Measurements of the isotopic composition of cosmic nuclei with Z = 7-20 are reported. These measurements were made with a new version of a Cerenkov x total E telescope. Path length and uniformity corrections are made to all counters to a RMS level  1%. Since the Cerenkov counter is crucial to mass measurements using the C x E technique - special care was taken to optimize the resolution of the 2.4 cm thick Pilot 425 Cerenkov counter. This counter exhibited a beta = 1 muon equivalent LED resolution of 24%, corresponding to a total of 90 p.e. collected at the 1st dynodes of the photomultiplier tubes

Kish, J. C.

Schrier, D. A.

Webber, W. R.

English

NASA Technical Reports Server

OG 4.3-4
88
COSMICRAY ISOTOPE_ WITHA NEW
_V X TOTALENERGYTELESCOPE
F.R. Flebber,J.C.K'zsh& D.A,_hrier
L__ o.fNew Hrzmpsltire
.f_rrh,o;m,,NH 0,.9824
I. Introductionand Ex-p_erirnentalData. Inthispaper we reportmeasurements ofthe
isotopicompositionof cosmicray nucleiwith Z = 7-20,Thesemeasurements were
made witha new versionof a Cerenkov x totalE telescope,Thistelescopeand the
detailsof the balloonflightare describedin paper OG 4.1-5,Path length and
uniformitycorrectionsare made to allcounters to a RMS level( 17o,Since the
Cerenkovcounteriscrucialtomass measurements usingthe C x E technique- special
care was taken to optimizethe resolutionof the 2.4 cm thickPilot425 Cerenkov
counter. This counter exhibiteda _ = I rnnon equivalentLED resolutionof 24Z,
correspondingto a totalof90 p.e.collectedatthe istdynodesof thephotomultiplier
tubes.
Events to be analyzedusingthe C x E mass analysistechniqueare firstselected
accordingtochargeby a two dimensionalmethod usingboth dE/dx xE and dE/dx xC
matrices. Three separatedE/dx measurements are utilized.Charge overlap is
neglible.Mass histogramsare constructedfrom C x E matricesforeach charge as
illustratedinFigurei forOxygen nuclei.Mass histogramsforN, O,Ne and Mg nuclei
are shown in Figure2, and _)Al, Si,S, Ar and_Ca nucleiin Figure3. The massresolutionis_ ~ 0.23AMU for and 0.27AMU for t_Si.
The datafrom the 30 hour balloonflightissummarized inTableI.Column I givesthe
energyintervalformass analysis,The upper limitistakentobe C/Cm_ Y = 0.45forMg
and heaviernuclei.Column 8 givesthe number ofeventsobserved."''_rorsare shown
onlyforisotopeswhere significantmass overlapoccurs- allothererrorsaretaken to
be statistical.Column 3 showsthe chargefractionforeach isotopecorrectedtoequal
energy/nucleonintervals.And finallyColumn 4 shows thischargefractioncorrected
tothetopoftheatmosphere,
2. _Zt._.Rr._,ionof the Data. The basicgoal of thisexperimentisto compare the
observedisotopicratioswiththoseexpectedafterinterstellarpropagationinorderto
derivethe cosmicraysourceabundance ratios.The secondaryabundances produced
duringpropagationarecalculatedusingnew crosssectionsmeasured by our group at
the BEVALAC (Webber et al,,paper OG 7.2-2).The propagationprogram utilizesa
simpleexR_uenti_ path lengthdistributioni hydrogenwitha mean path lengthke =
23.0_ P-_"_g/cm_ above 5.SGV and k_ = 8.33_below 5.5GV.The solarmodulatlon
parameter ¢ = 600 MV. At a_interstell-arenergy 800 MeV/nuc appropriateto these
measurements,he ~ 6.8g/cm",
The extrapolationto the sourceforselectedisotoperatiosisshown in TableIf.Also
shown for comparison are previouslymeasured isotoperatios(ata slightlylower
energy)from a sun_ by Wiedenbeck,1984. These difIerslightlyfrom the original
valuesquotedby Wiedenbeckand co-workersfrom theISEEexperiment.
Belowisa chargeby chargesummary ofour results.
hRkr.ag_IL_Nitrogenabove the Cerenkov thresholdstopsnear the end of the 2nd and
 
I   PE MEASUREMENTS I H   
CERENKOV  AL  J...&<) PE 
W   Web er, . . l.Sh At  . S:hri  
Space .science Center 
University 01 e  ampshire 
f)ur am,  3824 
G -4 
1. Intrpductipn and Experjmental ata, In this paper e report easure ents of the 
isotopic co position of cos ic ray nuclei ith   7-20. hese easure ents ere 
ade ith a ne  version of a erenkov x total E telescope. This telescope and the 
details of the balloon tlight are described in paper OG 4.1-5. ath length and 
uniformity corrections are ade to all c ters lo a S level < 170. ince the 
Cerenkov counter is crucial to mass easure ents using the C x E technique - special 
re as taken to timize th  resolution f th  .4  thick ilot  er  
counter. is ter ibited  (3  1 muon ivalent  resolution f %, 
corresponding to a total of 90 p.e. collected at the 1st dynodes of the photo ultiplier 
es. 
ts t   lyzed sing th     ass lysis technique re first s lected 
according to charge by a two di ensional ethod using both dE/dx xE and dE/dx xC 
atrices. Three separate dE/dx easure ents are utilized. Charge overlap is 
neglible. ass histograms are constructed from  x E atrices for each charge as 
illustrated in Figure 1 for xygen nuclei. ass histograms for N, 0, Ne and g nuclei 
are shown in Figure 2, and Igr Al, Si. S, Ar and2~a nuclei in Figure 3. The mass 
solution s (1 .... 23  or 0  27 U or Si. 
The data from the 30 hour balloon flight is summarized in Table 1. Column 1 gives the 
energy interval for mass analysis. The upper limit is taken to be C/C = 0.45 for Mg 
and heavier nuclei. olu n 2 gives the nu ber of events observed. Wrors are sho n 
only for isotopes here Significant ass overlap occurs - all other errors are taken to 
be statistical. Column 3 shows the charge fraction for each isotope corrected to equal 
energy/nucleon intervals. And finally Column 4 shows this charge fraction corrected 
to the top of the atmosphere. 
2. Interpretatipn of the Data, The basic goal of this experiment is to co pare the 
observed isotopiC ratios with lhose expected after interstellar propagation in order to 
derive the cos ic ray source abundance ratios. The secondary abundances produced 
during propagation are calculated using new cross sections easured by our group at 
the BEVALAC ( ebber et aI., paper OG 7.2-2). The propagation progra  utilizes a 
simple e~~enti~ path length distribution in hydrogen with a mean path length he = 
23.0 f3 P . glcm above 5.5GV and "'A. = 8.33 (3 below 5.5GV. The solar modulatlOn 
parameter (l = BOO MY. At ~interstelfar energy .... 800 MeV /nuc appropriate to these 
measurements, he .... B.Bg/cm . 
The extrapolation to the source for selected isotope ratios is sho n in Table II. lso 
sho n for co parison are previously easured isotope ratios (at a slightly lower 
energy) from a swmnary by iedenbeck, 1984. These differ slightly from the original 
values quoted by iedenbeck and co-workers from the ISEE experiment. 
Below is a charge by charge summary of our results. 
Njtroe;en, Nitrogen above the Cerenkov threshold stops near the end of the 2nd and 
https://ntrs.nasa.gov/search.jsp?R=19850025716 2020-03-20T18:03:50+00:00Z
OG 4.3-4
89
lasttotalE counterinour telescope.The resultingenergyrange ofanalysisisnarrow,
thus limitingthe statisticalccuracy of the data. The resultsobtained_4_reare
9_nsistentwithearlieresultsshowing a significantlygreaterabundance of _'N than
"_N at earth.
The 170 and 160 abundances thatwe observeare slightlylargerthan,but
consistentwiththoseoriginallyrepolr_edby Wiedenbeckand Greiner,1981a. Itisseen
that the secondary productionof "0 is~ 10 x the solarsystem abundance ratio
making itvery clif_cultto achievea meaningfulsourceabundance determinationof
thisisotope.
Neon. The relativeabundances for21Ne and 22Ne we me@pure are ingood agreement
_iththosereportedby Wiedenbeck and Greiner..1981n_Ne isconsistentwithbeing
allsecondaryand the source abundance ratio_Ne/_VNe thatwe deriveis~ 4 x the
solarsystemvalueinagreement withearlier,!;_easureme_s.
The relativeabundances of _'_'MEand _-_Mgwe measure are again
consistentwith,but slightlysmallerthan thoseoriginallyreportedby Wiedenbeckand
Greiner,1981a. (They agree even better with the average abundance ratios
summarized by Wiedenbeck, 1984 - see TableIf)These slightlylower abundance
fractions- coupledwitha secondaryproductionwhich appearsto be 20 - 40L larger
than that used by the above authorsleadstocosmicra_sour_abundances ofthese
nucleithatare 1.43+ 0.50_the _glarsystemratiofor_"Mg/*'_¢-4_,and 1.24± 0.28x
the solarsystem ratiofor_'VMg/_=Mg.These valuesare lowerthan thoseoriginally
reported by the above authors,but are in agreement withinthe quoted + i a
experimentalerrors.They are alsoconsistentwithcosmicray sourcetosolarsystem
ratiosofone.
Al_The fraction26Al/27Alof 2.2± 1.8Zthatwe measure compares withthe
fractionof3.6± 2.9Lreportedby Wiede_eck, 19_
The fractionswe measure for_oSi and _Si are about i _ lowerthan those
originallyreportedby Wiedenbeck and Greiner,1981b.For the secondaryproduction
oftheseisotopeswe obtain~ 30-4070more than appearstohave been obtainedby the
above authors.Thisleadsto cosmicray sourcefractionsoftheseisotopeswhich are
0.79± 0.42and 0.62± 0.58x the solarsystemvaluesrespectively.Thesevaluesare,_
2 a belowthe originalvaluesquotedby the aboveauthors.About i a ofthisdifference
isdue to thel_er secondaryproductionwe use.
For _'=Sour sourceabundance fractionis~ i _ lowerthan thatreportedby
Wledenbeck,1984. In arrivingat a sourceabundance we use a secondaryproduction
~ 3370largerthan thatwhich appears to have been t_ed by _j_denbeck.The actual
cosnmcray sourceabundance ratioswe findforboth "_S and _'_Sare consistentwith
zero. This i not a realisticvalue,however, _pce the.interstellarsecondary
productioniss 5 x thesourceabundance ratiofor_'-_Sand the experimentalerrorsin
allmeasurements todatearegreaterthan thesourceabundance fractionitself.
Argon & Calcium.Both of these chargesare somewhat differenthan the previous
charges_scussej_ Individuallythey are dominatedby one ratherrareisotopein the
source,_"Ar or =_'Caand the possiblesourceabundances ofthe otherisotopesare
expected to be completelydominated by interstellarsecondary productionifwe
considersolarsystemabundance fractions.The isotopicabundance fractionsthatwe
measure as shown in _ble ] are,_ndeedconsistentwithpurelysecondaryproduction
withthe exceptionof o_Ar and ="Ca. The fractionsoftheseisotopeswe measure are
~ 1.5x largerthan expectedforpure solarsystemabundanceshowever.Thiscouldbe#
suggestiveof a somewhat largerabundance of theseisotopesrelativeto Fe in the
cosnmc ray source. Unfortunatelywe are unableto deriveabsoluteratiosof these
isotopestoFe from thisanalysisto confirmthissuggestion.
" 3._ In thisanalysiswe flnd2_nedecisivexample of an isotopicabundance
differenceinthe cosmicray s_ ce, ,_Ne ashas been observedseveraltimesbefore.
We alsofinda suggestionthat M_ & _°Mg areenhanced but onlyatthe I a level.For
G -4 
 
last total E counter in our telescope. The resulting energy range of analysis is narrow. 
thus limiting the statistical accuracy of the data. The results obtained wre are 
r~nsistent ith earlier results sho ing a Significantly greater abundance or  than 
  . 
Owen. The 170 and 16  abundances that we observe are slightly larger than. but 
consistent with those originally repo{g.ed by Wiedenbeck and Greiner. 19B 1 a. It is seen 
t t th  ry r tion t 0 1s ....   the lar tem  r tio 
aking 1t very ditIicult to achieve a eaningful source abundance determination ot 
his isotope. . 
NeooThe relative abundances tor 21Ne and 22Ne we m~fure are in good agreement 
with those rep rted  ie e ec  a  reinerZz. 981~O e 1s c sistent ith eing 
all secondary a  the s rce a a ce ratio Ne/ Ne that e derive is .... 4 x the 
solar system value in agreement with earlier zgeasuremegts. 
Ma£oesium...... he relative a a ces t Mg a  '*Mg e eas re are a ain 
c sistent ith. t slightly s aller t a  t se riginally re rted  ie e eck a  
reiner. a. ( ey a ree e e  tter ith the a erage a a ce ratios 
s ari   i ck.  - s  le II) s  slightly low r ndanCE: 
tractions - coupled ith a secondary production hich appears to be 20 - 40% larger 
than that used by the above authors leads to cosmic ra~t,0ur§~. abundances of these 
nuclei that are 1.43 ± 0.50 ~ the ~~lar system ratio tor g/"Mg. and 1.24 ± 0.28 x 
the solar system ratio tor 6Mg / Mg. hese values are lower than those originally 
reported by the above authors. but are in agree ent ithin the quoted ± 1 a 
e erime tal errors. e  are also c sistent ith c s ic ra  s rce to s lar s stem 
tios   
Aluminum. The fraction 26 l /27 AI of 2.2 ± 1.8% that we easure co pares with the 
traction of 3.6 ± 2.9% reported by Wiede~6eck. 19~ . 
Silicon,  ractions e easur  r 8   8i e uL 1 a ow r h  e 
originally reported by iedenbeck and reiner. 1981b. For the secondary production 
of these isotopes e obtain .... 30-40% ore than appears to have been obtained by the 
above authors. This leads to cos ic ray source fractions of these isotopes hich are 
0.79 ± 0.42 and 0.62 ± 0.58 x the solar system values respectively. These values are .... 
2 a below the original values quoted by the above authors. bout 1 a of this difference 
is due to the l~r;ger secondary production we use. 
8ulpher. For -rs our source abundance fraction is .... 1 a lower than that reported by 
iedenbeck. 1984. In arriving at a source abundance e use a secondary production 
.... 33% larger than that which appears to have been ~d by "&4denbeck. The actual 
cosmic ra  source abundance ratios e find for both 8 and 8 are consistent ith 
zero. This is not a realistic value. however. §~ce the· interstellar secondary 
r tion is .....   t  s r e  r tio for S  t  rimental rrors in 
all eas re ents t  ate are reater t a  t e s rce a a ce fraction itself. 
r£oo & CalcjlllJL Both of these charges are so e hat different than the previous 
charges gHscusse,fu Individually they are dominated by one rather rare isotope in the 
source. Ar or Ca and the possible source abundances of the other isotopes are 
expected to be co pletely do inated by interstellar secondary production if e 
consider solar system abundance tractions. he isotopic abundance fractions that e 
easure as shown in ~reble I ar~Ondeed consistent with purely secondary prodUction 
ith the exception of r and a. The fractions of these isotopes e easure are 
"" 1.5 x larger than expected for pure solar system abundances ho ever. This could be 
suggestive of a so e hat larger abundance of these isotopes relative to e in the 
cosmic ra  source. nfortunately e are unable to derive absolute ratios of t ese 
isotopes Lo e fro  t is a alysis t  firm t is s estion. 
3. SUmmary In this analysis we find2%ne decisive example of an isotopic abundance difference in the cosmic ray s~~ce. 2~e as has been observed several times before. 
e also find a suggestion that g & g are enhanced but only at the 1 a level. For 
gO OG4.3-4
all of the other isotopes we measure, tncludlz_ egS/& 30Si, our results ate consistent
witha solarsystemisotopiccomposition.About301_of thedifferenceinthesource
abundanceratioderivedinthispaperand thosepreviouslyreportedappearstobe
due todifferencesinthecrosssectionsused,theremainingdifferencesareinthe
experimentalresultsthemselves.
4.Acknowleda_rnents.ThisworkwassupportedbyNASAgrantNGR -30-002-052
Wiedenbeck,M,E.,_,Gretner,D.E.,Phys,Rev.,_.682,1981a
Wiedenbeck,M,E.,& Gretner,D.E,,Ap.J.,_&.Z..L122,1981b
Wiedenbeck, M. E,,Pros. IBth ]CRC,B...147,1983
Wiedenbeck,M.E.,paperpresentedatCOSPARsy_osiun_Graz.,August,1984
6.Pi__ureCaptions.
_goUre1..Cx E matrixofeventsforOxygennuclei.Calculatedmasslinesfor150,180,
and I°0areshown,
l_gure 2. Mass histogranm for N, O,Ne and Mg nuclei.
Figure3.MasshistogramsforAl,Si,S,ArandCanuclei
CI
GIML1-81
. E2 - STOP .............
OXYGEN o" =0.25 AMU o- =0.29 AMU
14N '5N '50 _60 '70 '80 'gN20Ne21Ne22N. ?--SM_41,/R_I_Mg
119c 806c 215c 599c
.,, ,oo Fig.2
'" f
E2 '_ 0
,, \ ,,=, \
I H 15 15 16 17 18 111920 21 22 2;5Z'425 26
,_60 Moss Number
Fig. I
90 OG 4.3-4 
all of the other isotopes e easure. lnclud1ne 29Sl at 3OS1. our results are conslstent 
With a lolar s stem isotopic c sition. b t ~ f the l1!erence in the s rce 
abundance ratio derived in this paper and those previously reported appears to be 
due to differences 10 the cross lections uled. the rem.a1ning d.1.fterences are In the 
per1mental esults hemselves. 
4. c le ume ts is 'Work 'Was lupported  S  rant  -30-0 2-052. 
5. References. 
ie enbeck. .  .. & reiner. .  .. s. e  .. .ia...JS82. a 
i nbeck. .  ..  r iner. . ., . J., .2llJ.122, 1b 
iedenbeck, . ., r c  18  J  .&J47,  
iedenbeck, . ., paper presented at 05PAR symposium. raz., ugust. 1984 
6. Fie-ure aptions, ~ure 1.1£ x E atrix of events tor xygen nuclei. alculated ass lines tor 150, 16 , o  0 e hown. 
Fi r  . ass isto rams t r , . e  g lei. 
Figure 3. ass histograms tor l, 51. 5, r and Ca nuclei 
i .1 
\ 
.' , 
, 
, 
, 
. " 
, 
I LI- 1 
-ST  
OXYGEN 
::> 
::!l 
<t 
ci 
"-
!? 
100 
,co \8 10 
I 14 15 
C1' 3 U 
11> 160170180 
~ ~ ~ ~ 
 
16 7  
19 20 21 22 
. No  Ne 
~ ~ t ~ 
'-~ 
 
9 21  
Mass Number 
C1'   
23 24 25 26 
rrrr 
~
3  
Fig. 2 
I 
324   
Mass Number 
Table I 
Isotopic Abundances 
Energy In te rva l  
(MeV/nuc) 
Events Observed ,.. % o f  Charge 
equal E int .  
% o f  Charge 
a t  Top of  A t m  
Isotope 
TABLE I f  
Isotope Fractjons 
Wiedenbeck, 1984 (%I 
1.7i0.4 
1.9k0.2 
2155 
5Bt6 
27~4 
27t3 
13*2 
7.2i1.7 
Secondary 
Production (a )  
2.1 
2.1 
20.5 
16.5 
8.6 
10.1 
3.3 
3.8 
CosRl~c 
Ray Source 
0 )  
0.8i0.6 
0.7i0.6 
-1.ti4.5 
46.9k9.0 
18.524.6 
17.3t4.0 
3.6*2.7 
2.6i2.3 
0.2i6.4 
-0.726.7 
Solar 
System (%I * 
0.2 
0.3 
12.2 
12.9 
14.2 
5.1 
3.4 
0 .8 
4.4 
Rat io  This Measurement 
(%I  
(T·O.27 
2721129~ 
81 51 81 81 
UJJ 
291c 
91 
as
 
 top1 C , bunda
 r e 1   ,'. ,;   
l to /n
!ON 383 - 450 49 39.7 
"N 375 - 438 70 60.3 
160 390 - 485 752 94.1 17 0 386 - 472 22 3.0 
"0 381 - 460 19 2.S 
2°Ne 410 - 554 121 55.0 
21Ne 406 - 542 23 11.0 
HNe 401 - 530 67 34.0 
2~Mg 429 - 610 270 66.5 
25Mg 425 - 601 66:tS 17.0 
26Mg 420 - 592 61 16.5 
"AI 435 - 635 5±3 5.0 
21Al 430 - 627 94 95.0 
28 51 446 - 642 251 88.1 
2951 441 - 637 18il 6.3 
105i 436 - 632 16 5.6 
325 462 - 660 64 68.7 
335 457 - 656 14 15.2 
"5 453·- 651 15 16.1 
HAr 478 - 618 33 63.5 
17Ar 474 - 674 2 3.8 
leAr 470 - 669 16 30.8 
3'Ar 466 - 665 0 0.0 
~oAr 462 - 660 1 1.9 
-oCa 494 - 697 31 46.1 
'lea 490 - 692 -3 4.5 
'2Ca 486 - 688 16 24.0 
~3Ca 482 - 684 10 15.0 
"'Ca 478 - 680 7 10.4 
* Ass\lmi~g (HAf' res ~ 3.0%. rocaJ res .. 6.8% 
11
s r i
iO n I easure e t iedenbeck, 
( } ( ) (X) 
170/160 2.9±0.7 . 10.4 .1 
180/160 2.810.7 . ±0.2 .  
2iNe/uNe 19.4:t4.1 l±  0.5 
nNe/,oNe 63.4:tS.6 S8i 6.5 
25Mg/'"Mg 27.l±4.4 7;1;4 .  
26Mg'''Mg 27.4:t2.6 :1:3 0.  
"51/ 28 51 6.9:t2.0 :1:2 .3 
HS1/285i 6.4:1:1.8 . ±1.7 .B 
uSr'S 20.7:1:5.8 20.5 
'"SI ,.s 22.5i6.1 28iS 23.2 
OG 4.3-4 
~ffi 
67c 
Fig.3 
S  
   
38.2±5.6 
61.8±5.1 
94.4 
2.8tO.6 
2.7±0.6 
54.7 
10.6i2.l 
34.7%4.0 
64.S 
17.5:1:2.6 
17 .712.4 
2.2i1.8 
97.8 
88.7 
5.9i1.8 
5.411.5 
69.9 
14.5:tl.9 
15.6±4.1 
63.7 
Predicted* 
"""""l2.'b-
2.612.0 12.8 
31.41S.7 38.9 
0.0 0.0 
2.2:1:2.2 5.7 
46.9 30.8 
4.1:1:2.7 6.2 
23.8:t6.6 22.0 
14.3±5.1 19.5 
10.9:1:4.4 21.2 
mic l
a  
(X) ( ) 
O. :tD.6 
O.7:t0.6 
.114.5 .3 
6.9:t9.0 2.2 
. :1:4.6 2.9 
 . :t4.0 4.2 
. :1:2.7 .1 
. :t2.3 .4 
O.b6.4 O.S 
. 7±6. 7 .4 


Cosmic ray isotope measurements with a new Cerenkov X total energy telescope

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