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c THE I O N I Z I N G RhDIATlONS I N SUPNRSONIC ' I ' I ~ S P O I I T I : I JGIITS By T m t z Foelsche NASA Langley Research Cent.es Langley S t n t l o n , Ihmpton, V:i.
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I c I I THE I O N I Z I N G RADIATIONS I N SUPERSONIC TRANSPORT' FLIGHTS By T r u t z , Foelsche NASA Langley Research Center SUMMARY Commercial supersonic t r a n s p o r t planes :ire envisioned to ciul se a t :ilti- tude:; u p t o 23 km or 75,000 f e e t . The exposure t o crew and p'ssengers from i s estimutcd G a l a c t l c and Solar Cosmic Rays u t t h e s e i i l t i t u d c s on p 0 1 ~ routes a n d cumpared with the mxirnwn permissible dose rate:, ( M P D ) rit.cd In t h e guide l i ne6 c,T the Federal Radiation Council or t h e Interrxitiimnl Conunission for Radiation P r o t e c t i o n .
The dosc e q u i v a l e n t i n rem from G a l a c t i c Cosm-ic R:Ldiutlort ~ t t c r u i s e a t t i - T h i s iinpLIes t h a t t h e crcw t u d e s on p o l a r r o u t e s i s estimated as $2 mrem/hr.
520 percent of t h e MPD f o r r a d i a t i o n w o r k e r s ( 5 r.e~n/ye:tr), should experience a t 20 hours/week f l i g h t duty o r 10 hours i n 23 km alLit.ude, ir c v : ~ : : i v e me:t:;ure: during i n t e n s e and e n e r g e t i c solar f l a r e events Itre taken. The above dosc sate from G a l a c t i c CGSFIC Rays is consiciered as an upper I . i m i t bei:ause the t'w:t neutron flux a n d t h e buildup f a c t o r s of secondaries i n the tT2j r*uLanc tire iw::!uned conservatively 1.1 igh.
* Estimates of dose rates f o r t h e most important; i n t e n s e a n d energetic. f l r t r v e v e n t s (Solar Cosmic Radiatj on) show t h a t i n cruise ;Lit i tudes :it high l a t i tudes and i n impact zones, e.g., during t h e February ' 2 5 , L956 event, 1 to ) i remjhr m i g h t have been reached. Such doses are undesir.:ible f u r the crew mil espscictlly i'or passengers, even If t h e i r occurrence i s v e r y t'cire.
I f evasive measures a r e c a r r i e d out i n thesc cue::, such 11s descending t o 110,000 feet (12 km)? t h e r a d i a t i o n doses received by 1):L:;sengers fruai ki01:~r und G a l a c t i c Cosmic Hays appear n e g l i g i b l e (=lo p e r r r n t of 1 . k .!PI) u f 0.5 reIi\/yeaF ;it 2 polar flights/month) except for t h e e r f e c t s of ccrtairl ~.~iar:tct,cl-lstti.
b i o l o g i c a l e f f e c t i v e components of G a l a c t i c Cosmj I- Ray:; which :lpperw only i n high a l t i t u d e s , i .e. , heavy primaries arid st:trs. The:;c I.ornpontwto nnd 11 L :,I> t h e fast neutron fluxes u s t h e y occur i n t h e humun b o d y i r i t,hc pnc;:;t'rigcr p I : ~ P are not well-known i n t h e i r i n t e n s i t y except t h a t thi:, inte1l:;It.y I s very l { w ( e . g . , heavy p r i m a r i e s , -1 hlt/g/day; stars, -1000 tlLt,:;/&:/ct'Ly) m d w i 1 1 n o t ._ - More rescarc-h ; ~ p p e ; ~ m nc'ccswty on produce a s i g n i f l c a n t l o n i z a t l o n dose.
t h e i r fluxes and on t h e i r effect:; a t t h e very low dose::, w h l <-h w n i ~ l t i IT ~ ~ i ~ o m - tered a t a reasonable :imount of f l y i n g , t o determine itior~ ~*Lo:;ely Ilic. risk involved f o r e s p e c i a l l y s e n s i t i v e persons such as pregnant prtsser~ger's a i d c h i l d r e n .
, d By Trutz Foelsche Langley Research Center INTRODUCTION Supersonic commercial a i r p l a n e s as they a r e envisioned f o r t h e near f u t u r e a r e planned t o c r u i s e i n a l t i t u d e s up t o about 75,000 f e e t o r 23 lan. A t t h i s a l t i t u d e t h e r e i s only 36 g/cm2, o r 3.6 percent of the mass of' the atmosphere above t h e a i r p l a n e , which p r o t e c t s a g a i n s t space radiation:: i f their energy I s not t o o high.
This air l a y e r s u f f i c e s , for instance, t o s h i e l d a g a i n s t t h e soft b e l t r a d i a t i o n s and a u r o r a radiations t h a t reach t h e uppermost atmosphere during magnetic storms; however, it does not suffice t o p r o t e c t a g a i n s t g a l a c t i c cosmic r a y s ( G . C . R . ) which p e n e t r a t e deep i n t o t h e atmosphere, down t o sea l e v e l and below s e a l e v e l , or against e n e r g e t i c s o l a r cosmic rays, which a r e observed i n some cases a l s o a t sea l e v e l . Ir, e s t i p a t i n g t h c c f f c c t s of space r a d i a t i o n s on crew and passengers of SST airplanes one is t h e r e f o r e mainly ron- cerned with G.C.R. and e n e r g e t i c s o l a r cosmic rays ( S . C . R . ) .
It might be w e l l t o r e c a l l I n t h e beginning t h e maximum permissible expo- sure l e v e l s f o r normal peace time operations, as l i s t e d I n t h e p r o t e c t i o n g u i d e l i n e s of the I n t e r n a t i o n a l Commission f o r Radiation P r o t e c t i o n (ICRP) or of t h e Federal Radiation Council.
Table I Condition Ty-pe of exposure Dose, rem Radiation worker: Accumulated dose 5 t-lrne:: number of yenrs (a) Whole body, head and beyond :xge 18 trunk, a c t i v e blood f ormtng organs, gonads, o r l e n s of eye (b) Bone Body burden 0.1 microgram o f rndium 226 o r i t s b i o l o g i c a l equivalent Population: (a) I n d i v i d u a l Year 0.5 (whole body) (b) Average 30 years 5 (gonads) These l o w permissible doses f o r continuilq p c x e L i m opercition:;
- low i n
comparj son t o t h e stitncl:irdc for space crc'ws i n thc prcscIit piorieer period - irc t h e reason t h a t the Low l e v e l G.C.R. have t o be i.ikcn i n t o Lwnsideration :it commercial supersonic t r a n s p o r t f l i p b t s , ecpeci:~Ily .,iricc the G . C . R . p r d u c c i r i SST a l t i t u d e s a dose rate higher by orders oC in:qyli t u t l e .mcl h a v e d i f rcrcwt ch:w- w t e r i s t i c s , than t h e r a d i a t i o n s i L t se:l Icvel.
It m i g h t be emphasized, t h a t t h e dose wllues preseut,vd i n the followin[: are e s t i m a t e s with emphasis on upper l i m i t s .
Sirlcc noL 1.11 conrpoi\ents :md thcir b i o l o g i c a l e f f e c t s a r e accurately known, * L mf'ety f a c t o r i s included.
GALACTIC COSMIC RAYS W e m i g h t r e c a l l first some q u a n t i t a t i v e d a t a on G . C . R . F i g u r e 1 shows the decrease of dose rate toward the equator, o r the shieldinlt: effect of the earth's maypetic f i e l d according t o balloon measuremeiiCs of' Neher and WIrickler and coworkers. (Reference 1.) It decreases by a f a c t o r of 20 durint: s o l a r rnaxinium years (at an a l t i t u d e of about km). A second f a c t i s indlcnted by this fib:- w e , namely t h a t t h e i o n i z a t i o n I s h i a e r by a factor 2 d u r l n g s o l a r m i riimum years than during s o l a r rnaxirrlunl years i n l : - l t i t u ~ l e s .rbove =>3".
W L A H MINIMUM (NtIHEF?), I5 G / l M ' NORMA1 ' IONIf I\ I ION 20 ' A I L Aft MAXIMUM IONIZATION/UNIT TIME IO M ' (ARRITRARY UNITS) I.0RBUSI-I OF( HI AS1 5OLAH MAXIMUM IO G/CM2 0 20 40 60 00 br OMAGNE rIc LATITUDF- Figure 1.- T o t a l i o n i z a t i o n at atmospheric depth of LO g/m2 rtc ti furic- (Frcxn t i o n of geomagnetic l a t i t u d e a t solar m i n i m u m ; t i i d mxLrriwn.
ref. 1, J, R. W-inckler.)
d " W e derive from the figure, that t h e dose rate i s h i & e s t near t h e poles We and about c o n s t a n t above 50° magnetic l a t i t u d e clurlni: s o l a r a c t i v i t y ycnrs.
a r e , therefore, mainly concerned w i t h t h e r a d i a t i o n on polar r o u t e s .
the v a r i a t i o n of t h e p a r t i c l e f l u with a l t i t u d e , especi- Figure 2 shows peak at &bout 60 g/cm2 atmospheyic depth according t o t h e ally the t r a n s i t l o n famous f i r s t rocket measurements of Van A l l e n and T a t c l up t o a l t i t u d e s of 160 km.
Flgure 3 shows t h e change c f the cornpositlon of t h e G.C.R. beam penetr:lttrtG through t h e atmosphere. Down t o 36 g/cm2 from above t h e n u c l e t r component i s p r e v a l e n t (protons, h e l i o n s , heavy n u c l e i , and neutrons, which Latter are n o t included ‘In the figure). A t sea l e v e l mainly t h e h:Lrd m d Lightly i o n i z i n g corn- ponent, n:rmeLy, p-mesons, :ire l e f t . W e d e r i v e f ~ o m this f i g u r e t h a t n t SST -1ltitudcs w e have rutinly protons, a cmd neutrons, which protiuc-c i r t t i s s u e p n r t l - c l e s with a high l l n e a r e n e r a transfer (LET), o r i o n d e 1 1 s t L y t l o r i g t h c l r Lr:wk i f t h e i r energy i s i n t h e 0.5 t o LO Mev range. The r a d i a t i o n : ~ t h i g h :iltiLudes will t h e r e f o r e hnvc : L higher b i o l o g i c a l c f f e c t i v e n e s s Lhan t,hc Lightly l o n i z l ng r a d i a t j oris i n low a l t i t u d e s .
G / C M ~ 1033 270 56 12 2.9 1 . 0 0 ASCENT 0 DESCENT SINGLE- COUNTER IMPULSES ALTITUDE ABOVE SEA LEVEL, KM Fi;:~lrC: ; I . - T o t a l intcr1:;iLy lip t o vr’ry hi.[:ri ! I 1 t i t.11(1( I i i i f ’ I . U I ’ C ’ C ~ 1 1 . y ( b ‘ t - o r r l l*ef. 2, J. A.
11r1:;hic.Lded :;inKle courltcr i n rncdiurn l . c t t i i u ~ J ~ ~ : .
v‘tii A l l e n :ind H . E. ‘ C ; t t c 1 .)
G / C M 2 490 204 76 3629 12 5
I & I I I I I I 1
PARTICLES PER M2 PER SECOND PER STERADIAN (PROTONS, HELIONS, HEAVY NUCLEI) 0 20 40 60 75 80 100 120 ALTITUDE ABOVE SEA L E V E L IN 1,000 FT F i g u r e 3.- Altitude p r o f i l e of p a r t i c l e t r a n s i t i o n of cosmic ray beam ~ ‘ 1 t h e atmosphere.
(From ref. 3, H . J. S c h a e f e r . ) F Figure 4 shows the increase of t o t 3 1 ion1 zation with a l t i t u d e i n high .l.atitudes during m a x i m u m and m i n i m years according t o balloon mc:i::urements 01' Nehcr over a period of 20 years. W e derive from these nieiinurements two important of our estimates of t h e exposure at SST n l t i t u d e s , ii:lrncLy, the numbers as basis o v e r a l l ionization a t 36 g:/cmZ atmosphere depf,h (1) During s o l a r a c t t v i t y years of mrad - mrad
"15 mrad or =lo0 - - 0.625 -
day week hr Etnd ( 2 ) During solar minimum years of , . ' I , mrad mrad
e 0 - or 140 mrad 0.84 -
&Y week hr.
The number f o r a c t i v i t y years i s easy t o remenlber - 1 0 0 Inrad/week is t h e sale number as t h e MPD (maximum permissible dose r a t e ) for r a d i a t i o n workers i n rem, - r e m namely, 100 m * = 0.625 ms, o r 5 -.
week h r year I '
-
3 0
- NO CUTOFF
- REDUCED CUTOFF
IONIZATION 20 IN 1 5 - MILLIREP/24 HRS
-
IO
1' CUTOFF
5 -
c Fimire h . - Altitude p r o f i l e of the t o t a l i o r i i i n t i o n i n a year of h i - h (1337) and Low (19>4) solar a c t i v i t y . ( F n m r e f . $, H . J . Schnef'er.)
The :ibove numbers a r e r a d doses measured i n a small i o n i z a t i o n chamber. I n an SST a i r p l u n e t h e surrounding mrisses of higher Z number and Lhc t i w m body i t s e l f produce addi tionaL secondaries in nuclear c o l l i s i o n s , which i n c r e a s e the r a d dose absorbed i n t i s s u e . On t h e brisis of measurements of the i n c r e a s e of secondaries under t h i c k l a y e r s of m a t e r i a l , Van Allen suggested o . f a c t o r of 2 t o 3 f o r t h e dose increase a t these a l t i t u d e s bel-ow shields of s e v e r a l c m thicknesses of aluminum o r s t e c l . If' w e adopt t h e f'actor 2 w e would obtai.11 t h u s a s rad dose r a t e s f o r continuous exposure R t 'i",,OOO f e e t o r 280 *ad - i n s o l a r maximum o r s o l a r minimum ycars, r e s p e c t i v e l y ,
200 m a d
week week or i n r a d two t o t h r e e times t h e MPD.
For t h e crew of SST, hovever, the average dose r a t e remains s u b s t a n t i a l l y a t these a l t i t u d e s below t h e MPD f o r t h e i r professional l i f e , because they A t only 1/16.8 of t h e t i m e (10 hours/week f l i g h t time a t '(5,000-f't a l t i t u d e ) .
80 hours/month f l i g h t duty, a8 i s usual today, about 40 hours would be spent i n c r u i s i n g a l t i t u d e s .
, To estimate t h e rem dose r a t e o r "dose equivalent" ( s e e r e f . b ) , w e hrtve t o remember t h a t t h e r a d i a t i o n i n 23-km a l t i t u d e c o n s i s t s mainly of n u c l e i e s p e c i a l l y protons, neutrons, and u - p a r t i c l e s . The b i o l o g i c a l l y most effect-ive components a r e t h e s l o w evaporation protons, a ' s and oLher nuclei (-10 Mev t energy), which o r i g i n a t e i n nuclear c o l l i s i o n s i n t h e human body, and t h e ener- .In the hydrogen con- g e t i c neutrons which produce heavy i o n i z i n g r e c o i l protons t a i n i n g t i s s u e .
Schaefer, Erebs, and e s p e c i a l l y Van Allen ( r e f . 5 ) estinintcd t h e b i o l o g i c n l e f f e c t s i n t h e human body of t h e heavy prongs of cosmlc rtry induced Lit.rLrs by comparison with equivalent amounts of incorporl-Lted rnd.ium. The G t a r components high s p e c i f i c i o n i n i t i o n , resemble cls~scly of low energy being of s h o r t range and i n energy and l o n i z i n g c h a r a c t e r i s t i c s t h e a - p a r t i c l e s arid recoi 1 nuclei from t h e r a d i o a c t i v e decay of radium and i t s follower product::. The number of stars i n t i s s u e w a s estimated by Van Allen, on t h e b a s i s of meiisuremerits i n nuclear a t high a l t i t u d e s , t o be 830 p e r gram of b i o l o g l c n l m u t e r i a l per day.
emulsions stars is equival-ent, with r e s p e c t t o energy deposition, t o This number of O.Oj5pC rdd-ium within t h e human body. This would be .L/3 of t h e maxZmum p e r - m i s s i b l e burden of Ra226, a t continuous s t a y a t 75,OOO L'cet, a l t . i t u d e . If w e i n t e n d t o a s s e s s t h e r a d i a t i o n exposure of t h e crew, both n i q b c r t i , t h a t f o r t h e i o n i z a t i o n rad dose and t h a t f o r the radium equivrilcnt hive t o he divided by 16.8 because t h e crew i s i n 7'1,OOO r e e t only <lbout LO hour::/weck. (The dose r a t e i n mrad/hr must be multiplied by 10 t o o b t a i n the dose p e r week.) Thus we o b t a i n , as approximate exposure f o r t h e crew from G a l . C . R . a t high l a t i t u d e s , c 'i Fraction Overall ionizat-i on: of MPD m a d . .
2 X (0.625 - 0.84) - x 10 = 12.5 - 16.4 mrem/10 hours (week) .
hr Nuclear L Lars :
0.033pc ~$26/16.8 = 1/j MPD/16.8 . . . . . . . . . . . . . . . . . . q g
-
" 1 7 % A s was already emphasized by Van Allen t h j s estimate of t h e "rem" dose o r of t h e b i o l o g i c a l e f f e c t contains l a r g e u n c e r t a i n t i c s . The d i s t r i b u t i o n of stars i s uniform throughout the body, while t h e radium accumulates t o 9'7 per- cent o r more within t h e bones. Thus t h e b i o l o g i c a l e f f e c t of the stars may be lower o r higher than t h a t of an equivalent body content of Rii226, dependent on whether t h e concentration near t h e bone marrow o r a uniform d i s t r i b u t i o n over o t h e r s e n s i t i v e organs i s more e f f e c t i v e .
Furthermore, t h e number of stars seems t o be higher i n t i s s u e i f one includes 1- and 2-prong s t a r s , whlch are d i f f i c u l t t o observe i n photoemulsions.
Also t h e e f f e c t of secondary neutrons i n t i s s u e i s riot included except i n t h e factor 2 which was a t t a c h e d t o t h e r a d dose. Their energy deposition ( r e c o i l protonc) is not measured adequately i n the i o n chambers of Neher, which were f i l l e d with argon. The energy deposited by f a s t secondary neutrons i n the human body by means of heavily i o q i z i n g r e c o i l protons i n s u b s t a n t i a l l y higher imparted t o heavy argon atoms. Although t h e c o n t r i b u t i o n of t h a n t h e energy t h e s e neutron r e c o i l s t o t h e r a d hose i s low, the r e c o i l s from a fast r1CUtrc)n I have a high LET ( l i n e a r enerQy t r a n s f e r ) o r y u d i t y f a c t o r .
- I '
I' A more comprehensive approach t o estimate t h e close cquivalcnt o r thc r c m dose i s , t o compile measurements and t h e o r e t l c a l ctil cul ati ons o i i t h e b j o Logl c:~ll,\r most e f f e c t i v e components e s p e c i a l l y on t h e neutrons .ind on charged hcnvlly / ' / , i o n i z i n g p a r t i c l e s , and on t h e i r s p e c t r a , and t o mriltlply t h e l r flux i n t h e I d i f f e r e n t energy ranges with t h e i r doGe coriverslon :ind q u a l i t y fuctoi-r; f u r t,hI R energy range.
On t h e b a s i s of neutron d a t a of Hess e t :il. (rei'. 6 ) , Sobcrniann ( r e f . -0, Lingenfelter ( r e f . 8), La1 e t a l . ( r e f . g), Korff, H:i;ynies et ELI. ( r e f . lo), *Lnd t h e c a l c u l a t i o n s of Patterson e t a l . (ref. 11) , S. P . Shcn (rei'. 12) comcs i n t h i s way t o t h e r e s u l t t h a t the neutrons i n , t i r would produce a rcrn close* of a t most twice t h e rad dose measured i n an Argon i o n i z a t i o n chamber a t SST' a l t i - tudes and high l a t i t u d e s . The primaries nrld secondarlcS. I n a i r produce in t i s l )I' ' sue about 8 y t o 1,000 stars/g-day a s mentioned before.
I f each star cieposiLs , !'
l o c a l l y about 50 Mev on t h e average, t h e r e s u l t i n g physic*i.l. dose would be 0.03 mrad/hr.
I f a q u a l i t y f a c t o r of 10 for t h e heavy i o n i z i n g components and L r e c o i l s i s assumed, t h e dose equivalent i n rem would than be 0.3 mrem/hr o r 4 0 percent of t h e ionchamber dose rate in r a d / h r . Because of t h e implied con- , s e r v a t i v e assumptions on fast neutron f l u x find energy deposit and q u a l i t y fuc- Ij.
t o r of stars, w e assume here, thrit t h e dose equivzlent i n rem from neutrons md .
stars combined i s equal to the ionchamber dose i n r a d . Taking tigain i n t o -w The neutron flux t o dose conversion f.1ctor.s are Like11 fronl Hzndbook 63
"Protection A6;iinst Neutron Radirttlon up t c 30 Mil Lion E l e c t r o n Volts ."
z U. S. Dcp irtrncnt of Comnlerc-e N:ition:rl RureJu of' StmcLxrds , November 1957.
account by a f a c t o r of 2 t h e secondaries produced i n the e ~ \ v i r o r m c r i L ~ l mncscs of' t h e a i r p l a n e of higher z-number than a i r , t h e dose b.llunce i i i the : i i r p l : i n c i n 7>,OOO feet i n high l a t i t u d e s would than be a t most Lhe foL'Lowing: Rad dose from charged p a r t i c l e s ( i o n chamber) Maximum neutron and star rem dose m r e m
200 - 280 _r 1.23 - 1.67 -
( i n c l u d i n g t h a t produced by week h r necondarlec from t h e a i r p l a n e ) m r e m
1.9 - 2.3 -
hr o r t h r e e t i m e s t h e ion chamber dose rate.
The high c o n t r i b u t i o n from neutrons i s based on t h e u s m p t i o n t h a t t h e f a s t neutron flux i n t h e s e a l t i t u d e s corresponds t o t h e spectrum c a l c u l a t e d by Hess i n 4 0 g/cm2 atmospheric depth from data i n (ref. 6 ) and that t h e flux of secondaries i s doubled by t h e aircraft. Unfortunately whlle t h e ripproximilte shapes 01 t h e neutron s p e c t r a a r e f a i r l y w e l l *knowri, i'ue ~ ~ ' u b o i u i t f L i u ~ V C L ~ U C G are s t i l l u n c e r t a i n . More recently d i r e c t measurements with d e t e c t o r s t h n t w e h i g h l y s e l e c t i v e t o f a s t neutrons (1 t o 10 MeV) , by Mendell rind Korff ( r e f . 13) gave neutron i n t e n s i t i e s i n these a l t i t u d e s t h a t were lower by LX fuct,or of about 3.
On t h e b a s i s of t h e more conservative rissumpt,ions the exposure of t h c crew a t 10 hours/weck duty i n 75,000 f e e t on high l a t i t u d e router; would then bc nbout 1 9 t o 25 percent of t h e MPD; corresponding a d d i t i o n s helve t o tx made f o r ascwit and descent. The exrict values depend on t h e c o n t r i b u t l o n of iieutrori:: which I s u n c e r t a i n by it f a c t o r of 3 and the c o n t r i b u t i o n of sccond:irie:; f'rorn t h e aLr- p l a n e which i s d i f f i c u l t t o c a l c u l a t e and may havc t o be inemured f o r difl'eyent types of a i r c r a f t .
A t :xltitudes of 10 t o 11 km (30 t o 3',,000 ft) whcrv CUT' ::ubsonic Jets ot* today c r u i s e , t h e ion chamber dose r a t e i n high 3:i t i t.utlcn ~ r i t l I l i t , r)r\ii t.1.c 111 1.1 LIS i s lower by about a f a c t o r of 3. The number clf st:irs i s , liowc'vcr, :it 1en:;I.
smaller by a k i c t o r o€ 4.
The ion chnmber dose i s ( S C C ffg. 4 . ) : & =? rnrnd/dtiy = 0.21 rnrad/hr Because t h e r a d i a t i o n in these lower a l t i t.udcs contains f'cwer nucleons and nuclel t h e production rate of secondaries i n t h e s t r u c t . u r u c ) f t h e a i r p l a n e and of star:; and r e c o i l s i n t h e hunicm body i s smaller tlirtri i n high a l t i t u d e s . W e a l l o w t h c r e f o r e only a f a c t o r of 2 t o t h e ionchamber dose rdte as tlic qutility arid buildup f;tctor and o b t a i n nbout 0 . 4 mrem/hr . i s 3 rough approximation f o r t h e less b i o l o g i c d e f f e c t i v e r a d i a t i o n a t 3@ t o j>,@OO f e e t or 9 t o 10.5 k r i ~ :*lLitudc i l l high l a t i t u d e s .
I A HEAe PRIMARIES With r e s p e c t t o heavy primaries I m i g h t add here only R s h o r t remnrk on t h e i r frequency a t 75,000 f e e t i n hlgh lat-ltudes.
* I /
I O
Pmax ALTITUDE, 1000 FT , The compilation of balloon f l i g h t meafiurements of Ytigoda i n figure 3 shows Furthermore from t h e com- t h a t i n 75,000 feet about 1 hit/crn3/day i s obtained.
prehensive t h e o r e t i c a l studies of H. Schaefer ( r e f . 3) it can be seen t h a t the heavier primaries ( Z > 20) can p e n e t r a t e only very seldom t o t h e s e relatively l o w a l t i t u d e s .
Thus t h e above number of h i t s is mainly produced by t h e lighter n u c l e i
C , N , O - up t o N e (More data on heavy primaries and on considerations of t h e i r
e f f e c t s a r e given i n references 15 and 22 and references t h e r e i n ) .
a
SOLAR C O S M I C l0,OOO 4,000 .I4 2,000 . I O .0 5 CHAMBER ROENTGENS/HOUR COUNTS/SEC OR 103 CHAMBER PULSES/SEC -COUNTER IGC G JULY 15. 1959
LAUNCHED 0804 UT -4
SATELLITE UNIT NO 8 1100 JULY 1 5 3 1 HOURS AFTER
uvLLLLI_I 3 2
FLARE ONSET ATMOSPHERIC DEPTH, g/cm2 Figure 6. - A l t i t u d e dependence d u r i n g a pt".ic>d of' h i ;:h i i i t , t - i i : . , i L y .
This f l i g h t ascended between 0800 arid 1100 i i t i i v t . i . . : - . . 1 1 t.imc. < > i i (From r e f . 1, J. R . W i r1c.klc.v.)
J u l y 15, 1939.
I n f i g u r e 6 dose rates a c t u a l l y measured within the xtmosphere R L a l<)w energy event of extreme s i z e ( J u l y 1 4 , 1979) a r e given. By Low ciiergy evciit Is understood an event i n which the p a r t i c l e spectrct 1':iLl oft' stceply wtth mer-py and no r e l a t i v i s t i c p a r t i c l e s tire measured ( E 5 300 Mcv). Suvh cxtt-cine c>vcril.s 5 yc:tr.:; of r o i i x L n i u r n occurred with a frequency of 1 t o 3 p e r y e w during t h c a c t i v i t y of t h e last solar cycle. A t u depth of 5 g/cml- : ~ t ) c > i i t . 0.14 rad/lir. wns measured, and a t a depth o f j 6 g/cm2 about 1 mratd/hr i s estini:it.ed. These dose rates were v a l i d 29 hours a f t e r onset of t h e s o l a r cvcrit I n t.he decrcasiri:; phttsc- of t h e event and may have been higher by a frictor ot' 10 :tt,t,hc pc>:tlr of the event., Because of t h i s low dose r a t e i t zc'cm:; J u s t i f i a b l c , thcrefort., * i . e . , 10 mrad/hr.
t o consider t h e low energy events as u minor hazard, even though the dose cwn- t r i b u t i o n from neutrons w a s n o t measured i n t h e riitzogen chiunbcr :uid is riot; included. Three such events occurred i n 1959. (May 12, J u l y 10, Lmd J U L Y 14.)
A fourth extreme event, on J u l y 16, 1959, c a l l e d "medium energy event" was of g r e a t e r s i g n i f i c a n c e . An i n c r e a s e of rieutzons n t sen l e v e l m s observed iinplied p a r t i c l e s w i t h energies above 500 M e V , which p e n e t r a t e much which , deeper i n t o t h e Rtmosphere snd produce e n e r g e t i c secondaries which reach sea I t s s p e c t r a were similar i n i n t e n s i t y and energy t o those of t h e l e v e l .
November 12 (and November 15) event i n 1960, which a r c more completely h a m .
fl r, NOV. 13, 1960, 16 03 ' u NOV. 12, 1900, L3.30 PROTONS Calculated from data der ENERGY, BEV The n u m b e r s ZO', 25', , . . . . are the m i n u t e s after solar cosinic, ray onset, observed on earth 0350.
Figure ' 7 . - FJ:-tr.e-p.irtiCle s p ~ c t t - n .
W e consider h e r e the spectra on November 12, : L t ??so U.T., :md on
November 13, 16@3 U.T. ( f i g . 7) 10 and 27 hours, r c s p e c t i v c l y , nfter t h c pur- t i c k flu o n s e t . The two spectra a r e determined from Inewurcmcnts w i L i 1 r o c k e t s i n F o r t Churchill launched by Goddttrd GCI e n t i s t s , from t h e measure- ments of Winckler w i t h balloons arid from t h e measuremenfs of Van Allen :md Lin w i t h Explorer VII. Furthermore, t h e neutron measurements a t Deep River by Carmichael, S t e l j e s , and McCmcken are taken i n t o considertilion ( r e f . 17, and \ I r e f e r e n c e s t h e r e i n c i t e d ) .
By f a r t h e h i g h e s t doses a t SST a l t i t u d e s a r e produced by "high energy" events such as t h a t of February 23, 1936. I n t h i s case t h e sea l e v e l monitors recorded a neutron i n c r e a s e of 3600 t o 5000 percent i n high l a t i t u d e s o r i n impact zones, r e s p e c t i v e l y . During t h e November 1 . 9 6 0 "medium energy" events t h e .
neutron monitor i n Deep River (Canada) recorded a m a x i m u m i n c r e a s e t o 225 per- cent only, I n t h e same figure 7 approximate prompt s p e c t r a 3f the February 23,
-
l9'16 h i g h e n e r m event :ire shown.
The interlsities in the (00 Mev rznw were of t h e s<me o r d e r of magnitude as those of medium ciler'u e v e r i t s i n t h e 70 Mcv ranKc (about 500 t o 1,000 p:irticlcs/cm;? s e c s t e r a d ) . 13cc L U : ; ~ of Lhc 1urt:e flux o f high energy p a r t i c l e s t h i s would have been t h e most, irnpol-tiLnt everit of tlie Last c y c l c with r e s p c c t t o i m p l i c a t i o n s t o t h c SST. U n f o r t u n d x l y i t s C l u e s bctween 100 rind 1,000 Mev are n o t as well known as the i n t e n s i t i e s or Lhe November 12 e v e n t ; however, based on t h e s p e c t r a of Simpson, rne.i:;ur.cd 1 t o 10 hours Lfter o n s e t ( r e f . 16), and on t h e balloon me:rsurement:, of' V t n A1lc.n :Ind WinckLcr ( r e f s . 17 and 18) and t h e e s t i m a t e s of Fowler and P e r k i n s , 131-istol, Gre.Lt. l3riLTiin (ref. 19) d e r i v e d from t h e 5O-fold I n c r e a s e of iieutrnri:. i n Lccds, l?rif;l:J.1d, the s p e c t r a f o r t h e f i r s t hours l i e i n thc broad s t r i p inci.iczttcc1 i n l'i,qir*e 7 . The measurements are e x t r a p o l a t e d t o lower energies by the ti.1l;hc.d I i n c s .
W e see t h e Simpson 0500 U.T. Spectrum 70' a f t e r C . R . clnset ( f l a r e m;ix 0342), t h e estimate of the Goddard group for 0430, t h e e x t r a p o l a t i on bnch tu t h e t i m e of t h e maximum of t h e Chicago monitor ( O h l > ) on t h e b r i s i s of bxlloon measurements about 19 hours later by Van A l l e n ,Lnd Wincklcr, arid estimate from H . Schaefer based on t h e 3600 p e r c e n t n e u t r o n increase i r\ t h e Durhm moni tor.
' I The estimates of t h e B r i s t o l group are subst:intiaLly tii(<hcr I n t h e l o w c t 1 c J . t ~ range znd are o n l y used down t o 900 Mev.
I I i .
..
DOSE RATE, RAD/HR I rl I 10-3 100 x 1,000 FT I I I ] F i g u r e 8 c a The do:;e rates w i t h i n i h c atmosphere d e r i v e d from t h e w s p e c t r a f o r , t h e 12 flovcnibcr 1c)GO medium energy cverit and t h c Fc'Dru:lry l V > o h i g h energy cverit a r e :;lwwri i r i f i L u r c 8. on Novcmber 12, A t j 6 t;/crn2 a l t i t u d e are obLiiined: m r : d r a d 0.:) t o 2 - I n t h e e a r l y phases.
19Go: >o - , on February 23, 1956: fir kir
I i
SUNS POTS 1939- 1959 -I----- CLASS 1 FLARES 1935-1957
!i. !
_--_--- CLASS 2 FLARES 1935-1959 I * . - - -. -. . ..
CLASS 2 FLARES 1954-1959 I ' 1 NORMALIZED TO 100 7% OBSERVING TIME
--%--
400 i -, - - . -. - CLASS 3 FLARES 1935- 1957
300 - b i' YEAR More i n f o m a t i o n about these events I c ccirittt 1 1 u d in 1’it;ut-e 10.
b NASA In t a b l e 11 the exposure of the crew u~idc-rextreme condition::, i . e . , on p o l a r routes, averaged over the 11-year s o l n r cycle i s sutiur~:~rlzed nccordi!lp; t o these rough estimates. The crew f l i g h t time i s ussumed t o bc 80 hours/month of which 40 hours a r e a t 23 km (73,000 f t ) a l t i t u d e . Exposure during ascent and descent i s disregarded.
The frequency, dur:ltions, :md spectra of f l a r e events important i n SST a l t i t u d e s a r e taken as those of the last solar cycle, which w a s the most a c t i v e cycle of t h i s century. No evtzsive metisures such a6 diving t o lower a l t i t u d e s , i f a f l a r e event i s in progrecs, are assumed. There is no indication t h a t events of l a r g e r s i z e ( l a r g e r Lntenslty 2nd duration of the penetrating components) than t h e February 1936 event cannot occur; however, - they should be very r a r e .
From table I1 it i s Eeen, t h a t t h e average r e m dose r a t e from Galactic and solar C . R . would amount t o about 30 percent of t h e MPD of 3 rem/year, i . e . , For the crew the main contribution, i .e., 21 percent of t h e MPD ~ 1 . 3 rem/year.
comes from Gal. C . H .
It i s d i f f i c u l t t o say how trustworthy t h i s number i s , since the contribution from additional secondaries originating i n the x i i p l a n e and especially t h e contribution of neutrons is not w e l l known.
It should be however, a t most, too high by a f a c t o r of 2. Furt.hermor*e, since t h e c x w will probably be on duLy f u i a ----'---I I I I ~ A L I I ~ ~ ~ ~ u, - E r ) E L, J b - A - .~ni,-c.
Mpc f ~ r r ; r d I n t , f o n workers r e f e r r i n g t o 50 years duty i s not d i r e c t l y upplicable and is c i t e d here only t,c> have a rough comparison with the maxinlm permissible rndlation exposure i n Taking evasive measures i n case of cncrgetl c f'lare cvellts other professions.
t h e exposure of t h e crew on polar routes would be c 2 0 percent of the MPD of I .I I, :."'"!!
y I' 1 , I l : .
. ' , I I & : , I , ', y < ' I , I ' ~ - l ' i MPD i w i x l m i m yermleslblc 2 o.> rrm/yr rate for popultltlin.
The exposure of passengers under extreme conrii ti ons !uid without, e v a s i v e W e iisswnc tiere measures i n c a s e of s o l a r events, is given i n titble IIL.
2 f l i g h t s = 2 hours/month, t h a t i s 24 hours f l i g h t t i r n c , per yeur i n 23 hi : i l t , i - t u d e on p o l a r r o u t e s . For w c h s h o r t period:: t h e o v c r d L loriizatlon do6e 1.11 r t n i from G a l a c t i c C.R. i s small and may be neglected. With respcc.t; t o Llie qucutlon, f i r s t di scussed by H e m n n Schaefer, concerning pregiiruit I'cmale p:ir:sciiger!; we mention t h e number of heavy primary-hits/cm3. Thc f'octu:; is rnost s c n s i t i v c : t o i r r a d i a t i o n i n t h e e a r l y d i f f e r e n t i a t i o n s t a g e betwceri 1'1 d:tys :md 6 weeks m d IT w e tissumr' !L ucnsiLive v ~ d u r u n c ~ h a s i n t h i s period 3 volume ot' 4 . 3 t o 1 . 2 cmj.
o f ( 5 rm) 3 t h e 2.5 x h i t s / ( ; 3 m)j/month, would r L f l ' l I c t L ' . 5 of 1,000 i'enule p a s s e n g e r s pregnnnt i n t h e second month, who f l y 9 time:; i n t h i s peciod. Fiir- a f " thormore, from t h e number of stars of 830 t o LOOO/cm'~ tir;sue/>'ll hour:; wou1ci b e o b t a i n e d on the average 2 stars/( 3mm)j/month f o r the s:me pa:;:;el\gers. l3cc:tuse of t h e u n c e r t a i n t i e s with r e s p e c t t o t h e c i z e of tlie scn:;itive volurrie, which i s asswried r a t h e r a r b i t r a r i l y , t h e u n c e r t a i n t i e s i n the numlwr of he:ivy prinutry h i t s and t h e e f f e c t i v e n e s s of heavy p r i m a r i e s m d stars, t h c r e i s no proof A S y e t t h a t t h e i r e f f e c t s on t h e s e passeiigers can b r cornpktcly n e g l e c t e d .
Without e v a s i v e measures the dose f o r passengers from solar e v e n t s a r e e s t i m a t c d as high n s k . 3 rem p e r 1 1 y e a r s , i f we m:re t h e extreme 'Lssurnptian t h a t this passenger encounters all major e n e r g e t i c e v e n t s of t h e solar c y c l e .
This would be a n zverage dose r a t e of 0.4 rem/year or SO perc'ent of the m , i . u i i u n I n sumrnary it m i ght be said:
I f appropriate precautions a r e taken - a6 &vine, down t o s u f € i c i e n t l y l o w
a l t i t u d e s o r r e r o u t i n g of the a i r p l a n e t o lower geomgnetlc l a t l tudes i n case o€ e n e r g e t i c solar events - the i o n i z a t i o n exposure of passengers m d crew i r i supersonic f l i g h t s l i e s s i g n i f i c a n t l y below t h e mnx-lmum permisslble dose rat.cn, as defined by t h e Federal Radiations Council o r ICW for t h e commonly known more l i g h t l y i o n i z i n g r a d i a t i o n s (protons and neutrono i l r l d even Including No a).
permj s s i h l c dose f o r heavy primaries is s t a t e d ( f o r p r o t e c t l o n purpose::), o r f o r r e r o i l s 3 r d c e r t a i n components of stars which :ire uriiformLy distr.ibuted through t h e human body. TheGe components are new arid i n low a l t i t u d e s unknown r j r L t Le; I r t inadequately explored phenomenon.
I n d i c a t i o n s are t h a t such heavy i o n i z i n g components :ire very e f f e c t i v e i n O n t h e other hmd, t h e i r intenc-lty i n SST n l t l t u d e r , up t o germinating t i s s u e .
23 kin i E very low and not well laiom~. It mlght be t h c r e f o m :idv-Lr.nble f o r s e n s i t i v e passengers t o avoid. exposure t o t h i s klnd o ! ' ratitation unt-ll there i:; proof t h a t the e f f e c t s of such low j n t e n s i t l e s ( a i hc Iieglected.
1 6 12. Petty, A . F., Jurkevich, I., Shen, S . P. : "Ozone, N i t r i c Oxide, and Radia- t i o n ECfects on a Supersonic Transport." G.E. Go., C o n t r a c t FA-WA--llnl.
?
P t , .
rncreasc at High A l L j L u t i t . on F t ~ I i r i i ~ u y : ' j , l9',11."
L8. Winckler, J. R . : "Cosmic-Ray Pliys. Rev., v o l . 104, n o . l., second o e r . , O c t . L , LY'-,II), p . L%'O.