Activation analysis to identify materials for use as catcher for micrometeoroid

Cooper, T.

Schmitt, R. A.

English

NASA Technical Reports Server

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
Manned Space Center 
Activation Analysis for Selected Elements in  Micrometeorites 
and Hypervelocity Projectiles 
Annual Progress Report: July 1 ,  1969 - July 1 ,  1970 
"Investigation of suitable catcher materials for 
hypervelocity projectiles, and the analysis  of 
Na, Mn, W ,  Fe,  Co, Sc ,  Zn, and Cr i n  simu- 
lated samples. '' 
By Roman A .  S chmitt , Principal Investigator 
Department of Chemistry 
Oregon State  University 
Corvallis , Oregon 97 33 1 
and 
T hurman Cooper, ass i s tan t  
Prepared under Grant NGL 38-002-032 
https://ntrs.nasa.gov/search.jsp?R=19710003724 2020-03-12T00:43:08+00:00Z
1.n an  attempt t o  find a suitable catcher for micrometeorites, several  
l ikely candidates have been investigated. Of these  "99.99999% pure" KC1 
crysta ls  and ultra high purity s i l icon appear to be the  most advantageous 
materials for such  a purpose. 
CONTENTS 
. . . . . . . . . . . . . . . . . . . . . .  Introduction 1 
. . . . . . . . .  Experimental: Catcher Materials Investigated 2 
. . . . . . . . . . . . . . . . . . .  1 . Aluminum 2 
. . . . . . . . . . . . . . . . . .  2 . Polyethylene 2 
3 . B e r y l l i u m  . . . . . . . . . . . . . .  3 
. . . . . . . . . . . . . . . . . . .  4 . Carbon .  3 
. . . . . . . . . . . . . .  6 . Silicon . .  i 0  4
. . . . . . . . . . . . . . . . . .  Summary and  Conclusion 5 
. . . . . . . . . . . . . . . . . . . . . . . . .  Table I1 7 
INTRODUCTION 
The possibility of many theories of origin make the composition of 
micrometeorites of great interest  t o  the  geochemist and cosmochemist. 
One possibility ex is t s  that  dust  may have kxisted in ga lac t ic  space  
prior t o  and concomitant with the  formation of our solar  system,  resulting 
from expulsion of g a s e s  into space  by s ta rs  of unstable composition such  
a s  novas.  This implies that  a t  l e a s t  some micrometeorites might be the  
most primitive samples of solid matter subject  t o  analysis  in  our solar  
system,  perhaps predating even the sun 's  formation. Such a n  analyt ical  
finding would present strong evidence that  the  formation of our planetary 
system and the sun  itself was due t o  a condensation process whereby 
g a s e s  and dust  particles gravitated into dense  matter in a central  region 
of ga lac t ic  space  and thereby created our solar system. 
Secondly, some micrometeorites must surely be the resul t  of a 
grinding process from coll isions in space  of large meteorites. Therefore, 
it would be of interest  t o  correlate the  composition of micrmeteorites 
with the meteorites which have been recovered on earth. 
Third, the  origin of some solar dus t  might be from expulsion of mat- 
ter  from a planet or moon by volcanic act ivi ty  or by coll ision of large 
meteorites such  a s  those  thought responsible for most craters on t h e  moon. 
Thus, if  t he se  t iny dust  particles could be collected and analyzed, 
evidence pro or  con could be presented for each  of the  differing theories 
of origin. 
Although there a r e  incredibly large numbers of micrometeorites in 
space ,  the flux density is very low due to  the  immense volume they occupy. 
A further complication in obtaining enough material for analysis  is the  rapid 
decrease  in particle density with increasing mass of the  micrometeorite, 
such  that  a square meter s ized  catcher orbited for 126 years has  a 65% 
probability of capturing a particle larger than 100 micrograms, 
When dealing with such small quanti t ies of matter, two requirements 
must be met -- a sufficient analytical  tool t o  detect  elements a t  the  nano- 
gram leve l ,  and a material serving a s  a catcher free of the  elements sought 
after, High flux activation ana lys i s  is the  proper tool ,  and our investiga- 
t ions  a r e  aimed a t  finding a suitable catcher, "%us, we are determining the  
contamination leve ls  of a n u m b s  of elemean;ka s f  interest  Lo u s  in  the most  
convenient catchers  available.  
ALUMINUM: 
This w a s  t h e  f irst  ca tcher  material  proposed and s tudied.  From t h e  
ana ly t i ca l  r e s u l t s  of ac t ivat ing aluminum fo i l s ,  the  conclus ion w a s  reached  
tha t  t h e  production of 2 7 ~ g  and 2 4 ~ a ' b y  (n, p) a n d  (n,  a) reac t ions ,  r e s p e c -  
tively, from 2 7 ~ 1  completely ruined a n y  hope of determining t h e s e  e lements  
i n  t h e  sample  i t s e l f ,  Thus ,  further inves t igat ion of aluminum was aban- 
doned.  
POLYETHYLENE: 
This  material h a s  t h e  advantage  of being chemically const i tu ted  of 
only  carbon a n d  hydrogen, both e lements  which produce negligible ac t iv i ty  
upon irradiat ion wi th  neutrons.  
The e lements  Mn, Na a n d  W w e r e  analyzed m polyethylene samples  
tha t  had been  bombarded by hypervelocity par t ic les  without diff iculty in  t h e  
OSU TRIGA reactor  a t  a flux of 7 x 10" neutrons/crnz sec. The a n a l y s i s  of 
i ron by t h e  comparator technique using iron wire s tandards  w a s  performed 
i n  a high f lux reactor  (the complete report is contained i n  t h e  third quarterly 
report  for t h e  period January 1 t o  March 3 1 ,  197 0). The iron content  w a s  
found t o  vary from 1 6  micrograms t o  less t h a n  o n e  microgram depending o n  
whether t h e  project i le  w a s  fayal i te  or o l iv ine .  The sens i t iv i ty  for scan-  
dium w a s  less than a nanogram in  t h i s  high f lux irradiation whi le  chromium 
a n d  cobal t  sens i t iv i t i e s  were  less t h a n  1 0  nanograms. 
Although t h e  high flux irradiat ion showed grea t  promise, t h e  polyethy- 
l e n e  chemical ly  decomposes  i n  t h e  high neutron f lux with subsequent  re-  
l e a s e  of H z .  The second  progress report for t h e  period October 1 - Decem- 
ber 31,  1969 presents  a ca lcula t ion which indicates  tha t  one  gram of p las -  
tic would completely decompose in to  Hz a n d  C in  470 minutes a t  1014 neu- 
trons/cmz sec (i. e. complete decomposit ion for i rradiat ion of a micrometeo- 
r i te-containing sample) ,  
In a simulated s tudy of micrometeori tes,  three  samples  e a c h  of poly- 
e thylene  containing g l a s s ,  o l iv ine ,  a n d  fayal i te  which had been impacted 
in to  the  p l a s t i c  were analyzed by ac t ivat ion a t  1013/cm2 sec for 6 hours .  
The amount of iron i n  e a c h  sample  ( save  one)  w a s  fairly e a s i l y  determined 
by counting on a 3 0  cc Ge(Li) de tec to r ,  even  a t t h i s  low flux by t h e  com- 
parator technique;  a n d  scandium, chromium, coba1"cnd zinc were  deter -  
mined a s  upper l imits  by taking three  t imes  t h e  s tandard  devia t ion  of t h e  
a r e a  a t  t h e  energy a t  which  t h e  photopeak for t h e  part icular  e lement  occurred 
\ (3 a calcula t ion) .  Knowing t h e  maximum ac t iv i ty  d u e  t o  t h e  e lement ,  u s e  
. of known c r o s s  s e c t i o n s ,  i so top ic  f rac t ions ,  e t c . ,  a l lowed ca lcu la t ion  of 
tne  maximum amount of t h e  e lement  i n  ques t ion  present .  I t  is apparent  from 
Ihe resu l t s  of ca lcu la t ions  performed in  t h e  a b o v e  manner,  exhibi ted  i n  T a b l e  
I ,  t h a t  t h e  s e n s  i t ivi ty of t h e  method is very h igh,  
BERYLLIUM: 
Many low Z e lements  h a v e  t h e  following nuc lea r  cha rac te r i s t i c s  making 
them i d e a l  ca tche r  matrices:  
1, Short half life from (n,  7) r eac t ions .  
2. Low c r o s s  s e c t i o n s  for f a s t  neutron r e a c t i o n s ,  and  shor t  half 
l i v e s  of products .  
3 .  Stab le  so l id  s t a t e s  which d o  not r e l e a s e  g a s e s  upon irradiat ion.  
Beryllium metal ,  obta ined from U.S . Bureau of M i n e s ,  Albany, Oregon,  
t h u s  appeared  ideal ly  su i t ed .  The pures t  sample  obta inable  w a s  however ,  
so g r o s s l y  contaminated tha t  a "forest"  of gamma l i n e s  and  a n  in tense  brem- 
strahlung ac t iv i tv  w a s  t h e  r e s u l t  of counting o n  a Ge(Li) de tec tor .  Due to t h e  
tox ic  nature of beryllium s a l t s  n o  effort w a s  made to further inves t iga te  baryl- 
l ium compounds.  
Inquir ies  w e r e  made of a l l  major carbon suppl iers  to find t h e  pures t  
carbon ava i l ab le .  Again, a s  wi th  beryllium meta l ,  "pure" carbon proved 
qui te  impure for our  purposes ,  a n d  no  purpose would have  been se rved  i n  
identifying t h e  gamma li 'nes a n d  quantizing t h e  r e s u l t s ,  
KC1 CRYSTALS: 
The phys ica l  chemis t ry  department has  kindly provided us  wi th  KC1 
c r y s t a l s  which  a r e  99.99999% pure,  Activation of s i x  samples  of t h e  pure 
c r y s t a l s  was performed in  t h e  high f l u  reac"sr at Missour i  for t w o  weeks 
a-an avemge f l u  of 7. g? xu13 neiltrons/cm% see, "I;e samples  were actt- 
vated in pure aluminum foil along with an  iron wire standard and then  encap- 
sul ized in a standard aluminum container which was welded s h u b o  that no 
leakage of liquid under pressure was possible .  After activation the  samples 
were cooled for three weeks and shipped back for ana lys i s .  
It was immediately apparent from the spectrum obtained with a 30 cc 
Ge(Li) detector that  bremstrahlung activity from a high energy beta emitter 
was  s o  large a s  t o  completely eliminate any hope of instrumental ana lys i s .  
A beta absorption curve identified the  extremely high activity a s  due t o  3 2 ~  
and 3 5 ~ ,  the former produced from 3 5 ~ 1  (n, a), and the la t ter  by 3 5 ~ 1  (n, p). 
An attempt t o  separate  the interfering elements by a n  iron hydroxide 
co-precipitation of the  desired elements, while the 3 2 ~  and 3 5 ~  remain in  
solution,  failed,  s ince  the  3 2 ~  a l s o  precipitated along with the iron. We 
then attempted t o  remove the 35s and 3 2 ~  act ivi t ies  by ion exchange tech-  
niques.  
After some t r ia l  and error, it was found that  the 3 2 ~  activity could be  
removed by passing a neutral solution of the KC1 crystal  through a column 
charged with Dowex 1 x 8 resin.  Experiments with standard solutions veri- 
fied that  a l l  cations of interest  passed eas i ly  through the column while the  
3 2 ~  (presumably a s  ~ 0 g ) r e m a i n e d  on the resin.  However, the  3 5 ~  could 
be removed only by passing the  element from the  Dowex column through a 
column loaded with Ag 50 W-4X cation exchange res in ,  which retains t h e  
cations of interest  while passing through the  3 5 ~ .  The cations a re  then 
recovered by elution with a strong HC1 solution. 
The resu l t s  of ana lyses  of two crysta ls  a r e  presented in Table 11. 
These resul ts  verify that  t hese  crysta ls ,  especial ly  KC1, a r e  of excep- 
t ional purity with sensi t ivi t ies  for the  elements reported in the  picogram 
t o  nanogram range. Apparently iron is much higher in NaCl than KC1. One 
may note t he  high Rb contamination for KCl. 
SILICON: 
Samples of pure si l icon were obtained from three major suppliers 
and a re  being investigated a t  present for contamination levels .  Although 
the work i s  still in its infancy and will be  covered more thoroughly in the  
next project report; t he  init ial  activations a r e  encouraging with very Bow 
contamination leve ls  . 
S UMMARU AND GONGLmLON: 
It  appears that  an  excellent candidate for a catcher  material is  t h e  
phenomenally pure KC1 "home grown" here a t  OS U. However, being un - 
sat isf ied with tedious and dangerous radiochemical procedure necessary 
for separation of the high levels  of 3 2 ~  and 35s act ivi t ies  arising from 
fas t  neutron reactions on 3 5 ~ 1 ,  we a re  continuing the search for the  ideal  
catcher.  Polyethylene is suitable only for micrometeorite ana lys i s  in t he  
microgram range due t o  t he  problems with H2 pressure buildup during long 
irradiations a t  high flux. We have hopes tha t  zone refined Silicon is t h e  
answer  for analysis  of micrometeorites in the  nanogram range, desp i te  the  
fac t  that  three major elements,  Si, Al and Mg a r e  undeterminable. 
TABLE 1 
Amounts of Selected Elements Imbedded in Poiyethyiene 
Catchers a s  a Result of Hyper-Vblocity Empact, Micrograms 
NASA 
Material Number Fe Sc Cr Co Zn 
Glass 
Olivine #7 9 & 1  0.0003 0.02 0.004 0.1 
B-6-4 *1.74).9 0.0002 0.02 0.004 0.1 
B-13-1,2 0.7 fg.2 0.0003 0.02 0.004 0.1 
Fayalite #6 12  k1 
B-8-2,3 . 4hl 
B-12-1 . 17kI 
Masses listed are from 3 a calculations except for Fe values. 
All values are in micrograms 
TABLE I1 
- 
Crystal  Thermal 
TY pe Neutron Flux Fe Rb S c  Cr Co Zn Sr 
KC1 
' NaCl 
* determined by comparator technique. 
a l l  other determinations by 3 U,calculations, and thus is a n  upper limit. 
all values reported a s  ppb. 


Activation analysis for selected elements in micrometeorites and hypervelocity projectiles Annual progress report, 1 Jul. 1969 - 1 Jul. 1970

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