V01ume 184, num6er 2,3
PHY51C5LE77ER5 8
29 January 1987
5P1N5 0 F 12C + 12C R E 5 0 N A N C E 5 V1A 7 H E 12C(12C, aa)160 REAC710N W.D.M. RAE, P.R. KEEL1N6 and 5.C. A L L C 0 C K
Department 0fNuc1earPhy51c5,Ke61eR0ad, 0xf0rd 0X1 3RH, UK Rece1ved25 Au9u5t 1986
We have mea5ured the 5p1n50f 12C+•2C re50nance5wh1chdecayt0 the 9r0und 5tate 0f 160 v1a exc1ted5tate5 0f 2°Ne u51n9a n0ve1 a-a an9u1ar c0rre1at10n9e0metry. 8etween EcM= 19 and 27 MeV we f1ndthat 5p1n50f 12 and 14 d0m1nate many 0f the re50nant cr0555ect10n5. We 065erve 4ua11tat1ve1yd1fferent re5u1t5f0r a-decay5v1a the 10w1y1n96and5 1n 2°Neand th05e wh1ch pr0ceed v1a the 18.54 MeV 8+ 5tate 1n 2°Ne. We 1nterpret 0ur re5u1t51n term5 0f N11550n5trut1n5kyca1cu1at10n5and recent ac1u5term0de1ca1cu1at10n5f0r 24M9.
7he 0r191n 0f the re50nance5 065erved 1n ~2C+ 12C 5catter1n9 15 0ne 0f the m05t 1ntr19u1n9 pr061em5 1n nuc1ear phy51c5 [1 ]. Narr0w re50nance5 were f1r5t 065erved 6e10w the C0u10m6 6arr1er [ 1,2 ] 6ut are n0w kn0wn t0 ex15t we11 a60ve the 6arr1er [ 1,3-6]. 7he recent 065ervat10n that many 0fthe re50nance5 a60ve the 6arr1er decay n0n-5tat15t1ca11y t0 exc1ted 5tate5 0f 2°Ne 15 part1cu1ar1y 1ntere5t1n9 a51t 5upp0rt5 an 1nterpretat10n 0f the5e re50nance5 1n term5 0f 5hape 150mer1c 5tate5 1n 24M9 [3]. H0wever, 5p1n mea5urement5 are nece55ary t0 c0rre1ate the re50nance5 wh1ch decay v1a exc1ted 5tate5 0f 20Ne w1th 0ther data where many 5p1n5 have 6een mea5ured 6y c0nvent10na1 techn14ue5 [4-6 ]. F0r 5tate5 1n 20Ne wh1ch them5e1ve5 a-decay t0 the 160 0+ 9r0und 5tate a - a an9u1ar c0rre1at10n mea5urement5 can y1e1d 1nf0rmat10n 0n the re50nance 5p1n5 [ 7 ]. 7he u5e 0f a - a an9u1ar c0rre1at10n5 t0 mea5ure 5p1n5 0f a pr1mary c0mp0und nuc1eu5 15 a n0ve1 app11cat10n 0f the techn14ue and re4u1re5 50me e1uc1dat10n, 0 n e 0f the ear11e5t app11cat10n5 0f the a - a an9u1ar c0rre1at10n techn14ue wa5 t0 mea5ure 5p1n5 0f 2°Ne v1a th15 5ame react10n [ 8 ]. 1n the5e exper1ment5 the pr1mary a-part1c1e (a1) wa5 detected at a centre 0f ma55 an91e t21 = 0 ° and then the an9u1ar c0rre1at10n 0f the 5ec0ndary a-part1c1e (a2) 15 pr0p0rt10na1 t0 1PJ,(t22) 12 where J~ 15 the 5p1n 0f 2°Ne and t22 15 the an91e 6etween the a2-160 re1at1ve ve10c1ty and the 6eam d1rect10n. H0wever there are 0ther 5pec1a19e0metr1e5 [7]. 1ft22=0 °- (0r 180 ° ) the 0370-2693/87/$ 03.50 • E15ev1er 5C1enCe Pu6115her5 8.V. (N0rth-H011and Phy51c5 Pu6115h1n9 D1v1510n)
an9u1ar C0rre1at10n 0f a1 determ1ne5 the re1at1ve 0r61ta1 an9u1ar m0mentum, 11, 6etween the pr1mary a-part1C1e and the 2°Ne nUC1eu5, wh11e 1f 12~=t•22 (0r Q1=122+180 °) the an9U1ar C0rre1at10n 15 pr0p0rt10na1 t0 1PJ0(t21) 12 where J0 15 the 5p1n 0 f t h e pr1mary re50nance 1n 24M9. 7h15 1atter re5u1t can 6e under5t00d a5 f0110w5: 5 1 n c e t2~=t22 (0r t21 = 922+ 180 ° ) the re1at1ve 0r61ta1 an9u1ar m0mentum 6etween the tw0 a,part1c1e5 mu5t 6e 1dent1ca11y 2er0. 7hu5 the an9u1ar d15tr16ut10n 0f the tw0 a-part1c1e5 a5 a funct10n 0f ~21 mu5t 6e 1dent1ca1 t0 that wh1ch w0u1d have 6een 06ta1ned 1n the ca5e 0f decay v1a a 51n91e 5p1n-2er0 part1c1e. 1n th15 w0rk we u5e the 9e0metry ~¢~1~ ~2 "~-180 ° and the effect5 0f the f1n1te an9U1ar aCCeptanCe are 1nC1Uded 1n the the0ret1Ca1 an9u1ar C0rre1at10n Ca1CU1at10n5. 7he exper1ment5 Were perf0rmed U51n9 12C 6eam5 fr0m the 0Xf0rd F01ded 7andem aCCe1erat0r. We U5ed natura1 C tar9et5 0f n0m1na1 th1Ckne55 25 #rn/Cm 2 0n Wh1Ch a 5/dCm 2 197AU 1ayer wa5 dep051ted. 7he a-part1c1e5 were detected 1n c01nc1dence u51n9 tw0 5 cm 10n9 p051t10n 5en51t1ve 5111c0ndetect0r5 wh1ch were p051t10ned 11 cm fr0m the tar9et 0n 0pp051te 51de5 0f the 6eam. 7he p051t10n re501ut10n 0fthe detect0r5 wa5 6etter than 0.5 mm, h0wever the 0vera11 1a60rat0ry an9u1ar re501ut10n 0f A 0 L = 0 . 6 ° wa5 d0m1nated 6y the 1 mm d1ameter 0f the c0111mated 12C 6eam. A my1ar a650r6er wa5 p1aced 1n fr0nt 0f the detect0r at the m05t f0rward 1a60rat0ry an91e5 t0 5t0p e1a5t1ca11y 5cattered 12C nuc1e1. 0 n e 133
V01ume 184, num6er 2,3
PHY51C5 LE77ER5 8
detect0r c0vered the an9u1ar ran9e 15 ° ~ 0v <~60 ° 1n 3 0r 4 5eparate an9u1ar 5ett1n95 wh11e the 0ther detect0r c0vered the ran9e - 6 0 ° ~ < 0 5 ~ < - 1 2 0 ° 0n the 0pp051te 51de 0f the 6eam 1n 3 0r 4 an9u1ar 5ett1n95. Rutherf0rd 5catter1n9 0ff 11C and 197AU Wa5 m0n1t0red 6y a 5eparate detect0r t0 check re1at1ve 6eam n0rma112at10n and t0 m0n1t0r the tar9et th1ckne55. 1n f19. 1a we 5h0w a typ1ca1 three-60dy Q-va1ue 5pectrum, Q3. 7he 0vera11 Q3 re501ut10n wa5 500 keV. 7he peak5 1n th15 5pectrum c0rre5p0nd t0 5tate5 1n 160. 7h15 5pectrum wa5 ca1cu1ated u51n9 the m1551n9 m0mentum 6y a55um1n9 that the tw0 part1c1e5 detected 1n c01nc1dence were a-part1c1e5. 1n f19. 16 we 5h0w a typ1ca1 tw0-60dy Q-va1ue 5pectrum Q2 9ated 6y the 160 9r0und 5tate peak 1n the Q3 5pectrum. 7h15 f19ure wa5 9enerated 6y a55um1n9 that the a-part1c1e detected 1n the 6ackward detect0r wa5 the pr1mary a-part1c1e and app1y1n9 k1nemat1c c0rrect10n5 t0 the mea5ured ener9y. 7he f1na1 ener9y re501ut10n ach1eved wa5 typ1ca11y 125 keV. Pr0m1nent peak5 have 6een 1a6e11ed 6y the1r exc1tat10n ener9y 1n 2°Ne. M05t 0f the 6r0ader peak5 1n th15 5pectrum c0rre5p0nd t0 event5 1n wh1ch the a-part1c1e 1n the f0rward detect0r wa5 the pr1mary a-part1c1e [ 9 ], 1n the Q2 5pectra 9ated 6y the 6.92 and 7.12 MeV 5tate5 1n 160 we 065erve peak5 at 15.16 MeV and at 18.5 MeV at certa1n centre 0f ma55 ener91e5. 7he5e are pr06a61y the 15.159 MeV 6 + and 18.538 MeV 8 + 5tate5 wh1ch have 6een a5519ned t0 the K=02- 6and 1n 2°Ne [ 10]. 7he 15.159 MeV 5tate wa5 n0t 065erved 5tr0n91y 1n the 1nc1u51ve data 0f ref. [ 3 ]. 1n f19. 1c we 5h0w a typ1ca1 a-¢~ an9u1ar c0rre1at10n 1n c0nt0ur f0rm. We u5e 0ur c0nvent10na1 an9u1ar def1n1t10n5 [ 11 ]. Here 0* 15 the centre 0f ma55 an91e 0f the exc1ted 2°Ne nuc1eu5 (0*=121 + 180 ° ) and 9t ( = - 9 2 2 ) 15 the an91e 6etween the a2-160 re1at1ve ve10c1ty and the 6eam d1rect10n. 1n f19. 1d we 5h0w the data 0f f19. 1c avera9ed a10n9 a d1rect10n para11e1 t0 the r1d9e5 1n the data and 1a6e11ed 6y the va1ue 0f 0* at the 1nter5ect10n w1th the 0 * = - ~ 11ne. 7h15 15 51m11ar t0 the pr0cedure u5ed 1n ref. [ 11 ]. We have f1tted the5e an9u1ar c0rre1at10n data u51n9 a 9enera1 f0rma115m [ 12 ]
134
29 January 1987
d 2 0"
d/2~ dt2~,
0~ ~u~T~I(J1m111--m11J00) [1
X 3hJ y h ( 0 , ) d ~ 1 0 ( ~ 1 ) 2 J0 7he 5h5, are parameter5 1n 0ur f1t wh1ch determ1ne the amp11tude5 and pha5e5 0f the d1fferent c0ntr16ut10n5 t0 the decay pr0ce55. 70 51mp11fy the f1tt1n9 pr0cedure we have made certa1n appr0x1mat10n5: (a) 0n1y 0ne va1ue 0f/1 = J 0 - J 1 151nc1uded 1n the f1t f0r each 5p1n J0 1n 24M9. 7h15 15 a rea50na61e a55umpt10n 51nce 1t 15 11ke1ythat 6arr1er penetrat10n fact0r5 d0m1nate the 065erved a-w1dth5. (6) 0n1y 0ne 1ntermed1ate d15crete 5tate w1th 5p1n J1 1n 2°Ne 15 c0ntr16ut1n9. (c) A max1mum 0f three re50nance5 1n 24M9 are c0ntr16ut1n9 at any 0ne EcM. 1n f19. 2a we 5h0w 5evera1 f1t5 t0 an9u1ar c0rre1at10n data, 7he 4ua11ty 0fthe5e f1t5 5u99e5t5 that m05t 0f 0ur appr0x1mat10n5 are rea50na61y va11d. 1ndeed 51nce 0ur data 1nc1ude the 5pec1a1 an91e5 0 ° = - ~ where the an9u1ar c0rre1at10n depend5 0n1y 0n J0 [ 7 ] 0r data are 1ar9e1y 1n5en51t1ve t0 11, the a1-2°Ne re1at1ve an9u1ar m0mentum, and adm1xture5 0f 0ther J1 va1ue5.1n f19. 26 we p10t 15~t°J,12 a5 a funct10n 0fEcM. We 065erve 5harp re50nance-11ke feature5, the d0m1nant 5p1n5 6e1n9 J0 = 12 and 14. Near the re50nance5, where 0ne 5p1n d0m1nate5 we 6e11eve 0ur f1t5 t0 6e un14ue. Away fr0m the re50nance5 we c0u1d f1nd 0cca510na11y tw0 0r m0re 5et5 0f 5p1n5 wh1ch y1e1ded 51m11ar22. 1n the5e c1rcum5tance5 we have ch05en the 5p1n5 wh05e amp11tude5 var1ed m05t 5m00th1y w1th ener9y. We 06ta1n 4ua11tat1ve1y 51m11ar re5u1t5 fr0m f1t5 t0 an9u1ar c0rre1at10n data f0r decay5 pr0ceed1n9 v1a the 9,03 MeV 4 + and 8.78 MeV 6 + 5tate5 1n 2°Ne. 7he d0m1nant 5p1n5 are a9a1n J0 = 12 and 14 a1th0u9h there 15 50me ev1dence f0r J0 = 16 near EcM = 25 MeV fr0m the f1t5 t0 the 8.78 MeV 6 + data. We 5ummar15e 0ur re5u1t51n ta61e 1 where we make c0mpar150n5 w1th 0ther w 0 r k [ 4 - 6 ]. Led0ux et a1. [ 3 ] 5u99e5ted that the5e re50nance5 are a c0nt1nuat10n 0f the 6arr1er re50nance5 1n 24M9 [ 1 ]. Led0ux et a1. a150 1nterpreted the re50nance5 a5 5tate5 a550c1ated w1th the tr1ax1a1 (e = 1.26, y = 42 ° ) m1n1mum 1n the N11550n 5trut1n5ky (N5) ca1cu1a-
V01ume 184, num6er 2,3
PHY51C5 LE77ER5 8
1/~40
12C (12C,C~C[,) 95.
ECM
= 29
29 January 1987
12C ( 12C,0, 0t ) 66005
160
MeV
C)
613 MeV {3-)
An9utQr C0rretC1f10n
9.03 MeV 4 +
6.05 MeV ( 0 +)
20
, EcM =
19.5MeV
4J
100
-20 960
Q) 160 5pectrum (03)
tJ
e"
6 92MeV
(2 +) MeV (1-)
0 tJ
712
/,80
-100
10 36 MeV 0.61
{{+
,• t
0.~-
0
0
1
1
1
,
1
1
( L,+)~ 11.10MeV
,36,0~-, ~,
20
f1t1 1 40
{
~ t
1 ,
60
,
8
d)
100
-~* ( de9
-Q3 (ch0nnet5)
12C(12C,a.0t) 160 9.5. 2•80
Ec~M=19 MeV
6)
2°Ne 5pecfrum (02) 903
(t,•)
==
.
8 1195
1213
c 12/-,0 8~/8 1
16*) 1
0 LJ
782 N 717(2*]1 }1
5,2
t 3-)
0
~°~A 11] .3•.4 ,v
280 -02 (ch0nne15)
560
F19. 1. (a) A three-60dy Q-va1ue 5pectrum f0r the 12C(12C,eta) 160 react10n. 7he peak5 1n th15 5pectrum are 1a6e11ed 6y exc1tat10n ener9y 1n 160. (6) A tw0-60dy Q-va1ue 5pectrum 9ated 6y the 160 9r0und 5tate 1n Q3. 7he (narr0w) peak5 1n th15 5pectrum are 1a6e11ed 6y exc1tat10n ener9y 1n 2°Ne. F0r an exp1anat10n 0f the un1a6e11ed (6r0ader) peak5 5ee text. (c) A typ1ca1 tt-tt an9u1ar c0rre1at10n 1n c0nt0ur f0rm 9ated 6y the 9r0und 5tate peak 0f 160 1n Q3 and the 9.03 MeV 4 + 5tate 0f2°Ne 1n the (22 5pectrum. 0* and {u are def1ned 1n the text. 7he max1ma 1n the an9u1ar c0rre1at10n are cr055-hatched. ( d ) 7he an9u1ar c0rre1at10n 0f (e) pr0jeeted 0nt0 the 0* = - ~ 11ne (5ee text and ref. [ 11 ]).
135
V01ume 184, num6er 2,3
PHY51C5 L E 7 7 E R 5 8
29 January 1987
0) 11.59 MeV 8+
6) 11 9 5 MeV 8 + 1
ECM= 2~).50 MeV
0./* 02 0 0.~.
Ec.:20.25MeV
6
0.2
2~ E
2
0
0
EcM.=20.00 MeV 5j °
2 12
,~ j~ ~
~ : 12
10 8
0
EcM = 19.75 MeV
6
0.2
2 0
0 0.2,
6 /,
Ec r4 = 19.50 MeV
- -
1
0 ~:10 •
0.2 0 10
50
90
130
18
170
20
22 24 Ec.M(MeV)
0••" ( de9. )
f=16
26
28
F19. 2. (a) An9u1ar c0rre1at10n5 f0r decay5 wh1ch pr0ceed v1a the 11.95 MeV 5tate 1n 2°Ne pr0jected 0nt0 the 0 * = -~u 11ne (5ee text). Data f0r 0 * < 9 0 ° c0rre5p0nd t0 the pr1mary u-part1c1e 6e1n9 detected at 6ackward an91e5; f0r 0*> 90 ° the pr1mary ct wa5 detected at f0rward an91e5. 7 h e the0ret1ca1 ca1cu1at10n51nc1ude the exper1menta1 ener9y and an91e thre5h01d5 and have 6een avera9ed 1dent1ca11y t0 the data (5ee ref. [ 11]). (6) 7 h e m0du1u5 54uared 0f the react10n amp11tude5 15~,j, J0 12, a5 a funct10n 0 f centre 0f ma55 ener9y, Ecw, deduced fr0m f1t5 t0 t h e data. Here we 5h0w data f0r decay5 pr0ceed1n9 v1a the 11.95 MeV 8 + 5tate 1n 2°Ne t0 the 9r0und 5tate 0f 160.
7a61e 1 Re50nance51n 12C( 12C, 0.0.) 16095 7h15 w0rk
EcM 19.5 19.5 20.25-20.5 (22.0 22.25-22.5 23.0-23.5 (24.25-24.5 24.75 25.75 a)
0 t h e r w0rk
J~
Channe1 ~)
EcM
J~
12 + 14 + 14 + 12 + 14 + (12 + ) 12:-, 14 + (12 + ) (14% 16 + ) 14 +, (16 + )
a, 6 a, 6 a, 6, c 6, c 6, c 6, c a, 6 a a, 6, c a, 6
19.2 19.8 20.2
12 + 6) 14 + c) 12 +, 14 + 6)
-) 22.5 23.3 -) 24.7 25.95
12 + d) 14 + a) 14 + d) 14+a)
a v1a 8.78 MeV 6 + 1n 2°Ne, 6 v1a 9.03 MeV 4 + 1n 2°Ne, cv1a 11.95 MeV 8 + 1n 2°Ne.
~ Ref. [6]. c) Ref~ [5]. d) Ref. [4]. t10n5 0f Leander and Lar550n [ 13]. Recent ca1cu1at10n5 u51n9 the ct-c1u5ter m0de1 [ 14 ] 5u99e5t that the 6arr1er re50nance5 are 6etter de5cr16ed 6y the ref1ect10n a5ymmetr1c m1n1mum 1n the N 5 ca1cu1at10n5. 0 u r 065ervat10n5 0f 5p1n5 0f 12 and 14 are n0t 1nc0n136
515tent w1th th151nterpretat10n [ 14], a1th0u9h the 14 + re50nance5 near E c M = 2 0 MeV and the 16 + re50nance near E 7 M = 25 MeV d0 n0t f1t ea511y 1nt0 the5e 5y5temat1c5. 1n c0ntra5t t0 the a60ve re5u1t5 we 065erve a 4u1te
v01ume 184, num6er 2,3
PHY51c5 LE77ER5 8
d1fferent 6ehav10ur f0r the a-decay5 wh1ch pr0ceed v1a the 18.54 M e V 8 + 5tate 1n 2°Ne. 1n f19. 3a we pre5ent the avera9e cr055 5ect10n5 mea5ured f0r the 8.78 M e V 6 +, 9.04 M e V 4 + a n d 11.95 M e V 8 + 5tate 1n 2°Ne (decay1n9 t0 the 9r0und 5tate 0 f 160) wh11e 1n f19, 36 we c 0 m p a r e the avera9e cr055 5ect10n f0r the 15.16 M e V 6 + a n d 18.54 M e V 8 + 5tate5 (decay1n9 t0 the 6.92 0r 7.12 M e V 5tate51n 160). 7 h e d a t a f0r the 18.54 M e V 8 + 5tate 5h0w 1n add1t10n t0 1ntermed1ate 5tructure re50nance5 a 51n91e 6 r 0 a d 5tructure wh1ch peak5 at E c M ~ 25 MeV. 1t 15 tempt1n9 t0 a550c1ate th15 6 r 0 a d 5tructure w1th the 9r055 5tructure re50nance 065erved 1n 12C+ 12C 1ne1a5t1c 5catter1n9 at a 51m11ar centre 0 f ma55 ener9y [ 15 ]. 7 h e a-c1u5ter m0de1 [ 14] 5u99e5t5 that the5e 1ne1a5t1c 5catter1n9 re50nance5 are a550c1ated w1th the
a)
29 January 1987
h19h1y d e f 0 r m e d tr1ax1a1 m1n1mum 1n the N 5 ca1cu1at10n5 [ 13]. 0 u r 065ervat10n 0f the5e 9r055 5tructure re50nance5 decay1n9 v1a the 18.54 M e V 5tate 1n 2°Ne 5u99e5t5 that th15 5tate 1n 2°Ne m a y 6e a550c1ated w1th the h19h1y d e f 0 r m e d tr1ax1a1 6 a n d pred1cted 1n that nuc1eu5 [ 13 ]. 1n c0nc1u510n we have u5ed a n0ve1 app11cat10n 0 f a - a an9u1ar c0rre1at10n mea5urement5 t0 determ1ne 5p1n5 0 f ~2C+1=C re50nance5, 7 h e re50nance5 065erved 1n 0ur d a t a c0rre1ate we11 w1th th05e wh1ch have 6een 065erved prev10u51y. 7 h e re50nance5 065erved 1n 12C( 12C, a)2°Ne 6etween E c M = 19 a n d 27 M e V are d0m1nated 6y 5p1n5 0 f 12 a n d 14.7he5e re5u1t5 are c0n515tent w1th recent pred1ct10n5 0 f an ac1u5ter m0de1 0 f 24M9. We 065erved 4ua11tat1ve1y d1fferent re5u1t5 f0r decay5 v1a the 10w 1y1n9 r0ta-
12 C (12C,C(
12C(12C,ct 6),160 9.5. 1
1
1
C( ) 16016.92 1
1
2+ 7.121 ~ ]
L
1
18.54 MeV
8.78 M 0 V
8•
0.10 01023
0.05 t0
t0
E
/~.
E 1
0
1
1
0.018
1
.03 MeV ~+~ 0.2 9
0.013
4--
9m
15.16 Mev
0.1 0.04 0
2 ~
0
>,
0.15
u
11.95 MeV
0
0.03
0J
0.02
0.10 0.05
0.01 0 18
20
22
2/, EC.M (MeV)
26
28
18
2~0
2•2 2•4 Ec.~ (MeV)
2r6
28
F19. 3. (a) Avera9e mea5ured cr055 5ect10n5 f0r decay5 pr0ceed1n9 t0 the 9r0und 5tate 0f ~60 v1a the 8.78, 9.04 and 11.95 Mev 5tate51n 2°Ne a5 a funct10n 0fEcM. Here the err0r 6ar5 are 5ma11erthan the 512e0fthe data p01nt5. (6) Avera9e mea5ured cr055 5ect10n5f0r decay5 pr0ceed1n9 t0 the 6.92/7.12 Mev 5tate51n ~60 v1a the 15.16 and 18.54 Mev 5tate5 1n 2°Ne a5 a funct10n 0f Ecra. 8e10w EcM= 23.5 Mev the 18.54 Mev 5tate can n0t 6e 1dent1f1ed1n the (22 5pectrum. 137
V01ume 184, num6er 2,3
PHY51C5 LE77ER5 8
t10na1 6and5 1n 20Ne a n d decay5 Wh1Ch pr0Ceed v1a the 18.54 M e V 8 + 5tate 1n 2°Ne. 0 U r d a t a 5Upp0rt the 1nterpretat10n 0 f ~2C + 12C re50nance51n term5 0 f 5hape 150mer1C 5tate51n 26M9.
ReferenCe5 [ 1 ] K.A. Er6 and D.A. 8r0m1ey, 7reat15e 0n heavy 10n 5c1ence, V01. 3 (P1enum, New Y0rk, 1984) p. 201. [2 ] E. A1m4v15tet a1., Phy5. Rev. 1ett. 4 (1960) 515. [3] R.J. Led0ux et a1., Phy5. Rev. C 30 (1984) 866. [4] E.R. C05man et a1., Phy5. Rev. C 21 (1980) 2111.
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29 January 1987
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