Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 52 (2019)

Measurement of impurity nuclides in 10.75 MeV/nucleon 136 Xe beamin the atmosphereT. Kambara∗1 and A. Yoshida∗1
On the basis of a fee-based facility sharing program,1)
private companies in Japan use 95 MeV/nucleon Ar and70 MeV/nucleon Kr beams from the RIKEN Ring Cyclotron (RRC) to simulate single event eﬀects (SEE) ofsemiconductor devices by high-LET components of thecosmic rays.2) Recently, the demand for heavier ionswith higher LET for the SEE test has signiﬁcantly increased, which has led us to prepare for fee-based Xeion irradiations. Because the samples are irradiatedin the atmosphere at RIBF, the beam passes throughvarious materials before the sample and fast secondary
nuclides produced by nuclear reactions in the materials
may contaminate the beam. We study the beam impurities with radiochemical measurements and previously
reported results for the Kr beam.3)
During a machine-study beamtime in February
2018, we measured the beam impurities of a
10.75 MeV/nucleon 136 Xe beam from RILAC2 andRRC. The setup at the E5A beamline is shown in Fig. 1.
The beam spot was spread with a pair of wobbler magnets on the beam line. The beam passed through aKapton window with a thickness of 25 µm and diameterof 50 mm into the atmosphere, followed by an ionization chamber (IC), AE-1341S, which was produced by
Applied Engineering Inc,4) to measure the beam intensity.
In the IC, the beam passed four 6 µm thick mylar foils
and a 15 µm thick Al-foil electrode. A test sample of aSi wafer (100 mm diameter and 0.5 mm thick) was attached directly to the exit of the IC to simulate semiconductor devices of clients. The total length of the beam
path in the atmosphere was approximately 39 mm. No
energy-degrader plates were used in these irradiations.
From the output-current measurement of the IC, thetotal number of primary Xe ions was estimated to beapproximately 1.17 × 1010 for a 10 minutes irradiation.
According to SRIM calculation,5) the energy of the primary Xe ions was approximately 2.3 MeV/nucleon at
the surface of the sample in which the ions stopped.
We measured the γ rays from the irradiated sample
with a Ge detector 12 times from 7 min to 17.2 days
after the irradiation. We analyzed the observed γ-ray
peaks according to the tabulated transition energies,lifetimes, and branching ratios,6) and identiﬁed 15 radionuclides from 135 Xe to 159 Ho. Then, we extrapolated
the decay curves of the radioactivity to the end of theirradiation time to obtain the production probabilitiesof the radionuclides normalized to one incident 136 Xeion.
Figure 2 shows the obtained nuclide-production prob∗1RIKEN Nishina CenterFig. 1. Schematic diagram (left) and photograph (right) of
the setup of irradiation.

Fig. 2. Measured production probabilities of radionuclides.
Because the tabulated γ-emission probabilities of 158 Ho
are in the relative values, the maximum probability is
assumed to be 100% of the parent decay.

abilities. Because the Xe ions in the sample had much
lower energy than the Coulomb barrier, all the observed
radionuclides were produced in the upstream materials
and implanted in the sample. The ratios of the observed radionuclides in the beam were below 10−4 andthe total impurity would be below 1%.
Dy (Z = 66) and Ho (Z = 67) can be produced onlyin the Al electrode of the ionization chamber. We suppose that the Ho-isotopes were produced through thecomplete nuclear fusion reactions followed by multiple
neutron emissions, and the observed 155 Dy and 157 Dy
were mostly the daughters of 155 Ho and 157 Ho, respectively.
References

1) http://ribf.riken.jp/sisetu-kyoyo/ (in Japanesetext).
2) T. Kambara, A. Yoshida, RIKEN Accel. Prog. Rep. 48,
239 (2015).
3) T. Kambara, A. Yoshida, Record of 2018 IEEE Radiation Eﬀects Data Workshop (REDW), p. 94.
4) http://www.o-yo-giken.co.jp/ .
5) J. F. Ziegler, http://www.srim.org/ .
6) R. B. Firestone, Table of Isotopes (Wiley Interscience,1998).

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