Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 56 (2023)
RIKEN
Accel. Prog. Rep. 56 (2023)

Source preparation technique for Ag211 At for alpha spectroscopy
S. Fujino,∗1 T. Kojima,∗2 K. Mori,∗1 T. Yamada,∗1,∗3 Y. Wang,∗4 X. Yin,∗4 and H. Haba∗4211

At has attracted a considerable amount of interest
because of its potential advantages in targeted alphatherapy. High-resolution alpha spectrometry is one of
the most important techniques in radiochemical analyses and precise radioactivity measurements. Electroplating is widely used as a conventional technique toprepare α sources. However, there are several diﬃculties in applying this method to the measurement of211
At such as its short half-life and high volatility. To
overcome such diﬃculties, we studied another practical
approach using a Ag plate without electroplating.
In this study, carrier-free 211 At was producedby the 209 Bi(α, 2n)211 At reaction using the RIKEN
AVF cyclotron.1) Three diﬀerent chemical forms of
100 kBq/mL of 211 At solutions were prepared as listed
in Table 1. To reduce the radioactivity loss due to thevolatility of At, ascorbic acid (AA) was added to solution (II) considering the result of a previous study onAt retention using AA by Toyoshima et al.2) At is also
expected to have stable alkalinity; thus, NaOH wasadded to solution (III). Ag plates with a thickness of0.1 mm were used to ﬁx 211 At. Approximately 30 µLof each 211 At solution in Table 1 was directly dropped
onto a Ag plate. Sources were dried in a desiccatorwith silica gel. After drying process, sources were measured using a ZnS (Ag) scintillation detector with a 2πgeometry to evaluate the deposition yield of 211 At onsilver. A Si detector was also used to obtain an α
spectrum from each source with the deﬁned sourcesdetector geometry in vacuum. In addition, imagingplate (IP) was used to conﬁrm the distribution of radioactivity in an active area on the Ag plate with 211 Atsolution (I).
Table 1. 211 At solutions used in the present study.

At solutions

Chemical form

(Ⅰ)

211At

211

At in H2O

(Ⅱ)

211At+AA

211

At in 1 µg/mL AA aqueous solution(Ⅲ)

211At+NaOH

At in 50 µg/mL NaOH aqueoussolution

2113.E+07Figure 1 shows the measured α spectra obtained bythree diﬀerent types of sources. Two major peaks of211At (Eα = 5.87 MeV) and 211 Po (Eα = 7.45 MeV)
∗1
∗2
∗3
∗4

were observed in each spectrum. As shown in Fig. 1,the 211 Po peaks obtained by source (II) shifted to thelower energy side by approximately 20 keV comparedto those for source (I). This could be due to selfabsorption caused by AA. However, the full width at
half maximum (FWHM) of the 211 At peak of source(II) increased by only 4 keV compared with that forsource (I); thus, it could not cause a large uncertainty
in the activity measurement. In contrast, a signiﬁcantdegradation in the spectrum was observed for source(III) compared with the two other sources. The deposition yield of each 211 At source was determined as aratio of the 2πα count rate to the activity of 211 At.
The resulting deposition yields were 88.3% ± 1.2%,
98.4% ± 1.3%, and 40.3% ± 6.8% for sources (I), (II),and (III), respectively, indicating that AA contributes
to the retention of 211 At during drying. However, theresults obtained for source (III) may be aﬀected by
self-absorption, resulting in underestimation of the deposition yield.
Figure 2 shows the distribution of 211 At on a Ag
plate for 211 At solution (I) with an IP. Although theGraduate School of Science and Engineering, Kindai University
School of Science and Engineering, Kindai University
Atomic Energy Research Institute, Kindai University
RIKEN Nishina Center- 162 -PSL intensity

211Fig. 1. Measured α spectra obtained by 211 At sources.

2.E+0725

1.E+071790.E+00

191725

1Pixel Number (30 pixels (=6 mm) in height and width)

Fig. 2. Distribution of 211 At on a Ag plate.

Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 56 (2023)

diameter of the 211 At solution drop before drying wasaround 6 mm, 99% of the radioactivity of the source
was concentrated within a diameter of 2 mm. In themeasurements with a deﬁned solid angle, an extensionof the active area might increase the uncertainty inthe evaluation of the geometric eﬃciency. Therefore,a source with a small active area, such as that prepared in the present study, could have the advantagethat the activity could be determined with a smaller
uncertainty.
References
1) Y. Wang et al., RIKEN Accel. Prog. Rep. 53, 192(2019).
2) A. Toyoshima et al., Radiat. Saf. Manage. 18, 13 (2019).

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