1:45 PM - 3:15 PM
[SGL21-P07] Pre-Dose effect in dose response of barite for ESR dating
Keywords:electron spin resonance, barite, dating, sea-floor hydrothermal activitiy
ESR dating of barite (BaSO4) has been shown to be practically useful for those occurring in the sea-floor hydrothermal area [1] and ages were obtained in samples taken in the sea-floor hydrothermal areas in Okinawa Trough and Ogasawara [2]. The main radiation source in those barite crystals is the Ra replacing Ba. The natural radiation creates SO3- radicals in barite, the amount of which is measured by electron spin resonance (ESR), and the natural radiation dose is estimated hence deduced the age of formation.
It is necessary to introduce the regeneration method, instead of the conventional additive dose method in order to obtain precise and reliable equivalent natural radiation dose, hence the accurate age, where the sample will be once heated to erase the natural signal, the dose response is obtained by irradiation, and the equivalent dose is obtained as the corresponding signal intensity in the regenerated dose response line of curve.
In the present paper, two samples were employed, one taken from a hydrothermal area in Okinawa Trough, for which ESR ages were estimated to be 70-150 yrs (Sample A), and the other taken in Izu-Ogasawara Arc, the age of which was estimated to be nil from its occurrence (Sample B). The samples were irradiated to 100, 300 and 1000 Gy, then heated at 400C to erase the signal The samples were again irradiated up to 500 Gy to see the dose response.
The observe dose responses for the Sample B were about the sample for those given the pre-doses while the sensitivity was found to be larger for larger pre-dose in Sample A. The correct radiation doses cannot be obtained for samples such as A, in which the sensitivity changes with pre-doses, when the regeneration method is employed. This would be why the dose recovery (a test to see if artificially given dose is obtained correctly) was not successful in the presentation we made last year.
References
[1] Okumura, T., Toyoda, S., Sato, F., Uchida, A., Ishibashi, J., Nakai, S. (2010) ESR Dating of marine barites in chimneys deposited from hydrothermal vents. Geochronometria, 37, 57-61.
[2] Fujiwara, T., Toyoda, S., Uchida, A., Ishibashi, J., Nakai, S., and Takamasa, A. (2015) Subseafloor Biosphere Linked to Global Hydrothermal Systems; TAIGA Concept, Springer, Tokyo, 369-386.
[3] Fujiwara, T. (2018), Ph.D Thesis, Okayama University of Science.
It is necessary to introduce the regeneration method, instead of the conventional additive dose method in order to obtain precise and reliable equivalent natural radiation dose, hence the accurate age, where the sample will be once heated to erase the natural signal, the dose response is obtained by irradiation, and the equivalent dose is obtained as the corresponding signal intensity in the regenerated dose response line of curve.
In the present paper, two samples were employed, one taken from a hydrothermal area in Okinawa Trough, for which ESR ages were estimated to be 70-150 yrs (Sample A), and the other taken in Izu-Ogasawara Arc, the age of which was estimated to be nil from its occurrence (Sample B). The samples were irradiated to 100, 300 and 1000 Gy, then heated at 400C to erase the signal The samples were again irradiated up to 500 Gy to see the dose response.
The observe dose responses for the Sample B were about the sample for those given the pre-doses while the sensitivity was found to be larger for larger pre-dose in Sample A. The correct radiation doses cannot be obtained for samples such as A, in which the sensitivity changes with pre-doses, when the regeneration method is employed. This would be why the dose recovery (a test to see if artificially given dose is obtained correctly) was not successful in the presentation we made last year.
References
[1] Okumura, T., Toyoda, S., Sato, F., Uchida, A., Ishibashi, J., Nakai, S. (2010) ESR Dating of marine barites in chimneys deposited from hydrothermal vents. Geochronometria, 37, 57-61.
[2] Fujiwara, T., Toyoda, S., Uchida, A., Ishibashi, J., Nakai, S., and Takamasa, A. (2015) Subseafloor Biosphere Linked to Global Hydrothermal Systems; TAIGA Concept, Springer, Tokyo, 369-386.
[3] Fujiwara, T. (2018), Ph.D Thesis, Okayama University of Science.