Interaction of the radiation with a molecule knocks an electron from the molecule. radiation a. Molecule ¾ ¾ ¾ ion + e - This can destroy the delicate balance of chemical reactions in living cells. The resultant changes might lead to genetic mutation, cancer, or cell death. The nuclei of rapidly dividing cells, such as those in bone marrow and lymph system are. Because cancer cells also rapidly divide, they are susceptible to the effects of ionizing radiation, which is why it can be used for cancer treatment. Intensity Vs Distance Effects of ionizing radiation on the human body vary with:. the of the radiation.. the from the body. a. The intensity of the radiation decreases with the square of the distance. I A d B = I d OR 3. the of exposure. B A 4. the inside or outside the body. a. a and b are not very dangerous outside the body because they can be stopped by several layers of clothing. b. a and b are much more dangerous when placed inside the body because they are taken up by surrounding tissue. c. alpha emitters are almost never used internally in medicine. Ch Page 3
5. amount of a. A dental hygienist shields a patient from radiation by: b. A dental hygienist protects themselves from radiation by: Problem: If radiation from a radioactive source is measured at 8 mci at a distance of 3.0 meters, what would it be at a distance of 9.0 meters? Problem: A beta emitting source gives 50 units of radiation at a distance of 4.0m. At what distance does the radiation drop to one tenth it s original value?.7 Detecting and Measuring Radiation Devices used for measuring radiation.. Photographic film badge. The film is protected from light, but other radiation can penetrate. Can identify if instrument shielding is faulty Or user practices are faulty Ch Page 4
. Scintillation counter. Add sample to a solution containing a phosphor that emits a unit of light for each a or b or g-ray that strikes it. 3. Geiger counter. As radiation enters the tube through a small window, it ionizes argon atoms and produces electrons conduct a tiny electric current between the walls and the center electrode. Measurement Units (you will not be asked about this section) Depend on what is being measured Decay Events / Decay Rate. Curie (Ci): Ci = 3.7 x 0 0 disintegrations/s (This is the decay rate for g of radium.) a. mci = millicurie = 0.00 Ci = 3.7 x 0 7 disintegrations/s b. mci = microcurie = 0.00000 Ci = 3.7 x 0 4 disintegrations/s Ch Page 5
. Becquerel - SI unit for measuring the number of radioactive disintegrations (decay events) occurring each second in a sample. a. Bq = disintegration/s Energy Absorbed. Rad (radiation absorbed dose) is the unit for measuring the amount of energy absorbed per gram of tissue exposed to a radiation source. a. Rad = R = x 0-5 J/g. Gray - SI unit for measuring the amount of energy absorbed per kilogram of tissue exposed to a radiation source. a. Gy = J/kg = 00 rad Ionizing Intensity. Roentgen is a unit for measuring the ionizing intensity of radiation. It measures the capacity of radiation to affect matter in general. Tissue Damage. Rem (roentgen equivalent for man) measures the amount of tissue damage caused by radiation. It takes into account the differences in energy for different types of radiation a.. Rem = the amount of radiation that produces the same effect as rad of X-rays. b. Sievert (Sv) - SI unit for tissue damage. Sv = 00 Rem.8 Artificial Transmutation Definition - the change of one element into another brought about by bombardment of an atom with a high-energy particle. Creates an unstable nucleus is the heaviest naturally occurring element. All trans-uranium elements have been produced by bombardment reactions. Ch Page 6
Preparation of Cobalt-60 Cobalt-60 is a man-made isotope used for radiation therapy of cancer patients. It s synthesis involves 3 steps:. Stable Fe-58 is bombarded with a neutron to form? 58 6Fe + 0n. Unstable Fe-59 decays by beta emission to from the stable product? 59 6Fe - 0 e + 3. Stable Co-59 is then bombarded with a neutron to form? 59 7Co + 0n Cobalt-60 decays by beta (and gamma) emission (t ½ = 5.3 years). These beta particles are then aimed at cancerous tumors. Tumors are more susceptible to radiation because they are. Problem: Bombardment of U-38 with an alpha particle yields a neutron plus what other nuclide?? 58 9 4 0 U + He n + Problem: Balance the following transmutation nuclear equations: 40 8 4 a) Ar + He p + 38 9 4 b) U + 3 He 4 n + 35 9 0 90 38 c) U + n Sr + Xe 0 43 54 + 0 n Ch Page 7
.9 Nuclear Fission and Fusion Lighter and heavier elements are less stable than mid-mass elements near iron-56. Fission: The fragmentation of heavy nuclei into smaller ones.. Heavy nuclei - gain stability and release energy if they fragment to yield mid-mass elements. Fusion: the joining together of light nuclei.. Light nuclei can gain stability and release energy if they fuse together. Trying to get more like most stable atom: Ch Page 8
Nuclear Fission. The huge amounts of energy that accompany these processes are the result of mass-to-energy conversions. They are predicted by Einstein s equation:. Doesn't occur in exactly the same way each time. 3. Uranium-35 - more than 400 different fission pathways with 800 fission products identified. a. A frequently occurring pathway b. 3 neutrons released induce 9 more fissions 7 neutrons Ch Page 9
chain reaction - a reaction that continues to occur even if the supply of neutrons from outside is cut off - if a small sample size - many of the neutrons escape before initiating additional fission events critical mass - a sufficient amount of radioactive nuclide that allows the chain reaction to become self-sustaining Enormous amounts of heat are generated during nuclear fission. a. Fission of.0g of U-35 can produce of energy. b. Some countries generate as much as 80% of their power through nuclear fission. c. Products of fission reaction are themselves still radioactive with very long half-lives. Problem: According to the following reaction, what other isotope besides tellurium-37 is produced by nuclear fission of U-35 35 37 9 U + 0n 5Te + 0n + Nuclear Fusion Fusion: the joining together of light nuclei.. Release enormous amounts of energy.. This is how the sun produces energy. Among the reactions are: 3 3 3 4 H+ H He He+ He He + H 3. Fusion of hydrogen nuclei - a potential power source. a. hydrogen isotopes are cheap and plentiful b. fusion products are non-radioactive and nonpolluting (helium) 4. Technical problems to achieving a practical and controllable fusion. a. to initiate the process, T = 40 x 0 6 K Problem: Complete the following fusion reaction H + H 0n + This is how we d like to produce our energy some day. Ch Page 0
The following material is not in the book. We will cover if there is sufficient time left at the end of the semester. USES OF FISSION TECHNOLOGY Nuclear Reactors Fuel: U-38 enriched with 3% The concentration of U-35 is too low to go supercritical. Fuel is in the form of UO encased in Zr or steel rods Heat from the decay reaction is used to heat water to steam to drive turbines. Steam must be cooled before being released, so usually located Control rods: made of Cd or B are used to slow down the reaction because they can Nuclear Reactor Schematic Ch Page
Atomic Bomb The force of the explosion of the conventional chemical explosive forces the two pieces of U-35 together. Together, they now have enough mass to reach critical mass and sustain a. USES OF FUSION TECHNOLOGY Unlike fission technology where we have found positive uses (nuclear power plants) and negative uses (atomic bombs), For fusion technology we have only fully mastered the limitations on the negative side. For the Hydrogen Bomb (H-bomb), which uses fusion of hydrogen, it achieves the required temperature by using For power generation this would be great because we would not have radioactive waste to dispose of, however, we have only done it on small scale. Question: What kind of container could we use to perform the reaction that would withstand the required temperature of 0 6 K? Ch Page