Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 47 (2014)

Method for preparing ultra-thin sources for low-energy particle
spectrometry
H. Kikunaga,∗1,∗2 H. Haba,∗1 and J. Kanaya∗1
Generally, internal conversion electrons originate
from the K shell. If the decay energy of a nuclear isomer is less than the binding energy of an inner-shellelectron, the emission of an electron from the shell
is forbidden, in which case the isomer interacts withouter-shell electrons. As a result, the probability ofinternal conversion is aﬀected by the outer-shell electron state, namely the chemical state. Examples of thistype of nuclides are 99 Tcm (2.17 keV) and 229 Thm (7.6eV). The goal of our research is to measure such lowenergy internal conversion electrons of various chemical states. For high-resolution energy spectrometry, it
is necessary to prepare radionuclides as a thin source.
In this report, we attempt to prepare an ultra-thinsource using the Self-assembled Molecular (SAM) technique. The performance of the SAM substrate wasinvestigated through radio-tracer experiments.
RIKEN Ag-based multi-isotope tracers and singleisotope tracers were used for the experiments. Themulti-tracers were produced by irradiation of a Ag
metal plate with a 14 N ion beam accelerated by theRIKEN Ring Cyclotron. Ag target material was removed by a precipitation method with the use of hydrochloric acid. Single-isotope tracers were preparedusing the AVF cyclotron at CYRIC, Tohoku University.
The procedure for the preparation of SAM substrates was similar to that described in Ref1) . An Al
plate 25 mm in diameter was polished and rinsed withdistilled water. After drying, the Al plate was treatedwith 1 vol.% 3-aminopropyltriethoxysilane (APTES)
in absolute toluene through chemical vapor deposition
in a self-made PTFE cell at 100 ◦ C for 2 h; subsequently, it was rinsed with methanol and absolutetoluene. Phosphonation of the terminal amino groupsof APTES was performed with phosphoryl chloride andγ-collidine in absolute acetonitrile, and the sample wasthen rinsed with absolute acetonitrile and distilled water. The coupling of the SAM substrate and radionuclides was carried out in an aqueous solution or an
isopropyl alcohol solution.
The bound radionuclides were assayed by γ-ray spectrometry with an HPGe semiconductor detector. A γray spectrum of a multitracer-SAM sample is shown inFig. 1. The γ-peaks of 46 Sc, 54 Mn, 65 Zn, 75 Se, 83 Rb,85Sr, 88 Zr, 88 Y, 101 Rh, and 102 Rhm are observed in thespectrum. By comparison of γ-peak counts of each nuclide, we found that the yield of nuclides with oxidation

states +3 and +4 is relatively high. On the other hand,
22Na and 57 Co were not detected, although these nuclides were included in the multi-tracer solution. Thistendency was found regardless of the reaction solvent
to be combined with radionuclides.
To conﬁrm the uniformity of the SAM source, theα source was prepared with 241 Am tracer and subjected to autoradiography. A photograph taken using
an imaging plate is shown in Fig. 2. The deviation of α
activity is observed at the upper-left part of the image.
This deviation probably originates from ﬁne scratcheson the Al plate. With the exception of this part, the αactivity is spread uniformly over the entire SAM substrate. Although there are still some problems, thepresent method will provide us with a reliable ultrathin source after some improvements.

∗1References∗2RIKEN Nishina Center
Research Center for Electron Photon Science, Tohoku University- 278 -Y

88Mn, 46Sc
54

102

75

101

102

102
Rhm
m
Rh

SeRh
Se, 88Zr
102
Rhm
85
Sr, 83Rb
102m
Rh

88

Y

75
Se, 101Rh
Rh
101

103

75

Counts / channel

104

101
100

0500

1000
Energy / keV

1500

2000

Fig. 1. An example of a γ-ray spectrum of a multitracerSAM sample.

Fig. 2. Photographic image of a 241 Am-SAM sample takenusing an imaging plate.

1) A. Shida et al.: Surf. Coat. Technol. 169-170, 686(2003).