Journal of Nuclear and Radiochemical Sciences, Vol. 1, No. 2, pp. 81−82, 2000

81Notes
Preparation of Multitracer by Thermal Neutron Fission of 235U
Koichi Takamiya,a Masaaki Akamine,a Seiichi Shibata,*,a Atsushi Toyoshima,bYoshitaka Kasamatsu,b and Atsushi Shinoharab
aResearch Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan
Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japanb

Received: May 23, 2000; In Final Form: August 8, 2000
Radiochemical procedures for preparing a multitracer using thermal neutron fission of 235U were established. Thetarget material of natUO2 mixed with the catcher material for the fission products was irradiated at the research
reactor (KUR) of the Research Reactor Institute of Kyoto University. After irradiation, the multitracer solution
mainly consisting of fission products was prepared by quick removing of the target material. The multitracer
enables simultaneous tracing of various elements, and comparison of their chemical behavior under strictly identical experimental conditions.

In the field of medical, pharmaceutical, biological and environmental science, radioactive isotopes are employed to trace
the chemical behavior of various elements in a system.
Although the trace analysis method using radioactive isotopes
is highly sensitive, only one or two sort of tracers is usuallyapplied in the experimental research. Recently, the researchgroup at the Institute of Physical and Chemical Research(RIKEN) reported the preparing method of tracer solutions
containing multiple radioactive isotopes (multitracer) without
carrier materials.1-3 They are preparing the multitracer solutions by heavy-ion reaction using the RIKEN Ring Cyclotron,and providing them to scientists in the various research fields.
However, available elements are limited by their own halflives and reaction yields. In the heavy-ion reaction, neutrondeficient isotopes are dominantly produced. Therefore,
another method to prepare multitracers containing radioactive
isotopes, which cannot be produced by heavy-ion reactions, isurgently required.
We tried to prepare a multitracer by thermal neutron
induced fission of 235U using Kyoto University Reactor (KUR),
because in nuclear fission neutron-rich isotopes are produced
in relatively high yields in comparing with charged-particle
induced reactions. A use of a multitracer prepared by nuclear
fission of 235U was reported by Uchida et al.4 They applied themultitracer solution without chemically separating the target
material of uranium to the adsorption study of fission products
onto ion exchangers. In this work, we newly developed thepreparation method for the multitracer solution by quick
removing of the target material of uranium.
A mixture of nat UO 2 and catcher material by which thefission products recoiled out from the UO2 were captured wasirradiated by thermal neutrons in the reactor. After irradiation,
the catcher material was dissolved in a dilute acid, and the UO2
undissolved was removed by filtering. The multitracer solutions prepared were provided for the purpose of medical
research at Kanazawa University.
In this note, we report the radiochemical procedures established for preparing the multitracer and the results of investigating some salts as efficient catcher materials.
In order to prepare the multitracer solution efficiently, thefollowing parameters for the sample preparation were examined; 1) catcher material, 2) mixing ratio of UO2 to catchermaterial, 3) particle size of the catcher material and 4) sample
shape for irradiation. The catcher materials used in this work
*Corresponding author. E-mail: shibata@HL.rri.kyoto-u.ac.jp.
FAX: +81-724-51-2632.

were NaCl, LiF and MgCl2 by considering that these salts aresoluble in water and easy for a quick chemical treatment. The
mixing ratios ([UO2 ]/[catcher material]) examined were as
follows; 1:1, 1:3, 1:10 and 1:30. The mixture was ground in an
agate mortar to make it uniformed size. The particle sizes
were controlled by the grinding time. In this work, we refer tothe particle size as coarse and fine depending on the grinding
time. For irradiation, powdered and pellet samples wereprepared. The pellet samples were prepared using the fineground powder. The content of samples is tabulated in Table 1.
The sample prepared was wrapped with an aluminum foil
and sealed into an evacuated quartz tube. The tube wasinserted into a polyethylene capsule and irradiated using thepneumatic transferring system (Pn-2) at KUR. The thermal
neutron flux at Pn-2 is reported to be 2.8 × 1013 n/cm2/sec. The
irradiation times were 1-10 min as indicated in Table 1.
TABLE 1: Contents of Irradiated Samples
Catcher
Material
NaClForm
Powder (coarse)

Powder (fine)Pellet

MgCl2
LiF

Powder (fine)Powder (fine)

Weight /mg
UO2:Catcher
0.95 : 2.95
1.12 : 9.68
1.06 : 29.74
1.09 : 1.11
1.07 : 3.33
1.05 : 29.45
5.12 : 5.18
2.48 : 7.72
1.25 : 10.85
0.37 : 10.43
1.00 : 29.61
0.90 : 9.60

Irrad. Time
10min
1min
1min
5min
5min
1min
2min
2min
5min
2min
5min
5min

After cooling for a few tens of minutes, the irradiatedsamples were picked up from the capsule. The fission products captured by the catcher material were dissolved in 0.1 NHCl, while the UO 2 remained undissolved. The solution
containing fission products was filtered with suction to separate the UO2. Gamma rays from an aliquot of the solution andthe UO2 on the filter paper were measured by a Ge detector.
The peak areas of spectra were calculated using the BOB peakanalysis code.5 Assignment of the radioactive isotopes to eachpeak in the spectra was carried out on the basis of their energies and half-lives. Several measurements were usually© 2000 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 12/28/2000

Takamiya

82 J. Nucl. Radiochem. Sci., Vol. 1, No. 2, 2000

to environmental, pharmaceutical and cytological sciences are
now being planned.

TABLE 2: Mean Capturing Efficiencies
CatcherForm
Weight /mg Weight Ratio Capturing
Material
UO2:Catcher Catcher/Total Efficiency
NaCl
Powder (coarse) 0.95 : 2.95
0.76
0.78 ± 0.04
1.12 : 9.68
0.90
0.86 ± 0.02
1.06 : 29.74
0.970.88 ± 0.01
Powder (fine) 1.09 : 1.11
0.50
0.82 ± 0.01
1.07 : 3.33
0.76
0.89 ± 0.01
1.05 : 29.45
0.97
0.97 ± 0.00
Pellet5.12 : 5.18
0.50
0.72 ± 0.05
2.48 : 7.72
0.76
0.85 ± 0.05
1.25 : 10.85
0.90
0.95 ± 0.01
0.37 : 10.43
0.97
0.97 ± 0.01
0.97
0.84 ± 0.03
MgCl2 Powder (fine) 1.00 : 29.61
LiF
Powder (fine) 0.90 : 9.60
0.91
0.58 ± 0.07

1Capturing Efficiency

performed for the sample at appropriate time intervals in orderto determine the half-lives of the radioactive isotopes responsible for each peak. Because of the limited energy resolutionof the Ge detector and the interference due to Compton scattering of the gamma rays from by-products induced by thecatcher materials, the radioactive isotopes emitting low energy
gamma rays and with low production yields were not detected
precisely. Therefore, the separation method for the catcher
material from the multitracer solutions is under investigation.
An example of identified isotopes is as follows; 91Sr, 95,97Zr,
105
Ru, 106Rh, 131,132I, 132Cs, 140Ba, 140La and 141,143Ce.
Capturing efficiency of fission products by catcher materials
was estimated by a ratio of Y catcher /Y total for each productnuclide, where Y catcher indicates the yield of the nuclide
captured in catcher materials and Ytotal the total yield estimatedby summing Ycatcher and the yield observed for the filter paper.
There was no difference among the efficiency of each nuclide
within the experimental error. The capturing efficiency of thewhole sample is evaluated from the averaged value of the efficiencies for all identified nuclides. The obtained meancapturing efficiency for each sample is tabulated in Table 2.
Figure 1 shows the mean efficiency for each sample as afunction of the weight ratio of Wcatcher/Wtotal, where Wcatcher andWtotal are the weight of the catcher material and of the sample,respectively. Open and closed circles in Figure 1 show theefficiencies obtained for coarse and fine powder samples withthe catcher material of NaCl, respectively. Square anddiamond in the figure show those with LiF and MgCl2, respectively. The efficiencies obtained for pellet samples are shownas triangles. Solid and dashed lines indicate the results of theleast square fitting for the mean efficiencies of powder andpellet samples with NaCl, respectively.
The capturing efficiency in the case of LiF is much lower
than that of NaCl or MgCl2. This might be dependent on mean
atomic size of catcher material, since that of LiF is smaller
than that of NaCl or MgCl 2 . The sample preparation withMgCl2 was much more difficult than that with NaCl, becauseof its high hygroscopicity. Comparing coarse and fine powder
samples with NaCl, the capturing efficiencies for the fine
powder sample are higher than those for the coarse one. Thismay be explained by that fission fragments produced in fineparticles can recoil out easily than those in coarse particles.
The capturing efficiencies for pellet samples are almost thesame as those for fine powder samples except for the sample of
low weight ratio. Since the UO2 tends to contaminate more themultitracer solution from the sample of low weight ratio thanthat from the one of high ratio, an identification of fission
products is relatively difficult in the case of the low weightratio sample. The larger statistical fluctuation of the capturing
efficiency for the sample of low weight ratio than that for thesample of high ratio is probably understood by the reason
above.
As shown in Figure 1, the sample mixed with NaCl as acatcher material is most efficient for preparing multitracer
solutions. Concerning the handling of samples, the pellet
sample is more convenient than the powder sample. In case ofpellet samples, it is possible to irradiate several samples simultaneously. The multitracer solutions prepared above are extensively used for the biological research to trace the element
distribution in mice. In this research, the multitracer solutions
obtained from the sample containing NaCl as a catcher material are especially useful, because a physiological salt solution
can be easily prepared. The detail of this work will be reported
elsewhere. Besides the above biological research, applications

0.9
0.8
0.7
0.6
0.5
0.4

0.5

0.6

0.7

0.8

0.9

1

WCatcher /WTotal
Figure 1. The mean capturing efficiency for each sample correlatedwith the weight ratio. Open and closed circles show the efficiencies
obtained for coarse and fine powder samples with the catcher materialof NaCl, respectively. Square and diamond in the figure show thosewith LiF and MgCl2, respectively. The efficiencies obtained for pellet
samples are shown as triangles. Solid and dashed lines indicate theresults of the least square fitting for the mean efficiencies of powder
and pellet samples with NaCl, respectively.

References(1) S. Ambe, S. Y. Chen, Y. Ohkubo, Y. Kobayashi, M.
Iwamoto, M. Yanokura, and F. Ambe, Chem. Lett. 149(1991).
(2) F. Ambe, RIKEN Rev. No. 4, p. 31 (1994).
(3) S. Ambe, S. Y. Chen, Y. Ohkubo, Y. Kobayashi, H.
Maeda, M. Iwamoto, M. Yanokura, N. Takematsu, and F.
Ambe, J. Radioanal. Nucl. Chem. 195, 297 (1995).
(4) Y. Uchida, I. Tomita, and K. Tomura, J. Ion Exchange 9,166 (1998).
(5) H. Baba, T. Sekine, S. Baba, and H. Okashita, JAERI-M
1227, p. 66 (1973).