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Reika Yokochi

Reika Yokochi is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Reika Yokochi rather than just read about it. In short: Reika Yokochi (横地玲果, born November 9, 1975 in Saga, Kyushu Prefecture, Japan; died on February 17, 2024 in Chicago, USA) was a Japanese geochemist who worked on the origin and geological behavior of volatile elements. She held the position of Research Professor in the Department of the Geophysical Sciences at the University of Chicago.

Reika Yokochi — main illustration
Reika Yokochi — illustration

Key takeaways

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Reference excerpt

Reika Yokochi (横地玲果, born November 9, 1975 in Saga, Kyushu Prefecture, Japan; died on February 17, 2024 in Chicago, USA) was a Japanese geochemist who worked on the origin and geological behavior of volatile elements. She held the position of Research Professor in the Department of the Geophysical Sciences at the University of Chicago. Yokochi led a laboratory specializing in the purification and analysis of noble gases for dating and tracing water circulation within Earth's crust.

Education and early career Yokochi completed her doctoral studies in earth sciences at National Polytechnic Institute of Lorraine (French: L'Institut National Polytechnique de Lorraine) in 2005, supervised by Bernard Marty. Her PhD thesis focused on understanding the origin of volatile elements in Earth. She identified noble gases of solar origin in Earth's deep mantle. She also worked out the contribution of 244Pu-decay (t1/2=81 Myr) to fissiogenic 136Xe* in the deep Earth, suggesting a protracted loss of volatiles from Earth's mantle. Between 2005 and 2008, she was a postdoctoral researcher with Neil C. Sturchio at the University of Illinois Chicago, after which she joined the University of Chicago as researcher in 2008.

Research activities Yokochi's research focuses on noble gas geochemistry. She uses noble gases radionuclides, notably Krypton-81 (81Kr; t1/2=230,000 yr), to study the age and circulation of groundwater in major aquifers worldwide, including the Nubian Sandstone Aquifer, Floridan Aquifer, and the geothermal waters of Yellowstone. Krypton-81 is produced by cosmic rays in the atmosphere and then dissolves into rainwater, eventually seeping into groundwater. The overall abundance of krypton in the atmosphere is only about 1.10 parts per million by volume (ppmv), and within this, the fraction of 81Kr is extremely small, about 5 × 10−13. Yokochi crafted a device capable of efficiently extracting krypton from vast quantities of groundwater, thus facilitating the accurate quantification of 81Kr using Atom Trap Trace Analysis (ATTA).

In a study of the Nubian Sandstone Aquifer in Israel's Negev Desert, Yokochi and colleagues utilized radiokrypton (81Kr) to date groundwater, discovering two major water recharge events. The first, about 38,000 years ago, originated from the Mediterranean, and the second, around 361,000 years ago, from the tropical Atlantic. These events, coinciding with periods of low orbital eccentricity, reveal the sensitivity of moisture transport to orbital forcing. The study highlights groundwater's potential as a record of ancient precipitation and long-term subsurface water storage. Application of 81Kr to the Floridan Aquifer revealed freshwater recharge from the Last Glacial Period. Additionally, it detected fossil seawater predating the Last Glacial Maximum, indicating slow seawater movement and a limited but significant exchange of solutes with the ocean, contributing to the aquifer's dolomitization. Yokochi also conducted experiments aimed at understanding how volatile elements are trapped in ices under conditions relevant to the formation of comets and icy moons. The results of those experiments showed that ice surfaces have heterogeneous adsorption energies, influenced by initial ice-deposition temperatures and thermal annealing. Adsorption sites with higher energy play a significant role at low pressures and higher temperatures, conditions relevant to the protosolar nebula. The experiments also showed that gas trapping occurs primarily through the burial of gas adsorbed on newly formed ice surfaces. Yokochi's experiments indicate that the formation temperature of comet 67P/Churyumov-Gerasimenko, as suggested by the observed Ar/H2O ratio, was around 40 K. Yokochi contributed to the analysis of gases in samples returned from the Ryugu asteroid by JAXA's Hayabusa2 mission.

Awards and recognition Yokochi received the Young Scientist Award from the Geochemistry Research Association of Japan in 2012; the same year, she was also named a NASA Planetary Science Early Career Fellow.

Personal life Reika Yokochi was married to Nicolas Dauphas, a fellow planetary scientist; the couple has two children. She died on February 17, 2024 from EGFR-driven lung cancer, a disease that disproportionately affects nonsmoking women of East asian ancestry. Air pollution by particles less than 2.5 microns in diameter seems to be a factor contributing to the onset of EGFR-driven lung cancer.

References

Illustrations

Reika Yokochi: Reika Yokochi (in the center) and fellow scientists extracting gases from a water production well in the Negev Desert.
Reika Yokochi (in the center) and fellow scientists extracting gases from a water production well in the Negev Desert.
Reika Yokochi: Variations in 136Xe*/4He* and 21Ne*/4He* in deep mantle samples from the Kola Peninsula reflect magmatic processes. By interpolating this correlation to the known 21Ne*/4He* production ratio of the mantle, Yokochi and Marty estimated the deep mantle 136Xe*/4He*, indicating that 33-60% of 136Xe* comes from decay of 244Pu (t1/2=81 Myr) while the rest comes from decay of 238U (t1/2=4.5 Gyr).[4]
Variations in 136Xe*/4He* and 21Ne*/4He* in deep mantle samples from the Kola Peninsula reflect magmatic processes. By interpolating this correlation to the known 21Ne*/4He* production ratio of the mantle, Yokochi and Marty estimated the deep mantle 136Xe*/4He*, indicating that 33-60% of 136Xe* comes from decay of 244Pu (t1/2=81 Myr) while the rest comes from decay of 238U (t1/2=4.5 Gyr).[4]
Reika Yokochi: 81Kr forms in the atmosphere from cosmic ray interactions. In the Sinai, rainwater dissolves this isotope and stable krypton, infusing it into groundwater at recharge sites. As groundwater flows from these sites, 81Kr decays. Analyzing the 81Kr/krypton ratio in groundwater from the Negev indicates a recharge time of 360 kyr.[6]
81Kr forms in the atmosphere from cosmic ray interactions. In the Sinai, rainwater dissolves this isotope and stable krypton, infusing it into groundwater at recharge sites. As groundwater flows from these sites, 81Kr decays. Analyzing the 81Kr/krypton ratio in groundwater from the Negev indicates a recharge time of 360 kyr.[6]

Worked examples

Example 1 — a first encounter with Reika Yokochi

Start with the simplest possible case. Write down what Reika Yokochi claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Reika Yokochi before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Reika Yokochi ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Reika Yokochi

In research
Reika Yokochi appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Reika Yokochi in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Reika Yokochi is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1975 births, 21st-century Japanese women scientists, Japanese geochemists, so understanding it makes those chapters shorter.
In everyday life
Look for Reika Yokochi outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.
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How to study Reika Yokochi in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Reika Yokochi means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Reika Yokochi out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Reika Yokochi in simple terms?

Reika Yokochi (横地玲果, born November 9, 1975 in Saga, Kyushu Prefecture, Japan; died on February 17, 2024 in Chicago, USA) was a Japanese geochemist who worked on the origin and geological behavior of volatile elements. She held the position of Research Professor in the Department of the Geophysical…

Why does Reika Yokochi matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Reika Yokochi?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Reika Yokochi.

Tags

  • 1975 births
  • 21st-century Japanese women scientists
  • Japanese geochemists
  • Living people
  • Scientists from Saga Prefecture

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