CO9-1

Stability of Caprolactam Resin against γ-Ray Irradiation in HNO3T. Nishida1, M. Nogami1, and N. Sato25-membered ring would be necessary to obtain plural
neighboring C=O groups under the present irradiation
condition.

1

Graduate School of Science and Engineering Research,Kinki University
2
Research Reactor Institute, Kyoto University
INTRODUCTION: We have previously reported thatthe property of structure change in a cyclic monoamide
resin consisting of poly-N-vinyl-ε-caprolactam (VEC)
with a 7-membered ring by γ-ray irradiation in HNO3 isdifferent from that in polyvinylpolypyrrolidone (PVPP),
another cyclic monoamide resin with a 5-memberedring[1]. Namely, while relatively stable plural neighboring C=O groups (structure (a) in Fig. 1) were introduced for PVPP[2], such neighboring C=O groups were
not observed for VEC. In this study, to clarify the moredetailed degradation property of VEC, other irradiatedsamples were prepared and analyzed. Water-soluble
N-methyl-ε-caprolactam (MEC) was also irradiated in
HNO3 to evaluate the stability of VEC quantitatively.
NOVECFig.2. Expected major route of change in chemical structure of VEC by γ-ray irradiation in HNO3
In a 1H NMR spectrum, neat MEC showed four signals; (A)3.4，(B)2.9, (C)2.4, (D)1.6 ppm, respectively.
The calculated residual ratios are shown in Fig. 3 together with the relationship between the position of hydrogenin the structure of MEC and that of the signal. The residual ratios calculated from (A), (B) and (D) show anearly identical trend, where the residual ratios decreaselinearly with an increase in dose, and ca. 50 % and 75 %are decomposed at 1 and 2 MGy, respectively. On theother hand, the residual ratio calculated from (C) is foundhigher than the three other systems, which would be because the signal (C) overlaps with that of degraded compounds. The dependence of residual ratio of N-butylpyrrolidone (NBP), one of the water-soluble 5-memberedrings, under the irradiation in 6 M HNO3 on dose is difference from that of MEC. Namely, the decrease in theresidual ratio of NBP decreased steeply and then gently[3]. As the result, comparing the stability of MEC
with that of NBP, the residual ratio of MEC is higher thanthat of NBP at less than ca. 0.6 MGy, and vice versa at
more than 0.6 MGy.

N
COOH

NOH
OH

HOPVPP

COOH

HN

HNO
HOOC

OONH

HOO

(a)

Succinic acid

NH2

COOH
COOH

Fig. 1. Expected major route of change in chemical
structure of PVPP by γ-ray irradiation inHNO3[2].
EXPERIMENTS: γ-Ray irradiation to VEC was carriedout similarly to the earlier study (max. 1.5 MGy)[1].
For the sample of MEC, a solution containing 1 mol/dm3(= M) MEC and 6 M HNO3 was prepared. The sample
solution was put in a Pyrex tube and irradiated by the60
Co source at max. 8.8 kGy/h up to 2.1 MGy at room
temperature under ambient atmosphere. Irradiated samples were analyzed by 1H and 13C NMR. DMSO-d6
containing a known weight of TMS which is a standard
material was used as the NMR solvent. The residual
ratio of MEC was calculated by the area ratio of eachsignal with that of TMS.

Rssidual ratio/%

100(B)

7550
2500.0(A)ABCD0.5(C)

(D)
1.0

1.52.02.5(D) (D)Dose/MGy

RESULTS: A crystal was observed from the supernatantobtained from the irradiated VEC. The crystal wasidentified as succinic acid by 13C NMR analysis. Thestructure change in VEC is expected from the result asshown in Fig. 2, which suggests that the major route ofchange in chemical structure of VEC is basically identicalto that of PVPP and that the resulting dicarboxylic acids
differ corresponding to the number of carbon in the cyclicmonoamides. The scheme is consistent with the abovementioned fact that plural neighboring C=O groups were
not observed for VEC. These facts also imply that aFig.3. Dependence of residual ratio of MEC on dose.
REFERENCES:[1] T. Nishida et al., KURRI Progress Report 2013(2014) 295.
[2] M. Nogami et al., J. Radioanal. Nucl. Chem., 296(2013) 423-427.
[3] M. Nogami, et al., Sci. China Chem., 55 (2012)
1739-1745.

採択課題番号 26013 アクチニルイオン配位性アミド化合物の耐ガンマ線性に関する研究 通常採択
（近大・理工）西田哲大、野上雅伸（京大・原子炉）佐藤信浩

138

CO9-2

Search for Ultraviolet Photons from Precipitated 229mTh Samples

Y. Yasuda, Y. Kasamatsu, Y. Shigekawa, T. Ohtsuki1, K.
Takamiya1, A. Shinohara

RESULTS: In the case of the hydroxide and fluoride
samples of 229mTh grown for about 2 h, the count rates ofphotons were almost the same with those of the background. In contrast, for the 229mTh samples grown forabout 13 h, the photon emissions decaying for time weredetected and the half-lives were about 1 h for hydroxideand 3 h for fluoride. For example, the result for the229m
ThF4 sample grown for about 13 h is shown in Fig. 2.
These decaying photon emissions, however, did not seemto be the simple decay curve. In addition, if the half-livesof 229mTh were several hours, the photon emissions areexpected to be observed for the samples grown for 2 h.
Therefore, these photons might derive from the Cherenkov radiation induced by the decay of daughter nuclides
such as Bi or Pb. To clarify the origin of these photons,
we plan to purify 229mTh before measurement.

Graduate School of Science, Osaka University
Research Reactor Institute, Kyoto University

1INTRODUCTION: The first excited state of 229Th
lies in extremely low energy level. The excitation energy
was reported to be 7.8 ± 0.5 eV [1]. This energy corresponds to vacuum ultraviolet light, and it is expected thatthe decay rate of 229mTh varies drastically depending on
their chemical forms [2]. Furthermore, chemical conditions can affect the decay mode of 229mTh (internal conversion and/or gamma ray transition). It is also expectedthat 229mTh can be applied to a nuclear clock which has
about two orders higher precision than the most precise
optical clock [3]. Hence, many studies have been performed to observe the decay of 229mTh, especially on
photon detection. However, there are not clear results
directly observing the decay. It is important to observe
the photons emitted from the 229mTh on various chemical
conditions to understand the decay property of the state.
This report describes the results of photon detection forthe several samples containing 229mTh with different
chemical forms: hydroxide and fluoride.

REFERENCES:[1] B. R. Beck et al., LLNL-PROC-415170 (2009).
[2] E. V. Tkalya et al., Phys. Rev. C 61, 064308 (2000).
[3] E. Peik et al., Europhys. Lett. 61, 181 (2003).

EXPERIMENTS: Thorium-229m was separated fromthe mother nuclide 233U by using anion-exchange method.
About 200 mg of 233U, containing less than 1 ppm of 232U,
was adsorbed on the anion-exchange resin (Dowex 1×8,200-400 mesh, 2.5 mL). Five-milliliters of 9 M HCl solution was poured into the column several times to remove
229m
Th and the daughter nuclides. After 229mTh was grownin the column for a certain time: about 2 or 13 h, 5 mL of
9 M HCl solution was passed through the column to elute229m
Th. To prepare the hydroxide samples, 20 µL aliquotof samarium standard solution was added and then aqueous NH3 was added to the eluent until the solution became basic. When the fluoride samples were prepared, 30µL aliquot of samarium standard solution and 2 mL ofHF solution were added to the eluent and the solution
was stirred for 2 min. Thorium-229m was coprecipitatedwith samarium as hydroxide or fluoride form. Each precipitate was collected on a polypropylene filter and heated to dryness.
Setup for photon detection is schematically illustrated inFig. 1. To measure vacuum ultraviolet ray from 229mThsamples, we used a photomultiplier tube (PMT) for photon counting, Hamamatsu R6837, which detects 4-10 eV
photons with higher than 10 percent quantum efficiency.
Signals from PMT were amplified with the pre-AMP andPM-AMP. Noise was cut with the discriminator, and thesignal data were accumulated in the multichannel analyzer.

Fig. 1. Schematics of the experimental setup for photon
detection.

Fig. 2. Count rate of photons for the 229mThF4 samplegrown for about 13 h.

229m
採択課題番号 26079
Th の紫外光及び電子測定
即時採択（大阪大院・理）安田勇輝、笠松良崇、重河優大、篠原厚（京大・原子炉）大槻勤、高宮幸一

139