Title Proton Induced Reactions on ⁹Be from 4 to 6 MeV ... · Bull. Inst. Chem. Res., Kyoto Univ., Vol. 52, No. 1 . Proton Induced Reactions on 9Be from 4 to 6 MeV Masaharu YASUEl-,

Title Proton Induced Reactions on ⁹Be from 4 to 6 MeV (MemorialIssue Dedicated to the Late Professor Yoshiaki Uemura)

Author(s) Yasue, Masaharu; Ohsawa, Takao; Fujiwara, Noboru; Kakigi,Shigeru; Nguyen, D.C.; Yamashita, Sukeaki

Citation Bulletin of the Institute for Chemical Research, KyotoUniversity (1974), 52(1): 177-201

Issue Date 1974-07-25

URL http://hdl.handle.net/2433/76528

Right

Type Departmental Bulletin Paper

Textversion publisher

Kyoto University

Bull. Inst. Chem. Res., Kyoto Univ., Vol. 52, No. 1

Proton Induced Reactions on 9Be from 4 to 6 MeV

Masaharu YASUEl-, Takao OHSAWA, Noboru FUJIWARA, Shigeru KAKIGI, D. C. NGUYEN*,

and Sukeaki YAMASHITA**

Received January 5, 1974

Excitation functions and angular distributions for the 9Be(p, p)°Be, °Be(p, d)OBe, and 9Be(p, a)OLi reactions have been measured over the range of proton bombarding energies from 4.0 to 6.0 MeV. In the 9Be(p, p0)°Be(g'nd), °Be(p, p2)9Be(2.43), and °Be(p,,a2)°Li(3.56) reactions, a resonance has

been observed at Ep=4.7 MeV, corresponding to the 10.8 MeV state in 10B. The spin-parity of the 10.8 MeV state in 10B has been determined to be 2+ by the analysis of the angular distributions

for the (p, 132) and (p, a2) reactions. In the °Be(p, a1)6Li(2.18) and °Be(p, a2)OLi(3.56) reactions, a resonance corresponding to the 11.5 MeV state of 10B has been observed at Ep=5.5 MeV.

In the 9Be(p, p0)°Be(g'nd) and 9Be(p, a0)6Li(g'nd) reactions and in the 9Be(p, pi)9Be(1.67) reaction, new resonances have been observed at Ep=4.5 MeV (Ex(10B)=10.6 MeV) with a width

of 200 keV and at Ep=5.1 MeV (Ex(10B)=11.2 MeV) with a width of 300 keV, respectively. Besides, a gross bump with a width of about 1 MeV has been found in the °Be(p, p0)9Be(g'nd) reaction

around Ep=4.5 MeV.

I. INTRODUCTION

Evidence for a singlet deuteron (d*) production, that is, the formation of a p—n

pair in a 'So state, has been reported by many authors.") Studies on the (p, d*) and (3He, d*) reactions on light nuclei2) revealed that the singlet deuteron is described as

a single particle on the surface of the nucleus. If so, it is expected that the excitation functions for the emission of singlet deuterons

can be a probe to the study on the strength of the p—n correlation in a singlet state, i.e. the strength of the probability of the d* clustering in the nucleus.

As an example for the existence of the d* clustering in the nucleus, a 3.56 MeV state in 6Li is mentioned. The configuration of the 3.56 MeV state of 6Li is interpreted

to be [a+d*] .17r =0+ T=1 through the study on the electron scattering from 6Li.3) A 10B nucleus is also an odd-odd nucleus as 6Li is so, and the 8.9 MeV and 10.8

MeV states in 10B are found in the excitation functions of the 9Be(p, a2)6Li (3.56)• reaction by Marion.4) If the d* correlation exists in the 8.9 MeV and 10.8 MeV states in 10B, these states will be described in the configuration of a d* coupled to a

8Be core . The 8Be core decays into two alpha particles in the free space. Consider- ing the structure of the 3.56 MeV state in 6Li, therefore, the excited states in 1°B with

* tQ Ei , *R*, I -'N., : a, • y4 jj : Institute for Chemical Research, Kyoto University, Kyoto.

** ilfr(f 9Ji : Nara Women's University, Nara. t Present Address: Institute for Nuclear Study, University of Tokyo, Tokyo.

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M. YASTJE, T. OHSAWA, N. FUJIWARA, S. KAKIGI, D. C. NGUYEN, and S. YAMASHITA

11.30' (9/21

6.66i' 7/2- r

4.yy4% 3/2-4.7' 3/2 1@8i •r 3.04 5/2+

2.43 5/2- V

3/2-

K.13/2 K =1/.2Positive-Parity Levels

Fig. 1. Low-lying states of 'Be shown as two rotational bands with K= 1/2 and K=3/2 for the negative-parity states, together

with the positive-parity states. Cited from Ref. 5.

21.475 Lie+ d

19.647 +p 18

.47 ........ /)7 . 79 (2+120' I 17.250 -17.4____19.3 12+r;11 Lie +t•1618.82+,1-0 18.66?

17.786Be' +t LI +He15 .042

Be' +He3

141+) (0.71.112.56

-9.27 I i.53 10,,, Bee +2n:B.48014','§i///e T.'!11 Hee + a :7.416-Z38 7 55 2+3'~ _ 9-W 31-I;1 eee+ n:[email protected] ...Vat-7.2

~6.18 6.26 2-o+`_8.078e438-€58_- 5.962+'I=_'7.777.560+I2=1,B9+n

` '6.57 6.68.--------I-6.587-3_Q,.28- - -. 5.143: Bee + a

6.028 -5.92 6.03-1.-13a-r8.'+p 3.372+ Bee+d I+; I+;4.050:89+p 5.115.17~-2~o_.`3.36

4.461 4.77 3+;0 (21-IO

Lie +a3.59 2+;O

[2.00] 1.74 2.15 0+;$11 .60] 0 {I(OIU

Belo 0.717 ItoR+10 Q-3+io

Bto Fig. 2. The mass-10 isobaric triad. Cited from Ref. 7.

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Proton Induced. Reactions on 9Be

the configuration [sBe+d*] will be observed in the 9Be (p, a2)6Li (3.56) reaction. Hence the excitation function for the 9Be (p, a2)6Li (3.56) reaction can be a probe to study the d* clustering in the 1°B nucleus.

Figure 1 shows the level scheme for a 9Be nucleus. Negative parity states in 9Be are interpreted in the strong-coupling model to a k = 3/2 rotational band or a k =1/2 rotational band.5) While, positive parity states are described in the weak-coupling model in terms of the configuration of a neutron in is-2d shells coupled to a 8Be core.6) If the coupling between d* and 8Be core is strong in the excited states of 1°B, the states decay into the negative parity states of 9Be following an emission of a proton. While, if the coupling is weak, the states will decay into the positive parity state of 9Be.

Figure 2 shows the level scheme for the mass-10 isobaric triad.7) The 10.8 MeV state is observed in the reaction 9Be (p, n)9B, 9Be (p, a2)6Li (3.56), and 10B (e, e')10B* reactions.4'8'9) The 11.5 MeV state is observed in the 11B (3He, a)" °B reaction.')

Hitherto these high excited states have not been investigated by the proton scatter-

ing channels. As mentioned above, the 9Be (p, p')9Be channels give a clue to the

problem whether the coupling between two particles outside of the core and the 8Be core is strong or weak. Therefore, it is interesting to study these high excited states through the proton scattering channels.

In the present experiment, in order to study the structure of the 10.8 MeV and the 11.5 MeV states in 10B, excitation functions and angular distributions for the proton induced reactions on 9Be i.e. (p, p), (p, d), and (p, a) reactions were measured over the the range of proton energies from 4.0 MeV to 6.0 MeV, corresponding to the excitation energies in 10B from 10.2 MeV to 12.0 MeV.

II. EXPERIMENTAL PROCEDURE

A proton beam from the tandem Van de Graaff accelerator of Kyoto University was brought into a 100 cm scattering chamber through an analyzing magnet. A beam defining hole of 3 mm in diameter was placed at the entrance to the scattering chamber. The beam spot at the target was about 2 by 3 mm2. The beam energy spread was about 10 keV.

A self supporting 9Be target of 35 µg/cm2 was prepared by the vacuum evapora-tion method as follows.

To evaporate beryllium metal under high vacuum onto clean gass slides coated with nitro-cellulose. A tangusten boat was used to heat the beryllium for the evaporation with the electron bombarding method. The foils were then floated off the glass in an acetone bath and deposited on the target holders. Energy losses in the target are 2.2 keV for 5 MeV protons and 26 keV for 5 MeV alpha particles. The thickness of the target was calibrated with a 9Be-foil of 2.53 mg/cm2 thickness, comparing the yields for the protons elastically scattered from 9Be nucleus. Photograph 1 shows the set-up system for the detector in the scattering chamber.

A detector was set on the arm and two detectors were set on the turn table. For the measuring of protons and deuterons, two silicon surface barrier detectors of 500 µm depletion depth and that of 1000 µm depth were used and Al-foils of suitable thickness were placed in front of each counter to stop alpha particles and recoil lithium ions.

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M. YASUE, T. OHSAWA, N. FUJIWARA, S. KAKIGI. D, C. NGUYEN, and S. YAMASHITA

Apt* i<t wp

~^r

Photo 1: Set up in the scattering chamber. Three silicon surface barrier detectors are mounted on the holders.

For the measurement of alpha particles, detectors of 50 pm, 25 pm, and 20 pm depletion

depth were used.

On the measurement for the excitation function, three detectors were set at 45°,

115°, and 150° with respect to the beam axis. The solid angles subtended by the counters

were of 0.4, 1.1, and 1.7 m sr, respectively. The incident proton energy was changed

from 4.0 MeV to 6.0 MeV in 50 keV or 100 keV steps.

On the measurement for the angular distributions, detectors on the arm consisted

of 20 pm and 1000 pm counter telescope, and on the turn table, two detectors of 500

pm and 25 pm thickness were set 10 degrees apart from each other. A monitor counter of 500 pm depletion depth was set at the angle of 150 degree.

Protons and deuterons were detected with the 20 pm-1000 pm counter telescope

and the 500 pm detector. At the same time alpha particles were detected with thin

detectors of 20 pm and 25 pm thickness.

ND 160

L I SSD I--------I Pre-Amp I----ADD —I Div I—IAtt I—I Amp!--------' 4K PHA D (I) 500(1 In-----------

A B 'SSD I--------J Pre-Amp I—I Div]—' Att l—I Ph. Inv l-lAmpl—I Ph.InvlCoinc. Gate 201.

l AmPIIJ------ ---Div I—EM------------------------------------------- Scaler I

-------------------- Discrif Ioate -----CM•-[ScalerND2200

4KPHA

D (2) 5 l SSD'------- Pre-Amp ------------------DivAttAmp-------------------------------------------Delay®IAmp H 5001.1.--------I Att I' Amp' JSCA----------------I I------------------I Gatel_--------------- OR Gate

'ScalerI)

I-----------------

----------- flout Gate ---------------

D (3) At ®iPre-Am. —I Div I.---------I Amp l— Ph. Inv Discri Gate 2511I-1 Scaler'

!SSD---------!-------'Pre- Amp!------------------------7 N D 160 Monitor (500p)1K PHA

Block Diagram of Electric Circuit System

Fig. 3. The electric circuit diagram.

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M. YASUE, T. OHSAWA, N. FUJIWARA, S. KAKIGI. D, C. NGUYEN, and S. YAMASHITA

•

Photo 1: Set up in the scattering chamber. Three silicon surface barrier detectors are mounted on the holders.

For the measurement of alpha particles, detectors of 50 gm, 25 gm, and 20 gm depletion

depth were used.

On the measurement for the excitation function, three detectors were set at 45°,

115°, and 150° with respect to the beam axis. The solid angles subtended by the counters

were of 0.4, 1.1, and 1.7 m sr, respectively. The incident proton energy was changed

from 4.0 MeV to 6.0 MeV in 50 keV or 100 keV steps.

On the measurement for the angular distributions, detectors on the arm consisted

of 20 gm and 1000 gm counter telescope, and on the turn table, two detectors of 500

gm and 25 gm thickness were set 10 degrees apart from each other. A monitor counter of 500 gm depletion depth was set at the angle of 150 degree.

Protons and deuterons were detected with the 20 gm-1000 gm counter telescope

and the 500 gm detector. At the same time alpha particles were detected with thin

detectors of 20 gm and 25 gm thickness.

NDI60

DESSSDf-------I Pre-Ampl---------------------------------------ADD—IDivI—IAttIHAmpl-----4K PHA (I)50011IA--------------- LE 155111---------JPre-Amp I—I DivI—IAtt I-1Ph.Invl-IAmpI—IPh.InvjCoinc. Gate

20 11_

I Amp IJl Div I— SCA ---------------------------------------------------------- I !Scaler I

-------------------- Discri l']Gate -----(ScalerfND 2200 4K PHA D (2) E I SSDJ------- Pre-Amp-----------------Div MI 1111Amp Delay LD IAmpH

500 11. IAmpI—J S C A I----------------I GateL, OR Gate

I IScalerl ----------- Rout Gate ----------------

1) (3) DE Em Pre-Am. —------- Amp I- Ph. Inv DiscriGate 2511

1551 f-------'Pre- Amp'----------------------7 N D 160 Monitor (5001i)1K PHA

Block Diagram of Electric Circuit System

Fig. 3. The electric circuit diagram.

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Proton Induced Reactions on 'Be

The signals from the detectors were processed by the circuits shown in Fig. 3 and fed to the pulse height analyzers, ND 160 and ND 2200. Over all energy resolutions

were 40 keV for protons, and 50 to 60 keV for alpha particles. Angular distributions were measured from 20 degrees to 160 degrees in steps of 5 degrees.

In the present experiment, in order to detect the outgoing particles such as protons, deuterons and alpha particles, the next attentions have been paid.

1. to prepare thin 9Be target in order to lessen energy losses of alpha particles in the target.

2. to identify protons and alpha particles each other. Over the energy range studied, kinetic energy of outgoing protons are too small to use the AE—E counter tele-

scope method. Hence protons were discriminated by stopping background particles with an Al foil of suitable thickness.

3. so as to use machine time efficiently, protons and alpha particles were measured simultaneously using a router circuit.

• III. RESULTS

Figures 4 and 5 show energy spectra at Ep =6.0 MeV, 6lab = 115°. In fig. 4, continuous spectra of alpha particles are observed on the lower channel side of the peak

for the 9Be (p, ai)6Li (2.18) reaction. These are break-up alpha particles from 6Li and $Be. In fig. 5, these low energy alpha particles and lithium ions are deleted due

to an Al-foil of 5.4 pm thickness placed in front of the detector. And so one can observe a broad peak for the 9Be (p, p3)9Be (3.03) reaction.

2000-9Be+p Reactions °lab= 115° Ep=6.0 MeV nict

• x 10" - 6.0

a~ c1 c-

•

.c

°ctoo 16Li4.0

0 1+1+{glll I} a2Ilial IdOPoI1 w

li~11+1114!~!t 1{~I^- 111 4+ { IlI

1114"++~11~~+!ao 1/11I Id++d!pi1Iiiol.2. 0 2 I

+i

11'4~14,11+~ii,~~ - J\1Myl~i+~W,0141,1110pJYII!41,E! flqII1NI+JiII Ii JW41'ay001JIIaI j 1,

0 ---------------------------------------------------------------------------------------------------------------------------------100 200 300400 500., 600700 Channel Number

Fig. 4. Typical energy spectrum at Ep=6.0 MeV, Blab=115°. The solid line is the energy scale, 7.2 keV/ch. Error bars indicate statistical errors.

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M. YASUE, T. OHSAWA, N. FUJIWARA, S. KAKIGI, D. C. NGUYEN, and S. YAMASHITA

9Be + p Reactions Olab= 115° Ep' 6.0 MeV 2000-with anAl foil

f

- 6 .0

Icop C o.

s

(.)1>

c1000-{}-4.02 d °{r..

U1{ P°.{W-

4f1014FI 1I 1 . II if+- 2 .0 IF1 III 1 114

1r1II I I°. `II/IIIIH1NkI§IFH P,N~'NI,11 1411a/IV 11;I-

~i~'11111FId1144H1~1111111i1~11{nly~°abwx°dihxay"i/{w~f 1401 /1pir#~M,1'f~ 0 1,~. •• •f 0 100 200 300 400500600 700

Channel Number

Fig. 5. The energy spectrum at E7,=6.0 MeV, 0Iab=115°. An Al-foil of 5.4 pm thickness was mounted in front of the detector. See also caption of Fig.'4.

9Be(p.p0)9Begnd 200'Be (p.ps)'Be3,W(20) 150

20 100

OL(msr)l~15.i, ,} 50

2010 . d0m,30 d

o(sr)lab is

30 _ 25I

402010 10L___i______/$.04S055 364A4.5aA5,5 6.° 4$/4$

50I/105// 201 ,q0-~/ 40___4,5___/ 50 55 6.0 \55°/ /10 5^

30 I/~'Oldb-445/5.055 6. 84•

20 / iy40 __ 45 0 55 5, 1/5° 5 iOlab p _ 45115.

///// / 150 545 4s 5.0 53 6.0Ep(MeV)540 455.0556.0Ep(MeV)

1o.sIli)11:5 12.0 Eex("B)(MeV)------------------------------------105 11,0 11$ 12.0 EexB)(MeV)

Fig. 6. Excitation functions for the 'Be (p, po) Fig. 7. Excitation functions for the 'Be (p, p2) 'Be (g'nd)reaction . The ordinates are'Be (2.43) reaction. Ordinates are on

cross sections in mb/sr in the laboratorya linear scale. The blank part in the system. The abscissa is an incidentexcitation function at 01,0=45° is due

proton energy in MeV.Errors are to the contamination of Hydrogens. within the size of the dots. Solid lines

are smooth curves through the data.

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,Proton Induced Reactions on 9Be

9Be(p,p1)9Be(1.ei)

20

15

d-~~(mbAr)lab10 }dCT(mb/sr)lab9Be(p,p)9Be(s.o3) " 13.0 -

5+

i 2.0 - '45°I 53.0 - L0 - 3-a~1-::::-1~L#/1150 oi

0A125° 1.0-i

1

/i/ 04 .05.06.015 0°E04

.05.06.0 PEp° 1MeV) 10.5 11.0 11.5 12.0 Ex(10B)(MeV) I0.5 11.0 IL5 12,0 Ex(10B)(MeV)

Fig. 8. Excitation functions for the 9Be (p, ps) Fig. 9. Excitation functions for the 9Be (p, p3) 9Be (1.67) reaction. Error bars denote 9Be (3.03) reaction. Below Ep=5.0

statistical errors and ambiguities in MeV, the spectrum of p3 is situated at background subtructions.the background of alpha particles. So that only the data above 5 MeV are

shown.

9Be(p,«e)6LIgnd . 15

do(mb9Be(p.de)BBeg'nd d12Lab 10

10

5 5

do.'sr)lab

5 5404 .0 45 5.0 5.5 6 • 45' 4°5 3/ •34.0 4.5 5.0 5.5 6.'150°4 2 i 2 _3 it,i.,'0(ab 1 ,ekb2 .9470 45 ..0 5.5 6+

15°1 /' 04.0 4.5 5.0 5.56.0 Ep(MeV)0•150 4,0 4.55.0 5,5 6., EP(MeV) 10.5 11.0 11.512.0'Eex(70B)( MeV )10.5 11.0 11.5 12.0 Eex('°B)(MeV)

Fig. 10. Excitation functions for the 9Be (p, d5) Fig. 11. Excitation functions for the 9Be (p, as) °Be (g'nd) reaction. Solid lines are6Li (g'nd) reaction.

smooth curves through the data. Broken lines are DWBA calculations

with the code DWUCK.

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9Be(P,C06Li (2.18)

6 9Be(p, a.) 6Li ( 3.56)

+}} }+ }

4 (Infi } 6

v

22

2~

4

045° 0/----- ---45° ,/

/ 2Olab 2 // /elab

04.•5.06.0150°EP(MeV)04.0 5.06.015oEp(MeV) 10.5 1110 11.5 12'.0 Ex (10B) (MeV) 10.5 11.0 11.5 12.0 Ex(10B)(MeV)

Fig. 12. Excitation functions for the 9Be (p, ai) Fig. 13. Excitation functions for the 'Be (p, as) 6Li (2.18) reaction. Data at the angle6Li (3.56) reaction.

of 115° could not be measured due to the background of 6Li ions.

Figures 6 to 13 show the excitation functions for the proton induced reactions on 9Be at B>1ab=45°, 115° and 150°.

In the excitation function for the 9Be(p, po) 9Be(g'nd) reaction, as seen in Fig. 6, a gross structure is observed near Ep =4.5 MeV (Ex (1°B) =10.6 MeV). In the ex-

citation function for the 9Be (p, p2)9Be (2,43) reaction, as seen in Fig. 7, a resonance with 300 keV width is observed at Ep =4.7 MeV (Ex (1°B) =10.8 MeV). In the ex-

citation function for the 9Be (p, p1)9Be (1.67) reaction, as seen in Fig. 8, a resonance like peak is observed at Ep = 5.1 MeV (Ex (1 °B) =11.2 MeV). The excitation function

for the 9Be (p, p3)9Be (3.03) reaction, as seen in Fig. 9, is monotonic over the range of proton bombarding energies from 5 MeV to 6 MeV. In the region Ep < 5 MeV, the energy spectra for p3 are situated at the background of alpha particles. Hence

excitation functions for p3 were obtained only over the energy range from 5,to 6 MeV. In the 9Be (p, do)8Be (g'nd), and 9Be (p, a0)6Li (g'nd) reactions, as seen in Figs. 10 and 11, excitation functions are as a whole monotonically decreasing. However,

a weak resonance effect is observed at Ep =4.5 MeV (Ex (1°B) = 10.5 MeV) in the (p, oc°) reaction. In the 9Be (p, al)6Li (2.18) and 9Be (p, a2)6Li (3.56) reactions, as seen

in Figs. 12 and 13, excitation functions are complicated and gross peaks are observed at Ep =4.7 MeV (Ex (1°B) =10.8 MeV) and Ep =5.5 MeV (Ex (1°B) =11.5 MeV).

Figures 14 to 17 show angular distributions for the 9Be (p, p2)9Be(2.43), 9Be (p, a°)6Li (g'nd), 9Be (p, al)6Li (2.18), and 9Be (p, (x2)6Li (3.56) reactions at Ep =4.6,

4.8, and 5.5 MeV. In the (p, oc°) reaction as seen in Fig. 15, the angular distributions

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9Be( p, P2)9Be2n410 - 9Be(P,a(o)6Lignd (g-)mb \d~CM(~r)

((Cjr>1mb~15 1dS21cr1OSr)

5-' 1010 - 15 -

110

10- III

Q

150----1_-,, . , . as MeV5r ,0 30 6• 90 INIsoao I 0r=3, 0 .o 120 xso :o5.5MeV

5 fI\1 j0 • -1/y~i'~~~/'1 1•5f I•1

+16090xmI0 g00a.~_L.—~Laa.1.v~J_ Is0 80 "MeV 5 /030'. - 030's0• -s0'i20'Is0-1004.6MeV0 A30 60 90 120 Iso xao4.6 MeV

OCH (06501E)eCM (aegreo)

Fig. 14. Angular distributions for the 19Be Fig. 15. Angular distributions for the 'Be (p, Po) 'Be (2.43) reaction at Ep=4.6(p, ao) 5Li (g'nd) reaction.

MeV, 4.8 MeV and 5.5 MeV. The ordinate is cross section in mb/sr in

the center of mass system. The abscissa is angle in degrees.

9Be(P,az)6Li2nd d_cm~.9Be(P,«1)6L115110 - (d12)GM(~Sr) 10

()„(m)) S

70-10 \ 5 t

10

/V 5 -0 .`ly~..60l\yy5730s'oiii90' i•o Iso5.5 MeV i I20 I50:0

5.5 MeV1

(i / 1.§. 55I II

°OJ-30yJ60~-90y1120 _0 4.s MeV'03,,00260 990120 150

002LL120 Iso leo 4.6 MeV '6090120 „o 1604.6 MeV0m60 90 eucd or e)Oce(degree)

Fig. 16. Angular distributions for the 'BeFig. 17. Angular distributions for the 'Be (p, a1) 6Li(2.18) reaction.(p,a2) 5Li (3.56) reaction.

are similar in shape each other and show diffraction type structure typical of a direct reaction. However, in the (p, p2), (p, (xi), (p, 02) reactions, as seen in Figs. 14, 16, and 17, angular distributions change in shape with the incident proton energy and show a

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resonance effect due to the 10.8 MeV and 11.5 MeV states of 10B. Table I shows the total cross section for the (p, a) reaction. These values are 4t A0, where A0 is the zero order coefficient of the Legendre polynominals best fitted to the data. Yields for the

(p, a0), (p, al), and (p, a2) reactions are same order each other.

Table I. Total Cross Section for 9Be (p, a)6Li Reactions in a Unit of mb.

EP (MeV) (1), ao) (1), ai)(1), az)

4.6 75.5±1.3 39.0±1.827.7±1.3

4.8 69.2±1.8 66.6±1.828.3±0.5

5.576.6±1.132.3±1.0

Figure 18 shows the angular distribution for the 9Be (p, p2)9Be (2.43) reaction over the range of proton energies from 4.2 MeV to 6.0 MeV. Above Ep =5.5 MeV, angular distributions show forward peaking, but below Ep=5.2 MeV, display falling in forward angles.

El 10 — (a) Ep• 4.2 MeV — g.10 -(b) Ep. 4.45 MeV T..T,-- cocoY

E

v 0 5——5—- v-- .8--

U r r r r r0 i i i i i. o 30 60 90 120 150 180 0 30 60 90 120 150 180

8cm(degree)8cm(degree)

15-------------------------------------------------15 ------------------------------------------

" 10——0 10 -- T. .-

mU'- 1- u'

jj E-E.

5 _ (c) Ep~4.55 MeV —5 _ id) Ep= 4.65 MeV —

0 30 60 90 120 150 180 0 30 60 90 120 150 180 8cm(degree)ecm(degrP>'

(186)

Proton Induced Reactions on 9Be

- (e) Ep- 4.7 MeV-- (f) P-4.8 MeV 15 -_15--

10 --0 1C--.i.-

cc A•A- aa6 .

CJC •O_b

b5_b5

O 30 60 90 120 150 1800 30 60 90 120 150 160

Ocm(degree)Ocm(degree)

~5 - (g) Ep- 5.0 MeV_15 - (h) Ep- 5.2 MeV _ ,

11iI -05--

v

O 30 60 90 120 150 1800 30 60 90 120 150 180 ecm (degree)Ocm(degree)

20-------------------------------------------------20------------------------------------------------------

(i) Ep- 5.5 MeV -- (j) Ep- 6.0 MeV -

15 _15__

U-V-..F

0 -~10-- A•A as

Cb

b .0b 5-_5-_

O 30 60 90 120 150 180 010 60 90 120 150 180 Ocm(degree)ecm(degree)

Fig. 18. Angular distributions for the 9Be (p, pQ) 913e (2.43) reaction. (a) Ep=4.2 MeV, (b) E5=4.45 MeV, (c) Ep=4.55 MeV, (d) Ep=4.65 MeV,

(e) E5=4.7 MeV, (f) Ep=4.8 MeV, (g) Ep=5.0 MeV, (h) Ep=5.2 MeV, (i) Ep=5.5 MeV, (j) Ep=6.0 MeV.

Solid curves are the best fit of Legendre function of order 4 to the data. Errors are smaller than the dots when not shown.

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•

IV. DISCUSSION

The present experiment has been performed with the purpose to find the d* cluster-ing in the excited states in 1 °B. If the d* clustering can exist in the 1 °B, it is an essential

point that the coupling between the d* clustering and. the 8Be core is weak. The interaction between p and n in a I S° state is weak and unbound by — 50 keV in free

space. If the interaction between the p — n pair and a 8Be core is strong, the p — n

pairing in a 1 S0 state is broken and cannot form the d* clustering. As stated in the introduction, the strength of the interaction between the p — n pair and the 8Be core can be investigated through the 9Be(p, p')9Be* reactions. And the existence of the d* clustering can be searched via the 9Be(p, a2)6Li (3.56) reaction.

In the excitation function for the 9Be(p, a2)6Li (3.56) reaction, the 10.8 MeV and 11.5 MeV states of 10B were observed. As discussed above, it is a key-point to the existence of the d* clustering that these states are enhanced also by the proton

inelastic channels leading to the positive parity states in 9Be, i.e. 9Be(p, pi) 9Be (1.67) and 9Be(p, p3)9Be (3.03) reactions. Experimental results show that the 10.8 MeV state is not observed by the (p, pi) and (p, p3) channels, but by the 9Be(p, p2)9Be*

(2.43) channels, and that the 11.5 MeV state is not found in the (p, p') channels. These facts indicate that the 10.8 MeV and 11.5 MeV states in 1°B cannot be described in terms of the configuration [8Be core + d*] such as expected from the weak coupling model. Over a range, of excitation energies in 1°B from 10.2 MeV to 12.0 MeV, the 10.6 MeV, 10.8 MeV, 11.2 MeV, and 11.5 MeV states were observed. The following is the discussions on these states.

(1) The 10.6 MeV State and the 10.8 MeV State.

Hitherto the 10.8 MeV state in 1°B has been studied by many authors'', 8) through the 9Be (p, n) and 9Be (p, y) reactions. Morion et al. observed two peaks near Ep= 4.7 MeV. Similarly in the present experiment two peaks are observed at EP =4.5 MeV

(Ex(1 °B) =10.6 MeV) and at Ep =4.7 MeV (Ex(1 °B) =10.8 MeV) in the 9Be(p, p0) reaction, as seen in Fig. 19. Dotted lines in the Fig. 19 are the optical model calcula-tions. Above the dotted lines, one can observe a gross bump with a width of about 1 MeV around EP =4.5 McV(Ex(1 °B) =10.6 MeV). Usually the broad resonance structures with width of several hundreds keV are interpreted in terms of the "door. way" states.10) The key-point for the validity of the interpretation in terms of the "door way" states is that the similar broad resonance structures are to appear regularly

with a separation energy of several hundreds keV. Other broad resonances such as a width of 1 MeV have not been reported yet on the excited states in 10B. So that another interpretation must be invoked.

The gross peak at EP =4.5 MeV is situated near the threshold energy of 4.65 MeV for the channel, 9Be + p—>n + 9B(2.33). The fast rising in the yield curves for the 9Be

(p, n) reaction at Ep =4.5 MeV is ascribed to the effect of the threshold.8) At the thresh-old energy, the relative energy between a decaying neutron and a residual nucleus 9B* is small, and long is the time when the neutron stays in the range of nuclear interactions.

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200------------------------------------------

Olab=45°

•

160-

120 --

o c 0Iab=115° 40 -

30-

20 ---------

40-- Olab=150°

20

0 ------------------------------------------4.0 5.0 6.0

Ep ( MeV)

Fig. 19. Excitation functions for the 'Be (p, po) 'Be (g'nd) reaction. Solid lines are smooth curves through the data. Broken lines

are optical model calculations.

Therefore, it is expected that the probability for the 9B(2.33) and n to de-excite into the initial channel, 9Be(g'nd) and p, is large. Namely the anomaly in the elastic scattering at Ep =4.5 MeV is ascribed to the next two step reaction.

9Be +p--*[9B(2 .33)+n]-->9Be(g'nd)+p

At 1 MeV above the threshold, the time length when the neutron stays in the interaction range is about 3 x 10-22 sec, which is the same order as the interaction time in the direct nuclear reaction. And so the width of the anomaly is reasonable in value. The 2.33 MeV state 9B is analogue to the 2.43 MeV state in 9Be which is the ground state rotation-al band. The similarity of the structures of 9B(2.33) and 9Be(g'nd) will enhance the

probability for the excitation to the 9B(2.33)+n and for the deexcitation to the 9Be (g'nd)+p. Hence it is natural to conclude that the 4.5 MeV anomaly in (p, Po) reac-tion is due to the above mentioned two step reaction.

As seen in Fig. 11, the 10.6 MeV state is excited weakly in the 9Be(p, a0)6Li(g'nd) reaction, too. Hence the 10.6 MeV state in 10B is a T=0 state.

The 10.8 MeV state is observed also in the 9Be(p, p2)9Be(2.43) and 9Be(p, a2) 6Li(3.56) reactions and weakly in the 9Be(p, al)6Li(2.18) reaction. The 9Be(p, al) 6Li(2.18) and 9Be(p,a2)6Li(3.56) reactions can excite T=0 and T=1 states, respec-tively. Therefore, the 10.8 MeV state may be iso-spin impure or doublet.

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As stated in Ref. 11, the total cross section for the 9Be(p, p2)9Be(2.43) reaction can be successfully fitted to the one-level formula of Breit-Wigner type, and the analysis with the formula gives a width of 300 keV. Hence one can conclude that the 10.8 MeV

state in 1°B is a single level of a , width of 300 keV, and the iso-spin mixing is due to the tail of the 10.6 MeV state.

Resonance reaction theory predicts that the angular distribution can be expressed by the formula 12

K da/dS2 = E AL PL (cos 0 ), (1)

• L=o

where L is even, K =Min 2(1i, J, If). li and If are orbital angular momentums in the initial and the final channels, respectively.

J is the total angular momentum, i.e. the spin for the intermediate state. In the 9Be

(p, a2)6Li(3.56) i',o+ T=1 reaction, J=l f, and parity is (—)I".Therefore, J is natural spin parity. According to the possible values of J, values of K are listed in Tables II and III in terms of the (p, p2) and (p, a2) reactions.

Table II. Possible Values for J, K, l , and l f in the 9Be (p, p2)9Be (2.43) Reaction.

10B lIlr JK sI=1s =2 sr=2sr=3

0* 13 0 0, 2 2 22, 4 0 or 2

2* 1,3 1,3 1,3 1,3,5 2or4 2,4 2,4 2,4 0,2,4 0,4or6

4* 3,5 3,5 3,5 1,3,5,7 2,6or8

c: total angular momentum, 1;, : orbital angular momentum in initial channel, If: that in final channel, s,: channel spin in initial channel,

sr : that in final channel, K: maximum order in the Legendre polynominals, 9Be -I- p —*1oB—, P2 + 9Be (2.43)

3/2- 1/2+ JR l/2+ 5/2- In this case, si=r or 2- and sr =2- or 3-.

Table III. Possible Values for J, K, h, and I in the 9Be (p, a2)6Li (3.56) Reaction.

loB lIlr K J'

si=1- sI=2'sr =0+

0+100 F0, 2 2 10 or 2 2+ 1,31,3 22or4 3-2, 4 2, 4 34 or 6

4+3, 5 3, 5 46 or 8

9Be .+ p .—,loB—*a2+°Li (3.56) 3/2- 1/2+ pr 0+ 0+

In this case, s,=1- or 2-, and Sf =0+.

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Angular distributions for (p, p2) reaction, in Fig. 18, were analyzed in terms of Le-gendre polynominals up to order four by the method of a least square fit. As shown in Fig. 18, the good fitness of the polynominals to the data means that the order four is sufficient for fitting. Figure 20 shows the coefficients in the Legendre expansions so obtained. Errors shown in Fig. 20 are the probable errors arising from the errors in data and from the difference between the fitted curve and the experimental points. The coefficients Ao is related to the total cross section (6) by the formula

Ao =o-/47.(2)

Broken lines in Fig. 20 are coefficients in Legendre polynominals fitted to the values calculated with DWBA theory. Normalization of calculated values to the experimental

I5 -------------------------------------------------- ''Ao • ; AI •;A2 +;A3 A;A4

is

—54.05.0 6.0

Ep (MeV)

Fig. 20. Energy dependence of the coefficients in Legendre polynominals fitted to the angular distributions for the 9Be (p, P2) 9Be (2.43)

reaction shown in fig. 18. Solid lines are smooth curves through the data. A dotted line denotes values estimated to be continuous

background from a fit of the one level formula to the data. Broken lines are DWBA calculations with the code DWBA I.

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data were performed at Ep=6.0 MeV in terms of the value of A0. A dotted line in Fig. 20 is the expected contribution of the direct reaction part, as stated in Ref. 11. The difference between the dotted and the broken curves shows a similar trend as that

between data and calculations in the elastic scattering as seen in Figs. 19 and 20. Hence the difference between the expected direct reaction terms and the DWBA calculations

can be attributed to the anomaly in the elastic scattering around Ep =4.5 MeV. Figure 20 indicates that the 4.7 MeV resonance is due to the L=0 and L=2 terms

in the Legendre expansions, and that the variations of the L =1 and L =3 terms are attributed to the interference between the direct and the resonance reactions. Therefore,

one obtains K=2, where K is the maximum order in Eq. (1). According to Table II possible values for J" are 1-, 2+ or 4+.

Figure 21 is the angular distribution for the 9Be(p, a2)6Li(3.56) reaction at Ep = 4.6 MeV, which shows the 90° symmetric shape characteristic of the resonance reaction.

So that the data in Fig. 21 was also analyzed in terms of Legendre polynominals. Figure 22 is the variation of chi-squares and A0 versus the maximun order K in the

Legendre expansions. Fit to data indicates K=4. According to Table III, possible values for are 2+ or 3 Considering the two cases in the (p, 132) and (p, a2) reac-

tions, possible values for Jr are limitted to the value of 2+. Hence one can assign the 10.8 MeV state in 1°B to be 2+.

The following is the consideration on the structure of 10B(10.8). The total width of the 2.43 MeV state of 9Be is 90% due to p-wave neutron emission

to the 2+ state of 8Be. So that, the 2.43 MeV state of 9Be is interpreted in terms of the configuration of a p-shell neutron coupled strongly to the 8Be(2+).20) If so, consider-

ing the fact that the 10.8 MeV state of 1°B is strongly excited by the 9Be(p, p2)9Be(2.43) reaction, one can propose that the 10.8 MeV state of 1°B is a state of a proton and a

neutron coupled strongly to the 2+ state of 8Ee. If the 2+ spin of 1 °B(10.8) is due to

9Be(P,cz2, 6L 6Ep-4.6 MeV -

4+}`

E}

^2

030 60 90 120 I50 180 0c (degree)

Fig. 21. Angular distribution for the 'Be (p, as) 'Li (3.56) reaction at E5=4.6 MeV. Error bars denote the statistical errors and the

ambiguities of background subtractions. The solid line is the best fit of Legendre polynominals of order 4 to the data.

(192)


15— 4---- 4

Ao"

• coChi-Square 4 5_2•

•-----------

•------------ 0 , i I I . '0 2 4 6 8 10

K ( Maximum Order)

Fig. 22. Variations of chi-square and Aa versus maximum order IC in Legendre polynominals. Ao is a coefficient of the zero order

in polynominals. Errors are the probable errors arising from the errors in data and from the difference between the fitted curve and the experimental points. Errors are smaller than the dots when not shown.

the 2+ spin of the 8Be core, the valence nucleons must couple S =0+ and T =1. There- fore, the proton and the neutron must be in the same orbit each other to couple S=O. The 10.8 MeV state decays also to the a2+6Li(3.56) channel, and the 6Li(3.56) is a

state of a proton and a neutron in 1p3/2 shell coupled to an alpha core. If one assumes that in the decay of 10B(10.8) to a2 and 6Li(3.56), the relative wave function between the proton, the neutron and the alpha is not disturbed so strongly, it is naturally con-

cluded that the 10.8 MeV state of 1°B is the configuration of a proton and a neutron in 1p shell coupled to 8Be(2+) i.e. [p(lp-shell)+n(1p-shell)+9Be(2+)] ,n=2+,T=r

As seen in Table II, the fact that the 2+ state of 10B(10.8) permits the p-wave proton emission is consisted with the above configuration.

(2) The 11.2 MeV State in 10B and the 9Be(p, pi) 9Be(1.67) Reaction.

The 11.2 MeV state has been excited only by the 9Be(p, p1)9Be(1.67) reaction. Angular distributions for the (p, pi) reaction have been measured at E=5.2 MeV

and 6.0 MeV. As seen in Fig. 23, angular distributions show sharp peaking in forward angles and flat shapes in backward angles. These structures are similar to Ishiwari's

data at Ep =6.9 MeV and 7.3 McV.i2) The transition of 9Be(g'nd)3/2- to 9Be(1.67)1/2+ is produced via the single particle excitation mode i.e. the excitation of a neutron from

the 1p 3/2 shell to the 2s 1/2 shell. In backward angles, the momentum transferred to a valence neutron is large. Therefore, if one consider the 1.67 MeV state of 9Be

' to be an effect of the final state interaction between a neutron in the 1 s 1/2 shell and

a 8Be, the sharp peaking in forward angles is reasonable. At Ep =5.2 MeV, near the resonance energy, the angular distribution doesn't

show resonance like shapes. Therefore, it is expected the 11.2 MeV state is not such a resonance as described in terms of R-matrix theory.11)

As stated in Ref. 13, considerations on the kinematics for the 9Be(p, p1)9Be(1.67)

( 193 )

M. YASUE, T. OHSAWA, N. FuJIwAxA, S. KAKIGI. D. C. NGUYEN, and S. YAMASHITA

9Be(p;p1)9Be(1.67)

2.0 -2 .0 - 9Be(p,p1)9Be(1.67) - Ep = 5.2 MeV

Ep= 6.0 MeV -~~

1.0 - 1.0 -

b 'bD

j b +} } 1+. + } $ _ _ }~}t ++ 4

+4i 444 + 4 444044t

0 30 60 90 120 150 180 0 30 60 90 120 150 180 ecm( degree) ecm(degree)

Fig. 23. Angular distributions for the 'Be (p, pi) 'Be (1.67) reaction.

reaction and analyses with Watson-Migdal theory indicate that the 11.2 MeV state is an effect of overlapping of two body resonances in the p — n — B Be system.

(3) The 11.5 MeV State in 10B.

The 11.5 MeV state is observed in the 11B(3He, 00' °B reaction.7) In the present experiment, the state was excited also by the 9Be(p, al)6Li(2.18) reaction and weakly by the 9Be(p, a2)6Li(3.56) reaction. Therefore, the 11.5 MeV state is impure in isospin.

In the 11B(3 He, c)1 ° B reaction, the observed width is 270 ± 50 keV. However, in the 9Be(p, al) and (p, a2) reactions, the width is about 500 keV. The large width in the alpha emitting channels shows that the 11.5 MeV state in 1°B has a large alpha particle

reduced width. However, the state wasn't observed in the 9Be(p, a0)6Li(g'nd) reaction.

Figure 24 shows the partial wave scattering amplitudes for the 9Be(p, a)6Li reaction at Ep=5.5 MeV. Partial wave amplitudes for the (p, al) reaction is one order or two

orders greater than those for the (p, a0), (p, a2) reactions or those for the (p, p0) scattering, respectively. If one assumes the high spin value such as 4+ for the 11.5 MeV state, it is reasonable that the state cannot be observed in the (p, a°) and (p, p) reactions.

As seen in Figs. 16 and 17,' the angular distributions show complicated shapes which are characteristic of the mixing of several levels. Besides the state is isospin impure. Hence one can conclude that the 11.5 MeV state is not a single level.

(4) Optical Model and DWBA Analyses.

Over the energy range from 5.0 to 6.0 MeV, excitation functions for Po, 132, and

d0 are monotonically decreasing functions of energy and the angular distributions for '

p2 show very little change with energy. These data suggest that the reaction is pre- dominantly a direct process over the energy interval. In order to perform a distorted

wave Born approximation (DWBA) calculation, elastic scattering from 9Be was analyzed in terms of optical potential model. The optical potential used had a form of surface

absorption type, namely,

(194 )


10 -----------------------------------------

tn 'Po .d

0 'aO N-1

faI00-x;a1 a;a2 eo \

t. \ •10-`J•; \ — Uf \ \

CS •• \

X 2\\ \

—

cts

cH O 10 -\\ —

N\ -1\

W•I 0~;\ ll~ —

O1 1

db,

1-5 ..,i. . . , 05 10

L

Fig. 24. Variations of the absolute values of partial wave scattering amplitudes for the 'Be (p, a) 6Li reaction versus the angular

momentum. Calculations were performed with the code DWUCK. Incident proton energy is 5.5 MeV.

pa: Imaginary part of the amplitudes of (L+1/2) wave for the 'Be (p, Po) 'Be. a5: Real part of the amplitude of L

wave for ao. al: that for al. a2: that for a2.

V = — VR(r, rR, aR) + 4ialWs(d/dr) f (r, r1, a1) +o'IVso(h/mrzc)z(1/rs0A113)(d/dr).f(r, rso, as0)+Vcoul(r, re),(3)

where f is the usual Woods-Saxon form factor

f(r, r0, a)={1+exp[(r—roA1/3)/ao]}-1(4)

and the Coulomb potential Vcoul was that of a uniformly charged sphere, namely,

Valid =(zZez/2Rc)(3—rz/Rc2), for r_<Rc=reA1/3

(zZez/r),for r>Re,(5)

(195)


z and Z being the charges of the incident and target particles, respectively. The code SEARCH, written by Wada and modified by Koike, was used to perform automatic

searches for potential parameters. Figures 25 and 26 show angular distributions for the elastic proton scattering from

9Be, at Ep=6.0 MeV and 5.0 MeV. These data were cited from Ref. 14. For the 6.0 MeV data, two sets of parameters were obtained. As shown in Table IV, SET 1

represents the best fit to the 6 MeV data and requires a large real potential and small radius. SET 2 are the shallow potential parameter sets. These ambiguities relate well-depth and radius parameters by the formula

VoR0^, constant .

SET 3, in Table IV, is the best fit to the 5.0 MeV data. As seen in Fig. 26, fitting to the data is worse compared to that at 6.0 MeV. Besides, SET 3 has a large value for the imaginary part. This property in SET 3 is attributed to the effect of a 4.5 MeV bump

103 - A 9Be (p , po) 9Be -

Ep=6.O MeV

• U\

E~\

b ..

10 — •

0 30 6 0 90 120 150

ectw(degree) Fgi. 25. Angular distribution for the proton elastic scattering from 9Be at Ep=6.0 MeV.

Solid curve: optical model calculation with parameters SET 1 in Table IV. Dotted curve: that with SET 2. Broken curve: that with SET 4. Data were

cited from Ref. 14.

(196)

Proton Induced Reactions on 'Be.

9Be(p,p,)9Be

Ep=5.O MeV

03-

s U Ul

E

y 102 - b

• --------------------------------------------------------------

• 1O0 30 60 90 120 150

0CM(degree)

Fig. 26. Angular distribution for the proton elastic scattering from 'Be at E„=5.0 MeV. Solid curve is an optical model calculation with parameters SET 3

in Table IV. Data were cited from Ref. 14.

Table IV. Optical Potential Parameters for Protons and Deuterons.

SET 1 SET 2 SET 3 SET 4 SET 5

proton proton proton proton deuteron VR 56.1 41.2 47.6 55.0 84.0

rR 1.18 1.49 1.18 1.40 1.15 aR 0.48 0.40 0.78 0.50 0.81

W, 24.3] 21.9 35.8 25.0 15.6 r, 1.96 1.89 1.96 1.40 1.34

a, 0.22 0.22. 0.22 0.50 0.68.

Vt, 9.47 5.0 5.25

rt, 1.18 1.49 1.18

a1, 0.48 0.40 0.78

X2 23.8 I 72.1 154 Potentials are surface absorption type.

SET 1, 2, and 4 are at E=6.0 MeV, SET 3 is at E,=5.0 MeV, and SET 4 is at Ed-5.0 MeV.

as shown in Fig. 19. Universal optical potential parameter sets applicable to 1p shell nucleus are reported by Watson et al.15) SET 1 is similar to Watson's parameter

set. The spectroscopic quadrupole moment of the ground state of 9Be is measured from

nuclear magnetic resonance experiments to be Qs = 3.4 fm2. 1 6) Nillson model calculations predict the deformation of the harmonic oscillator single particle potentials

of fl 0.8 to reproduce the value for Qs. These facts suggest that 9Be is highly deformed in its ground state. The 2.43 MeV state in 9Be is a member of the ground state rotational band (K =3/2-) and the enhancement of the width of the 2.43 MeV state over

(197)


20--------------------------------------------------- 9Be (p

,p2)9Be(2.43)

EP=6.0MeV

--141 1Nf \\

` \ : k4

U

L\ N y 1

t +++

0 -------------------------------------------------------------- 0 30 60 90 120 150

OcM (degree) Fig. 27. Angular distribution for the 9Be (p, ps) 9Be (2.43) reaction at Ep=6.0 MeV.

Solid curve: DWBA calculation with the code INS—DWBA I. Dotted curve: that with the code DWUCK and with potential parameters SET 1.

•Broken curve: that with the code DWUCK and with parameters SET 2.

single particle value is approximately 20: 1.17) Therefore, it is interesting to analyze the 9Be(p, p2)9Be(2.43) reaction with DWBA theory, using a collective-rotational

description of 9Be with a 3/2--5/2- spin sequence. Calculations have been carried out with the code DWUCK, using a collective form

factor,

/{ F(r)= - [VR(RRI aR)(dI dxR)J(x R)],-(6)

where f is a Woods-Saxion form factor in Eq. (4). Results of the calculations are presented in Fig. 26. Fits to the data are worse. Tentatively calculations have

been retried with the code INS-DWBA I, using the potential parameters SET 4. As shown in Fig. 27, fits to the data are improved. Using the SET 4, calculations have

been carried out over the range from 4.0 to 6.0 MeV with DWBA I. The results are shown in Fig. 20. Comparison of calculations with the data gives a deformation

12 by the formula

$2 -(aexp/Qtreor)(1 +(SKA, 0)(1 +aKB4O) *1/[(1+(-)1)2 (IAKAIOIIBKB)2(2Sa+1)], (7)

where IA, IB, Sa are spins of target nucleus, residual nucleus and incident particles, respectively. KA and KB are the projection of the spin on the nuclear symmetry

axis. At Ep =6.0 MeV, the formula (7) gives 132 =1.6.

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The large value for N2 indicates that the coupling between the ground state and the 2.43 MeV state is strong. Hence, the coupled channel analysis is invoked to des-cribe the 9Be(p, p)9Be reaction. Recently Votava et al.s> calculated coupled channel analyses for the 9Be(p, p)9Be reaction at Ep =13 MeV and gave the deformation

N2=1.1. However, fits to the data are not so improved compared to our results. In coupled channel equations, a simple Y20 deformation is assumed to describe

the deformed optical potentials. However, recent Nilsson model calculations on 9Be indicate the necessity for the higher order terms other than Y20i i.e. the sort of defor-mation which one might envisage for the g'nd-2.43 MeV rotational states is a dumbell of two alpha particles.' 8) Hence, in the coupled channel calculations, these higher

order terms must be taken into account in terms of the deformed optical potentials.

Id- 9Be(p,do)8Be Ep=4.6MeV

v

co co

0—•

.•

0 30 60 90 120 150 6cM(degree)

Fig. 28. Angular distribution for the 9Be (p, d0) 9Be (g'nd) reaction at Ep=4.6 MeV. Dotted curve: Data. Solid curve: DWBA calculation with the code DWUCK, and potential parameters SET 1 for protons and SET 5 for deuterons.

Figure 28 shows the angular distribution for the 9Be(p, d0)8Be(g'nd) reaction

at Ep =4.6 MeV. The binding energy of a neutron in 9Be is —1.67 MeV and smallest in the stable nucleus. Hitherto the 9Be(p, d)8Be reaction has been mentioned as an significant example for the direct reaction process. As seen in Fig. 19, around Ep = 4.6 MeV a gross anomaly is observed in the (p, Po) scattering. It is interesting to investigate the effect of the anomaly onto the (p, d) reaction. Hence, the (p, do) reac-tion has been analyzed with the DWBA code DWUCK, using the potential parameter

SET 1 for protons and SET 5 for deuterons. Parameters for deuterons (SET 5) were deduced from the optical potential formula of Perey's.19) As seen in Fig. 28, the phase is reproduced. However, the calculated value are small compared to the data. The discrepancies in the absolute value will be attributed to the anomaly in the (p, Po) channel.

(199)

•


Table V. Energy Levels of '°B is a Range of Excitation Energies from 10.2 MeV to 12.0 MeV.

present workprevious works(s)

E), (MeV) Es (lOB) P (keV) J", T decay P (keV) decay (MeV)channelschannels

4.5 10.6 1 MeVPo

4.5 10.6 200, 0 Po, as

4.7 10.8 300 2+, 1 Po, P2, 500 n, az az, (at)

5.1 11.2 300pi

5.5 11.5 500 isospin al, az 270+50 impure

(a) See References 4, 7, and 8.

CONCLUSIONS

Excited states of 10B in a range of excitation energies from 10.2 MeV to 12.0 MeV are summarized in Table V. The 10.8 MeV state is J' ='2+, T=1. The configura-

tion of 10B(10.8) has been assinged [p(p-shell)+ n(p-shell)+ 8 Be(2+)] Jn-2+,T=1. The 11.5 MeV state has a large alpha particle width and is not a single level. The anomaly in the (p, p0) scattering at E, =4.5 MeV is an effect of the two step reaction,

relating strongly to the threshold of the neutron decay. Namely the anomaly is an effect due to a kind of 3 body interaction in the p — n — 8Be system. For the further

study on the broad anomaly with a width of about 1 MeV, it is hoped for to treat the 9Be+p reaction as a three body system such as the p—n-8Be .

ACKNOWLEDGMENTS

The authors would like to thank Professor T. Yanabu, the late Professor Y. Uemura for their interest and encouragments throughout the work. Their thanks are also due

to the members of Tandem Accelerator Laboratory of Kyoto University for their hos-

pitalities and to Dr. M. K: Brussel for his permission to use his data and to Dr. T. . Ohnuma for use of the code DWUCK and to Drs. T. Wada and M. Koike for use of

the code SEARCH. Calculations were carried out with the TOSBAC 3400/M41 computer at INS of

Tokyo University.

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(1970). (3) Yu. A. Kudeyarov, Yu. F. Smirnov, and M. A. Chebotarov, Soy. J. Nucl. Phys., 4, 751

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Title Proton Induced Reactions on ⁹Be from 4 to 6 MeV ... · Bull. Inst. Chem. Res., Kyoto Univ., Vol. 52, No. 1 . Proton Induced Reactions on 9Be from 4 to 6 MeV Masaharu YASUEl-,