nucleus contains neutrons and protons,
also referred to as nucleons. The electrons
orbit the nucleus.
The protons have a positive charge, the electrons a negative
charge, and the neutrons are not charged.
The electrons are responsible for chemical
reactions (e.g., formation of molecules).
The nucleons are responsible for nuclear
reactions (e.g., radioactive decay).
Nomenclature
Z = Number of Protons (determines the chemical element)
N = Number of Neutrons (determines the isotope of the
element)
A = Neutrons plus Protons (atomic mass of the isotope)
XA
Z NX = Chemical Symbol
A = Z + N
The chemical symbol and the atomic mass define the individual nuclide. (e.g., 3H has 1 proton and 2 neutrons).
Isotopes of an element have the same number of protons, but a different number of neutrons in the nucleus.
Forces in a Nucleus
Hydrogen-3 (Tritium) Helium - 3
p
n
n
Nuclear force of neutron on proton
Nuclear force of proton on neutron
p
n
p
Nuclear force of proton on proton
Nuclear force of proton on proton
Electrostatic force of proton on proton
Electrostatic force of proton on proton
Nuclear force is an attractive force between each of the nucleons (i.e., neutrons and protons) over relatively short distances.
Electrostatic force is a repulsive force between the like charged protons over a greater distance than nuclear forces.
Radioactive DecayThe nuclides, as with most things in nature, want to be at their lowest energy state which is a stable nucleus.
Radioactive decay occurs in nuclides where the nucleus is unstable.
For stable nuclides with low atomic masses, the number of neutrons is equal to, or approximately equal to the number of protons (except for 1H which only has one nucleon).
As the atomic mass of the nuclide increases, the ratio of neutrons to protons must be greater than one for it to be stable, suggesting that more neutrons are required to provide nuclear forces to offset the electrostatic repulsive force between the increased number of protons.
The nucleus may also become unstable when energy is added to it, placing it in an excited state. An example of this would be a free moving neutron inside of a reactor being captured by the nucleus of a 238U nucleus.
The nuclide reaches its stable state by undergoing radioactive decay.
Types of Radiation
There are four types of radiation of interest:1) Alpha () which is a positively charged helium
nucleus (2 protons and 2 neutrons).2) Beta () which is a negatively charged electron.3) Gamma () which is a packet of energy with zero
rest mass.4) Neutron (n) which is a released neutron. Mainly a
concern during nuclear reactor operation.
Alpha Particle
Helium-4 Nucleus(2 neutrons, 2 protons)
Slow moving, but high energyCannot penetrate material easilyStopped by one piece of paperStopped by dead layer of skin
Example of Alpha Decay
Alpha particle
Radium-226 Radon-222
(88 protons, 138 neutrons) (86 protons, 136 neutrons)
Alpha decay occurs when the nuclides of high atomic mass have a lower neutron to proton ratio than stable nuclides and ejects an alpha particle.
Alpha decay is rare for nuclides with low or intermediate mass numbers.
Beta Particle
ElectronFast moving, Medium energyCan penetrate material wellStopped by 100 to 150 pieces of paperStopped by 0.5 -1 centimeter of water
Example of Beta Decay
Beta particle
Carbon - 14 Nitrogen - 14(6 protons, 8 neutrons) (7 protons, 7 neutrons)
Beta decay occurs when the nuclides have a higher neutron to proton ratio than stable nuclides.
A neutron converts to a proton, electron (), and a neutrino.
A neutrino is a high energy particle with zero rest mass with high penetrating capability.
Gamma Decay
Electromagnetic radiationSimilar to light, x-rays, radio waves
Emitted only by certain nucleiSpeed of light; low to high energyHighly penetratingStop half of the s with about 1 cm of
leador 5 to 15 cm of water
Example of Gamma Decay
238U + neutron 239U +
Gamma decay occurs as a means of removing energy from the nucleus of an excited nuclide.
The gamma may be ejected alone or in conjunction with the emission of another radioactive particle (e.g., ) to reduce the nucleus energy.
Examples of Neutron Emission
There are Neutron (n) emissions associated with the following reactions.
2H + 1H + neutron9Be + 2 (4He) + neutron
9Be + 12C + neutronNeutron emissions of interest in a nuclear reactor occur when the excited nucleus of a specific high atomic mass nuclide
splits into two or more smaller nuclides during the fission process.
235U + n 135I + 97Y + 3nNeutrons with high kinetic energy are released in the process.
Half-life
Each radioactive nucleus has a certain probability of decay per timeSome decay quickly (fractions of a second), some later (thousands of years)Rate of decay depends on the number of nuclei availableAs number decreases, rate of decay decreases
Half-life
In theory, all the radioactive material will never totally decayDefine Half-lifeTime for half of the sample to decay
Example Half-lives - Natural
Uranium-238 (In soil)4.5 Billion years
Potassium-40 (in soil and body)1.3 Billion years
Carbon-14 (In all living tissue)5730 years
Hydrogen-3 (in all water)12 years
Example Half-lives - Natural
Radium-226 (In soil - produces radon)1600 years
Radon-222 (in soil and air)3.8 days
Polonium-214 (radon progeny that decays in lungs)164 microseconds (0.000164 s)
Example Half-lives - Medical Uses
Iodine - 131 (Thyroid treatment)8 days
Technetium-99m (Nuclear medicine)6 hours
Gold-198 (Tumor therapy)2.7 days
Activity
Activity = Decays per timeUnits:1 Becquerel = 1 decay per second (dps)1 Curie = 37 Billion dps1 microCurie (Ci) = 37,000 dps1 picoCurie (pCi) = 0.037 dps
Example Activities - Regulations
Typical maximum alpha emitting radionuclide allowed without a license (some exceptions)0.1 Ci
Typical maximum beta emitting radionuclide allowed without a license (some exceptions)10 Ci
Example Activities - Natural Radioactivity
Uranium-238 in cup of soil (typical)0.003 Ci = 3000 pCi
Radon-222 in air0.5 pCi per liter (outdoor air)1 to hundreds of pCi per liter (houses)
Potassium-40 in human body0.1 Ci
Radiation Dose Equivalent
Different radiations do different amounts of biological damageDose Equivalent = Dose X QFQF = Quality factorBetas, Gamma: QF = 1; Alpha: QF = 20
UnitsRem (1 mrem = 0.001 rem)Sievert (Sv) [1 Sv = 100 rem)]
Radiation Exposure
Old unit of exposureAmount of radiation present in airOnly applicable for x-rays and gamma
radiation
Units:Roentgen (R)1 R exposure in air will produce about
1 rad dose in human tissue
Example Doses
Natural annual background radiationcosmic: 27 mrem (0.27 mSv)Terrestrial: 28 mrem (0.28 mSv)Internal: 39 mrem (.039 mSv)
[total natural (excl. Radon): ~100 mrem]
Radon-lungs: 2400 mrem (24 mSv) [effective whole body: 200 mrem]
Source: NCRP Report #93
Example Doses
Medical Radiation (Effective Whole Body Dose Equivalent)Chest X-ray: 8 mrem (0.08 mSv)Head CT scan: 111 mrem (1.11 mSv)Barium Enema: 406 mrem (4.06 mSv)Extremity X-ray: 1 mrem (0.01 mSv)
Source: NCRP Report 100