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1-1 Lecture 1: RDCH 710 Introduction Class organization §Outcomes §Grading Natural actinide species §Ac, Th, Pa, U §U Transuranic synthesis and characterization.

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Presentation on theme: "1-1 Lecture 1: RDCH 710 Introduction Class organization §Outcomes §Grading Natural actinide species §Ac, Th, Pa, U §U Transuranic synthesis and characterization."— Presentation transcript:

1 1-1 Lecture 1: RDCH 710 Introduction Class organization §Outcomes §Grading Natural actinide species §Ac, Th, Pa, U §U Transuranic synthesis and characterization Lecture 1 notes based on LANL radiochemistry course

2 1-2 Course overview Unique chemical properties of actinide elements are described and related to their electronic characteristics Using nuclear properties in understanding actinide chemistry is provided. Presentations are given on exploiting the chemical behavior of the actinides in separation, the nuclear fuel cycle, environmental behavior, and materials. The goal of the course is to provide students with an understanding of the actinide elements for support in graduate education and research. §Breadth of research and applications of actinides §Address unifying concepts §Basis for further exploration of topics by students

3 1-3 Course outcomes Understand the role of oxidation-reduction reactions in actinides Evaluation and utilizing actinide speciation and complexation Understanding the impact of f-orbitals on actinide chemistry Ability to interpret spectroscopy of the actinides Ability to discuss in detail the chemistry of various actinide elements Explain how to use actinide nuclear properties in experiments Understand the fundamental reactions that drive actinide environmental chemistry Understand and explain various separation methods for the actinides Describe and understand a range of actinide solid phases Understand the reactions behind synthesis of actinide compounds Basic understanding of computational actinide studies

4 1-4 Grading Classroom participation (15 %) 2 Exams (35 % each) §Based on homework Homework (15 %) §Based on lectures §In class assignment The examinations are based upon subject matter presented in class. Homework questions will be given primarily at the completion of the topic

5 1-5 #Date Topic 1Monday26-AugIntroduction: Discovery and synthesis of actinides 2Wednesday28-AugBrief generalized overview of actinide chemistry 3Monday02-SepHOLIDAY 4Wednesday04-SepChemistry of Actinium 5Monday09-SepChemistry of Actinium 6Wednesday11-SepNo Class: Reading chapters Ac, Th 7Monday16-SepNo Class: Reading chapters Pa, U 8Wednesday18-SepNo Class: Reading chapters Np, Pu up to metal 9Monday23-SepChemistry of Actinium 10Wednesday25-SepChemistry of Thorium 11Monday30-SepChemistry of Thorium 12Wednesday02-OctChemistry of Thorium 13Monday07-OctChemistry of Thorium 14Wednesday09-OctChemistry of Protactinium 15Monday14-OctChemistry of Protactinium 16Wednesday16-OctChemistry of Uranium 17Monday21-OctChemistry of Uranium 18Wednesday23-OctChemistry of Uranium 19Monday28-OctChemistry of Uranium 20Wednesday30-OctChemistry of Uranium (Take Home Quiz 1) 21Monday04-NovChemistry of Neptunium 22Wednesday06-NovChemistry of Neptunium 23Monday11-NovHOLIDAY 24Wednesday13-NovChemistry of Neptunium 25Monday18-NovChemistry of Neptunium 26Wednesday20-NovChemistry of Plutonium 27Monday25-NovChemistry of Plutonium 28Wednesday27-NovChemistry of Plutonium 29Monday02-DecChemistry of Plutonium 30Wednesday04-DecChemistry of Plutonium (Take Home Quiz 2)

6 1-6 Thorium Natural thorium consists 100% of the isotope 232 Th Thorium more common in nature than uranium §Basis of utility of thorium fuel cycle Average content in the earth's crust of 10 ppm §Pb about 16 ppm in the earth's crust Specific radioactivity for thorium lower than that of uranium §Longer Th half life 234 Th (t ½ = 24.1 d) is used after separation from natural uranium for tracer studies Different Th minerals §Monazite (phosphate minerals) §Sm monazite, also contains U §Range of oxides Thorium in sea water is < 0.5x10 -3 g/m 3 §Lower than uranium because of lower solubility of tetravalent state of Th Monazite sands Thorianite, ThO 2

7 1-7 Monazite Analysis: Age Mapping http://coe.nucl.nagoya-u.ac.jp/Cultural01_E.html

8 1-8 Alpha spectroscopy analysis

9 1-9 Uranium Natural uranium consists of 3 isotopes § 234 U, 235 U and 238 U §Members of the natural decay series Earth’s crust contains 3 - 4 ppm U §About as abundant as As or B U is also chemically toxic §Precautions should be taken against inhaling uranium dust àThreshold limit is 0.20 mg/m 3 air àSimilar to Pb U is found in large granitic rock bodies formed by slow cooling of the magma about 1.7 - 2.5 E 9 years ago

10 1-10 Uranium U is also found in younger rocks at higher concentrations called “ore bodies” §Ore bodies are located downstream from mountain ranges àAtmosphere became oxidizing about 1E9 years ago àRain penetrated into rock fractures, oxidizing the uranium to U(VI) àDissolving uranium as anionic carbonate or sulfate complexes àDissolved uranium migrated downstream, reducing material was encountered §Inorganic (pyrite) or organic (humic) matter àReduction to insoluble tetravalent compounds

11 1-11 Uranium For many minerals uranium is U(IV) §most important mineral is uraninite (UO 2+x, x = 0.01 to 0.25) Carnotite (a K + U vanadate) species U is often found in lower concentrations §Order of 0.01 - 0.03% in association with other valuable minerals àApatite (phosphate rock), shale, or peat URANINITE: UO 2 CARNOTITE K 2 (UO 2 ) 2 (VO 4 ) 2 1-3 H 2 O AUTUNITE Ca(UO 2 ) 2 (PO 4 ) 2 10 H 2 O

12 1-12 Uranium: natural levels and mining

13 1-13 In situ mining Acidic solution (around pH 2.5) Separation by ion exchange, solvent extraction, precipitation

14 1-14 Np synthesis Neptunium was the first synthetic transuranium element of the actinide series discovered §isotope 239 Np was produced by McMillan and Abelson in 1940 at Berkeley, California §bombarding uranium with cyclotron-produced neutrons  238 U(n,  ) 239 U, beta decay of 239 U to 239 Np (t 1/2 =2.36 days) §Chemical properties unclear at time of discovery àActinide elements not in current location àIn group with W Chemical studies showed similar properties to U First evidence of 5f shell Macroscopic amounts § 237 Np à 238 U(n,2n) 237 U *Beta decay of 237 U à10 microgram

15 1-15 Pu synthesis Plutonium was the second transuranium element of the actinide series to be discovered §The isotope 238 Pu was produced in 1940 by Seaborg, McMillan, Kennedy, and Wahl §deuteron bombardment of U in the 60-inch cyclotron at Berkeley, California à 238 U( 2 H, 2n) 238 Np *Beta decay of 238 Np to 238 Pu §Oxidation of produced Pu showed chemically different 239 Pu produced in 1941 §Uranyl nitrate in paraffin block behind Be target bombarded with deuterium §Separation with fluorides and extraction with diethylether §Eventually showed isotope undergoes slow neutron fission

16 1-16 Am and Cm discovery Problems with identification due to chemical differences with lower actinides §Trivalent oxidation state 239 Pu( 4 He,n) 242 Cm §Chemical separation from Pu §Identification of 238 Pu daughter from alpha decay Am from 239 Pu in reactor §Also formed 242 Cm Difficulties in separating Am from Cm and from lanthanide fission products

17 1-17 Bk and Cf discovery Required Am and Cm as targets §Needed to produce theses isotopes in sufficient quantities àMilligrams §Am from neutron reaction with Pu §Cm from neutron reaction with Am 241 Am( 4 He,2n) 243 Bk §Cation exchange separation 242 Cm( 4 He,n) 245 Cf §Anion exchange

18 1-18 Cf data Dowex 50 resin at 87 °C, elute with ammonium citrate

19 1-19 Einsteinium and Fermium Debris from Mike test §1 st thermonuclear test New isotopes of Pu §244 and 246 àSuccessive neutron capture of 238 U §Correlation of log yield versus atomic mass Evidence for production of transcalifornium isotopes §Heavy U isotopes followed by beta decay Ion exchange used to demonstrate new isotopes

20 1-20 Higher Z intensity related to yield

21 1-21 Md, No, and Lr discovery 1 st atom-at-a-time chemistry § 253 Es( 4 He,n) 256 Md Required high degree of chemical separation Use catcher foil §Recoil of product onto foil §Dissolved Au foil, then ion exchange Nobelium controversy §Expected to have trivalent chemistry §1 st attempt could not be reproduced àShowed divalent oxidation state § 246 Cm( 12 C,4n) 254 No àAlpha decay from 254 No àIdentification of 250 Fm daughter using ion exchange For Lr 249, 250, 251 Cf bombarded with 10,11 B New isotope with 8.6 MeV, 6 second half life §Identified at 258 Lr

22 1-22 Overview Naturally occurring actinides §Th, U, and daughters §Decay chain Production of transuranic elements §New element eventually becomes target for heavier §Particles àNeutrons *Limitations of neutron reactions àCharged particles

23 1-23 Questions What are the course outcomes? What is the purpose of the course? How are the natural concentration considerations of thorium and uranium similar and different. What are some mineral phases of U and Th? How was Np discovered? How was Pu discovered? What is used to separate trivalent actinides? What elements were discovered during weapons testing? How were they made? Which elements are examined by atom-at-a-time methods?

24 1-24 Pop Quiz During the discovery of Np the isotope 239 Pu was also produced. Why was Pu not discovered in this experiment?

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