Lanthanum-138

Natural Occurrence and Challenges in Isotopic Separation

Naturally occurring lanthanum comprises two isotopes: stable ¹³⁹La (99.91%) and radioactive ¹³⁸La (0.09%) . The low abundance of ¹³⁸La necessitates advanced separation techniques to isolate it from the dominant ¹³⁹La. Electromagnetic separation (calutrons) and gas centrifugation are theoretically applicable but face practical challenges due to lanthanum’s high atomic mass and chemical reactivity . Industrial-scale enrichment remains limited, with most ¹³⁸La supplies derived from specialized isotopic enrichment facilities .

Isotopic Enrichment Techniques

Electromagnetic Separation

In this method, lanthanum ions are accelerated through a magnetic field, causing slight trajectory deviations based on mass differences. While effective for low-throughput research applications, scalability issues and energy costs limit its industrial use .

Laser Isotope Separation (LIS)

LIS exploits subtle differences in electron excitation energies between isotopes. For lanthanum, tunable lasers selectively ionize ¹³⁸La atoms, which are then separated via electric fields. Although theoretically promising, technical complexities in laser tuning and ionization efficiency hinder widespread adoption .

Chemical Exchange Methods

Ion-exchange chromatography using crown ethers or cryptands has been explored for lanthanum isotope separation. These ligands exhibit preferential binding to specific isotopes based on ionic radius differences. However, separation factors remain low (<1.005), requiring multistage processes for meaningful enrichment .

Synthesis of this compound Compounds

This compound Oxide (¹³⁸La₂O₃)

Enriched ¹³⁸La₂O₃ is synthesized via direct oxidation of metallic ¹³⁸La under controlled conditions:

$$4 \, \text{La} + 3 \, \text{O}$$2 \rightarrow 2 \, \text{La}2\text{O}_3

The reaction proceeds exothermically at 400–600°C, yielding a white crystalline solid . Post-synthesis, the oxide is purified through recrystallization from nitric acid to remove residual ¹³⁹La contaminants .

This compound Chloride (¹³⁸LaCl₃)

Metallic ¹³⁸La reacts with hydrochloric acid to form the chloride:

$$2 \, \text{La} + 6 \, \text{HCl} \rightarrow 2 \, \text{LaCl}$$3 + 3 \, \text{H}2

The product is dehydrated under vacuum at 200°C to obtain anhydrous ¹³⁸LaCl₃, a hygroscopic solid used in scintillator production .

These materials are used in nuclear physics research, radiation dosimetry, and scintillator manufacturing .

Research Applications and Recent Advances

Scintillator Detectors

LaBr₃:Ce crystals doped with natural lanthanum (containing 0.09% ¹³⁸La) serve as self-contained β-particle detectors. The isotope’s decay produces measurable signals without external sources, enabling precise β-spectroscopy . Recent studies achieved a 5% accuracy in low-energy β-spectra measurements using 3″×3″ LaBr₃:Ce detectors .

Key Physicochemical Properties

Types of Reactions: Lanthanum-138 undergoes several types of chemical reactions, including:

Oxidation: this compound reacts with oxygen to form lanthanum oxide (La₂O₃). This reaction occurs slowly at room temperature but can be accelerated at higher temperatures.

Reduction: this compound can be reduced by hydrogen to form lanthanum hydride (LaH₃).

Substitution: this compound can participate in substitution reactions to form various lanthanum compounds, such as lanthanum chloride (LaCl₃) when reacted with hydrochloric acid.

Common Reagents and Conditions:

Oxygen: For oxidation reactions, atmospheric oxygen is sufficient.

Hydrogen: For reduction reactions, hydrogen gas is used under controlled conditions.

Hydrochloric Acid: For substitution reactions, concentrated hydrochloric acid is commonly used.

Major Products Formed:

Lanthanum Oxide (La₂O₃): Formed from oxidation.

Lanthanum Hydride (LaH₃): Formed from reduction.

Lanthanum Chloride (LaCl₃): Formed from substitution with hydrochloric acid

Nuclear Physics and Radioactive Decay Studies

Overview
The decay of $^{138}\text{La}$ primarily occurs through electron capture (66.4%) and beta decay (33.6%), resulting in the formation of $^{138}\text{Ba}$ and the emission of gamma rays (1435.8 keV) and beta particles (255 keV) . The long half-life and low abundance (~0.09% in natural lanthanum) make it an ideal candidate for studying nuclear decay processes.

Case Study: Scintillator Detectors
Research has demonstrated the effectiveness of using lanthanum bromide ($\text{LaBr}_3:\text{Ce}$) scintillator detectors for measuring the beta energy spectrum emitted by $^{138}\text{La}$. These detectors allow for precise measurements of beta particle energies, which is essential for understanding the decay characteristics of isotopes undergoing second forbidden unique transitions . The experimental setup utilized advanced computational techniques to analyze the decay data, revealing significant deviations from expected results at low energies .

Gamma Spectroscopy

Overview
The unique properties of $^{138}\text{La}$ make it a useful isotope for gamma spectroscopy without the need for radioactive sources. The gamma emissions from its decay can be harnessed to calibrate detection systems effectively .

Application in Scintillators
The presence of $^{138}\text{La}$ in lanthanum halide scintillators ($\text{LaCl}_3:\text{Ce}$ and $\text{LaBr}_3:\text{Ce}$) can both complicate and enhance their performance. While its decay contributes to background noise in low-count spectra, it also provides a means for self-calibration due to its predictable gamma emissions . The energy resolution of these scintillators (3-4% at 662 keV) allows for improved detection capabilities compared to traditional sodium iodide detectors .

Geochronology

Overview
Recent studies have introduced innovative methods for using $^{138}\text{La}$ as a geochronometer, which involves measuring the ratio of $^{138}\text{Ba}$ produced from its decay to determine the age of geological samples . This technique is particularly beneficial for dating ancient rocks and minerals.

Case Study: Amîtsoq Gneiss
A study conducted on samples from the Amîtsoq gneiss in West Greenland applied this geochronological method, demonstrating its efficacy in determining geological timelines based on the decay rates of $^{138}\text{La}$ . The findings indicated that this method could provide more accurate age estimates than traditional radiometric dating techniques.

Biological and Medical Applications

Overview
Lanthanum compounds, including those containing $^{138}\text{La}$, have been investigated for potential applications in biological tracing and cancer treatment . The ion $\text{La}^{3+}$ serves as a biological tracer for calcium ions, which is crucial for various physiological processes.

Table 1: Properties of this compound

Table 2: Applications of this compound

The mechanism of action of lanthanum-138 primarily involves its radioactive decay processes. This compound undergoes beta decay and electron capture:

Beta Decay: Approximately 34% of this compound decays by converting a neutron into a proton, resulting in the formation of cerium-138 and the emission of a beta particle and a gamma photon.

Electron Capture: About 66% of this compound decays by capturing an electron, converting a proton into a neutron, and forming barium-138 along with the emission of a gamma photon.

These decay processes release energy in the form of gamma photons, which can be detected and measured, making this compound useful in various applications .

Comparison with Similar Isotopes

Comparison with Lanthanum-139

The stable isotope $^{139}\text{La}$ dominates natural lanthanum. Key differences are summarized below:

The stark contrast in abundance and stability underpins $^{139}\text{La}$’s dominance in industrial applications, while $^{138}\text{La}$’s radioactivity limits its utility.

Other Radioactive Lanthanum Isotopes

Over 36 artificial lanthanum isotopes (e.g., $^{137}\text{La}$, $^{140}\text{La}$) have been synthesized, but none occur naturally. Regulatory data from Wisconsin statutes indicate permitted microcurie values for these isotopes, reflecting their higher radioactivity and shorter half-lives compared to $^{138}\text{La}$ :

• $^{137}\text{La}$: 10 µCi
• $^{140}\text{La}$: 100 µCi
• $^{138}\text{La}$: 100 µCi

These isotopes are typically short-lived (hours to days) and produced via neutron irradiation or particle accelerators.

Comparison with Isotopes of Adjacent Elements

This compound shares characteristics with other long-lived primordial isotopes, such as:

Key Observations:

• $^{138}\text{La}$ has a shorter half-life than $^{115}\text{In}$ but longer than $^{176}\text{Lu}$, positioning it intermediately among primordial radionuclides .
• All three isotopes undergo beta decay, contributing minimally to natural background radiation due to their scarcity.

Lanthanum-138 ($^{138}\text{La}$) is a naturally occurring radioactive isotope of lanthanum, with a half-life of approximately $1.05\times 10^{11}$ years and an abundance of about 0.09% in natural lanthanum. Its biological activity is of interest due to its potential applications in medicine, environmental science, and its role in biological systems.

Lanthanum, as part of the lanthanide series, shares chemical similarities with calcium and other biologically relevant metals. This similarity allows it to participate in various biochemical processes. Recent studies have indicated that lanthanides, including lanthanum, can influence microbial growth and enzyme activity.

• Enzyme Activity : Research has shown that lanthanum can act as a cofactor for certain enzymes. For instance, studies involving the enzyme XoxF from Methylophilus methylotrophus demonstrated that lanthanum could be incorporated into the enzyme's structure, enhancing its catalytic activity compared to other lanthanides like cerium and neodymium .
• Microbial Uptake : The uptake mechanisms for lanthanides in bacteria suggest that they may utilize specific transport systems akin to those used for iron acquisition. Genetic studies have identified lanthanophore systems that facilitate the selective uptake of lanthanides, indicating their biological significance .

Case Study 1: Lanthanum Carbonate in Chronic Kidney Disease

A multi-center, placebo-controlled trial investigated the effects of lanthanum carbonate on cardiovascular markers in patients with stage 3b/4 chronic kidney disease (CKD). The study involved 278 participants and measured various biomarkers:

The results indicated no significant differences between the lanthanum carbonate and placebo groups regarding these markers, suggesting that while lanthanum may have some effects on mineral metabolism, its direct impact on cardiovascular outcomes in CKD patients requires further investigation .

Case Study 2: Environmental Impact and Microbial Growth

Lanthanum's role in promoting microbial growth has been documented in various studies focusing on its effects on plant growth and soil microorganisms:

• Bahiagrass Growth : A study showed that lanthanum significantly promoted root growth and photosynthetic activity in bahiagrass (Paspalum notatum). The presence of lanthanum improved the electron transport rate during photosynthesis without increasing chlorophyll content, indicating that it enhances photosynthetic efficiency rather than biomass accumulation .

The mechanisms through which lanthanum exerts its biological effects include:

• Metal Ion Substitution : Lanthanum can substitute for calcium in biological systems, affecting enzyme activities and metabolic pathways.
• Transport Systems : The identification of specific transporters for lanthanides suggests a sophisticated mechanism for their uptake in microbial systems, allowing them to thrive in environments where these metals are present .

Basic Research Questions

Q. What are the critical nuclear properties of Lanthanum-138 that influence experimental design?

La-138 has a half-life of $1.02 \times 10^{11}$ years, a spin of $5^+$, and a specific activity of $938.02 \, \text{Bq/g}$. Its decay constant ($\lambda$) is $2.13 \times 10^{-19} \, \text{s}^{-1}$, and it exhibits a metastable isomer ($^{138\text{m}}\text{La}$) with an excitation energy of $72.57 \, \text{keV}$ and a half-life of $116 \, \text{ns}$. These properties necessitate long-duration experiments and high-sensitivity detectors for activity measurements . Researchers must account for its low specific activity by optimizing sample mass and detector efficiency to minimize statistical uncertainties .

Q. Which spectroscopic techniques are most effective for characterizing La-138 in complex matrices?

Gamma spectroscopy is optimal for identifying La-138 due to its distinct decay pathways. Mass spectrometry (e.g., TIMS or ICP-MS) is recommended for isotopic abundance analysis, requiring calibration against certified reference materials. For nuclear magnetic resonance (NMR), La-138’s quadrupole moment ($+0.45 \, \text{barn}$) and gyromagnetic ratio ($3.56 \times 10^7 \, \text{rad T}^{-1} \text{s}^{-1}$) enable studies of local electronic environments, though its low natural abundance ($0.0888\%$) demands enriched samples .

Q. How does the metastable state 138mLa^{138\text{m}}\text{La}138mLa affect decay studies?

The $^{138\text{m}}\text{La}$ isomer introduces competing decay channels, complicating activity calculations. Researchers must differentiate between ground-state ($^{138}\text{La}$) and isomer decays using high-resolution gamma detectors or coincidence counting. Time-resolved spectroscopy can isolate the isomer’s $116 \, \text{ns}$ half-life, but requires precise timing calibration to avoid signal overlap .

Advanced Research Questions

Q. What experimental strategies mitigate challenges posed by La-138’s low specific activity?

• Sample Enrichment : Use neutron-activated or isotopically enriched La-138 to increase signal-to-noise ratios.
• Background Reduction : Employ passive shielding (e.g., lead-copper composites) and active veto systems to minimize cosmic-ray interference.
• Long-Term Data Acquisition : Implement automated counting systems with periodic calibration checks to account for instrumental drift over extended periods . Statistical methods like Bayesian analysis or Poisson regression are critical for interpreting low-count data, as standard Gaussian approximations may underestimate uncertainties .

Q. How can researchers resolve discrepancies in reported decay constants for La-138?

Discrepancies often arise from calibration errors or inhomogeneous sample matrices. To address this:

• Cross-Validation : Compare results across independent labs using traceable standards (e.g., NIST-certified sources).
• Systematic Error Analysis : Quantify uncertainties in detector efficiency, sample geometry, and dead-time corrections using Monte Carlo simulations .
• Meta-Analysis : Apply weighted least-squares fitting to aggregated literature data, prioritizing studies with documented uncertainty budgets .

Q. What statistical frameworks are suitable for analyzing La-138’s decay data in low-activity scenarios?

• Poisson-Bayesian Hybrid Models : Combine Poisson likelihoods for count data with Bayesian priors to incorporate prior knowledge (e.g., half-life estimates).
• Error Propagation : Use the Guide to the Expression of Uncertainty in Measurement (GUM) framework to propagate uncertainties from detector calibration, sample mass, and counting time .
• Threshold Filtering : Apply minimum detectable activity (MDA) criteria to exclude data points below the instrument’s detection limit, reducing false positives .

Q. How do La-138’s nuclear binding energy discrepancies impact theoretical models?

Reported binding energies vary by up to $1.24 \, \text{MeV}$ due to differences in mass spectrometry techniques. Researchers should:

• Benchmark Calculations : Compare experimental data with ab initio nuclear models (e.g., shell model or density functional theory) to identify systematic biases.
• Collaborative Databases : Contribute to repositories like the Atomic Mass Evaluation (AME) to improve global consistency .

Q. Methodological Guidelines

• Data Reporting : Adhere to the Beilstein Journal’s standards: report uncertainties to one significant digit beyond instrumental precision and avoid the term "significant" without explicit statistical testing (e.g., $p < 0.05$) .
• Ethical Replication : Document experimental protocols in supplementary materials, including raw data tables and instrument calibration certificates, to enable independent verification .