RIKEN Accel. Prog. Rep. 48 (2015)

Ⅱ-9. Instrumentation

Implantation of 7 Be and 22 Na beams for wear diagnostics application
A. Yoshida,∗1 T. Kambara,∗1 H. Takeichi,∗1 H. Yamaguchi,∗2 T. Nakao,∗2 D. Kahl,∗2 R. Uemoto,∗3 andN.Takahashi∗4
To develop a method for wear diagnostics of industrial material using RI beams,1,2) intense beams of 7 Be
(T1/2 = 53 days) and 22 Na (T1/2 = 2.6 years) provided
by CRIB were implanted in the surface of machineparts. Here we describe the generation and characterization of the RI beams.
The 7 Be beam was produced via H(7 Li,7 Be)n reaction. A beam of 5.7 MeV/A 7 Li2+ with an average intensity of 1.7 particle µA (pµA) was introduced
to CRIB and passed through a cryogenic H2 gas target at a pressure of 760 Torr and cooled by liquid
N2 to 90 K. The produced 7 Be4+ beam was introduced to a dedicated vacuum chamber at the F2 focal
plane. A position-sensitive Si detector (PSD, Hamamatsu S5378-02), an energy degrader, and a rotating
irradiation sample holder were installed in the chamber. The energy and proﬁle of the RI beam were measured using the PSD. The energy of the 7 Be beam was
4.16 MeV/A, and the beam spot size was 4.8 × 8.1 mm
in FWHM when the momentum spread was set to ±3.1%. The relatively large beam-spot size seems related
to a halo of the beam spot at the gas target. The implantation rate of the 7 Be beam was approximately 60
kBq/h, according to a gamma-ray measurement after
the implantation.
The 22 Na beam was produced via the H(22 Ne,22 Na)nreaction. A 6.1 MeV/A 22 Ne7+ beam with an averageintensity of 0.25 pµA was introduced to the H2 gas
target at 400 Torr and 90 K. The energy and size ofthe 22 Na11+ beam at F2 was 3.67 MeV/A and 4.7×4.3
mm in FWHM, respectively, with a momentum spreadof ±3.1 %. The implantation rate was approximately
0.3 kBq/h.
For wear-loss diagnostics, the depth proﬁle of implanted RI should be controlled and characterized accurately. The depth proﬁle was controlled using a rotating energy degrader that had eight foils of diﬀerent
thicknesses. The foils were circularly placed on a wheelof diameter 14 cm rotating at 12 rpm so that they crossthe RI beam path one by one. An additional degrader
foil can be mounted on a beam collimator with a diameter of 10 mm placed downstream of the wheel.
To study the implantation-depth proﬁle, we ﬁrst irradiated a stack of 2-µm-thick Al foils with the RI
beams, and measured the radioactivity of each foil witha Ge detector. Then we obtained the beam-energy
spectra by the PSD, and calculated the range distribution of the ions in Al with the SRIM code3) . Figure
∗1
∗2
∗3
∗4

RIKEN Nishina Center
Center for Nuclear Study, Univ. of Tokyo
S.H.I. Examination & Inspection, Ltd.
Sumitomo Heavy Industries, Ltd.

1 shows a case of a 22 Na beam with a narrow momentum distribution of ±1 % implanted to the stackafter the rotating degrader with a blank and seven Alfoils with thicknesses of 4.9, 7.6, 11.9, 16.9, 23.8, 27.4,
and 31.7 µm. The depth proﬁle with the stacked-foil
is shown by black circles as relative intensities of theradioactivity in the foils. The horizontal and vertical error bars indicate the thickness and the statisticalerror for each foil. The dotted line shows the SRIM
calculation of the range distribution from the energy
spectrum. Below a depth of 5 µm, the corresponding
energy spectrum could not be measured as it was below
the detector threshold. The triangles indicate normalized fractions of the foils obtained by re-binning therange spectrum according to the stack-foil thicknesses.
We multiplied a factor of 0.97 to the stopping power ofthe SRIM calculation for optimum agreement between
the stacked-foil measurement and the calculation.
The conventional stacked-foil method is reliable because it directly measures the implanted RI, but its
depth resolution is limited because assembling manythin foils as a stack is hard work. On the other hand,the energy measurement with a Si detector is simpler,
but the accuracy of the implantation-depth distribution depends on the range calculation. Here, we combined the two methods with a correction factor for theSRIM calculation results and obtained a continuous
implantation-depth proﬁle.

Fig. 1. Implantation-depth profile of 22 Na beam in stacked
Al foils.

References
1) A. Yoshida et al.: “Operation report of industrial cooperation team”, in this report.
2) A. Yoshida et al.: Nucl. Instr. Meth. B 317, 785 (2013).
3) J. F. Ziegler: “The SRIM code, the stopping and rangeof ions in matter”, http://www.srim.org.

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