Medical and biological semiconductor detectors for manned space flight mission

Ziemba, F. P.

English

NASA Technical Reports Server

! * ,  +--A 4 
8th QUARTERLY PROGRESS REPORT 
Submitted t o  
NATIONAL AERONAUTICS & SPACE ADMINISTRATION 
Manned Space Flight Center 
Houston, Texas 
SEMI CONDUCTOR DETECTORS 
SOLID STATE RADIATIONS, INC, 
2261 South Carmelina Avenue 
Lor Angelcs 64, California 
April ,  1964 
This work i e  supported by the National Aeronautics & Space Administration, 
Manned Spacecraft Center, General Reaearch Procurement Office, Houston 1, 
Texas, under Contract No, NASW-415 
PROJECT LEADER: F. P .  Ziemba 
WORK DONE BY: J .  Friedericha, J. Morose, J. Berdaner, e t  el. 
GPO PRICE $ 
CSFTI PRICE(S) $ 
-. Hard copy (HC) 
Microfiche (MF) 
i ff 653 July 65 
https://ntrs.nasa.gov/search.jsp?R=19650021320 2020-03-17T01:06:42+00:00Z
r) 
SECTION I - INTRODUCTION 
/ 
During t h e  previous quar te r , '  a p ro to type  proton dosimeter f o r  
The dosimeter cons is ted  of manned space f l i g h t  missions was developed. 
1) an 8-cubic rrun l i t h ium-dr i f t ed  s i l i c o n  nuc lear  p a r t i c l e  de t ec to r ;  
2) a low-noise, charge- renr i t ive  preampl i f ie r ;  3) a pu l se  he ight  i n t e g r a -  
t o r  employing an electrochemical  cel l  as an integrator:/ I t  was packaged 
complete wi th  aelf-contained,  rechargeable b a t t e r y  power supply i n  approx- 
imately 15 cubic jnches.  Readout was accomplished by means of a b a t t e r y -  
powered readout r e g i s t e r  providing direct readout  i n  terms of proton dose 
i n  rads .  
t h e  u n i t  was v e r i f i e d ,  u s ing  30 MeV protons from t h e  Univers i ty  of Southern 
Ca l i fo rn ia  acce le ra to r ,  which q u a l i t a t i v e l y  v e r i f i e d  the  previously c a l -  
cu la t ed  dose c a l i b r a t i o n .  
f e a s i b i l i t y  demonstration phase of t h e  t o t a l  e f f o r t  of developing a self- 
contained, miniatur ized dosimeter f o r  space environment. As a r e s u l t  of 
t he  d i f f i c u l t y  i n  a l l o c a t i o n  of funds for proceeding t o  t h e  next phase of 
t h e  program, no work w a s  performed dur ing  t h e  second month of t h i s  qua r t e r .  
Following the a v a i l a b i l i t y  of funding, t h e  program was again ac t iva t ed ,  
and work proceeded on t h e  design and f a b r i c a t i o n  of the apace dosimeter. 
h i r i n g  t h e  beginning of t h e  p re sen t  quar te r ,  a performance of 
This represents  t h e  conplet ion of t h e  breadboard 
SECTION I1 - CALIBRATION OF THE BREADBOARD MODEL 
Ca l ib ra t ion  of the breadboard system was accomplished wi th  the 
cooperat ion of the a c c e l e r a t o r  personnel of the Universi ty  of Southern 
Ca l i fo rn ia ,  who made a v a i l a b l e  t h e i r  30 MeV proton a c c e l e r a t o r  f o r  t h i s  
work. I n  order  t o  provide a la rge  a rea  and s o l i d  angle  f l u x  of protons,  
the primary beam from the acce le ra to r  was s c a t t e r e d  from a t h i n  gold t a r g e t  
and t h e  s c a t t e r e d  protons observed a t  an angle  of approximately 30 degrees 
t o  t h e  beam d i r e c t i o n .  Such an intermediate  s c a t t e r i n g  process was requi red  
t o  t ransform the  ex t r eme ly  small-area i n t e n s e  beam of protons from t h e  
machine i n t o  a d i f fuse ,  l a r g e  diameter f l u x  of pro tons  of s u f f i c i e n t l y  low 
i n t e n s i t y  t o  permit  s imula t ing  space r a d i a t i o n  e f f e c t s .  As adequate proton 
dose s tandards  were not  ava i lab le ,  t he  instrument i t se l f  was used as a 
means of measuring t h e  proton fluxJ The pu l se  output of t he  prototype 
- 2 -  
dosimeter was counted with the a i d  of a d i scr imina tor  and high-speed s c a l e r .  
Since a l l  events  above minimum ion iz ing  i n  t h e  de t ec to r  were counted, this 
provided a p r e c i s e  rneatili~eriint zf the f l 1 - 1 ~  of Frotons pass ing  through the  
de t ec to r .  The energy of the  protons was ca l cu la t ed  from the  knowledge of 
a s c a t t e r i n g  angle  and the kinematics of the S c a t t e r i n g  process .  Quite low 
count ing r a t e s  were used t o  avoid the  p o s s i b i l i t y  of pu l se  p i le -up  effects 
which could have introduced e r r o r s .  This is p a r t i c u l a r l y  aggravated because 
of t h e  r e l a t i v e l y  low duty cyc le  of the machine. 
t he  i n t e g r a t e d  dose observed was within experimental  e r r o r  of t h e  p red ic t ed  
dose on the basis of a measurement of the  flux. I t  war concluded from this 
meaeurement tha t  the calculated curve6 included i n  the reventh quarterly 
progress report should be valid for proton dore mearurement, The energy 
proton employed reprcrentr the mort c r i t i c a l  energy fo r  il do8inwtar. 
l a rger t  pulse heightr resu l t  from protons i n  t h i 8  energy range, 
I n  a series of measurements, 
The 
rgy resul t ing i n  lower ionization, end pr  
ng stopped i n  the mhielding material sum 
ng reduced pulre heightr. The calibration pointr obtr 
entered i n t o  the data reported i n  the previous report, since 
available a t  the time of t ha t  r e p o r t ' r  writing. 
t 
SECTION 111 - DESIGN OF THE MTNIArURIZED DOSIMETER 
FOR S P A a  APPLICATION 
In  order t o  make the prototype dorimeter, developed during the  pre- 
viour quarter of the contract, suitable fo r  application a8 a rpaao dorimter 
f o r  the Apollo Program, three mador modifications a re  required: 
1) 
t u r i z a t i o n  techniques; 
Reduction i n  s i z e ,  weight and power consumption through mihie-  
2) 
i o n i z i n g  p a r t i c l e s  and Compton processes  from gamma rays.  
Extension of t h e  lower energy threshold  t o  inc lude  min imum 
3) 
operation. 
Modification of the readout t o  permit completely se l f -conta ined  
The reduction of size, w e i g h t  and power consumption is t o  be accoAplished by 
adopt ing  a micro-modular configurat ion f o r  all electronic c i r c u i t r y .  
type of cons t ruc t ion  a l l  r e a i s t o r s ,  inter-connect ions and small capac i to r s  
a r e  depos i ted  on a ceramic subs t ra te ,  semiconductors and l a r g e  capac i to r s  
be ing  a t t ached  l a t e r  a s  d i s c r e t e  components. 
I n  this 
A conservat ive estimate i n d i -  
- 3 -  
cates t h a t  t h e  e n t i r e  e l e c t r o n i c  c i r c u i t r y  can be reduced t o  a volume of 
considerably lese than 1 cubic  inch. The problem of power consumption 
is belng arraciceri L I K W U & ~ I  -1 L' -- oyr --*-&---+4 LGleuLAb n n v n m < n m + i  _..-..-___ _ _  nn _ _ _  nf the circuits involved. 
Every e f f o r t  is  made t o  opera te  t r a n s i s t o r s  i n  t h e i r  cut-off  o r  nea r ly  
cut-off mode, except i n  t h e  presence of a pu lse .  I n  order  t o  maintain 
reasonable  t r a n s i s t o r  c h a r a c t e r i s t i c s ,  s tanding  c u r r e n t s  of from 20-30 
microamperes a r e  requi red  f o r  each s tage .  For even t h e  most e l a b o r a t e  
instrument ,  no more than 20 such s t ages  should be required.  This, then, 
e e t s  a m i n i m  power requirement of approximately 0.5 mill iamperes f o r  
the ent i rv  ryrtem. 
..-. a rea8on8ble, dynamic range of outputr from the amplifier. Since thr8rhold8 
of approxirartely 0.5 vo l t r  a r e  involvmd i n  the pulre uralyrie pr00.00, a 
l i r h  a requiluament for approximately 6 vol t r  on the p 
the  llRsnilnrm of power required would be i n  the nei 
millimlqpercr, or approxLmntely 3 milliwatts. Thio p 
determiner the phyricrl afze and weight of the battery 
8 given number of hour8 of operation. For example, if a 
nickel cadmium type battery were ured, SO0 haurr operation 
ing, would be provided by approximately 2 cubic i 
.I45 lbr.;  1000 how0 of operation without recharging, w o u l d  be provided 
by approximte 
w h i l e  posri bly ted t o  u8e in spacecraft, could provide 5#800 h u  of
operation with I voluns of 2.5 cubic incher and a weight of . 3  lbu. 
t i ona l  dry cella gr $a c service l i fe  of approximately SO0 haurr in approx- 
imate ly  3 cubic  inches  and .14 lbs .  Considerably b e t t e r  factorr can be 
expected from improved cell  types now ava i l ab le .  
c a r r i e d  on t o  determine the  f e a s i b i l i t y  of t h e  use  of some of t h e s e  advanced 
cell  types.  The dynamic range of t h e  prototype dosimeter was i n t e n t i o n a l l y  
l i m i t e d  t o  inc lude  only those cont r ibu t ions  which o r ig ina t ed  from f a s t  pro- 
tons .  
The voltage requfrement i r  bared on the necesrity fo r  
c incher of battwy weighing -395 lbr.  Mercury cello, 
Conven- 
Inves t iga t ion  i s  be ing  
This energy threehold  was e s t a b l i s h e d  by cons ider ing  the  minimm s i z e  
pula@ W h -  c a d  b. ubtund SF- b J U  La*--+ J U y a D w I  - o r - "  o n m - m i  =------ npntnn under -___. conridera- =--- 
t iono  
)Hf@tr, the p u l ~  height from aueh Mgh energy protom I s  about 1-l& thm8 
minimum ion iz ing .  
Since it i r  the high energy protanr that produce th. rechad'pulre 
For t h i s  reason, a t h re sho ld  set s l i g h t l y  greater than 
, I  
t - 4 -  
minimum i o n i z i n g  w c u l d  e l imina te  cont r ibu t ions  from minimm i o n i z i n g  
p a r t i c l e s  and from Compton and pho toe lec t r i c  processes  from a l l  but t h e  
most e n e r g e t i c  g a m  rays.  I n  a 2mn de tec to r  this threshold  is approx- 
imately 1 MeV. 
personnel  of t h e  Manned Spacecraft  Center, it was deemed d e e i r a b l e  t o  
i n t e g r a t e  dose from a s  wide a range of r a d i a t i o n  types  as poss ib le .  
p r inc ip l e ,  it would be des i rab le ,  then, t o  i n t e g r a t e  pu l se  he igh t s  all t h e  
way down t o  0. 
f i n i t e  no ise  output of t he  detector .  This noise,  i n  t h e  most quiet detec- 
t o r  preampl i f ie r  combination which can be considered, is  of t h e  order  of 
15 keV 0. Thus, t o  avoid i n t e g r a t i n g  noise  pulses ,  i t  would be impor- 
t a n t  t o  set a th reshold  a t  l e a s t  twice o r  t h r e e  times t h i s  value,  i n  order  
t h a t  occasional,  large-noise  pulses  w i l l  no t  cont r ibu te .  This would i n d i -  
cate a th reshold  of the  order  of SO keV. While t h e  in t roduc t ion  of such 
a threshold  does introduce some e r r o r s  i n  i n t e g r a t i n g  dose from g a m  rays,  
t h e  e r r o r  i s  pr imar i ly  introduced f o r  extremely s o f t  X-rays, and f o r  t h i s  
reason i s  probably of less rad iobio logica l  s ign i f i cance  than might be a t  
f irst  assumed. If the  threshold,  then, i s  t o  be s e t  a t  50 keV and pulses  
a r e  t o  be accepted from t h e  most heavi ly  ionized proton t o  be encountered, 
i . e .  one which i s  completely stopped i n  the  de t ec to r ,  t he  i n t e g r a t o r  sys-  
t e m  must be l i n e a r  t o  g r e a t e r  t h a n  20 MeV. This  r e q u i r e s  a dynamic range 
of almost 4 orders  of magnitude i n  pulse  height  acceptance. If t h e  lower 
threshold  i s  of the  order  of 0 .5  v o l t s  as set  by the  energy gap of a s i l i -  
con diode, then a l i n e a r  response would be required i n  excess of 1000 volts. 
This is c l e a r l y  n e i t h e r  p r a c t i c a l  nor i n t e r e s t i n g  i n  a battery-powered, 
compact device. I n  i t s  p lace  a technique of  using separa te  channels f o r  
var ious  energy events  will be employed. h k i l e  t h i s  in t roduces  some com- 
I n  diacusaing t h e  dosimeter problem wi th  t h e  t e c h n i c a l  
I n  
This, as a matter of  p rac t i ce ,  cannot be done due t o  t h e  
p l i c a t i o n  i l l t o  t h e  i i i te#rStor,  i t  ri3:SXFS CGRsid€rably t h e  &y'ZaKiiC range  
respznse recpired. 3:: any i ~ d i v i d e l  c e ~ m e n t ,  2nd f e r  this r e a g n n  lemd.; 
i t s e l f  much more r ead i ly  t o  the  microminiaturized d e s i q  undertaken. Essen- 
t i a l l y ,  t h ree  channels a r e  provided, each having a dynamic range of approx- 
imately 1 O : l :  t he  most s e n s i t i v e  channel having a threshold  a t  50 keV, and 
t h e  s a t u r a t i o n  l e v e l  of 500 keV; the  second - a th reshold  of 500 keV, and a 
Sa tu ra t ion  l e v e l  of 5 MeV; and the t h i r d  - a threshold o f  5 MeV, and a 
s a t u r a t i o n  level  of  50 M e V .  These three channels a r e  summed i n t o  the  i n t e -  
gra t o r  through capac i to r s  wh%e ma\gnitude of capaci tance i s  proportioned t o  
e - 5 -  
t ake  i n t o  account t h e  varying s e n s i t i v i t y ,  i . e .  t he  low energy channel i s  
s u m d  through a small  capac i tor  and the  high energy channel through a l a r g e r  
capac i to r .  Thus, l i n e a r i t y  i s  preserved i n  the  f i n a l  i n t e g r a t e d  ouipui, 
even though the  g r e a t e s t  dynamic ranges which must be accomnodated by any 
given channel, i s  only 1 0 : l o  
Self-contained Readout 
I n  order  t o  make the  instrument useful without t h e  necess i ty  f o r  
connection t o  ex te rna l  equipment, i t  was deemed desirable by personnel of the 
Manned Spacecraf t  Center t o  use a readout means which could be incorporated 
i n  t h e  dosimeter package i tself .  
cell is e s s e n t i a l l y  a t i m e  required f o r  backplating, var ious  ti& 
have been co 
Since the  readout of t h e  electrochemical  
red. 
tch movement, which is e s e e n t i a l l y  a tuning-fo 
mally powered by a small cell cmtaine 
eans of non-destructively i n t e g r a t i n g  t 
ng the hands of the  watch i n  response t o  tho electrical 
readout signal. As the  space required by such a watch movement is under 
1/10 cubic  inch, and t h e  r e l i a b i l i t y  and s u i t a b i l i t y  far space environment 
f o r  t h e s e  movements has been demonstrated previously,  t h i s  would seem t o  
c o n o t i t u t e  a very p r a c t i c a l  reedout system. 
i n  which t h e  readout proceas can be used. 
cell  is manually read out a t  the time when t h e  information is desired,  by 
depressing a but ton and observing t h e  advance of the  watch movement. If a 
more autometic procedure is required, it would be necessary t o  inc lude  a 
timer which would switch the  system t o  readout, say every f i v e  minutes or  
so, and a c c u m l a t e  t h e  dose automatical ly .  The disadvantage of this l a t t e r  
method is t h e  l ack  of f l e x i b i l i t y  f o r  the  as t ronaut  observing very r ap id  
changes i n  accumulated dose. 
t i a t e  readout, the s t o r e d  information would not  be ava i l ab le .  A bet ter  
a l t e r n a t i v e  would c o n s i s t  of using an E c e l l  wi th  very l imi t ed  amount of 
p l a t a b l e  ma te r i a l  when t he  t o t a l  amount of p l a t a b l e  mater ia l ,  which wmld 
correspond, f o r  example, t o  1/10 of a rad, were p l a t e d  onto the  receiving 
One of the most i n t e r e s t i n g  f o r  t N a  purp 
There a r e  e s s e n t i a l l y  two modes 
I n  t h e  first, the  electrochemicel  
On t he  o the r  hand, should he neglect t o  i n i -  
e l ec t rode .  The end p o i n t  would be de tec ted  and used t o  e i t h e r  i n i t i a t e  read- 
out o r  simply reverse  t h e  ce l l  The dose i n  u n i t s  of 1/10 rads  would then 
simply be the  number of c e l l  r eve r sa l s  which could be recorded e i t h e r  on 
.I - 6 -  
I t he  Accutron, or on another  type of register. This has t he  disadvantage 
of requi r ing  a re lay- type  of revers ing device, which may prove cumbersome 
f o r  in t roduct ion  i n t o  the package. 
a l t e r n a t i v e s  of these  t h r e e  methods, each w i l l  be c a r r i e d  t o  rne ‘urea&oard 
po in t  i n  order  t h a t  t h e  advantages and disadvantages can be adequately 
evaluated. 
I n  order  t o  provide MSC with t h e  
i SECTION I V  - PROGRAM FOR THE NEXT QUARTER 
I t  is expected t h a t  the next quarter will permit t h e  micro- 
miniaturization to  be virtually complete. 
from conponcnt ruppliers. 
be breadboarded and prerented for consideration by MSC, 
Some delays m y  be introduced 
In addition, the E cell  readout technique6 will 
! 


The development of medical and biological semiconductor detectors eighth quarterly pro- gress report

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server