The reactions 64Zn(3He, d)65Ga and 64Zn(3He, α)63Zn

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<ul><li><p>2 ] Nuclear Ph3~stcs A100 (1967) 416--424, (~) ,North-HollandPubhshtng Co, Amsterdam B 2 G I </p><p>Not to be reproduced by photoprlnt or m~crohlm ,a ~thout ~ruten permtsslon from the puohsher </p><p>THE REACTIONS 64Zn(aHe, d)6SGa AND 64Zn(aHe, ~)6aZn </p><p>M G BETIGERI~, H H DUHM**, R SANTO, R STOCK +** and R BOCK Max-Planck-lnstltut [ur Kernphvsd,, HeMelberg, Germany </p><p>Recmved 11 Aprd 1967 </p><p>Abstract The reactmns e'aZn(aHe, d) 65Ga and 6~Zn(aHe, ~)6~Zn have been studied at incident ~He energy of 18 MeV using a broad range magnetic spectrograph and an E-dE telescope Angular d~stnbutmns have been obtained and are analysed by the DWBA theory The results g~*e mformatmn about the ~Zn ground state configuratmn as well as the neutron hole states m ~aZn and the single proton states in nSGa, respectively </p><p>NUCLEAR REACTIONS 64Zn(aHe, d), (~He, ~) E = 18 MeV, measured ~(E, Ot, E "aZn, ('~Ga deduced levels, l, spectroscopic factors Enrmhed target </p><p>1. Introduction </p><p>The nucleus 64Zn has two protons and six neutrons filhng the 2p}, 2p} and If, </p><p>single particle states with the closed fx shell as its core From the small spacing of </p><p>these shell model orbttals, a considerable mlxmg ts expected for the proton as well </p><p>as the neutron configmatlons in the ground state o fZn ~sotopes Most of the prevtous work on 65Ga consisted m the study of ground-state fl-decay *) to levels in 65Zn, </p><p>leading to a ground-state spin assignment of 2 a-- It was, therefore, of mtel est to study the reachon 64Zn(aHe, d)6SGa and to obtain mformatlon regarding the posmons </p><p>of the single proton states and their strengths Recent (p, d) work 2) on Zn Isotopes has provided some mstght into the neutron </p><p>configuratton in these isotopes In the (a He, :~) reaction, higher/-wtlues are kmemat&gt; </p><p>cally favoured and as such the f, hole states can be expected to be more eastly detected </p><p>m the (3He, J) reaction than m the (p, d) reactton, so that m some sense the t\~o </p><p>reactions ate complementary The prevtously knm~n lnformatmn was hmtted to a) fi-decay a) of 63Zn b) energtes of some low-lying levels m 63Zn thzough the study~ s) of the reaction 63Cu(p,n) In the present study, the low-lying levels m </p><p>63Zn upto an exmtat~on of 3 2 MeV have been investigated </p><p>2 Experimental method and results </p><p>The (3He, d) and (~He :~) reactions on 64Zn were studied ~lth the Heidelberg </p><p>Tandem Van-de-G~aaff accelerator using a 3He beam of 18 MeV The zeactlon prod- </p><p>* On lea~e of absence of Atomic Energy Estabhshment Bombay,, India ** Present address Lax~tence Radiation Laboratory, Berkeley, U S </p><p>iF+ Present address Nlels Bohr Institute, Copenhagen, Denmark </p><p>416 </p></li><li><p>64Z; (3 I te ) REACTIONS 417 </p><p>aE 200 E </p><p>o ~1C2, </p><p>L) </p><p>I i i </p><p>e4Zn(SHe m)~Zn E3He = 18MeV 25 </p><p>I 2 </p><p>i !' ]~, </p><p>45 bO 55 </p><p>1AOa 12 C I o ao </p><p>is </p><p>"~ Ji s 1 i I 1~ </p><p>I' ,., '~ ~/~ </p><p>i I </p><p>L I I I 1 I i 60 65 70 75 80 85 90 </p><p>Distance along the photo plate </p><p>Fig l The spect rum o f f -par t i c les resul t ing f rom 6~Zn(aHe, ~)6aZn at 25 The numbers on the hnes cor respond to the levels m 63Zn The same number ing ~s also to be found m table I </p><p>1 ~ I I I I I I I </p><p>04 - ~' 64 Zn (3He,O63Zn </p><p>i ~ '~ E3He=18MeV 01~ ', </p><p>,J_, </p><p>04 </p><p>m B ,E, 1 </p><p>o41:,,," </p><p>f ~ ~t_,,_. O1 '~ u, " / - - . </p><p>004~ ~ ~ </p><p>O01L I~ I I ~ I </p><p>0 o 20 40 60 </p><p>i% </p><p>I I i </p><p>E </p></li><li><p>418 M G BET1GERI etal </p><p>ucts were analysed by a single gap magnetic spectrograph at forward angles and sam- </p><p>ultaneously by a dE-E telescope at larger angles The resulting magnet spectrum for c~-parUcles at 25 w~th respect to the mcadent beam as shown m fig 1 The numbers on the peaks an the spectrum correspond to the levels m 6 3Zn In figs 2 and 3, the </p><p>64Zn(3He, (x ) l~3Zn , E3He=18MeV </p><p>'1 I I I I I </p><p>1 </p><p>O4 E x = 1065 </p><p>[=13 </p><p>01 "" </p><p>02: ~ " . ~ - </p><p>01 ~q ~,,: </p><p>~-~ Ex=1216 004 ,~',~ </p><p>20 - ~, t=3 </p><p>10 ~'- 11.1 | </p><p>04 "~'. Ex=1704 </p><p>02 L -~-. [=3 I-E-1 </p><p>o Ot 004 {~ Ex=1924 </p><p>,~1~ 002 ' ~ ' ' , ~"~-gF t" 10 * , , "'L </p><p>04 - - - - '4 , , E x = 2 651 </p><p>02 ,~ =3 </p><p>01 " ' -~= </p><p>\ </p><p>004 ~' - </p><p>- E x = 2 764 </p><p>. . . . . -,% t=3 </p><p>\ </p><p>" ' t ~ =3 Z </p><p>- , # EX=2936 </p><p>"-~'" ~:~ l __ l ' I ' I Io Ex=3024 -: - x \O </p><p>\ \ :3 - = </p><p>_ " ; , ' . q </p><p>. . . . " l l I \ \ - \ \ z~ \ </p><p>E x =3 372 </p><p>=3 </p><p>001 ; I J I [ i 001 ~ 10" 3(7 50 ~ eCM 10 = 30 50* eCM </p><p>Fig 3 Angular dlstrlbut]ons to the rest of levels m e3Zn The closed circles represent the magnet data and the crosses refer to the telescope data, the dashed curves being the DWBA calculations </p><p>angular dBtnbut lons for the first 14 levels upto an excltaUon energy of 3 23 MeV m 63Zn are shown The closed circles are the magnet data and the crosses represent the </p><p>telescope data The open circles m fig 2 result from an addmonal scattering chamber measurement employing 8 surface barrier detectors Since both the elasncally scattered 3He parncles and the ~-parUcles resulting from the (3He, ~) reacnon are samultane- </p><p>ously recorded an the telescope measurements, normahzataon to absolute umts of cross section was relaUvely easy The error associated with each point in the forward </p></li><li><p>6aZn(3He) REACT IONS 419 </p><p>10 f ~ , </p><p>64Zn (3He d)65Ga ] i t I </p><p>1() </p><p>4 </p><p>2 </p><p>10 </p><p>O4 </p><p>2 </p><p>10 </p><p>O4 </p><p>O2 </p><p>01 </p><p>4 2 r-ci </p><p>th </p><p>,E, O4 </p><p>oC:~ -ol-o 2 </p><p>1 </p><p>0,4 </p><p>O2 </p><p>Ex C~ D </p><p>r 1 </p><p>r ~, E x 0062 ,r </p><p>'. </p><p>, - ,~ Ex-O 191 </p><p>/ ',~ ~ 3 </p><p>i l </p><p>Ex=0655 </p><p>Xi </p><p>~ ~ ~ Ex:O 822 </p><p>%1 =1 </p><p>01~- ,, "~' , Ex=1083 </p><p>004~ ,,/f ",.__.,, e:4 </p><p>oo2b' ] / k"~4~l I I I I I I </p><p>O 20 40 60 co4 </p><p>1 </p><p>04 </p><p>O2 </p><p>1 t 04 / 02 ', </p><p>01 </p><p>E3He=18 MeV i I J I I I i I </p><p>E x - ~ ~,70 </p><p>X 1 </p><p>E x - 1867 </p><p>1 </p><p>4 </p><p>2 </p><p>1 </p><p>04 </p><p>02 </p><p>01 </p><p>04 </p><p>02 </p><p>01 </p><p>Ex-2034 </p><p>d 1~ 4 / ' c </p><p>E x 2 206 </p><p>/ </p><p>1 </p><p>4 </p><p>2 E - 2 819 </p><p>04 "',, </p><p>2 ~ w, Ex=2 922 'Z </p><p>" ' - . - g2 </p><p>04 </p><p>02 </p><p> 2o 4o 6o %M </p><p>Fig 4 Angular dlstribuhons to the levels in ~SGa, the dashed curves being the DWBA calculations </p></li><li><p>420 M G BET IGERI el a[ </p><p>TA~CE 1 </p><p>Summary of results obtained in G~Zn(JHe, c~)~3Zn </p><p>Level E,~e l J= S No (MeV) (assumed) (N ~ l 8) </p><p>0 0 1 1- 2 6O 1 0 192 3 5 6 20 2 0 641 1 ~ 1 70 3 1 065 1+3 ~ I " 037/045 </p><p>(45~, ' ,155) 4 1 216 3 7 0 36 5 1 704 3 ~ - 0 69 6 1 924 1 ~ - 0 23 7 2 160 weak 8 2 520 weak -- 9 2 650 3 7 1 90 </p><p>10 2 760 3 7 - 0 50 11 2 850 3 7,- 0 25 12 2 940 3 r - 0 26 13 3 020 3 7- 0 55 14 3 370 3 ~- 0 87 </p><p>Eex e (p, d) S (MeV) </p><p>0 1 35 0 20 2 80 0 64 0 84 1 04 0 70 </p><p>1 22 0 25 I 68 0 85 1 91 030 </p><p>2 64 0 40 </p><p>A normahzat lon factor N ~ 18 2 was used m the calculations </p><p>TABLE 2 </p><p>Summary of results obtained m G~Zn(~He, d)~oGa </p><p>Level E~xe l J'~ (2Jr- 1 )5 No (MeV) (assumed) </p><p>0 0 000 1 ~,- 1 34 1 0 062 l }- 1 04 2 0 192 3 ) - 5 05 3 0 655 1 1.~ 0 63 4 0 82l 1 ~ ~ 0 24 5 1 08~ 4 ~ ~ 0 39 6 1 670 1 ~ 0 14 7 1 867 I ~- 0 10 8 2 034 4 q ~ 3 90 9 2 206 3 ~- 0 58 </p><p>10 2 819 2 ~+ 0 16 11 2 922 2 2, ~ 0 59 </p><p>A normahzatmn factor N -- 4 4 was used m the calculattons </p><p>d l lec t lon is approx imate ly 10~,~, w i th the er ro l s in the backwa ld ang les be ing o f t i le </p><p>o rder o f 20 , ; The resu l t s fo r 6azn ,ue summar ized m tab le 1 </p><p>The angu lar d tsmbut Jons fo r the low- ly ing leve ls m SGa resu l t ing f rom the 6aZn </p><p>(3He, d ) react ion are shm~n m fig 4 The cha~acter l s t l c dependence o f the shape o f </p><p>the angu lar d~st r lbut~ons on the angu lar momentum I rans fer can be seen c lear ly , w~th </p><p>l = 1 d tsmbut Jons peak ing at l0 ~, / = 2 d l s t r lb tmons peak ing at 17 5 ~, l = 3 peak ing </p><p>at 25 ~ and I = 4 d~st~lbut lons at 30" The reason x~hy th i s characte l l s t l c dependence </p></li><li><p>64Zn(3He) REACTIONS 421 </p><p>of the shape of the angular d is t r lbunons ~s absent m the case of the (3He, ~) react ion </p><p>has been discussed elsewhere 6) The results for 65Ga are col lected m table 2 </p><p>In either case, the energy cal ibrat ion is accurate to _ 15 keV </p><p>3. DWBA ca lcu la t ions </p><p>Theorenca l predlctmns for the react ions 6a'Zn(3He, 3{)63Zn and 64Zn(3He, d )gsGa </p><p>angular d is tnbuUons were obta ined by per forming DWBA calcu latmns using the </p><p>Oak R idge code JUL1E t These are shown in figs 2, 3 and 4 as dashed curves The </p><p>TABLE 3 </p><p>Sets of potentml parameters for aHe, ~ and deuterons used m the DWBA calculatmns </p><p>Particles V W r o r e a Vs o r,~ a w 4X W' (Mev) (Mev) (fm) (fro) (fro) (Mev) (fro) (fm) (MeV) </p><p>aHe 165 24 I 3 1 4 0 723 8 1 6 0 81 -- d 87 -- I 15 1 15 0 81 5 1 34 0 68 77 :~ 180 26 1 48 1 46 0 56 - - - - - </p><p>optmal mode l parameters used in the calculatmns are listed in table 3 The aHe </p><p>parameters were obta ined by fitt ing the elastm scattering data 7) on 64Zn at 19 5 MeV </p><p>The start ing values of the parameters were taken f rom ref 7 and were adjusted to Dye </p><p>C -T" ' -V- - - -~- -" -F - - - - " ' -F - - ' r ""~ -~ i i --Y--'-7 - '3 - " -7 - r ' '~ </p><p>C4~ 2~ 3 64 _ ,_.n( 'a Hc) ,_q </p><p>04 </p><p>02 </p><p>01 </p><p>-~E, 004 </p><p>~, ,~ 002 </p><p>C01 </p><p>OO04 </p><p>0002~ </p><p>.... O o </p><p>X.~\ </p><p>2 </p><p>Es,~, I t 5"deV </p><p>%-..~ t;\ \ </p><p>I I I </p><p>i q </p><p>q </p><p>-i </p><p>~'</p></li><li><p>422 M G BETIGERI et a[ </p><p>l = 1 transfer seemed to be not very sensmve to the various deuteron potential sets, the present set was chosen to fit an l = 3 dlstrlbutton No radial cut-off was used </p><p>Inclusion of sptn-orb,t interaction In both the channels did not bring any difference </p><p>In the structure of the (3He, d) angular distributions for - and 2 a - except that the </p><p>cross section for ~- was higher than that of 21 - by 14 ~a/o </p><p>4. Discussion </p><p>4 l THE 64Zn(3He, d)~Ga REACTION </p><p>In the absence of any other data on 65Ga, the spin assignments can only be ten- </p><p>tatlve The first two l = I distributions, corresponding to the 0 000 and 0 062 MeV </p><p>levels, are interpreted to be 2p~ and 2p~, respectively The ground state assignment </p><p>of 23-- is suggested by the fl-decay measurement ~) leading to 65Zn and also by the </p><p>simple shell model The l = 3 character of the angular distribution and the strong </p><p>excltatton of the level at 0 192 MeV suggest a lf~ assignment to this level A strong </p><p>l = 4 transition is found to the state at 2 034 MeV whtch seems to contain most of </p><p>the lg~ strength A much weaker 1 -- 4 transition is seen to the 1 083 MeV state </p><p>Smce in N = 31 nuclei the lg} neutron strength is usually concentrated in one smgle level, the origin of this addltmnal 1 = 4 transttlon in the 64Zn(3He, d)6SGa leactlon </p><p>Is not clear The low excitation energy and the small cross section may point to an </p><p>explanation of this level m terms of core-exotatmn Some indication for this is pro- vided by the results of 64 66Zn(t ' ~)6s, 6SCu measurements ~0) </p><p>TABLE 4 </p><p>Total strength of the single pamcles as compared with the theoretical ~alues </p><p>2pg 2p_~ lf~ lg3 </p><p>S(experlmental) 1 9 1 67 5 63 4 29 </p><p>S(theoretlcal) 2 0 I 6 2 0 5 2-4 8 8 0 </p><p>Since the sum-rule values for proton capture in T&lt; states depend on the average number of neutrons in the corresponding shells, only the upper and lower hmlts can be given for the theoretical lf~ and 2p~ proton strength because ot the nuxmg of If1_ and 2p~. neutron states m the "4Zn ground state (see subsect 4 1) </p><p>The excitation energies and the strengths for the various single particle states are given m table 4 Using the DWBA normalization constant of Bassel ~ 1 ), the transition </p><p>strengths for 2p~, 2p~ and lf~_ ale in good agreement with the predicted values, implying a relatively pule (2p~)o 2 p loton configuration of the 64Zn ground state </p><p>4 2 THE e'~Zn(~He, ~)63Zn REACTION </p><p>In 63Zn, both the ground state and the second excited state at 0 641 MeV show 1 = 1 pattern However, the angular distribution corresponding to the ground state transition has more structure In investigations of (~, p) leactlons lz), the </p><p>transmons with j = l - wele found to have more structure than transitions with </p></li><li><p>4Zn(3He) REACTIONS 423 </p><p>j = 1+ in their angular dlsmbutions This j-effect was quahtatwely reproduced by the DWBA theory with the inclusion of spin-orblt coupling In the (3He, ~) reaction, we expect a similar j-effect to be produced m DWBA calculations With parameters of table 3, on inclusion of spin-orbit coupling in the 3He channel, the calculations lead to the curves shown In fig 2 1 e the 1 = transmon turned out to be more structured than the j = ~z transition m its angular distribution, favouring a - assignment to the ground state of 63Zn On the other hand, the fl-decay data 3) as well as j-effect arguments from the (p, d) work 2) suggest j = 3- for the ground state of 63Zn In addition, results of investigation of j-dependence in some (3He, c0 reactxons i3) indicate that experimental j = 2 ~- transitions may have more structure than - transitions, so that further measurements are needed to clarify the situation The strong transition to the level at 0 192 MeV shows an l = 3 shape, which is in agree- ment with the assignment of ~- to this level from 63Cu(p, n)63Zn work 5) Most of lf~ strength is exhausted by this level alone The level number 3, corresponding to an excitation energy of I 065 MeV, seems to be a doublet, since the line width is higher than for the nelghbourmg lines and shows an asymmetry which varies with angle Indicating that two different/-values contribute to this peak Wxth the exception of the 1 92 MeV level, which exhibits an l = 1 dlsmbutmn, all other levels favour an / = 3 assignment Of course, l = 4 cannot be ruled out </p><p>In ref 2) the centre of gravity of lf~ hole states in 63Zn IS calculated to lie at 2 64 MeV A strong l = 3 transition is observed at an excitation energy of 2 65 MeV in our measurement Since the If? states are expected to be much more split than lf~ states, all l = 3 transitions to levels beyond 1 MeV have been assumed to be - For getting spectroscopic factors we used a normahzation factor N = 18 2, which was obtained by normahzlng the I f I_ strength to its sum rule value considering only T&lt; states With this normahzatmn, however, the sum of 2p~, 2p~ and lf~: spectroscopic factors exceed the expected sum by about a factor of two On the other hand, a reasonable value for the summed 2p~, 2pi_ and lf~ strength is found in the (p, d) work of ref 2, where only one If I state was detected at 2 64 MeV Renormahzmg our spectroscopic factors with N = 40, our results are pretty close to the (p, d) results Using this renormahzatlon the summed 2p~, 2p~. and lf~ strength of levels 0, 1, 2, 3 and 6 amounts to ~S = 5 8, whlch is in agreement with the expected </p><p>strength 5 6 </p><p>5 Conclusion </p><p>The results of the reaction 64Zn(3He, ~)63Zn reveal appreciable admixtures of 2p~, 2p+ and I f , single particle components m the neutron configuration of the ground state of 64Zn, m agreement with the (p, d) work 2) The average number of neutrons outside the core, however, exceeds the expected value by a factor of two when normahzed to the strength of I f : hole states This behavlour seems to be con- fined not only to the 64Zn(3He, ~)63Zn reaction but is also observed in SaCr(3He, ~) and S4Cr(p, d) reactions 6,14) as well as the 64 66Zn(t ' 7) reactions 10) A similar </p></li><li><p>424 r~ G BETIGERI et al </p><p>difficulty amses in the 64Zn(3He, d) reaction, where the l = 4 strength is found to have only half of the expected value when the nolmahzatlon constant N = 4 4 is used Since, in the present study, the range of the excitation...</p></li></ul>