1 ~ Nuclear Physics A106 (1968) 577--590; (~) North-Holland Publishiny Co., Amsterdam

Not to be reproduced by photoprint or microfilm without written permission from the publisher

L E V E L S T R U C T U R E O F 49V

D E D U C E D F R O M S°Cr(t, ~) AND 4STi(3He, d) R E A C T I O N S

D. B A C H N E R *, R. S A N T O , H. H. D U H M Tt and R. B O C K Max-Planck-lnstitut fiir Kernphysik, Heidelberg, Germany

and S. HINDS tit

A WRE Aldermaston, En#land

Received 31 August 1967

Abstract: The level scheme of 49V has been investigated using the ~°Cr(t, c0 and 48Ti(~He, d) reactions. Angular distributions have been measured and spectroscopic factors have been extracted by

DWBA analysis. The data indicate particle-hole and configuration mixing in the proton states involved. The excitation of states of the (f~_)3 configuration is discussed in connection with pos- sible target excitation processes.

E [ NUCLEAR REACTIONS s°Cr(t,~), 48Ti(3He, d), E t = 13 MeV, E3He ~ 18 MeV; measured

I ~r(E~, 0), <r(E d, 0). 49V deduced levels, l, spectroscopic factors. Enriched targets. I

1. Introduction

Neut ron stripping and pick-up experiments on f~ shell nuclei have revealed large deviations f rom the simple shell-model picture consisting o f appreciable admixtures o f higher shell-model orbitals to the pure f~_ configuration as well as particle-hole components 1,2). A similar behaviour is expected for the p ro ton configuration in f~

shell nuclei, but this is not as well confirmed experimentally. The present investigation o f the 5 0Cr(t ' a) reaction was therefore undertaken to study the proton configuration o f the 5 0Cr ground state and hole states in 49V. The level energies o f 49V are known f rom the 52Cr(p, ~) [ref. 3)] and '~9Ti(p, n) [ref. 4)] reactions, but no spins were

determined except the ground-state spin, which was found to be ~- f rom fl-decay 5). Indirect informat ion on some 49V levels was previously obtained by the observation o f the analogue states o f 49V in the 5°Cr(3He, ~)49Cr reaction 6). Strong l = 2

and 1 = 0 transitions were observed in this reaction corresponding to excited d- and s-hole states in 49V at about 0.8 MeV and 1.6 MeV, respectively. Complementary information about the 49V levels is provided by the measurement of the 48Ti(3He, d)

reaction, which preferentially excites the single-proton states f rom the f~ shell and higher orbitals. Observed l = 2 and l = 0 distributions give an estimate for the amount o f particle-hole admixtures in the 48Ti ground state.

* Permanent address: Institut ffir Strahlen- und Kernphysik der Universit/it B~nn, Germany. ** Present Address: Lawrence Radiation Laboratory, Berkeley, California, USA.

tTt Now at Daresbury Nuclear Physics Laboratory, near Warrington, England.

577

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4°V LEVEL STRUCTURE 579

The level scheme of 49V was investigated theoretically by Bayman, McCullen and Zamick 7) on the basis of a pure f÷ model. By coupling the three protons, states with spin 7 - , ~ - , ~ - , ~ - , ~ L - and '2 --s-- are expected from this model, the ~- state being the ground state. Only the 2 z - member of this sextuplet can be excited by a first-order stripping or pick-up process. The cross sections of the a2- and ~- states may give an estimate for the amount of mixing of these (f÷)3 configurations with p~ and f~ single- particle strength. Since the Nilsson-Coriolis coupling model, where orbits 12 and 13 especially are highly mixed, can describe the order of the low-lying levels properly 8), one expects some p~ and f~ strength within these levels. The excitation of the high- spin states, however, would point to a different type of reaction mechanism as target-excitation processes or compound-nucleus reactions.

2. Experimental procedure

The (t, ~) experiment was performed with the Aldermaston Tandem using a triton beam of 13 MeV. The ~-groups were analysed by a broad-range multi-angle spectrograph with an energy resolution of about 20 keV. The (3He, d) data were taken at the Heidelberg Tandem using a broad-range single-gap spectrograph. Self- supporting targets of high enrichment were used in the case of 4STi, whereas the 50Cr targets were prepared by evaporation onto a thin carbon backing.

Energy spectra for the S°Cr(t, ~ ) 4 9 V and 4STi(3He, d)49V reactions are shown

in fig. 1. For the (t, ~) reaction, angular distributions have been measured between 5 ° and 102.5 ° in 7.5 ° steps. Due to the high triton background, however, no use could be made of the 5 ° and 12.5 ° spectra. For the 48Ti(aHe, d) reaction, spectra were only taken for seven angles between 5 ° and 30 °, which, in most cases, was sufficient to fix the/-value by means of the DWBA analysis. Absolute cross sections were deter- mined for 48Ti by adjusting the measured elastic 3He cross section at 6 MeV to the Rutherford cross section.

3. Analysis

DWBA analyses of the (t, ~) and (3He, d) angular distributions have been perform- ed with the code J U L I E t . The optical parameters used are listed in table 1. The

TABLE 1

Optical-model parameters used in the DWBA calculations leading to the angular distribbtions of figs. 2 and 3

V W r r e a r ' a' Wd VB.o. Ref. (MeV) (MeV) (fro) (fm) (fm) (fm) (fm) (MeV) (MeV)

t 144 20 1.36 1.25 0.678 1.45 0.841 5 9) 183.7 26.6 1.4 1.4 0.564 12)

SHe 165 20.2 1.14 1.3 0.723 1.6 0.81 5 11) d (85.7) 1.15 1.3 0.81 1.44 0.61 66.4 10)

t We thank Dr. Drisko for making available the JULIE code.

5 8 0 D . B A C H N E R e t al.

triton potential was derived from an optical parameter set found by Hafele et al. 9 ) i an analysis of elastic triton scattering from 52Cr at 15 MeV. For the deuterons th parameters of Siemssen and Mayer-B6ricke ~ 0) were used with an energy-depender real potential. The resulting DWBA curves are shown in figs. 2 and 3 together wit the experimental data. The stronger (3He, d) distributions allow/-assignments wit

105 _

10 4

1 0 3 :

103 i

102 I

103-~

10 2

104

103

103: _

102

I I I I I

\

, I , \

I I I I

Ex= 0.000 ~=3

0x

...-,,

< * ~,\\ •

\ ~, _,.. + -

\ E x = 0.090 • \ ) \ g=3

' , , Ex =0.153

\

"<+-~,\ +

~ ' \ [ E x = 0.752 \ ~ ,~=2 \

\*

Ex= 1.025 ÷ \4/~-\,,

(L7) *'*- ~'",-÷. . . I I I I I t

200 400 60° 800 100° @CM

X,k_ m, \ Ex=1.148 *\'.*_ ~ £:3 \ ÷

\ '<< Ex=1610 ~ (~ =5)

" , , j ++ ~'× = 1.652""

iJ \_ £=O

*\ \ ' ,:x

.//*~\ * Ex = 1.999 \

v i _ \ + £ = 0

\ \ l . / ' [ \ \ \

E x = 2.189

÷ ÷ ÷ ' ~ + + ,L

I

I I I I I

0 ° 0 ° 20 ° 4 0 ° 6 0 ° 8 0 ° IO0°@CM

Fig. 2(a). Angular distributions of or-particles from the 5°Cr(t, ct) reaction at 13 MeV. The dash~ curves represent DWBA calculations.

little ambiguity. At higher excitation energies, however, the angular distributioz become less structured within the range of measured angles. The (t, c0 transition on the other hand, exhibit little structure because of the often-mentioned angula momentum mismatch 11), but they provide much help in identifying/-values in vie of the complementarity of (3He, d) and (t, ~) reactions in exciting proton-partic

~gV LEVEL STRUCTURE 581

and proton-hole states, respectively. From the comparison of the (aHe, d) and (t, ~) transition strengths for ! = 0, l -- 2, one obtains, of course, an estimate for the s-, d-hole admixtures contained in the +8Ti ground state, and comparing the l -- 1 and l = 3 transition strengths in both reactions one obtains, similarly, the f+ and p+ particle admixtures in the 50Cr ground state.

103 I i I i I I I I I 103

102 !''~ "F ~\+ Ex=2266~ =3 IO2 /

"-qk\ '~ { + { { 10 3 101 \ \

\

10 2 ..e+\ 102 Ex =2.314

~,~ ,~\ ~ = 1

103 { \ -~ ~ 101

't \ 10 2; 10 2 '+~ & . 2 . ~ 5

\\~ ~'\'l' £ = 2

\

102; "\ 102 + E x = 2.736

lo 3 ~ 4, ÷ 4. + 4, ~{ lo 3

102 \',,~-4,. ,~ Ex=2.394 q 102 \ , 'L g=2

J + t 4. ÷ 101 \ / X 101

\ ,.-

f ? I I ; I I P I I

0 ° 20 ° 40" 60" 80 ° 100 ° OCM 0 °

I I I I I I I I I I I

÷ +, Ex= 3.132 ÷

, +

j " Ex = 3.248 ~" // + ' "

\ -

Ex =3.345 + +++++ + ,, + +

\ ,L Ex =3.699 ~'' '~, ÷ £ = 2

\ L / z \

't +t \ \

"~\ \

i -~ \ \ t + Ex:3"763 ~ ~.\+ g=3

\',,~ {+ \

I

] I I f I I t I I I

20o 400 600 80o 100° @CM

Fig. 2(b). See caption to fig. 2(a).

4 . D i s c u s s i o n

The spectroscopic factors l!sted in table 2 were obtained for the (3He, d) data by the DWBA analysis 13) with a normalization constant of N = 4.42. Since absolute cross sections have not been determined for the (t, ~) data and the normalization constant is not well known, the spectroscopic factors for the (t, cQ reaction were normalized to the expected s{ strength: Czss~ = 2.0. This normalization is probably

582 D. BACHNER et aL

only slightly too high for ' °Cr , since in a recent ' °Cr(aHe, d) experiment t4), th~ 2.23 MeV l = 0 state, which is presumably the ld~ hole state, was only weakl,. excited. We obtain from the ~STi(aHe, d) reaction a value of about 10 % 2s hol, admixture within the proton configuration of the 48Ti ground state. Unfortunately thi value is associated with a large error since it results from unfolding the peak a

lo 4

103

103'

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1011

0 o

I I I I I

,, E x :4 .280 \i'~x I~ =2

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X \

\~ "~k Ex = 4.402 \ g:3 \4t~ \

\ E x = 4.646

\

E x = 4.680

g=2

i" i '* + ¢ \t \ \

', . ~ E x = 4 . 7 4 3

\ \

I I I I I 20 ° ,40 ° 60 ° 80 ° IO0"@CM

I0"

103

l o 2'

103'

lo2E

lo3i

102 t

103i

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101 [

0 o

I I I I 1

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~, E x :5.072

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\ {i/-\\

~1 ~ Ex = 5.522 / ~ ~ :0

v \4 i~\ k/ \

I I I I I 20 ° 40 ° 60 ° 80 ° IO0°@CM

Fig. 2(c). See caption to fig. 2(a).

1.65 MeV by a superposition of DWBA curves with 1 = 0 and l = i. We attribu the l = 1 distribution to a level a t 1.67 MeV.

The main d~ hole strength in 49V is found to be concentrated in the level at 0.7~ MeV. This is in fair agreement with an excitation energy of about 1 MeV predict~ for the d~ hole state by the formula of Bansal and French ts). In addition to t~ strong transition, a number of l = 2 transitions are observed with appreciable cro

49V LEVEL STRUCTURE 583

section up to an excitation energy of 6.56 MeV, indicating a large f ragmentat ion o f

the ld hole strength. The sum of l = 2 spectroscopic factors (cf. table 3), however, exceeds the expected d~ strength, so that some higher l = 2 transitions very likely proceed to ld~ states. The l = 2, 0.752 MeV level is also excited in the 48Ti(3He, d)

10

10-1

10

1

10 -1

1

10 -1

I I I I I i I

E×=O.OO£

, t & / * / ' / ,k.

Ex=0.155 /I ~,,g=l *-.

Ex:OZ50

N/

Ex:I.672

,\ / x~/\ £=0\, / \,

\ /

"Ex=2.193 £=3

Ex=2.204 £=3

I I I I I I

0 o 10 o 20 ° 30°OCM

I I I I I I

E×=2.279_ _-- ,~ ÷/~,-.\ £ =1

- / / +\X ~ #. "--. ~

Ex=2.317

\

- Ex=2821 "

Ex = 3.137

Ex=3.152 - +

++ ++ +,

"t \

', l/lf ',t v

Ex=3.248 g=O '

0 o 10 ° 20 ° 30°OcM

Fig. 3(a). Angular distributions of deuterons from the 48Ti(3He, d) reaction at 18 MeV. The dashed curves represent DWBA calculations. The levels at 1.672 MeV and 3.748 MeV seem to be doublets since their angular distributions can only be fitted by a superposition of two different /-values.

reaction. Its strength o f excitation corresponds to about 15 % pro ton d~ hole ad- mixtures in '~8Ti, which is comparable with the amount of neutron d~ hole strength observed in the Ca region 16).

A number of I = 3 transitions are observed in (3He, d) as well as in the (t, ~) reaction in addit ion to the ground state. The strongest o f these transitions seen in

584 D. BACHNER et al.

(3He, d) goes to the level a t 4.65 MeV which, according to its exci ta t ion energ3

should be the ma in f{ state. In (t, c 0 , this level is also excited, and we ob ta in an est

mate o f a b o u t 20 % f{ s t rength con ta ined in the 50Cr g round state. A m o n g the oth{

low-lying 1 = 3 t rans i t ions the 2.19 MeV and 2.82 MeV states are ra ther strongl

• 1 L_ I i I I t I _ _ 1

F ÷ Ex--3"401 _11.- , . . *~ "~., ~ =1

10-~ ",.. ~ ~ 1;

1 ~ 10 ~

10 10 Ex=3.922

1 - ~-.~ ~* 10

1 1" *~ Ex=4,012 ~ ~\~=I

10 -'1- , 10 -1 Ex=4135 -

10_1: g=3 -

F__.X=4224 -

I .~,r- .~ ~=1 -; 10 -1 ".. ,t,-

\

! I I I '1' / I

0 o 10 ° 20 ° 30°@CM 0 °

I I I I I t [

- ,/*--*-- Ex=425"3--- = / "~\~=I -

..,,_, ~=4.379~

÷ ~ Ex:4-502-

" ",..gx=l -

Ex=4645 - g=3

..,~_, .. Ex=4.852:- *~=1 .

"Ii "# "~ ~ \ ,I,

Ex=4.945_-

~-,~. , i =1 !

E~=5.057- g=l

I I I I I I

10 ° 20 ° 30°@CM

Fig. 3(b). See caption to fig. 3(a).

exci ted in the (3He, d) reac t ion t. The observed exci ta t ion energies of these states a

close to values pred ic ted by McCul len , Bayman and Z a m i c k 7) for higher ½- state

F o r a 5 - ass ignment , however, we would expect to excite these states in the (t,

react ion, too, bu t this was no t observed exper imental ly . This suggests a { - assig

t A similar situation seems to occur in the 4~Ti(aHe, d) reaction studied by Rosner and Pullen z Here two l = 3 transitions are observed to states at 2.548 MeV and 2.724 MeV with apprecia[ strengths and are assigned ~-.

49V LEVEL STRUCTURE 5 8 5

ment to these states 4). Adopting this assignment, we obtain for the collected fl strength of the lower-lying T~ . . . . levels

(3He, d) Z(2J--I.-1)C2Sf~_ = 4.5,

(t, ~) ~ C2Sf~ = 3.45.

The (3He, d) strength is smaller than the value of 5.6 to be expected for the lower

t0

10-1

1

1

10-1

1

10-1

I I 1 { 1 1

Ex=5.216 L___,~ *-*~ \£ =1

E x = 5 2 5 7

- * \ £=1

1

i

104

I l l l l l

. Ex= 5.718

¢

Ex=5.826 t .~=3

Ex=~37o- 1 ~b E~:~sse £=1

~ - ~ g=l -7 . - ,

• 1 Ex=5.947 :

lo --,.<

Ex=5.987 1 ~ , £=1

10-1 L-- ÷" # - -

0 o 10 ° 20 ° 30°@CM 0 ° 10 °

I I I I I I

10

Ex=614E 1 ~ t'4-~,£ = 1

1~- , . Ex= 6 220-:

{ ' - --+

F Ex= 633-3

1 I- ! f i - \ f . £= l .

10 l + Ex=6.474

1L- 4, + ÷- l Ex =6.555 :

l t : - t - , ~ = l - "-(-'! t , Ex=6 603-~

I o

20 ° 3 0 e c M 0 ° 10 ° 20 ° 30°®cM

Fig. 3(c). See caption to fig. 3(a).

isospin states * from pure f~ configurations but can easily be explained by assuming the number of effective proton holes Neff = 4.8 and neutron holes Vef f = 1.6 which is consistent with about 20 % core excitation derived from the (3He, d) transitions to the d~ and s~ states discussed above.

t The expected strength is given by the expression 2](2J -L 1)C 2 S~k =/~ref r - ~tf/5.

586 D . BACHNER et al.

TABLE 2

Exci ta t ion energies, /-values f rom D W B A analyses and a s sumed spins

Level Ex 1 j C2S C2(2j+1)S ~) b) ~) ~,b) ~,b) ~) b)

0 0.000 0.000 1 0.090 (0.092) 2 0.153 0.155 3 0.752 0.750 4 1.025 1.025 5 1.148 6 (1.183) 7 1.531 8 1.610 9 1.652

10 1.672 11 1.999 12 2.189 2.193 13 2.204 14 2.241 15 2.266 16 2.279 17 2.314 2.317 18 2.358 19 2.394 20 (2.425) 21 2.681 22 2.736 23 2.812 24 2.821 25 3.132 3.137 26 3.152 27 3.248 3.248 28 3.345 29 3.388 30 3.401 31 3.465 32 3.699 33 3.748 34 3.763 35 3.929 3.922 36 3.976 37 4.005 4.012 38 4.042 39 4.090 40 4.135 41 4.152 42 4.224 43 4.253 44 4.280 45 4.379 46 4.402 47 4.448 48 4.511 4.502

0.000 3 ½- 2.96 4.3 0.091 3 ~- 0.21 0.152 1 ] - 0.12 0.17 0.749 2 ~+ 2.7 0.36 1.025 (7) a) 1.140 (3 ~- 0.1 ) 1.157 1.521 1.607 (5) d) 1.647 0 ~+ 1.54 0.21 1.664 1 ~- 0.50 1.999 0 e) ½+ 0.12 2.184 3 (~-) t) 0.79

3 (~-) t) 0.63 2.240 2.266

2.312 2.357 2.395 2.413 2.679 2.796 2.820

3 (~-) 0.07 1 -~- 0.55 1 ~- 0.02 1.31

2 0.41

2 0.12 3 ( t - ) t) 0.79 4 ~+ 0.25

0 ½+ 0.13 0.01

1 0.02

2 0.46 1 0.08 3 ({-) 0.09 0.18 1 0.29

1 0.04

3 (~-) 0.10

1 0.08 1 0.05 2 0.55 1 0.04 3 (~-) 0.12

1 0.22

49V LEVEL STRUCTURE

TABLE 2 (cont inued)

Level Ex 1 j C2S C2(2j + I )S ~) b) ¢) ~,b) ~,b) . ) b)

49 4.538 50 4.587 51 4.599 52 4.646 4.645 3 (~--) 0.42 2.11 53 4.680 2 0.13 54 4.743 2 0.19 55 4.838 4.852 1 0.27 56 4.871 57 4.945 1 0.02 58 4.959 0 ½+ 0.05 59 5.018 5.017 3 (~-) 0.11 60 5.057 1 0.05 61 5.072 2 0.15 62 5.130 63 5.146 64 5.216 1 0.15 65 5.239 66 5.257 1 0.03 67 5.285 0 ½+ 0.07 68 5.355 (2 0.21) g) 69 5.375 5.370 1 0.02 70 5.403 3 (~--) 0.35 71 5.522 0 ½+ 0.09 72 5.554 73 5.590 5.597 1 0.03 74 5.631 (2 0.16) g) 75 5.676 1 0.04 76 5.718 1 0.03 77 5.826 3 (,'] - ) O. 13 78 5.890 5.889 1 0.02 79 5.931 (2 0.14) g) 80 5.947 3 (~-) O. 10 81 5.979 82 5.987 1 0.06 83 6.045 1 0.04 84 6.058 (2 0.27) g) 85 6.146 1 0.10 86 6.170 87 6.184 88 6.218 6.220 1 0.05 89 6.258 90 6.286 91 6.309 92 6.333 1 0.05 93 6.353 94 6.368 95 6.392 96 6.430 97 6.467

587

588 D. BACHNER et al.

TABLE 2 (continued)

Level E x l j C2S C2(2jq-1)S

98 6.474 99 6.521 6.521

100 6.555 1 0.22 101 6.563 2 (0.22) g) 102 6.603 1 0.17 103 6.661

a) 50Cr(t ' a)49V. b) 4aTi(3He ' d)49V. e) Ref. a), s2Cr(p ' a)49V. All spectroscopic factors are extracted by DWBA calculations assuming the spins of column 6. d) The angular distributions to levels 4 and 8 are discussed in the text. e) In the 5°Cr(aHe, ~) reaction to the analogue state, a clear l = 0 angular distribution has been observed. f) The 6- assignment for these states is discussed in the text. Levels 12 and 13 could not be resolved at all angles. Although levels 23 and 24 coincide within the accuracy of the energy calibration, wc label these levels as different states, since they correspond to different/-values. g) The/-assignment of these states is based only on four or five points.

TABLE 3

Summed spectroscopic strength of the 6°Cr(t, ~) and 4aTi(aHe, d) reactions compared with pure shell-model predictions

s0Cr(t, c¢)49V 48Ti(3He, d)40V experimental predicted experimental predicted

C2S (2J+1)C2S

2.00 a) 2.00 0.22 s½ P~ Pk d~ d~ f~ f~ g~-

0.14 4.68 5.71 4.00 0.36

6.00

1.60 3.20

0.63 5.00 4.80 3.45 4.00 4.48 5.60

0.25 8.00

a) Normalized.

Although the cross sections to the states at 0.090 MeV and 0.153 MeV seem to be partially due tc target excitation, we list their spectroscopic factor as for pure single-particle states.

A n u m b e r o f l = 1 t r a n s i t i o n s a re o b s e r v e d in t he (3He , d ) r e a c t i o n c o r r e s p o n d i n g

t o p~ a n d p~ p r o t o n s ta tes . A s m a y b e seen f r o m t a b l e 3, t h e e x p e r i m e n t a l l = 1 sum

a g r e e s w i t h t h e s u m ru le va lue , so t h a t al l t h e p~ a n d p÷ s t r e n g t h s eems to b e cove red .

A l t h o u g h t h e l o w e r l = 1 s t a t e s s h o u l d b e p~, a d i s t i n c t i o n b e t w e e n p~ a n d p~ c a n n o t

b e m a d e f r o m o u r d a t a a n d c o n s e q u e n t l y s e p a r a t e c e n t r o i d s c a n n o t b e d e t e r m i n e d .

I t s h o u l d b e n o t e d t h a t a t h i g h e r e x c i t a t i o n ene rg i e s t h e a n g u l a r d i s t r i b u t i o n s o f the

( 3 H e , d ) r e a c t i o n a re r a t h e r flat, a n d a c l e a r / - a s s i g n m e n t is d i f f icul t i n m o s t cases .

49V LEVEL STRUCTURE 589

Besides the 3 - state at 0.153 MeV to be discussed later, only a weak l = 1 transition is observed in the (t, ct) reaction to the predominating p~ level at 2.314 MeV, indi- cating that the (p~)Z proton component in the 5°Cr ground state is small. The level sequence ½-, ~- , 3- for the first three states is well known from other nuclei in this region and is usually ascribed to the different coupling of a (f~)3 configuration. The other members of this multiplet, i.e. 9- , ½~ - ~ 5 - , 2 , are expected at higher energies and are not so well confirmed experimentally. From this multiplet, only the ~- state can be excited by a first-order stripping or pick-up process. Apparently mixing of single- particle components into the (½)3 configuration may take place in the case of the ~- and 3- states * and allows for an excitation of these states in a direct process. This may be especially due for the 2 ~- state at 0.153 MeV, which is excited with l = 1 both in (3He, d) and in (t, ct).

The relative intensity of this transition in the (t, ~) reaction is much too strong as compared with the "pure" p~ state at 2.32 MeV. This may be explained by the more complicated configuration of the 0.153 MeV state, for example, assuming (p~)~ components contributing to its wave function. (This component could be reached in 50Cr(t ' ~) if the 50Cr ground state contained (p~)4 components.) Another possibility would be target excitation in the (t, ~) reaction in addition to the simple pick-up

5- level at process. This is supported by the unexpectedly strong excitation of the ~- 0.09 MeV in (t, e), which is not excited in a recent 5°Cr(d, 3He) experiment 2~). In 48Ti(3He, d), this state is only weakly excited (in fact only at 25 ° a clear observation of this level was possible), confirming the small f~ single-particle components.

If the 5 - , 3 - members of the (f~)a configuration are at least partly excited via a second process, we also expect to find transitions to the ~- , ½1 - , ~_5 - states of this multiplet. Since the excitation of these states is even more forbidden in a usual pick- up reaction, their angular distributions cannot readily be calculated. As has been pointed out by several authors 18.19) however, the gross structure of the angular dis- tribution is determined by the total angular momentum transfer. For high/-transitions the (t, e) reaction is localized in a region outside of the nuclear surface where the form factors approach their asymptotic behaviour determined by the separation energy of the proton. Hence, the shape of the angular distribution may be rather independent of the details of the form factor in the nuclear interior.

Two states at 1.025 MeV and 1.607 MeV in 49V, which are presumably the high- spin states of the (f7) 3 multiplet, were excited in the (t, c0 reaction with rather flat angular distributions, which can be described by l = 5 and 1 = 7 DWBA curves as shown in fig. 2. Again these states have not been observed 21) in 5°Cr(d, 3He).

t A mixing of this kind was used in calculations by Auerbach 17) and was found to improve the agreement with experimental data especially for the ~- states.

590 D. BACHNER et al.

5. Conclusions

A large spl i t t ing o f s-, d-, f- and p-s t rengths in 49V has been observed ind ica t ing

apprec iab le conf igura t ion mixing in the states involved. The levels were identif ied on

the basis o f / - v a l u e s and t rans i t ion s t rengths in the react ions studied. The f~ levels

were s t rongly excited in bo th the (t, e) and the (3He, d) reactions. The other s t rong

levels in 50Cr(t ' ct) were identif ied as the s-, d-shell p ro ton-ho le states and the s t rong

levels in 48Ti(3He, d) were assigned as f~ and p-shell p ro ton-par t i c l e states. The so

defined hole states were also observed in (3He, d) but with weak exci ta t ion, their

s t rengths indica t ing the a m o u n t of hole admix tu re in the 4aTi g round state. Similar ly

the par t ic le states were weakly excited in 50Cr(t ' c0 indica t ing the a m o u n t o f par-

t icle admix tu re in the 50Cr g round state. States of p r e d o m i n a n t (f~)aj ~ - configura-

t ions were found to be excited in (t, c~) and (except for the 3 - level) no t in (3He, d).

Targe t exci ta t ion processes or c o m p o u n d reac t ion mechan i sm m a y account for the

exci ta t ion of these levels in the (t, e) react ion.

The au thors wish to t h a n k Professor Gen tne r for his interest in this work and Drs.

R. Stock and O. Hansen for s t imula t ing discussions. They also t h a n k the scanning

g roup for the careful scanning of the nuclear emulsions.

References

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