12. Others

概要

TITLE:

12. Others

AUTHOR(S):

CITATION:

12. Others. KURNS Progress Report 2022, 2021: 239-254

ISSUE DATE:
2022-07

URL:
http://hdl.handle.net/2433/275854
RIGHT:

CO12-1 Determination of natural cobalt content as impurity in iron cyclotron yokes
G. Yoshida, K. Nishikawa1, K. Takahashi, H. Nakamura,
H. Yashima2, M. Inagaki2, S. Sekimoto2, T. Miura, A.
Toyoda, H. Matsumura, and K. Masumoto

Japan iron and steel federation were employed as references and prepared in the same way. For analysis of
short-lived nuclides generated by neutron irradiation,
samples were irradiated at Pn-3 with 1 MW during 10 s,
and measured with a Ge detector immediately after irradiation. Next day of 10s irradiation, samples were irradiated at Pn-2 with 5 MW during 3000 s, and measured
with a Ge detector after short lived nuclides were attenuated.

Radiation Science Center, KEK
1
Quantum Life and Medical Science Directorate, QST
2
Institute for Integrated Radiation and Nuclear Science,
Kyoto University
INTRODUCTION: In Japan, the number of establishment of accelerator facility had increased rapidly
since the 1990s. Most of them are cyclotrons for Positron
Emission Tomography (PET) drug production and are
expected to be decommissioned in the near future, considering their useful life. When the decommissioning of
accelerators, the generation of radioactive waste resulting
from activation and their disposal become significant
issue. Therefore, it is important to quantify the degree of
activation in the whole facility, and it can predict the
amount of generated radioactive waste accurately in order
to facilitate decommissioning.
We focused on the iron yoke of PET cyclotron which
accounts for a large amount of weight in the facility, and
developed the activation estimation tool using Monte
Carlo simulation. In this method, 3D-model which can
reproduce the actual cyclotron is established and the rate
of nuclear reactions for each modeling element is calculated by PHITS [1]. As a pilot study for this method, we
performed the calculation for the PET cyclotron at the
Nishina Memorial Cyclotron Center (MNCC) in the
Takizawa Research Institute of the Japan Radioisotope
Association in Takizawa City, Iwate Prefecture. The calculated reaction rate gradient agreed well with the radioactivity depth gradient of the actual yoke determined by
the core boring method. However, we could not discuss
whether the absolute values of radioactivity are consistent
or not because the concentration of cobalt which content
as impurity in the iron yoke has not been quantified.
In this study, we analyzed trace element concentrations in
some iron and steel samples with neutron activation
analysis (NAA) which suitable for trace element analysis
of ppm order. We have been used NAA for quantification
of trace elements in accelerator facility concretes [2],
though this is the first time to apply this method for metallic materials. The feasibility of NAA for determination
of trace elements in the steel sample was also verified in
this study.
EXPERIMENTS: Irradiation samples were prepared
from iron yoke of PET-cyclotron in NMCC. Chips were
taken from the surface layer where no activation was observed, using a drill. Iron chips were washed with boiled
water twice and with acetone, then dried and weighed by
100 mg as an irradiation sample. Japanese iron and steel
certified reference materials (JSS001-8, JSS003-7,
JSS050-8, JSS651-16, JSS-652-16) distributed by the

RESULTS: The results of the 10s irradiation showed
56
Mn and 28Al peaks in the γ-ray spectra of all samples.
Relative value of radioactivity was consistent with the
nominal values of manganese and aluminum in the
standard sample. We measured the 3000s irradiated samples with a Ge detector one month after irradiation. The
result of the long time irradiation showed 59Fe and 60Co
peaks in the γ-ray spectra of all samples, though that in
some samples the 59Fe peak was too large and masked the
60
Co peak. Remeasurement of these samples after the
59
Fe had decay enough are mandatory.
The cobalt concentration in the iron yoke of the NMCC
cyclotron was estimated to be approximately 40 μg/g.
From this value and the 60Co reaction rate, the radioactivity distribution was derived as shown in Fig.1 and agreed
very well with the actual radioactivity depth distribution.
In conclusion, it was found that aluminum, manganese,
and cobalt in iron samples in an accelerator can be determined accurately using NAA.

Fig. 1. Depth distribution of 60Co activity in the
iron yoke of PET-cyclotron at NMCC.

REFERENCES:
[1] G. Yoshida, H. Matsumura et al., The 3rd JSRM /
JHPS Joint Conference (1C5-4), online, 1-3. Dec. 2021.
[2] G. Yoshida, K. Nishikawa et al., J.Radioanal.
Nucl.Chem. 325 (2020) 801-806.

R2080
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CO12-2 Neutron Resonance Spectrometry for Nuclear Security and Safeguards Education

RESULTS: As shown in left part of Fig. 1, a resonance
dip of 109Ag was clearly observed in the time spectrum
with the sample of silver plate (thickness: 1.0 mm) successfully, with measurement of 60,000 sweeps and 20
msec. range. The accelerometer was running at 50Hz
with pulse-width of 4 micro sec. per pulse. The time
spectrum was recorded within about 20 minutes. The
energy of this dip was estimated to be 5.3 eV derived

300

count / usec

EXPERIMENTS: Samples of six different elements
(Ag, In, Mn, Co, Cd, U) were irradiated at
KURNS-LINAC to record neutron transmission spectrum.
A 3He proportional counter followed by a multiple-stop
time spectrometer (ORTEC EASY-MCS) was located
behind the sample at 13m experimental room and generated timing signal of neutron detection. A signal from the
accelerator was used as the start signal of the time spectrometer. The timing calibration between start signal and
output signal of the 3He proportional counter was performed with an oscilloscope by gamma-flash signal generated at the Ta target of the accelerator. The sample of
Uranium was arranged at in front of the neutron irradiation port and time spectra of neutron transmission were
recorded. Five students participated in the experiment
over computer network by Zoom meeting software.

CONCLUSION: We proposed pulsed neutron spectrometry as a candidate for the nuclear regulatory educational
course to deepen the understanding of the nuclides in
nuclear fuel cycle and performed online training program.
The results showed that online program was able to support for students to understand the difference of the
cross-sections of 235U and 238U for low energy neutron.

200

100

100
50

10
0
10-2

-1

10
time of flight (msec)

Fig. 1.

10

5
0.01

0

0.05 0.1
time of flight (msec)

0.5

1

ToF spectrum of Ag (left) and In (right).
2000

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90
80
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60
50
40
30
0.01

count / usec

INTRODUCTION: In order to support nuclear facility
regulations in Japan for safe use, it is necessary to develop educational training course with broad knowledge
associated with nuclear engineering. Nuclear facilities
include reprocessing, nuclear fuel factories, research facilities, etc. in addition to nuclear power plants, it is important to teach not only the knowledge of radiation, reactor physics, but also the physics of nuclear material
itself at each stage of the nuclear fuel cycle. The
knowledge of physical and chemical properties of nuclear
material is also needed for effective regulation. As a part
of this human resource development, we have proposed
an isotope ratio measurement training program with uranium using pulsed neutron spectrometry as a candidate
for the nuclear regulatory educational course to deepen
the understanding of the nuclides in nuclear fuel cycle.
Observation of the neutron resonance absorption phenomena of natural, enriched and depleted uranium will
develop the understanding of the isotope itself and the
properties of the nucleus of uranium. In this fiscal year,
as the pandemic of Covid-19 limited our student to travel
to Kyoto University, we tried to establish an online experiment to acquire neutron resonance absorption spectra
of various samples.

count/usec

Department of nuclear safety engineering, Tokyo City
University
1 KURNS
Research Reactor Institute, Kyoto University

from the source-detector distance of 12 m and dip position of 0.377 msec. The first energy level of 109Ag is 5.19
eV [1]. There is a good agreement between the experimental result and literature value. In right part of Fig. 1,
time spectrum with In plate (thickness: 1 mm) were obtained. There were three resonance dips corresponding to
115
In. We confirmed the dips corresponded to resonant
absorption energies of 1.46 eV, 3.85 eV, 9.07eV[1]. Fig. 2
shows the time spectrum of natural Uranium (left) and
enriched Uranium (right, 235U amount of 0.416 g) samples. We can observe three clear resonant dips corresponding to the first, second and third levels of 238U nucleus in the left part of Fig. 2. In the observed time spectrum of enriched U, we can see the first resonance wide
dip of 235U around 0.3 eV at TOF of 1.5 msec. and several weak resonance dips at 0.29 msec. and 0.34 msec. The
screen of the PC acquiring these spectra was shared with
online students through Zoom-meeting software. The
online students were able to observe the acquisition of
neutron transmission spectra in real time. The experimental system and conditions were explained online with
a video taken in the morning of the day when the experiment was carried out. Interviews with students after
training showed that the content of the experiment could
be understood online.

count/usec

J. Kawarabayashi, R. Sasaki, R. Watanabe, A. Miura, T.
Takeuchi, D. Ibuki and J. Hori1

0.05 0.1
0.5 1
time of flight (msec)

1000
900
800
700
600
500
400
300
0.01

0.5 1
0.05 0.1
time of flight (msec)

Fig. 2. ToF spectrum of natural U (left) and enriched
U (right).
REFERENCES:
[1] S. F. Mughabghab, Atlas of Neutron Resonances.

R3024
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CO12-3 Structural Analysis of Additives in Lubricants by Small-Angle X-ray Scattering
T. ...

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