nuclear chemistry. discovery of radioactivity radiation - energy emitted in the form of...

NUCLEAR CHEMISTRY

Discovery of Radioactivity Radiation - energy emitted in the form of electromagnetic waves (i.e. light, microwaves, x-rays, etc..) 1895 Roentgen discoverer of x-rays - Nobel Prize 1901. video clipvideo clip Becquerel followed-up on Roentgens work storystory Marie and Pierre Curie 1899 Rutherford alpha and beta rays Radioactivity spontaneous emission of particles and energy from atomic nuclei.

ELECTROMAGNETIC SPECTRUM LOWER ENERGY HIGHER ENERGY

Ionizing and Non-ionizing radiation Non-ionizing radiation (long-wavelength) - Ionizing radiation (shorter wavelength)- Both transfer energy to matter!

UV radiation damage

Isotopes Atoms of the same element that contain different numbers of neutrons. What chemical symbol do these atoms have? What is their atomic number? What is the mass number of the atom on the left?

Isotope Tables http://en.wikipedia.org/wiki/Isotope_table_% 28divided%29 http://en.wikipedia.org/wiki/Isotope_table_% 28divided%29

NOTATION Uranium 238 238 mass number ( p + n ) U 92 atomic number ( # p )

Nuclear Radiation It is a form of ionizing radiation that is caused by changes in the nucleus of an atom. Remember: unstable nucleus = radioactive atom change in identity of atom as the nucleus breakdown (radioactive decay). How is this dangerous? -Unstable nuclei can emit high-speed particles from the nucleus thus releasing energy (nuclear radiation).

Stable vs. Unstable isotopes Radioactive Isotopes: unstable atoms, due to a nucleus with too many or too few neutrons relative to the number of protons. No amount of neutrons can hold a nucleus together once it has more that 82 protons. All of the elements with an atomic number greater than 82 have only unstable isotopes. Unstable atoms emit energy in the form of radiation when they break down (decay) Large nucleus (unstable) nucleus + energy Reaction is EXTREMELY exothermic; called nuclear energy; mass is lost in the process

Nuclear RadiationAlpha radiation, low penetrating power 2+ Ex: Radium-226 Beta Radiation, Moderate penetrating power Ex: carbon-14 Gamma Radiation, Very high penetrating power 0 Cobalt -60

3 types of nuclear radiation: Alpha & beta particles and gamma rays Charge of each Gamma rays highest energy similar to x-rays frequency. UVA, UVB, UVC rays from the sun UVC (100-290 nm wavelength) UVA (320 -400nm wavelengths)

ALPHA PARTICLE The same as a helium nucleus 2 protons and 2 neutrons 4 mass of 4 amu He 2 Has a 2+ charge because of 2 protons LOWEST PENETRATING POWER

BETA PARTICLE The same characteristics as an electron (not from an energy levelemitted from the nucleus) 0 essentially no mass e -1 charge of -1 HIGHER PENETRATING POWER

Gamma Emission gamma emission usually occurs in concert with other forms of decay that produce nuclei in nuclear excited states ignoring the alpha decay event, gamma emission looks like this:

GAMMA RADIATION Pure electromagnetic energy with high frequency and short wavelength No mass or charge associated with it MOST PENETRATING POWER

Strength of alpha, beta, and gamma radiation

PENETRATING POWER OF NUCLEAR RADIATION

Background radiation Background radiation: a constant level of radioactivity that results from natural sources and from sources related to human activity. o You cant completely eliminate background radiation its essentially everywhere: soil, water, food, rocks, etc o Currently, 500 mrem (millirem) is the established US background radiation limit for the general public EPA_Cosmic Radiation ~8% of our annual radiation exposure comes from outer space. The closer we get to outer space the more we are exposed to cosmic radiation (such as during flights). Full Body Scanners at Airports

Fyis.. BED (Banana Equivalent Dose) The equivalent dose for 365 bananas (one per day for a year) is 3.6 millirems(36 Sv).Sv Bananas are radioactive enough to regularly cause false alarms on radiation sensors used to detect possible illegal smuggling of nuclear material at US ports. Other foods that are above avg. for radioactivity in food include: potatoes, kidney beans, nuts, and sunflower seeds.

Ionizing radiation in you!

UNITS OF RADIATION DOSAGE GRAY= SI unit that is equivalent to the dose absorbed: 1 gray = 1 Joule per 1 kilogram of body tissue SIEVERT: SI unit that is used to express the ability of radiation to cause ionization in human tissue RAD: abosrbed dose similar to gray REM: absorbed dose similar to Sievert Copyright by Houghton Mifflin Company. All rights reserved. 24

Radiation Doses Causing Death

Effect of Ionizing Radiation

Ionizing radiation worksheet Units How much is safe? Look at 3 main factors: 1. Radiation Density (how much per given volume) 2. Dose (how much total received) 3. Energy associated with that type of radiation Biological effects of ionizing radiation: Large doses (but less than 200 rems) can causes changes in DNA or proteins in the body than can result in mutations leading malfunctioning proteins that are unable to do their job in the body, to cancer, or birth defects, etc.. Low level radiation does not produce as unique effects or obvious mutations attributable to the radiation exposure that is easy to distinguish from other injuries or illnesses it can take years for symptoms to even show (making it nearly impossible in some cases to attribute to radiation damage) Chemotherapy vs. radiation therapy Radiation Risk from Medical Imaging Cancer and Radiation

TRANSMUTATION INVOLVES THE RELEASE OF RADIATION A Radioisotope emits, or gives off, radiation from its nucleus Each isotope emits a certain type of radiation; it has a specific decay mode The radiation can be in the form of particles or rays

NUCLEAR TRANSMUTATION (natural) Original New Radioisotope Isotope + Radiation 238 234 4 U Th + He 92 90 2

A CLOSER LOOK U-238 has alpha decay Total mass before and after must be equal 238 234 4 U Th + He 92 90 2 Total of atomic numbers must also balance

How can you use decay mode information? Can you determine the new isotope if you know the decay mode? For example, Th-232 is an alpha emitter. 232 4 Th ? + He 90 2

STRATEGY *mass numbers must balance 232 = 228 + 4 Th ? + He 90 = 88 + 2 *atomic numbers must balance How do we know what the new isotope is?

CHECK THE PERIODIC TABLE! The new isotope has a mass number of 228 and an atomic number of 88. 228 ? 88 each element has a unique atomic number The new isotope is Radium-228 which is a beta emitter!

What happens to Ra-228? 228 0 Ra ? + e 88 -1 (beta particle) Balance the mass numbers and the atomic numberscareful of that -1)

And the result of the decay is mass number stays same 228 Ac atomic number increases by 1 89 Actinium a new element with a greater atomic # This is a beta emitter as well! When will it stop???

not until a stable isotope is formed! The change from one radioisotope to another in a specific sequence is called a decay series We will explore some transmutations that are part of the uranium-238 decay series... You will be given two radioisotopes and their decay modes. Determine what the product of each transmutation will be

Start off examples are: U-238 is an alpha emitter: 238 234 4 U Th + He 92 90 2 Th-234 is a beta emitter: 234 234 0 Th Pa + e 90 91 -1

U-238 decay series U-238 Th-234 Pa-234 U-234 Th-230 Ra-226 Rn-222 Po-218 Pb-214 Bi-214 Po-214 Pb-210 Bi-210 Po-210 Pb-206 (stable)

Take your time and think it out 1.Write the symbol of the radioisotope in the proper notation on the reactant side 2.Write the notation for the radiation type emitted on the product side 3.Total up the mass numbers on top so the total mass is balanced on each side 4.Total up the atomic numbers on the bottom so they are balanced as well 5.Use Periodic Table to identify the element by its atomic number

One very special isotope U-238 Th-234 Pa-234 U-234 Th-230 Ra-226 Rn-222 Po-218 Pb-214 Bi-214 Po-214 Pb-210 Bi-210 Po-210 Pb-206 (stable) Rn-222 is a gas!

Figure 6.34 Page 626

THIS IS NOT A CHEMICAL CHANGE! Chemical reactions involve atoms rearranging by breaking and forming bonds involving electrons TRANSMUTATION involves changes in the nucleus that change the actual identity of the element These reactions are called NUCLEAR because they involve the atoms nucleus

Transmutation Some isotopes are naturally unstable and spontaneously change to another isotope of a different element This change from one element to another is called TRANSMUTATION and can happen 2 ways: 1)by radioactive decay (natural) OR 2) when particles bombard the nucleus of the atom. (nuclear reactor)

are a large fraction of potassium atoms radioactive? are a large fraction of tellurium atoms radioactive? are a large fraction of uranium atoms radioactive? no, a tiny fraction is radioactive! yes, more than 1/2 of tellurium atoms in nature are radioactive. ALL uranium atoms are radioactive!

Why is there still uranium on earth? It takes a long time to decay. (need to consider how long it takes for a radionuclide to decay)

HALF LIVES

Half Lives Half-life - is the time required for one half of original atoms to decay The half-life is unique to that isotope. Knowing the half-life of a radioisotope can determine how harmful or useful that substance can be.

Half-Life: A Radioactive Clock the time during which half of a sample of radioactive atoms will decay into their daughter atoms. after one half-life 50% of the radioisotopic nuclei will have decayed into their daughter nuclei

Common Radionuclide Half-Lives

Copyright by Houghton Mifflin Company. All rights reserved. 62 Parent IsotopeHalf-Life (yr)Daughter Product Lead-21022Bismuth 210 Carbon-145730Nitrogen-14 Uranium-235704 millionLead-207 Potassium-401.25 billionArgon-40 Uranium-2384.5 billionLead-206 Thorium-23214.0 billionLead-208 Rubidium-8748.8 billionStrontium-87

Decay Chain of Uranium

Half-Life: A Radioactive Clock Rutherford says: half-life is a time during which there is a 50-50 chance a radioactive atom will undergo nuclear decay If the half life of a radioactive atom is a small amount of time will it be more of less likely to decay than a different radioactive atom with a long half life? MORE LIKELY!

Radiometric Dating

Radiocarbon Dating Why do living things maintain a constant concentration of carbon-14? Shouldnt it be consistently decaying in all material? Where do new sources of 14 C come from?

Radiocarbon Dating

Radiometric Dating

Example Calculations How long will it take for a sample containing 1 gram of radium 223 to reach a point where it only contains 0.25 grams of radium 223 if a half- life is 12 days? Answer: 1 gram 0.5 grams = 12days 0.5 grams 0.25 grams = 12 days 12 days + 12 days = 24 days Copyright by Houghton Mifflin Company. All rights reserved.70

Calculations with half-life A particular plant is 50,000 year old, how many carbon-14 half-lives have occurred? A: 8.7 half-lives If the plant original had 30o counts of C-14 atoms, roughly how many radioactive C-14 atoms are left in the plant after 50,000 yrs? ~0.7 counts

NUCLEAR CHEMISTRY IN MEDICINE Diagnostic & Therapeutic Uses

Nuclear Chemistry in Medical Field X-rays CT or CAT scan MRI no radiation PET scan Radiation Therapy

Therapeutic http://www.cancer.gov/cancertopics/factshee t/Therapy/radiation http://www.cancer.gov/cancertopics/factshee t/Therapy/radiation

NUCLEAR REACTORS

Fission vs. Fusion Fission: Splitting a heavy nucleus into two nuclei with smaller mass numbers. = Nuclear transmutation! Fusion: combining two light nuclei to form a heavier nucleus. Copyright by Houghton Mifflin Company. All rights reserved.78

Nuclear Power Plant http://www.nrc.gov/reactors/power.html

nuclear chemistry. discovery of radioactivity radiation - energy emitted in the form of...

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