Level structure of 46Ti

Nuclear Physics A l l 0 (1968) 161--175; (~) North-Holland Publishiny Co., Amsterdam Not to be reproduced by photoprint or microfilm without written permission from the publisher

LEVEL STRUCTURE OF 46Ti LARS BROMAN+

a n d D. J. P U L L E N

Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania tt Received 9 N o v e m b e r 1967 Abstract: T h e 45Sc(SHe, d)46Ti a n d 47Ti(SHe, cc)4STi reactions have been studied with 15 M e V aHe2÷

ions using a b r o a d - r a n g e magnetic spectrograph. D e u t e r o n a n g u l a r distributions were m e a s u r e d between 7 ° a n d 60 ° for transitions leading to 106 states up to 11.4 M e V excitation energy in 4STi. With the aid o f distorted waves calculations, p r o t o n orbital a n g u l a r m o m e n t u m transfers a n d spectroscopic strengths have been obtained for states up to 7.6 MeV. T r a n s i t i o n s to m o r e t h a n 30 states up to 11 MeV excitation in 'tSTi were also f o u n d in the (3He, ~) reaction study, b u t no g r o u n d state transition was observed. F o u r excited states in 4~Ti have been identified in both reactions as probable isobaric a n a l o g states f r o m which the C o u l o m b displacement energy for the 48Sc-'6Ti pair is calculated to be 7.61 :t:0.03 MeV. E

N U C L E A R R E A C T I O N S 4~Sc(SHe, d), E = 15 MeV; m e a s u r e d cr(Ed, 0). 'lTi(SHe, :c), E = 15 MeV; m e a s u r e d t~(E~). 46Ti deduced levels, l, ~. Enriched (4~Ti) target.

1. Introduction

The present study of the *SSc(3He, d)46Ti reaction is part of a general programme of investigation which is being carried out in this laboratory of nuclei in the If~ shell excited by means of the (3He, d) reaction. For 46Ti, definite spin-parity assignments have previously been obtained only for the ground and first two excited states, these being determined from measurements of the 46Sc fl-decay ~) and the *TTi(p, d) reaction 2). Level energies have been rather well established up to about 4 MeV excitation from studies of the *SSc(p, 7), *6Ti (p, p'y) and *TTi(d, t) reactions t-v), but tentative spins and parities have been obtained for only a few of them. The present investigation was undertaken since the (3 He, d) reaction is capable of yielding considerable spectroscopic information, and no previous study of the *SSc(3He, d) reaction has been reported. Of additional interest in this investigation was the identification of the T = 2 states in 46Ti which are analogs to the low-lying levels of 46Sc. To aid in their identification, the 47Ti (3He, ~)46Ti reaction was also performed. 2. Experimental procedures and results

The 45Sc(3He, d) and 47Ti(3He, ~) reactions were both studied using 15 MeV 3He2+ ions from the University of Pennsylvania tandem accelerator. The charged * Present address: D e p a r t m e n t o f Physics, C h a l m e r s University o f Technology, GOteborg, Sweden. tt W o r k s u p p o r t e d by the Nation',d Science F o u n d a t i o n . 161

162

L . B R O M A N A N D D . J. P U L L E N

reaction products were momentum analysed in a broad-range magnetic spectrograph and detected in nuclear emulsions. Excitation 4

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Fig. 1. Deuteron spectrum from the ~Sc(SHe, d)~Ti reaction, measured at an incident energy o f 15.0 MeV and a lab angle of 50'L 2.1. T H E 4~Sc(aHe, d)46Ti R E A C T I O N

Self-supporting targets of 45Sc were used for this study and were prepared by an evaporation technique from scandium metal. The target thicknesses were estimated (to within + 2 5 ~ ) to be 120 #g/cm 2 by a differential weighing procedure. A deuteron spectrum measured at a lab angle of 50 ° is shown in fig. 1. The over-all energy resolution was 30 keV (fwhm) and a total of 106 groups could be identified as corresponding

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to states in 46Ti up to 11.4 M e V in excitation energy. The excitation energies given in tables 1 and 2 are the means o f values obtained at four different angles. Angular distributions of the deuterons were extracted for the levels up to 7.6 M e V excitation. These are displayed in fig. 2 and cover the angular range 7 ° to 60 ° in the

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2.2. T H E

47Ti(aHe, cc)*STi R E A C T I O N

The 47Ti targets were prepared by evaporating titanium metal, enriched to 79.5 % in 47Ti, directly o n t o 2 5 / ~ g / c m 2 thick carbon foils m o u n t e d on tantalum frames. The targets employed in the present study were 75-t-25 # g / c m 2 in thickness. Alphaparticle spectra were recorded at 15 ° , 20 ° and 25 ° and the spectrum obtained at 25 °

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TABLE 1 Results f r o m t h e ~Sc(aHe, d)4STi reaction for levels between Ex = 0 a n d 7.6 M e V

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51

(keV)

(mb/sr)

(deg)

\ 2 J l + 1/ C2S

g.s. 891 2014 2974 3074 3247 3310 3455 3598 3737 3861 3955 4049 4158 4206 4394 4533 4620 4723 4846 4999 5045 5098 5187 5326 5383 5557 5618 5816 5899 5982 6029 6088 6141 6214 6246 b) 6335 6427 6556 6623 6744 6856 6897 6979 7049 7101 7147 7204 7294 7349 7433 7565

0.12 0.83 0.86 0.20 0.05 0.12 0.40 0.19 0.18 0.36 0.39 0.68 0.50 0.12 0.12 0.03 1.16 0.48 0.37 0.29 0.06 1.41 0.85 0.14 0.19 0.58 1.23 0.42 1.29 O. 13 0.26 0.45 0.93 0.09 0.37

23 12 11 25 19 26 26 19 27 12 12 12 12 13 27 12 27 12 26 12 13 <7 12 ' 14 12 13 12 12 < 7 12 27 12 < 7 13 <7

3 1+3 1+3 3 2 1+3 3 2 1+3 1 1+3 1+3 1 1+3 3 1 3 1 1+ 3 1 -]- 3 1+ 3 0 1 1 -]-3 1 1+3 1+3 1 0 1+ 3 1+ 3 1 0 1+3 0

0.53 0.25+0.96 0.20+0.72 0.50 0.09 0.01 + 0 . 2 4 0.90 0.27 0.02+0.36 0.06 0.06 + 0 . 3 1 0.09+0.57 0.08 0.02+0.14 0.23 0.004 2.11 0.06 0.03 ± 0 . 5 9 0.03 + 0.08 0.01 -]-0.05 0.06 0.13 0.02+0.17 0.02 0.07+0.40 0.14+0.41 0.06 0.06 0.02 + 0.04 0.02 +0.31 0.05 0.03 0.01 + 0 . 0 8 0.01

0.64 1.69 0.97 1.57 1.64 0.36 0.48 0.27 0.75 0.59 0.51 0.85 0.51 1.38 2.19 3.75

12 12 12 12 13 27 12 12 12 12 12 12 12 12 12 !2

1 1 1+3 1 1 -]-3 1+3 1 1 4-3 1 -]-3 1 1 1+ 3 1 1 1 1

0.06 0.16 0.09+0.22 0.03 0.13+0.51 0.02+0.33 0.04 0.02+0.14 0.09-I-0.18 0.08 0.06 0.09 + 0.20 0.06 0.16 0.25 0.42

a) T h e estimated uncertainty in excitation energy is 12 keV for levels 1 t h r o u g h I l, 15 keV for levels 12 t h r o u g h 30 a n d 20 keV for levels 31 t h r o u g h 51. a) Level only weakly excited.

168

L. B R O M A N A N D D . J .

PULLEN

is shown in fig. 3. The over-all energy resolution was 40 keV. Some 34 g r o u p s could be identified as c o r r e s p o n d i n g to states in 46Ti, a n d these are labelled numerically. The principal c o n t a m i n a n t g r o u p s are seen to be due to the presence o f 12C, ' 6 0 a n d 4aTi in the target. G r o u p s c o r r e s p o n d i n g to the light c o n t a m i n a n t s could be readily identified by their characteristic energy change with angle, a n d those arising from 4aTi were identified by c o m p a r i s o n with an a l p h a spectrum o b t a i n e d in a previous 8) study o f the 48Ti(aHe, ct)47Ti r e a c t i o n in this l a b o r a t o r y . TABLE 2 Energy levels in ~6Ti between 7.6 and 11.5 MeV from the 4sSc(3He, d)4~Ti reaction Level

£×a) (keV)

Level

52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69

7665 7707 7764 7849 7920 7971 8026 8090 8115 8230 8303 8402 8466 8513 8552 8625 8673 8797

70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87

Exa ) (keV) 8884 8945 9019 9053 9124 9197 b) 9242 b) 9360 9418 b ) 9472 b) 9608 9670 9741 9816 9847 9887 9978 h) 10042

Level

88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105

F_~a) (keY) 10212 10256 10321 10374 10441 10526 10602 10670 10730 10782 10858 10935 10980 11051 11110 11167 11299 11416

a) The uncertainty in excitation energy is 20 keV for levels 52 through 71 and 25 keV for levels 72 through 105. ~) Suggested T = 2 state. The general b a c k g r o u n d o f a l p h a particles which a p p e a r s in the lower half o f the spectrum p r o b a b l y arises from a high density o f states which are only relatively weakly fed in the (3He, :~) reaction. In table 3 are listed the excitation energies o f states in 46Ti which c o r r e s p o n d only to those groups which a p p e a r well a b o v e the a l p h a particle b a c k g r o u n d at all three angles.

3. Distorted waves analysis The a n g u l a r distributions f r o m the 45Sc(3He, d)46Ti reaction study were analysed by the distorted waves ( D W ) t h e o r y using the code J U L I E . A S a x o n - W o o d s potential was used for the p r o t o n b o u n d state as well as for the ingoing a n d o u t g o i n g channels.

46Ti LEVELSTRUCTURE Excitation 5

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Fig. 3. Alpha-particle spectrum from the 47Ti(~He, ~)4eTi reaction measured at an incident energy o f 15.0 MeV and a lab angle o f 25 °. Groups corresponding to states in 4STi are labelled numerically, and those corresponding to contaminant states are indicated by the chemical symbol for the residual nucleus.

The potential also included an l . s coupling term for the bound state and deuteron elastic scattering. Calculations were performed for Q-values of 4.35, 2.35, 0.35, - 1.65 and -3.65 MeV and for 2s~, ld~, If.} and 2p~ proton capture. For Q-values more negative than - 5 . 5 MeV, which corresponds to the break-up energy of the 3He projectile, no DW calculations are available. The optical-model parameters employed in the calculations are given in table 4. For a (3He, d) reaction on a target nucleus with spin Ji, the relation between the observed maximum cross section and the DW prediction is given by 9) (do-) = 442Jr+1 Zfi ox. " 2J +1

C2SO.Dw,

(1)

where Jr is the final state spin, S the spectroscopic factor and C an isospin Clebsch-

170

L. BROMAN AND D. J. PULLEN TABLE 3 Energy levels o f 4eTi f r o m the 47Ti(3He, ~t)4STi reaction Level 0 1 2 3 4 5 6 7 8 9 10 11

Exa) (keV)

Level

E a) (keY)

Level

g.s. b) 889 e) 2030 3238 3313 3597 3836 3919 3955 4021 4314 4381

12 13 14 15 16 17 18 19 20 21 22 23

4437 4530 4573 4708 4802 5039 5117 5203 5321 5535 5710 5903

24 25 26 27 28 29 30 31 32 33 34

Exa) (keV) 6305 9214 a) 9399 a) 9495 a) 9860 9966 a) 10033 10347 10519 10647 10943

a) T h e estimated uncertainty in excitation energy is 15 keV for levels 1 t h r o u g h 12, 20 keV for levels 13 t h r o u g h 24 a n d 30 keV for levels 25 t h r o u g h 34. b) N o t observed. e) Since the g r o u n d state is n o t observed, the first excited state is a s s u m e d to be at 889 keV a n d all o t h e r excitation energies are obtained from this value. a) Suggested T = 2 state. TABLE 4 Optical-model potentials a) Particle

V

ro

a

W

I4/"

r0"

a'

Vs.o.

roe

•~He d p

177.8 112 b)

1.14 0.974 1.20

0.723 0.912 0.65

25.72 0 0

0 73.2 0

1.548 1.439 0

0.80 0.60 0

0 6 b)

1.40 1.30 1.25

a) T h e potentials for SHe a n d d were o f the form V(r) -- -- V(1 ~ e x p ) -a x - - i ( W - - W ' ( d / d x ' ) ) ( 1 + e x p x') -1 ÷ Vs.o.(h/Mxc)2(l/r)(d/dr) (l + e x p x) -I l . a + Vc(r, re) , with x = (r--roA$)/a, x" ~= (r--ro'A~)/a" a n d r e = r0cA$. Vc is the Coul o m b potential. V, W, W" and Vs.o. are given in M e V a n d roe, r0, a, r0' a n d a" are in fm. T h e values were obtained f r o m Bassel 17). i,) T h e spin orbit part o f the potential was proportional to V, a n d its strength was 25 times the T h o m a s value.

Gordan coefficient, which takes into account the fact that states with the same Jr but different isospin T can be excited in the (3He, d) reaction. The measured values of the spectroscopic strength (2Jf+I)C2S/(ZII+I) are shown in column six of table I and the corresponding values of the transferred proton orbital angular momentum Ip in column five. 4. Discussion 4.1. T H E 45Sc(3He, d)lSTi R E A C T I O N

4.1.1. Transitions with odd lp values. O f those transitions for which angular distributions were obtained, 22 were observed to proceed with mixed lp = 1 -t- 3 orbital

4~1"i LEVEL STRUCTURE

171

angular momentum transfer, 17 with pure lp -- 1 and only five with pure lp = 3. These measurements therefore indicate a high degree of mixing between the If and 2p shell-model configurations. The pure lp = 3 transitions can lead to states with spins and parities 0 + to 7 +, whereas the lp = 1 + 3 transitions restrict the values to the range 2 + to 5 +. Thus, the 0 ÷ ground state is observed to be excited with pure Iv = 3, whereas the first two states at 0.891 MeV (2 +) and 2.014 MeV (4 +) are formed with mixed lp values. In view of the apparent mixing between the If and 2p orbitals, it would seem reasonable to assume that the pure lp --- 3 transitions lead only to 0 +, 1+, 6 + or 7 + states. This does not appear to hold strictly true, however since the third excited state at 2.974 MeV, which has been tentatively assigned 2 + from previous studies of the 45Sc(p, y) [ref. 4)] and 46Ti(p, p'v) [ref. 6)] reactions, appears to be fed only by lp = 3 in the present reaction. If the 2 + assignment is indeed correct, then this state probably has a rather pure (lf~) n proton configuration. The total spectroscopic strength for the lp = 3 transitions to levels up to 7.6 MeV, obtained by summing over the individual strengths listed in table l, is 11.3+_30 ~ . This can only correspond to the T = l components of the lf~ and lf~ strengths, since the first T = 2 state in 46Ti is not expected to lie below 9 MeV (subsect. 4.2). Assuming for the 4SSc ground state a pure (lf~_)n configuration, the expected 10) T = 1 components of the lf~ and lf~ strengths are 6 and 4.5, respectively, giving a total strength of 10.5. The agreement with the observed value is well within the experimental uncertainty. The total observed 2p strength is 3.2, and this appears to be rather evenly distributed over the excitation energy range of 7.6 MeV. The expected T = 1 component of the 2p~+2p.~ strength is 4.5, presumably indicating that a significant part of the 2p strength lies above 7.6 MeV. A number of intense transitions are indeed observed at higher excitations which have not been analysed in the present work and which may well account for the remaining 2p strength. Ginocchio 11) has calculated the low-lying level scheme of 46Ti within the framework of a pure (I f~)6 shell-model configuration; this is shown in fig. 4. Also shown is the experimental level spectrum below 4.6 MeV excitation energy, the lp values obtained in the present study and the spin-parity assignments based on previous investigations. Levels which are fed by transitions with no lp = 3 component are indicated by broken lines. A total of 11 excited states is predicted up to 4.2 MeV excitation by the (lf.~) 6 model, and 1l states up to 4.6 MeV are observed to be excited by lp = 3 or 1 + 3 transitions. In addition to the lp = 3 transition to the 2.97 MeV state, only three other pure lp = 3 transitions are observed in this excitation region, and these feed the levels at 3.31, 4.21 and 4.53 MeV. These may, therefore, correspond to the three predicted levels at 3.25 MeV (6+), 3.90 MeV (1 +) and 4.15 MeV (6 +) to which lp = 1 transitions are forbidden by the spin selection rules. The pure lp = 3 transition to the observed level at 3.31 MeV is also consistent with the previous tentative 6 + assignment to this state based on the 4SSc(p, 7) reaction study 4). Notwithstanding the ob-

172

L. B R O M A N A N D D . J. P U L L E N

served lfo2p admixing, no gross inconsistencies between the experimental and theoretical level schemes are a p p a r e n t , a l t h o u g h a m o r e detailed c o m p a r i s o n m u s t await m o r e precise d e t e r m i n a t i o n s o f the level spins. 5-~p

d 7r

3 I

3 1+3

4 --

6+

F

I

1+3 1+3

4+

I

2

3+

2+

1+3 2

3

(6 + )

1+.3

(2) 2 (4) (6) 2

6+

4+

2 . . . . . .

2+

3

2 2+

>

1+3

2

4+

4+

J

4+

z+ I +3

o-

2+

2+

3

o+

46Ti Exp.

o+

o+

46Ti ,5°Cr

50Cr

Theo.

Exp.

Fig. 4. Comparison of experimental and theoretical level schemes for 4GTiand ~°Cr. From left to right are shown the experimental '6Ti level scheme of table 1, the (1 f~)" model level scheme of Ginocchio [re('. ~1)], and finally the ~uCr level scheme from ref. 1~). The j n values for 46Ti are from refs. 1,5). It is also o f interest to c o m p a r e the experimental level scheme o f 46Ti with that f o r 50Cr ' since a simple feature o f the (i f~)" m o d e l is the existence o f cross-conjugate symmetry, i.e. the identity o f the ,(f~)%(f~)-q and the ,(f÷)q~(f~)- P configurations. Thus, in the ( l f l ) " model, 46Ti a n d S°Cr are identical. This s y m m e t r y is destroyed, however,

't~l'i LEVEL S T R U C T U R E

when higher configurations mix in. The 5°Cr level scheme Willmott 12) is also shown in fig. 4, and it is evident that schemes are rather similar up to about 3 MeV, they differ citations. Thus, cross-conjugate symmetry does not appear mentally for these two nuclei.

173

obtained by Twin and although the two level markedly at higher exto be observed experi-

4.1.2. Transitions with even lp values. Four of the observed stripping transitions exhibited typical lp = 0 distributions, and two were characteristic of lp --- 2. In view of the low excitation energies (3.0-6.2 MeV), these transitions presumably lead to 2s~ and Id~ hole states, thus implying admixtures of the [(lf~)7(2s~)-2]j=~ and [(lt~)7(ld~)-2]s= ~ configurations in the 45Sc ground state. The ld~ configuration should, in this model, lead to a quadruplet of states in 46Ti with J~ = 2-, 3-, 4 and 5- and with a center of gravity of about 4.8 MeV according to the formula of Bansal and French ~3). The two observed states excited with Ip = 2 occur at 3.07 and 3.46 MeV. The remaining two should, therefore, occur above 5 MeV but may be too weakly excited to be seen in the present study. In contrast to the four observed lp = 0 transitions, only two states in 46Ti are expected from the 2s½ configuration, and these should have J" = 3- and 4-. An alternative description of these hole states may be had from the deformed shell model 14). Thus, in this model, two states arising from a hole in the Nilsson orbit 8 should be fed with lp = 2 transitions and with a center of gravity around 3.6 MeV. The observed excitation energies are 3.07 and 3.46 MeV. Two states at about 4.3 MeV and two at about 6 MeV should be fed by lp = 0 transitions, and these arise from holes in orbits 11 and 9, respectively. The experimental energies are 5.04, 5.81, 6.09 and 6.21 MeV.

4.2. THE 47Ti(aHe,~t)4~TiREACTION Of interest in this reaction is the apparent absence of a transition to the 0 + ground state of 46Ti. However, since 47Ti has J~ = ~-, its principal configuration is presumably [~(f~)ov(f.~.)~]s=~ 2 5 in which case it is not possible to reach the 46Ti ground state by direct pick-up of a lfl neutron. This "anomalous" spin of 47Ti may also account for the seemingly high selectivity of states excited in the (3He, ct) reaction, only 24 being observed up to 6.3 MeV excitation in 46Ti, compared with 37 observed with the (3He, d) reaction. Since the ground state could not be located in the alpha-particle spectra, the level excitation energies listed in table 3 were obtained by reference to the first excited state, whose energy was assumed to be 889 keV from the present (3He, d) and other studies. 4.3. THE T = 2 STATES Sherr ~5) has arrived at a semi-empirical formula which describes the change in Coulomb displacement energy with mass number for nuclei in the lf~ shell. Applying

174

L. BROMANAND D. J. PULLEN

this formula to the 46Sc-46Ti pair, the T = 2 isobaric analog state to the 4"65C ground state is expected to occur at 9.2-9.3 MeV excitation in 46Ti. At higher excitations, a sequence of T = 2 states should appear corresponding to the low-lying states of 46Sc. Although these states can only take about 14 ~o of the total lf~ transition strength 1o), at these high excitation energies they should, nevertheless, appear in both the (3He, d) and (3He, ct) reactions as relatively intense transitions above a background of levels representing a high density of T = 1 states. Inspection of the alpha-particle spectrum of fig. 3 indeed shows several intense transitions to states in the 9-10 MeV excitation energy region in ¢6Ti, the first occurring at 9.21 MeV. Similarly intense transitions are also observed to states in this excitation region in the deuteron spectrum of fig. 1, the first corresponding to a level at 9.20 MeV. TABLE 5 Coulomb energies a) *TTi(3He, ct)46Ti Ex (keV) 9214 9399 9495 9966

4sSc(8He, d)4eTi Ex(keV) 9197 9242 9418 9472 9978

AEx(keV) 0 45 221 275 781

*~Sc(d, p)46Sc b) E~(keV)

ln

0 51 227 279 772

3 3 3 (1) 3

AE c (keY)

7612 7612 7606 7608 7621

a) The Coulomb energies were calculated from the relation ,dE c = M ( Z - - I ,

N)+Ex(Z-,L1, N)--M(Z,

N+I)--Ex(Z,

N + I ) q - M ( 0 , I ) - - M ( I , 0),

where (Z, N) designates the 4sSc target nucleus and M a ground state mass. The masses were taken from Mattauch et aL 18). The values of Ex(Z--1, N) were taken only from the 4SSc(3He, d)~6Ti reaction study. b) Ref. 1.).

The 455c(d, p ) 4 6 5 c reaction has recently been studied by Rapaport et al. 16), who observed strong transitions to the ground, 51, 227, 279 and 772 keV levels. If the 9.2 MeV level in 46Ti is identified as the isobaric analog to the 46Sc ground state, then the energy sequence of the strongly excited states at higher excitations agrees well with the sequence in 46Sc. These levels are listed in table 5 together with the calculated Coulomb displacement energy for each analog pair. Although in the (3He, e) reaction study the rather low energy resolution prevented the ground and first excited analog states from being resolved, they Were observed to be separated in the (3He, d) study. From the Coulomb energies of table 1, the mean value is determined to be 7.61 _+0.03 MeV. It is a pleasure to thank Professors R. Middleton and W. E. Stephens for their continued interest in this work, Dr. B. Rosner for many helpful discussions and

~Ti LEVELSTRUCTURE

175

Dr. R. M. Drisko for making the code JULIE available to us. The targets were made by Mr. L. Csihas and the scanning of the nuclear emulsions was performed by Mrs. K. Coliukus. References 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) 11) 12) 13) 14) 15) 16) 17) 18)

K. Way, in Nuclear Data Sheets, N R C 60-2-41 E. Kashy and T. W. Conlon, Phys. Rev. 135 (1964) B389 B. Erlandsson and K. Valli, Ark. Fys. 24 (1963) 31 J. Dubois and S. Maripuu, Ark. Fys. 24 (1963) 127 C. W. Lewis et al., Phys. Lett. 22 (1966) 476 J. N. Mo, P. J. Twin and J. C. Willmott, Nuclear Physics 89 (1966) 686 J. L. Yntema, Phys. Rev. 127 (1962) 1659 B. Rosner and D. J. Pullen, Phys. Lett. 24B (1967) 454 R. H. Bassel, Plays. Rev. 149 (1966) 791 J. B. French and M. I-I. Macfarlane, Nuclear Physics 26 (1961) 168 J. N. Ginocchio, Nuclear Physics 63 (1965) 449 P. J. Twin and J. C. WiIlmott, Nuclear Physics 78 (1966) 177 R. K. Bansel and J. B. French, Phys. Lett. 11 (1964) 145 F. B. Malik and W. Scholz, Phys. Rev. 150 (1966) 919; L. Broman, Ark. Fys. 35 (1967) 371 R. Sherr, Phys. Lett. 24B (1967) 321 J. Rapaport, A. Sperduto and W. W. Buechner, Phys. Rev. 151 (1966) 939 R. H. Bassel, private communication J. Mattauch et al., Nuclear Physics 67 (1965) 1