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The B10(He3, pα)2He4 reaction
Volume 12. number 1
]PHYSIC~ L E T T I ~ h S
TI|E
t ~m,h~r
l~4
BlOt|tie 3, pcc)2lle" { t t ~ A C T I O N
J. E. ETT~R, M, ~. V4AGC~)NER, H.D. HOLMGI~EN~ C, MOAZED and A, A, JAFFI~
U~t~er,~tfy of Mar~'~ ~ * Colle£'e P~lrk, Mar)lc~J Roc'e|vod 20 July I~4,
The bombardment oi B 10 with He 3 can lead to a four-body final state, consisting of one 9roton and three ~ particles, even at low bombarding energies. The question eoncer,~ing tLe nature of the process by which tl'dsfour-body final state is for~ned~ that is, whether the reaction proceeds to the tour-body final state by a single-stage, quasiinstantaneous breakup or by a series of sequential processes - or in bo~ mannfrs - is of l~Lrtlcular interest. The 1ollowmg sequtnttal processes are energetically possible at low born"bardln~ esergzen:
F
p+C12~a1+Beg~a2+c~3
~*al+B9 BI0+He3~
~
(1)
p+Be 8 ~ a 2 ~ a 3 (H)
~c~2+Li5 ~ a 3 + p
(HI)
~.Li5+Be 8 ~ a 2 • ~
Lp.~t
(Iv)
For a reaetmn which proceeds to a feur-i~od', final state it zs possible to specify cot .iletaly the nature or state of the mter.nedaat', s j s t e m s by the measuxement of the energies and darections of two particles m coincidence, /~ ,, E2~ 01, ~2. However~ if the relative momentu~ of the two unobserved particles corresponds to a d~screte state (or reso:~nce) in the inte.medtale system, the third body, then the kinematic I:~havlour of the two observed particles zs the same as m ~he case of a three-b~dy final state - even ~'bough the third body may eventually break up rote two o r more par~mtes, ha such cases a kinematic curve w~tl apFear m the ~ o - d a m e n s m n a i energy spectrmn El(E2) corresponding to each available state of the third body. The curve will be broadened into a band when the state i s broad. The various states of intermedmte s y s t e m s in the ssquential processes wluch lead to this eflecttve three-body final ~tate will appear as points (segments ior broa~ s:aLes) on th~ ki~emat~c curve correspondxng to the three-body final state. When the relative motion of the two unobserw~i 42
p a r t i c l e s does n ~ correspond to = s t a l e of the third body~ the 1o¢t hat the variou~ a~lt~er~ia~ proeeszes on ~h~ two-d/raenaiom~l etmr-gy spectrum are r~omewhat less narrowly ro~rlc~l~ though kinematics ~till Ilm~. each ~ q u e ~ t i a l process to certain r e g m n s of the a p e e t r ~ . The k ' - ~ m a t m r e g i o n s associated with a glve~ p r o c e s s , . s a g e in a c h a r a c t e r i s t i c rammer with the. angles at which the p a r t i c l e s a r e ob6erved. The e~anges in shape and size, a s well aB the position of tim region, OROn ~ t b l e one to l&Ynti~ the proce~s ~ s ¢ ~ t a l e d vdth fl-~ reglov. In our initial study of the Bl0(He3,pa)2He 4 r e action we have chosen to m e a s u r e the energy and direchon of the protcs~ and one of the ~ p a r h c l e s . Two sohd state de,.~cturs were used, one placed at ~p and one at 0a , Fig, i r e p r e s e n t s a two-dthmnsional e~terg?? spectrUmEp(Ea~ at fixed .ap and 0~r for coincident ( e e n ~ observed in the'two detectors. This particmar figure is for 0p = +60o, 0a = .100o and a bombarding energy of 2.45 MeV. The picture was obtained by applyir g the s i g n a l from the p r o ton detector to the x axis and the s i g n a l f r o m the a-particle detector to the y "axisof anxy oscilloscope a~d intensifying the t r a c e whene~er a coincidence occurred between the two signals. Although low energy protons were observed in the spectm.u~ of the a - p a r t i c l e detector at e a these events did not cause any ec:,fusion in the two chmenslonat energy spectrum sL'~ee the a p a r t i c l e s coincident with such events could not be detected in the detector at 0,~. The B 10 (He3, 2 p ) B l l reaction ~e the only competing r e action which could be observed in t~m two-dimensional energy spectrum of coincident events. Fig. 2 shows the kinematic regions, for the s a m e combination of angles and bombarding energy as fig. I, for sequential processes of the types (ID, OH) and (IV) through all _~ergettcally * Research s~aported in part by the U.S.Atomic Ener'~Commission.
V~ume 1~, ~um~ber I
PHYSICS L~TTERS
I September 1964
~
• ÷SO*
~o.-ioo"
S
~
/
8e~Sa
s~
i ~ . 1. The ezperime~tl two-dtmeelonal energy spectrum of calnc~$ent proton and ~ l ~ ' t t e l e from the reactim~ B10(lie3,p~)2H~ 4 at eo ~ +60o, 9. = -100 ° for a bombarding e ~ r g y of 2.4~"MeV a c c e s s i b l e combinations of i n t e r m e d i a ~ states and for a l l combinations of observed ~ partte]e (~1, ~ 2 o r ~3) in coincidence with the proton~ Each kinematic region in this figure i s labell,.~i and the corresponding s e r i e s of sequentml proc e s s e s , s t a t e s of the intermechate systemL ~'~d the p a r t i c l e s observed a r e given in table 1. The sequential ser~es of ~he type (I) yield kinemattc c u r v e s on the two-dimeesional energy spectr,~m which are Just vertical lines, i.e., discrete-~morgy proton groups observed at 0 . associa~l,c with the forrnation of C 12 in the v~arioas accessible excited states. T h e positions of these proton groups a r e indicated along ~ ~,,c'~on enc:,,V axis in, fig. 2 and labelled ~,ith ~ e appropriate energy of e g c i t a h e n of C 12. If a p a r t i c u l a r state of C12 decays by the em~.esion of an a p a r t i c l e leaving the two r e m a i n i n g ~ p a r t i c l e s in a state of Be s and i f the f i r s t ~t p~rttcle i s observed at the angle 0a, the event would appear at the i n t e r section of the vertical line corresponding to t h e state of C 12 with the kinematic curve corresponding to the state of B e 8 which is formed. Events in which one of the a particles f r o m the breakup of the B e 8 is seen instead are restricted to other s e g m e n t s of the v e r t i c a l line, In many cases the kinematic segments overlap.
Fig, 2. The calonla~ed two--dimensiov~l energy s~e¢ tram of coinclde~t particles from the reaction B 0 (He3,p.~)2He4 st 8v = +60 °. 0. ----!0~ for s bcm~---~aIng ez~ergy Of 2 45"MoV~ The process oorrespo~ix~ to each kmemahc region is indicated by a letter e ~ l a ~ m ~ , t in table 1. The posltmn of each of the discrete-~ner~ proton group~ produced by process I ts mdtcate~ b~ st" arrow along the Eu axis lab~dod with the ener~ ~t ex~Itatlon of the s.~sontated state of C12 Th~ ~er~i¢~l line passing thron~ h Ep = 3 MoV repreaonts ~he m~%1 ~ mum energy proton wKlch can pass through the sbo sorber in front of the proton detector, and ~e~eh,~ that region of the .'wo-dimensional spectrum c,f ~ which is excluded in the experime~tel elA~ctr,,m~ fig. 1, Table I Reaction
Particles
B9
II
P=I
2.34
H
P~2
2.34
g. s g
Bt-~
I t:~
e
11
P~2
II ,6"
g, w,
g h
III HI
lrl P:2
2.3t 2.34
"~ -~
t |
j k
tli III
P~I 1~ 2
11.6~ 11 62
---
~ . #
m n o P
IV D/ IV IV
P~I P"l P~I
~ -"
Z.~ g" ~
| 1
P~2
"" ~
~ ~ g ~
S ~
r
IV
Iz:2
--
~, •
j
-,
-
s,
{ 2"~ t
O
Volume 12, number 1
PIIYSICS LETTgRS
Under the experimezltal conditions of our m e a s u r e m e n t s and at a oombardmg enert,~' of 2.45 MeV effects ccald have been observed due to states of C 12 m the range of excitation ee~r~y extending f r o m about 10,5 to 18 MeV, el 139 fr~z,~ 0 to 12.5 MeW, of Fc 8 from 0 to 8 MeV, and ¢,f Lt 5 f r o m 0 to 1 ~ M, V. Comparison of fig, 1 ~ith fig. 2 and in part~e ular a comparison e t sueh f i g u r e s at varlotm m~gles, enables one to identify many of the v a r i o u s p r o c e s s e s which cat. ,~ccur. The allowed kinematic r e g m n s on the experimental s p e c t r u m of fig. 1 a r e of course broadened, compared to those of fig. 2, by level widths: t a r g e t thickness and the hnfte *~hd angles of the detectors. Vertical lines~ proton groups f r o m reactions of type (D for a number of s t a t e s of C 12, a r e clearly seen in hg. 1, and a r e labelled with the energy of excitation of the corresponding state of C12. Along the vertical, E a , axis the expected posltionJ of the ~ - particle groups f r o m reactions of type (H) and (HI), where a 1 m detected, a r e mdmated for the 2.34 MeV P~d 11.62 MeV states of E 9 previously observed m the B10(He 3, c0B9 reaction 1), T : o r e is no evidence for the f o r m a ben of other states m B9 between these two s t a t e s * . The intense horizontal hne n e a r the position c o r responding to the formation of the 11.62 MeV state of B9 m p r i m a r i l y due to accidental come,done es between He 3 particles elantically s e a t tered at 0c~ and r e a c h o n protons at ~p. The r a t h e r intense spot on this hoe n e a r the mtersectlon of the 15.11 MeV proton group a r i s e s mainly f r o m 2uch accidental events in which the protons a r e due to the C12(He 3, Po)N 14 rea~hon m the carbon foil target baekmg. No evidence is seen for the decay of the 15.11 MeY state of C 12 to either the ground o r f i r s t excited state of Be 8 or :(or the direct breakup of this state rote three a particles. The Be8(g.s.) ~nematxc curve and the Be8(2.9) Mnemahc band a r e also clearly vmxble hi h g , I. The ruther large w~dth of the 2.9 MeV state of Bet(the L = 2 a - a scattering resonance) broadens ~ts curve rote a band. The v e r y l a r g e #idth of the 11.4 MeV state of BeS(the L = 4, a-c~ resonance) and the restrmtion due to the available energy produces a kinematic r e , o n in the low e n e r g y corner of the two-dimensional e n e r g y spectrum. Little can be said a b o ~ this :(tom h g . 1. The hormontal line rozrespondmg to ".lie mite,1 * The broad peak observed m me a particle sty,strum from thin reaction at aa energy, correepondthg to a state m B9 at about 2.5:t MeV set, tally is due *o the B{0(He3,p)C 12 reacttou to the 16 11 MeV lcvol of C 2 in ~Meh the observed ~ part, cle resu!t~ ~rom the decay of th~ level to the ground state of Be? 44
£ ~rrcff.tmr ~:~64,
e~at~s]G~] Ji ~rl t~ p~rtlci~, whl~h i~ ~k-tec~tg#.1 zd 0(~ * with tht; f~rl~a[~ cl~t ~Jf th~ fLrst ex~ff~d ~t~te cd B E t~q b "~,eis~ri~ ~e~-i: In f ~ I , ~tt c l ~ d ~ i ~
iylm ~ID. Point (a) 1~ the ~ r r e s l ~ i d n ~ kl~e~ m a l l region in fig. 2. The rem~d.nder of the l,ort~ zontai line corre,pc~td~ to the B9(Z.34) decaying by the alternate s e ~ l ~ (l~ Into an a paxtieis and IA5(g.s.) which titan decays tnt~ art ~ p a r t i c l e and the o b s e r v e d proton. The eorrespermhr~g r e galen ,n fig, 2 i s (g). At m a n y e o m b i n a t i a ~ of angle p r o c e s s (g) i s m o r e procmunced ~ at 0p = *80 o, So# ~, -100 o. The total ergitrlb~l*~ f r o m p r o c e s s (g) a p p e a r s to be at iea~t a~ l a r g e ns that from (a). H e n c e the B9(2.34) s y s t e m dec a y s a l a r g e fraction of the t i m e by c~ e m m s i o n leaving Lib~g.s,). The r a t h e r intense broad r e g i o n (r) wideh c o r responds to the reaction B10(He3~ Li5)BeS(g.s,) can also be seen. Other contributions f r o m iMs reaction and s i m i l a r one~ leading to BoB{g,9) a r e possibly indicative* by the Cvmtmtmt~ distrl~ button of events 'along the BeS~g.a.) k i n e m a t i c c u r v e and the E~,,.8(2.9) k i n e m ~ i c band, /~ additlem, the intense a r e a n e a r the intersection of (q) and (o) may he due to thls p r o c e s s , Another intense a r e a i s o b s e r v e d n e a r the m t e r s e c ' i o n of the k i n e m a t i c r e g i o n s (0 and (o). Since p r o c e s s (f) r e s a i t ~ f r o m the reaction p r o ceedmg uV~rough the 11.62 MeV s t a t e of B9, thin intense area m a y suggest that the 11.62 M e V state is ,excited in the p r e s e n t e x p e r i m e n t : Howe v e r , it h a s not been posmbte to identify other contributmns f r o m this state because of the cornpeting p r o c e s s e s which o c c u r Lu the s a m e r e g m n s of the two-damenslonai e n e r g y s p e c t r m n . The l a r g e contribution from reaetlons of the type (IV) is part,cularly interesting. ' I ~ s m a y mdacate timt suc~ reactions proceed by t h e g t c k u o of a neutron and proton f r o m B 10 by the H e O f o r m m g Lz5 wlueh i s often in the f i r s t excAed state. O r possibly the p r o c e s s i s m o r e appropriately d e s c r i b e d a s tile pickup of a neutron by He 3 to f ~ r m an a particle which then i n t e r a c t s strongly with ' a e proton in the final state through the "very broad p~ r e s o n a n c e seen in the elas¢lc s c a t t e r i n g of protons on lie4o Another i n t e r e s t i n g feature of the reaction i s the comparable prohabitittes for r e a e U o n s of type (It) and type (flI) for the 2.34 MeV state of B~v. T M s s u g g e s t s that the a p a r t i c l e reduced width of the 2.34 M.~V state of B 9 m at least com~&rable to the proton reduced width. Iience~ the
V~l~*nd~ 12~ ~ r ~ e r
~
PHYSICS LETTERS
cltmter c . ~ l g u r a t i c a l , Li 5 + ~i~ m a y be of con~td~rabls importance in this state, The lack of ev~".ts in tPm r e g i o n between the B e e ~ . s . ) k i n e m a t i c c u r v e and tim Be8(2,9) klne~,~ttc I ~ d m p a r t i c u l a r s t r i k i n g R i s also apItareet tl~t t h e r e a r e k t ~ i n t e n s i t i e s in v a r i o u s ,treas of tim two-dimemsional s p e c t r u m w h e r e ~ t e W~uld expect eon.trlbt~ions f r o m sequential processes - and f r o m those pro:esees which are perhaps more appropriately described as quasiIns~ntsnemm breakup processes in which the final s t a t e is e t r ~ l y modulated by the i n t e r a c tions b~tween the ~arious c l u s t e r components. T h e s e o b s u r v a t t o n s lead us back to tim question posed at tim beg~ming of this l e t t e r concerning the r ~ J m e r in w M c h the r e a c t i o n p r o c e e d s to the four-body final ,~tate. The general conclusion which one can d r a w f r o m the above o b s e r v a t i o n s i s that the B10(He 3, pa)2He4 reaction p r o c e e d s to the four-body final s t a t e p r i m a r i l y through s e q u s n t m l two-body decays o r by p r o c e s s e s in which two-body mteraction,~ m the final state ~ t r o ~ t y modulate the decay. Another way of looking at the r e s u l t s i s the following : The s y s t e m h a s an e n e r g y which i s
THE
1 September 1964
d e t e r m i n e d by the a r b i t r a r y bombarding energy. One would t h e r e f o r e not expect the c r i t e r i a for resonac,.'e in the two-body interaction of the eoml;onents into which the s y s t e m b r e a k s up to be s a t i s f i e d by all p a i r s of components. One component o r p a i r of components wilt have to s e p a r a t e f r o m the o t h e r s at a non-resonant e n e r g y except, perhaps, m s p e c i a l c a s e s , The r e s u l t s of the e x p e m m e n t indicate that the r e m a i n i n g components a r e left vnth a c h a r a c t e r i s t i c resonant ene r g y . In c a s e the remaaning s y s t e m consists of t h r e e p a r t i c l e s and it undergoes f u r t h e r decay, two of the p a r t i c l e s a r e again left at an appropriate r e l a t i v e e n e r g y to interact strongly. In other words, the total e n e r g y of the s y s t e m appears to be p a r U q o n e d a m o n g the components of the final state in such a m a n n e r that a s many of the components a s p o s s i b l e have a r e l a h v e e n e r g y such that they i n t e r a c t strongly.
l~ef ~re~zce 1) T.R. Fisher and W.Whaling, BuU Am.Phys.Soe. 8 (1963) 598.
Be9(He 3, a)2He 4 REACTION
C. MOAZED, J . E . E T T E R , H.D. HOLMGREN and M. A. WAGGONER Umvers;ty of Ma~,land *. CoUege Park, Maryland Reoetved 27 July 1964 The Q - v a l u e s for many He 3 and tmt~um reduced r e a c t i o n s on light nuclei a r e sufficiently high that it i s p o s s i b l e f o r the s y s t e m s to decay to 3- o r 4-body final s t a t e s . Whenever such a m u l tlbody decay o c c u r s , continua a p p e a r m the s i n g l e p a r t i c l e s p e c t r a f o r the reaction. The study of the single p a r t i c l e s p e c t r a i s frequently inadequate to d e t e r m i n e whether the continua a r e due to s e quentml o r quasi-instantax, eous breakup p r o c e s s e s . If q u a s i - i n s t a n t a n e o u s breakup p r o c e s s e s occ u r at low e n e r g i e s , one would expect such p r o c e s s e s to a p p e a r in the Be9(He 3, a ) 2 H e 4 reaction, since all s t a t e s of the i n t e r m e d i a t e Be S s y s t e m a r e unbound f o r any sequential p r o c e s s e s . In addRion the p a r t i c u l a r l y l a r g e Q - v a l u e f o r 3-body breakup (19.006 MeV) should enhance any q u a m instantaneous b r e a k u p contributlous. Studies of
the s p e c t r a and angular dzstrlbutlons for the Be9(He 3, a)2He 4 reaction at bombardlr~yt~er~;~e~ of 3 and 4 MeV by E r s k m e and Browne ) and Dorenbusch ard Browne 2) have shown the ex~s* fence of a laxg~ continuum m the ~ particle s~,~ t r u m . Dorenbusch and Browne 3) have fitted the shape of t h i s continuum by a s s u m i n g that the * ~action p r o c e e d s p r i m a r i l y by an instant,meows breakap of s t a t e s of the compound nucleus, C 12, into tlu, ee a p a r t i c l e s . The u r l g m of the continuum can, h e ~ e ~ r . uniquely detarmmed for the 3 a-parhcle ttnai state by measuring the energies of t~o ef the ,~ partlcles~ E A and EB, at angl~s t~A a n d , B C,~t * Research supported in part b~ the U 8.Atc~,,, ~ F~,¢I~-~ Comlnlssion.
]PHYSIC~ L E T T I ~ h S
TI|E
t ~m,h~r
l~4
BlOt|tie 3, pcc)2lle" { t t ~ A C T I O N
J. E. ETT~R, M, ~. V4AGC~)NER, H.D. HOLMGI~EN~ C, MOAZED and A, A, JAFFI~
U~t~er,~tfy of Mar~'~ ~ * Colle£'e P~lrk, Mar)lc~J Roc'e|vod 20 July I~4,
The bombardment oi B 10 with He 3 can lead to a four-body final state, consisting of one 9roton and three ~ particles, even at low bombarding energies. The question eoncer,~ing tLe nature of the process by which tl'dsfour-body final state is for~ned~ that is, whether the reaction proceeds to the tour-body final state by a single-stage, quasiinstantaneous breakup or by a series of sequential processes - or in bo~ mannfrs - is of l~Lrtlcular interest. The 1ollowmg sequtnttal processes are energetically possible at low born"bardln~ esergzen:
F
p+C12~a1+Beg~a2+c~3
~*al+B9 BI0+He3~
~
(1)
p+Be 8 ~ a 2 ~ a 3 (H)
~c~2+Li5 ~ a 3 + p
(HI)
~.Li5+Be 8 ~ a 2 • ~
Lp.~t
(Iv)
For a reaetmn which proceeds to a feur-i~od', final state it zs possible to specify cot .iletaly the nature or state of the mter.nedaat', s j s t e m s by the measuxement of the energies and darections of two particles m coincidence, /~ ,, E2~ 01, ~2. However~ if the relative momentu~ of the two unobserved particles corresponds to a d~screte state (or reso:~nce) in the inte.medtale system, the third body, then the kinematic I:~havlour of the two observed particles zs the same as m ~he case of a three-b~dy final state - even ~'bough the third body may eventually break up rote two o r more par~mtes, ha such cases a kinematic curve w~tl apFear m the ~ o - d a m e n s m n a i energy spectrmn El(E2) corresponding to each available state of the third body. The curve will be broadened into a band when the state i s broad. The various states of intermedmte s y s t e m s in the ssquential processes wluch lead to this eflecttve three-body final ~tate will appear as points (segments ior broa~ s:aLes) on th~ ki~emat~c curve correspondxng to the three-body final state. When the relative motion of the two unobserw~i 42
p a r t i c l e s does n ~ correspond to = s t a l e of the third body~ the 1o¢t hat the variou~ a~lt~er~ia~ proeeszes on ~h~ two-d/raenaiom~l etmr-gy spectrum are r~omewhat less narrowly ro~rlc~l~ though kinematics ~till Ilm~. each ~ q u e ~ t i a l process to certain r e g m n s of the a p e e t r ~ . The k ' - ~ m a t m r e g i o n s associated with a glve~ p r o c e s s , . s a g e in a c h a r a c t e r i s t i c rammer with the. angles at which the p a r t i c l e s a r e ob6erved. The e~anges in shape and size, a s well aB the position of tim region, OROn ~ t b l e one to l&Ynti~ the proce~s ~ s ¢ ~ t a l e d vdth fl-~ reglov. In our initial study of the Bl0(He3,pa)2He 4 r e action we have chosen to m e a s u r e the energy and direchon of the protcs~ and one of the ~ p a r h c l e s . Two sohd state de,.~cturs were used, one placed at ~p and one at 0a , Fig, i r e p r e s e n t s a two-dthmnsional e~terg?? spectrUmEp(Ea~ at fixed .ap and 0~r for coincident ( e e n ~ observed in the'two detectors. This particmar figure is for 0p = +60o, 0a = .100o and a bombarding energy of 2.45 MeV. The picture was obtained by applyir g the s i g n a l from the p r o ton detector to the x axis and the s i g n a l f r o m the a-particle detector to the y "axisof anxy oscilloscope a~d intensifying the t r a c e whene~er a coincidence occurred between the two signals. Although low energy protons were observed in the spectm.u~ of the a - p a r t i c l e detector at e a these events did not cause any ec:,fusion in the two chmenslonat energy spectrum sL'~ee the a p a r t i c l e s coincident with such events could not be detected in the detector at 0,~. The B 10 (He3, 2 p ) B l l reaction ~e the only competing r e action which could be observed in t~m two-dimensional energy spectrum of coincident events. Fig. 2 shows the kinematic regions, for the s a m e combination of angles and bombarding energy as fig. I, for sequential processes of the types (ID, OH) and (IV) through all _~ergettcally * Research s~aported in part by the U.S.Atomic Ener'~Commission.
V~ume 1~, ~um~ber I
PHYSICS L~TTERS
I September 1964
~
• ÷SO*
~o.-ioo"
S
~
/
8e~Sa
s~
i ~ . 1. The ezperime~tl two-dtmeelonal energy spectrum of calnc~$ent proton and ~ l ~ ' t t e l e from the reactim~ B10(lie3,p~)2H~ 4 at eo ~ +60o, 9. = -100 ° for a bombarding e ~ r g y of 2.4~"MeV a c c e s s i b l e combinations of i n t e r m e d i a ~ states and for a l l combinations of observed ~ partte]e (~1, ~ 2 o r ~3) in coincidence with the proton~ Each kinematic region in this figure i s labell,.~i and the corresponding s e r i e s of sequentml proc e s s e s , s t a t e s of the intermechate systemL ~'~d the p a r t i c l e s observed a r e given in table 1. The sequential ser~es of ~he type (I) yield kinemattc c u r v e s on the two-dimeesional energy spectr,~m which are Just vertical lines, i.e., discrete-~morgy proton groups observed at 0 . associa~l,c with the forrnation of C 12 in the v~arioas accessible excited states. T h e positions of these proton groups a r e indicated along ~ ~,,c'~on enc:,,V axis in, fig. 2 and labelled ~,ith ~ e appropriate energy of e g c i t a h e n of C 12. If a p a r t i c u l a r state of C12 decays by the em~.esion of an a p a r t i c l e leaving the two r e m a i n i n g ~ p a r t i c l e s in a state of Be s and i f the f i r s t ~t p~rttcle i s observed at the angle 0a, the event would appear at the i n t e r section of the vertical line corresponding to t h e state of C 12 with the kinematic curve corresponding to the state of B e 8 which is formed. Events in which one of the a particles f r o m the breakup of the B e 8 is seen instead are restricted to other s e g m e n t s of the v e r t i c a l line, In many cases the kinematic segments overlap.
Fig, 2. The calonla~ed two--dimensiov~l energy s~e¢ tram of coinclde~t particles from the reaction B 0 (He3,p.~)2He4 st 8v = +60 °. 0. ----!0~ for s bcm~---~aIng ez~ergy Of 2 45"MoV~ The process oorrespo~ix~ to each kmemahc region is indicated by a letter e ~ l a ~ m ~ , t in table 1. The posltmn of each of the discrete-~ner~ proton group~ produced by process I ts mdtcate~ b~ st" arrow along the Eu axis lab~dod with the ener~ ~t ex~Itatlon of the s.~sontated state of C12 Th~ ~er~i¢~l line passing thron~ h Ep = 3 MoV repreaonts ~he m~%1 ~ mum energy proton wKlch can pass through the sbo sorber in front of the proton detector, and ~e~eh,~ that region of the .'wo-dimensional spectrum c,f ~ which is excluded in the experime~tel elA~ctr,,m~ fig. 1, Table I Reaction
Particles
B9
II
P=I
2.34
H
P~2
2.34
g. s g
Bt-~
I t:~
e
11
P~2
II ,6"
g, w,
g h
III HI
lrl P:2
2.3t 2.34
"~ -~
t |
j k
tli III
P~I 1~ 2
11.6~ 11 62
---
~ . #
m n o P
IV D/ IV IV
P~I P"l P~I
~ -"
Z.~ g" ~
| 1
P~2
"" ~
~ ~ g ~
S ~
r
IV
Iz:2
--
~, •
j
-,
-
s,
{ 2"~ t
O
Volume 12, number 1
PIIYSICS LETTgRS
Under the experimezltal conditions of our m e a s u r e m e n t s and at a oombardmg enert,~' of 2.45 MeV effects ccald have been observed due to states of C 12 m the range of excitation ee~r~y extending f r o m about 10,5 to 18 MeV, el 139 fr~z,~ 0 to 12.5 MeW, of Fc 8 from 0 to 8 MeV, and ¢,f Lt 5 f r o m 0 to 1 ~ M, V. Comparison of fig, 1 ~ith fig. 2 and in part~e ular a comparison e t sueh f i g u r e s at varlotm m~gles, enables one to identify many of the v a r i o u s p r o c e s s e s which cat. ,~ccur. The allowed kinematic r e g m n s on the experimental s p e c t r u m of fig. 1 a r e of course broadened, compared to those of fig. 2, by level widths: t a r g e t thickness and the hnfte *~hd angles of the detectors. Vertical lines~ proton groups f r o m reactions of type (D for a number of s t a t e s of C 12, a r e clearly seen in hg. 1, and a r e labelled with the energy of excitation of the corresponding state of C12. Along the vertical, E a , axis the expected posltionJ of the ~ - particle groups f r o m reactions of type (H) and (HI), where a 1 m detected, a r e mdmated for the 2.34 MeV P~d 11.62 MeV states of E 9 previously observed m the B10(He 3, c0B9 reaction 1), T : o r e is no evidence for the f o r m a ben of other states m B9 between these two s t a t e s * . The intense horizontal hne n e a r the position c o r responding to the formation of the 11.62 MeV state of B9 m p r i m a r i l y due to accidental come,done es between He 3 particles elantically s e a t tered at 0c~ and r e a c h o n protons at ~p. The r a t h e r intense spot on this hoe n e a r the mtersectlon of the 15.11 MeV proton group a r i s e s mainly f r o m 2uch accidental events in which the protons a r e due to the C12(He 3, Po)N 14 rea~hon m the carbon foil target baekmg. No evidence is seen for the decay of the 15.11 MeY state of C 12 to either the ground o r f i r s t excited state of Be 8 or :(or the direct breakup of this state rote three a particles. The Be8(g.s.) ~nematxc curve and the Be8(2.9) Mnemahc band a r e also clearly vmxble hi h g , I. The ruther large w~dth of the 2.9 MeV state of Bet(the L = 2 a - a scattering resonance) broadens ~ts curve rote a band. The v e r y l a r g e #idth of the 11.4 MeV state of BeS(the L = 4, a-c~ resonance) and the restrmtion due to the available energy produces a kinematic r e , o n in the low e n e r g y corner of the two-dimensional e n e r g y spectrum. Little can be said a b o ~ this :(tom h g . 1. The hormontal line rozrespondmg to ".lie mite,1 * The broad peak observed m me a particle sty,strum from thin reaction at aa energy, correepondthg to a state m B9 at about 2.5:t MeV set, tally is due *o the B{0(He3,p)C 12 reacttou to the 16 11 MeV lcvol of C 2 in ~Meh the observed ~ part, cle resu!t~ ~rom the decay of th~ level to the ground state of Be? 44
£ ~rrcff.tmr ~:~64,
e~at~s]G~] Ji ~rl t~ p~rtlci~, whl~h i~ ~k-tec~tg#.1 zd 0(~ * with tht; f~rl~a[~ cl~t ~Jf th~ fLrst ex~ff~d ~t~te cd B E t~q b "~,eis~ri~ ~e~-i: In f ~ I , ~tt c l ~ d ~ i ~
iylm ~ID. Point (a) 1~ the ~ r r e s l ~ i d n ~ kl~e~ m a l l region in fig. 2. The rem~d.nder of the l,ort~ zontai line corre,pc~td~ to the B9(Z.34) decaying by the alternate s e ~ l ~ (l~ Into an a paxtieis and IA5(g.s.) which titan decays tnt~ art ~ p a r t i c l e and the o b s e r v e d proton. The eorrespermhr~g r e galen ,n fig, 2 i s (g). At m a n y e o m b i n a t i a ~ of angle p r o c e s s (g) i s m o r e procmunced ~ at 0p = *80 o, So# ~, -100 o. The total ergitrlb~l*~ f r o m p r o c e s s (g) a p p e a r s to be at iea~t a~ l a r g e ns that from (a). H e n c e the B9(2.34) s y s t e m dec a y s a l a r g e fraction of the t i m e by c~ e m m s i o n leaving Lib~g.s,). The r a t h e r intense broad r e g i o n (r) wideh c o r responds to the reaction B10(He3~ Li5)BeS(g.s,) can also be seen. Other contributions f r o m iMs reaction and s i m i l a r one~ leading to BoB{g,9) a r e possibly indicative* by the Cvmtmtmt~ distrl~ button of events 'along the BeS~g.a.) k i n e m a t i c c u r v e and the E~,,.8(2.9) k i n e m ~ i c band, /~ additlem, the intense a r e a n e a r the intersection of (q) and (o) may he due to thls p r o c e s s , Another intense a r e a i s o b s e r v e d n e a r the m t e r s e c ' i o n of the k i n e m a t i c r e g i o n s (0 and (o). Since p r o c e s s (f) r e s a i t ~ f r o m the reaction p r o ceedmg uV~rough the 11.62 MeV s t a t e of B9, thin intense area m a y suggest that the 11.62 M e V state is ,excited in the p r e s e n t e x p e r i m e n t : Howe v e r , it h a s not been posmbte to identify other contributmns f r o m this state because of the cornpeting p r o c e s s e s which o c c u r Lu the s a m e r e g m n s of the two-damenslonai e n e r g y s p e c t r m n . The l a r g e contribution from reaetlons of the type (IV) is part,cularly interesting. ' I ~ s m a y mdacate timt suc~ reactions proceed by t h e g t c k u o of a neutron and proton f r o m B 10 by the H e O f o r m m g Lz5 wlueh i s often in the f i r s t excAed state. O r possibly the p r o c e s s i s m o r e appropriately d e s c r i b e d a s tile pickup of a neutron by He 3 to f ~ r m an a particle which then i n t e r a c t s strongly with ' a e proton in the final state through the "very broad p~ r e s o n a n c e seen in the elas¢lc s c a t t e r i n g of protons on lie4o Another i n t e r e s t i n g feature of the reaction i s the comparable prohabitittes for r e a e U o n s of type (It) and type (flI) for the 2.34 MeV state of B~v. T M s s u g g e s t s that the a p a r t i c l e reduced width of the 2.34 M.~V state of B 9 m at least com~&rable to the proton reduced width. Iience~ the
V~l~*nd~ 12~ ~ r ~ e r
~
PHYSICS LETTERS
cltmter c . ~ l g u r a t i c a l , Li 5 + ~i~ m a y be of con~td~rabls importance in this state, The lack of ev~".ts in tPm r e g i o n between the B e e ~ . s . ) k i n e m a t i c c u r v e and tim Be8(2,9) klne~,~ttc I ~ d m p a r t i c u l a r s t r i k i n g R i s also apItareet tl~t t h e r e a r e k t ~ i n t e n s i t i e s in v a r i o u s ,treas of tim two-dimemsional s p e c t r u m w h e r e ~ t e W~uld expect eon.trlbt~ions f r o m sequential processes - and f r o m those pro:esees which are perhaps more appropriately described as quasiIns~ntsnemm breakup processes in which the final s t a t e is e t r ~ l y modulated by the i n t e r a c tions b~tween the ~arious c l u s t e r components. T h e s e o b s u r v a t t o n s lead us back to tim question posed at tim beg~ming of this l e t t e r concerning the r ~ J m e r in w M c h the r e a c t i o n p r o c e e d s to the four-body final ,~tate. The general conclusion which one can d r a w f r o m the above o b s e r v a t i o n s i s that the B10(He 3, pa)2He4 reaction p r o c e e d s to the four-body final s t a t e p r i m a r i l y through s e q u s n t m l two-body decays o r by p r o c e s s e s in which two-body mteraction,~ m the final state ~ t r o ~ t y modulate the decay. Another way of looking at the r e s u l t s i s the following : The s y s t e m h a s an e n e r g y which i s
THE
1 September 1964
d e t e r m i n e d by the a r b i t r a r y bombarding energy. One would t h e r e f o r e not expect the c r i t e r i a for resonac,.'e in the two-body interaction of the eoml;onents into which the s y s t e m b r e a k s up to be s a t i s f i e d by all p a i r s of components. One component o r p a i r of components wilt have to s e p a r a t e f r o m the o t h e r s at a non-resonant e n e r g y except, perhaps, m s p e c i a l c a s e s , The r e s u l t s of the e x p e m m e n t indicate that the r e m a i n i n g components a r e left vnth a c h a r a c t e r i s t i c resonant ene r g y . In c a s e the remaaning s y s t e m consists of t h r e e p a r t i c l e s and it undergoes f u r t h e r decay, two of the p a r t i c l e s a r e again left at an appropriate r e l a t i v e e n e r g y to interact strongly. In other words, the total e n e r g y of the s y s t e m appears to be p a r U q o n e d a m o n g the components of the final state in such a m a n n e r that a s many of the components a s p o s s i b l e have a r e l a h v e e n e r g y such that they i n t e r a c t strongly.
l~ef ~re~zce 1) T.R. Fisher and W.Whaling, BuU Am.Phys.Soe. 8 (1963) 598.
Be9(He 3, a)2He 4 REACTION
C. MOAZED, J . E . E T T E R , H.D. HOLMGREN and M. A. WAGGONER Umvers;ty of Ma~,land *. CoUege Park, Maryland Reoetved 27 July 1964 The Q - v a l u e s for many He 3 and tmt~um reduced r e a c t i o n s on light nuclei a r e sufficiently high that it i s p o s s i b l e f o r the s y s t e m s to decay to 3- o r 4-body final s t a t e s . Whenever such a m u l tlbody decay o c c u r s , continua a p p e a r m the s i n g l e p a r t i c l e s p e c t r a f o r the reaction. The study of the single p a r t i c l e s p e c t r a i s frequently inadequate to d e t e r m i n e whether the continua a r e due to s e quentml o r quasi-instantax, eous breakup p r o c e s s e s . If q u a s i - i n s t a n t a n e o u s breakup p r o c e s s e s occ u r at low e n e r g i e s , one would expect such p r o c e s s e s to a p p e a r in the Be9(He 3, a ) 2 H e 4 reaction, since all s t a t e s of the i n t e r m e d i a t e Be S s y s t e m a r e unbound f o r any sequential p r o c e s s e s . In addRion the p a r t i c u l a r l y l a r g e Q - v a l u e f o r 3-body breakup (19.006 MeV) should enhance any q u a m instantaneous b r e a k u p contributlous. Studies of
the s p e c t r a and angular dzstrlbutlons for the Be9(He 3, a)2He 4 reaction at bombardlr~yt~er~;~e~ of 3 and 4 MeV by E r s k m e and Browne ) and Dorenbusch ard Browne 2) have shown the ex~s* fence of a laxg~ continuum m the ~ particle s~,~ t r u m . Dorenbusch and Browne 3) have fitted the shape of t h i s continuum by a s s u m i n g that the * ~action p r o c e e d s p r i m a r i l y by an instant,meows breakap of s t a t e s of the compound nucleus, C 12, into tlu, ee a p a r t i c l e s . The u r l g m of the continuum can, h e ~ e ~ r . uniquely detarmmed for the 3 a-parhcle ttnai state by measuring the energies of t~o ef the ,~ partlcles~ E A and EB, at angl~s t~A a n d , B C,~t * Research supported in part b~ the U 8.Atc~,,, ~ F~,¢I~-~ Comlnlssion.