Age and growth pattern determination of manganese nodules were explored. Two methods are discussed: (1) measurement of the presence of radioactive iodine isotopes; which is effective only up to 3.105 years, and (2) measurements of magnetism. The growth rates of three nodules were determined. The surface of the nodule was recent, and the overall age of the nodule could be determined with accuracy of better than 30%. Measurement of paleomagnetic effect was attempted to determine wider age ranges, however, the measured sign changes could not be interpreted as paleomagnetic reversals

Beiersdorf, H.

Heye, D.

English

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RADIOACTIVE AND MAGNETIC INVESTIGATIONS
D. He;;e and H. Beiersdorf
(NASA-T14- 7 5 	 hA010ACTiVE AYL MAGNETIC	 NISI- 2,.d4ri
INVESTIGATIONS (Nationai Aerunautics and
Space Administration) 14 p aC A02/8k A01
CSCL 20K	 uucla5
uj/72 41144
Translation of "Radioaktive and Magnetische Untersuchurngen,"
Source unknown, pp 716-725 (without references)
NATIONAL AERONAUTICS AND SPACE ADITINISTRATION
WASHINGTON, D.C. 0546
	 JULY 1979
STANDARD TITLE PAGE
1.	 Rer ,ort No.
NASA TM-7550
2.	 Government Accoss-on No. 1.	 Roapront's Cotol,r tan,
_
S. 
MY
 Date
	 -
_
d.	 Title and Subtitle
RADIOACTIVE AND MAGNETIC
6.	 Performing Organisation CodeINVESTIGATIONS
7.
	 Author(s) 8.	 Performing Organisation Report No.
D. Heye and He Beiersdorf 10. Work Unit No.
CQ" tSw- r Grant No.
^	 3199a
11.
Performing Organization Nom. and Address
13.	 Type of Report and Period CoveredLeo Kanner Associates
Redwood City, California 	 94063 Translation
12.	 Sponsoring Agency Nome and Address
National Aeronautics and Space Adminis-
tration, Washington, D.Ce	 20546
11	 Sponsoring Agency Code
15.	 Supplementary Notes
Translation of "Radioactive and Magnetische
Untersuehungen," Source unknown, pp 716-725, (without references)i
16	 Abstract
The article concerns age determination and growth pattern
determination of manganese nodules.
	 Two methods are dis-
cussed:	 the first involves measurement of the presence
of radioactive iodine isotopes, and is effective only
up to 3.105 years.	 An attempt was made to measure the
paleomagnetic effect in order to determine greater ages,
but the particular approach pursued by the investigators
Evidently failed.
17.	 Key Words (Selected by Author(s)) 18.	 Distribution Statement
Unclassified - Unlimited
4 
19.	 Security Classif. (of this report) 20.
	 Security Clossif. (of this page) 21. No. of Pages 22,	 Price
I
Unc:Lessified Unclessii'ied lb
NASA•HQ
RADIOACTIVE AND MAGNETIC INVESTIGATIONS
D. Heye and H. Beiersdorf
Rate and Conditions of Growth in the Investigated Nodules
Radiation measurements were compiled and evaluated for 	 16*
five nodules (Figs. 1-3). Two of the nodules BPI (Blake
Plateau, Atlantic Ocean) and the nodule M1 (east of Madagas-
car, Indian Ocean) showed no heightened radioactivity near
the surface. As was mentioned above, in such cases one assumes
that the nodules have not grown for the last 3p10 6 years, or
have even decreased in size. In the case of the nodule in the
Blake Plateau, this result is in agreement with results of Ku
and Broecker [19691, who came to the same conclusion for this
region. The results for the other nodules will be discussed
individually.
Nodule J1
This nodule is probably located in the central Pacific
Ocean; similar nodules are known to exist there. (For compe-
titive reasons, the corporations who own the rights to most
of the useable nodules do not give their location with any
greater precision.) It has grown around a core (Fig. 3) and has
a maximum diameter of 6 cm. The nodule has a layered structure,
and the individual lines are fairly easily distinguishable in
cross sections of the nodule. The background radioactivity due
to the presence of U and Th in the nodule is low, amounting to
about 10 tracks/mm2 per month.
The evaluation of data for regions 1-4 resulted in the
determination of median growth velocities s - 10.7, 14.3, 4.09
* Numbers in the margin indicate pagination in the foreign text.
1
and 15.1 mm/106 years, respectively (see also Table 1). It is
apparent from a visual inspection of the growth lines on the
investigated section surface that the nodules in regions 1 and 4
grew at approximately equal rates, in region 2 at a somewhat fas-
ter rate, and in region 3 at only about 1/3 of the rate of regions
1 and 4. If one now takes into account the possibility of error
in the individual results of Table 1, then the relative relation-
ship of the determined growth rates is in good agreement with the
picture of the visible layer formation. For the various axes one
thus arrives at various growth rates, and for the whole nodule one
can extrapolate an age of about (2.3±.3)•106 years.
Nodule HI 
This nodule from the Pacific Ocean also exhibits easily
discernible growth lines, and grew around a large core. For the
outer layers, one obtains the same growth rates for both region
1 and region 2, within allowable margins of error; this is in
good agreement with visual observation. The median growth rate
is s - 6.8 mm/106 years. For this nodule, one can extrapolate
a total age of between 1.5 and 2 million years. In both regions,
a varying degree of U or Th activity was noted.
Nome G1 d
This nodule also is located in the Pacific Ocean, and the
visible growth lines suggest a complex growth history. One can
clearly see that a smaller nodule grew into the structure a longer
period of time ago ( i.e. t > 3 . 105 years) and that one should
expect evidence for a diversity of growth environ^ents. The U
	 20
ana Th concentration also varies greatly throughout the nodule,
and in comparison to the other nodules, is quite high (Figs. 1, 2
and Table 1).
In region 1, there was no difficulty with the evaluation
of data, and a growth rate of s : 3.6 mm/10 6 years was ascer-
2
Io
1\
'I\
Hid
A
	 A
100
	 2
1	 1	 7 =(TT)
	 I	 2	 21mm)
Figs. 5, 6, and 7: Corrected distribution of o-traces in the
examined nodules as a function of the depth.
tained. For region 2, we suspect a possible change in the
growth rate (the exterior 1.7 mm with s • 5.6 and then with
s s 22 m/106 years) . In the graphical approximation for
background N1 (U9 Th), these two lines remain invariant through
several approximation steps. Based on the initial growth rate,
the intersection of the two lines occurs at an age of 3.105
rears, so that at this depth all but 6% of the Io must already
,eve disintegrated. In this connection, the frequency of
radioactive traces at greater depths of the nodule was also
3
taken into account, and this showed clearly the pure coincidence
of this series of data points. Therefore only the value of a •
5.6 mm/106 years is valid.
For region 3, there were similar difficulties; it at first
appeared that there was a change in the growth rate (slow on the
outside, rapid on the inside). These two lines again remained
invariant during the evaluation of the data, and therefore
region 4 was introduced into the evaluation as a control. In
evaluating the data for region 4, there was at first again the
suspicion of a change in growth rates, but with opposite sequen-
cing (fast on the outside, slow on the inside); but the second
line disappeared upon successive approximations for N1 (U, Th).
For region 4 then we conclude that there is a constant growth
rate of s = 7.4 mm/106 years. But since regions 3 and 4 are
directly adjacent, and the growth lines through both regions are
sufficiently traceable, one should also assume constant growth
for region 3. The calculation then yields a value s = 10.3
mm/106
 years. On the whole, the varying results in the 4 eva-
luated regions confirm the observable differences within this
nodule. Unfortunately, for large regions of the nodule the
layer lines cannot be sufficiently well traced so as to enable
one to read the relative growth rate changes off directly.
Because of this irregular growth, it does not seem to make
sense to extrapolate an over-all age for the nodule.
In summary, with these investigations it was possible to
determine the growth rate of 3 out of 5 nodules with a relative
error, in the most favorable case, of 7.3%, In these 3 cases,
the surface of the nodule was recent, and the over-all age of
the nodule could be extrapolated with an accuracy of better
than 30%.
4
`tic Investigations of Nenganese Nodes
As mentioned at the outset, the Io dating procedure for
manganese nodules is only applicable up to a limit of about
3 . 105 years. Occasionally possible K/A age determinations in
the care of the nodule, and Be/Al dating, which is feasible but
requires great experimental effort, do not seem suitable as a
general method for bridging tris gap at greater ages. The goal
of the measurements thftt were conducted within the framework of
this investigation then was to determine whether paleomagnetic
reversals were observable in these manganese nodules, and
useable for purposes of dating.
When these investigations were planned at the end of 1970,
this question was completely unclarified. In addition, it
remains an open question whether during the time of formation
the nodules have always remained in the same position on the
ocean floor, and whether therefore it is even possible for a
magnetic polarity change to 'grow in' in a regular manner at
all. In these investigations, correct results are obtained
only if the assumption of constant position of the nodule is
accurate. All that is known is that the nodules contain rela-
tively large quantities of iron, and that the mineral Goethit
has been found [ Hering, 19711.
In addition, successful attempts have been made to ex-
tract meteorite particles from ground-up manganese nodules by
means of a hand magnet [Finkelmann, 19701. All of the to us
available nodules were located in low latitudes, and it there-
fore made sense to investigate the horizontal magnetic compo-
nents. Before artificial resin was poured around the nodules,
their magnetic properties were measured, in order to deter-
mine, if possible, the north-south magnetic axis. Later, for
purposes of magnetic investigation, an about 5 mm thick slice
perpendicular to this axis was cut out of the nodule. That is,
5
the sliced was sawed so that any natural residual magnetism
in tho north-south direction would lie perpendicular to the
plane of the slice.
Because of the low growth rate of the nodules, it became
clear that the zones of varying magnetic polarity, if they are
in fact present, are arranged in very fine layers, and there-
fore one should strive to develop a measuring procedure of high
resolution.
Measur_ iag Proced, uEg for Magnetic ILvesiggtion
Within the confines of a magnetic shield, the nodule slice
to be measured is placed between the sensors of a saturated core
magnetometer, and the vertical field components are measured at
numerous points. A photograph or diagram of the sample, with a
pointer, positioned outside of the magnetic shield permits a
precise orientation of the sensors wJth respect to the sample
slice. The sensors and the pointer can be positioned at var-
ious heights, so that the entire surface of the slice can be
measured (see Fig. 8). Because the measured values are very
low (fields <10- 6 Oersted), before and after each measurement
the sensors were removed from the measuring region, and the
zero setting checked. By means of Helmholtz coils, one can use
this arrangement to undertake demagnetization by means of alter-
nating fields, up to a maximum of 250 Oersted.
The two sensors of the saturated core magnetometer are
arranged symmetrically about the sample at a distance of 2mm
and are switched so that in this position a field measurement
can be carried out. With this arrangement, only that component
of the field that is perpendicular to the plane of the slice is
measured. Magnetization components directed parallel to the
plane of the slice are not measured, since the field component 722
6
I
b
Probe
H • Spde
C
\AEscht ^ 9 d
Fie. 8: Sketch of the magnetic measurement system for small
slices of manganese nodules with the sensors S, and S 2, the
sample and the Helmholtz coil system H.
Key: a diagram of sample	 c H coil
b sample	 d shielding
since in this symmetric arrangement such field components act
on each of the two sensors with the same magnitude but with
opposite sign, and therefore cancel each other out. Even in
cases in which there are inhomogeneities in such magnetization
components, these can have an effect only if they disturb this
symmetry. And even if this is the case, the disturbance re-
mains small, because in such cases the nature of the maximal
asymmetry from 2.5 mm (slice surface) to the medium measuring
height of the sensors, about 20 mm, becomes a factor.
If in slices that are taken from manganese nodules the
residual magnetism is not oriented precisely perpendicularly
to the plane of the slice, then the magnitude of the measured
effect is merely lowered. The relation between the perpendicu-
lar magnetization components in the slice and the measured field
remains the same, so that variations in magnetic intensity or
polarity among the layers of the nodule lead to changes in the
measured magnetic field at the appropriate points. If one
neglects the degree of resolution possible with the measuring
apparatus, one also obtains a one-to-one relationship in the
opposite direction, that is, between the measured field changes /723
and the here relevant magnetization components.
These claims were subjected to scrutiny and substantiated
by means of experiments with especially constructed control
samples. These samples were made from pourable resin and fine
iron filings, in a thickness of 5 mm, and were magnetized
perpendicularly (and at other angles) to the surface to be
measured. In the case of a wedge-shaped sample, for example,
which was measured at points of various thicknesses, a reso-
lution capacity (half value width) of 11 mm was determined
(Fig. 9).
In simulations of regions of varying polarity, it can be
seen that zones of a width greater than 6 cm register as
changes in the polarity of the magnetic field, while smaller
zones can be measured only as intensity changes. For nodules
of low growth rate (a < 10 mm/106 years), this means that any
zones of reversed polarity that might exist appear in the mea-
surements not as a change in sign, but as a change in the in-
tensity of the measured magnetic field. In order to conclu-
sively resolve such cases, it has proven advisable to prepare
and measure small samples of only a few millimeters in size. t^
By means of comparative measurements of synthetic samples
8
#Rfft
a
i
	
Itsko	 \.
	
Leo .--	 ^	 ^	 '^._
	
IISM)	 ^.-
^oo	 ./
I 1 Skd
too
S	 0	 5 mm
Fig. 9: Magnetic measurements of the perpendicular component
at various positions over wedge-shaped sample in order to
determine the resolving power. The sample was magnetized per-
pendiculkarly to the plane of the above diagram. (Thickness
of the slices 5 mm)
inside and outside of the shielding, it was determined that
at certain points there is considerable diverEence between
the measurements in the two cases, for example in the case of
large plates, and at the edges of plates. The probable expla-
nation is that the long measuring sensors, made of highly per-
meable material, apparently lead the field lines in part in
9
the direction of the shielding, where the lines close off.
This does not affect the possibility of establishing a on-
to-one relationship between residual magnetism and field
changes, and vice versa, but a comparison with theoretical
models is thei-efore not possible.
In this connection, it should be mentioned that for mag-
netic fields of varying gradients, as is always the case here,
the medium measuring height in the long sensors of about 20 mm
changes somewhat, and is in any case by no means constant.
Experimentally, measurements of the induced magnetization
(relative susceptibility) were made for various nodules. For
this purpose, a constant magnetic field was created by means
of the Helmholtz coils. A more detailed description of these
results will be omitted, since no changes were found within
the investigated nodule slices.
Measurements of Residual Magnetism in Manganese Nodules
In addition to the five nodules whose radioactive pro-
perties were investigated, one additional nodule was measured.
For three of these six nodules, the magnetic measurements yiel-
ded regions of varying sigh; however, these could not be sen-
sibly correlated to the growth pattern of the nodule. In the
case of one nodule, the magnetization was so 'soft' that after
demagnetization with an alternating field of 3 Oersteds, the
sign change disappeared.
As an instance of these investigations, the results for
nodule M1 are given. The nodule has a maximum diameter of
10 cm, grew around a stone splinter, and grew together with a
smaller nodule. Fig. 10 repro,, .q ents the results diagramma-
tically, and it is clear that the regions of varying polarity
10
M1
../	 a	 0	 0.	 1	 1	 1	 i.	 •
	
•.•••	
I 1 q
	 r	 1	 I	 i	 1••
	 .	 1
	
^a	 1	 ••••	 ^1 [l ^	 ^	 X	 1	 1	 1	 1	 1!
	
t l	 •
!	 !	 !	 L' (1	 0	 1	 1	 1	 1	 •	 •	 •	 7
n ;l Cl i	 Y
• --^1_" r--^-^'
Ip	 1	 0	 7	 6	 S	 t	 ]	 1	 1	 0	 /n•
Fig. 10: Results of the magnetic meaaurementa on a slice of
the manganese nodule M1. The intensities and the measured
changes of sign are represented.
are not centrally located. After demagnetization in an alter-
nating field, there was no fundamental change. A better rela-
tionship between regions of varying polarity and the direction
of growth did n^* result.
In conclusion, the results of the magnetic investigations
of the manganese nodules indicate that the measured sign chan-
ges cannot be interpreted as paleoma gnetic reversals. Further
investigations are planned in this direction, during which
other approaches will also be tried.
11
In conclusion, we would like to thank Dr. D. Horn of
the Lamont-Doherty Observatory for making nodule M1 avail-
able to us for these investigations. In addition, we thank
Dr. Wendt and diplom physicist Mr. Meyer for their stimula-
ting suggestions concerning the interpretation of our mea-
surements of radioactivity. Special thanks is due to the
physical engineer Mr. Kerkhoff, who carried out the radio-
active as well as the magnetic measurements with great en-
thusiasm. We would furthermore like to thank the master
mechanical technician, Mr. Haupt, Who built the measuring
apparatus for the magnetic investigations.
12


Radioactive and magnetic investigations

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