RIKEN Accel. Prog. Rep. 50 (2017)

Research Activities 1991–2016

Nuclear Chemistry Laboratory
F. Ambe ∗1
When the RIKEN Ring Cyclotron (RRC) was readyfor utilization, I proposed two new research subjects formy nuclear chemistry group: the development of a multitracer technique and in-beam Mössbauer spectroscopyusing 57 Mn.
The former involves the preparation of multielemental radioactive nuclides by the fragmentation oftarget nuclei and their application to trace the behaviorof elements in various research ﬁelds. In 1990, we starteda series of studies to develop radiochemical proceduresfor the preparation of multitracers, namely the removalof the target material from the solution of an irradiatedtarget, leaving as much as possible of the radionuclides,
and the application of the multitracers thus obtained tochemistry and other ﬁelds.1) More than ﬁfty elements
were studied using this technique, with twenty or moreof them being traced simultaneously.
Signiﬁcant features of the multitracers are as follows:(1) High eﬃciency: a single experiment usually yields
information on twenty or more elements. (2) Accuratecomparison of the behavior of a number of elements isrealized under strictly identical experimental conditions.
(3) Serendipity: since many elements are included in every multitracer, it is often possible to discover new important or interesting behavior of an element, which is
not the main subject of the investigation. (4) All thetracers are carrier-free, that is, the multitracers containslight amounts of stable isotopes of the tracers, which
can disturb the experiment. (5) Some multitracers contain scarcely obtainable tracers such as 28 Mg and 47 Ca.
Typically, a beam of 12 C6+ , 14 N7+ , or 16 O8+ ions withan energy of 135 MeV/nucleon is used against Au, Ag,and Cu targets. The irradiated target is dissolved, andthe target material is removed, leaving the radioactive
nuclides in a solution. For example, in the simplest caseof an Ag target, it is dissolved in nitric acid, and Ag
is removed as AgCl precipitate. The measurement ofthe tracers is performed by means of conventional Ge
detectors.
The multitracers were used for the investigation of
behavior of various elements in chemistry, biochemistry,and biology in cooperation with more than 10 groups inuniversities and research institutes.1,2) The behavior ofelements in rats and mice was most extensively studied
by diﬀerent groups. The uptake, excretion, and retention of various elements were studied in organs of Al-,
Cd-, and Vitamin D-overloaded or Se-deﬁcient rats incomparison with those of normal ones. The following
studies were also made on various elements: the transportation through the blood-brain barrier and retention
in diﬀerent parts of the brain, labeling of immunoglobulin G, reactions with blood components and transport
proteins, and in vivo and in vitro binding with liver∗1

Chief Scientist of Nuclear Chemistry Laboratory (1988–1998)

S-22DNA.
In the case of plants, the uptake and accumulation ofelements in mushrooms, carrots, and marigolds as wellas the subcellular distribution and translocation of radionuclides were studied. In chemistry, the adsorptionof metal ions on α-Fe2 O3 , formation of metallofullerenes
with higher-group elements, eﬀects of model acid rain on
the adsorption of trace elements upon soils, and stability
constants of humate complexes with various metal ionswere studied.
In this period, investigations using unstable nuclei
as probes, namely Mössbauer spectroscopy and timediﬀerential perturbed angular correlation (TDPAC) of γrays, were continued with the use of cyclotron-produced
radionuclides in cooperation with the magnetism groupof RIKEN, and a project using short-lived 57 Mn produced by RRC was newly started.3) With the use of
the source nuclide 61 Cu produced by the α-irradiationof a Ni-V alloy disk, 61 Ni-Mössbauer spectra of chromitespinels, Cu1−x Nix Cr2 O4 , were measured. Both Hhf andEFG were found to be well related to a lattice distortion.
In Cu0.9 Ni0.1 Cr2 O4 , the Hhf was 790 kOe, which is thelargest among the values for Ni2+ ever reported. Carrierfree 99 Rh produced by the proton irradiation of 99 Ru waschemically separated from the target and was doped in
YBa2 Cu3 O6.8 and YBa2 Cu3 O6 . Their Mössbauer emission spectra and TDPAC showed that 99 Ru ions arisingfrom 99 Rh are tetravalent and occupy the Cu sites.
119Sn-Mössbauer emission spectroscopy usingcyclotron-produced 119 Sb as the source nuclide was applied to the in situ study of the chemical state of 119 Sb5+
adsorbed on α-Fe2 O3 . The state of 119 Sb5+ was shown
to change depending on the pH value of the solution incontact with the powder samples on the basis of broadening of the spectra due to the magnetic interaction.
A setup for in-beam Mössbauer spectroscopy was constructed at RIPS of RRC in order to measure the spectraof 57 Fe with 57 Mn (half-life 87.2 s) produced as a beamby the projectile fragmentation of 59 Co. With the useof a parallel-plate avalanche counter for detection of theinternal conversion electrons, we succeeded in the ﬁrst
observation of Mössbauer spectra of 57 Fe following thedecay of 57 Mn nuclei. However, the quality of the spectra
was not satisfactory because of β-rays from 57 Mn. Later,
Dr. Y. Kobayashi and his coworkers overcame this diﬃculty by developing an anti-coincidence detection system
and also realized time-dependent measurement with thesystem. Now, 57 Mn-Mössbauer spectroscopy is used asa unique method for atomic-scale study of reactions insolids.
References
1) F. Ambe, ed., RIKEN Rev. No. 13 (1996).
2) Y. Yano, S. Enomoto, eds., RIKEN Rev. No. 35 (2001).
3) F. Ambe, ed., RIKEN Rev. No. 16 (1997).