Remotely controlled rare gas analyzer with chemical reaction as energy source considered for radioactive dating of lunar surfac

Eberhardt, P.

Geiss, J.

English

NASA Technical Reports Server

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t 
P H Y S I K A L I S C H E S  INS T I T U T  
U N I V E R S I T Y  O F  B E R N E  
B ERNE, S WI T ZERLAND 
FINAL REPORT 
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NATIONAL AERONAUTICS AND SPACE u u  3 5  
b 
(0 
I 
ADMINISTRATION RESEARCH 
NO. NsG-157-61 
GRANT 
"STUDIES ON THE RADIOACTIVE 
DATING O F  THE LUNAR S U R F A C E t 1  
P. Eberhardt and J. Geiss 
August, 1966 
https://ntrs.nasa.gov/search.jsp?R=19670004333 2020-03-16T17:13:30+00:00Z
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I. EXPERIMENTAL AND TECHNICAL STUDIES 
I. 1 Introduction 
The extraction and analysis of r a r e  gases  f rom sil icate mater ia ls ,  
such as t e r r e s t r i a l  rocks and stone meteorites,  i s  routinely performed 
in  many laboratories. From the measured concentrations and isotopic 
compositions, K/Rr, U, Th/He, I 129 /Xe 129 ages, radiation ages and 
other data can be derived. The gases a r e  released by heating and melting 
the sample in specially designed extraction systems at temperatures  of 
up to  1800 C. Induction o r  internal res is tance heaters  a r e  used and the 
power consumption is in the order of severa l  kwh. A variety of get ters  
cleans the evolved gases. After severa l  purification steps the r a r e  gases  
a r e  analyzed in suitable mass  spectrometers.  The analysis of a single 
sample requires a large number of individual operations, especially during 
the extraction and purification stage. 
0 
In the framework of ou r  studies on radioactive dating of the lunar 
surface,  the feasibility of remote-controlled r a r e  gas analysis had to be 
investigated. The main problem was to  show that a simple,  lightweight, 
rugged r a r e  gas extraction and purification system with negligible external 
power consumption could be developed. No straightforward adaptation of 
currently available extraction systems seemed possible due to  their  high 
power consumption. No serious difficulties a r e  expected for  the remote- 
controlled mass spectrometric analyses of the extracted r a r e  gases. Mass 
spectrometers s imi la r  to those used in  upper atmosphere r e sea rch  (cf. 
Nier et  al., 1964) could be employed. 
e 
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I. 2 Development of a Rare Gas Extraction System Suitable for Remote- 
Controlled Operation 
To liberate r a r e  gases quantitatively f rom sil icate mater ia ls  , 
0 
temperatures  of 1500 C and higher a r e  necessary (Geiss and Hess ,  1358; 
Reynolds, 1963). The required temperature can be lowered considerably 
by using a flux such as NaOH at 600 (Wasserburg and Hayden, 1954) o r  
N a  B 0 at 1100-1200 (Geiss and Hess, 1958). However, flux has sev- 
era1 drawbacks: relatively long reaction t imes,  evolution of large quanti- 
t i e s  of gases such as H i n t h e  case of NaOH, difficulties in removing 2 
atmospheric contamination, and f oaming. 
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0 
2 4 7  
Wet chemical techniques could also be used for the extraction of 
r a r e  gases. Paneth and coworkers dissslved i ron meteorites in  sulfuric 
acid saturated with potassium persulfate and were able to recover He and 
Ne quantitatively (Chackett, Reasbeck and Wilson, 1953). However, hydro- 
fluoric acid would be required for  dissolving sil icates and an elaborate 
purification system would be necessary to remove water vapors,  etc. The 
recovery of Ar and the heavier r a r e  gases  f rom the solution might a lso 
be difficult. 
W e  therefore decided to develop a high-temperature extraction 
system with a chemical reaction as heat source. Thermite, a mixture of 
i ron oxide and aluminum, seemed a suitable energy source. Temperatures 
higher than 1500 C a r e  reached and the heat of solidification of the molten 
i ron would prolong the period of t ime the sample is at high temperature. 
Figure 1 shows a c ros s  section of the final version of the complete ex- 
traction and purification system. The sample is contained in a Mo-extrac- 
tion crucible, The walls of the extraction crucible a r e  lined with Ti-sponge, 
held in place by a Mo-insert. The Ti-sponge acts as getter for  the cleanup 
of the evolved gases, A circular opening, d 7  m m  in  diameter ,  allows the 
introduction of the sample after the whole extraction system has been 
assembled. All par ts  which a r e  in  contact with the vacuum system a r e  
thoroughly pre-degassed, Brazing is done in high vacuum. The thermite 
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mixture is held in a graphite crucible. A graphite l iner prevents the contact 
of the molten iron with the Mo-crucible. A Mo-radiation shield acts also as  
supporting s t ructure  of the graphite crucible. The whole assembly is en- 
closed in a sealed can, preventing the escape of any gas f r o m  the reaction. 
The can i o  filled with CO at 1/3 atmosphere to facilitate the ignition of the 
thermite (ignition in  vacuum proved to  be very difficult); The total weight 
of the system ready to operate is below 500 g, the diameter 7 cm, and the 
length 13 cm. 
2 
Several complete systems were built and tested, some with slightly 
la rger  overall  dimensions. A large number of t es t s  were also made with 
the outer can replaced by a flanged vacuum container. 
The same basic principle of design can also be used to  heat several  
Mo-crucibles simultaneously, thus permitting the simultaneous extraction 
of severa l  samples. Such a four-sample extraction system was developed 
and tested, Some of the results reported here  were obtained with four- 
sample thermite extraction systems, 
I. 3 Performance of the Extraction System 
The temperature of the bottom of the Mo-crucible was measured 
with a W-W, Re thermocouple. The exact location of the thermocouple junc- 
tion is indicated in Figure 1. F r o m  melting point determinations it was 
concluded that the measured temperature  agrees  within 20 to 30 C with the 
temperature  reached by the sample. Figure 2 shows a typical temperature  
curve. A maximum temperature higher than 160OOC was reached. The 
maximum temperature depends on severa l  design parameters ,  as can be 
seen f rom Figures 3 and 4. 
0 
The overall extraction and pruification performance of the system 
was tested with 0.5 to 2 g samples of stone meteorites.  The temperatures  
reached were sufficient to coir?pletely melt the meteorite sample into a 
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glassy bead. The total p ressure  during the extraction was measured with 
a Pi ran i  gauge. Figure 5 shows a typical pressure- t ime curve. Shortly 
a f te r  the ignition, the pressure r a i se s  to approximately 100 mm Hg, but 
within 20 minutes the Ti-sponge get ter  reduces it by 5 c r d e r s  of magnitude. 
The clean-up is sufficient t o  allow a direct  mass spectrometr ic  analysis 
of the extracted r a r e  gases. Figure 6 shows the m a s s  spectrum in the 
m a s s  range of 2 to  44 obtained f r o m  the extraction of approximately 2 
g rams  of the stone meteorite Finney. The thermite extracticn system had 
been connected to  a statically opcrated U H V  m a s s  spectrometer.  After the 
extraction sys tem had cooled down (approximately 20 min. ), the gases  were 
admitted to  the mass  Spectrometer and the spectrum given in  Figure 6 was 
40 obtained. Interference f rcm background was well below 5 percent for  Ar , 
He 3' and Ne 
Ar 
background could be fur ther  reduced if  a second (cold) get ter  would be added. 
. Some background corrections had to  be applied for  21,22 
. The presence of Artt prevented the measurement  of Ne". The 36 ,38  
In Table 1 the He, Ne and Ar isotopic compositions obtained in this 
extraction are given and compared with values f rom standard laboratory 
extraction systems (Eberhardt et al., 1966). The agreement is within the 
assigned e r ro r s .  The total amounts of He and N e  released were estimated 
f r o m  ion beam intensities and agree with the values obtained with the 
isotopic dilution method (Eberhardt et al.,  1966). 
The extraction yield for Ar was tested in  severa l  extractions of th2 
same meteorite. The results a r e  given in Table 2. All amounts have been 
estimated f rom the ion beam intensities in  the mass spectrometer  and may 
be subject t o  e r r o r s  of up t o  10 percent. The average concentration fcr 
the thermite extractions agrees within 5 percent with the result  of the 
conventional method, A re-extraction cf the areon f rom the glassy melt  of 
sample remaining in the extraction crucible gave l e s s  than cne percent of 
the total  I',r . These results indicate that He, Ne and Ar a r e  quantita- 
tively released, despite the relatively short  heating time. 
40 
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11. THEORETICAL STUDIES 
Under this grant, a general theoretical  study on age determinations 
and other applications of r a r e  gas measurements  on lunar surface mater ia l  
was car r ied  out and published by P. Eberhardt (1964). This work has shown 
the grea t  importance which should be attached to r a r e  gas measurements  
in lunar surface material. Such measurements  could be applied for  the 
determination of the ages of surface features of the moon, The histcry of 
the high energy particle radiation field in the so la r  system can be investi- 
gated by measuring spallation products in lunar surface material. From 
this, results superior  to those obtained f rom measurements  on meteori tes  
and on t e r r e s t r i a l  samples can be expected, Spallation products and neutron 
produced isotopes can be used for  studying erosion rates  at the surface of 
the moon. All these methods a re  outlined and discussed in detail in the 
paper by P. Eberhardt (1964). 
In a le t ter  to the Journal of Geophysical Research we have suggested, 
i n  collaboration with P. Signer f rom the University of Minnesota, an ex- 
periment for the determination of the composition of the so la r  wind 
(P. Signer, P. Eberhardt,  and J. Geiss, 1965). The method outlined in 
this publication was in  part  conceived as a resul t  of the wcrk performed 
under this grant. 
111. INVENTIONS 
No inventions required to be reported have been made in the per-  
formance of work under the grant. 
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REFERENCES 
Chackett K. F., P. Reasbeck, and E. J. Wilson; Recent studies on iron 
meteorites.  11. Determination of the helium content; Geochirri. 
Cosmochim. Acta - 3, 261-271, 1953. 
Eberhardt P. ; Rare gas  measurements i n  meteorites and possible appli- 
cations to the lunar surface; Technical Report, submitted to NASA 
in  March 1965. 
Eberhardt P., 0. Eugster,  J. Geiss, and K. Marti; Rare  gas  measure-  
ments in 30 stone meteorites; Z. Naturforschg. =, (4), 414-426, 
1966. 
Geiss J. and D. C. Hess; Argon/potassium ages and the isotopic composi- 
tion of argon f r o m  meteorites; Astrophys. 3. - 127, 224-236, 1958. 
Nier A . O . ,  J.H. Hoffman, C.Y. Johnson, and J. C. Holmes; Neutral 
composition of the atmosphere in the 100- to 200-kilometer range; 
J. Geophys. Res. - 69 ( 5 ) ,  979-989, 1964. 
Reynolds J. H. ; Xenology; J. Geophys. Res. 68, 2939-2956, 1963. 
Signer P., P. Eberhardt, and J. Geiss; Possible determination of the 
solar  wind composition; J. Geophys. Res. 70 - (9), 2243-2244, 1965. 
Wasserburg G. J. and R. J. Hayden; The branching ratio of K ; Phys. Rev. 
40 
- 93, 645, 1954. 
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method 
The rrnite 
The rmit  e 
Thermite 
Thermite 
Thermite 
Average thermite 
(standard deviation] 
Conventional 
S amp 1 e 
size, g 
0. 50 
1. 24 
0.55 
0. 50 
0. 50 
40 Ar 
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x 10 cc STP/g 
4. 6 
4. 6 
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5.7 
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5. 2 
Table 2 Argon-40 yield of 5 different thermite extractions 
on samples of a stone meteorite. For a detailed 
description of the conventional extraction system 
see  Eberhardt e t  al . ,  1966. All r a r e  gas con- 
centrations were estimated f rom the ion beam 
intensity in the mass  spectrometer and may be 
subject to  e r r o r s  of up to  10 percent, 
. 
SAMPLE 
INTRoOUC~ION 
SPRINGS 
SWPORIW 
CRUCIBLE 
GRAPHIIE 
INIMONIU 
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LOCATION OF 
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K K r B M N U Y  
RADIATION 
W E L D  
GRAPHITE 
CRUCIBLE 
GRAPHITE 
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F& ONE SAMPLE EXTRACTION AN0 PURIFICATION SYSTEM 
W l l H  THERMITE HEATING IHOOEL 631 
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GRAPHITE LINER WALL THICKNESS 
FJgure 3 Dependence of the maximum temperature reached by 
the sample on the wall thickneacr of the graphite liner. 
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. .. 
1400 
1200 
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300 400 500 GRAMS 
THERMITE 
. .  
Figure 4 ' Maximum t e q e r a t u r e  reached by the sample in a four- 
sample extraction eystem (Type 64-1) for different 
amounts of thermite mixture. 
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INTENSITY ( arbitcary units ) 
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V 


Studies on the Radioactive Dating of the Lunar Surface Final Report

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