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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

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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

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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

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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

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# Date   Topic1 Monday 26-Aug Introduction: Discovery and synthesis of actinides2 Wednesday 28-Aug Brief generalized overview of actinide chemistry3 Monday 02-Sep HOLIDAY4 Wednesday 04-Sep Chemistry of Actinium5 Monday 09-Sep Chemistry of Actinium6 Wednesday 11-Sep No Class: Reading chapters Ac, Th7 Monday 16-Sep No Class: Reading chapters Pa, U8 Wednesday 18-Sep No Class: Reading chapters Np, Pu up to metal9 Monday 23-Sep Chemistry of Actinium

10 Wednesday 25-Sep Chemistry of Thorium11 Monday 30-Sep Chemistry of Thorium12 Wednesday 02-Oct Chemistry of Thorium13 Monday 07-Oct Chemistry of Thorium14 Wednesday 09-Oct Chemistry of Protactinium15 Monday 14-Oct Chemistry of Protactinium16 Wednesday 16-Oct Chemistry of Uranium17 Monday 21-Oct Chemistry of Uranium 18 Wednesday 23-Oct Chemistry of Uranium19 Monday 28-Oct Chemistry of Uranium 20 Wednesday 30-Oct Chemistry of Uranium (Take Home Quiz 1)21 Monday 04-Nov Chemistry of Neptunium22 Wednesday 06-Nov Chemistry of Neptunium23 Monday 11-Nov HOLIDAY24 Wednesday 13-Nov Chemistry of Neptunium25 Monday 18-Nov Chemistry of Neptunium26 Wednesday 20-Nov Chemistry of Plutonium27 Monday 25-Nov Chemistry of Plutonium28 Wednesday 27-Nov Chemistry of Plutonium29 Monday 02-Dec Chemistry of Plutonium30 Wednesday 04-Dec Chemistry of Plutonium (Take Home Quiz 2)

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Thorium• Natural thorium consists 100% of the isotope

232Th• 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

• 234Th (t½ = 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/m3

§ Lower than uranium because of lower solubility of tetravalent state of Th

Monazite sands

Thorianite, ThO2

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Monazite Analysis: Age Mapping

http://coe.nucl.nagoya-u.ac.jp/Cultural01_E.html

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Alpha spectroscopy analysis

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Uranium• Natural uranium consists of 3 isotopes

§ 234U, 235U and 238U§ 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 à Threshold limit is 0.20 mg/m3 airà Similar 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

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Uranium

• U is also found in younger rocks at higher concentrations called “ore bodies”§ Ore bodies are located downstream from mountain ranges

à Atmosphere became oxidizing about 1E9 years agoà Rain penetrated into rock fractures, oxidizing the

uranium to U(VI) à Dissolving uranium as anionic carbonate or sulfate

complexes à Dissolved uranium migrated downstream, reducing

material was encountered§ Inorganic (pyrite) or organic (humic) matter

à Reduction to insoluble tetravalent compounds

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Uranium

• For many minerals uranium is U(IV)§ most important mineral is

uraninite (UO2+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 à Apatite (phosphate

rock), shale, or peat

URANINITE: UO2

CARNOTITE

K2(UO2)2(VO4)2• 1-3 H2O

AUTUNITE

Ca(UO2)2(PO4)2•10 H2O

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Uranium: natural levels and mining

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In situ mining

                                                                                       

Acidic solution (around pH 2.5)Separation by ion exchange, solvent extraction, precipitation

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Np synthesis

• Neptunium was the first synthetic transuranium element of the actinide series discovered§ isotope 239Np was produced by McMillan and Abelson in

1940 at Berkeley, California§ bombarding uranium with cyclotron-produced neutrons

à 238U(n,g)239U, beta decay of 239U to 239Np (t1/2=2.36 days)§ Chemical properties unclear at time of discovery

à Actinide elements not in current locationà In group with W

• Chemical studies showed similar properties to U• First evidence of 5f shell• Macroscopic amounts

§ 237Npà 238U(n,2n)237U

* Beta decay of 237Uà 10 microgram

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Pu synthesis• Plutonium was the second transuranium element of the actinide

series to be discovered§ The isotope 238Pu was produced in 1940 by Seaborg,

McMillan, Kennedy, and Wahl § deuteron bombardment of U in the 60-inch cyclotron at

Berkeley, Californiaà 238U(2H, 2n)238Np

* Beta decay of 238Np to 238Pu§ Oxidation of produced Pu showed chemically different

• 239Pu 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

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Am and Cm discovery• Problems with identification due to chemical

differences with lower actinides§ Trivalent oxidation state

• 239Pu(4He,n)242Cm§ Chemical separation from Pu§ Identification of 238Pu daughter from alpha

decay• Am from 239Pu in reactor

§ Also formed 242Cm• Difficulties in separating Am from Cm and

from lanthanide fission products

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Bk and Cf discovery

• Required Am and Cm as targets§ Needed to produce theses isotopes in sufficient

quantities à Milligrams

§ Am from neutron reaction with Pu§ Cm from neutron reaction with Am

• 241Am(4He,2n)243Bk§ Cation exchange separation

• 242Cm(4He,n)245Cf§ Anion exchange

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Cf data

• Dowex 50 resin at 87 °C, elute with ammonium citrate

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Einsteinium and Fermium

• Debris from Mike test§ 1st thermonuclear test

• New isotopes of Pu§ 244 and 246

à Successive neutron capture of 238U § 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

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• Higher Z intensity related to yield

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Md, No, and Lr discovery

• 1st atom-at-a-time chemistry§ 253Es(4He,n)256Md

• 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§ 1st attempt could not be reproduced

à Showed divalent oxidation state§ 246Cm(12C,4n)254No

à Alpha decay from 254Noà Identification of 250Fm daughter using ion exchange

• For Lr 249, 250, 251Cf bombarded with 10,11B• New isotope with 8.6 MeV, 6 second half life

§ Identified at 258Lr

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Overview

• Naturally occurring actinides§ Th, U, and daughters§ Decay chain

• Production of transuranic elements§ New element eventually becomes target for

heavier§ Particles

à Neutrons* Limitations of neutron reactions

à Charged particles

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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?

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Pop Quiz

• During the discovery of Np the isotope 239Pu was also produced. Why was Pu not discovered in this experiment?