NUCLEAR CHEMISTRY. Changing one element into another by bombarding it with particle bullets in a particle accelerator.

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Joel Copeland
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1 NUCLEAR CHEMISTRY Word Artificial transmutation Atomic Mass Unit (amu) * Atomic number * Average Atomic Mass * Half-life Isotope * Mass number * Natural radioactivity (Radioactive Decay) Neutron * Nuclear charge * Nuclear fission Nuclear fusion Nucleon * Nucleus * Particle accelerator Definition Changing one element into another by bombarding it with particle bullets in a particle accelerator. 1/12 the mass of a C-12 atom, the approximate mass of protons and neutrons. The number that identifies an element, equal to an atom s number of protons. The average mass of a sample of element that is determined by the mass and abundance of every isotope of that element. The time it takes for half the mass of a sample of radioactive isotope to undergo decay. The period of time in which any given nucleus has a 50% chance of undergoing radioactive decay. Atoms of the same element that contain different numbers of neutrons and therefore differ in atomic mass as well. The sum total of the protons and neutrons in an atom. The spontaneous breakdown of an unstable nucleus into a more stable nucleus and a decay particle (alpha, beta-negative, betapositive or gamma). The particle that has no charge and has a mass of 1 a.m.u. The net positive charge of the nucleus, equal to the number of protons in the nucleus. The process whereby a large nucleus is split by artificial transmutation into smaller nuclei with the release of a large amount of energy derived from the conversion of a tiny bit of mass into energy. The process whereby two small nuclei are combined to form one larger nucleus with release of a huge amount of energy derived from the conversion of a tiny bit of mass into energy. A particle that exists in the nucleus (protons and neutrons.) The central core of the atom, consists of protons and neutrons and has a net positive charge. A device that uses electromagnetic fields to accelerate charged particles. Proton * A particle that represents a unit charge of +1 and a mass of 1 a.m.u.

2 Nuclear Stability Nuclear Stability: the larger (more massive) a nucleus is, the harder it is for it to stay together. When a nucleus is RADIOACTIVE, it gives off decay particles and changes from one element to another. This is also known as NATURAL DECAY or NATURAL TRANSMUTATION. Atoms with an atomic number of 1 through 83 have at least one stable (nonradioactive) isotope, but all isotopes of elements with an atomic number of 84 or more are radioactive. Nuclei can be considered or depending on the ratio of NEUTRONS to PROTONS. For the first 20 elements, atomic numbers 1-20 the ratio of neutrons protons = 1. To determine if an isotope is stable,just plug in the numbers Elements over atomic number, element named have NO KNOWN STABLE ISOTOPES. This means they are all RADIOACTIVE! This decay results in the emission of particles and/or radiant energy. Radioactivity is associated with some sort of disintegration or decay of the NUCLEUS. Most isotopes are.

3 There are 3 types of Natural Decay ( that leads one elements atoms becoming atoms of another element) ***** Technically there is 1 other but it doesn t change the identity) Decay Type Symbol Notation Mass Charge What Happens to the atom Penetrating Power GAMMA RAYS Then, there is one more type of decay, called gamma decay (γ). This takes the form of a highenergy particle of light that is given off as the nucleus becomes more stable. It does not change the identity of the element. It has no mass or charge, and is so energetic that it can only be stopped by a 30-cm thick layer of concrete or a 1-foot thickness of solid lead. Gamma can be given off by itself, or it can be given off with any of the other types of decay.

4 This diagram shows the path taken by radioactive particles as they pass through an electric field. On the left is a shielded container that holds a sample of radioactive substance, with a small hole at the end to allow decay particles to stream out in a straight line. Above and below the stream are electrically charged plates, which deflect (change the path of) the beams as they come out. Positive-charged particles (like alpha and positron) are attracted to the negatively charged plate. Negative-charged particles (like beta) are attracted to the positively charged place. The gamma rays, having no charge, pass through undeflected. On the right side is a screen that has been coated with zinc sulfide (ZnS), which is a phosphor (material that glows when energized particles hit it).

5 Nuclear Energy Radioactive decay gives off energy. The molten core gives us our planet s magnetic field, which shields us from high-energy particles given off by the sun (such as high-energy protons given off during solar flares). The energy that is given off during a nuclear change comes from the MASS DEFECT...a little bit of mass that is destroyed (so little that you would hardly even miss it) and converted into huge amounts of energy. A HUGE amount of energy can be created by destroying a TINY amount of mass. How Can Radioactivity Be Detected? 1) Radioactivity can expose protected photographic film. 2) Radioactive isotopes cause phosphorescent (glow-in-the-dark) materials to glow. 3) Radioactive decay particles are charged, and they ionize (give a charge to) matter that they pass through.

6 <Q$RSO#SF=TKGR# GQFCBOR$#SF=TKGR# KL!## #M% N#C! # O P.Q N$ #MO34 #L$ % ##N$ #MO 34! BK $.Q NK #MO R( ML$ % ##NK #MO R(! BK $.Q N# #MO C OL!### N# #MO C! # O P.Q N$ #M$ 34 SL!### N$ #M$ 34!TTTTTQTTTTTTTUV@#2(6#WUF#N'2'-0#*0,9#(NNX UL!# 2L!# %L!# NL $ % # K$L $ % # KKL!# K#L $ % L# KML $ % L KOL!# The half-life of U-238, according to Reference Table N, is 4.51 X 109 years (4.51 billion years). The oldest rocks on Earth consist of a 1:1 ratio of U-238 to Pb-206. This means that the Earth s oldest rocks are 1 half-life of uranium old. How old is the Earth? 4.51 billion years old! Looks pretty good for its age, doesn t it?

7 HALF - LIFE Radioactive Decay is a RANDOM process. The half-life of a radioactive isotope is defined as the period of time that must go by for half of the nuclei in the sample to undergo decay. During one half-life period: - Half of the radioactive nuclei in the sample decay into new, more stable nuclei If a sample contains 1000 nuclei of a radioactive isotope now, 500 will undergo decay over the course of one half-life. - Half the mass of the radioactive isotope is converted into a new, more stable isotope If a sample contains 4.0 grams of a radioactive isotope now, after one half-life, 2.0 grams will remain undecayed, the other 2.0 grams will be made up of a new, more stable isotope. After one half-life, half (50%) of the original amount of the sample will have undergone radioactive decay. After a second half-life, one quarter (25%) of the original sample will remain undecayed. After a third half-life, one eighth (12.5%) of the original sample will remain undecayed. NOTE: The actual half-life time is constant. If the half-life is 10 days, then 2 half-lives would take 20 days, 3 half-lives take 30 days, 4 half-lives take 40 days and so on. The half-life of many radioactive isotopes can be found on Reference Table. Examples:

8 USES OF RADIOACTIVE ISOTOPES Many radioactive isotopes are very useful to us! Here is a sampling of isotopes that we have put to good use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rradiation of food: kills bacteria, allowing it to be stored for a longer time without having to pasteurize. Pasteurizing involves heating the food to kill bacteria, which can change the flavor of the food. Irradiation does not change the flavor. Radioactive isotopes are often used medically in the body to either treat cancer or to detect potential problems. Since radioactivity itself can cause cancer with exposure, any isotopes administered to a person should have a short half- life and be quickly eliminated from the body (usually via urination).

9 NATURAL RADIOACTIVITY HOMEWORK A) Multiple-Choice Questions: write the answer in the space to the left of each question. 1) Which decay particle will deflect towards a positively charged plate? 2) Which particle will pass through an electric field undeflected? 3) Which particle will, when given off, cause the atomic number of the decaying nucleus to INCREASE by one? 4) Which particle is given off by a decaying nucleus of K-37? 5) Which particle has the greatest mass? 6) Which particle can only be stopped by a 1-foot thickness of lead? 7) Which element has no stable isotopes, only having radioactive ones? a) Si b) Am c) Cu d) C Given the unstable isotope symbol, mass, and decay type, determine the daughter nuclide (decay product) by writing the complete nuclear equation (use atomic numbers and symbols from the periodic table). 23( (9/.0(1:;.<.=(>,?@09A$B A$B $ 9A.EA$B B% F< AG8.1(9/.0(1:;.<.=(>,?H)9%C #G(65I(<.=(>,?J,9#A# KG5,-:1),/<.=(>,?H9KC BG8.1(/.0(1:;.<.=(>,?L.9M NG5,-:1),/<.=(>,?O.9AP MG(65I(<.=(>,?Q9#B$ CG8.1(9/.0(1:;.<.=(>,?R9#$ %G8.1(9/.0(1:;.<.=(>,?S69#$%

10 Look up how each of the following isotopes undergoes decay on Reference Table N and then write the complete decay equation for each isotope. # AKC F- ##$ R) #KP JT KC H PP S=

Aim:How can we determine the particles emitted from radioactive

Aim:How can we determine the particles emitted from radioactive decay? Nuclear Stability: The larger (more massive) a nucleus is, the harder it is for it to stay together. Natural transmutation (natural