Modern Analytical Methods in Radiogenic Isotope Geochemistry A

Modern Analytical Methods in Radiogenic Isotope Geochemistry: A Semester Long Applied Course Jeff Vervoort Washington State University

Motivation: Finding a mechanism to train a group of students to use the laboratory safely and intelligently …so that the students: Understand what they are doing. Gain the skills and knowledge so that they can do further independent geochemical work (e. g. , thesis research, etc. )

Context Audience: This course is designed for beginning graduate students and advanced undergraduates. The pre-requisites for the course are Introductory Geochemistry and (ideally) radiogenic isotope geochemistry. Skills and concepts that students must have mastered: A basic understanding of chemistry and geochemistry is required. An understanding of the principles of radiogenic isotope geochemistry would be advantageous.

Structure of the Course Structure: This is a laboratory based course with lectures scheduled to provide background for the laboratory work. By necessity, the course is front-end loaded, with heavy scheduling of lecture and lab sessions at the beginning and a much lighter (scheduled) load at the end of the semester (but replaced with independent project).

Goals: Understand the principles behind different geochemical methods (e. g. , sample preparation; solution chemistry; mass spectrometry). Know the quality of the data (precision, accuracy). This is important for the correct interpretation of the data (not all data are created equal). Gain the skills and knowledge so that the students can do further independent geochemical work (e. g. , thesis research, etc. ). Think critically (question everything!).

Course Structure: Laboratory & Lecture Laboratory work drives the lectures

Projects: Group Project: Class works on one project collectively (e. g. , Rb-Sr and Sm-Nd isotope geochemistry) Individual Project: Students work on independent projects of their choosing

Lecture Introduction to the elements Geochemical behavior of the elements Sample preparation Ion chromatography Rb-Sr and Sm-Nd chromatography Use of isotopic tracers; principles of isotope dilution Determination of analytical blanks Fundamentals of mass spectrometry TIMS; MC-ICPMS; mass bias; interference corrections Data reduction Assessment of data (Precision, accuracy, quality) Interpretation of data Presentation of results (e. g. , epsilon values etc. )

Laboratory Introduction to the laboratory (including safety training) Fundamental laboratory techniques (mixing acids, pipetting) Titration of acids Cleaning protocol Sample dissolution and treatment Ion chromatography e. g. , Rb-Sr, Sm-Nd, Lu-Hf, Pb, etc. Collection of blanks Preparation of samples for mass spectrometry Mass spectrometry standards; unknowns; blanks Data reduction (mass bias & interference corrections, etc. )

…all lab and lecture topics are presented in the context of the group class projects

Group Project: Class works on one project collectively (e. g. , Rb-Sr and Sm-Nd isotope geochemistry) …end product: Submit short report on results (reduce, present, and interpret isotope data)

Laboratory Introduction to the laboratory (including safety training) Fundamental laboratory techniques (mixing acids, pipetting) Titration of acids Cleaning protocol Sample dissolution and treatment Ion chromatography e. g. , Rb-Sr, Sm-Nd, Lu-Hf, Pb, etc. Collection of blanks Preparation of samples for mass spectrometry Mass spectrometry standards; unknowns; blanks Data reduction (mass bias & interference corrections, etc. )

Lecture Introduction to the elements Geochemical behavior of the elements Sample preparation Ion chromatography Rb-Sr and Sm-Nd chromatography Use of isotopic tracers; principles of isotope dilution Determination of analytical blanks Fundamentals of mass spectrometry TIMS; MC-ICPMS; mass bias; interference corrections Data reduction Assessment of data (Precision, accuracy, quality) Interpretation of data Presentation of results (e. g. , epsilon values etc. )

Independent Project Proposal Students submit a proposal for their project Research Plan Details of the analytical methods Analytical work Students in charge of their own schedule End Products Written: Detailed methods section Oral: Presentation of research and results

What has worked (students): *This IS problem based learning *Students have learned to think critically *Hands-on techniques are an effective way to teach geochemical fundamentals (relevance) *Many unexpected (and very intriguing) results *Results have led to further work and impressive end products (presentations at meetings; providing the basis for thesis work and further research)

Independent Projects Examples: Sr-Nd isotopes in the Talkeetna Arc Hf-Nd isotopes in the Aleutian Arc Sr-Nd-Pb-Hf isotopes in mantle xenoliths Sr-Nd-Pb isotopes of Canary island volcanics HFSE chemical separation protocol Ca isotope chemistry and analysis Sr isotopes in stream and soil water Sr isotopes in paleosols LA-ICPMS zircon dating of lower crustal xenoliths

What has worked (Instructor): *Moves the instructor in new and unexpected directions (letting the genie out of the bottle) *Find out interesting things along the way (serendipity) *Can be used to set up new techniques in the lab

What has not worked: *Diverse interests in this course …students want different aspects from this course …hard to focus on the scientific literature in depth *Only works (in my class) with small numbers. *Very time consuming.

Challenges/Problems: *Diverse interests in this course …students want different aspects from this course …hard to focus on the scientific literature in depth *Time consuming *This kind of course can only accommodate a few students *Scheduling (irregular hours; irregular times throughout the semester) *Need to start with a common (group) project so that students can help each other (avoids chaos) *Project results may not be interesting

Applicability: *This course grew out of my needs at WSU, but has applicability to other departments and situations --applicable to other analytical techniques --senior thesis work --promoting undergraduate research

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