.Acta Physica Academiae Scientiarum Hungaricae, Tomus 28 (1--3), pp. 5--11 (1970)

T H E 19F(d, p)2~

R E A C T I O N AT Ed = 600 keV* By

B.

SCHLENK

and

J.

Z1M 93

INSrITUTE OF NUCLEAR RESEARCH OF THE IIUNGARIAN ACADEMY OF SCIENCES, DEBRECEN

(Received 12. IX. 1968)

The angular distributions of ten proton groups from the tSF(d, p)2~ nuclear reaction have been measured at E d = 600 keV. DWBA calculations reproduce the angular distributions of five proton groups, and lcad to acceptable spectroscopic factors. At very low deuteron bombarding energies, the DWBA analysis is largely independent of uncertainties in deuteron optieat potentials.

1. Introduction Several a u t h o r s [ 1 - - 7 ] h a v e studied the p r o t o n groups f r o m the r e a e t i o n ~tF(d, p)2~ with b o m b a r d i n g energies below 10 MeV. Spectroscopic i n f o r m a tion on 2~ has b e e n deduced a n d the r e a c t i o n m e c h a n i s m has been studied. H o w e v e r , t h e r e is a lack of i n f o r m a t i o n in the b o m b a r d i n g e n e r g y r a n g e below 1 MeV, p a r t i c u l a r l y in the case of groups with low Q values. T h e p r e s e n t p a p e r reports the a n g u l a r distribution m e a s u r e m e n t s of ten p r o t o n groups at Ea = 600 keV. A D W B A analysis has b e e n p e r f o r m e d for the investigation of the reaction m e c h a n i s m of t h e different groups.

2. Apparatus and method T h e cascade g e n e r a t o r of the I n s t i t u t e of Nuclear Research (Debrecen, H u n g a r y ) , p r o v i d e d a b e a m of 600 ~ 6 keV deuterons. T h e high v o l t a g e of t h e cascade g e n e r a t o r was m e a s u r c d w i t h a r o t a r y - t y p e v o l t m e t e r , c a l i b r a t e d with (p, ~) resonances on 19F, 7Li a n d 27A1. T h e ion b e a m passed t h r o u g h a ]2 ~ m a g n e t i c a n a l y s e r a n d collimator before striking the t a r g e t placed in the centre of the t a r g e t c h a m b e r [8]. The p r o t o n s p e e t r a were m e a s u r e d w i t h an O R T E C SBCJ-25-300 s e m i c o n d u c t o r detector, which could be r o t a t e d f r o m 15 ~ to 155 o.

* Dedicated to Prof. A. SZALAYon Iris 60th birthday. ** Present address: Central Research Institute for Physics, Budapest. .4et~ Physica Ar

Scientiarum ltungaricae 28, 1970

6

B. SCit[LENK and J. ZIM/Ÿ

T h e d e t e c t o r pulses were routed t h r o u g h a charge-sensitive p r e - a m p l i f i e r a n d m a i n a m p l i f i e r and a f t e r a d e q u a t e pulse f o r m i n g were fed to a 512-channel a m p l i t u d e analYser. A 3 m g / c m 2 Al foil was p l a c e d in f r o n t of the d e t e c t o r to absorb the s c a t t e r e d deuterons. A R C A 8342 A m u h i p l i e r with a 1 m m t h i c k CsI c r y s t a l m o u n t e d in the v a c u u m c h a m b e r at an angle of 90 ~ was used as t h e m o n i t o r counter. The ion current was m e a s u r e d b y a c u r r e n t i n t e g r a t o r c o n n e c t e d to the F a r a d a y cup receiving the ion c u r r e n t . T h e t a r g e t was CaF 2 e v a p o r a t e d on a Cu foil of a b o u t 0.5 m g / c m 2 thickness. T h e CaF_, coating v a r i e d b e t w e e n 20 and 25 keV for 600 keV deuterons. T h e t a r g e t thickness was d e t e r m i n e d b y m e a s u r i n g the b r o a d e n i n g of tl~e 340 keV 19F(p, 7) resonance. Our m e a s u r e m e n t p r o c e d u r e was as follows: first, the relative a n g u l a r distributions of the v a r i o u s p r o t o n groups were d e t e r m i n e d b y m e a n s of t h e m o n i t o r counter, at a b o m b a r d i n g ion c u r r e n t i n t e n s i t y of 1--1.5 r Then, the absolute differential cross-sections of the p r o t o n groups were m e a s u r e d at an angle Ol~b = 60 ~ a n d the relative a n g u l a r distributions were s t a n d a r d i z e d to those values. I n the a b s o l u t e m e a s u r e m e n t s , the b o m b a r d i n g ion c u r r e n t was reduced to 0.5 q a n d the c o n s t a n c y of the t a r g e t thickness was monitored during the course of m e a s u r e m e n t b y the m o n i t o r counter.

3. Results Fig. I shows a t y p i c a l p r o t o n s p c c t r u m recorded at a b o m b a r d i n g energy of Ed = 600 keV a n d at a 90 ~ lab. angle, using a CaF 2 target. The letters Po, Pi, P2 etc. a b o v e the p e a k s in the s p e c t r u m refer to the p r o t o n groups corresp o n d i n g to transitions to t h e ground, first, second etc. excited states of the final nucleus; this n o t a t i o n is used b y ROUT et al. [3]. The p r o t o n groups f r o m o x y g e n and carbon impurities are indicated b y the s y m b o l s of the final nuclei. T h e p e a k s corresponding to p r o t o n groups Po, P7 a n d P12 could not be o b s e r v e d on a c c o u n t of their w e a k intensities; p r o t o n g r o u p Pi0 could be detected at some angles, b u t ir was i m p o s s i b l e to d e t e r m i n e its angular distribution, also on a c c o u n t of its w e a k i n t e n s i t y . As p r o t o n groups Pla, P~4 a n d P15 could not be isolated from one a n o t h e r , their t o t a l a n g u l a r distribution was m e a s u r e d . H o w e v e r , on the basis of m e a s u r e m e n t s [3] carried out at higher energies, it can be assumed t h a t the t o t a l angular distribution of those three groups is p r o b a b l y due p r e d o m i n a n t l y to groups P13 and P14" Fig. 2 shows the r e s u h s of angular d i s t r i b u t i o n m e a s u r e m e n t s in the c e n t r e - o f - m a s s f r a m e of reference. The errors i n d i c a t e d in connection with the e x p e r i m e n t a l angular distributions refer to the r e p r o d u c i b i l i t y errors of t h e m e a s u r e m e n t and e v a l u a t i o n . T h e error of the ahsolute value of the differential cross-section is a b o u t 3 0 % on the average. .4eta Physica Academiao Scientiarum Itungczricae 28, 1970

THE ZgF(d,p)~oF REACTION

i% 3000 A

+ e~,,

n

C '3 (o)

25001

2000-

0 '7 (o)

91

x J-

m 1500t"

15

I017(I)

..i.-, r" 0

IPI

10001

IP4 500-

J 0 5o

~6o

~91

2£

2~0

36o

350

~6o

4~o

channel number Fig. 1. E,lergy spectrum of protons coming from the 19F(d, p)'-'~ nuclear reaction measured

a t a bombarding energy E d == 600 keV at 90 ~ 4. I n t e r p r e t a t i o n of results The diffcrential cross-sections o b t a i n e d in the m e a s u r e m e n t s h a v e b e e n c o m p a r e d with t h e calculations b a s e d on the D W B A model. Two sets of optical p o t e n t i a l p a r a m e t e r s used b y CHAGNON [9] to describe t h e a n g u l a r correlations of the 19F(d, p 7)2~ nuclear reaction at Ed ---- 470 k e u h a v e been e m p l o y e d for the p r e s e n t D W B A calculations. The results of t h e D W B A analysis are also shown in Fig. 2. The calcula t e d t h e o r e t i c a l curves are given only w h e n a similarity is f o u n d b e t w e e n the m e a s u r e d and calculated angular distributions. Fig. 2 shows the curves o b t a i n .4cta Physica Academiae Scientiarum H, tng~,ricae 28, 1970

B. SCHLENK and J. ZIM.~NYI

Po

6-

tzb/Sr

~-0

p,

~-0.652

8

{

3-

6.

2-

4,

f.

2

,

~b/Sr

,

,

p,

,

,

o

i

,

,

,

,

,

,

,

~5/.~,. 4,

~-0.828

0.4,-

J.

0.3. 0.2f

O,f,

,

,

,

b/Sr

,

,

,

~

,

,

,

E,- tos9

P,

,

/~b/s"

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,

,

,

,

,

,

,

,

,

,

8-

,

,

,

,

,

,

,

,

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,

2

O- M3

M3 ~0

2"

05J ,

,

,

,

/'a~/Sr

.

.

.

.

~

.

,

~ --2,966

.

,

.

.

.

.

.

'ubB~

4

'~B

0.5-

o" " .fir

go"

~o'

r2o" " ~o'Oc~o" " .Co" " 91 ' ~

Angular distributions of various p r o t o n groups from the l~ o b t a i n e d at E a = 600 keu The continuous curves indicated are t h e culations using t h e t w o different potential p a r a m e t e r sets Fig.

2.

' rJo" ' t~o'e~

p)2~ nuclear reaction results of D W B A cal(M3 and B3)

ed by both potential parameters M3 and B3. (See also Table I.)The stripping strengths (2J + 1)S pertaining to the various proton groups have been determined by matching the theoretical curve with the measured points by the method of least-squares. The resuhs obtained in this way are given in Tab]e II, Acta

Physic.

Academiae

Scientiarum

Hungarieae

28, 1970

T H E ~gF(d,p)~-0F REACTIO.N

9

Table I

Potential parameters used in the DWBA calculations [9] Potential label Cut off radius (fn,)

Deuteron V(MeV)

.M3

B3

4.8

4.5

r0(fm)

69 15 1.46

rc(fm) a(fm) r£

1.3 0.63 0

a '(fm)

0 0

W(Mr

W'(MeV)

100 0 1.0 1.3 0.9 1.55 0.5 80

Proton 55

55 0 1.25 1.25 0.65 1.25 0.47

V(M~V)

W(M~V) ro(fm) re(fin) a(fm) r£ a'(fm) IV'(MeV)

0 1..25 1.25 0.65 1.25 0.47 30

30

Table II

Quantities (2J + 1)S and (2J + 1)S/(2J + 1)S s obtained from DWBA analyses by the application of M3 and B3 potentials, and from earlier resuhs (i)

(z) --

Index of preton groups

!

Ez (MeV)

I (3) ! (4) i I (2j+ 1)0 In

Pi

i i

3.528 i 3.491 I 2.966 I 2.048 'i, 0.828!

0 0 1

0.652

2

i

i

(2J + 1)S

s

~)

Ir

Pu Pi3 Pu p~ p~

(2JŸ

(5)

2 2

0.88 0.88 0.07 1 0.06 0.99

(6)

I

(s) (2j + 1)s

(2J-V 1)S

Potential M 3

I

(7)

[ 2 J + 1)Stheo r

i Potential B3

0.73

0.52

0.74

0.52

0.07 1.41 0.08

0.05 1 0.06 1.03

0.07 1.41 0.08 1.51

0.05 1 0.06 1.07

1.44

(9)

0.58 0.06 0.81

a) Ref. [71 b) Ref. [10] Acta Physiea Acodemiae Scientiarum Hungaricae 28, 1970

l0

B. S C H L E N K and J. Z I M 9 3

Columns 5 and 6 indicate the stripping intensities ( 2 J - / 1)S and the values of (2J-1- 1)S/(2J + 1)S s relative to p r o t o n group Ps, determined b y means of the poteutial p a r a m e t e r s M3; columns 7 and 8 gire the same quantities o b t a i n e d b y means of the p o t e n t i a l p a r a m e t e r s B3. Column 4 gives the spectroscopic factors relativo to p r o t o n group Ps o b t a i n e d b y EL BEDEWI [7] at an energy of 9 MeV on the basis of BUTLER'S m e t h o d . P r o t o n groups Pi, P2 and Ps exhibir stripping angular distributions corresponding to a n e u t r o n c a p t u r e with orbital angular m o m e n t u m In = 2; p r o t o n group Pll has orbital angular m o m e n t u m In - - 1, and p r o t o n groups 1913 @/914 have orbital angular m o m e n t u m 1~ = 0. h should be n o t e d here t h a t the angular distributions of p r o t o n groups p~, P2,/gs,/913 @ Pl.~ also exhibit a stripping n a t u r e in the e n e r g y range Ea 1.5--2.5 MeV, whereas t h a t of p r o t o n group Pll is v e r y e n e r g y d e p e n d e n t [3, 4]. The e x p e r i m e n t a l l y determined angular distributions of the other p r o t o n groups involved in these investigations P0, P:~, P4, P£ P0 eould not t)e f i t t e d with the D W B A model.

5. Conclusion On the basis of the preceding Section ir can be concluded t h a t some of tl~e angular distributions of the l~ p)2~ reaction can be described b y t h e D W B A model. Nevertheless, one can raise questions a b o u t the v a l i d i t y of the fit achieved. The arguments connected with this problem can be s u m m e d u p as follows: 1. At the given b o m b a r d i n g energy c o m p o u n d nucleus processes could p l a y an i m p o r t a n t role. Because of this fact one can expect the a p p e a r a n c e of a direct reaction mechanism chiefly for the p r o t o n groups with large spectroscopic factors. According to the measurements carried out at higher energies [7], the spectroscopic factors relating to Pi, P3 and P13 @ P14 groups are high, while those for other groups are smaller, generally b y one order of m a g n i t u d e . The results of the D W B A analysis d e m o n s t r a t e d in Fig. 2 agree q u a l i t a t i v e l y with these expectations; n a m e l y , the description of the angular distributions ~ Ps and P13 @ P14 can be regarded as quite good. Not only ate the angular distributions well r e p r o d u c e d b n t the spectroscopic factors obtained ate also acceptable. The fits for the P2 and Pll groups are less convincing, while in the case of the other groups (Po, P3, P4, P~, Po) the D W B A description failed. 2. The analysis of the l~ p 7) 90 F reaetion at E a = 470 keV shows t h a t the (d, p ~) angular eorrelation can be well deseribed on the basis of the D W B A model [9]. I t is h a r d l y probable t h a t the good D W B A fit of two i n d e p e n d e n t m e a s u r e m e n t s (differential eross-seetion of ~gF(d, pl)2~ and angular eorrelation of l~ Pi Y)2~ with the same set of p a r a m e t e r s is only a eoineidenee. The (d, PsY) and (d, P~3+1~ Y) angular eorrelations h a v e not been m e a s u r e d _lcta Physica Academiae Scicntiarum Hungaricae 23, 1970

TttE ~~F(d,p)-"~F REACT1ON

1|

a n d , t h u s , t h e r e is n o p o s s i b i l i t y f o r s u c h c o m p a r i s o n . I t is ~~orth m e n t i o n i n g t h a t t h e f i t s o f (d, p 7) a n g u l a r e o r r e l a t i o n s , r e l a t i n g to t h e P3, P i a n d P5 g r o u p s do not seem eonvineing. I n s u m m a r y , i t a p p e a r s t h a t s o m e o f t h e (d, p) r e a e t i o n s a t v e r y l o w deuteron l)ombarding energy can be interpreted with the DWBA model. I t is w o r t h w h i l e t o c o m p a r e t h e s p e e t r o s e o p i e f a e t o r s o b t a i n e d in t h e p r e s e n t m e a s u r e m e n t w i t h t h o s e o b t a i n e d b y DAZAI in e a l e u l a t i o n s b a s e d on t h e shell m o d e l [10]. (See also e o l u m n s 5, 7 a n d 9 o f T a b l e I I . ) T h e a g r e e m e n t between the measured and ealeulated speetroseopie faetors (within ah order o f m a g n i t u d e ) s u g g e s t s t h a t t h e e o n f i g u r a t i o n a s s u m p t i o n s o f t h e shell m o d e l e a l e u l a t i o n s r e l a t i n g t o t h e e n e r g y s t a t e s a t E~ = 0.652 MeV, 0.828 M e V a n d 2.048 MeV m a y b e r e g a r d e d as j u s t i f i e d . M o r e o v e r , i t m a y b e n o t e d h e r e t h a t elose a g r e e m e n t h a s b e e n f o u n d l)etween the angular distributions and the absolute values of the differential eross-seetions obtained from the two different deuteron potentials. Therefore, i t m a y b e s u r m i s e d t h a t t h e D W B A a n a l y s i s is l a r g e l y i n d e p e n d e n t , a t v e r y l o w d e u t e r o n b o m b a r d i n g e n e r g i e s , o f u n e e r t a i n t i e s in t h e d e u t e r o n o p t i e a l potentials. We ate indebted to our colleague Dr. B. Gu subjeet.

for valuable discussions on this

REFERENCES 1. S. TAKEMOTO et al., Phys. Rev., 101, 772, 1956. 2. K. ONo et aL, J. Phys. Soc. Japan, 14, 117, 1959. 3. V. M. ROUT et al., Nucl. Phys., 45, 369, 1963. 4. EL BErIAY et al., Nucl. Phys., 56, 224, 1964. 5. F. D. SE~VARD et al., Phys. Rey., 107, 159, 1957. 6. D. A. BIIOMLEY et al., Phys. Rey., 89, 396, 1953. 7. F. A. EL BEDEWI, Proc. Phys. Soc., 69, 221, 1956. 8. B. SCrrLENI~ et al., ATOMKI K6zI., 8, 232, 1966. 9. P. IR. CnAGNOr~T, Nucl. Phys. 59, 257, 1964. 10. T. DAZAL Progr. Theor. Phys., 27, 433, 1962.

PEAKI~Hft ~"F(d, p) 2~ IIPH

Ea ~

600 K3B

E;. HIYlEHI~ n M. 3 H M A H b H Pe3~oMe HCC:EeAoBaHo yFJ1OBOe pacnpexenen~e xec~qTri rpynlt IIp0TOHOB Ha ~iAepHofi peaKn~nn VJF(d, p)ZOF npri E a = 600 KaB. PacqeTbI no MeToay ncKan
Acta Physica Academiae Scientiarum Hungaricue 28, 1970