1. Fundamentals of Radiation
Target Audience: 8th Grade
Includes: Speaker notes and several graphics
General Description: General overview of the fundamental concepts associated with understanding radiation (29 slides)
This presentation provides a basic overview of the fundamentals of radiation science. Topics covered include the structure of the atom, radioactive decay, types of radiation, and ways to measure radiation dose and exposure.

2. Partial Periodic Table
This table shows the first 10 elements of the Periodic Table as an example. They are grouped according to their electron structure which dictates how they will react chemically. It also identifies the chemical element for the given atomic number (Z), or the number of protons in its nucleus. There are 94 naturally occurring elements. Tranuranic elements have atomic numbers higher than that of Uranium (U, element 92), which is the last stable element of the periodic system. Group I elements - Because of the great chemical reactivity of the alkali metals (easily form positive ions), none exist in nature in the elemental state. Group II elements - The alkaline-earth metals are never found as free elements and are moderately reactive metals. They are harder and less volatile than the alkali metals (Group I), these elements all burn in air.
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).

3. Structure of the Atom
The nucleus contains neutrons and protons, also referred to as nucleons. The electrons orbit the nucleus.
The electrons are responsible for chemical reactions (e.g., formation of molecules).
The protons have a positive charge, the electrons a negative charge, and the neutrons are not charged.
The nucleons are responsible for nuclear reactions (e.g., radioactive decay).
Everything is made of molecules – tables, chairs, food, even the cells in your body. Molecules are made of even smaller parts, which are called atoms. Atoms are so small that it takes millions of them just to make a speck of dust.
There are at least different 92 naturally occurring types of atoms. These different types of atoms are known as elements. The elements are listed on the periodic table.
As small as atoms are, they are composed of even smaller basic particles. There are three basic particles in most atoms – protons, neutrons, and electrons.
Protons carry a positive electrical charge. Neutrons have no electrical charge. Protons and neutrons are bundled together at the center of the atom, this central core of the atom is called the nucleus. Electrons have a negative charge and move around (orbit) the nucleus.
The orbiting electrons of the atom can reside only in distinct energy levels. That’s why it takes a photon of a minimum energy level to interact with the electron to place it in an excited state, or to eject the electron entirely.

4. X A = Z + N Nomenclature A X = Chemical Symbol Z N
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)
A = Z + N
We use the number of protons to identify atoms. For example, an atom of oxygen has 8 protons in it’s nucleus and an atom of lead has 82 protons. Single atoms generally have the same number of positively charged protons and negatively charged electrons. As a result, the atom as a whole does not have an electrical charge.
The nucleus in every atom of an element always has the same number of protons, but the number of neutrons may vary. Atoms that contain the same number of protons, but a different number of neutrons are called isotopes of the element.
All atoms are isotopes. To distinguish which isotope of an element we are talking about, we total the number of protons and neutrons to get the atomic mass. Usually an isotope is distinguished by writing the atomic mass after the element’s chemical symbol. For example, an atom of carbon typically has 6 protons and 6 neutrons and would be written as C-12 or 12C. However, another isotope of carbon, the one sometime used for radiocarbon dating of old objects, has 6 protons and 8 neutrons. This isotope would be written C-14 or 14C. A X
X = Chemical Symbol 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.

5. Forces in a Nucleus Hydrogen-3 (Tritium) Helium - 3
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.
Just as the orbiting electrons of the atom can reside only in distinct energy levels, the same is true for the nucleons of the nucleus. It takes a specific amount of energy to overcome the binding energy (nuclear forces) between the nucleons, or to place the nucleus in an excited state.
Hydrogen-3 (Tritium)
Helium - 3

6. Radioactive Decay
The 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.
Excited electrons release photons when they drop to a lower energy state. Since the energy levels are at discrete energy levels, the energy of the photon created is equal to the difference between these energy levels. The same is also true for the excited nucleons.
The isotope undergoing the decay process is called the Parent.
The isotope left after the Parent has undergone decay is called the daughter, ot progeny.

7. 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 particles are relatively heavily charged particles (+2). Because of their size and high charge, they react readily with the materials they are penetrating and therefore have a small penetrating range. The high positive charge rips electrons from surrounding materials leaving negatively charged ions (charged atoms) which cause cell damage. This is called ionizing radiation. Due to low penetrating ability of the alpha particles, they are mainly a concern when inhaled or ingested where they can cause ions inside of the body.
Beta particles are also ionizing radiation but have a higher penetrating ability.
Photons are a major concern due to their high penetrating ability and the increased shielding required. Photons of sufficient energy can eject electrons from an atom also forming ions. This is the major source of radiation dose at operating nuclear power plants.
Neutron radiation is mainly a concern at nuclear power plants during operation. Ample shielding is in place around the reactor during operations, with access to high neutron dose areas closely controlled. There are also neutron sources which are used at nuclear power plants to provide the initial neutrons to start the reactor. There are also neutron sources used at research institutes of concern.

8. Alpha Particle Helium-4 Nucleus Slow moving, but high energy
(2 neutrons, 2 protons)
Slow moving, but high energy
Cannot penetrate material easily
Stopped by one piece of paper
Stopped by dead layer of skin

9. Example of Alpha Decay
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.

10. Beta Particle Electron Fast moving, Medium energy
Can penetrate material well
Stopped by 100 to 150 pieces of paper
Stopped by centimeter of water

11. Example of Beta Decay
The neutrino is not important for the purposes of this slide presentation, but was added for completeness and to identify that there are other subatomic particles associated with nuclear reactions. Neutrinos are generated as part of the reaction inside of a nuclear reactor, but have a low probability of reacting with matter (none that can be easily measured as with the four forms of radiation mentioned). The Navy would pay dearly to have a method to measure neutrinos since it would be a method for identifying the location of nuclear powered submarines under the cover of the ocean.
It is not relative but may be interesting to some to know that the negatively charged beta particle (i.e., electron) also has a positively charged counter part (positron), as does the neutrino (i.e., antineutrino). Each subatomic particle is grouped, with several particles under each group.
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.

12. Gamma Decay Electromagnetic radiation Emitted only by certain nuclei
Similar to light, x-rays, radio waves
Emitted only by certain nuclei
Speed of light; low to high energy
Highly penetrating
Stop half of the s with about 1 cm of lead
or 5 to 15 cm of water
The name X-rays are given to those photons that are generated from electrons dropping down from an excited state to a lower energy level. Gamma radiation is used to refer to photons generated from the nucleus. Photons are strange creatures that travel at the speed of light and have no rest mass. They have both properties of waves and particles.

13. 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.
This is a common reaction in civilian nuclear power plants where the majority of the fuel is U-238. The U-239 undergoes - decay to Np-239, which undergoes - decay to Pu-239. Pu-239 also has a high probability of undergoing the fission process inside of a nuclear reactor.

14. Examples of Neutron Emission
There are Neutron (n) emissions associated with the following reactions.
2H +   1H + neutron
9Be +   2 (4He) + neutron
9Be +   12C + neutron
Neutron 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 + 3n
Neutrons with high kinetic energy are released in the process.

15. Half-life
Each radioactive nucleus has a certain probability of decay per time
Some decay quickly (fractions of a second), some later (thousands of years)
Rate of decay depends on the number of nuclei available
As number decreases, rate of decay decreases
The half-life for a given isotope is an average quantity which is obtained through scientific measurements. This half-life which is given in units of time does not change, however the rate of decay (disintegrations per unit time) does change as the number of nuclides available to under go decay decreases.

16. Half-life
In theory, all the radioactive material will never totally decay
Define Half-life
Time for half of the sample to decay
This is especially true inside of a nuclear reactor since as the nuclide is decaying, it is also being produced from the decay of its parent.

17. Half-life
This graph shows the exponential decrease in the number of the isotope with the passage of time (assuming that it is no longer being produced). After a relatively short number of have lives, the isotope is for all practical purposes is gone. It should be remembered that the half-lives can be from fractions of seconds to millions of years. It is beneficial for research that an isotope have a long enough half-life to be useful, but not too long to require an extended wait for the desired decay to take place. The same is true for radioactive waste. It would be nice if the half-life of long lived highly radioactive nuclides could be reduced. This is being researched in a method called Transmutation, where the long lived radioactive nuclides are subjected to neutron bombardment to change it from an isotope with a long half-life to another isotope with a shorter half-life.

18. 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
Carbon 14 is used in carbon dating of living fossils. All living matter reach a steady state build-up of carbon in its system. After death, the carbon 14 is no longer being replaced and slowly decays over time. By measuring the decay rate per time, and knowing the half-life for carbon 14, the scientist can determine how long ago the living organism died.

19. 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 ( s)

20. Example Half-lives - Medical Uses
Iodine (Thyroid treatment)
8 days
Technetium-99m (Nuclear medicine)
6 hours
Gold-198 (Tumor therapy)
2.7 days

21. Activity Activity = Decays per time Units:
1 Becquerel = 1 decay per second (dps)
1 Curie = 37 Billion dps
1 microCurie (mCi) = 37,000 dps
1 picoCurie (pCi) = dps

22. Example Activities - Regulations
Typical maximum alpha emitting radionuclide allowed without a license (some exceptions)
0.1 mCi
Typical maximum beta emitting radionuclide allowed without a license (some exceptions)
10 mCi

23. Example Activities - Natural Radioactivity
Uranium-238 in cup of soil (typical)
0.003 mCi = 3000 pCi
Radon-222 in air
0.5 pCi per liter (outdoor air)
1 to hundreds of pCi per liter (houses)
Potassium-40 in human body
0.1 mCi

24. Radiation Dose Dose = Energy absorbed per mass Units: Rad
Gray (Gy) [1 Gy = 100 rad)

25. Radiation Dose Equivalent
Different radiations do different amounts of biological damage
Dose Equivalent = Dose X QF
QF = Quality factor
Betas, Gamma: QF = 1; Alpha: QF = 20
Units
Rem (1 mrem = rem)
Sievert (Sv) [1 Sv = 100 rem)]
The Federal Regulations allow for so much exposure to personnel working around radioactive material. This is based on the expected effects on the person exposed to a given amount of radiation. The organs of the body are more sensitive to radiation than other parts of the body, therefore, the arms and legs are allowed to receive more radiation dose than the trunk of the body. Developing cells are even more susceptible to radiation damage, therefore, lower limits are set for pregnant women to protect the embryo.
The exposure can be over a short period of time (Acute) or over a longer period of time (Chronic). For acute exposure of rem, there is expected to be no observable effects. For exposure of rem, there may be slight blood changes with no other observable effects. For rem, vomiting may occur in 5% to 50% within three hours with fatigue and loss of appetite. Moderate blood changes are likely, with recovery expected within a few weeks. For rem, vomiting, fatigue, and loss of appetite in 50% to 100% within 3 hours. Loss of hair, severe blood changes, hemorrhage and infection. In untreated patients, death occurs in 0% to 80% within 2 months. For rem, vomiting occurs within one hour. Severe blood changes, hemorrhage, infection, and loss of hair. In untreated patients, death occurs in 80% to 100% within 2 months.

26. Radiation Exposure Old unit of exposure Units:
Amount of radiation present in air
Only applicable for x-rays and gamma radiation
Units:
Roentgen (R)
1 R exposure in air will produce about 1 rad dose in human tissue

27. Example Doses Natural annual background radiation
cosmic: 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
Based on risks associated with general exposure to radiation, it is assumed that there is some negative effect of radiation on the body even at low exposure rates. This cannot be easily proven, and is considered to be a conservative assumption. There are some that believe that exposure to low levels of radiation may even be helpful in keeping the body healthy. Once again, this is very hard to prove.

28. 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

29. Radiation Safety Radioactive materials produce a dose rate per time
To reduce total dose:
Minimum time
Half the time - half the dose
Shielding
Maximum distance
Twice the distance - one-fourth the dose
Minimizing the time can be an easy one to control. By planning ahead, the time to perform a job can be reduced. Also, knowing where the exposure rates are for a given work area can assist in identifying where to stand when performing work.
Shielding is extensively used throughout the industry. By shielding an area to be worked, the exposure rates can be reduced significantly. However, it is counterproductive if the person hanging the shielding receives more dose than the worker would have had he performed the work without the shielding.
The dose rate drops as the square of the distance. Therefore, by using an extension on a tool, the dose may be able to be cut significantly.