CO9-1 Search for the Ultraviolet Photons Emitted from 229mTh Samples Reacted with HF Gas

INTRODUCTION: Thorium-229m lies in the extremely low energy level and the excitation energy wasreported to be 7.8 ± 0.5 eV [1]. The energy corresponds
to vacuum ultraviolet photon (λ=160 nm). Because of thelow energy, it is expected that 229mTh decays by internalconversion or gamma-ray transition depending on its
chemical condition. Recently, it was reported that the229m
Th neutral atom decays by internal conversion with ahalf-life of 7 μs, and that the 229mTh2+ ion in the isolated
system decays with a half-life of longer than 60 s [2, 3].
It suggests that 229mTh2+ ion may decay by gamma-raytransition (photon emission). However, the photons from229m
Th have never been observed. To observe the photons,
in this study we performed following experiments: First,
we prepared 229mTh as recoil products (high valence
229m
Th ions). Subsequently, 229mTh ions were directly
reacted with hydrogen fluoride gas. Since the lowest
binding energy of the outermost electron in ThF4 is 8.3
eV [4] which is larger than the 229mTh excitation energy,
7.8 eV, it is expected that 229mTh is not able to decay byinternal conversion. Finally, the photon detection wasperformed for the sample.
EXPERIMENTS: To obtain 229mTh ions as recoil
products, we prepared thin 233U sample by electrodeposition. A 10 μL aliquot of the 233U solution in 0.1 M HNO3
(24 μg/μL of 233U) and 10 mL of isopropanol were placed
into the 30-mm diameter electrodeposition cell. Using aPt wire as the anode, 233U was electrodeposited on a Ptfoil (0.02 mm thickness) with a current of 17 mA. The
electrodeposition yield was determined by alpha spectroscopy to be 54% corresponding to 17.8 ± 0.3 μg/cm2of 233U in thickness. The 233U sample was set in the Collection Apparatus for Recoil Products (CARP) [5]. In
collecting 229mTh ions, He gas or He/HF mixture gas wereguided into the CARP and the required voltage was applied to guide 229mTh ions onto the copper plate. After229m
Th was collected for several hours to 1 day, photon
detection was performed. To detect the photons, we used
the photomultiplier tube (PMT, HAMAMATSU R6836),
which detects 4-10 eV photons. The PMT was cooled toabout 10°C and set in vacuum.
RESULTS: In the result of photon detection for the229m
Th samples collected in He gas, weak decaying photon counts were observed as shown in Fig.1 (a). This time
variation can be fitted with the decaying curve of two
half-life components, 212Pb and 213Bi. However, thiscount rate was lower than the expected value (2 cps) for229m
Th, and therefore we tried to detect the photons emit-28006

2Count Rate [cps]Graduate School of Science, Osaka University
1Research Reactor Institute, Kyoto University

ted from the 229mTh sample reacted with HF gas. In thiscase, decaying photons were also observed as shown in
Fig.1 (b). However, the count rate of photon emitted fromthis sample was almost the same as that from the sample
collected in He gas. This fact indicates that these photons
mainly originated from daughter nuclides such as 213Bi,
209
Tl, 212Bi, and 208Tl. Thorium-229m might not be reacted sufficiently. To reduce the photons induced by daughter nuclides, we will use the electrodeposited sample ofnewly purified 233U.

(a)
100

1
[×105]

0.5
Time [s]2Count Rate [cps]Y. Yasuda, Y. Kasamatsu, Y. Shigekawa, T. Ohtsuki1, K.
Takamiya1, A. Shinohara(b)1000.5Time [s]11.5[×105]

Fig. 1. The photon counts for the 229mTh samples. Solidcurves describe the fitted curves containing two decaying components. Fig.1 (a) shows the counts for229m
Th sample prepared in He gas for about 15 h and(b) shows that reacted with HF gas for about 25 h.
REFERENCES:[1] B. R. Beck et al., LLNL-PROC-415170(2009).
[2] L. von der Wense et al., Nature 533 (2016) 47-51.
[3] B. Seiferle et al., Phys. Rev. Lett. 118 (2017)042501.
[4] N. Trautmann, J. Alloys Compd. 213/214 (1994) 28.
[5] Y. Shigekawa et al., Rev. Sci. Instrum. 87(2016)053508.

CO9-2 Stability of Triphosphine Trioxide Extractant against γ-Ray Irradiation in HNO3
M. Nogami, E. Tamaru, S. Maeda and N. Sato1
Faculty of Science and Engineering, Kindai University1Research Reactor Institute, Kyoto University
INTRODUCTION: We have been paying attention to
one of triphosphine trioxides, 1,1,3,5,5-pentaphenyl1,3,5-triphosphapentane trioxide (PPTPT : Fig. 1) for apotential versatile extractant [1,2]. The most distinguished nature of PPTPT would be its unusual high selectivity to U(VI) in HNO3 of very low concentrations [3].
Another expected nature of PPTPT is higher chemical
stability in acid media. In principle, phosphine oxides
do not undergo acid hydrolysis unlike compounds notcontaining phosphorus such as diamides, and ester phosphates such as tri-n-butylphosphate (TBP). In addition,
PPTPT has no ether bonds which are known to decrease
the stability of extractants in acid media[4], although they
have been sometimes included in chemical structures ofextractants to increase extraction properties. Based on
the above, radiation stability of PPTPT was investigatedmainly from the identification of degradation products inthis study.
(b)

(c)

(a)

(c)

(a)

attributed to the hydrogen atoms at (c) in Fig. 1 is significantly decreased after irradiation. This suggests thatthe bond cleavage occurred between phosphorus andmethylene carbon.
For comparison, PPTPT was treated with 9 M HNO3containing 10 mM Nd(III) or Fe(III), or 3 % H2O2 atboiling temperature for 6 h. It was also treated similarly
with conc. HNO3. Under these conditions, little structure changes were observed for 1H NMR spectra. Thiswould indicate high chemical stability of PPTPT in
HNO3 media. On the other hand, 1H NMR analysis for
PPTPT treated with aqua regia at room temperature for 1day suggests the similar bond cleavage to the irradiated
PPTPT. Further 1H and 13C NMR analyses for PPTPT
treated with aqua regia suggest that formic acid and twokinds of phenylphosphoric acid were generated as thedegraded compounds (Fig. 3). Large portion of formic
acid might be decomposed to CO and H2O. Such apathway of degradation was similar to some extent to thatof octylphenyl-N,N’-diisobutylcarbamoylmethyl phosphine oxide (CMPO), a conventional bidentate phosphineoxide extractant, by γ-ray irradiation [5].
So far, the detailed pathway of degradation for irradiated PPTPT is not confirmed. However, it is expectedthat the pathway is close to that shown in Fig. 3.

(a)

(a)

Fig. 1. Chemical structure of PPTPT.
EXPERIMENTS: For γ-ray irradiation to PPTPT, thesamples were prepared by mixing PPTPT of white crystal
with H2O, 3 and 9 mol/dm3 (= M) HNO3, respectively.
The mixture was put in a Pyrex tube and irradiated by the60
Co source at ca. 3.7 kGy/h up to 1.6 MGy at room
temperature under ambient atmosphere. Irradiated samples were analyzed by 1H and 13C NMR.
RESULTS: PPTPT irradiated in H2O showed powderedstate. While, those irradiated in 3 and 9 M HNO3 turned
into brown viscose oil. 1H NMR spectra of neat PPTPT
and that irradiated in 9 M HNO3 are shown in Fig. 2. It
can be seen that the signal at ca. 1.5 ppm which is
(1)

(a)

CHCl3

(c)

TMS

(b)

(2)

HNO3

Fig. 2. 1H NMR of PPTPT : (1) neat, (2) irradiatedin 9 M HNO3 (solvent : CDCl3).

28057

Fig. 3. Expected structure change in PPTPT by treatment
with aqua regia.
REFERENCES:[1] M. Nogami et al., Energy Procedia, 71 (2015)
123-129.
[2] K. Hashimoto, et al., Abst. ASNFC 2015, Tokyo, Japan,
2B-24 (2015).
[3] M. Nogami, et al., J. Radioanal. Nucl. Chem., 284(2010) 195-199.
[4] C. Madic, et al., Nuclear science and technology, Final report, EUR19149, European Commission, 44(2000).
[5] J. N. Mathur, et al., Sep. Sci. Technol., 33 (1998)
2179-2196.