Isotope measurement

1. Isotope Measurements Based on Laser Spectroscopy

1.1 Upgrading Resonance Ionization Mass Spectrometry (RIMS)
-Development of RIMS Based on Isotope Selection with Doppler Shift of Laser Ablated Atoms-

DS-RIMS:
Absorption frequency is unique for each element because of its characteristic energy level. Absorption frequencies have slight differences between each isotope even in the same element.(the so-called Isotope Shift) Atoms with a given velocity in thermal motion feel the Doppler-shifted frequency and can absorb the phton with the absorption frequency of the adjacent isotope. Therefore, each isotope excited by the irradiation of narrowband laser has unique velecity. Isotope Analysis can be performed by its velocity difference (Fig.1).

Fig.1 Conceptual drawing of DS-RIMS

We successfully demonstrated that each isotope can be separately detected. New Isotope Analysis Technique (Fig.2)!!

Fig.2 Ca mass spectra obtained using DS-RIMS.

We won "Young Scientist Award (Best Ponster)" on International Conference on Laser Probing-LAP 2004 (Argonne, USA, 2004).

[Published papers]

1. Higuchi Y, Watanabe K, Kawarabayashi J, Iguchi T , "Development of trace isotope analysis using resonance ionization mass Spectrometry based on isotope selection with Doppler shift of laser ablated atoms", J. Nucl. Sci. Technol. 43 (2006) 334-338.
2. Y. Higuchi, K. Watanabe, J. Kawarabayashi,, T. Iguchi, "Trace Isotope Analysis Using Resonance Ionization Mass Spectrometry Based on Isotope Selection with Doppler Shift of Laser Ablated Atoms", KEK Proc. 2005-12 (2005) 170-176.

1.2 Applications of RIMS
-Origin Determination of Agricultural Products Based on Sr Isotope Analysis-

Water-soluble Sr isotope ratio in soil corresponds to geological age of that area. We, therefore, can identify an origin of agricultural products by measuring the Sr isotope ratio. The conventional mass spectrometers, such as ICP-MS, TIMS etc., need a lot of work and time for sample preparations to suppress the isobar interference. In this study, We have developed the origin determination technique based on Sr isotope analysis using laser ablation assisted RIMS (LA-RIMS).

We succesfully detected strontium with sub ppm level in agricultural products by LA-RIMS. The precision, however, is still not sufficient to identify an origin of agricultural products. We have to improve the detection efficiency as well as the precision.

Fig.3 LA-RIMS spectra obtained from a brown rice grain.

This research links to "Development of Strontium Isotope Analysis in Bones for Research on Ancient Migration Route."

[Published papers]

1. Watanabe K, Higuchi Y, Kawarabayashi J, Iguchi T , "Development of the isotope analysis technique for inorganic trace elements using laser ablation assisted resonance ionization mass spectrometry (LA-RIMS)", J. Nucl. Sci. Technol. 43 (2006) 325-329.

1.3 Isotoope Analysis Based on Cavity Ring-Down Absorption Spectroscopy Using Continuous Wave Laser (CW-CRDS)

Cavity Ring-Down absorption spectroscopy (CRDS) is one of the ultra long path absorption spectroscopies and has extremely high sensitivity. In this technique, a part of the incoming laser light is confined into an optical cavity, which consists of a pair of high reflection mirrors, and the intensity of the confined light exponentially decreases due to multi-reflection by mirrors and absorption by gas filled into a cavity. The decay rate depends on the concentrations of absorbing species. Although the pulsed laser are applied as a light source, we have developed the CRDS using continuous wave (CW) laser, whose linewidth is much narrower than that of the pulsed laser, for isotope analysis. For a CW laser, the light can be confined only under the on-resonance condition on the cavity length. When the cavity length is rapidly changed from on-resonance to off-resonance condition, the confined light gradually leaks and the leakage light intensity exponentially decreases (Fig.4).

We successfully demonstrated that ¹²CO₂ and ¹³CO₂ can be separately detected by CW-CRDS (Fig.5).
PROBLEM: Poor precision !! → We have to improve it by using the stronger absorption line at 2μm.

This research links to "Study on carbon cycling in forest based on carbon isotope analysis using laser spectroscopy".

[Published papers]

1. Tomita H, Watanabe K, Takiguchi Y, Kawarabayashi J, Iguchi T, "Rapid-swept CW cavity ring-down laser spectroscopy for carbon isotope analysis", J. Nucl. Sci. Technol. 43 (2006) 311-315.
2. H. Tomita, Y. Takiguchi, K. Watanabe, J. Kawarabayashi, T. Iguchi , "Radioactive Gas Monitoring Using Cavity Ring-down Laser Spectroscopy with CW Infrared Diode Laser" J. Radiation Protection Bulletin., Proc. ISORD-3 (2005) 179-182.

2. Development of Highly Sensitive Inductively Coupled Plasma Mass Spectrometry (ICP-MS) Using Sepation/Enrichment Technique

The use of ICP-MS (Inductively Coupled Plasma Mass Spectrometry) allows to perform the simultaneous multielement determination of major-to-ultratrace (ppb-sub-ppt level) elements in the samples. Therefore, ICP-MS are now employed for elemental analyses in various fields. However, seawater analysis is still a challenging research target, because the high contents of dissolved salt in seawater cause instrumental drift, isobaric polyatomic interferences, signal suppression and clogging of the sample introduction system in ICP-MS. We have developed the chelating resin-packed minicolumn to apply to preconcentration of trace metals in seawater for their determination by ICP-MS (Fig.6).

The trace elements in natural waters, such as ground water, river water and seawater, were determined by using the chelating resin-packed minicolumn (Fig.7).

[Published papers]

1. H. Haraguchi, Y. Zhu, R. Hattori, A. Itoh, and T. Umemura, "Multielement Analysis of Commercial Mineral Waters by Chelating Resin Preconcentration and ICP-MS," Biomed. Res. Trace Elements 15 (2004) 355-357.
2. A. Itoh, Y. Zhu, and H. Haraguchi, "Distributions of Major-to-Ultratrace Elements among the Particulate and Dissolved Fractions in Natural Water as Studied by ICP-AES and ICP-MS after Sequential Fractionation," Anal. Sci. 20 (2004) 29-36.
3. Y. Zhu, R. Hattori, E. Fujimori, T. Umemura, and H. Haraguchi, "Multielement Determination of Trace Metals in River Water Certified Reference Material (JSAC0301-1) by Micro-mist ICP-MS after 100-fold Preconcentration with a Chelating Resin-Packed Minicolumn," Anal. Sci. 21 (2005) 199-203.

3. Development of Dynamic Three-Dimensional Imaging Using Multi-pinhole Gamma Camera

We have developed the gamma camera combining Multi-pinehole collimator and high spatial resolution flat panel X-ray detector (FPD) for dynamic 3D imaging of RI tracer in vivo (Fig.8).

Fig.8 Principle of Dynamic 3D imaging using multi-pinhole gamma camera.

We successfully aquired 3D images by using prototype detector (Fig.9). We can aquire a image for about 10 seconds, if we can use a highly sensitive FPD.

Fig.9 Distribution of radiation source and reconstructed image.

[Published papers]

1. Takemoto H, Watanabe K, Kawarabayashi J, Iguchi T, Uritani A, "Development of dynamic three-dimensional multi-pinhole gamma camera", J. Nucl. Sci. Technol. 43 (2006) 344-347.