Journal of Nuclear and Radiochemical Sciences, Vol. 19, pp. 14-19, 2019

ArticlesMössbauer study of iron oxide nanoparticles produced by laser ablation of metallic iron inwater and effects of subsequent laser irradiation
Shota Amagasa and Yasuhiro Yamada*
Department of Chemistry, Tokyo University of Science, Kagurazaka, Shinjuku-ku, Tokyo 162-8601 Japan
Received November 3, 2019; Accepted November 15, 2019; Published online November 27, 2019
Laser ablation of a metallic iron block in a flow of water was performed to produce both iron and iron oxide
nanoparticles. The X-ray diffraction patterns and Mössbauer spectra for the particles indicated that the resulting
material consisted of α-Fe and Fe0.89O nanoparticles. Transmission microscopy images demonstrated that theseparticles were spherical with diameters in the range of 5 to 45 nm with an average size of 20 nm. The particles
were re-suspended in water and irradiated with laser light, following which the particle size was decreased andthe material was further oxidized to amorphous Fe2O3. These results establish that laser ablation and laser irradiation have different effects when processing iron and iron oxide particles.

1. Introduction
Laser ablation in liquid (LAL) is a very useful, conventional
means of producing metal particles. While the wet chemical
synthesis of nanoparticles typically requires numerous chemical reagents and complicated handling processes, LAL provides a very simple method of generating nanoparticles while
reducing the amount of reagents.1 Furthermore, so-called
naked nanoparticles without coating materials can be obtainedusing LAL, which provides a facile approach to studying theproperties of such materials. Laser-based synthesis and processing have been studied extensively, as has the LAL processitself. Both fragmentation and melting resulted from laser
irradiation (LI) of particles suspended in liquid have beenfound to be important. 2 Laser ablation (LA) of a metal has
been shown to produce a plasma vapor that is rapidly quenchedby the surrounding solvent to produce particles. In the casethat the surrounding solvent is itself decomposed by theplasma vapor, the subsequent reactions can produce particles
of various metal compounds. The chemical composition andstructure of these nanoparticles can be controlled by tuning
the LA conditions and varying the solvent.3 In addition, in thecase that LA is performed in a stagnant solvent, the resulting
particles can be said to undergo LI. LI increases the temperature of particles, and the fragmentation and melting of the particles change their chemical composition or their shapes.
Using this LAL technique, it is possible to produce metastable materials, and our own group has demonstrated the generation of metastable copper oxide particles (Cu 4O3) by LA inwater.4 We have also reported the reaction of iron in organic
solvents to produce iron carbide particles. The LA of iron inalcohols gave α-Fe, γ-Fe, Fe3C and amorphous iron carbides.5
Using this technique in conjunction with a solvent f low
allowed separation and collection of the different nanoparticles
immediately after production, preventing further photochemical reactions of the material. The effect of LI on iron carbide
nanoparticles produced by LA has also been studied,6 and has
been shown to increase the particle size and to change thecomposition to pure Fe3C.
The LA of iron in various liquids has been examined.7,8 The
formation of α-Fe particles via LA of iron in water has been
investigated,9 with the surfaces of the α-Fe particles protected*Corresponding author. E-mail: yyasu@rs.kagu.tus.ac.jp
Fax.+81-3-5261-4631

by surface-stabilizing reagents. The fabrication of FeO
nanoparticles based on LA of a pure iron plate in poly (vinylpyrrolidone) solutions has also been reported, during which
the particle size was controlled by varying the surfactant concentration.10 Generally, LA of metallic iron in water without
an adequate supply of surfactant produces iron oxide particles.
It has been proposed that the LA process generates Fe clusters
that react with adjacent H 2 O molecules to form Fe(OH) 2
nanopar ticles, which subsequently decompose to FeO
nanoparticles at high temperature and pressure. In other work,
iron oxide nanoparticles consisting of a mixture of hematiteand magnetite were obtained by LA of metallic iron in water.11
The size of such iron oxide nanoparticles can evidently be controlled by applying LI,12 although Mössbauer spectra of theparticles were not obtained in previous studies.
In the present study, LA of metallic iron in flowing water
was performed to produce LA particles that were then further
modified by LI in water. These LA and LI processes wereanalyzed separately to better understand the LAL mechanism.
2. Experimental
The experimental setups employed in this study was almost
the same as those described in our previous paper.5 Briefly, an
airtight vessel attached to a cellulose acetate filter (pore size:
3.00 μm) and a diaphragm pump was employed to perform
LAL. The water (200 mL) used in this process was degassed
before use. An 57Fe-enriched (96%) iron block (6 × 5 × 1 mm3)
was placed in the water and the vessel headspace was filledwith Ar to eliminate contact with air. The vessel was maintained at atmospheric pressure. Light (532 nm, 10 Hz, 100 mJ·
pulse -1, beam diameter of 6 mm) from a Nd:YAG laser(Continuum, Surelite I-10) attached to a second harmonic generator was employed to perform LA. The laser pulses wereintroduced through a convex lens directly attached to the glass
vessel and the water flow was maintained at a continual rate of
250 mL min-1. The nanoparticles collected on the filter weredried in a flow of Ar.
To study the effect of LI, the LA particles were re-suspended in water in a glass vial open to the ambient atmosphereand subsequently irradiated with non-focused laser light (fluence: 350 mJ·cm-2·pulse -1) for 10000 pulses. The water was
stirred continuously to avoid precipitation of the particles. The
resulting LI particles were collected by centrifugation and fil-© 2019 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 11/27/2019

15

J. Nucl. Radiochem. Sci., Vol. 19, 2019

tration.
The LA and LI particles were assessed using Mössbauer
spectroscopy (Wissel, MDU1200, 57Co/Rh source), X-ray diffraction (XRD; Rigaku, RINT2500, Cu-Kα) and transmission
electron microscopy (TEM; JEOL, JEM-2100).
3. Results and discussion
3.1. LA particles. XRD patterns for the LA particles wereacquired (Figure 1) and these patterns could be assigned to a
combination of α-Fe metal (PDF#006-0696) and Wüstite FeO(PDF#01-089-0687). The diameters of the α-Fe and FeO particles were estimated using Scherrer’s equation, based on thewidths of the XRD peaks, to be 30 and 26 nm, respectively. A
TEM image of the LA particles is provided in Figure 2. These

Yamadaparticles were evidently spherical having a distribution ofdiameters in the range of 5 to 45 nm, with an average size of
20 nm. This result was in agreement with the diameters estimated from the XRD patterns. However, it was not possible todistinguish α-Fe and FeO in the TEM images.
Mössbauer spectra of the LA particles were obtained at temperatures from 3 to 293 K (Figure 3), and the resulting
Mössbauer parameters are summarized in Table 1. The spectrum acquired at 293 K (Figure 3g) was fitted to give a combination of a sextet, a doublet and a singlet. The Mössbauer
parameters for the sextet were those for α-Fe, while the doublet
and the singlet were assigned to Fe2+ and Fe3+ species, respectively, in iron oxide particles. As only α-Fe and FeO wereidentified based on the XRD patterns for the samples without
Fe3+ species, the Fe3+ indicated by the Mössbauer spectrum isbelieved to have been associated with defects in the FeO lattice
structure. The highly energetic Fe atoms produced by LAreacted with the surrounding water molecules to generate ironoxide particles in addition to α-Fe. FeO typically has a highconcentration of defects, while Fe2+ has both bulk Oh anddefect-associated positions. Therefore the Fe2+ in the FeO produced a doublet at room temperature.
The same sample was examined at lower temperatures andthe Fe2+ doublet was found to become broader at 200 K (Figure
3f ), while magnetic components appeared below 100 K(Figures 3a, b, c, d and e). Wüstite FexO is known to become
antiferromagnetic below approximately 195 K. This value

NumberFigure 1. XRD patterns for (a) LA particles and (b) LI particles produced in water.

20
10
0

0

20 40 60
Diameter / nm

Figure 2. TEM image of LA particles and particle diameter distribution. The diameters of 129 spherical particles in the TEM image
were measured to show the histogram.

Figure 3. Mössbauer spectra of the LA particles.

J. Nucl. Radiochem. Sci., Vol. 19, 2019

Mössbauer study of iron oxide nanoparticles produced by laser ablation of

16

TABLE 1: Mössbauer parameters of the LA nanoparticles shown in Figure 3.
Temp.

shape

species/sites

δmm/s

ΔEQ mm/s

Sextetα-Fe*
00
DoubletFe2+
0.96(0)0.64(0)SingletFe3+0.21(1)–
200 K
Sextetα-Fe*
00
DoubletFe2+
1.05(5)0.83(4)SingletFe3+0.09(7)–
100 K
Sextetα-Fe*00
SextetFe3+/ Oh
0.81(2)0.81(5)SextetFe2+/Def. Oh–0.15(28)0.05(5)SextetFe2+/Bulk Oh
1.14(3)0.20(3)
DoubletFe3+/Int. Td
0.26(1)3.64(2)
DoubletFe3+0.35(1)0.58(3)77 K
Sextetα-Fe*00
SextetFe3+/ Oh
0.80(2)0.54(4)
SextetFe2+/Def. Oh–0.05(4)–0.02(7)SextetFe2+/Bulk Oh
1.13(3)0.25(4)
DoubletFe3+/Int. Td
0.28(1)3.85(3)
DoubletFe3+0.45(1)0.69(2)
50 K
Sextetα-Fe*00
SextetFe3+/ Oh
0.67(2)0.41(3)
SextetFe2+/Def. Oh–0.01(3)–0.02(6)SextetFe2+/Bulk Oh
1.22(3)0.33(3)
DoubletFe3+/Int. Td
0.27(1)4.02(2)SingletFe3+0.28(2)–30 K
Sextetα-Fe*00
SextetFe3+/ Oh
0.63(2)0.32(3)
SextetFe2+/Def. Oh
0.10(3)0.08(7)
SextetFe2+/Bulk Oh
1.22(3)0.33(3)
DoubletFe3+/Int. Td
0.27(1)4.06(3)SingletFe3+0.19(3)–
3K
Sextetα-Fe*00
SextetFe3+/ Oh
0.60(12)0.18(3)
SextetFe2+/Def. Oh
0.20(2)0.36(5)SextetFe2+/Bulk Oh
1.40(5)0.31(5)
DoubletFe3+/Int. Td
0.26(2)4.10(3)SingletFe3+0.28(2)–* The δ and ΔEQ values of α-Fe were fixed to zero in the fitting procedure.
293 K

represents the Néel temperature (T N) for this material, which
will vary depending on the value of x.13 The structure of the
Mössbauer spectra acquired in this study were in agreementwith this magnetic character of FexO. FexO exhibits a non-zero
ΔEQ because it contains defects. The Mössbauer spectrum of
FeO also comprises a combination of sextets reflecting the different Fe sites produced by defects. The Mössbauer spectra ofthese compounds have been studied extensively and reported
in the literature.14 The Mössbauer spectrum obtained at 3 K(Figure 3a) is highly complex and was fitted to give a combination of four sets of sextets, one doublet and one singlet. Oneof the sextets was assigned to α-Fe, while the remaining three
sextets and the doublet were assigned to FexO according to theliterature.14 The sextet having the largest hyperfine magnetic
field (H = 51.4 T) was attributed to substitutional octahedral
high-spin Fe3+, which provided charge neutrality to the defectcluster. The sextet having the highest area intensity was
assigned to bulk octahedral high-spin Fe2+. The line width of
this sextet was extremely broadened as a result of the varietyof environments caused by defects or the large surface area of
the nanoparticles. Another sextet (H = 44.7 T) was assigned to
the Fe2+ associated with the substitutional Fe3+, which was
expected to produce a large hyperfine field at the Fe2+ sites.

HT
33.0(0)––33.7(2)––33.8(1)49.5(2)41.9(2)33.4(2)––33.78(6)50.4(2)43.5(2)35.8(2)––33.7(6)51.0(1)44.4(2)37.6(2)––33.7(7)51.4(1)45.0(2)38.1(2)––33.6(1)51.4(1)44.7(2)39.4(3)––Γmm/s
0.33(1)0.59(1)0.95(3)0.81(8)1.23(6)
1.21(14)0.56(4)0.66(9)0.76(9)2.44(11)0.43(4)0.91(6)0.44(3)0.62(8)0.88(13)
2.24(12)0.46(4)0.62(4)0.52(3)0.70(6)1.00(10)2.15(8)0.49(4)
1.23(6)0.52(3)0.73(6)
1.11(11)
2.19(9)0.57(4)1.01(9)0.50(4)0.74(6)0.74(6)2.08(11)0.45(5)0.29(6)

Area
%
20(1)
64(1)
16(1)
21(4)
65(7)
14(6)
12(1)
6(1)
7(1)
64(4)
1(0)
11(1)
12(1)
8(2)
9(2)
59(5)
4(1)
9(1)
12(1)
10(1)
11(2)
55(3)
4(1)
8(1)
11(1)
12(2)
13(2)
55(4)
5(1)
4(1)
11(2)
18(2)
17(3)
49(5)
4(1)
1(1)

The doublet having a large ΔEQ value of 4.10 mm/s was due toFe3+ at tetrahedral sites. This unusual large quadrupole interaction of ca. 4.0 mm/s was also reported in the literature14.
The low intensity Fe3+ singlet has not been reported in the literature, and might be associated with defects or with the surfaces of the nanoparticles, which were not highly crystalline.
This component appeared as a singlet below 50 K but transitioned to a doublet at 77 and 100 K. With increasing temperature, the area of this nonmagnetic component became larger
while the intensity of the peak associated with substitutional
octahedral high-spin Fe 3+ decreased. This phenomenon
occurred because the substitutional octahedral high-spin Fe3+
in the smaller crystals had a lower blocking temperature.
The Fe2+/Fe3+ ratio in the FexO nanoparticles was estimatedbased on the areas of the Mössbauer spectral components
acquired at low temperatures, to give a value of 3.06. Thus,
the stoichiometry of the FexO nanoparticles was determined to
be Fe0.89O assuming that charge balance was produced by thecoexistence of Fe2+ and Fe3+. The Mössbauer spectra therefore
indicated that the nanoparticles produced by LA in water consisted of α-Fe and Fe0.89O, while more stable iron oxides suchas hematite, Fe2O3, or magnetite, Fe3O4, were not produced.

17

J. Nucl. Radiochem. Sci., Vol. 19, 2019

field distribution of the spectrum obtained at the lowest temperature of 3 K was narrow with a larger mode of H = 49 T
(Figure 5a and Figure 6a). However, this value was still
smaller than that for bulk maghemite (H = 51 T). The temperature dependence of the Mössbauer spectra of the present LI
particles was similar to that reported for amorphous Fe2O3
synthesized via the thermal decomposition of PrussianBlue.16,17 A very small portion of the Fe2O3 was evidently in theform of γ-Fe2O3 nanoparticles, although the Mössbauer spectra
could not be used to differentiate between the two materials
because the γ-Fe2O3 nanoparticles were too small. The LI particles fabricated in this study are therefore believed to havecomprised both amorphous Fe2O3 and nanocrystalline γ-Fe2O3
particles.
These experimental results confirm that LI decreased thesize of the particles while increasing the extent of oxidation.
The mechanism by which laser light interacts with colloidal
nanoparticles has been discussed on a theoretical basis in theliterature.18 We also performed similar calculations to estimate
the laser fluence necessary for melting of the α-Fe and FexO
particles in our experiments. The basic assumption of themodel is that all the energy absorbed by a particle is expended
100(e) 293 K

95100(d) 77 K

95
Relative intensity (%)

3.2. LI particles. The LA particles described above wereagain suspended in water and LI was performed. The XRD
pattern for the resulting LI particles (Figure 1b) contains no
sharp peaks, indicating the absence of a periodic crystal lattice. TEM images of the LI particles are presented in Figure 4,
and show that this material consisted of spherical iron oxide
particles with a diameter of ca. 10 nm, in addition to amorphous iron oxides. The high-resolution TEM image of thespherical particles in Figure 4 shows an interplanar distance,d, of 0.25 nm that corresponds to the (311) lattice planes ofmaghemite γ-Fe 2 O 3. These results demonstrate that LI
decreased the size of the LA particles.
Mössbauer spectra of the LI particles are provided in
Figure 5, and the parameters are summarized in Table 2. The
spectrum obtained at 293 K contains a paramagnetic doublet
that was assigned to Fe(III) oxide species (Figure 5e). The
observed isomeric shift, δ = 0.37 mm/s, corresponds to highspin Fe3+ with octahedral coordination. The spectra at 77 K
and 50 K still show a doublet but these peaks are now broader
because of the appearance of magnetic components (Figure 5d
and c). The effect of temperature on the shape of the
Mössbauer spectra likely results from magnetic relaxation,although the spectra could not be fitted assuming a single
relaxation time. Because the amorphous and crystalline
nanoparticles generated in this study had a distribution ofrelaxation times (due to variations in the size of crystalline
regions), the Mössbauer spectra were fitted assuming a distribution of hyperfine magnetic fields (Figure 6). The hyperfine
magnetic field distributions were evaluated using a method
reported by Hesse.15 Upon decreasing the temperature to 30 K,
the field distribution shifted to larger values, with a mode at
H = 43 T (Figure 5b and Figure 6b). The hyperfine magnetic

Yamada90100(c) 50 K

9692100(b) 30 K9810098(a) 3 K

96
-10

-5

0

5

10

Velocity (mm/s)

Figure 5. Mössbauer spectra of LI particles. The temperatures areshown in the figure.

TABLE 2: Mössbauer parameters for the LI amorphous
particles and nanoparticles for which data are provided in
Figure 5.

Figure 4. TEM and HR-TEM images of LI particles.

Temp.
δ mm/s
ΔEQ mm/s
H* T
293 K
0.37(1)0.79(1)77 K
0.48(1)0.82(1)50 K
0.48(1)0.00(1)
430 K
0.48(2)0.00(1)43
3K
0.47(1)–0.01(1)49* mode of hyperfine magnetic distribution.

Γ mm/s0.54(1)0.60(1)

Mössbauer study of iron oxide nanoparticles produced by laser ablation ofJ. Nucl. Radiochem. Sci., Vol. 19, 201918(c) 50 K

PHi(b) 30 K(a) 3 K

0

40

20

60

Figure 7. Calculated critical laser fluence values for melting α-Fe
and FeO particles at λ = 532 nm. Legend: (Fe (S)) = heating to themelting point of Fe, (Fe (L)) = melting of Fe particles, (FeO (S)) =heating to the melting point of FeO, and (FeO (L)) = melting of FeO
particles.

H (T)Figure 6. Hyperfine magnetic field distributions of Mössbauer spectra shown in Figure 5a, b, and c. The temperatures are shown in the
figure.

in the particle heating and melting processes. The absorption
efficiency, Qabsλ (d), varies with the laser wavelength, λ, andparticle diameter, d, and was calculated based on the Mie theory. The MiePlot v4.6 software program19 was employed to
calculate Qabsλ (d), using refractive indices, n, and extinction
coefficients, k, for α-Fe (n = 3.4342 and k = 3.4186) and FeO(n = 2.8882 and k = 0.50800) at λ = 532 nm previously reported
in the literature.20,21 The critical laser fluence, J, required topromote a phase transition was then determined from theequation 18,21,22

J=

2
d
ρΔH λ
,
3
Qabs(d)where ρ is the particle density and ΔH is the enthalpy required
to reach the melting point (ΔHt) or the enthalpy of melting(ΔHm). Calculations used the following values reported in theliterature:24 α-Fe: ΔHt = 58.645 kJ·mol-1 and ΔHm = 13.807
kJ·mol -1; FeO: ΔH t = 79.081 kJ·mol -1 and ΔH m = 24.058
kJ·mol-1. The critical laser fluence values required to reach themelting point and to complete the melting process were calculated using these parameters (Figure 7). As the laser fluence
was 350 mJ·cm-2·pulse-1 and the particle sizes ranged from 5 to
45 nm in the present study, the calculations demonstrate that
all the α-Fe and FeO particles would be expected to absorb
sufficient energy (more than 30 times of the critical fluence) tomelt in the water, and that these particles would also havereacted with the surrounding water molecules to oxidize.
Amorphous Fe2O3 would have been produced by the rapid
cooling of iron oxide nuclei.
4. Conclusion
The LA of metallic iron in a flow of water was found to pro-

duce both α-Fe and FexO nanoparticles. These particles were
spherical with an average diameter of 20 nm. Mössbauer
spectra of the particles were acquired between 3 and 293 K,
and the stoichiometric composition of the oxide was estimatedto be Fe0.89O. The α-Fe and Fe0.89O nanoparticles were subsequently re-suspended in water and irradiated with laser light(λ = 532 nm), during which they were further oxidized toamorphous Fe2O3 and γ-Fe2O3 nanoparticles. Our calculations
for laser f luence indicate that the original LA particles
absorbed sufficient energy to melt and to oxidize during the LI
process. The results of this work confirm that LA and LI havedifferent effects when employed for the fabrication of iron andiron oxide nanoparticles in water. In particular, LI can successfully reduce the size of nanoparticles while also promoting
oxidation to form amorphous Fe2O3 and γ-Fe2O3 nanoparticles.
References(1) H. Zeng, X. W. Du, S. C. Singh, S. A. Kulinich, S. Yang, J.
He, W. Cai, Adv. Funct. Mater. 22 (7), 1333 (2012).
(2) D. Zhang, B. Gökce, S. Barcikowski, Chem. Rev. 117 (5),3990 (2017).
(3) V. Amendola, M. Meneghetti, Phys. Chem. Chem. Phys. 15(9), 3027 (2013).
(4) K. Amikura, T. Kimura, M. Hamada, N. Yokoyama, J.
Miyazaki, Y. Yamada, Appl. Surf. Sci. 254 (21), 6976
(2008).
(5) S. Amagasa, N. Nishida, Y. Kobayashi, Y. Yamada,Hyperfine Interact. 237, 110 (2016).
(6) S. Amagasa, N. Nishida, Y. Kobayashi, Y. Yamada,Hyperfine Interact. 238, 83 (2017).
(7) A. De Bonis, T. Lovaglio, A. Galasso, A. Santagata, Appl.
Surf. Sci. 353, 433 (2015).
(8) A. Kanitz, J. S. Hoppius, M. del Mar Sanz, M. Maicas, A.
Ostendorf, E. L. Gurevich, ChemPhysChem 18 (9), 1155
(2017).
(9) Y. Vitta, V. Piscitelli, A. Fernandez, F. Gonzalez-Jimenez,
J. Castillo, Chem. Phys. Lett. 512 (1–3), 96 (2011).
(10) P. Liu, W. Cai, H. Zeng, J. Phys. Chem. C 112 (9), 3261
(2008).

19

J. Nucl. Radiochem. Sci., Vol. 19, 2019(11) V. Amendola, M. Meneghetti, G. Granozzi, S. Agnoli, S.
Polizzi, P. Riello, A. Boscaini, C. Anselmi, G. Fracasso, M.
Colombatti, J. Mater. Chem. 21 (11), 3803 (2011).
(12) V. Amendola, P. Riello, S. Polizzi, S. Fiameni, C.
Innocenti, C. Sangregorio, M. Meneghetti, J. Mater. Chem.
21 (46), 18665 (2011).
(13) F. B. Koch, M. E. Fine, J. Appl. Phys. 38 (3), 1470 (1967).
(14) C. Wilkinson, P. D. Battle, D. A. O. Hope, A. K.
Cheetham, G. J. Long, Inorg. Chem. 23 (20), 3136 (1984).
(15) J. Hesse, A. Rübartsch, J. Phys. E: Sci. Instrum. 7, 526(1974).
(16) R. Zboril, L. Machala, M. Mashlan, V. Sharma, Cryst.
Growth Des. 4 (6), 1317 (2004).
(17) L. Machala, R. Zboril, A. Gedanken, J. Phys. Chem. B 111

Yamada(16), 4003 (2007).
(18) A. Pyatenko, H. Wang, N. Koshizaki, T. Tsuji, Laser
Photonics Rev. 7 (4), 596 (2013).
(19) P. Laven, Appl. Optics, 42 (3), 436 (2003).
(20) W. S. M. Werner, K. Glantschnig, C. Ambrosch-Draxl, J.
Phys. Chem. Ref. Data 38 (4), 1013 (2009).
(21) Th. Henning, B. Begemann, H. Mutschke, J. Dorschner,
Astron. Astrophys. Suppl. Ser. 112, 143 (1995).
(22) Y. Ishikawa, N. Koshizaki, A. Pyatenko, Trans. Electron.
Inf. Syst. 135 (9), 1066 (2015).
(23) A. Pyatenko, H. Wang, N. Koshizaki, J. Phys. Chem. C
118 (8), 4495 (2014).
(24) M. W. Chase, J. L. Curnutt, H. Prophet, A. N. Syverud, L.
C. Walker, J. Phys. Chem. Ref. Data 3 (2), 311 (1974).