Journal of Nuclear and Radiochemical Sciences, Vol. 8, No. 2, pp. 113-115, 2007

Determination of Trace Amount of Manganese in High-purity Iron
S. Sekimoto,*,a T. Kobayashi,b K. Takamiya,a and S. Shibataaab

Research Reactor Institute, Kyoto University, Kumatori, Osaka 590-0494, Japan
College of Humanities and Sciences, Nihon University, Sakurajosui, Tokyo 156-8550, Japan

Received: October 23, 2006; In Final Form: April 9, 2007
Trace amount of manganese in high-purity iron samples was determined by INAA using Tc-Pn at KUR, ICP-MS,and ICP-AES. It was confirmed that the INAA using Tc-Pn was able to determine several tens of ppb Mn as animpurity in iron samples without correcting a contribution of the 56Mn produced by the fast neutron-induced reaction on 56Fe. Based on the results, the INAA using Tc-Pn was applied to the determination of trace amount ofmanganese in some fragments of the Gibeon iron meteorite in order to estimate cosmogenic 55Mn in those fragments.

1. Introduction
Manganese is one of the most sensitive elements for instrumental neutron activation analysis (INAA).1 In determining
trace amount of manganese in samples like iron meteorites by
INAA, a contribution of the 56Mn produced by the fast neutroninduced reaction 56 Fe(n,p) 56 Mn must be corrected.1 In thiswork, we confirmed that several tens of ppb of manganese inhigh-purity iron samples can be determined by INAA using thethermal column pneumatic transport system (Tc-Pn) at Kyoto
University Reactor (KUR) without correcting a contribution of
the 56Mn produced by the fast neutron-induced reaction. Tc-Pn
is utilized to minimize contributions of epithermal and fastneutrons effectively.
Manganese contents in iron meteorites are very low; they
were measured in a range of 40 to 90 ppb using radiochemical
neutron activation analysis (RNAA).2 In the Gibeon iron meteorite, depth profiles of cosmogenic nuclides (10Be) and stable
nuclides (3He, 4He) were measured by Honda et al.3– 6 They
reported that 10Be in the fragments from the deeper part of thisiron meteorite is much lower than those from the surface.3,4 In
this work, we applied the INAA using Tc-Pn to the estimationof the amount of cosmogenic 55Mn in the fragments from thedeeper part and from the surface of the Gibeon iron meteorite.
2. Experimental
2.1. Determination of trace amount of manganese inhigh-purity iron samples. High-purity iron samples, JSS0035, JSS009-2, JSS001-4, and JSS001-5 (JSS009-2 is an ironoxide sample, and the others are metallic ones) are commercially available from the Japan iron and steel federation, andthe impurity contents in those samples are indicated in theattached certificates.7–10 Before irradiation of the samples, thesurfaces of JSS001-4 and JSS001-5 were leached with dilutenitric acid to remove contaminants which adhered to those surfaces in sample-manufacturing. By leaching, the sample
weight was reduced to about 75%. About 250 mg of each highpurity iron sample was irradiated with manganese comparators. The manganese comparators were prepared frommanganese standard solution. The neutron irradiation was carried out for 60 min using Tc-Pn at KUR, whose thermal andfast neutron fluxes are reported to be 4 × 1011 n cm–2 s–1 and 8 ×*Corresponding author. E-mail: sekimoto@HL.rri.kyoto-u.ac.jp.
Fax: +81-72-451-2632.

ReactorcoreabcdefFigure 1. Six positions where Cd-ratios were measured in the thermal column at KUR.

107 n cm–2 s–1, respectively.11 After irradiation, γ rays of 56Mn
(846 keV) emitted from each sample were measured by a low
background Ge detector.
To evaluate the effect of epithermal and fast neutron induced
reactions at some irradiation positions in Tc-Pn, the Cd-ratiosof gold were measured at six positions shown in Figure 1. The
ratios at the positions from “a” to “f” were 220, 230, 250, 230,150, and 140, respectively. Based on the ratios obtained, all theirradiations of iron samples were performed between “a” and“d”.
Besides INAA, inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission
spectrometry (ICP-AES) were also utilized to determine theamount of manganese in the same samples in order to compare
the results with those obtained by INAA. For ICP-MS andICP-AES, it is necessary to separate bulk iron from the samples
to prevent the mass matrix effect of 56Fe. The iron samples of100–350 mg were dissolved in conc. HNO3 or aqua regia. Theiron was separated by anion exchange (DOWEX 1-X8, 100–200 mesh) and solvent extraction using diisopropylether. The
solution after iron-separation was subjected to ICP-MS andICP-AES. The yield in this chemical separation was estimatedto be more than 90% using 56 Mn radiotracers in a separate
experiment.
2.2. Determination of manganese in the Gibeon ironmeteorite. We applied the neutron activation analysis using
Tc-Pn to the determination of trace amount of manganese infive fragments of the Gibeon iron meteorite: G. 003, G. 102, G.
105, G. 2001, and G. 99. Neutron irradiations for all the fragments were carried out in the same manner as those for thehigh purity-iron samples. Since iron meteorites contain heterogeneously inclusions like troilite (FeS) which contains 300–
800 ppm of manganese as an impurity, 2 ,12 it seems to benecessary to remove such inclusions thoroughly in the determination of trace amount of elements represented by manganese© 2007 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 10/19/2007

114 J. Nucl. Radiochem. Sci., Vol. 8, No. 2, 2007

Sekimoto

TABLE 1: Result of Mn contentaSample
JSS003-5 (metal)
JSS009-2 (oxide)
JSS001-4 (metal)

INAA
25.5 ± 0.3 ppm
750 ± 15 ppb
26 ± 2 ppb

ICP-MS25.2 ± 0.6 ppm
884 ± 30 ppb
65 ± 3 ppb

ICP-AES25.1 ± 0.1 ppm
830 ± 8 ppb

JSS001-5 (metal)

25 ± 1 ppb

ee

Certified Value
27 ± 1 ppma
<2 ppmb
30.6 ± 5.5 ppbc

e30 ± 10 ppbd

Reference 7. bReference 8. cReference 1. dReference 10. eSee text of sec. 3.1.

TABLE 2: Mn concentrations in five fragments of the Gibeon iron meteoriteaSample

Surface-leachingafter NAA / times

Weight / g

Mn concentration / ppb

G. 003
G. 003
G. 003
G. 102
G. 102
G. 105
G. 105
G. 2001
G. 99

01
2010
1
000.4239
0.39930.38260.17720.15970.24900.23400.25180.1239507 ± 45330 ± 33333 ± 44101 ± 1582 ± 21401 ± 36414 ± 43645 ± 34
154 ± 14

G. 99*

00.1159942 ± 28

10Be content / dpm kg–1

0.00007a

0.00016a
0.0005b
0.49b
1.17a

Reference 6. bReference 13.

in iron meteorites.2 In this work, to investigate the effect of theinclusions, the fragments of G. 003, G. 102, and G. 105 wereleached with acid after neutron irradiations. G. 102 and G. 105
were leached once ultrasonically with 1.5 N HNO3 for 2 min,and G. 003 twice.
3. Results and Discussion
3.1. High-purity iron samples. The contents of manganesein the high-purity iron samples measured by INAA, ICP-MS,
and ICP-AES are listed in Table 1. The certified values ofmanganese contents in these samples are also included. TheINAA results agreed with the certified values for all the samples within experimental uncertainties, indicating that the contribution of the 56Mn produced by fast neutrons was negligiblysmall in this irradiation condition. The contribution of the fastneutron induced reaction was estimated to be <1 ppb Mn in
JSS001-4 and <5 ppb in JSS001-5 by subtracting the certified
values from the INAA results.
The results from ICP-MS and ICP-AES were consistent withthe certified values for JSS003-5 and JSS009-2, while for
JSS001-4 and JSS001-5, which have only 0.03 ppm Mn, wecould not obtain the results consistent with the certified values.
The contamination in the chemical treatment seemed to affectthe determination of trace amount of manganese.
Consequently, it was confirmed that the INAA using Tc-Pn
can determine trace amount of manganese in high-purity ironsamples more exactly and easily than the other methods.
Therefore, the INAA using Tc-Pn was applied to the determination of manganese in the iron meteorite.
3.2. Cosmogenic 55Mn in the Gibeon iron meteorite. The
manganese contents in five fragments of the Gibeon iron meteorite determined by NAA are summarized in Table 2, which
includes the results of some fragments leached once or twice
after neutron irradiation. Cosmogenic 10Be in these fragments
measured by Honda et al.3,4,6,13 are also indicated in Table 2. It
is expected that the Gibeon fragments with lower 10Be content
tend to be less exposed by cosmic rays and to have lower cos-mogenic 55 Mn. However, the Gibeon fragments with lower
10Be do not always have lower manganese contents as indicatedin Table 2. G. 003 with the lowest 10Be has higher 55Mn content
than G. 102, while G. 99 with the highest 10Be has lower 55Mn
than G. 003 and G. 105. The observed trend of manganesecontents in these fragments can be probably explained by theinclusions contained in the Gibeon iron meteorite. It seems
that the manganese content measured in each fragment isaffected by relatively high contents of manganese in troilite.
Among three fragments leached after irradiation, only themanganese content of G. 003 was reduced by 30% after onetime leaching, indicating that the leaching removed troilite.
Both G. 99 and G. 99* were cut off from different parts of thesame fragment. The difference in manganese contents between
two parts can also be explained by the troilite included heterogeneously in the fragment. For the determination of cosmogenic 55Mn in the Gibeon fragments, it is required to remove
inclusions completely.
4. Conclusion
Trace amount of manganese as an impurity in four kinds ofhigh-purity iron samples was determined by three analyticalmethods. About 30 ppb Mn in the iron samples could be determined by INAA using Tc-Pn at KUR without correcting a contribution of the 56 Mn produced by the fast neutron-induced
reaction. Neutron activation analysis using Tc-Pn was applied
to the determination of 55Mn in five fragments of the Gibeon
iron meteorite. From the measurements for those fragmentswith surface-leaching, it was found that manganese derived
from the troililte inclusions interfered in the estimation of cosmogenic 55Mn in the Gibeon fragments. The complete removalof such inclusions will lead to estimation of cosmogenic 55Mn
in the Gibeon iron meteorite.
Acknowledgement. We are grateful to Prof. M. Honda, theUniversity of Tokyo, for his suggestion of this work and forsupplying the Gibeon iron meteorite, to Prof. K. Tomura,Determination of Trace Amount of Manganese in High-purity Iron

J. Nucl. Radiochem. Sci., Vol. 8, No. 2, 2007 115

Rikkyo University, for supplying JSS001-4, and to Mr. Y.
Nakano, Kyoto University, for the operation in neutron-irradiation using Tc-Pn at KUR.

(5) K. Nagao and M. Honda, Abst. 29th Symp. on Antarctic
Meteorites, NIPR, Tokyo, June 7, 2005 (2005), p 49.
(6) M. Honda and K. Nagao, Abst. 29th Symp. on Antarctic
Meteorites, NIPR, Tokyo, June 7, 2005 (2005), p 21.
(7) Japanese Iron and Steel Certified Reference Materials,Certificate of Analyses, JSS003-5 (2004).
(8) Japanese Iron and Steel Certified Reference Materials,Certificate of Analyses, JSS009-2 (1994).
(9) Japanese Iron and Steel Certified Reference Materials,
Certificate of Analyses, JSS001-4 (1994).
(10) Japanese Iron and Steel Certified Reference Materials,
Certificate of Analyses, JSS001-5 (2001).
(11) T. Takeuchi, Radioisotopes 46, 395 (1997).
(12) V. F. Buchwald, Handbook of Iron Meteorites, Vol. 1, Univ.
Calif. Press, Berkeley (1975), p 82.
(13) M. Honda (private communication, 2006).

References(1) K. Tomura and H. Tomuro, J. Radioanal. Nucl. Chem. 242,147 (1999).
(2) M. Honda, H. Nagai, and T. Shimamura, Proc. Institute of
Natural Sciences, Nihon Univ. 26, 123 (1991).
(3) M. Noguchi, M. Honda, H, Matsuzaki, Y. Oura, and H.
Nagai, Geochim. Cosmochim. Acta 67, Suppl. 1, A340
(2003).
(4) M. Noguchi, H. Matsuzaki, M. Setoguchi, M. Honda, andH. Nagai, Abst. 28th Symp. on Antarctic Meteorites, NIPR,Tokyo, June 3, 2004 (2004), p 64.