Measurement of high-dynamic-range thorium isotopic ratios using continuous-wave resonance ionization mass spectrometry

Journal Article · Fri Apr 15 00:00:00 EDT 1994 · Analytical Chemistry (Washington); (United States)

DOI:https://doi.org/10.1021/ac00080a014· OSTI ID:7267689

Tissue, B M ^[1]; Pickett, D A; Fearey, B L ^[2]

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1. Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States)
2. Los Alamos National Lab., NM (United States)

We have developed continuous-wave resonance ionization mass spectrometry (cw-RIMS) methods to measure [sup 230]Th/[sup 232]Th isotopic ratios. The overall Th ionization detection efficiency using a 1 + 1 RIMS process (narrow-band laser for the resonant step and a high-power ultraviolet- (UV-) Ar[sup +] laser for the ionization step) is 0.10%. Measurement of the [sup 230]Th/[sup 232]Th ratio (4.096 x 10[sup [minus]4]) of a laboratory standard shows that the cw-RIMS method has internal precision comparable to thermal ionization mass spectrometry measurements ([approximately] 0.5%, 2[sigma][sub m]), but introduces a small bias (2-4%), which is correctable by calibration with an isotopic standard. The bias is due to intrinsic laser-induced biases in the 1 + 1 RIMS process and in a nonresonant process due to the UV-Ar[sup +] laser alone, which contributes approximately 3% to the total Th[sup +] signal. Laser power dependence experiments show that neither the resonant nor the ionization step is entirely saturated; therefore, the isotopic bias is probably due to differences in the transition strengths of the isotopes. The reproducibility of the RIMS-induced bias is dependent on the reproducibility of the laser parameters, but can be kept within the precision of the measurements ([approximately] 0.5%). Ratio measurements of the 4.096 x 10[sup [minus]4] standard and of a sample of Table Mountain Latite demonstrates that cw-RIMS can accurately measure [sup 230]Th/[sup 232]Th ratios when the laser-induced biases are calibrated and kept constant. 41 refs.., 8 figs., 3 tabs.

• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 7267689
• Journal Information: Analytical Chemistry (Washington); (United States), Vol. 66:8; ISSN 0003-2700
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
58 GEOSCIENCES
THORIUM 230
MASS SPECTROSCOPY
THORIUM 232
CALIBRATION
COMPILED DATA
EVALUATION
IONIZATION
ISOTOPE DATING
ISOTOPE RATIO
LASERS
ACTINIDE ISOTOPES
ACTINIDE NUCLEI
AGE ESTIMATION
ALPHA DECAY RADIOISOTOPES
DATA
EVEN-EVEN NUCLEI
HEAVY ION DECAY RADIOISOTOPES
HEAVY NUCLEI
INFORMATION
ISOTOPES
NEON 24 DECAY RADIOISOTOPES
NUCLEI
NUMERICAL DATA
RADIOISOTOPES
SPECTROSCOPY
SPONTANEOUS FISSION RADIOISOTOPES
THORIUM ISOTOPES
YEARS LIVING RADIOISOTOPES
400102* - Chemical & Spectral Procedures
400702 - Radiochemistry & Nuclear Chemistry- Properties of Radioactive Materials
580000 - Geosciences