5:15 PM - 6:30 PM
[SCG47-P06] Towards the zircon alpha recoil track dating: Test of americium radiation source
Keywords:ART, age determination
In the earth sciences, dating is one of the most fundamental data sources that provide a time scale for past phenomena. Alpha recoil track (ART) dating observes radiation damage formed by the recoil of the parent nuclide during alpha decay. Hayasaka et al. (2018) performed ART dating on zircons, but the estimated ages were younger than expected. Possible reasons of age underestimation are (1) unreliable counting of ART and (2) less understanding of ART formation process in zircon. In order to investigate ART formation, it is necessary to artificially generate ARTs in zircon and observe them. The purpose of this study is to establish a method to artificially create ART in minerals.
Hashimoto et al., (1980) successfully formed ART artificially in muscovite by an experiment using 252Cf. However, since 252Cf not only undergoes alpha decay but also spontaneous fission, there is a risk of contamination of the surrounding area due to the sputtering phenomenon. Therefore, we tested whether the same experiment is possible using 241Am. Two sources were used: a 3MBq americium source from the Isotope Science and Engineering Research Facility of Kanazawa University, and an americium solution electrodeposited on a metal plate. Muscovite samples were irradiated under the vacuum by placing them on top of the radiation source, during a certain period of time, and then etched to check if ARTs are formed. Number of tracks were counted for 20 screens with the size of 1mm squares.
Although various irradiation patterns were tried, the number of tracks did not increase significantly after the irradiation. Because 3MBq americium source is covered with 1~2μm of gold and palladium, this coating may prevent the daughter nuclides from being ejected in the sample direction. In case of the electrodeposited plates that we made, no increase of ARTs was found. Attached americium concentration may be too low to create the significant number of ART. Therefore, experimental procedure should be modified to create an electroplated source with a higher concentration.
Hashimoto et al., (1980) successfully formed ART artificially in muscovite by an experiment using 252Cf. However, since 252Cf not only undergoes alpha decay but also spontaneous fission, there is a risk of contamination of the surrounding area due to the sputtering phenomenon. Therefore, we tested whether the same experiment is possible using 241Am. Two sources were used: a 3MBq americium source from the Isotope Science and Engineering Research Facility of Kanazawa University, and an americium solution electrodeposited on a metal plate. Muscovite samples were irradiated under the vacuum by placing them on top of the radiation source, during a certain period of time, and then etched to check if ARTs are formed. Number of tracks were counted for 20 screens with the size of 1mm squares.
Although various irradiation patterns were tried, the number of tracks did not increase significantly after the irradiation. Because 3MBq americium source is covered with 1~2μm of gold and palladium, this coating may prevent the daughter nuclides from being ejected in the sample direction. In case of the electrodeposited plates that we made, no increase of ARTs was found. Attached americium concentration may be too low to create the significant number of ART. Therefore, experimental procedure should be modified to create an electroplated source with a higher concentration.