核理研研究報告 第38巻 2005年

38 2005

38 2005

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Preface
This issue of Research Report of Laboratory of Nuclear Science reports research activities of the
LNS performed in the 2004 academic/ﬁscal year (April 2004, March 2005). Major research activities are
based on the electron accelerator complex consisting of the 300-MeV LINAC and the 1.2-GeV STB ring.
The accelerators have altogether provided a beam time of about 3,300 hours for various experiments
through the year.
In this year, ( γ, K0) measurements with the NKS spectrometer ﬁnished at the experimental hall 2,
where a construction of a larger spectrometer called New NKS spectrometer has been planned. A seriesof ( γ, η ) experiments have been performed with SCISSORS at the GeV γ-ray experimental hall using
a new tagging photon system. The measurements on (e, e'p) reactions have also been performed at theexperimental hall 2 by using a 200-MeV stretched beam extracted from the STB ring. Experiments oncoherent radiation were performed by using pulsed electron beams from the LINAC. Various radioactive
isotopes were produced by using high intensity beams below 50 MeV at the experimental hall 1. They
were served for element analyses as well as for detailed study of decay properties.
We hope that this Report will serve as a quick overview of the present LNS activities over a varietyof nuclear research ﬁelds.

Jirohta KASAGI
Director

Research Report of Laboratory of Nuclear Science
Volume 38, 2005
Contents
Ⅰ．Nuclear Physics
Ⅰ－１

Photoproduction of Neutral Kaons on Liquid Deuterium Target

1

Kyou Tsukada, Toshiyuki Takahashi, Takaomi Watanabe, P. Bydvžovský,Mitsuhiko Ejima, Yuu Fujii, Kenta Futatsukawa, Osamu Hashimoto,
Kentarou Hirose, Takatsugu Ishikawa, Satoru Kameoka, Hiroki Kanda,
Fumiaki Kato, Sari Kinoshita, Tadashi Kinoshita, Takeshi Kon, Osamu Konno,
Kazushige Maeda, Akihiko Matsumura, Yuusuke Miura, Fusashi Miyahara,
Haruhisa Miyase, Tadashi Nakabayashi, Kenichi Nonaka, Atsushi Ohtani,
Yuichi Okayasu, Masamichi Oyamada, Atsushi Sasaki, Hajime Shimizu,
Tadaaki Tamae, Hirokazu Tamura, Tatsuo Terasawa, Hiroaki Tsubota,
Satoshi N. Nakamura, Hiroshi Nomura, Mifuyu Ukai, Daisuke Uchida,
Hirokazu Yamauchi, Hirohito Yamazaki, Keisuke Yawata, and Masaki Wakamatsu
Ⅰ－２

Photoproduction of η-mesons off C and Cu Nuclei for Photon Energies below 1.1GeV

8

Tadashi Kinoshita, Hirohito Yamazaki, Hiroshi Fukasawa, Katsuya Hirota,
Takatsugu Ishikawa, Jirohta Kasagi, Atsushi Kato, Tomoyoshi Katsuyama,
Koichi Kino, Tadashi Nakabayashi, Kenichi Nawa, Kenyu Okamura, Yutaka Saitoh,Katsunori Satou, Mitsuhiro Sengoku, Koutaku Suzuki, Shinya Suzuki,
Tatsuo Terasawa, Hiroki Kanda, Kazushige Maeda, Toshiyuki Takahashi,
Yuichi Aruga, Hiroki Fujinoya, Akiko Iijima, Michitaka Itaya, Yusuke Ito,
Takahiro Iwata, Hiroshi Kato, Tomoyuki Kawamura, Takuma Michigami,
Masateru Moriya, Takahiro Sasaki, Yasuhisa Tajima, Sayuri Takita,
Tomohiro Noma, Masakazu Yamamoto, Hiroshi Yoshida, Yuuki Yoshida,
Osamu Konno, Tomoyuki Maruyama, and Tetsuhiko Yorita
Ⅰ－３

Comparison of the 40Ca(e, e'p) Cross Section at Low Momentum Transfer Region
with Relativistic Calculations

18

Ryo Hashimoto, Tadaaki Tamae, Takeji Fujibayashi, Osamu Hashimoto,
Kentaro Hirose, Takatsugu Ishikawa, Hiroki Kanda, Osamu Konno,
Kazushige Maeda, Haruhisa Miyase, Satoshi N. Nakamura, Masashi Nanao,
Itaru Nishikawa, Tsutomu Otsuki, Teijiro Saito, Yoshiyuki Sato,
Kazunori Takahashi, Hirokazu Tamura, Hiroaki Tsubota, Masaki Wakamatsu,
Hirohito Yamazaki, and Hiroyuki Yuki
Ⅰ－４

Test Operation of Spin-Filter Polarimeter for Deuteron
Itaru Nishikawa, Masayoshi Watabe, and Tadaaki Tamae

22

Ⅱ．RadiochemistryⅡ－１

Observation of α-decay of 229mTh Produced from 229Ac

25

Hidetoshi Kikunaga, Yoshitaka Kasamatsu, Koichi Takamiya,Toshiaki Mitsugashira, Mitsuo Hara, Tsutomu Ohtsuki, Hideyuki Yuki,
Atsushi Shinohara, Seiichi Shibata, Norikazu Kinoshita, Akihiko
Yokoyama, and Takashi Nakanishi
Ⅱ－２

Search for the Decay of 229mTh by Photon Detection

35

Yoshitaka Kasamatsu, Hidetoshi Kikunaga, Keiji Nakashima,
Koichi Takamiya, Toshiaki Mitsugashira, Takashi Nakanishi, Tsutomu Ohtsuki,
Hideyuki Yuki, Wataru Sato, and Atsushi Shinohara
Ⅱ－３

Life-time Measurement of 7Be in Beryllium Metal

36

Tsutomu Ohtsuki, Hideyuki Yuki, Masakatsu Muto, Jirohta Kasagi, and Kaoru Ohno
Ⅱ－４

Photon Activation Analysis of Impurities in KTa1-xNbxO3 Single Crystals

42

Kohji Shikano, Tsutomu Ohtsuki, Hideyuki Yuki, Kazuo Fujiura, and Masahiro Sasaura
Ⅱ－５

Distribution of 59Fe, 60Co and 85Sr as Low-level Radioactive Wastes Included in
Nonﬂammable Organic Materials in the Decomposition by Supercritical Water
with RuO2

48

Tomoo Yamamura, Isamu Satoh, Wataru Sugiyama, Mitsuyuki Takahashi,
Yoshinobu Shiokawa, Hiroshi Tomiyasu, and Tsutomu Ohtsuki

Ⅲ．List of Publication
55

Ⅳ．Approved Experiments
Ⅳ－１

Former Term in 2004

57

Ⅳ－２

Latter Term in 2004

58

核理研研究報告 第38巻 目 次
Ⅰ．原子核物理
Ⅰ－１

Photoproduction of Neutral Kaons on Liquid Deuterium Target1

塚田暁，高橋俊行，渡辺崇臣，P. Bydvžovský，江島光彦，藤井橋本治，広瀬健太郎，石川貴嗣，亀岡

木下

忠，近

中林

匡，野中健一，大谷岳志，今野優，二ツ川健太，覚，神田浩樹，加藤文章，木下沙理，

收，前田和茂，松村彰彦，三浦勇介，宮原房史，宮瀬晴久，篤，岡安雄一，小山田正学，佐々木厚，清水田村裕和，寺沢辰生．坪田博明，中村哲，野村肇，玉江忠明，洋，鵜飼美冬，内田大介，山内大和，

山崎寛仁，八幡啓介，若松正樹
Ⅰ－２

Photoproduction of η-mesons off C and Cu nuclei for photon energies below
1.1GeV木下

8忠，山崎寛仁，深澤宏司，広田克也，石川貴嗣，笠木治郎太，加藤篤志，

勝山知義，木野幸一，中林匡，繩

健一，岡村憲有，齋藤雄高，佐藤勝則，

千石光洋，鈴木耕拓，鈴木伸哉，寺沢辰生．神田浩樹，前田和茂，高橋俊行，
有賀雄一，藤野屋大樹，飯島晶子，板谷道隆，伊藤祐輔，岩田高広，加藤宏，

川村知行，道上琢磨，守屋昌輝，佐々木隆浩，田島靖久，瀧田さゆり，乃万智洋，山本正和，吉田浩司，吉田祐樹，今野
Ⅰ－３

收，丸山智幸，依田哲彦

Comparison of the 40Ca(e, e'p) Cross Section at Low Momentum Transfer Region
with Relativistic Calculations18

橋本亮，玉江忠明，藤林丈司，橋本治，広瀬健太郎，石川貴嗣，神田浩樹，

今野

收，前田和茂，宮瀬晴久，中村哲，七尾晶士，西川 至，大槻勤，

斉藤悌二郎，佐藤祥幸，高橋一憲，田村裕和，坪田博明，若松正樹，山崎寛仁，
結城秀行
Ⅰ－４

Test Operation of Spin-Filter Polarimeter for Deuteron西川22至，渡部政義，玉江忠明

Ⅱ．放射化学
Ⅱ－１

Observation of α-decay of 229mTh Produced from 229Ac
菊永英寿，笠松良祟，高宮幸一，三頭聰明，原篠原

Ⅱ－２厚，柴田誠一，木下哲一，横山明彦，中西Search for the Decay of

229m

光雄，大槻

Ⅱ－３

Th by Photon Detection

Ⅱ－４

渉，篠原

32
孝，大槻

勤，

厚

Life-time Measurement of 7Be in Beryllium Metal
大槻勤，結城秀行，孝笠松良祟，菊永英寿，中島啓二，高宮幸一，三頭聰明，中西
結城秀行，佐藤25

36

勤，結城秀行，武藤正勝，笠木治郎太，大野かおる

光量子放射化分析法による KTa1-xNbxO3単結晶中の不純物分析
鹿野弘二，大槻勤，結城秀之，藤浦和夫，笹浦正弘

42

Ⅱ－５

Distribution of 59Fe, 60Co and 85Sr as Low-level Radioactive Wastes Included in
Nonﬂammable Organic Materials in the Decomposition by Supercritical Water
with RuO2
山村朝雄，佐藤伊佐務，杉山48
亘，高橋三幸，塩川佳伸，冨安

博，大槻

勤

Ⅲ．論文リスト
55

Ⅳ．課題採択結果
Ⅳ－１

平成16年度前期

59

Ⅳ－２

平成16年度後期

60

Ⅰ．Nuclear Physics

Research Report of Laboratory of Nuclear Science, Tohoku University Vol. 38 (2005)

1(LNS Experiment : #2446, #2506)

Photoproduction of Neutral Kaons on Liquid Deuterium Target
K. Tsukada1, T. Takahashi1＊ , T. Watanabe1†, P. Bydžovský2, M. Ejima1, Y. Fujii1,
K. Futatsukawa1, O. Hashimoto1, K. Hirose1, T. Ishikawa3, S. Kameoka1‡, H. Kanda1,
F. Kato1, S. Kinoshita1, T. Kinoshita3, T. Kon1, O. Konno5, K. Maeda1,
A. Matsumura1, Y. Miura1, H. Miyahara3, H. Miyase1, T. Nakabayashi3, K. Nonaka1,
A. Ohtani1, Y. Okayasu1, M. Oyamada1, A. Sasaki4, H. Shimizu3, T. Tamae3,
H. Tamura1, T. Terasawa3, H. Tsubota1, S. N. Nakamura1, H. Nomura1, M Ukai1§,
D. Uchida1, H. Yamauchi1, H. Yamazaki3, K. Yawata1, and M. Wakamatsu1

3
4Department of Physics, Tohoku University, Sendai, 980-8578
2
Nuclear Physics Institute, 25068, R ež, Czech Republicˆ1

Laboratory of Nuclear Science, Tohoku University, Sendai, 982-0826

Department of Electrical and Electronic Engineering, Akita University, Akita, 010-8502

We have performed the experiment of K0 photoproduction on the liquid deuterium target with
Neutral Kaon Spectrometer (NKS) at LNS-Tohoku. The K0s were measured via K0S → π＋π－ decay channel
in the threshold region. The momentum spectra of K0 photoproduction cross sections were derived andcompared with the calculations using representative models.

§1. Introduction
The investigation of the kaon production on a nucleon by the electromagnetic interaction provides
invaluable information on the strangeness production mechanism, strength of meson-baryon coupling
constants and structure of hadrons, being labeled by the strangeness degree of freedom. Such studies
using beams of real photons and electrons have been conducted both experimentally and theoreticallysince the 1950' s, taking advantage of the electromagnetic interaction that is understood better than the
hadronic interaction. Until now, the experimental studies have been carried out in p(γ, K ＋)Λ, p(γ, K ＋)Σ0
and p(γ, K0)Σ ＋ reactions among six isospin channels [1-5]. However, no data have been measured forthe other three channels on a neutron. Theoretically, phenomenological models have been constructedbased on measured channels so far. The isobar models, Kaon-MAID [6] and SLA [7], were adopted in
the present analysis. The predictions of the photon energy dependence and the kaon angular
distribution of the other three channels on a neutron using these models are quite different.
Present address : Institute of Particle and Nuclear Studies (IPNS), High Energy Accelerator＊

Research Organization (KEK)†

Present address : Department of Physics, Gifu University, Gfu 501-1193‡

Present address : Computing Research Center, High Enegy Accelerator Research Organization (KEK)§

Present address : Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai, 980-8578

2
The lack of the key data for strangeness photoproduction of the three channels on a neutron is dueto the experimental difficulties to measure neutral kaons and to prepare a neutron target. The
measurement of these three strangeness production channels provides much information on thestrangeness photoproduction mechanism. In particular, the n(γ, K0)Λ reaction has following features.
(1) Since no charge is involved, the t-channel Born term does not contribute. (2) It is a mirror reaction top(γ, K ＋)Λ. For the hyperon resonance exchange terms, a coupling constant, gKΣN, changes its sign fromthe isospin symmetry, gK Σ = －gK+Σ , resulting the different interference effect. Furthermore, the number
0

0

n

0

p

of resonances to be considered is small in the threshold region. Therefore, the n(γ, K0)Λ reaction is
expected to play an essential role to investigate the strangeness photoproduction mechanism.
In this paper, we present the results of photoproduction of neutral kaons on deuterons near thethreshold.

§2. Experiment
We carried out the experiment of the d(γ, K0) reaction in the threshold region, Eγ = 0.8 ～ 1.1 GeV.
The K0s were measured in π＋π－ decay mode with Neutral Kaon Spectrometer (NKS) which we installedin LNS-Tohoku. Figure 1 shows a schematic view of NKS which consists of a dipole magnet of 107 cm
diameter and 60 cm gap with 0.5 T, straw drift chambers (SDC), cylindrical drift chambers (CDC), an
inner hodoscope (IH), an outer hodoscope (OH) and electron veto counters (EV). The detector
conﬁguration was symmetric against the beam line. The solid angle of NKS was about π sr. The CDC
and SDC were used to measure particle momenta in the horizontal plane by trajectory reconstruction.
The magnetic field map was calculated by TOSCA. IH and OH were used for the time-of-flightmeasurement and event triggers. The momenta and time-of-flights were used for the particle
identiﬁcation. As a trigger condition, we required more than two charged particles; at least one event
both in the left and right arms in coincidence with a tagger signal. EVs were employed to reduce theserious background triggered by γ → e＋e－ conversion. They covered vertically ± 2.5 cm in the horizontal
plane at OH's positions. The geometrical acceptance was reduced by 8 %.
The photon beam was generated from the 1.2 GeV electron beam via bremsstrahlung and its energy
was tagged by the STB-tagger system [8]. Typical tagged photon intensity was 2 × 106/sec and tagging
efﬁciency was 79 ± 1 %. Total experimental period was about 1000 hours.
In order to investigate the K0 elementary production process on a neutron, the liquid deuterium
target with a thickness of 3.2 cm was used. The target system was developed for this experiment andprovided the stable liquid-state deuterium during the experimental period [9]. The density of the target
was estimated to be 0.17 g/cm3 from the temperature of the target and the pressure.

3

Fig.1. Schematic view of the Neutral Kaon Spectrometer (NKS).

§3. Analysis
The momenta of particles were derived from the curvature of trajectories. Besides, the velocities ofparticles were calculated from the time of ﬂight and the ﬂight length. The e＋e－ events were removed byrejecting the events of which the vertex position was upstream the target. Figure 2(a) shows the vertex
point distribution of the π＋π－ events. An opening angle (η) cut of － 0.9 < cosη < 0.8 was applied in orderto remove the e＋e－ or vertex mis-reconstruction events. The vertex resolution was estimated to be 1.3
mm in RMS in the beam direction. Most of events were originated in the target. Backgrounds throughsuch as a multi pion productions, N＊ and ρ, whose production cross sections are much larger than thatof kaon production. Hence, no peak is observed in the invariant mass spectrum as shown in Fig. 2(b) for
events in the target region. K0 events are enhanced by selecting vertex points in the decay volume,
because K0S has a relatively long life time of cτ=2.68 cm. Figure 2(c) shows the invariant mass spectrum
when events in the decay volume are chosen. The peak of K0S is clearly seen as shown in the ﬁgure. The
number of K0 events is about 900 for the present data. In order to obtain the cross section, we deﬁned_ M(π＋ π－ ) < 0.54 GeV/c2. Momentum distributions of K0
the gate in the invariant mass spectrum, 0.46 <were obtained after subtracting background contributions. The origin of the backgrounds wereconsidered as (1) leakage from the target region due to the finite resolution of the vertex point
reconstruction, and (2) wrong combination betweenπ＋ from K0 andπ－ fromΛ. The ﬁrst one was estimatedfrom the events originated in the target region, and the second one was estimated by Geant4 simulation.
These estimations gave the shape of the backgrounds, and the magnitude of the backgrounds were
adjusted by ﬁtting the invariant mass spectrum. Figure 3 shows the ﬁtting result assuming a gaussian
for K0 and the shapes of backgrounds as estimated in the photon energy from 0.9 to 1.0 GeV (ELow) and4

Fig.2. (a) Vertex distribution for π＋π－ events. The beam comes from left to right. Events come mainly
from the target region. (b), (c) An invariant mass spectrum of π＋π－ events with the gate thatthe vertex is in the target for (b) and outside the target denoted by decay volume for (c).

form 1.0 to 1.1 GeV (EHigh).
The acceptance of NKS was calculated by a Geant4 simulation. The geometry of NKS wasconsidered realistically, and the position and time resolution of the detectors were taken into account.
Various analysis efﬁciencies were also estimated in the acceptance. Figure 4 shows the contour plot of
the acceptance map. We used the data with momentum (P) and angle (cosθ) of K0 in the effective regions
shown in the ﬁgure because the acceptance is very low out of these regions. In this paper, the results in
Region 1 are presented.

§4. Results and Discussion
The obtained momentum spectra of K0s are shown in Fig.5. The backgrounds contributions are
already subtracted. The integrated momentum range is limited as mentioned in the previous section.
The obtained spectra are compared with the calculations using the representative two models, KaonMAID [6] and Saclay-Lyon A (SLA) [7]. The lines represent calculations in the plane wave impulse
approximation framework using Bonn OBEPQ (One-Boson-Exchange-Potential in Q-space) deuteronwave function [10] by Bydžovský et al. [11]. The Kaon-MAID model is the only model to predict theelementary cross section of K0 photoproduction on a neutron assuming SU(3) symmetry. On the other
hand, SLA has an adjustable parameter for K0Λ photoproduction, since the ratio of the decay width
between the charged and neutral K1 resonance (RK K ) is unknown. In Kaon-MAID, this ratio was
011γ

obtained from the γ + p → K + Σ process. Therefore, the elementary cross sections of SLA are calculated0＋

assuming various rK K . Kinematical regions are also selected for the calculations similarly to the
1 γexperimental data.
Since we measured only K0, the Σ production process may contribute in addition to K0Λ production.
From the estimation using Kaon-MAID, the contributions of Σ production are negligibly small in the

5

Fig.3. Fitting results of invariant mass spectra in photon regions from 0.9 to 1.0 GeV (ELow, left)
and from 1.0 to 1.1 GeV (EHigh, right). The contribution around 0.4 GeV/c2 comes from thewrong combination background and that around 0.6 GeV/c2 comes from the leakage of thetarget events. The peak near 0.3 GeV/c2 comes from the e＋e－ events.

Fig.4.

The contour plot of the acceptance map of NKS. The effective regions, Region 1, Region 2
and Region 3, are overdrawn by solid lines.

ELow region and sizable large at lower momentum in the EHigh region. The prediction based on the
Kaon-MAID model is consistent with our data in the ELow region but too large in the EHigh region
even if the Σ contribution is involved. The spectra calculated by SLA with rK K = － 1.9 well account for
1 γ

the present results at both energy regions.
In the ELow region, the shape of the momentum spectrum in the laboratory system mainly depends
on the angular distribution in the center of mass system. From the momentum distributions using SLA
with various rK K values, it is favored that the K0 photoproduction on a neutron has a backward peak in
1 γ

the center of mass system.

6

Fig.5. Momentum dependences after the correction for efﬁciencies and subtraction of backgrounds.
The lines represent the calculations using Kaon-MAID (solid), SLA(rK K = － 1.6, dotted),
SLA(rK K =－1.9, solid), SLA(rK Kγ=－2.0, dashed), SLA(rK K =－2.5, solid) and SLA(rK K =－3.0,
dash-dotted). The photon energy ranges are from 0.9 to 1.0 GeV(ELow, left) and from 1.0 to
1.1 GeV(EHigh, right). Error bars are overdrawn for the (statistic) and (statistic ＋
systematic) errors.
1 γ

1 γ

1

1 γ

1 γ

§5. Summary
We have successfully measured neutral kaons, bombarding a liquid deuterium target with a photon
beam in the threshold region from 0.8 to 1.1 GeV. It was the ﬁrst data for K0 photoproduction on the
deuteron in this energy region. The momentum spectra of K0 production were compared with theoretical
spectra calculated assuming isobar models for the elementary process and a realistic deuteron wave
function for the target nucleus. The present experiment has demonstrated the usefulness of the neutralkaon measurement for the investigation of photo strangeness production reactions.

Acknowledgement
This work was supported by Grant-In-Aid for Scientiﬁc Research from The Ministry of Education ofJapan, Nos. 09304028, 12002001, 14740150 and 16GS0201.

References[1]

D. S. Carman et al.: Phys. Rev. Lett. 90 (2003) 131804.

[2]

J. W. C. McNabb et al.: Phys. Rev. C69 (2004) 042201.

[3]

K. H. Glander et al.: Eur. Phys. J. A19 (2004) 251.

[4]

M. Q. Tran et al.: Phys. Lett. B445 (1998) 20.

[5]

R. G. T. Zegers et al.: Phys. Rev. Lett. 91 (2003) 092001.

[6]

F. X. Lee, T. Mart, C. Bennhold, and L. E. Wright : Nucl. Phys. A695 (2001) 237.

7
[7]

T. Mizutani, C. Fayard, G. H. Lamot, and B. Saghai : Phys. Rev. C58 (1998) 75.

[8]

H. Yamazaki et al.: Nucl. Instr. and Meth. A536 (2005) 70.

[9]

H. Kanda et al.: Research Report of LNS, Tohoku University 37 (2004) 27.

[10]

R. Machleidt, K. Holinde, and C. Elster : Phys. Rept. 149 (1987) 1.

[11]

P. Bydzovsky, M. Sotona, O. Hashimoto, and T. Takahashi : private communications.

Research Report of Laboratory of Nuclear Science, Tohoku University Vol. 38 (2005)

8(LNS Experiment : #2371, #2397, #2413, #2433)

Photoproduction of η-mesons off C and Cu Nuclei
for Photon Energies below 1.1 GeV
T. Kinoshita1, H. Yamazaki1, H. Fukasawa1, K. Hirota1＊ , T. Ishikawa1, J. Kasagi1,
A. Kato1†, T. Katsuyama1, K. Kino1‡, F. Miyahara1, T. Nakabayashi1, K. Nawa1,
K. Okamura1, Y. Saitoh1, K. Satou1, M. Sengoku1, H. Shimizu1, K. Suzuki1,
S. Suzuki1, T. Terasawa1, H. Kanda2, K. Maeda2, T. Takahashi2§, Y. Aruga3,
T. Fujinoya3, A. Iijima3, M. Itaya3, Y. Ito3, T. Iwata3, H. Kato3, T. Kawamura3,
T. Michigami3, M. Moriya3, T. Sasaki3, Y. Tajima3, S. Takita3, T. Noma3,
M. Yamamoto3, H. Y. Yoshida3, Y. Yoshida3, O. Konno4, T. Maruyama5, and T. Yorita6
1

Laboratory of Nuclear Science, Tohoku University, Sendai 982-0826
2

3

Department of Physics, Tohoku University, Sendai 980-8578
Department of Physics, Yamagata University, Yamagata 990-8560
45
6

Ichinoseki National College of Technology, Ichinoseki 021-8511

College of Bioresource Sciences, Nihon University, Fujisawa 252-8510

Japan Synchrotoron Radiation Research Institute, Mikazuki 679-5198

The η-meson photoproduction cross sections have been measured on C and Cu targets for photon
energies between 600 and 1100 MeV to investigate the behavior of the S11(1535) resonance in a nucleus.
The excitation functions of the cross section as well as angular and momentum distributions ofη-mesons are in quantitative agreement with Quantum Molecular Dynamics (QMD) model
calculations, in which the η-meson emission processes other than the S11(1535) resonance are also
incorporated as proposed in the η-MAID model. It is shown that the excitation of the D15(1675)
resonance might play an important role for Eγ＞ 900 MeV.

§1. Introduction
The behavior of hadrons in the nuclear medium is one of the most intriguing topics in hadron andnuclear physics. Photon induced reactions are advantageous to producing hadrons deeply inside a
nucleus because photons are hardly absorbed. Modiﬁcations in appearances may always be observed.
Most of them originate simply from the basic effects of the nuclear medium, such as the Fermi motionof nucleons, Pauli blocking of the ﬁnal state and collisions with nucleons. In addition, an interesting
possibility has been proposed; i.e., mass modiﬁcation arising from partial restoration of chiral symmetry

Present address : RIKEN, Wako 351-0198＊†

Present address : Japan Cycle Development Institute, Tokaimura 319-1194‡

Present address : Center for Nuclear Study (CNS), University of Tokyo, Wako 351-0198§

Present address : High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801

9in the nuclear medium [1, 2]. The effects of the mass change of the ρ-meson have been studied inρ photoproduction on nuclear targets [3, 4] as well as in the hadron reactions [5]. However, masschange of baryons has not been studied well except for the Δ resonance [6].
The S11(1535) resonance is proposed to be a candidate of the chiral partner of the ground state
nucleon, and its resonance energy is expected to shift down by about 100 MeV in the nuclear medium
where chiral symmetry is partially restored [2]. The S11(1535) resonance is known to decay into the Nηchannel with a large branching ratio of 30-55% [7], while other nucleon resonances in this energy region
hardly decay to the Nη channel. Therefore, the excitation and decay of the S11(1535) resonance is adominant feature of the η photoproduction off the nucleon in the region of photon energies below 1000
MeV [8, 9]. It is, thus, expected that the properties of the S11(1535) resonance in the nuclear medium
can be studied through the η photoproduction off nuclei.
The measurements of A(γ,η) reactions have been reported by Röbig-Landau et al. on C, Ca, Nb and Pb
for Eγ＜ 800 MeV [10], and by Yorita et al. on C, Al and Cu for Eγ＜ 1000 MeV [11]. In both measurements,
the S11(1535) resonance is clearly observed in the excitation function, which can be reproduced by acalculation taking into account the basic effects of the nuclear medium with parameters deduced fromthe total cross section of the γp → ηp reaction. It seems, however, that the success of the interpretationof the A(γ, η) reaction with the S11(1535) resonance alone is partially due to the lack of the quality inthe previous data for Eγ＞ 800 MeV [11] as well as those of the γp →ηp reaction.
In the last several years, there were essential progresses in experimental and theoretical works on
the reaction. For the experimental side, precise measurements for Eγ＞800 MeV have improved considerably
the available data base [12-18] This led theoretical analyses to be more reliable for including
contributions of all the resonances in this energy region as well as direct η production processes. Of
particular interest is the fact that both of the analyses performed by Saghai et al. [8] and by Chiang et al.
[9] have come to the same conclusion that another S11 resonance, S11(1650), also contributes in the total
cross section of the γp →ηp reaction in such a way that the two S11 resonances interfere destructively.
All these arguments raised the interest to study the behavior of the S11 resonance again bymeasuring A(γ, η ) reactions with improved quality for the photon energies higher than 800 MeV. In
this letter, we present the experimental results and compare them with calculations based on the
Quantum Molecular Dynamics model (QMD) which is improved so as to include other processes thanthe S11(1535) resonance.

§2. Experimental Procedure
The experiment was performed at the Laboratory of Nuclear Science (LNS) in Tohoku University
by using tagged photon beams from the 1.2 GeV Stretcher-Booster Ring [19]. Two series ofmeasurements were carried out in different setups: the first one at the photon beam line 1 in theexperimental hall 2 and the second at the photon beam line 2 in the GeV-γ experimental hall. The
former tagging system is described in detail in Ref. [20] and a part of data obtained in the ﬁrst series
was reported in Ref. [21]. Photon beams of the same quality can be used at both beam lines. In thepresent work, the photon energy was covered from 600 to 850 MeV with Ee ＝ 920 MeV and from 800 to

10

4

10

3

events

10

10

2

10

1

0

200

400

600

800

invariant mass [MeV]1000

Fig.1. Invariant mass spectrum reconstructed from two photons. The solid line represents theexperimental data and the dotted line the result of the simulation.
1120 MeV with Ee ＝ 1200 MeV. The total tagged photon intensity was about 107 Hz with a duty factor
of about 80%. The size of the beam at the target position was about 6 mm (rms). The targets used were
C and Cu with thicknesses of 40 and 5 mm, respectively.
Two photons from an η-meson were detected by an electromagnetic calorimeter consisting of 206
pure CsI crystals with plastic veto counters. The shape of the crystal is truncated-trapezoidal with ahexagonal cross section and its thickness is 30 cm for 148 pieces (type-A) and 25 cm for 58 pieces (type-B);
the performance of the type-B is described in detail in Ref. [22]. In the ﬁrst series of the measurements,
they were assembled to 6 blocks and placed on three turn tables to change detector positions as reported
in Ref. [22]. In the second series, they were rearranged to 4 blocks placed in such a way that two＜φ＜17°
forward blocks covered angles 15° ＜θ＜ 72° with respect to the beam direction and angles－17°
withrespect to the horizontal plane and two backward blocks 95°＜θ＜ 125and －12°＜φ＜ 12°for both sides ofthe beam direction. The different arrangements of crystals served to check the acceptance of thedetection system.
All the data were collected using a similar data acquisition system as reported in Ref. [11]. In thepresent work, the main trigger for the data acquisition required at least one signal from the tagging
counters and two signals from the CsI detectors. The maximum counting rate of a CsI detector was
about 10 kHz and that of a tagging counter was about 200 kHz. The dead time of the data taking wasabout 8%. A time resolution for e-γ coincidences of 800 ps (FWHM) was achieved and the chancecoincidence ratio was about 3%.
The η-mesons were identiﬁed via their two photon decay with an invariant mass analysis. In Fig.1,
the invariant mass spectrum (Mγγ) measured in the present work is shown by the solid line. Two prominent
peaks corresponding to π0 and ηmesons are clearly seen on the continuum background, which is considered
to originate mainly from multi π0 events. We simulated the two π0 production process by the Monte
Carlo simulation. The result is shown by the dotted line in Fig.1. The shape is well fitted with an
exponential function, exp(aM2 γγ＋ bMγγ). In order to deduce double differential cross sections, d2σ/dθ/dp,
the invariant mass spectrum was constructed for the polar angle from 0 °to 110 °by 10 °steps and forthe momentum from 0 to 1100 MeV by 100 MeV steps. The yield of η-mesons in each spectrum was11deduced by subtracting the background events in the η mass region, which were estimated with thefunction ﬁtted to the continuum for each bin of the incident photon energy and the η-meson polar angle
and momentum. Absolute cross sections were deduced by taking into the account a thickness of thetargets, counts of tagging counters, a tagging efﬁciency, a geometrical acceptance and a branching ratio(η →γγ) [7]. The tagging efﬁciency was measured with a total absorbing lead glass detector positioned in
the direct beam. The geometrical acceptance of the detection system was calculated by the Monte Carlosimulation based on GEANT3 [23]. The systematic uncertainties of the overall normalization come fromthe photon flux (1%), the background determination (5%) and the geometrical acceptance (5%).
Consequently the overall systematic uncertainty is 7%.

§3. Results and Discussion
Differential cross sections of the (γ,η) reaction were deduced for the polar angles from 0°to 110°with
respect to the photon beam direction by integrating the double differential cross sections. We show
excitation functions of the η photoproduction cross section, which were deduced by integrating
differential cross sections for 0°＜θ＜ 110°, on C and Cu targets in Fig.52(a) and 2(b), respectively. Missing
yields for θ＞ 110 °were estimated to be 2% of the integrated values at most, and the total cross sectionin the present work is the angle integrated one. For comparisons, also plotted are the previously
reported data on C indicated with open squares up to 800 MeV [10] and with open circles up to 1000
MeV [11] and on Cu with open circles up to 1000 MeV [11]. It can be said that the present data and thereported ones are in good agreement. Moreover, the statistical accuracy is much improved for thephoton energies higher than 800 MeV. The shape of the total cross sections for C and Cu is quite similar
as expected. The cross section increases rapidly from the threshold energy (561 MeV for C and 550 MeV
for Cu), shows a broad bump structure which has the maximum at around 850 MeV, and gradually
decreases as the photon energy increases. This trend has been known from the previous investigations[11] to be basically due to the excitation of the S11(1535) resonance in a nucleus. The present data for C
and Cu may serve for detailed comparisons with model calculations.
In Fig.2(c), ratios of the cross section of Cu to that of C (σCu /σC ) are plotted against the photon
energy. One can roughly say that the observed η-mesons are mainly emitted from the surface region of
the nucleus and those emitted in the deeper region are absorbed in the nuclear medium, since the ratios
are close to 3.05 (the dotted line), corresponding to the ratio of A2/3 for Cu to C. However, there exist
non-negligible and systematic deviations from the A2/3 dependence for photon energies larger than 800
MeV; the ratio becomes about 3.5 at about 900 MeV. This requires more careful and detailed analysis.
In order to explain the present data, we have performed a QMD model calculation in a different way
from the previous one [11] as follows. At ﬁrst, the proton and the neutron are treated independently so as tosee the effect of the difference of the elementary cross sections forγp →ηp and γn →ηn. This modiﬁcation isnecessary, because a rather large difference between the total cross sections of γp →ηp and γn →ηn has
been predicted by the unitary isobar model, η-MAID [9]. The simple relationσ(γn →ηn) /σ(γp →ηp)＝2/3,
established empirically for Eγ＜800 MeV [25] and used in the previous model calculations [11, 24], might not
be correct at the higher energy region. Secondly, the effect of the interference between two S 11

12
100

(a) C(γ,η)

60

20

ab

17.5

40
20

3

(a) γp→ηp

15

1
2

4

QMD input
MAID, full calculation
single resonance

12.5

σ[µb]

σ[µb]

80

0
300 (b) Cu(γ,η)

Mainz
GRAAL
Bonn

10

σ[µb]

7.5
5

200

ab

2.5

100
3

0
20

1
2

4

17.5
15

4
3

QMD input
MAID, full calculation
MAID, double S11
MAID, D15(1675)

10
7.5
5

2
1

(b) γn→ηn

12.5

σ[µb]

σCu / σC0
5 (c) ratio

2.5

600

700

800

900

1000 1100 1200

0Eγ[MeV]

Fig.2. Cross sections ofηphotoproduction measuredon C(a) and Cu(b). The data measured
in the present work are indicated by thesolid circles, those at KEK [11] by theopen circles and at Mainz [10] by thesquares. The solid line is the result of thepresent QMD calculation. Contributions ofvarious processes are plotted by the dottedlines labeled with numbers; label 1 forthe double S11 resonance, label 2 for theP11(1710), label 3 for the D15(1675), andlabel 4 for the direct processes. The dotdashed lines are contributions due toprotons (label a) and neutrons (label b).
The calculation in the previous work by
Yorita et al. [11] is plotted by the dashedline. (c) Ratio of the cross section of theCu(γ, η) reaction to that of the C(γ, η)
reaction. The dashed line shows the ratioof A2/3 (A: mass number) and the solidline is the result of the QMD calculation.

Fig.3.

700

800

900

1000

Eγ[MeV]

1100

1200

Excitation functions of cross sections forthe elementary reaction by calculation
based on the η-MAID: (a) the γp → ηpreaction and (b) theγn→ ηn reaction. The
solid lines are used in the present QMD
calculation and the dashed lines are theresults of the full η-MAID including all
the resonances and the direct process.
In (a), the excitation function used in
the previous work by Yorita et al. [11] isalso plotted by the dotted line as well as
experimental data from Mainz [12], GRAAL[16] and Bonn [18]. In (b), contributions of
the two resonances, S11(1535) and S11(1650),
destructively interfered, are shown by the
dot-dashed line, while that of theD15(1675) is shown by the dotted line.

resonances in this energy region, S11(1535) and S11(1650), is included in the calculation as the form of
the cross section. The reason of this modiﬁcation is as follows. Saghai et al. [8] and Chiang et al. [9] analyzed
the total cross section of the γp →ηp reaction. They came to the same conclusion that the experimentallyobserved cross section below 1100 MeV is not only due to the S11(1535) resonance but also due to theS11(1650), and both resonances make a destructive interference in the cross section of η production off
the nucleon. In the present QMD calculation, it is impossible to treat directly the transition amplitudes,
and, thus, the calculated cross section including a destructive interference term is incorporated instead13of an incoherent sum of two single resonances which cannot reproduce the experimental data well.
In Fig.3, the total cross sections of the N(γ, η) reaction are shown in order to explain input quantities
to the present QMD calculations. The experimental cross sections of the γp → ηp reaction are shown in
Fig.3(a); data plotted with circles from Ref. [12], triangles from Ref. [16] and squares from Ref. [18].
Also shown are the results of the η-MAID calculation, on which we have based for the elementary crosssection. The characteristic feature of the experimental data is a broad peak followed by a ﬂat region
with a small dip at 1010 MeV. The single resonance excitation can reproduce only the broad resonanceshape but fails to reproduce the dip and ﬂat as indicated by the dotted line, which corresponds to theelementary cross section used in our previous analyses [11]. The dashed line is the result of the full ηMAID calculation which includes all the resonances in this energy region with direct η production
processes. As mentioned above, the essential point is the destructive interference of the S11(1535) andthe S11(1650) resonances, which reproduces the dip and ﬂat behavior very well. Another non-negligible
process is the excitation of the P11(1710) resonance, which slightly contributes to the ﬂat region around1100 MeV. Therefore, we have included three resonance excitations, S11(1535), S11(1650), and, P11(1710)
and the direct processes in the cross section of the γp →ηp reaction for the QMD calculation. The total crosssection of the elementary γp→ηp reaction is calculated practically by summing up the cross sections of the
double S11, the P11, and the direct processes, although the exact calculation should be the square of sumof the amplitude of each process. The solid line in Fig.3(a) is the elementary γp→ηp cross section usedin the present QMD calculation, being slightly larger than the full calculation of the η-MAID.
For the cross section of the γn→ηn reaction, no experimental data have been reported so far. We, again,
follow the η-MAID calculation as shown in Fig.3(b). The dashed line corresponds to the full calculationof the η-MAID including all the resonances and the direct processes. We select the double S11 resonance,
the D15(1675) resonance as major processes of excitations and the direct processes for the QMD input.
The η-MAID calculation predicts rather large cross sections through the D15(1675) resonance excitation,
which is essentially prohibited in the γp→ηp reaction by the Moorhouse selection rule [26]. The cross section
through the two S11 resonances is calculated with the destructive interference term. It shows a dip ataround 1000 MeV as shown by the dot-dashed line in Fig.3(b), where one sees that a large contribution
from the D15(1675) resonance, which is plotted by the dotted lines, fills the dip and appears like ashoulder of the S11(1535) resonance. The sum of the cross sections of the selected processes, which is
employed as the elementary γn → ηn reaction, is shown by the solid line. The difference from the fullcalculation is very small as in the case for the γn →ηn reaction.
Having discussed the elementary cross sections, we now return to the C(γ, η) and Cu(γ, η)
reactions. In Figs.2(a) and 2(b), the cross sections obtained in the present work are compared with the
QMD calculations. As mentioned above, the elementary cross sections of the γp→ηp and γn→ηn reactions
are treated independently; they are the solid lines in Fig.3(a) and Fig.3(b) for proton and neutron,
respectively. The η-emission probability through the resonance excitation is calculated according to theBreit-Wigner resonance formula for the P11(1710) and the D15(1675) resonances. For the S11 resonanceexcitation in the present work, however, the cross section including the interference of the two S11
resonances is used as if a resonance of the mixed state which is not described by the single Breit-Wigner

14
Table 1. Parameters of nucleon resonances used in our calculation. A are photoexcitation
helicity amplitudes of nucleon resonances and βηN is Nη decay branching ratio. Thosein the last columm are used in the previous analysis [11].
p,n1/2,3/2

N＊
S11(1535)
S11(1710)
P11(1710)
D15(1675)
S11(1535)

Mass
[Mev]
1541
1638
1721
1665
1542

Width
[Mev]
191
114
100
150
150

βηN
[%]
50
7.9
26
17
55

A

p
1/2

[10

－3

+118
+68
+23
0
+102

A
A
GeV － 1/2]
－
－
－
－
－
－
－ 58
0
－
－
p,n
3/2

n
3/2

formula is excited, and the lifetime and the decay branch of the S11(1535) resonance is applied to themixed state. This approximation seems to be allowed, since the η-meson is mainly emitted via theS11(1535) resonance. The resonance parameters in the η-MAID are used for each resonance, and aresummarized in Table 1.
It should be noticed for the QMD calculations in the present work that the effective energies of theincident channel are calculated for each photon-nucleon collision with a nucleon bound in a mean ﬁeld
potential. The effective energy which results in the reduction of the η yield for the threshold region has
been discussed [24,27] and the result of such calculation improves the reproduction of the cross sections
below 800 MeV. Thus, we have calculated the effective total energy followed as W ＝ √s － U, where W is
the effective total energy, √s is the c.m. energy of the incident photon and a nucleon in the nucleus andU is the nucleon potential calculated from the mean ﬁeld potential in Ref. [28]. As described in Ref. [11],the Fermi motion of nucleons, the Pauli blocking, collisions of nucleon resonances with nucleons andthe absorption of the η-mesons are taken into account in the calculation.
In Fig.2(a) and 2(b), the dashed line is the results of the QMD calculation in which only theS11(1535) resonance is incorporated with the assumption of σn/σp ＝ 2/3. This corresponds to the previous
calculation in Ref. [11]. For both C(γ, η) and Cu(γ, η) reactions, the calculation reproduces data up to
950MeV. However, it underestimates the yield for Eγ＞ 1000 MeV. The solid line corresponding to the newrecipe covers the deﬁcit and reproduces the data well up to 1100 MeV. Contributions of each process arealso shown in Fig.2(a) and 2(b). As can be seen, in addition to the largest contribution of the double S11
resonance indicated by the dotted line 1, the contributions of the D15(1675) resonance and the directprocesses are expected for Eγ ＞ 900 MeV. The present calculation suggests that more than 18% of the crosssection at 1000 MeV originates from other processes than the excitation of the S11 resonances. It is ofparticular interest that the D15(1675) resonance plays an important role for higher photon energies,
since only neutrons can be excited in a naive quark model. The dot-dashed lines labeled a and b in Fig.2
correspond to the contributions of protons and of neutrons, respectively. The ratio of the contribution ofneutrons to that of protons is nearly 0.67 for C and 0.84 for Cu at Eγ＜ 800 MeV, where only the S11

resonance formation process can contribute, and becomes 0.97 for C and 1.23 for Cu at around Eγ＝ 1100
MeV due to the existence of the D15(1675) resonance. The change of the contribution of neutrons toprotons may explain the change of the ratio of the total cross section σCu /σC plotted in Fig.2(c), where thecalculated ratio is also shown by the solid line. The calculation explains the trend of the ratio very well,although it fails for the lowest two points.

15(a) C target
Momentum
Angulardistribution
distribution
Eγ=750 MeV

III

100

0

0

III

Eγ=880 MeV

100

0.2

Momentum
Angulardistribution
distribution
Eγ=750 MeV

III

300

0.8

0.6

200

0.4

100

0.2

400
0

0.8
0

III

Eγ=880 MeV

300

0.6

200

0.4

100

0.2

III

Eγ=980 MeV

100

0.2

dσ/dp[µb/MeV]00dσ/dp[µb/MeV]dσ/dθ[µb/rad]

0.1

50

dσ/dθ[µb/rad]

0.2(b) Cu target

0.1

50

0
400

0
0.8

III

Eγ=980 MeV

300

0.6

200

0.4

100

0.2

400
0

0.8
0

0.1

50

0

0

III

Eγ=1090 MeV

100

0.2

III

Eγ=1090 MeV

300

0.6

200

0.4

100

0.2

0.1

50

0

400

0

0
100

θlab[deg]

500

0
1000

p [MeV]

0

0

0
100

θlab[deg]

500

0
1000

p [MeV]

Fig.4. Angular distributions, dσ/dθ, and momentum distributions, dσ/dp, of the (γ, η) reaction
measured on C (a) and Cu (b). The present results are plotted with the closed circles for Eγ＝ 750, 880, 1000, and 1100 MeV. The solid line is the result of the QMD calculation and thedashed one represents without the contribution of D15(1675), and the dot-dashed line shows
only the contribution of D15(1675) resonance multiplied by 4.
The above discussion on Fig.2 requires at least the following; the elementary cross section ofthe γn →η n reaction exceeds that of the γp →η p for Eγ ＞ 1000 MeV, due to another process besides theS11 resonance formation. Recently, Kuznetsov et al. reported the nη and pη coincidence measurements inthe D(γ, η) reaction [29]. Their result that yields of the nη coincidence events are larger than those of
the pη events at around 1000 MeV is consistent with the present interpretation.
Additional effects that might possibly give rise deviations from the pure S11 resonance formation
may be seen in the angular and momentum distributions of the emitted η-mesons. They are shown in
Fig.4 for Eγ＝ 750, 880, 980, and 1090 MeV, and compared with the QMD calculations. The results for the
C target are shown in Fig.4(a), and the Cu target in Fig.4(b). All the angular distribution data show a broad
structure peaked at around 30°. This is a characteristic of the quasi-free s-wave η production. The solid lines
in the ﬁgures are the results of the QMD calculation, and the experimental data for both angular andmomentum distributions are essentially well reproduced by the corresponding calculations. The dashed16lines shows the results without the contribution of the D15(1675) resonance and the dot-dashed lines
correspond to the contribution of the D15(1675) resonance multiplied by 4. As shown, the contribution of
the D15(1675) resonance has a different structure in these distributions because of the d-waveηemission.
Since the contribution of the D15(1675) resonance is not large, the present data, unfortunately, cannot
give a ﬁrm evidence for the excitation of the D15(1675) resonance in both reactions.
As we have discussed above, the comparison of new data with the QMD model calculations suggests
strongly that the cross sections of η photoproduction off nuclei contain non-negligible quantities
through the process other than the S11(1535) resonance formation for the photon energies above 850
MeV. Thus, in order to investigate the change of the S11 properties in the nuclear medium such as themass shift proposed in Ref. [2], one needs precise data of the cross section for the γn →ηn reaction. The
present work has shown that the use of the elementary cross sections of η-MAID can reproduce theexperimental data very well but remains an interesting subject for future investigations.

§4. Conclusion
In summary, the η photoproduction cross sections were measured on the C and Cu targets for thephoton energies between 600 and 1100 MeV. The excitation functions of the total cross section as wellas angular and momentum distributions were in quantitative agreement with the QMD model
calculations in which the cross sections proposed in the η-MAID model were used for the elementary
reactions γp →ηp and γn →ηn. The agreement suggests that there is a difference in the shape of thecross sections between proton and neutron in a nucleus. In order to discuss the change of the propertiesof the S11(1535) resonance, the cross section of the γn → ηn reaction experimentally measured is highly
desirable to be incorporated in the model calculations.

Acknowledgements
We would like to thank the accelerator staff at LNS for their support during the experiment. This
work was partly supported by the Grant-in-Aid for Scientiﬁc Research (Nos. 1040067, 07740197, and15340069) of the Ministry of Education of Japan.

Reference[1]

T. Hatsuda and S. H. Lee: Phys. Rev. C46 (1992) 34.

[2]

H. C. Kim, D. Jido, and M. Oka: Nucl. Phys. A640 (1998) 77;
D. Jido, Y. Nemoto, M. Oka, and A. Hosaka: Nucl. Phys. A671 (2000) 471;
D. Jido, T. Hatsuda, and T. Kunihiro: Phys. Rev. Left. 84 (2000) 3252.

[3]

G. J. Lolos et al.: Phys. Rev. Lett. 80 (1998).

[4]

B. Krusche et al.: Phys. Rev. Lett. 86 (2001) 4764.

[5]

G. Agkichiev et al.: Phys. Rev. Lett B422 (1998) 405;
D. Adamova et al.: Phys. Rev. Lett. 91 (2003) 042301.

[6]

E. L. Hjort et al.: Phys. Rev. Lett. 79 (1997) 4345;

17
D. Plete et al.: Z. Phys A359 (1997) 55.
[7]

S. Eidelman et al., (Particle Date Group): Phys. Lett. B592 (2004) 1.

[8]

B. Saghai and Z. Li: Eur. Phys. J. A11 (2001) 217.

[9]G. Knöchlein, D. Drechsel, and L. Tiator: Z. Phys. A352 (1995) 327;

[10]

M. Röbig-Laudau et al.: Phys. Lett. B373 (1996) 45.

[11]

T. Yorita et al.: Phys. Lett. B476 (2000) 226;
H. Yamazaki et al.: Nucl. Phys. A670 (2000) 202c.

[12]

B. Krusche et al.: Phys. Rev. Lett. 74 (1995) 3736.

[13]

J. Ajaka et al.: Phys. Rev. Lett. 81 (1998) 1797.

[14]

C. S. Armstrong et al.: Phys. Rev. D60 (1999) 052004.

[15]

R. Thompson et al.: Phys. Rev. Lett. 86 (2001) 1702.

[16]

F. Renard et al.: Phys. Lett. B528 (2002) 215.

[17]

M. Dugger et al.: Phys Rev. Lett. 89 (2002) 222002.

[18]

V. Credé et al.: Phys. Rev. Lett. 94 (2005) 012004.

[19]

F. Hinode et al.: Proceedings of the 2005 Particle Accelerator Conf., Knoxville, TN, U.S.A., To be
published;
H. Hama et al.: Proceeding of the 18th International Conference on High Energy Accelerators(HEACC2001), Tsukuba, March 2001.

[20]

H. Yamazaki et al.: Nucl. Instr. Meth A536 (2005) 70.

[21]

H. Yamazaki et al.: Proceedings of the International Workshop on Physics with Gev Electrons andGamma Rays, Sendai, Japan, February, 2001, Universal Academy Press, Inc. pp. 151;
J. Kasagi: Prog. Theo. Phys. Suppl. 149 (2003) 215.

[22]

H. Okuno et al.: Nucl. Instr. Meth. A365 (1995) 352;
H. Yamazaki et al.: Nucl. Instr. Meth. A391 (1997) 427.

[23]

CERN Program Library Long Writeup W5013: Geant Detector Description and Simulation Tool,(1993).

[24]

J. Lehr, M. Post, U. Mosel: Phys. Rev. C68 (2003) 044601.

[25]

B. Krusche et al.: Phys. Lett. B358 (1995) 40.

[26]

R. G. Moorhouse: Phys. Rev. Lett. 16 (1966) 772.

[27]

T. Maruyama, S. Chiba: Prog. Theor. Phys. 111 (2004) 229.

[28]

K. Niita et al.: Phys. Rev. C52 (1995) 2620.

[29]

V. Kuznetsov et al.: hep-ex / 0409032.

Research Report of Laboratory of Nuclear Science, Tohoku University Vol. 38 (2005)

18(LNS Experiment : #2507)

Comparison of the 40Ca(e, e' p) Cross Section at Low
Momentum Transfer Region with Relativistic Calculations
R. Hashimoto1, T. Tamae1, T. Fujibayashi2, O. Hashimoto2, K. Hirose2,
T. Ishikawa1, H. Kanda2, O. Konno3, K. Maeda2, H. Miyase2, S.N. Nakamura2,
M. Nanao1, I. Nishikawa1, T. Otsuki1, T. Saito4, Y. Sato1, K. Takahashi2,
H. Tamura2, H. Tsubota2, M. Wakamatsu2, H. Yamazaki1, and H. Yuki1
1

3

Laboratory of Nuclear Science, Tohoku University, Sendai 982-0826
2
Department of Physics, Tohoku University, Sendai 980-8578

Department of Electrical Engineering, Ichinoseki National College of Technology, Ichinoseki 021-8511
4

Faculty of Engineering, Tohoku Gakuin University, Tagajo, 985-8537

The (e, e' p0) cross section of 40Ca measured using a 199.53 MeV continuous electron beam iscompared with theoretical calculations based on the relativistic distorted-wave impulse approximation(RDWIA). The theoretical values overestimate the experimental ones by a factor of 2 when the
spectroscopic factor is obtained from the (e, e' p) experiment in parallel kinematics, or by a factor of 1.4
when spectroscopic factor is obtained in constant (ω, q) kinematics.

§1. Introduction
Recently, the (e, e' p) reaction in the quasi-elastic region and the (γ, p) reaction above the giant
resonance region have been investigated in the relativistic framework [1-3]. The contributions of mesonexchange currents (MEC) and the choice of the one-body current operator were discussed in Refs. [1, 2].
In previous reports [4-6] we compared the reduced cross section obtained from 12C(e, e' p0) and thedifferential cross section obtained from 16O(e, e' p0) with theoretical calculations based on the relativistic
distorted wave impulse approximation (RDWIA). Both experiments were performed at a low momentum→|= 105.2 MeV/c. The result oftransfer region: energy transfer ω = 60 MeV and momentum transfer |qthese reports was that RDWIA overestimates the experimental data by a factor of 2. A large
contribution of the two-body seagull term was observed at high missing momentum region.
To investigate this reaction mechanism further, we choose 40Ca as a target and performed theexperiment. The 40Ca(e, e' p0) cross section obtained from this experiment is compared with calculations
based on RDWIA.

§2. Experiment
The experiment was performed at Laboratory of Nuclear Science, Tohoku University (LNS) using a
199.53 MeV continuous electron beam from the stretcher-booster (STB) ring. Incident electrons were
scattered with a natural calcium target of 19.0 mg/cm2 thickness. Scattered electrons were analyzed

19
their momentum at θe = 30° by a magnetic spectrometer (LDM) and detected with a vertical drift
chamber (VDC) placed on the focal plane of the spectrometer and with a backup counter, layered threeplastic scintillators behind the VDC. In this setup, ω is 60.0 ± 4.2 MeV and |q→| is 105.2 MeV/c.
Knocked-out protons were detected by SSD telescopes, which consisted of three layers of 1mm-thick
SSD' s. In order to degrade the energy of protons, a 6mm-thick aluminum disk was put in front of eachtelescope.
The normalization of our measured (e, e' p) cross section was performed by comparing the elastic
scattering cross section with that of Ref. [7]. We measured the elastic scattering cross section at θe =58.5°. The form factor of our experiment corresponds to that at θe = 46.0° with a beam energy 249.3

The measured cross sections are shown in
Table 1 and Fig.1. The 40Ca(e, e' p0) cross section
obtained from our experiment is compared with2

§3. Result and Discussion[nb/sr /MeV]MeV of Ref. [7].

10

theoretical calculations based on RDWIA [8].
The RDWIA treatment is same as in Refs. [1, 2].
The bound state wave function is a solution of1

a relativistic Hartree-Bogoliubov equation
using parameters NLSH [9]. The EDAD1
optical potential parameters [10] are used for
calculations of the scattering wave function. As-110

the choice of the electromagnetic operator is0

arbitrary, three current conservation operators,
cc1, cc2 and cc3, are used in the calculations.

10

20

30

40

50

60
θ p [deg]

Fig.1. The 40Ca(e, e' p0) cross section.

The spectroscopic factor Z(d 3/2 ) was

obtained from analysis of the quasi-elastic (e, e' p0) reaction [11], which included the results of two
different kinematics, parallel kinematics and constant (ω, q) kinematics. The factor was calculated forthe three current operators on each kinematics. The spectroscopic factors obtained from parallel
kinematics and constant (ω, q) kinematics are listed in Table 2. The present data are compared with
Table 1. Differential cross section of the40
Ca(e, e' p0) reaction.
θe

Cross section [nb/MeV/sr2]

0°
12°
24°
36°
48°
60°

6.901 ± 0.427
5.832 ± 0.392
4.512 ± 0.347
1.662 ± 0.213
0.791 ± 0.150
0.179 ± 0.078

Table 2. Spectroscopic factors for three current
operators in two kinematics.

cc1
cc2
cc3

parallel kinematics

constant (ω , q)

0.627
0.713
0.766

0.446
0.594
0.701

[nb/sr /MeV]

10

1

1

-1

10

10

0

10

20

30

40

50

60

-1

70 80
θp [deg]

0

20

30

40

50

60

70 80
θp [deg][nb/sr /MeV][nb/sr /MeV]

2

10

10

1

1

-1

10

10

10

The 40Ca(e, e' p0) cross section compared with theoretical calculations, using spectroscopic
factors obtained from the (e, e' p) experiment in the parallel kinematics. Calculations
include the MEC effect in the left panel, and does not in the right panel. Closed circles
show the present data, and solid, dashed, and dot-dashed lines represent theoretical
calculations with cc1, cc2, and cc3 current operators, respectively. θp is the out-going angleof the proton.

Fig.2.

2

10

2

2

[nb/sr /MeV]

20

0

10

20

30

40

50

60

70 80
θp [deg]

-1

0

10

20

30

40

50

60

70 80
θp [deg]Fig.3. Same as Fig. 2, but comparison with theoretical calculations using the spectroscopic factor
obtained from the (e, e' p) experiment in the constant (ω, q) kinematics.

21
theoretical calculations in Figs.2 and 3. The theoretical values are obtained using 3 one-body currentconservation operators and spectroscopic factors listed in Table 2. According to Figs.2 and 3, the MEC
effect is not important in the small θp region, corresponding to the lower momentum transfer region.
Calculations with spectroscopic factors obtained from parallel kinematics overestimate the data, at
forward angles, and are different from each other, as shown in Fig.2. In order to ﬁt calculations to thedata, a normalizing factor 0.423 is needed for the cc1 current, and 0.523 and 0.588 for the cc2 and, cc3
currents, respectively. Thus, theoretical values overestimate the experimental ones by a factor about 2.
This result is same as in previous reports [4-6]. As shown in Fig.3, calculations with spectroscopic
factors obtained from constant (ω , q) kinematics also overestimate the data by a factor of about 1.4,
but the calculation is equivalent to each other in the small θp region. The theoretical values are closer
to the experimental one than using a spectroscopic factor obtained in parallel kinematics, but still toolarge.

§4. Summary
Both theoretical calculations using the spectroscopic factor obtained in the parallel and constant (ω,q) kinematics. overestimate the experimental cross section, about factors 2 or 1.4, respectively. The (e,e' p) experiment at the low momentum transfer in 12C, 16O and 40Ca show some important contributions
is missing in the theoretical approach.
The authors would like to thank C. Giusti and A. Meucci for their relativistic calculations. They
also thank the accelerator group, the computer group and Mr. Matsuda for their assistance to theexperiment. This work has been supported by Grant-in-Aid for Scientific Research (KAKENHI)(No.14540239, No.17540229) from Japan Society for the Promotion of Science (JSPS).

References[1]

A. Meucci, C. Giusti, and F. D. Pacati: Phys. Rev. C64 (2001) 064615.

[2]

A. Meucci, C. Giusti, and F. D. Pacati: Phys. Rev. C66 (2002) 034610.

[3]

J. I. Johansson, H. S. Sherif, and G. M. Lotz : Nucl. Phys. A605 (1996) 517.

[4]

Y. Sato et al.: Research Report of LNS, Tohoku Univ. 33 (2000) 7.

[5]

T. Tamae et al.: Research Report of LNS, Tohoku Univ. 36 (2003) 19.

[6]

Y. Hayashi et al.: Research Report of LNS, Tohoku Univ. 37 (2004) 1.

[7]

B. B. P. Sinha et al.: Phys Rev C7 (1973) 1930.

[8]

C. Giusti and A. Meucci: private communication.

[9]M. M. Shaeme, M. A. Nagarajan, and P. Ring: Phys. Lett. B312 (1993) 377.

[10]

E. D. Cooper et al.: Phys. Rev. C47 (1993) 297.

[11]

G. J. Krammer: private communication.

22

Research Report of Laboratory of Nuclear Science, Tohoku University Vol. 38 (2005)

Test Operation of Spin-Filter Polarimeter for Deuteron
I. Nishikawa, M. Watabe, and T. Tamae
Laboratory of Nuclear Science, Tohoku University, Sendai 982-0826§1. Spin-Filter Polarimeter at LNS
We have developed a Lamb-shift type polarimeter for probing the polarization of an opticalpumping polarized deuteron gas target. The Lamb-shift polarimeter [1,2] is based on the 3-levelinteraction between D(2S1/2, ↑electron), D(2S1/2, ↓electron) and D(2P1/2, ↑electron) states in the spin-ﬁlter cavity.
The mechanism of the 3-level interaction in the spin-ﬁlter cavity is found elsewhere [3,4]. In this report
the equipment and the test operation result are described brieﬂy. A view of the spin-ﬁlter polarimeteris shown in Fig.1.

II

I

III
PM-tubespin-filter cavity
quenchingelectrodeCs cellbeam
monitorsolenoidal coils
Fig.1

A view of the spin-ﬁlter polarimeter.

1-1 Charge Exchange Section
Some of the deuteron ions extracted from a deuterium gas target are converted to D(2S) atoms by
the charge exchange reaction d+ + Cs → D(2S) + Cs + [5] in the Cs vapor cell. The cross-shaped Cs vapor
cell is composed of inner copper sleeves and outer ceramic sleeves which are heated by a nickel-chrome
ribbon heater. The cell is placed in the solenoidal coil to suppress the expected depolarization effect.
1-2 Spin-Filter Section
The spin ﬁlter cavity is placed in a solenoidal coil set which generates homogeneous magnetic ﬂux
in the central region of the cavity. The spin-ﬁlter coil set is composed of three main solenoidal coils of
hollow conductor, two correction solenoidal coils and iron yokes. The D(2S) atoms are injected into theaxial area of the cavity, and the longitudinal rf electric ﬁeld and transverse static electric ﬁeld quench
the D(2S) atoms which are non-selected or off-resonance. The cavity is made of brass, 26cm in fulllength, divided into 4-quadrant parts. It is operated at 1610 MHz in the TM010 mode with an rf powerof about 0.1 W.
1-3 Photon Counting Section
In this section the number of the D(2S) atoms passed the spin-ﬁlter cavity is counted. The D(2S)23
atoms contained in the beam are forcedly Stark-quenched in the electric ﬁeld produced by a cylindricalquenching electrode, accompanied by the emission of Lyman-alpha photons. Some of the decay Lymanalpha photons are detected by a UV PM-tube (Hamamatsu R6835) with MgF2 window, CsI cathode, andAC-coupled output. The output signals from the PM-tube are pulse-height-analysed and counted by
NIM modules and a DAQ-board on PC. The typical counting rate is ~400 photons/sec in the following
polarimetry operation.

§2. Test Operation of the Polarimeter
2-1 RF ion injector and beam line
The test operation of the spin-ﬁlter was done by injecting unpolarized deuteron atoms from an RFion- source. The overview of the RF-ion-source and the ion beam optics is depicted in Fig.2.

feed throughaccelerationelectrodes

stirring
Wien Filter electrodefocusing
electrodecurrent monitor------

to polarimeter++++++

D2 gasCryo Pump

RF ionizer

stirring
electrode(Ei=1.5keV)

Fig.2

Test-ion injector and beam line components.

The RF ionizer is composed of a Pyrex glass tube and an RF-coil. An 13.6MHz rf power of 25W was
supplied to the coil through a matching circuit. The partially-ionized and dissociated deuterium gas wasejected through a 1mm-diameter hole on a copper electrode. Ions were extracted and accelerated up to 1.5
keV by cylindrical electrodes and mass-analysed by a Wien filter. The magnetic flux (~1150 gauss at
the central point) was generated by two square permanent magnets in the Wien filter. The ion beam
was guided into to the Cs cell of the polarimeter by two stirring electrodes and a focusing electrode, andthe beam current was measured by a beam monitor at the end of the polarimeter. A typical current of
the passed ion beam was 0.3 nA at the monitor.
2-2 Test operation result
We measured the populations of the magnetic sub-states of unpolarized deuterons from the RF-ion
source. The ion beam energy was 1.5 keV and the Cs-cell temperature was 313K. A typical result andﬁtted curves are shown in Fig.3. In the figiue, the averaged count rate of photons detected by the PM

24
tube are plotted as a function of a mean magnetic flux on the beam axis in the cavity. At each data

Count Rate [/sec]

point photon pulses were counted in 10 seconds.

450

400

350

300

250
550

560

570

580

590

600

B [gauss]
Fig.3.

Observed peaks of the deuteron magnetic sub-state population:, dashed line (Gaussian +linear), dot-dashed line( a linear part of the ﬁtting. )In the ﬁgure the relative height of the three peaks on the straight line corresponds to the relative
populations of the nuclear magnetic sub-states of the D(2S) at the quenching electric ﬁeld. From theFig.3 we note S/N and stability are not sufﬁcient. Improvement of the homogeneity of the magnetic ﬂux
in the spin-ﬁlter region and suppression of background photons will be required.

References[1]

J.L. McKibben and G.G. Olsen : Phys. Rev. Lett. 20 (1968) 831.

[2]

S.K. Lemieux : Nucl. Instrum. and Meth. A313 (1993) 434.

[3]

G.G. Olsen and J.L. McKibben : “Theory of a Radio Frequency “Spin Filter” for a Metastable Hydrogen,
Deuterium, or Tritium Atomic Beam” LA-3725, Los-Alamos Scientiﬁc Laboratory (1967).

[4]

K. Kubo and K. Katori : “Spin and Polarization” Shin-Butsurigaku-Series no.27, Baifuukan-Press.
(1994).

[5]

P. Pradel et al. : Rev. Sci. Instrum. 45 (1974) 44.

Ⅱ．Radiochemistr y

Research Report of Laboratory of Nuclear Science, Tohoku University Vol. 38 (2005)

25(LNS Experiment : #2389, #2408, #2424, #2443, #2458, #2460, #2475, #2490, #2492, #2502,#2503, #2513, #2514, #2525, #2526, #2541, #2542)

Observation of α-decay of 229mTh produced from 229Ac
H. Kikunaga1, ＊ , Y. Kasamatsu2, K. Takamiya3, T. Mitsugashira4,
M. Hara4, T. Ohtsuki5, H. Yuki5, A. Shinohara2, S. Shibata3,
N. Kinoshita1, A. Yokoyama1, and T. Nakanishi1
1

Faculty of Science and Graduate School of Natural Science and Technology,
Kanazawa University, Kanazawa 920-1192

2

Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043

3
4

Research Reactor Institute, Kyoto University, Kumatori, Osaka 590-0494

The Oarai-branch, Institute for Materials Research, Tohoku University, Oarai-machi, Ibaraki 311-1313
5

Laboratory of Nuclear Science, Graduate School of Science, Tohoku University, Sendai 982-0826

We produced 229Th in the nuclear reaction 232Th(γ, p2n)229 Ac, followed by disintegration to 229m,gTh.
The α-decay signals from 229mTh were searched for and the alpha-particle events of the energy region
between 4.93 MeV and 5.05 MeV were observed in the separated thorium fraction from an actinium
source highly purified from the 232Th + γ reaction products. The energy values of the α-particles
coincide with those expected for 229mTh.

§1. Introduction
Recent investigations of 229Th have reported energy difference between the ground state 229gTh andthe ﬁrst excited state 229mTh to be (3.5 ± 1.0) eV [1, 2] or (3.4 ± 1.8) eV [3]. In those studies, 229m,gTh was
produced from the α-decay of 233U. Additional evidence for the existence of 229mTh was given by Burke etal. [4] using 230Th (d,t) particle reaction spectroscopy. The internal conversion process is prohibited in
Th because the energy of the isomeric transition from 229mTh to 229gTh is lower than the ﬁrst ionization229

potential of thorium. Therefore, the investigation of the 229mTh decay is expected to provide a strong
verification of the electron bridge mechanism (EBM) [5], which is a de-excitation process competingwith isomeric transition and α-decay. Since the probability of the EBM depends on the energy state of
the outer-shell electrons, the half-life of 229mTh can vary with its chemical state; hence the isomer is alsointeresting from a chemical viewpoint.
It is believed that no one has thus far succeeded in detecting a decay signal from 229mTh. In a few
studies, the observation of photons due to isomeric or EBM transitions was attempted by ultraviolet
and visible spectroscopy [6, 7], but there is still some doubt regarding the results [8, 9]. Browne et al. [10]searched for 229mTh from a sample prepared from approximately 25g of 233U. They tried to observe thegrowth of γ-rays associated with the α-decay of 229gTh due to the feeding from 229mTh, but observed noevidence of such growth. The failure to observe these events might be attributable to two reasons: the
difﬁculty in detecting extremely low energy photons and the small branching ratio from 233U to 229mTh,

26which is about 2%.
In order to address the ﬁrst difﬁculty, it seems reasonable to devise the identiﬁcation of 229mTh by
the detection of its α-decay. The most favorable decay-mode of 229mTh should be the direct γ-transitionor the EBM [5]. The observation of photon emission from the isomeric state requires detecting
ultraviolet-visible photons under considerable interference, such as α-particle induced fluorescence.
Such a measurement is very difﬁcult. On the other hand, the α-decay of 229mTh is undoubtedly nuclear
disintegration phenomenon, though as a minor decay-mode. The technique for α-particle detection iswell established and its detection is subjected to little interference from the background. Therefore, it isexpected that if α-particles from 229mTh exist, they are observable. The α-decay of 229mTh has been
discussed by Mitsugashira et al. [11] and Dykhne et al. [12]. Both expected the favored α-particle decays
from 229mTh had energies higher than those from 229gTh, i.e. 4.93-5.05 MeV. This implies that the partial
half-life of the α-decay of 229mTh is shorter than that of 229gTh.
To address the difﬁculty of the small branching ratio from 233U to 229mTh, we produced 229mTh fromβ-decay of 229Ac following a nuclear reaction process, whereas in all previous investigations on the
decay properties of 229mTh, the nuclide was produced from the α-decay of 233U. By using a suitable
nuclear reaction, it was expected that the 229Th sample would have a m/g ratio large enough to observe
the minor α-decay from 229mTh, although complicated chemical procedures for eliminating by-products
would be required.
Based on these ideas, we previously reported the detection of α-decays of 229mTh produced by the230

Th(γ, n) reaction [11]. Unfortunately, it appeared that the results contained interfering effects due topile-up of the α-particles from 230Th decay and β-rays of the other nuclear reaction products. In thisreaction system, the interference was unavoidable because it is impossible to chemically separate the229m

Th from the target 230Th and other thorium isotopes produced in the reaction.
In this study, we attempted to detect the α-decay signals from 229mTh produced using anotherreaction system. We obtained 229mTh from β-decay 229Ac that was produced through the reaction 232Th(γ,p2n). A sample of 229m,gTh was prepared using several chemical separation methods and was measured
with an α-spectrometer.

§2. Experimental
2.1 Preparation of the thorium dioxide target
A 232Th reagent, allowed to stand unprocessed for more than 40 years, contains daughter nuclei inradioactive equilibrium mixture, such as 228Ra and 228Ac. The 228Ac feeds 228Th that significantlyinterferes with the observation of the α-particles of 229mTh. Therefore, 228Ra and 228Ac should be removed
from thorium in radioactive equilibrium with its decay series nuclei just before bremsstrahlung
irradiation. To perform such chemical separation, about 1 g of thorium dioxide was dissolved in a
mixture of 10 mL of 13M (mol/dm3) nitric acid (HNO3) and a drop of 27M hydroﬂuoric acid (HF) under
heating, and the solution was passed through a column packed with anion exchange resin (Dowex 1X8,
100-200 mesh, 30 mmφ × 70 mm) to adsorb thorium isotopes. The resin was washed with 150 mL of 8M
HNO3 to remove radium and actinium, and then thorium isotopes were eluted from the column with27
150 mL of 2M HCl. A greater than 3-fold excess of saturated oxalic acid was added to the eluate under
heating, then the resulting precipitate, Th(C2O4)2, was aged for one night. The precipitate was washedwith distilled water and ignited at 800 ºC for 8 hours to produce thorium dioxide.
2.2 Bremsstrahlung irradiation
A sample of about 1.65 g of 232 ThO 2 was enclosed in a quartz tube for irradiation withbremsstrahlung radiation. The irradiation was carried out using the Electron Linear Accelerator at
Tohoku University. The accelerator was operated at an electron energy of 30 MeV with a mean currentof around 0.1 mA. The 232ThO2 target was placed in close contact with the back of a platinum converterand cooled with running tap water during the 1-hour irradiation. After the irradiation, the target was
chemically treated according to the procedure outlined in Fig.1 and the details given below.
2.3 Isolation of actinium from the irradiated target
The target material was dissolved in a mixture of 10 mL of 13M HNO3 and one drop of 27M HF
under heating, and diluted with water to 40 mL (diluted to about 4M HNO 3). In order to remove
thorium isotopes from the solution, including aimed actinium, solvent extraction with 40 mL of 1M
HDEHP-benzene was carried out three times in series. After washing the aqueous phase with 40 mL
benzene, actinium isotopes were co-precipitated with iron hydroxide by adding 1 mg of iron and 15M
ammonia water (NH3aq). The precipitate was then dissolved in 1M HNO3 and the solution passed
through a cation exchange resin column (Dowex 50X8, 200-400 mesh, 5.5 mmφ × 40 mm), which
adsorbs actinium isotopes. The resin was washed with 8 mL of 3M HNO3 to remove radium and iron.
Then actinium isotopes were eluted from the column with 12 mL of 8M HNO3. The solution was passed
through an anion exchange resin column (Dowex 1X8, 200-400 mesh, 5.5 mmφ × 40 mm) to completely
eliminate thorium from the solution. The actinium fraction containing rare earth ﬁssion products was
adjusted to a 9M HCl solution and passed twice in series through an anion- exchange resin column(Dowex 1X8, 200-400 mesh, 5.5 mmφ × 40 mm) to adsorb completely 231Pa produced from 231Th. These
purification procedures for actinium were carried out within about one hour after the end ofbremsstrahlung irradiation.
2.4 Preparation of 229m,gTh source for α-particle counting and spectrometry
To allow the decay of 229Ac (T1/2 = 62.7 min) and the growth of 229m,gTh isotopes, the puriﬁed actinium
fraction was left to stand for 3 hours after the end of the purification of actinium. The solution
containing thorium isotopes was adjusted to 8M HNO3 solution during these 3 hours and passed
through an anion- exchange resin column (Dowex 1X8, 200-400 mesh, 5.5 mmφ × 40 mm) to adsorb thethorium isotopes. The resin was washed with 20 mL of 8M HNO3 to remove rare earth ﬁssion products
and actinium isotopes. The thorium isotopes were eluted from the column with 5 mL of 2M HCl and coprecipitated with samarium hydroxide by adding 30 μg of samarium and 15M NH3aq. The precipitate
was collected on a 0.02-μm alumina filter (Whatman, ANODISC membrane) of 18 mm diameter toprepare a counting source. The ﬁlter was ﬁxed on a stainless-steel supporting ring and dried at 130 ºC.
All the chemical procedures were ﬁnished about 5 hours after the end of irradiation. The sample wasmeasured by α-ray spectrometry with a 450 mm2 silicon detector and a 2k-channel PC-PHA system.
The background count rate for this detector was about 20 counts/day in the energy range of 3 to 8 MeV

28

Fig.1. Chemical procedure for preparation of the 229m,gTh sample.
and less than 1 count/day in the energy range of 4.5 to 5.1 MeV. Collection of α-events was started
within 10 minutes of completing the counting source preparation and the accumulation of an α-ray
spectrum for 104 -sec was repeated 90 times.

§3. Results and discussion
An α-ray spectrum obtained as a sum of the first 30 spectra is shown in Fig.2. The α-peaks of
147

Sm, 232Th, 230Th, and 228Th and its daughters can be observed in the spectra. Some dozen α-counts areobserved between the 230Th peaks and the 228Th peaks, at an energy consistent with that expected for
229m,gTh. It was found that the ratio of the α-counts of 230Th/229Th/228Th was about 3/1/70, while it was

about 5500/1/10 for the thorium sample isolated from 230Th(γ, n) reaction products [11]. In thisexperiment, the count number of 230Th decays was relatively small and had no influence on theidentification of 229m,gTh. However, interference from 228Th on the observation of 229Th may haveoccurred, as discussed below, because the count number of 228Th decays was greater by a factor of sevenin this experiment.
A magniﬁcation of theα-spectrum for the region related to 229Th is shown in Fig.3 (a). The spectrumof the energy region differs from the spectrum expected for only 229gTh. The causes of this difference are
believed to be the peak tail from the peaks of 228Th and its daughters, α-counts from impurities, and/or
the existence of 229mTh.
228

Th was formed simultaneously with 229m,gTh by the β-decay of 228Ac produced in the 232Th(γ, p3n)

reaction in the source. It has the largest number of counts in the spectra and the energy region is29

Fig.2.

α-ray spectrum acquired over a counting duration of 3 × 105 s, starting 10
minutes after the chemical separation.

Fig.3. Expandedα-ray spectra acquired over a counting duration of 3 × 105 s, starting
10 minutes after the chemical separation (a), and acquired 1 week after thechemical separation (b).
higher than that of 229m,gTh. It was found, however, that the high resolution spectrum is little inﬂuenced
by the peak tail of 228Th. In Fig.3 (a) the 228Th peak has a FWHM of about 29 keV measured at 5423 keV.
A growth in time of the α-count rate was observed. These counts were identified by the energy
value as the α-peaks of 231Pa. The growth of 231Pa interfered with the identification of 229mTh. The
spectrum obtained one week after the chemical separation is shown in Fig.3 (b), overlaying Fig.3 (a),demonstrating the growth of 231Pa. It is thought that 231Pa was completely eliminated by the repetitive
anion exchange at the end of the chemical purification of the actinium fraction and, therefore, theobserved 231Pa may be the decay product of 231Th, produced in the 232Th(γ, n) reaction. The counting
source included 231Th because elimination of thorium was not complete. Although the decontamination

30
factor of thorium isotopes in the purified actinium fraction was estimated to be about 5 × 10 － 5,
sufﬁcient 231Pa was produced to interfere with the identiﬁcation of 229mTh because of the large crosssection of the 232Th(γ, n) reaction.
The spectrum in Fig.3 (b) can be reproduced by sum of the 229gTh spectrum and the 231Pa spectrum.
It indicates that the half-life of 229mTh is not as long as one week. On the other hand, the early spectrum
in Fig.3 (a), before the growth of 231Pa, differs from the spectrum expected for only 229gTh. In particular
the observed α-counts between 4.93 MeV and 5.05 MeV, which coincides with the expected energy of
229m

Th, were larger than those expected for 229gTh. It may be considered that the new α-emitter 229mTh

was observed in this work, although the α-peaks are not clearly deﬁned, probably due to poor counting
statistics.

§4. Conclusion
We attempted to produce 229m Th by the nuclear reaction 232 Th(γ, p2n) 229 Ac, followed bydisintegration to 229m,gTh. The alpha-events in the expected energy region for 229m,gTh were observedwith less interference than has been achieved in previous experiments. The spectral shape differs fromthat expected for only 229gTh, which may be due to presence of 229mTh. A better chemical separation ofactinium from thorium would eliminate the interference of 231Pa and allow more deﬁnitive results to beobtained.

Acknowledgement
The authors are grateful to the staff in the division of accelerators of the Laboratory of Nuclear
Science, Tohoku University.

References[1]

C.W. Reich and R.G. Helmer: Phys. Rev. Lett. 64 (1990) 271.

[2]

R.G. Helmer and C.W. Reich: Phys. Rev. C49 (1994) 1845.

[3]

V. Barci, G. Ardisson, G. Barci-Funel, B. Weiss, O. El Samad, and R.K. Sheline: Phys. Rev. C68(2003) 034329.

[4]

D.G. Burke, P.E. Garrett, T. Qu, and R.A. Naumann: Phys. Rev. C42 (1990) R499.

[5]

E.V. Tkalya, A.N. Zherikhin, and V.I Zhudov: Phys. Rev. C61 (2000) 064308.

[6]

G.M. Irwin and K.H. Kim: Phys. Rev. Lett. 79 (1997) 990.

[7]

D.S. Richardson, D.M.. Benton, D.E. Evans, J.A.R. Grifﬁth, and G Tungate: Phys. Rev. Lett. 80(1998) 3206.

[8]

S.B. Utter, P. Beiersdorfer, A. Barnes, R.W. Lougheed, J.R. Crespo López-Urrutia, J.A. Becker,
and M.S. Weiss: Phys. Rev. Lett. 82 (1999) 505.

[9]

R.W. Shaw, J.P. Young, S.P. Cooper, and O.F. Webb: Phys. Rev. Lett. 82 (1999) 1109.

[10]E. Browne, E.B. Norman, R.D. Canaan, D.C. Glasgow, J.M. Keller, and J.P. Young: Phys. Rev. C64(2001) 014311.

31
[11]

T. Mitsugashira, M. Hara, T. Ohtsuki, H. Yuki, K. Takamiya, Y. Kasamatsu, A. Shinohara, H.
Kikunaga, and T. Nakanishi: J. Radioanal. Nucl. Chem. 255 (2003) 63.

[12]

A.M. Dykhne, N.V. Eremin, and E.V. Tkalya: JETP Lett. 64 (1996) 345.

Research Report of Laboratory of Nuclear Science, Tohoku University Vol. 38 (2005)

32(LNS Experiment: #2389, #2408, #2424, #2443, #2458, #2460, #2475, #2490, #2492, #2502,#2503, #2513, #2514, #2525, #2526, #2541, #2542)

Search for the Decay of 229mTh by Photon Detection
Y. Kasamatsu1, H. Kikunaga2, K. Nakashima1, K. Takamiya3, T. Mitsugashira4,
T. Nakanishi2, T. Ohtsuki5, H. Yuki5, W. Sato1, and A. Shinohara1
1

2

Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043
Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa 920-1192
3

4Research Reactor Institute, Kyoto University, Kumatori, Osaka 590-0494
The Oarai-branch, Institute for Materials Research, Tohoku University, Oarai-machi, Ibaraki 311-1313
5

Laboratory of Nuclear Science, Tohoku University, Sendai982-0826§1. Introduction
The first excited state of thorium-229, 229mTh, is expected to show an intriguing decay property
because of its extremely low-lying excitation energy. The excitation energy has been reported to beeither 3.5 ± 1.0 eV or 3.4 ± 1.8 eV from the results of precise γ-ray spectroscopy conducted at the  decayof 233U.
In the disintegration process from 229mTh to 229gTh, the emission of internal conversion electrons isforbidden because the disintegration energy is lower than even the ﬁrst ionization energy of thorium
atoms. Thus the de-excitation from 229mTh to the ground state is expected to take place through a direct 
γ-ray transition or decay via an electron bridge (EB) mechanism in which part of the transition energy
is deposited to excite the valence-shell electrons of 229mTh. This implies that the half-life of 229mTh isdirectly affected by the chemical state of 229mTh.
Several experimental results have been reported by different groups about the detection of photons
emitted from 233U samples that contain a considerable amount of 229mTh produced through the α decay
from 233U with a branching ratio of about 2 %. These attempts were not successful, however, owing tointerference of radiation-induced ﬂuorescence from the materials around the radioactive 233U sample.
In our experiments, Th atoms were chemically separated by means of an anion exchange method
for removing the influence of intense radiation from 233U. As for the photon detection, the detection
efficiency was raised as high as possible by developing a novel detection system. In this report, thelimits of the half-life of 229mTh in HNO3 solution are deduced based on the experimental observations.

§2. ExperimentThorium-229m samples were prepared by a chemical separation from about 93mg of 233U containing
4.4 ppm of 232U by the following procedure. Uranium-233 was ﬁrst sorbed in 2 cm3 of an anion exchange
column (Dowex 1X8, 200-400 mesh) in 9M HCl solution and its descendants except for Bi and Tl were
eluted. After a given growth time, accumulated 229Th and 229mTh were eluted in 5 ml of 9M HCl solution
and separated from 233U. In order to thoroughly remove 233U, the eluate was again passed through33
another anion exchange column of the same resin in 9M HCl solution. We were able to accomplish thewhole chemical separation within only about 3 minutes. Following the separation, 1 mg of Al andapproximately 10 ml of concentrated ammonia water were added into the eluate. Thorium atoms were
coprecipitated with Al in the form of hydroxide. After the decantation of the supernatant liquid, theprecipitate was dissolved in 3 to 4 droplets of 8 M HNO3 in order to minimize the sample volume toprepare a quasi point source. The solution sample was transferred into a small quartz bowl of a size of 6
mm in internal diameter and 10 mm in height, and photon measurements were performed.
Taking a wide range of the expected half-life of 229mTh into account, two different experiments werecarried out varying the growth time: 2 and 17 hours for the ﬁrst and second experiments, respectively.
It took 18 minutes to accomplish the chemical separation and treatment in the ﬁrst experiment, and 30
minutes in the second.
In this work, we consider that the detection efﬁciency precedes the energy information. Although
the output signal of a photomultiplier (PM) has no information concerning the energies of incident
photons, therefore, we adopted the PM designed for single photon counting. In order to improve thedetection efficiency, an oval reflector was employed to focus as many photons as possible on thephotocathode of the PM.
The detection efficiency was estimated taking into account several parameters: the sample
geometry, the reflection efficiency of the reflector, the effect of a finite volume of the 229mTh solution
sample, the quantum efficiency of the PM, and the absorbance by the HNO3 solution. The wholedetection efficiency was accordingly estimated to be at least 4 × 10 －４ for the photons in the range
between 340 and 600 nm (3.6 - 2.1 eV).

§3. Result and Discussion
It should be noted that 229mTh accumulates, during the growth time, depending on THCl, and 229mTh
disintegrates, during the measurement, at the rate THNO3. Here, THCl and THNO3 denote the half-lives of229m

Th as a solute in HCl and HNO3 solutions, respectively. Since the chemical condition of 229mTh turns

during the preparation of the sample, the following discussion on THNO3 is based on the number of 229mTh
atoms grown in the HCl solution.
In Fig. 1 and 2 are shown the time variation of the photon counting rate for the ﬁrst experiment(2-hour growth time) and that for the second experiment (17-hour growth time), respectively. The
horizontal dashed lines represent the constant background level obtained by a blank measurement. It
is obvious from the ﬁgures that additional photons deriving from the 229mTh source as well as from theother descendants were not evidently detected.
Although the half-life cannot be determined, the limits of the half-life can be estimated from theresults. The estimation of the limit of THNO3 requires 1) the lower limit of the number of 229mTh atoms at
the end of the growth in the HCl solution and 2) the detection efficiency which has already been
estimated. The number of 229mTh atoms can be figured from the activity of 229mTh at the end of thegrowth time. If THCl is 3 minutes, which was taken for the chemical separation, or shorter, it would be
difficult to estimate the limit of THNO3 because of their decay loss during the separation. From these34

Fig.1. Time variation of the counting rate for photons emitted from 229mTh HNO3 solution sample
grown for 2 hours in the 9M HCl.

Fig.2. Time variation of the counting rate for photons emitted from 229mTh HNO3 solution sample
grown for 17 hours in the 9M HCl.

conditions, the limits were estimated as follows.
1) If THCl is shorter than 3 minutes, it is difficult by the present experimental method to observe
evident photon events for any half-life of 229mTh in HNO3 solution.
2) If THCl is longer than 3 minutes, THNO3 can be limited as ＜ 3 minutes or ＞ 60 hours as indicated bysolid line in Fig. 1. Especially referring to the case that THCl is longer than 3 hours, the number of229m

Th atoms accumulated during the growth time is almost constant in both experiments and35
THNO3 should be ＜ 2 minutes or ＞ 400 days as indicated by the solid lines in Fig. 2.
For further discussion about THNO3, more detailed information on THCl is necessary. A new device forthe preparation of a point source of 229mTh is now under development.

Research Report of Laboratory of Nuclear Science, Tohoku University Vol. 38 (2005)

36(LNS Experiment : #2427, #2442, #2457, #2474, #2489, #2499, #2512, #2524)

Life-time measurement of 7Be in beryllium metal
T. Ohtsuki1, Y. Yuki1, M. Muto1, J. Kasagi1, K. Ohno2
1
2

Laboratory of Nuclear Science, Tohoku University, Mikamine, Taihaku, Sendai 982-0826

Department of Physics, Yokohama National University, 79-5 Tokiwadai, Hodogaya, Yokohama 240-8501

The decay rate of 7Be (nucleus of electron-capture decay) was measured in Be metal. The half life of
7

Be in Be metal (Be metal (7Be)) is found to be 53.12 ± 0.05 days. We have found that the decay rate of

7

Be in Be metal is almost corresponding to that in graphite host, Lithium ﬂuoride host etc. reported

within the errors.

§1. Introduction
As ﬁrst suggested by Segré et al. [1-4], electron-capture (EC) decay rates depend on the density ofatomic electrons within the nucleus. Environment factors such as chemical form, pressure, etc. mayalter the electron contact densities at nucleus, and thus, affect the electron-capture decay rates. Here,the nucleus 7Be is a good candidate in which to look for such variations in environmental factors
because of its simplest electronic structure, 1s22s2, in the EC decay nucleus. The 7Be decays directly to
the 3/2 － ground state of 7Li with a branching of 89.6 %, and goes to the ﬁrst excited state in 7Li (1/2 － at
478 keV) with that of 10.4 %, which decays by γ emission to the ground state [5-7]. In recent research,
there have been several reports of variations as a function of the host metals [8-12] and chemical forms[13-15] and pressure [16-17]. Although, a precise measurement may be still needed to obtain theabsolute decay rate in the different circumstances [18-21].
Because of the uniform lattice structure (hcp) including 7Be in Be metal, the electron contact density
on 7Be nucleus should be essentially surveyed. In the present study, we have measured the half-life of
7

Be in Be metal by using a standard clock time.

§2. Experimental procedure
Be metal (hcp lattice structure) of 10 mm (in diameter) × 0.3 mm (in thickness) was utilized to
produce 7Be uniformly in the metal. After being washed with HCl solution, the Be metal was sealed in aquartz tube (vacuum packing) of 12 mm in diameter as a target. The irradiation with a bremsstrahlung(50 MeV electrons) was carried out at the Electron Linear Accelerator, Laboratory of Nuclear Science,
Tohoku University. The sample in a quartz tube was set in the middle of a sweep magnet placed on theaxis of the electron beam. A platinum converter in 2 mm thickness was set in front of the sweep magnet
to generate a bremsstrahlung. Then, the sample was irradiated only by the bremsstrahlung (allelectrons were ruled out by the magnetic field). Therefore, the damage to a lattice of Be metal was
confined to the minimum. The experimental setup for irradiation is shown in Fig.1. The 7Be can be37produced uniformly by the 9Be(γ, 2n) 7Be reaction in the Be metal. After irradiation, the sample was
baked in an electric oven of vacuum packing at 1100 ºC (a melting point of Be metal: 1278 ºC) for 1 hour
to recover the lattice defect even if the lattice defect occurs by the (γ, 2n) reaction. Finally, the sample
was washed again with HCl solution to clean up the surface.

Fig.1. Setup for irradiation of Be metal.
The two samples of Be metal(7Be) and 7Be@C60 for reference of the sample were placed in an
automated sample changer, which horizontally moved the samples in front of a γ-ray detector. This
allowed the decay rates of the two samples to be measured in a comparable way. The system is shownin Fig.2. The activities of the 7Be, the 478 keV γ-rays emanating from 7Be, was measured with a highpurity germanium (HPGe) detector (ΔEFWHM is 1.8 keV and 50 % relative efficiency) coupled to a
2048-channel pulse-height analyzer. Due to the excellent energy resolution of the HPGe detector, a goodFig.2. Experimental setup.

38
signal-to-noise ratio was obtained. The background was reduced by a lead shield. Therefore, thebackground peaks do not impair the determination of the half-life of 7Be in the present experiment. The
radioactivities of 7Be could be uniquely detected by means of its characteristic γ-rays, and any othersources were ruled out. We measured 330 points with durations of Td ~ 6 hours. Total measuring time
was now 170 days that was over three half-lives of 7Be. The start time for each run was taken from atime standard signal distributed via a long-wave radio center in Japan. Therefore, the uncertainty intime measurements can be neglected.

§3. Results and discussion
A typical γ-ray spectrum obtained in the sample of Be metal (7Be) is shown in Fig.3. The expected
γ line at Eγ = 478 keV and a natural background line at Eγ = 1461 keV can be seen as two giant peaks.
No peaks were seen at around Eγ = 478 keV when the 7Be sources was absent. In Fig.4, the exponential
decay curve of the 7Be activities for sample of Be metal (7Be) is shown as a function of the time (days).
The decay curve obtained in the present measurement was ﬁtted including the statistical errors by a
Minuit program distributed from the CERN Program Library. The statistical error is dominating theuncertainty in each data point in Fig.4. The uncertainty of our measurement is given by the uncertaintyof the slope of the straight line ﬁtted to the logarithm of the counts (i.e. counts per second) of the decay
spectrum. The result for the sample Be metal (7Be) is T1/2 = 53.12 ± 0.05 days. The dead time in the dataacquisition system is evaluated to be about 8 ~ 9 sec to the each running time. Therefore, theuncertainty due to the dead time is estimated to be almost 0.04 % and this value is smaller than theﬁtting errors of the half-life of 7Be. The counting rates of the natural background, which is the 1461
keV γ-rays emanating from 40K, is also shown in Fig.4. The data for 40K obtained was also ﬁtted with

Fig.3. Typical γ-ray spectrum of the 7Be in the sample of Be metal.

39
the same procedures. It was found that the ﬁtted line is corresponding to a horizontal one. (It should be
noted that we have also measured the half-life of 7Be in the sample of 7Be@C60. The result have beenpresented in another paper [22])The half-life obtained in the sample of Be metal ( 7Be), T 1/2 = 53.17 ± 0.05 days, is almost
corresponding to the data, LiF (7Be) and graphite etc., which is reported by Jaeger et al. and Norman etal. [8, 11], in which, the start time for each run were taken from the time standard signal distributed
publicly. Further, the half-life of 7Be in several host materials (Graphite, Boron nitride etc.) has beensummarized by Notrman et al. [11]. The value (T1/2) is almost with in 53.1 ~ 53.3 days as shown in Table 1.
Therefore, we found that the variation (T1/2) of 7Be for Be metal (7Be) almost corresponds to the data
presented so far.

Fig.4.

Exponential decay line of 7Be in the sample of Be metal (7Be). Backgroundradioactivities of 40K are also shown in the ﬁgure.
Table 1. Half-life of 7Be in Be Metal as determined with a leastsquared ﬁt. Half-lives previously measured are also shown
as a comparison.
Host material

T1/2

Ref. No.

Beryllium
Lithium ﬂuoride
Graphite
Boron niterideTantalumGold
Aluminum53.12 ± 0.05
53.12 ± 0.07
53.107 ± 0.022
53.174 ± 0.037
53.195 ± 0.052
53.311 ± 0.042
53.17 ± 0.02

This work
8)
11)
11)
11)
11)
15)

40

§4. Conclusion
We have measured the half-life of 7Be which is produced in Be metal using a HPGe detector taking
into account a standard time. We found that the half-life of 7Be in Be metal was T1/2 = 53.12 ± 0.05 days.

Acknowledgments
The authors are grateful to the technical staff of the Laboratory of the Nuclear Science, Tohoku
University for beam-handling.

References[1]

E. Segré: Phys. Rev. 71 (1947) 274.

[2]

R. Daudel: Rev. Sci. 85 (1947) 162.

[3]

E. Segré and C.E. Wiegand: Phys. Rev. 75 (1949) 39.

[4]

R.F. Leininger, E. Segré, and C. Wiegand: Phys. Rev. 76 (1949) 897.

[5]

R.B. Firestone, V.S. Shirley, C.M. Baglin, S.Y. Frank Chu, J. Zipkin, C. M. Lederer, and V. S.
Shirley: Eds. Table of Isotopes, 8th Ed. Vol.I (John Wiley & Sons, Inc., 1996).

[6]

Ajzenberg-Selove: Nucl. Phys. A490 (1988) 1.

[7]

G.T. Emery: Ann. Rev. Nucl. Sci. 22 (1972) 165.

[8]

M. Jaeger, S. Wilmes, V. Kölle, G. Staudt, and P. Mohr: Phys. Rev. C54 (1996) 423.

[9]

A. Ray, P. Das, S.K. Saha, S.K. Das, B. Sethi, A. Mookerjee, C. Basu Chaudhuri, and G. Pari:
Phys. Lett. B455 (1999) 69.

[10]

A. Ray, P. Das, S.K. Saha, and S.K. Das: Phys. Lett. B531 (2002) 187.

[11] E.B. Norman, G.A. Rech, E. Browne, R.M. Larimer, M.R. Dragowsky, Y.D. Chan., M.C.P. Isaac, R.J.
McDonald, A.R. Smith: Phys. Lett. B519 (2001) 15.
[12]

Z.Y. Liu, C.B. Li, S.G. Wang, J. Zhou, Q.Y. Meng, S.J. Lu, and S.H. Zhou: Chinese Phys. Lett. 20(2003) 829.

[13]

C.A. Huh: Earth and Planetary Sci. Lett. 171 (1999) 325.

[14]

H.W. Jphlige, D.C. Aumann, and H.J. Born: Phys. Rev C2 (1970) 1616.

[15]

F. Lagoutine, J. Legrand, and C. Bac: J. Appl. Radiat. Isot. 26 (1975) 131.

[16]

W.K. Hensley, W.A. Bassett, and J.R. Huizenga: Science 181 (1973) 1164.

[17]

L. Liu and C.A. Huh: Earth and Planetary Sci. Lett. 180 (2000) 163.

[18]

The half-life of 7Be in the different chemical forms has been measured in several experiments. It
should be noted that: Huh [13] has reported the half-life of 7Be in the different chemical forms,
Be2 ＋ (OH2)4, Be (OH)2, and BeO, and they claimed that the observed difference is as much as 1.5%
(in Ref. 13). In early study, Johlige [14] et al. have reported the half-life of 7Be in similar chemical
forms (Be2 ＋ (OH2)4, BeO, etc.) and the variations were only within around 0.1%.

[19]

A. Ray, P. Das, S.K. Saha, and S.K. Das: Science 287 (2000) 1203.

[20]

H. Geissel and G. Münzenberg: Eur. Phys. J. A13 (2002) 247: The half-life of 7Be depends on theplasma density in the vicinity of the 7Be nucleus. This value can be determined in experiments on

41
7

Be in different charge states which are planned at GSI.

[21]

J.A. Tossel: Earth and Planetary Sci. Lett. 195 (2002) 131.

[22]

T. Ohtsuki, H. Yuki, M. Muto, J. Kasagi, and K. Ohno: Phys. Rev. Lett. 93 (2004) 112501.

42

核理研研究報告

第38巻

2005

(LNS Experiment : #2523, #2539)

光量子放射化分析法による KTa1 － xNbxO3 単結晶中の不純物分析
鹿野弘二 1，大槻
1
2

勤 2，結城秀之 2，藤浦和夫3，笹浦正弘 3

函館工業高等専門学校（042-8501

函館市戸倉町 14 番 1 号）

東北大学理学部付属核理学研究施設（982-0826
3

NTT フォトニクス研究所（243-0198

仙台市太白区三神峯 1-12-1）

厚木市森の里若宮 3-1）

Photon Activation Analysis of Impurities in KTa1 － xNbxO3
Single Crystals
K.Shikano1, T.Ohtsuki2, H.Yuki2, K.Fujiura3, M.Sasaura3
1

2

Hakodate National College Technology, Tokura-cho 14-1, Hakodate, Hokkaido 042-8501
Laboratory of Nuclear Science, Tohoku University, Mikamine, Taihaku-ku, Sendai, Miyagi, 982-0826
3

NTT Photonics Laboratories, Nippon Telegraph and Telephone Corporation, Morinosato, Atsugi,
Kanagawa, 243-0198

The determination of Fe, Co, Ni, Cu, and Pt in KTa1 － xNbxO3 single crystals for opto-electronics
devices has been studied by using photon activation analysis. With this approach it was difficult todetermine these impurities non-destructively because of the large activity of nuclides with long halflives such as 182Ta and 92mNb produced from matrices. Therefore, chemical separation was studied toremove such nuclear interferents as 182Ta and 92mNb. 92mNb and 58Co were used as tracers. It was foundthat 58Co could be separated by the extraction with TPB and by the anion exchange.
KTa1 － xNbxO3（KTN）結晶中の不純物（Fe，Co，Ni，Pt）の光量子放射化分析法を検討した。その結果，
マトリックから半減期が 115d の 182Ta と 10.2d の 92mNb が生成し，これらの生成放射能が大きいことから非破壊分析が不可能であることが分かった。そこで，92mNb と 58Co をトレーサにして TPB による溶媒抽出，
陰イオン交換体による分離を試みた結果，Co のみを分離できる条件を明らかにした。

§１．はじめに通信容量の増大にともないネットワークの大容量化・高機能化を目的とした光部品の小型化，省電力化，高機能化の開発がすすめられている。KTa1 － xNbxO3（KTN）結晶は世界最高の電気光学効果を有し，光変調器や光スイッチなどの従来の LiNbO3 光デバイスの駆動電圧やサイズを一桁改善できると共に，次世代の高機能デバイス期待されている［1］。一方，材料開発において材料特性を向上する方法の一つとして，材料中の不純物濃度を明らかにし，材料作製条件を改善することにより純度を高める高純度化があげられる。半導体，光ファイバなどの通信用材料も高純度化により材料特性が向上し，今日の光通信技術が確立されてき43た。KTN 結晶についても同様であり，さらなる光学特性の向上には，高純度化が不可欠であり，したがって結晶中の不純物評価が重要な課題である。
本研究では，光量子放射化分析法により，KTN 結晶中の不純物を定量し，材料特性との相関を明らかにする。目的元素として，製造過程で汚染が予想される Fe，Co，Ni，Pt の定量を進める。まず，陰マトリッ
クから生成する放射性元素を明らかにするとともに放射能強度を測定し，非破壊分析の可能性を検討する。
隠比較標準試料を照射し，検出限界値を明らかにする。韻化学分離法の開発のため，トレーサ実験を行う。
試料溶解法を検討する。

§２．実
2.1 試

験
料

分析試料に用いた KTN 結晶は NTT フォトニクス研究所で作製された［1］。サイズは約10×10mm2 で厚さは約0.5mm である。比較のため，NTT フォトニクス研究所で作製された KTaO3（KT）結晶も使用した。
これらの結晶を約5×5mm2 に切断後，塩酸水溶液，蒸留水，アルコールにより超音波洗浄し，照射試料とした。また，標準試料には，市販の Fe，Co，Ni，Pt 箔を使用し，分析試料と同様に約5×5mm2 に切断し，照射試料とした。また，フラックスモニターには市販の Cu 箔を使用した。
2.2 照射と測定
光量子照射は東北大学理学部付属核理学研究施設の電子線ライナックにより行った。KTN 結晶と KT 結晶を HF － HNO3 系のエッチング液と蒸留水により超音波洗浄した後，フラックスモニターの Cu 箔とともにアルミニウム箔に包み，30MeV，100μA の条件で20min，1hr，8hr の条件で照射した。照射後，表面汚染を除去するため HF － HNO3 系のエッチング液と蒸留水により超音波洗浄した後，Ge 検出器－4096ch
波高分析装置により放射能測定を行った。また，標準試料として，Fe，Co，Ni，Pt 箔を分析試料と同様の方法で照射した。

2.3 化学分離
照射後，表面汚染を除去した分析試料を Na2CO3 とともに白金るつぼ中で溶融した。得られた溶融物は温水，HNO3 で溶解し，テフロン蒸発皿上で蒸発乾固した。これに HF 溶液を加え，イオン交換分離，溶媒抽出に用いた。これら分離法の分配係数はこれまで多く報告されている。ここでは，HF 系溶液による陰イオ
ン交換分離［2］ならびに HF-HCl 系溶液／ TPB による溶媒抽出［3, 4］を採用することとし，以下の操作で分離を行った。
陰イオン交換体として Dowex1-8（50-100mesh) の約５g を文献［5］にしたがい洗浄後，カラムに挿入し，1MHF 溶液を流して前処理した。このカラムに分析試料溶液を加え，1M フッ酸溶液を0.3ml/min の速度で流し，溶離液の放射能を Ge 検出器－4096ch 波高分析装置により測定した。
溶媒抽出は以下のように行った。蒸発乾固物を7MHF －5MHCl 溶液に溶解後，TPB 溶液とともに30分振とうした。有機相，水相の一定量を分取し，Ge 検出器－4096ch 波高分析装置により放射能測定した。

§３．結果と考察
3.1 非破壊分析の可能性
標 準 試 料 の Fe，Co，Ni，Pt か ら（γ, n）反 応 に よ り 58Co，57Ni，191Pt，195mPt が，ま た，（n, γ），
（γ,

44
第１表

Nuclear reaction of Fe, Co, Ni, Pt and nuclear interference produced by thematrix by Bremsstrahlung bombardment

Nuclear reaction

Half-lufe

Fe (γ, 2n) Mn
Mn (γ, p) 56Mn
59
Co (γ, n) 58Co
59
Co (γ, 2n) 57Co
58
Ni (γ, n) 57Ni
58
Ni (γ, 2n) 56Ni
192
Pt (γ, n) 191Pt
196
Pt (γ, n) 195mPt
41
K (n, γ) 42K
181
Ta (n, γ) 182Ta
181
Ta (γ, n) 180mTa→ 180mHf
180
Ta (γ, 2n) 178BTa→ 178m1Hf
93
Nb (γ, n) 92Nb

5.6d
2.6h
70.8d
78.8d
35.9h
6.1d
2.8d
4.0d
12.4h
115d
8.1h
5.5h
2.4h
4.0s
10.2d

54

52

57

Decay modeEC, β ,β－
EC, β＋EC, β＋EC, β＋
EC
EC
IT
β－
β－
EC, β－ITEC
IT
EC, β＋＋

Eγ, keV (%)
1434.1 (100)846.8 (98.9)
810.8 (99.4)
846.8 (99.9), 1238.3 (67.0)
1377.6 (77.6)
811.9 (74.1)
538.9 (13.7)
129.7 (2.81)
1524.7 (17.9)
1121.3 (35.0), 1189.1 (16.5), 1221.4 (27.4)
103.4 (0.6), 500.7 (12.8)
215.3 (81.7), 332.3 (94.4), 443.2 (85.3)
331.7 (31.8)
213.4 (82.4), 325.6 (94.1), 426.4 (97.0)
912.8 (1.7), 934.5 (99.2), 1847.3 (0.9)2n）および（γ, p）反応により 52Mn，56Mn，57Co，56Ni，が生成することがわかった。これらの核種の核デー
タを第１表に示す。第１表に示したように，56Mn の放出するγ線のエネルギーは846.8keV で 57Co からのγ線と同じであり，共存すると互いに妨害となり得る。しかし，半減期が2.58hr と短いため，照射後数日冷却することにより妨害は除去できる。
一方，マトリックからの妨害を検討するため，KTN 結晶と KT 結晶のγ線照射を行った。その結果，KT結晶からは，（n, γ）反応により 42K，182Ta が，（γ, n）反応により 180mTa，178BTa が，また，その壊変核種である 180mHf と 178m1Hf が生成することがわかった。また，600keV 以上のγ線領域では生成放射能が比較的小さいことがわかる。一方，KTN 結晶ではこれらの核種に加え，（γ, n）反応により 92mNb が生成することがわかった。また，700keV 以下の領域では，92mNb からの934keV のγ線によるコンプトン散乱によりバッ
クグランドが増大し，放射能測定の妨害となることがわかった。これら核種の核データも第１表に示す。
以上の結果から，マトリックから生成する半減期115d の 181Ta と10.2d の 92mNb が放射能測定の妨害核種といえる。これに対して，Fe，Co，Ni，Pt から生成した半減期が約1.5d から約300d までの核種を目的核種として，長時間照射して数日冷却後，放射能測定することにより，非破壊分析が可能と推測された。そこ
で，以下の検討を行った。
KT 結晶および KTN 結晶の100～200mg を8hr 照射し，表面汚染を化学エッチングにより除去した後，１週間冷却した。これを約１週間ごとに30000秒測定し，γ線スペクトルの変化を調べるとともに，52Mn，
58

Co，57Co，57Ni，56Ni，191Pt，195mPt について測定可能かどうかもあわせて調べ，非破壊分析の可能性を検討した。第１図，第２図に照射から１週間後，３週間後，５週間後の KT 結晶および KTN 結晶からのγ線スペクトルを示す。第１図と第２図から，KT 結晶では200～500keV におけるγ線は１週間以上冷却することで減衰することがわかった。一方，1000keV 以下の領域で 182Ta の1121～1221keV のγ線によるコ
ンプトン散乱の影響が生じ，測定の妨害になることがわかった。これに対し，KTN 結晶では，Nb が入ることにより生成放射能がγ線エネルギー全体で一桁以上増加すること，５週間の冷却により約一桁減少することがわかる。これは，92mNb の半減期が10.2d であることから，92mNb の影響が約一桁減少したことによる。
以上の結果から，マトリックスの放射能強度が１ヶ月の冷却後でも大きく，非破壊分析は困難であると結45論した。そこで，化学分離法による定量を検討した。

Fig.1.

γ-ray spectra of KTaO3 single crystal. Cooling for a) about 1 week, b) 3.4
weeks and c) 5.4 weeks after irradiation.

Fig.2.

γ-ray spectra of KTa1 － xNbxO3 single crystal. Cooling for a) 1.4 weeks, b) 3
weeks and c) 5.1 weeks after irradiation.

3.2 化学分離法の検討
3.2.1 溶解法の検討
化学分離を行うには，試料の迅速溶解が必要である。KT 結晶，KTN 結晶いずれも無機酸に溶解しにくい
ことは知られている。そこで，Na2CO3 によるアルカリ溶融を検討した。ここでは，KTN 結晶について検討した結果を示す。約80mg の KTN 結晶を Na2CO30.5g，1g，1.5g，2g により白金るつぼ中で加熱，溶融し，溶融時間を調べた。その結果，Na2CO3 2g を用いることにより，約２時間でほぼ溶融することがわかった。
その後，温水と硝酸により溶融物を溶解した。

3.2.2 イオン交換法の検討
３.１の結果から，181Ta，92mNb から 52Mn，58Co，57Co，57Ni，56Ni，191Pt，195mPt を分離する必要がある。
そこで，30分間照射した KTN 結晶を用いて分離条件を検討することとした。その結果，アルカリ溶融物を温水と HNO3 により溶解後，蒸発乾固したところ透明の結晶が析出した。これは，NaNO3 が析出したと思われた。これに1MHF 2ml を加えた後析出物を遠心分離し，沈殿物と上澄み液の放射能を測定した。その結果，マトリックス中の 92mNb のうち，約60％が沈殿物に含まれ，約40％が上澄み液に残留することがわかった。この上澄み液を再度蒸発乾固したところ，再度透明の結晶が析出した。これに1MHF 約2ml を加えて析出した結晶を溶解後，前処理した陰イオン交換体のカラムに注入，1MHF 溶離液を0.3ml/min の速度で流し，溶離液の放射能を測定した。その結果，はじめの３フラクションまでは何も検出されず，第４フラク
ション目から 92mNb が測定された。このことから，KTN 結晶中の不純物濃度が低く，照射時間が30分程度
では検出できないこと，また，上澄み液中の 92mNb の放射能が大きいため比較的早めに溶離し測定の妨害になり得ることがわかった。そこで，イオン交換分離の前に TPB 溶媒抽出による 92mNb の除去を検討した。

46
3.2.3 溶媒抽出による92mNb の除去
3.2.1と同様に，照射した KTN 結晶の溶融，溶融物の溶解，蒸発乾固，析出結晶の遠心分離を行った後，上澄み液を再度蒸発乾固し，7MHF －5MHCl 溶液を6ml 加えて析出結晶を溶解した。この溶液に TPB
15ml 加え，15分振とうした。遠心分離後，水相，有機相の放射能を測定した。その結果，92mNb の約90％が TPB により抽出され，水相の 92mNb が1/10まで除去できることがわかった。
3.2.4 Co の分離
続いて，58Co と 92mNb をトレーサに用い，溶媒抽出とイオン交換分離を組み合わせた分離操作で Co が化
学分離できることを確認する実験を行った。
3.2.3と同様に，照射した KTN 結晶の溶融，溶融物の溶解，蒸発乾固，析出結晶の遠心分離を行った後，上澄み液に HNO3 を加え，別に照射した Co 箔（13.61mg）を入れ，溶解した。溶解液を蒸発乾固した後，TBP 溶媒抽出をおこなった。水相を蒸発乾固した後，1MHF 溶液とし，3.2.2と同様にしてイオン交換分離を行った。第３図に，溶離液フラクション毎の 58Co と 92mNb の放射能強度の変化を示した。図に示したように，第１から第５フラクションまで１％から最大50％まで 58Co が溶離した。第１から第５フラクションまでの 58Co 放射能の合計から，Co が溶媒抽出とイオン交換を組み合わせた分離操作によりほぼ100％溶離し，損失のないことが分かった。一方，92mNb はいずれものフラクションにおいても検出限界以下であった。以上のことから，TBP 溶媒抽出とイオン交換分離を組み合わせた分離操作により 92mNb から 58Co を分離できることが分かった。

Fig.3. Elution curve for Co. Flow rate of 1 M HF solution was 0.3 ml/min.

§４

ま と め

KT 結晶，KTN 結晶中の Mn，Fe，Co，Ni，Cu，Pt などの不純物を分析するため，非破壊光量子放射化分析を検討した。その結果，マトリックスら生成する 181Ta と 92mNb の放射能強度が大きく非破壊分析が不可能であることが分かった。そこで，58Co と 92mNb をトレーサに用い，溶媒抽出とイオン交換分離を組み合わせた化学操作を検討した結果，58Co を収率ほぼ100％で分離できる条件を明らかにした。

47
今後は，他の不純物元素に対する本分離操作の有用性を検討するとともに，放射化分析における収率補正法について検討を進める。

参

考

文

献

[1]

M. Sasaura et al.: J. Cryst. Growth 275 (2005) e2099.

[2]

J.P. Paris: Anal. Chem. 32 (1960) 520.

[3]

T. Ishimoti et al.: Bull. Chem. Soc. Japan 33 (1960) 636.

[4]

S.M. Gasita et al.: Translated from Radiokhimiya, 26 (1984) 143.

[5]日本化学会編著：新実験化学講座１（基本操作Ⅰ）(1975) 472.

Research Report of Laboratory of Nuclear Science, Tohoku University Vol. 38 (2005)

48(LNS Experiment: #2518, #2530)

Distribution of 59Fe, 60Co and 85Sr as Low-level Radioactive
Wastes Included in Nonﬂammable Organic Materials
in the Decomposition by Supercritical Water with RuO2
T. Yamamura1, I. Satoh1, W. Sugiyama2, M. Takahashi1,
Y. Shiokawa1, H. Tomiyasu3, and T. Ohtsuki4
1

2
3

Institute for Materials Research, Tohoku University, Sendai 980-8577
Electric Power Research and Development Center, Chubu Electric Power Co., Inc., Nagoya 459-8522

Department of Chemistry and Material Engineering, Faculty of Engineering, Shinshu University, Nagano 380-8553
4

Laboratory for Nuclear Science, Tohoku University, Sendai 982-0826

We investigated the distribution behavior of iron, cobalt and strontium attached to nonﬂammableorganic materials, in solid, liquid and gas phases during the decomposition of these materials insupercritical water mixed with RuO2. The distributions of these elements were determined by using
their radioisotopes as simulated low-level radioactive wastes in order to ease the detection of trace
amounts of elements even in solid and gas phases. The obtained results indicate that all of the elements
investigated in this study (iron, cobalt, and strontium) can be recovered successfully by thissupercritical-water process using RuO2. Consequently, this process is suggested as a predominantcandidate for the treatment of nonﬂammable organic materials in low-level radioactive wastes (LLW).

§1. Introduction
Low-level radioactive wastes (LLW) generated at nuclear power plants can be classiﬁed into three
categories in Japan: the wastes with (i) very low-level, (ii) relatively low-level and (iii) relatively highlevel radioactivity. The conventional method for dealing with these wastes includes compression or
incineration before solidiﬁcation with mortar or concrete, and storing then in 200 L drum containers [1].
Even excluding the above-mentioned category (iii), more than half a million drum containers ﬁlled with
LLW were being stored at domestic nuclear power plants by the end of FY 2001. One of the reasons
why such a huge volume has accumulated is that the main components of the LLW are bulky
nonﬂammable organic materials. No practical method for compressing or decomposing these wastes has
been established yet and therefore volume reduction is not achieved satisfactorily.
A method using supercritical water with RuO2 as a catalyst [2] was recently developed for achieving
the complete gasiﬁcation of nonﬂammable organic compounds, including even such compounds as stablearomatic structures. One of the most important applications of this method would be the decompositionof nonﬂammable organic materials contaminated with low-level radioactivity, in order to reduce theirvolume. We have reported on an investigation using this method to decompose nonﬂammable organic
materials used in nuclear power plants [1]. For practical use, what is required is the removal of trace

49
quantities of radioactive elements attached to these plastics from gas and liquid phases and theirconcentration in the solid phase.
Radioisotopes contained in the LLW from nuclear power plants can be classiﬁed into two types byorigin. One type is the radioactivated materials in nuclear power plants, e.g. iron-59 and cobalt-60 fromthe stainless steel (SUS) used as a major construction material, and the other is the ﬁssion products ofuranium, such as strontium-90, which originate in the nuclear fuel, due to leakage.
In this study, the distribution of the above nuclides into solid, liquid and gas phases were
investigated by applying the supercritical-water reaction with RuO2 for decomposing the nonﬂammableorganic materials. The objective of this study is to elucidate the optimum conditions for theconcentration of the radionuclides into the solid phase. In order to detect trace quantities of elementseven in the gas and solid samples collected after supercritical-water reaction, radiometric analysis wasapplied.

§2. Experimental
Laminate sheeting, a popular product used in domestic nuclear power plants, is commerciallyavailable from Chiyoda Technol Corp., Japan. Reagents and radioactive reagents were used aspurchased. Strontium-85, the tracer of strontium, was prepared by bremsstrahlung irradiation of SrCO3
at the condition of 50 MeV, 100-120 μA, 8 hours with the electron linear accelerator (LINAC) at
Laboratory of Nuclear Science, Tohoku University. Radioactive iron and cobalt hydroxides, as simulated
radioactive scales of SUS, were prepared as follows already reported [3].
2.1 Supercritical-water reaction conditions
The supercritical batch-wise reactor made of hastelloy C-22 with a nominal inside volume of 10.8
cm was supplied by Taiatsu Techno Corp., Japan. A certain amount of radioactive compound and non3

radioactive carrier, 150 mg of laminate sheeting, 30 mg of RuO2 and 3 mL of water were loaded into theabove reactor. By using a temperature controller, the reaction condition of 450ºC-43 MPa was kept for
30 min.
After the reactor was cooled to room temperature, the volume of the gas produced by thesupercritical-water reaction was measured using a gas pressure meter and the gas was collected in a
100 mL gas vial; then everything (liquid and solid phases) remaining inside the reactor was recovered
and placed in a 10 mL polypropylene test tube. The inner surface of the reactor was rinsed with water
three times (total 6 mL) and the washings were collected and added to the contents of the reactor. The
supernatant liquid was separated into another polypropylene test tube by centrifuging these contents.
2.2 Determination of distribution factor
The radioactivity of 59Fe, 60Co, and 85Sr were determined from the areas of their peaks at 1099.3,
1173.2, and 514.0 keV, respectively, by using the γ-ray spectrometer (GEM-28185-P, ORTEC Inc.,
USA). The distribution of their radioactivity in solid, liquid and gas phases was determined as given by

50

Dphase ＝

AphaseAT(1),where Dphase designates the distribution ratio, AT and Aphase are the total radioactivity of each phase after
the supercritical-water reaction and the radioactivity of each phase respectively, and the subscription
phase is "sol", "liq" or "gas", referring to the solid phase, the liquid phase and the gas phase, respectively.

§3. Results and discussion
As reported previously [1], the laminate sheeting initially added is completely decomposed without
any solid residues by the supercritical-water reaction using RuO2. Also in this study, only the clear andcolorless supernatant solutions and inorganic precipitates are recovered in the all runs. The gases
produced during the decomposition of the laminate sheeting may consist of CH4, CO2 and H2, according
to our previous study [2]. Experimental conditions, the volume of the gas produced and the distribution
in three phases in experiments on 59Fe, 60Co, and 85Sr are summarized in Table 1.
3.1 Distribution of 59Fe and 60Co
There is a tendency for the iron to precipitate almost quantitatively and only a trace amount istransferred to the liquid when a small amount of carrier is added (Table 1). The gas produced during
the decomposition of the laminate sheeting contains no activity of 59Fe in any of the runs. This result
indicates that both the decomposition of nonflammable plastics and the recovery of iron in the solid
phase are successful. In contrast to the results for radioactive iron, about a quarter of 60Co distributes
Table 1. Distribution of Fe, Co, and Sr in three phases after reaction in supercritical-water of
nonﬂammable plastics [3]Element

Fe

CarriercompoundFe(OH)3

Amount ofcarrier/ mg

Tracer

SrCO3

102Dliq2)

102Dgas2)99097.5±1.5

2.5±0.0

0.0±0.0

1.3

0.60×10597999.9±1.6

0.1±0.0

0.0±0.0

2.94×105970100±1.4

0.0±0.0

0.0±0.0

3.90×105941100±1.4

0.0±0.0

0.0±0.0

8.33×104910375.4±1.0

24.6±0.2

0.0±0.0

9.02×10499076.7±0.823.3±0.2

0.0±0.0

4)

8.27×10492787.0±0.9

13.0±0.1

0.0±0.0trace

8.21×10296515.1±0.484.9±1.2

0.0±0.0

6.52×103

96032.3±0.567.7±1.0

0.0±0.0

2.97×10494478.0±0.3

22.0±0.1

0.0±0.0

1)
59

13 1)

Fe

4)

23 4)
230

Sr

102Dsol2)

3.12×105

2.3
Co(OH)3

Amountof gasphase/ mL3)

0.13 1)130 1)Co

Activity of Amounttracerof liquid
added
phase
/ Bq
/ mL

5
50

60

Co

85

Sr

1) Amount of Fe(OH)3 calculated on the basis of the amount of Fe(NO3)3·9H2O used to prepare Fe(OH)3.
2) Value indicates measurement error [8].
3) Value calculated from gas pressure after reaction.
4) Amount of Co(OH)3 calculated on the basis of the amount of CoCl2·6H2O used to prepare Co(OH)3.

51
Table 2. Distribution of Co and Sr in three phases when 200 mg of non-radioactive ironhydroxide1) was added for coprecipitation [3]Element

Co

Sr

CarriercompoundCoCl2・6H2O

Amount ofcarrier/ mg
not added
5

SrCO3

0.5

SrCO3

5

Sr(NO3)2

5

Tracer

60

Co

85

Sr

Activity of Amounttracerof liquid
added
phase
/ Bq
/ mL

Amountof gasphase/ mL3)

102Dsol2)

102Dliq2)

102Dgas2)

2.19×10592798.5±0.9

1.5±0.0

0.0±0.0

2.18×10592799.4±1.0

0.6±0.0

0.0±0.0

2.66×103920

7.3±0.1

92.7±1.0

0.0±0.0

4.55×10492191.7±0.3

8.3±0.10 0.0±0.0

5.82×1091697.2±0.6

2.8±0.1

3

0.0±0.0

1) 200 mg of Fe(OH)3 calculated on the basis of the 500 mg of FeCl3・6H2O used to prepare Fe(OH)3.
2) Error indicates measurement error [8].
3) Value calculated from gas pressure after reaction.

to the liquid phase. In order to shift the distribution to the solid phase, 200 mg of non-radioactive ironhydroxide was added to the reactor and the supercritical-water reaction was examined (Table 2).
Cobalt is quantitatively transferred to the solid phase, as seen only in the case of iron (Table 1). This
dramatic improvement could be explained by the coprecipitation of the cobalt with the iron. The gas
produced during the decomposition of laminate sheeting contains no activity of 60Co in any run.
3.2 Distribution of 85Sr
Table 1 indicates that 85Sr mainly stays in the liquid phase, and only a small amount is transferredto the solid phase, even when SrCO3 carrier is added. The gas produced during the reaction contained
no 85Sr in any run. To recover radioactive strontium as a solid, two additional examinations were
performed: (1) adding the non-radioactive iron hydroxide to the reactor before the reaction and (2)adding a precipitation reagent to liquid obtained after the reaction. In the case of examination (1), 200
mg of the non-radioactive Fe(OH)3 was added to the reactor before the reaction (Table 2), and thestrontium quantitatively transferred to the solid phase as seen only in the case of iron (Table 1). This
dramatic improvement in the recovery of strontium in the solid phase could be explained by the
coprecipitation of the strontium with the iron. In the case of examination (2), Na2CO3 or NaHCO3
aqueous solution was added to radioactive Sr(NO3)2 aqueous solution as follows: A certain amount of
non-radioactive Sr(NO3)2 as the carrier and 85SrCO3 dissolved in a 1 M HNO3 aqueous solution, which isthe simulated solution obtained after the supercritical-water reaction, was mixed into 3 mL of water ina polypropylene test tube. By adding 1 mL of 0.4 M Na2CO3 or NaHCO3 aqueous solution to the abovementioned solution, a white suspension was obtained in all runs. After centrifuging, the supernatantliquid phase was transferred to another polypropylene test tube with a polyethylene dropper. The
determined distribution of 85Sr in this examination (Table 3) indicates that Na2CO3 and NaHCO3 areexcellent precipitate reagents for strontium. Thus, strontium dissolved in the liquid obtained after thesupercritical-water reaction could be precipitated with Na2CO3 and NaHCO3 aqueous solution.

52
Table 3. Distribution of Sr in solid and liquid phases after adding precipitation reagent tosimulated solution obtained after reaction by supercritical-water mixed with RuO2 [3]Element

Sr

Precipitate
reagent

CarriercompoundAmount ofcarrier/ mg

TracerActivity oftraceradded/ Bq

102Dsol1)

102Dliq1)

Na2CO3 2)

0.5

5.03×10399.1±0.7

0.9±0.0

Na2CO35

5.13×10399.2±0.7

0.8±0.0

4.87×10399.1±0.7

0.9±0.0

4.81×10399.1±0.5

0.9±0.0

2)

NaHCO3 2)
NaHCO3 2)

Sr(NO3)2

85

0.5
5

Sr

1) Error indicates measurement error [8].
2) Adding 1 mL of Na2CO3 or NaHCO3 aqueous solution.

3.3 Precipitation mechanism in the case of Fe and Co
Under the conditions with small amounts (0.13 and 1.3 mg) of the non-radioactive iron hydroxide
as the carrier, iron is not recovered in the solid completely and still remains in the liquid (Table 1). One
possible explanation of these results is that the iron(III) could be simultaneously reduced to iron(II)during the reductive decomposition of the nonﬂammable organic materials. To obtain information on
the oxidation state of the dissolved iron under these conditions, 2,2' -bipyridyl, a colorimetry reagent for
Fe2+, were added to the liquid obtained after the supercritical-water reaction with 0.13 and 1.3 mg of
the non-radioactive iron hydroxide. The liquid turned pink and the absorption spectrum in the visible
region showed an absorption band at 520 nm, which is attributed to Fe2+ [4]. In the case of cobalt, thecolor of the liquid obtained after reaction was initially pale pink and changed to golden yellow when
2,2' -bipyridyl was added. Also non-radioactive condition, we prepared a cobalt(II) aqueous solution
using CoCl2·6H2O. The color of this solution was initially pale pink and changed to golden yellow when
2,2' -bipyridyl was added. These results indicated the production of Fe2+ in the liquid by the reactions
with 0.13 and 1.3 mg of the non-radioactive iron hydroxide and also Co2+ in the liquid by supercriticalwater reaction. These results show that iron(II) and cobalt(II) generated in the liquid after reaction.
Iron and cobalt added into the reactor before the reaction was Fe(OH)3 and Co(OH)3, respectively.
Therefore, iron(III) and cobalt(III) were respectively reduced to iron(II) and cobalt(II), and this meansthat a reductive mechanism is operating in the reaction using supercritical water mixed with RuO2. It
is worthwhile to note that the reduction of Co(III) to Co(II) requires very reductive conditions, as
indicated by the standard electrode potential of -1.92 V vs. SHE [5] in comparison with that of Fe(III) to
Fe(II), which is -0.771 V vs. SHE [5]. Once the divalent metal ion is formed, the cobalt(II) ion shouldhave greater solubility than the iron(II) ion on the basis of the solubility product Ksp obtained at theambient temperature for Fe(OH)2 and Co(OH)2 8 ×10 － 16 [6] and 1.6 × 10 － 15 [7], respectively.
Furthermore, all of the solids obtained after the supercritical-water reaction of iron showed
ferromagnetism when checked with a magnet. Thus, a non-radioactive sample was prepared by theprocedure wherein 200 mg of non-radioactive Fe(OH)3, 30 mg of RuO2, 150 mg of laminate sheeting and53
3 mL of water reacted under standard conditions. The X-ray powder diffraction (XRD) was performed
at RINT 2000 (Rigaku Corp., Japan) using CuK α1. The XRD pattern of the obtained solid agreed very
well with Fe3O4. Since the corresponding radioactive cobalt samples also exhibited ferromagnetic
behavior, the non-radioactive sample was prepared by the same way of iron samples. the XRD patternof the obtained solid agreed well with CoO. A detailed analysis of the solid obtained after the reaction
using supercritical water mixed with RuO2 is now underway.
With reference to the gasification mechanism proposed in ref. [2] for the decomposition of
nonflammable organics using supercritical water with RuO 2 catalyst, the atmosphere of thesupercritical-water reaction is suggested to be reductive. The above analysis of the solid phase obtainedin the reaction also supports this reductive mechanism, where a portion of iron(III) and all of cobalt(III)are reduced to iron(II) and cobalt(II), respectively.

§4. Summary
The present investigation indicates that during the decomposition of laminate sheeting, theproduced gas contains no radioactivity in any run. The distribution of Fe, Co, and Sr was determinedby radiometric analysis after laminate sheeting was decomposed using supercritical water mixed with
RuO2. Iron, cobalt and strontium were recovered as solids after the present supercritical-water reaction
by the addition of an excessive quantity of iron hydroxide before the reaction. In the case of strontium,almost all radioactivities were found in the liquid phase. However, by adding precipitate reagents tothe liquid phase obtained in the reaction, strontium can be recovered in the solid phase. This methodshould be a very effective way to decompose the nonﬂammable organic materials of LLW generated by
nuclear power plants.

References[1]

W. Sugiyama et al. : J. Nucl. Sci. Technol. 42 (2005) 256.

[2]

K.-C. Park et al. : Chem. Commun. (2003) 694.

[3]

W. Sugiyama et al. : J. Supercritical Fluid (2005) (Available online at doi:10.1016/ j.supﬂu.2005.02.
003).

[4]

M.H. Ford-Smith et al. : J. Am. Chem. Soc. 83 (1961) 1830.

[5]

A.J. Bard et al. : “Standard Potentials in Aqueous Solutions” , ed. ; IUPAC (Marcel Dekker): New York(1985).

[6]

D.L. Leussing et al. : J. Am. Chem. Soc. 75 (75) 2476.

[7]

A.O. Gübeli et al. : Helv. Chim. Acta 16 (1970) 1229.

[8]

G. Gilmore: “Practical Gamma-Ray Spectrometry” , ed. ; John Wiley & Sons: Chichester, 1995.

Ⅲ．List of Publication

Research Report of Laboratory of Nuclear Science, Tohoku University Vol. 38 (2005)

55

List of Publication（論文リスト）（2004.1～2004.12）
Papers Published in Refereed Journals
Strongly Enhanced Li + D Reaction in Pd Observed for Deuteron Bombardment on PdLix with Energies
between 30 and 75 keV.
J. Kasagi, Y. Yuki, T. Baba, A. Taguchi, M. Shimokawa, and W. Galster
J. Phys. Soc. Jpn. 73 (2004) 608-612.
Low energy nuclear reactions in metals.
J. Kasagi
Prog. Theor. Phys. Supp. 154 (2004) 365-372.
Nuclear Structure of the Spin-Isospin Excited States in 13N Studied via the (3He, t) and (3He, tp)
Reactions at 450 MeV.
H. Fujimura, H. Akimune, I. Daito, M. Fujiwara, K. Hara, K.Y. Hara, M.N. Harakeh, F.
Ihara, T. Inomata, K. Ishibashi, T. Ishikawa, T. Kawabata, A. Tamii, M. Tanaka, H.
Toyokawa, T. Yamanaka, and M. Yosoi
Phys. Rev. C69 (2004) 064327(1-11).
Isovector and Isoscalar Spin-ﬂip M1 Strengths in 11B.
T. Kawabata, H. Akimune, H. Fujimura, H. Fujita, Y. Fujita, M. Fujiwara, K. Hara, K.Y.
Hara, K. Hatanaka, T. Ishikawa , M. Itoh, J. Kamiya, S. Kishi, M. Nakamura, T. Noro, H.
Sakaguchi, Y. Shimbara, H. Takeda, A. Tamii, S. Terashima, H. Toyokawa, M. Uchida, H.
Ueno, T. Wakasa, Y. Yasuda, H.P. Yoshida, and M. Yosoi
Phys. Rev. C70 (2004) 034318(1-10).
The Effect of Deformation in the Isoscalar Giant Dipole Resonance.
M. Itoh, H. Sakaguchi, M. Uchida, T. Ishikawa, T. Kawabata, T. Murakami, H. Takeda, T.
Taki, S. Terashima, N. Tsukahara, Y. Yasuda, M. Yosoi, U. Garg, M. Hedden, B. Kharraja, M.
Koss, B.K. Nayak, S. Zhu, H. Fujimura, M. Fujiawara, K. Hara, H.P. Yoshida, H. Akimune,
M.N. Harakeh, and M. Volkerts
Nucl. Phys. A731 (2004) 41-48.
Excitation and Decay of the Isovector Spin-flip Giant Monopole Resonance via the 208Pb (3He, tp)
Reaction at 410 MeV.
R.G.T. Zegers, H. Abend, H. Akimune, A.M. van den Berg, H. Fujimura, H. Fujita, Y.
Fujita, M. Fujiwara, S. Gales, K. Hara, M.N. Harakeh, T. Ishikawa T. Kawabata, K.
Kawase, T. Mibe, K. Nakanishi, S. Nakayama, H. Toyokawa, M. Uchida, T. Yamagata, K.
Yamasaki, and M. Yosoi
Nucl. Phys. A731 (2004) 121-128.
Cluster Fragmentations of Deep (1s)-hole States in Light nuclei.
M. Yosoi, H. Akimune, I. Daito, H. Ejiri, H. Fujimura, M. Fujiwara, K. Fushimi, K. Hara,
K.Y. Hara, H. Hashimoto, T. Ishikawa, M. Itoh, Y. Itow, S. Kishi, T. Kawabata, K. Kawase,

56
M. Kinoshita, K. Kobayashi, M. Nakamura, K. Nakanishi, Y. Nakatsugawa, S. Nakayama,
T. Noro, E. Obayashi, S. Okumura, H. Sakaguchi, Y. Sakemi, M. Shiozawa, H. Takeda, T.
Taki, A. Tamii, M. Tanaka, S. Terashima, H. Toyokawa, N. Tsukahara, M. Uchida, T.
Yamada, T. Yamagata, Y. Yasuda, H.P. Yoshida, R.G.T. Zegers, and J. Zenihiro
Nucl. Phys. A738 (2004) 451-454.
Half-life of 7Be in Beryllium Metal.
T. Ohtsuki, H. Yuki, J. Kasagi, and M. Muto
Prog. Theor. Phys. Supp. 154 (2004) 392-396.
Enhanced Electron-Capture Rate of 7Be Encapsulated in C60 Cages.
T. Ohtsuki, H. Yuki, M. Muto, J. Kasagi, and K. Ohno
Phys. Rev. Lett. 93 (2004) 112501 (1-4).
Technetium (IV) Oxide Colloids Produced by Radiolytic Reactions in Aqueous Pertechnetate Solution.
T. Sekine, H. Narushima, T. Suzuki, T. Takayama, H. Kudo, M. Lin, and Y. Katsumura
Colloids and Surfaces A: Physicochem. Eng. Aspects, 249 (2004) 105-109.
A Prebunched FEL Using Coherent Transition Radiation in the Millimeter Wave Region.
Y. Shibata, K. Ishi, T. Takahashi, T. Matsuyama, F. Hinode, and Y. Kondo
Nucl. Instrum. and Meth. Phys. Res. A528 (2004) 162-166.
Observation of Millimeter-Wave Radiation Generated by the Interaction between an Electron Beam anda Photonic Crystal.
K. Yamamoto, R. Sakakibara, S. Yano, Y. Segawa, Y. Shibata, K. Ishi, T. Ohsaka, T. Hara, Y.
Kondo, H. Miyazaki, F. Hinode, T. Matsuyama, S. Yamaguti, and K. Ohtaka
Phys. Rev. E69 (2004) 045601 (R).

Papers Published in International Conference Proceedings
Photoproduction of ηMesons on Nuclei at LNS.
H. Yamazaki, T. Kinoshita, A. Katoh, T. Katsuyama, K. Kino, T. Nakabayashi, H. Shimizu,
T. Terasawa, J. Kasagi, H. Kanda, K. Maeda, T. Takahashi, Y. Aruga, T. Fujinoya, A. Iijima,
Y. Ito, T. Noma, Y. Tajima, H.Y. Yoshida, K. Hirota, T. Yorita, and O. Konno
Proceedings of the International Symposium “Electro-photoproduction of Strangeness on
Nucleons and Nuclei”, Edited by K. Maeda et al., World Scientiﬁc, (2004) 191--197.
Photoproduction of Neutral Kaons at LNS.
T. Takahashi, K. Dobashi, Y. Fujii, O. Hashimoto, K. Itoh, H. Kanda, M. Katoh, K. Maeda, A.
Matsumura, H. Miyase, T. Miyoshi, K. Mizunuma, Y. Miura, S.N. Nakamura, H. Nomura, Y.
Okayasu, T. Osaka, M. Oyamada, H. Tamura, H. Tsubota, K. Tsukada, M. Ukai, H.
Yamauchi, M. Wakamatsu, T. Watanabe, T. Ishikawa, T. Kinoshita, F. Miyahara, H.
Shimizu, T. Tamae, H. Terasawa, and H. Yamazaki
Proceedings of the International Symposium “Electro-photoproduction of Strangeness on
Nucleons and Nuclei”, Edited by K. Maeda et al., World Scientiﬁc, (2004) 198--207.

57

Review
Giant Resonances in Light Nuclei via the (e,e' n) Reaction.
T. Saito
Recent Res. Devel. Physics 5 (2004) 1057-1079.

Ⅳ．Approved Experiments

59

平成 16 年度前期採択課題一覧表
課題番号

課

題

名

申込責任者

採
択
シフト数

原子核関連分野
2506

Photoproduction of Neutral Kaons on Liquid Deuterium
Target

橋本

治

70

2507

低移行運動量領域における 40Ca(e, e'p) 反応の研究

玉江

忠明

28

2508

中性中間子光生成による原子核内核子共鳴状態の研究

山崎

寛仁

52

近藤

泰洋

8

放射光関連分野
2509

フォトニック結晶からのスミス・パーセル放射スペクトル測定桓

放射化学・物性関連分野
2510

長寿命放射性核種の環境中移行における基礎化学反応研究

関根

勉

2

2511

ファイバアンプ用ガラス中の軽元素の光量子放射化分析

鹿野

弘二

1

2512

標識化による金属内包フラーレン及びヘテロフラーレンの研究及
びその応用

大槻

勤

3

2513

Th-229m の製造と壊変特性の研究

中西

孝

2

2514

Th-229m の製造とその崩壊特性

三頭

聰明

1

2515

宇宙化学的試料および環境試料の光量子放射化分析

海老原

充

3

2516

電子ビームによるフリーラジカル生成の研究

結城

秀行

1

2517

金属及び半導体材料中の軽元素の定量のための分離・捕集法の開
発

桝本

和義

2

2518

超臨界水中におけるストロンチウムの挙動

佐藤伊佐務

2

2519

水素誘起空孔による拡散の促進

山崎

2

仁丈

60

平成 16 年度後期採択課題一覧表
課題番号

課

題

名

申込責任者

採
択
シフト数

原子核関連分野
2520

6

Li, 7Li ( γ , η) 反応による媒質効果の研究

石川

貴嗣

52

近藤

泰洋

12

放射光関連分野
2521

フォトニック結晶からのスミス・パーセル放射スペクトル測定棺

放射化学・物性関連分野
2522

長寿命放射性核種の環境中移行における基礎化学反応研究

関根

勉

2

2523

光量子放射化分析法による光通信用材料中の不純物評価

鹿野

弘二

1

2524

標識化による金属内包フラーレン及びヘテロフラーレンの研究及
びその応用

大槻

勤

3

2525

Th-229m の製造と壊変特性の研究

中西

孝

1

2526

Th-229m の製造とその崩壊特性

三頭

聰明

1

2527

宇宙化学的試料および環境試料の光量子放射化分析

海老原

2528

電子ビームによるフリーラジカル生成の研究

2529

充

3

結城

秀行

1

金属及び半導体材料中の軽元素の定量のための分離・捕集法の開
発

桝本

和義

2

2530

超臨界水中におけるストロンチウムの挙動

佐藤伊佐務

2

2531

水素誘起空孔による拡散の促進

山崎

仁丈

1

2532

DNA２本鎖切断の遺伝的影響；１倍体酵母と二倍体酵母の比較
研究

山本

和生

2

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核理研研究報告 第38巻 2005年

38 2005

38 2005