Alpha radioactivity of lunar surface at Surveyor 5, 6, and 7 landing site

Economou, T. E.

Franzgrote, E. J.

Patterson, J. H.

Sowinski, K. P.

Turkevich, A. L.

English

NASA Technical Reports Server

General Disclaimer 
One or more of the Following Statements may affect this Document 
 
 This document has been reproduced from the best copy furnished by the 
organizational source. It is being released in the interest of making available as 
much information as possible. 
 
 This document may contain data, which exceeds the sheet parameters. It was 
furnished in this condition by the organizational source and is the best copy 
available. 
 
 This document may contain tone-on-tone or color graphs, charts and/or pictures, 
which have been reproduced in black and white. 
 
 This document is paginated as submitted by the original source. 
 
 Portions of this document are not fully legible due to the historical nature of some 
of the material. However, it is the best reproduction available from the original 
submission. 
 
 
 
 
 
 
 
Produced by the NASA Center for Aerospace Information (CASI) 
https://ntrs.nasa.gov/search.jsp?R=19700010278 2020-03-12T00:58:17+00:00Z
e4
P
R:
 r
ALPHA RADIOACTIVITY UP`THE.LUNAR SURFACE
AT THE SURVEYOR V, VI, AND VII LANDING SITES
Anthony L. Turkevich, James H. Patterson.,
Ernest J. Franzgrote, Kenneth P. Sowinski, Thanasis E. Economou
.........
* L7 -
^^ IACCEBBIOti N MB
0	 f X^
D	 V	 ^"^'^	 ICODE)W
	
IPA1SE81 
	
?69
D	 ^C E ORY)
16 414ABA CR OR TMX OR AD NUMBERI
Reproduced by the
CLEARINGHOUSE
for Foderal ScianWic & Technical
information Springfield Ja 22151
%
rS
EFI-70-1
ALPHA RADIOACTIVITY OF THE LUNAR
SURFACE AT THE SURVEYOR V, VI,
AND VII LAN'DI'NG SITES
^a
r
3
Anthony L. Turkevich
Enrico Fermi Institute and Chemistry Depavtment
University of Chicago, Chicago, Illinois 60637
James H. Patterson
Chemistry Division, Argonn(.! Fational Laboratory
Argonne, Illinois 60439
Ernest J. Franzgrote
Jet Propulsion Laboratory, California Institute
of Technology, Pasadena, California 91103
Kenneth P. Sowinski
Enrico Fermi Institute
University of Chicago, Chicago, Illinois 60637
Thanasis E. Economou
:Enrico Fermi Institute
University of Chicago, Chicago, Illinois 60637
Submitted to Science
January 2, 1970
i
i
3
I01
ALPHA RADIOACTIVITY OF THE LUNAR
SURFACE AT THE SURVEYOR V, VI,
AND VII LANDING SITES
Anthony L. Turkevich
Enrico Fermi Institute and Chemistry Department
University of Chicago, Chicago, Illinois 60637
James H. Patterson
Chemistry Division, Argonne National Laboratory
Argonne, Illinois 60439
Ernest J. Franzgrote
Jet Propulsion Laboratory, California Institute
of Technology, Pasadena, California 91103
Kenneth P. Sowinski
Thanasis E. Economou
Enrico Fermi. Institute	 i
University of Chicago, Chicago, Illinois 60637
ABSTRACT
Evidence has been obtained for a radioactive deposit
on the lunar surface at Mare Tranquillitatis with a total inten-
sity of 0.09 ± 0.03 alpha dis. sec. -1 cm-2 . The presence of
Po 
2].n in close-to-equilibrium amounts indicates a continuous
turnover rate of lunar material at this site of less than 0.1
micron per year. The lack of such a deposit at two other lunar
sites suggests lower local concentrations of uranium there.
rI
The possibility of an alpha- emitting radioactive de-
posit on the lunar surface, arising from the decay in space of
radon isotopes diffusing out of lunar surface material, was s^g-
gested by Kraner, et al. (1). Recently Yeh and Van Allen (2) have
set upper limits on the amount of such alpha radioactivity using
data from the Explorer. 35 satellite orbiting the moon. The alpha-
scattering experiment performed at three locations on the moon
in 1967-1968 by Surveyor spacecraft has provided evidence for
such an alpha-active deposit in glare Tranquillitati.s. No such
evidence was found at Sinus Medii or outside of the crater Tycho.
The active deposit from radon (Rn ' t1/2 = 3.825d)
should contain, at equilibrium, daughter products emitting alpha
particles of energies 6.00, 7.69 and 5.31 MeV. The deposit from
thoron On220' tl/2 = 54 .5s) should be less intense if th e source
rock has a Th/U concentration ratio in the usual range, and should
emit alpha particles of energies 6.78 (1), 6.05 (0.33) and 8.78
(0.67) MeV, where the numbers in parentheses refer to the relative
intensities within the series. The deposit from both of these
r
radon isotopes as well as
0 219), should be on the
r
face. The Po21 and Poll
Bi212 and Po 212 daughters
from the even less abundant actinon
very top of the undisturbed lunar sur-
^^' daughters of Rn 222 and the Po2165
of Rn220, because of their relatively
short half-lives and those of their precursors should come to
equilibrium with their noble gas ancestors within a day or less.
The formation of Po 210 however, is held up by the 2.2y half-life
of its grandparent, Pb210 a
•2
Although not designed for this purpose, the Surveyor
alpha-scattering experiment (3,4,5) provided information on this
question of an active deposit on the lunar surface. Its sensi-
tivity was limited by the short operating time in certain stages
of the experiment, by the presence of a small amount of Es 254
(T = 6.44 MeV) placed close Uo the alpha detectors to provide
a check of the energy scale of the instrument, and by the
Presence of a small "background" produced by the scattering of
uncollimated alpha particles from the gold-lined interior of
the instrument. The cosmic-ray produced background in the alpha
detectors was very low.
In the second stage of operation of the experiment (3).
data were recorded while the instrument was suspended about 56 cm
above the lunar surface. In this position the alpha detectors
should hake measured any long-lived (e.g. po210^ T^ 5.31 MeV)
alpha activity on approximately 7000 cm  of lunar surface under-
neath the instrument. They should also have measured the rate of
the deposition of active products of Rn 222 through the amounts of
the short-lived progeny, i.e. Po 218 (6.00 MeV) and Po 214 (7.69
MeV). Because of shadowing by the spacecraft and by the over-
hanging instrument (30 cm diameter), the observed rate of
deposition is estimated to be only about 0.74 of that to be
expected on an open lunar surface. The proton detectors of the
Instrument should have been sensitive only to the 7.69 MeV
(PO 214 ) alpha particles because of the gold absorbers over
the detectors. The degraded alpha spectrum in this mode, how-
Ir
3
ever, is expected to be too smeared to be identifil':1ble.
In this stage of operation, the Surveyor V experiment
at Mare Tranquillitatis, gave moderately convincing evidence for
alpha particles of energy 5.31 and 6.00 MeV (see figure 1). The
presence of the former indicates that at least ,part of the sur-
face near the spacecraft had not been disturbed by the landing.
In addition to the evidence in the alpha spectrum, the over-
flow channel of the pulse-height analyzer, which recorded events
of energy greater than 7.3 MeV and therefore should have record-
ed the 7.69 MeV alpha particles also, showed an excess number
of events when the instrument was suspended over the lunar sur-
face as compared with that observed after the instrument was
lowered.
After the instrument was placed on the lunar surface,
any Rn222 emitted from the moon into the instrument cavity could
be expected (on a 3.8 day time scale) to escape and so the short-
lived daughters to disappear. On the Surveyor V mission there
was the expected decrease in the number of events in the over-
flow channel in thAs stage of operation, and also no evidence
for the 6.00 MeV alpha group, nor for the 5.31 MeV Po 210 alpha
particles. The latter disappeared presumably because either
the particular 80 cm  being examined by the instrument on the
lunar surface had been disturbed during the landing of the Sur-
veyor (television pictures of reference (6) show that, upon
^.	 landing, the footpads of the spacecraft ejected loose material
^:	 which cascaded down the 200 slope of the small crater in which
01
}
4
the Surveyor came to rest), or that the process of deploying
the instrument onto the surface disturbed it enough to bury
the Po 210 deposit in the small area being examined.
The three items of information obtained on the Sur-
veyor V mission about the equilibrium alpha activity of Rr;222
daughters on the unshadowed lunar surface are:
Po210: (3.3
	 1.1) x 10-3 dis sec -1 cm-2 ster-1
Po 214 : (1.5 t 1.1) x 10 -3 dis sec -1 cm-2 ster-1
P0218 : (1.8 f 1.4) x 10-3 dis see -' cm-2 ster-1
where the errors quoted here and elsewhere in this paper are
statistical at the la-level.
Although the individual values are only marginally sig-
nificant .,they are consistent with equilibrium within their res-
pective errors. The average activity at equilibrium of each of
the Rn222 daughters at Mare Tranquillitatis is calculated to be
( 2.3 f 0.7) x 10-3 dis sec-1 cm-2 cter-1 . On the assumption of
isotropic emissicAn, this is equivalent to a total alpha activity
on the lunar surface due to Rn222 progeny of 0.087 ± 0.026 dis
sec
-1
 cm-2.
In the case of the thoron (Rn220) deposit, the 6.78 MeV
alr/ha particles of Po 216 fall in a region of very low background
of the instrument, above the Es 254 peak. The other two possible
alpha groups fall in regions of the spectrum where the back-
ground was relatively high. The one event observed in the 192
min of measurement with the instrument suspended, at about the
right energy for Po216, with no events in the 4 channels below
1
r
5
or 6 channels above, is consistent with an activity of a Rn220
deposit about ten percent of the activity of the Rn 222 deposit.
With the instrument on the lunar surface, the Rn220.9
with its 54.5 see half life, is much less likely to escape from
f
e,the instrument cavity before decayiii than is the X222. The
resulting active deposit should be spread more or less uniformly
over the inside of the instrument. The 3506 min of measurement
on the lunar surface at Mare Tranquillitatis yielded an excess
in the region of 6.78 MeV of 1.7 f 1.0 events per 10 3
 min.
The evidence for a Rn220 deposit is thus less conclusive, since
it is based on only one alpha group. This data would corres-
pond to an emission rate of (8 f 5) x 10 -3
 Rn220 atoms sec-1
cm-2 , to be compared with the Rn222 emission rate calculated
from the data above of (58 f 17) x 10 -3
 atoms sec -1 cm-2.
On the basis of a Th/U ratio of 3, as observed on
	
ti
the returned Apollo 11 samples (7) and the assumption that
the two radon isotopes have the same probability of escaping
their matrices, simple diffusion theory indicates a ratio of
emissivity of Rn 222 to Rn220 of 75 to 1. Three possible ex-
planations for the lower observed ratio of about 7 to 1 are:
1. If the emissivity of radon in Mare Tranquillitatis is lar-
ger than in surrounding areas ol" the moon, the Rn222 deposit
will be lowered by the escape of the noble gas from the region
before decaying, with no compensating influx. Rn 220 , with its
shorter half-life, will decay much closer to its point of emis-
sion. 2. The effective diffusion constant in the lunar ma-
 
G^
ar
ter al may be smaller for Rn222 than for i1n' due either to
Wlocation of the parent uranium and thorium in different min-
era.ls or to the lowov oll festive temper ..tti1,,,,,-.' of the
	 (::'
lunar material from which the Rn 222 diffui.,os . `''^. Because of
its longer residence time, Rn222 may be removed preferentially
from the lunar "atmosphere", for example, by the solar wind,
before decaying.
r
The absolute amount of Rn
	 deposit observed at
Mare Tranquilltatis is a factor of seven lower than the
upper limits deduced by Xeh and Van Allen ( 2) for an average
for the moon. It is a factor of 25 lower than the value
calculated from diffusion theory using a concentration of
uranium of 0.5 ppm (7), a density of 3.0 gm cm -3 and an
effective diffusion constant of D = 10 -2 cm2 sec -1 . Al-
though this value of the diffusion constant is in the range
used in discussions of Rn 222 emission on the earth (8), its
applicability to the vacuum conditions on the moon is quest-
ionable. The absolute value of the Rn 222 deposit, moreover,
will depend on the variation in uranium content on the moon
on a scale of approximately 1000 km.
Data from Surveyor VI (Sinus Medii) and Surveyor
Vi2 (rim of highland crater Tycho) give no evidence of alpha
radioactive deposits. For these sites a limit can be set of
less than half of the p©210 activity observed at Mare Tran-
quillitatis, and less than one-third the amount of po218.
Thus, the concentration of uranium and thorium at these
two sites must be lower than in Mare Tranquillitatis, or
r
r^
the effective diffusion constant for radon isotopes must be
much sower.
The presence of a distinguishable Po 210 alpha
group., with an intensity comparable to those from Po lk
1	 and Po 218j in the data from the suspended-instrument-phase
of the Surveyor V operations, provides evidence on the time
scale of turnover or "gardening" effects on the lunar sur-
face. Po 210 has a 22 yr Pb 210 g-3rdparQnt=. Burial of t1kt::,
P0	 into as much as 1 micron of material would have smeared
out the alpha energy over 8 channels of figure 1. The inten-
sity of P0 210 alpha particles in the "peak" is, however,
comparable to that expected from the rate of deposition.
Thus, even the present crude data indicate a rate of dis-
turbance of the topmost lunar surface of less than one micron
in tei-as of years.
The pei °'^ inence of this limit to various possible
nmechanioms of disturbing the lunar surface differs with the
mechanism. Thus it can say nothing about the average rats,
due to processes of low frequency (less than one in tens of
	 a
years) but high efficiency, such as comets or moderately
large meteorites. On the other hand it should be applicable
to the rate of relatively continuous processes such as hop-
ping or turnover of surface particles, and to the rate of
erosion of the surface by micrometeorites, radiation or so-
lar wind. Experiments designed to measure this effect more
quantitatively by the same technique appear very promising.
10
t
.
8
FEFERENCES AND NOTES
1. H. W. Kraner, G. L. Schroeder, G. Davidson,. J. W. Carpen-
ter., Science 152, 123 ,E (1966) .
2. R. S. Yeh and J. A. Van Allen, Science 166, 37 0 (1969) .
3. A. L. Turkevich,,E. J. Franzgrote and J. H. Patterson,
Science 1^2, 277 (1969 );, Science 1 .58, 635 (1967);
A. L. Turkevich, J Y H. Patterson, E. J. Franzgrote,
American Scientist .96, 312 ( 1968).
4. A. L. Turkevich, J. H. 4 Patterson and E. J. Franzgrote,
Science 160`, 1108 (1968).
5. A. L. Tlarkevich, E. J. Franzgrote, and J. H. Patters on,
Science 162, 117 (1968).
6. E. M. Shoemaker, R. M. Batson, H. E. Holt, E. C. Morris,
J. J. Rennilson, and E. A. Whitaker, Surveyor V. Mission
Report, Part II: Science Results Tr-32-1246, Jet Pro-
pulsion Laboratory, Pasadena California, 7 (1967).
7. The Lunar Sample Preliminary Examination T ^am, Science
lam, 1211 (1969).
8. H. W. Kraner, G. L. Schroeder and R. D. Evans, in "The
Natural Radiation Environment" Chapter 10,, . 191, Univ-
ersity of Chicago Press, (1960.
9. Work at the University of Chicago aided by NASA Grant
NGR-14-041-128; at the Jet Propulsion Laboratory, by
NASA contract NAS-7-1000; and ' at the Argonne National
Laboratory by the AEC. Discussions with Professors N.
Ougarman and E. Anders of the University of Chicago are
appreciated.
1t
C
9
Figure Caption
Figure 1. Top: Data Recorded in the Alpha Mode by the Alt>ha
Scattering Instrument While Suspended Over the Lunar S urface
in Mare Tranguillitatis. The abscissae are the channel numbers
(energy) of the pulse height analyzer. The ordinates are events
per channel per 10 3 min. Statistical (1v') errors are indicated.
The peak at around channel 110 is due to Es 2,54 (Tai= 6 . ^i 4 MeV )
used as are energy marker on the detectors. The average efficien-
cy of *she alpha detectors for registering ,particles originating
on a sample at nominal distance was 4.1 x 10-.
Bottom: The Data of the Top Fart of the Figure After
Subtracting the ES 254 Contribution as Measured on Earth Before
Launch. The expected locatJ,ons of Fo210 and Po 218 alpha parti-
cles are indicated. The horizontal line at the left of the
figure indicates the level of scattering of uncollimated alpha
particles from the gold-lined interior of the instrument.
0
•
 .
,
.
.
"
':
t'"
 
;-
r 
.
.
 
"~
",
,,
 :.
,.~
,,!
,".
J:-
"
 
'. 
,'
''
' 
.
 
•
 .~
{t
 •
 
"
 
"
 
,/; 
60
0.
 
i 
50
0 
40
0 
c: 
30
0 
E ~ 
20
0 
o
 
"
 
-
.
 
Su
 rv
ey
or
 "
Il. 
Al
ph
a 
M
od
e 
B
ac
kg
ro
un
d 
Ph
as
'! 
o
n
 M
oo
n 
19
2.
3m
in
. 
t 
t 
+t 
Q)
 
10
0 
c:
 
I 
c 
+
 
~ 
0 
++
+ 
.
.
.
 +
.+
 
t. 
+
 
I 
~ 
! 
I. 
H
t
 +
+
+
t 
t 
~ 
I 
t+
.+
+ 
t 
+
- c Q
) >
 
lJ.J
 
80
 
40
 
01
 
t 
-
2
0
 
I 
! 
T 
.
 
T 
I 
l
I
t
 
I 
*llr
+lf~
lr~t
i~--
----
----
-~ 
•
 
I 
I 
•
 
I 
I 
1+
 
-
I 
•
 
t 
70
 
80
 
•
 
21
0 
PO
 
P0
21
 
5.
31
 M
eV
 
6.
00
 M
eV
 
90
 
10
0 
Ch
an
ne
l 
Nu
m
be
r 
Fi
 g.
1 
11
0 
12
0 


Alpha radioactivity of the lunar surface at the Surveyor 5, 6, and 7 landing sites

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server