11:00 AM - 1:00 PM
[SGL23-P05] Experiments on the formation of alpha recoil tracks using Am and Cf radiation
Keywords:Alpha recoil track, age determination
Alpha recoil track (ART) is the damage produced by the recoil of nucleis through the alpha decay chain of 238U, 235U, 232Th. Since the decay constants of uranium and thorium are determined and the ARTs increase with time at a certain rate, the age can be calculated by measuring the number of ARTs and the parent uranium and thorium concentrations.
However, when the ART dating method was applied to zircons of known age, the age was calculated to be younger than expected (Hayasaka, 2018). This may be due to underestimation of the number of ARTs due to uncertainties in ART identification, or to the fact that the process of ART formation, e.g., registration efficiently and effect of etching, is unknown, making it impossible to know whether ARTs are increasing in proportion to the time. In order to confirm this, it is necessary to artificially produce ARTs in zircon and observe them.
In this study, we aim to establish a method to artificially create ART in minerals as a first step to confirm whether ART increases with time.
Artificial creation of ARTs
In order to artificially create ARTs, heavy elements that undergo alpha decay must be applied to the mineral surface. A disc type alpha radiation sources is used, and ARTs are formed when nuclei moved by alpha-decay migrate toward the mineral. Nakashima et al. (2021) used a self-made 241Am source and a 3MBq 241Am metal plate, but it did not work well due to low concentration or coating on the source. In the present study, one 241Am sources (300 Bq) and two 252Cf sources (100 Bq and 1 kBq) were tested. The irradiation experiments were carried out at the Institute for Integrated Radiation and Nuclear Science, Kyoto University. The irradiation times were 1 day and 2 weeks for the Am source, and 5 minutes, 10 minutes, and 1 day for the Cf source. In this study, flakes of muscovite were used as the irradiated samples for observation. The ARTs formed on muscovite can be easily observed with a microscope because of the clear cleavage surface does not require consideration of noise or polishing effects, and the ART can be enlarged by etching (Googen and Wagner, 2000).
Results
For the samples irradiated by the Am source, the number of etch pits increased as the irradiation time increased. In the case of the Cf source, radioactivity was too strong not possible to examine the ARTs due to too many fission tracks produced by spontaneous fission in both sources.
However, when the ART dating method was applied to zircons of known age, the age was calculated to be younger than expected (Hayasaka, 2018). This may be due to underestimation of the number of ARTs due to uncertainties in ART identification, or to the fact that the process of ART formation, e.g., registration efficiently and effect of etching, is unknown, making it impossible to know whether ARTs are increasing in proportion to the time. In order to confirm this, it is necessary to artificially produce ARTs in zircon and observe them.
In this study, we aim to establish a method to artificially create ART in minerals as a first step to confirm whether ART increases with time.
Artificial creation of ARTs
In order to artificially create ARTs, heavy elements that undergo alpha decay must be applied to the mineral surface. A disc type alpha radiation sources is used, and ARTs are formed when nuclei moved by alpha-decay migrate toward the mineral. Nakashima et al. (2021) used a self-made 241Am source and a 3MBq 241Am metal plate, but it did not work well due to low concentration or coating on the source. In the present study, one 241Am sources (300 Bq) and two 252Cf sources (100 Bq and 1 kBq) were tested. The irradiation experiments were carried out at the Institute for Integrated Radiation and Nuclear Science, Kyoto University. The irradiation times were 1 day and 2 weeks for the Am source, and 5 minutes, 10 minutes, and 1 day for the Cf source. In this study, flakes of muscovite were used as the irradiated samples for observation. The ARTs formed on muscovite can be easily observed with a microscope because of the clear cleavage surface does not require consideration of noise or polishing effects, and the ART can be enlarged by etching (Googen and Wagner, 2000).
Results
For the samples irradiated by the Am source, the number of etch pits increased as the irradiation time increased. In the case of the Cf source, radioactivity was too strong not possible to examine the ARTs due to too many fission tracks produced by spontaneous fission in both sources.