radiation CHM 102 Sinex radiation ionize electrons break

radiation CHM 102/Sinex

radiation ionize electrons break bonds Source: http: //www. arpansa. gov. au/basics/ion_nonion. htm

…and now ionizing radiation Which form of radiation is the most penetrating? Which form of radiation is the most biological damaging?

Penetrating Power of Radiation a b g paper 0. 5 cm lead 10 cm lead Relative penetration power a: b: g 1: 100: 10, 000

…and now a pop quiz Most penetrating form of radiation? a b g wrong correct Easiest form of radiation to shield from? a b g correct wrong

Radiation Damage g-ray What happens when the water molecule is struck by the gamma ray? H water molecule . . 2 OH H 2 O 2 . OH (hydroxyl radical)

ü All forms of nuclear radiation are considered ionizing radiation. There energy is large enough to ionize electrons from a molecule. H 2 O + + e ü Ar Ar+ + e- This formation of ion pairs is the basis of the Geiger Counter. ü In some cases even bonds are broken. The products. formed can be extremely reactive, such as the OH radical! ü See how water and radiation can interact or the radiolysis of water – click here

Radiation Damage Radiation weighting factor, WR or relative damage that can be caused in a biological system. WR alpha 20 fast neutron 10 slow neutron 5 beta 1 gamma rays 1 Source: http: //www. euronuclear. org/info/encyclopedia/d/dose. htm Increasing biological damage Radiation

Why does an alpha particle have a high WR or cause a large amount of biological damage? answer Although alpha particles travel only short distances, they are massive and cause major damage in their path. Alpha particles are much more dangerous when inhaled or ingested compared to external exposure. Why? answer Clothes and dead skin cells provide shielding externally, while internally alpha particles have direct contact with cells.

Radiation detection Geiger-Mueller tube High voltage 800 -1200 v cathode Ar (g) anode + Ion pair formation: Ar Ar+ + e. Current flows due to production of ion pairs. thin window of mica incoming radiation a, b , or g

Radiation Protection U source detector How does the radiation level vary if the detector is moved away? start

Radiation Protection U source detector

Derive the mathematical relationship between activity and distance. Distance, m 1. 0 2. 0 3. 0 4. 0 5. 0 answer Activity, cpm 500. 0 125. 0 55. 6 31. 3 20. 0 This is known as the inverse square law. The intensity of the radiation drops as the square of the distance.

Radiation protections involves: • Shielding • Distance • Time of exposure So use these three factors to address the next slide.

lead-lined walls Rank the laboratory workers in terms of their safety 2 4 1 How could person 1 improve there hazardous situation? Limit time of exposure! 3 highly radioactive g-source safest: _____ > _____ 2 4 3 1

Large-scale Nuclear Reactions Natural uranium: 0. 7% 235 U, 99. 3% 238 U Nuclear reactors: 3 - 4% 235 U enriched 235 U as fuel in US commercial electric power production – controlled fission different kinetics! Nuclear weapons: 90% 235 U enriched atomic bomb: uncontrolled fission 235 U 239 Pu (Pu produced in spent fuel of nuclear reactors) H-bomb: fission-fusion - larger scale energy release How do you separate isotopes, same chemistry?

Isotope separation Calutron: production-scale mass spectrometer to separated uranium metal ions (235 U for Hiroshima bomb) gaseous diffusion: Graham’s Law used UF 6 (s) UF 6 (g) at 56 o. C to separate 235 UF 6 from 238 UF 6 gas centrifuge: spin mixture of 235 UF 6 and heavier gas to outside, lighter in center 238 UF 6 http: //en. wikipedia. org/wiki/Enriched_uranium

Where are most nuclear reactors located? World map of nuclear reactors http: //www. insc. anl. gov/pwrmaps/map/world_map. php

Oklo: Natural Nuclear Reactors 1. 7 – 1. 8 billion year old rock Level of 235 U was ~3% at that time TODAYü Many isotopes common in spent nuclear reactor fuel occur in rock ü 235 U is depleted to as low as 0. 44% (most 0. 7%) ü 239 Pu was naturally produced at Oklo http: //www. ocrwm. doe. gov/factsheets/doeymp 0010. shtml

Nuclear weapons Explosive power: 1 megaton = 106 tons of TNT Largest H-bomb tested: 50 Mtons Tsar Bomba (Russia) Atomic bombs used in wartime – Hiroshima: 60 kg 235 U 90, 000 deaths – Nagasaki: ~6. 4 kg 239 Pu 70, 000 deaths 13 kilotons 21 kilotons http: //en. wikipedia. org/wiki/Atomic_bombings_of_Hiroshima_and_Nagasaki

Fallout (airborne radionuclides) from weapons testing and reactor accidents • Atmospheric testing of nuclear weapons – 90 Sr in milk • Nuclear reactor accidents – Three Mile Island: 1979, radioactive gases released (Kr) – Chernobyl: 1986, radioactive nuclear fuel dispersed by chemical explosion, radiation measured globally!

Natural background radiation What is the largest source of to the average person? What is the largest source of background radiation to a person that smokes?

Sources of Background Radiation Source: http: //web. princeton. edu/sites/ehs/osradtraining/backgroundradiation/background. htm Estimate your background radiation exposure – click here If you smoke

Radioactive sources in your house Smoke detector 241 Am Gas mantles for camping lanterns 232 Th Constant glowing watch dials 3 H or 147 Pm while older vintage watches (pre 1970’s) 226 Ra Vintage orange plates Fiesta Ware and some older Cloisonné Jewelry 238 U based ceramic glaze http: //hps. org/documents/consumerproducts. pdf

Applications of Isotopes radioisotopes Nuclear medicine for diagnosis and treatment 99 m Tc, 131 I, t 1/2 = 6 hours, workhorse in nuclear medicine t 1/2 = 8 days, is used to diagnose and treat thyroid disorders Food irradiation to control pathogenic and spoilage bacteria 60 Co and 137 Cs Modern irradiation is mostly done with x-rays.

Dating objects Can determine N/No ratio using mass spectroscopy and calculate tage Consider using tritium, 3 H, with a half-life of 12. 32 yrs Present day rain water – 32 p. Ci/L water = No A 12 year old bottle of wine – 16 p. Ci/L A 25 year old bottle of scotch - 8 p. Ci/L 14 C with a t 1/2 = 5730 yr is used in archeology Parent/Daughter used in Earth Sciences for rocks an meteorites 235 U/207 Pb 0. 704 by 40 K/40 Ar 1. 25 by 238 U/206 Pb 4. 47 by 87 Sr/87 Rb 48. 8 by

stable isotopes Reaction mechanisms in chemistry The oxygen in the acetic acid is 16 O, while the ethanol contains 18 O. Which molecules does the OH group get removed from? The two paths below illustrate the possible reactions. The 18 O is all found in the ester. Mass spectroscopy is used to determine distribution of isotopes. answer