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Photoprotons from Zr
Volume 10, number 3
PHYSICS LETTERS
c a l l i n g the work of E.A. Sanderson to our a t t e n tion.
15 June 1964
Also, Vinh Mau, Thesis, University of Paris (1962) and to appear in Nuclear Physics. 7) B. Dudelzak and R. E. Taylor, J. phys. radium 22 (1961) 544. 8) P.Bounin and G.R.Bishop, J. phys. 24 (1963) 974. 9) R.S.Willey, Nucl. Phys. 40 (1963) 529. 10) M.K. Pal and M.A.Nagarajon, Phys. Rev. 108 1577. 11) D.Kurath, private communication, to appear in Phys. Rev.. 12) J. Goldemberg and W. C. Barber, private communication HEPL 320 (1964). 13) E.A.Sanderson, Nucl. Phys. 35 (1962) 557, especially note added in proof.
References 1) R.S.Willey, Physics Letters 6 (1963) 336. 2) H.P.Jolly, Physics Letters 5 (1963) 289. 3) V.Gillet and M.A, Melkanoff, Phys. Rev. 133B (1964) 1190. 4) G.R. Bishop, C. B~tourn~ and D. B. Isabelle, Nucl. Phys. 54 (1964). 5) V.Gillet, Thesis, University of Paris (1962). 6) V.Gillet and N. Vinh Mau, Physics Letters 1 (1962) 25.
PHOTOPROTONS
FROM
Zr
I. I. DUSHKOV, B. S. ISHKHANOV, I. M. KAPITONOV and B.A. YUR'EV Nuclear Research Institute, Moscow State University, Moscow, USSR and
V. G. SHEVCHENKO International Atomic Energy Agency, Vienna Received 26 April 1964
Recent m e a s u r e m e n t s of the (y,p) c r o s s - s e c t i o n s in heavy n u c l e i 1) as well as m e a s u r e m e n t r e s u l t s of a n g u l a r and e n e r g y d i s t r i b u t i o n s of photoprotons 21) have shown that in the ~'-energy r a n g e of 25-30 MeV t h e r e e x i s t quadrupole absorption peaks. The c r o s s - s e c t i o n in Rh 103 3) has two peaks out of which the one lying at the lower e n e r g y s e e m s to be of a dipole n a t u r e . The r e s u l t s of the (~,p) c r o s s - s e c t i o n m e a s u r e m e n t s c a r r i e d out with the A ~ 90-100 n u c l e i show that t h e i r peaks lie at 20-22 MeV, that i s 4-5 MeV higher than the ( r , n ) c r o s s - s e c t i o n peaks. F o r the n u clei c h a r a c t e r i z e d by this A v a l u e , the n a t u r e of the (y,p) c r o s s - s e c t i o n s r e m a i n s s t i l l a p r o b l e m . The p r e s e n t work d e s c r i b e s r e s u l t s of m e a s u r e m e n t s of the ( r , p ) c r o s s - s e c t i o n and of angul a r and e n e r g y d i s t r i b u t i o n s of photoprotons p r o duced by b r e m s s t r a h l u n g at E~m_ = 22, 25 and 34 MeV. The r e s u l t s obtained ~ s e r v e s p e c i a l attention as they can be c o m p a r e d with the detailed s h e l l - m o d e l c a l c u l a t i o n s of the y - a b s o r p tion c r o s s - s e c t i o n in Zr 90 r e c e n t l y made a v a i l able 4). The ~ - b r e m s s t r a h l u n g used in e x p e r i m e n t s was e m i t t e d by the 35 MeV b e t a t r o n of the Re310
200
Zr(y, n)
u Results . ~ o f ref. 4
150'
b
100,
50
1"0
V
15 Ey
\. ! 20
25
Fig. 1. Comparison of ~heoretical and experimental dat~. for I:b,e (~. n) reaction.
s e a r c h N u c l e a r P h y s i c s Institute of the Moscow State U n i v e r s i t y . The e x p e r i m e n t a l method and g e o m e t r y a r e d e s c r i b e d in detail in ref. 3 and 5. The r e s u l t s obtained a r e shown in figs. 1-5.
Volume I0, number 3 (rob)
PHYSICS
LETTERS
15 June 196!
Np
Zr(~,p)
• Results of ref. 4
300
60
40 200
20 100
/ |
J
3
°)" , li.s
1 .5
.2.5
.6.5
s.5
11
9
13 Ep (MeV}
Fig. 3b. Energy distribution of photoprotons at Eymax = 25 MeV.
Ey
Np
Fig. 2. Comparison of theoretical and experimental data for the (y,p) reaction.
5
150
Np~
;%:i.
ev
100 200 50 150
= 22 MeV 100
2
4
6
8
10
12
14
1"6 Ep (Me Fig. 3c. Energy distribution of photoprotons at Eymax = 34 MeV.
50
3
5
7
9
11
Ep (MeV)
Fig. 3a. Energy distribution of photoprotons at Eymax = 22 MeV. Let us f i r s t c o n s i d e r the photoproton p r o d u c tion c r o s s - s e c t i o n s . In figs. 1 and 2 c o m p a r i s o n i s made of the r e s u l t s obtained for the ( r , n ) and ( r , p ) c r o s s - s e c t i o n s in Z r with the calculation data in ref. 4. While for the (v,n) r e a c t i o n the a g r e e m e n t between t h e o r y and e x p e r i m e n t i s good, no a g r e e m e n t w h a t s o e v e r can be c l a i m e d ~ _ ~he (~,p) r e a c t i o n . A c c o r d i n g to the c a l c u l a t i o n s the m a i n peak of the ( r , p ) c r o s s - s e c t i o n would lie at 16 MeV with the second peak at ~ 23 MeV. The ( r , p ) c r o s s section m e a s u r e d in the p r e s e n t work o c c u r s at 22 MeV. B e s i d e s , the r e s o n a n c e width g r e a t l y d i f f e r s f r o m the c a l c u l a t e d value.
The e n e r g y d i s t r i b u t i o n s produced by b r e m s s t r a h l u n g at 22 and 25 MeV ~ire shown in figs. 3a and b. F o r the s p e c t r u m e m i t t e d by b r e m s s t r a h l u n g at E ~ m a x = 25 MeV, the photoproton s p e c t r u m was calculated by m e a n s of the s t a t i s t i c a l m o del 6). It is shown in fig. 3b. Its c o m p a r i s o n with the e x p e r i m e n t a l r e s u l t i n d i c a t e s that while the yield of photoprotons at e n e r g i e s below 7 MeV can be accounted for in t e r m s of the s t a t i s t i c a l t h e o r y , p r o d u c t i o n of higher e n e r g y p r o t o n s m u s t be m o s t l y due to the d i r e c t p r o c e s s e s . The c o n t r i b u t i o n made by the d i r e c t p r o c e s s e s a m o u n t s to as high a value as 35%. A c o m p a r i s o n with the s h e l l - m o d e l c a l c u l a t-ions does not show any s a t i s f a c t o r y a g r e e m e n t , fig. 3b. The c a l c u l a t e d s p e c t r u m t u r n s out to lie at e n e r g i e s much in e x c e s s of the e x p e r i m e n t a l ones 4). The e n e r g y d i s t r i b u t i o n produced by the 34 MeV B r e m s s t r a h l u n g is shown in fig. 3c. C o m 31
Vohn,ne 10, number 3
PHYSICS LETTERS
I(S) 1
10
Ep> 7 MeV I /
/ o 1£
~ Ep>4 MeV !
O*
•
0
i0 180"
~
6'0
120
Fig. 4. Angular distributions of photoprotons at Eymax = 25 MeV. I(~) . . . . . . . . . : Ep = 12 - 17 MeV
lOi o
~ E ~ - - 9 ÷ 1 2 M e V
1!t 0L
-L E n = 5 " 6 - 9 " 0 M e V
-V
t / ~
~
M
e
V
101 t
0~ 0
60
12o
9
1so
Fig. 5. Angular distributions of photoproton at E.fmax = 34 MeV.
312
15 June 1964
p a r i s o n of the s p e c t r a emitted by the 22, 25 and 34 MeV b r e m s s t r a h l u n g d e m o n s t r a t e s little or no a l t e r a t i o n in t h e i r s h a p e s , except for an i n significant growth in the h i g h - e n e r g y portion of the s p e c t r u m produced by the 34 MeV b r e m s strahlung. Fig. 4 shows the a n g u l a r d i s t r i b u t i o n of the p r o t o n s emitted in Zr p h o t o d i s i n t e g r a t i o n brought about by b r e m s s t r a h l u n g at Eyma = 25 MeV. It i s c h a r a c t e r i z e d by a c o n s i d e r ~ t ' ~ a n i s o t r o p y and is, in fact, s y m m e t r i c towards 90 o, which should be taken to m e a n that at E y = 22 MeV the (y, p) r e s o n a n c e is of a dipoTea~hca r a c t e r . The a n g u l a r d i s t r i b u t i o n s produced by the 34 MeV b r e m s s t r a h l u n g a r e shown in fig. 5. The sharp a s y m m e t r y o b s e r v e d in the shape of a n g u l a r d i s t r i b u t i o n s i m m e d i a t e l y suggests that in the y - e n e r g y r a n g e of 25-34 MeV t h e r e is a quadrupole a b s o r p t i o n peak, which is in conf o r m i t y with the r e s u l t s of ref. 7, a c c o r d i n g to which the quadrupole a b s o r p t i o n peak for Zr m u s t o c c u r at Ey ~ 27 MeV. 1) J.H. Carver, R. B. Taylor and W. Turchinetz, Australian J. Phys. 13 (1960) 617; Yu. I. Sorokin, V.G. Shevchenko and B. A. Yur'ev, Zh. Eksp. Teor. Fiz. 43 (1962) 1600; V. G. Shevchenko, B.A. Yur'ev and B.P. Levkin, Zh. Eksp. Teor. Fiz. 44 (1963) 808; M. E. Toms and W. E. Stephens, Phys. Rev. 92 (1952) 362. 2) V.G.Shevehenko and B. A. Yur'ev, Nucl. Phys. 37 (1962) 495. 3) B.S. Ishklmnov, E.N. KorntenKo, Yu. I. Sorokin, V.G. Shevchenko and B.A.Yur'ev, Zh. Eksp. Teor. Fiz. 45 (1963) 38. 4) B.S. Ishkhanov, K.V. Shitikova and B. A. Yurtev, in press. 5) N.N. Balamatov, B.S. Ishkhanov, V.G. Shevchenko and B.A.Yurtev, Vestn. Mosk. Univ., Ser. Fiz. Astr No. 2 (1964). 6) R. M. Osokina, Conf. on Direct Interactions and Nuclear Reaction Mechanisms, Padova, 3-8 September 1962. 7) V.G.Shevchenko, N,P.Yudin and B.A.Yur'ev, Zh. Eksp. Teor. Fiz. 46 (1963) 180.
PHYSICS LETTERS
c a l l i n g the work of E.A. Sanderson to our a t t e n tion.
15 June 1964
Also, Vinh Mau, Thesis, University of Paris (1962) and to appear in Nuclear Physics. 7) B. Dudelzak and R. E. Taylor, J. phys. radium 22 (1961) 544. 8) P.Bounin and G.R.Bishop, J. phys. 24 (1963) 974. 9) R.S.Willey, Nucl. Phys. 40 (1963) 529. 10) M.K. Pal and M.A.Nagarajon, Phys. Rev. 108 1577. 11) D.Kurath, private communication, to appear in Phys. Rev.. 12) J. Goldemberg and W. C. Barber, private communication HEPL 320 (1964). 13) E.A.Sanderson, Nucl. Phys. 35 (1962) 557, especially note added in proof.
References 1) R.S.Willey, Physics Letters 6 (1963) 336. 2) H.P.Jolly, Physics Letters 5 (1963) 289. 3) V.Gillet and M.A, Melkanoff, Phys. Rev. 133B (1964) 1190. 4) G.R. Bishop, C. B~tourn~ and D. B. Isabelle, Nucl. Phys. 54 (1964). 5) V.Gillet, Thesis, University of Paris (1962). 6) V.Gillet and N. Vinh Mau, Physics Letters 1 (1962) 25.
PHOTOPROTONS
FROM
Zr
I. I. DUSHKOV, B. S. ISHKHANOV, I. M. KAPITONOV and B.A. YUR'EV Nuclear Research Institute, Moscow State University, Moscow, USSR and
V. G. SHEVCHENKO International Atomic Energy Agency, Vienna Received 26 April 1964
Recent m e a s u r e m e n t s of the (y,p) c r o s s - s e c t i o n s in heavy n u c l e i 1) as well as m e a s u r e m e n t r e s u l t s of a n g u l a r and e n e r g y d i s t r i b u t i o n s of photoprotons 21) have shown that in the ~'-energy r a n g e of 25-30 MeV t h e r e e x i s t quadrupole absorption peaks. The c r o s s - s e c t i o n in Rh 103 3) has two peaks out of which the one lying at the lower e n e r g y s e e m s to be of a dipole n a t u r e . The r e s u l t s of the (~,p) c r o s s - s e c t i o n m e a s u r e m e n t s c a r r i e d out with the A ~ 90-100 n u c l e i show that t h e i r peaks lie at 20-22 MeV, that i s 4-5 MeV higher than the ( r , n ) c r o s s - s e c t i o n peaks. F o r the n u clei c h a r a c t e r i z e d by this A v a l u e , the n a t u r e of the (y,p) c r o s s - s e c t i o n s r e m a i n s s t i l l a p r o b l e m . The p r e s e n t work d e s c r i b e s r e s u l t s of m e a s u r e m e n t s of the ( r , p ) c r o s s - s e c t i o n and of angul a r and e n e r g y d i s t r i b u t i o n s of photoprotons p r o duced by b r e m s s t r a h l u n g at E~m_ = 22, 25 and 34 MeV. The r e s u l t s obtained ~ s e r v e s p e c i a l attention as they can be c o m p a r e d with the detailed s h e l l - m o d e l c a l c u l a t i o n s of the y - a b s o r p tion c r o s s - s e c t i o n in Zr 90 r e c e n t l y made a v a i l able 4). The ~ - b r e m s s t r a h l u n g used in e x p e r i m e n t s was e m i t t e d by the 35 MeV b e t a t r o n of the Re310
200
Zr(y, n)
u Results . ~ o f ref. 4
150'
b
100,
50
1"0
V
15 Ey
\. ! 20
25
Fig. 1. Comparison of ~heoretical and experimental dat~. for I:b,e (~. n) reaction.
s e a r c h N u c l e a r P h y s i c s Institute of the Moscow State U n i v e r s i t y . The e x p e r i m e n t a l method and g e o m e t r y a r e d e s c r i b e d in detail in ref. 3 and 5. The r e s u l t s obtained a r e shown in figs. 1-5.
Volume I0, number 3 (rob)
PHYSICS
LETTERS
15 June 196!
Np
Zr(~,p)
• Results of ref. 4
300
60
40 200
20 100
/ |
J
3
°)" , li.s
1 .5
.2.5
.6.5
s.5
11
9
13 Ep (MeV}
Fig. 3b. Energy distribution of photoprotons at Eymax = 25 MeV.
Ey
Np
Fig. 2. Comparison of theoretical and experimental data for the (y,p) reaction.
5
150
Np~
;%:i.
ev
100 200 50 150
= 22 MeV 100
2
4
6
8
10
12
14
1"6 Ep (Me Fig. 3c. Energy distribution of photoprotons at Eymax = 34 MeV.
50
3
5
7
9
11
Ep (MeV)
Fig. 3a. Energy distribution of photoprotons at Eymax = 22 MeV. Let us f i r s t c o n s i d e r the photoproton p r o d u c tion c r o s s - s e c t i o n s . In figs. 1 and 2 c o m p a r i s o n i s made of the r e s u l t s obtained for the ( r , n ) and ( r , p ) c r o s s - s e c t i o n s in Z r with the calculation data in ref. 4. While for the (v,n) r e a c t i o n the a g r e e m e n t between t h e o r y and e x p e r i m e n t i s good, no a g r e e m e n t w h a t s o e v e r can be c l a i m e d ~ _ ~he (~,p) r e a c t i o n . A c c o r d i n g to the c a l c u l a t i o n s the m a i n peak of the ( r , p ) c r o s s - s e c t i o n would lie at 16 MeV with the second peak at ~ 23 MeV. The ( r , p ) c r o s s section m e a s u r e d in the p r e s e n t work o c c u r s at 22 MeV. B e s i d e s , the r e s o n a n c e width g r e a t l y d i f f e r s f r o m the c a l c u l a t e d value.
The e n e r g y d i s t r i b u t i o n s produced by b r e m s s t r a h l u n g at 22 and 25 MeV ~ire shown in figs. 3a and b. F o r the s p e c t r u m e m i t t e d by b r e m s s t r a h l u n g at E ~ m a x = 25 MeV, the photoproton s p e c t r u m was calculated by m e a n s of the s t a t i s t i c a l m o del 6). It is shown in fig. 3b. Its c o m p a r i s o n with the e x p e r i m e n t a l r e s u l t i n d i c a t e s that while the yield of photoprotons at e n e r g i e s below 7 MeV can be accounted for in t e r m s of the s t a t i s t i c a l t h e o r y , p r o d u c t i o n of higher e n e r g y p r o t o n s m u s t be m o s t l y due to the d i r e c t p r o c e s s e s . The c o n t r i b u t i o n made by the d i r e c t p r o c e s s e s a m o u n t s to as high a value as 35%. A c o m p a r i s o n with the s h e l l - m o d e l c a l c u l a t-ions does not show any s a t i s f a c t o r y a g r e e m e n t , fig. 3b. The c a l c u l a t e d s p e c t r u m t u r n s out to lie at e n e r g i e s much in e x c e s s of the e x p e r i m e n t a l ones 4). The e n e r g y d i s t r i b u t i o n produced by the 34 MeV B r e m s s t r a h l u n g is shown in fig. 3c. C o m 31
Vohn,ne 10, number 3
PHYSICS LETTERS
I(S) 1
10
Ep> 7 MeV I /
/ o 1£
~ Ep>4 MeV !
O*
•
0
i0 180"
~
6'0
120
Fig. 4. Angular distributions of photoprotons at Eymax = 25 MeV. I(~) . . . . . . . . . : Ep = 12 - 17 MeV
lOi o
~ E ~ - - 9 ÷ 1 2 M e V
1!t 0L
-L E n = 5 " 6 - 9 " 0 M e V
-V
t / ~
~
M
e
V
101 t
0~ 0
60
12o
9
1so
Fig. 5. Angular distributions of photoproton at E.fmax = 34 MeV.
312
15 June 1964
p a r i s o n of the s p e c t r a emitted by the 22, 25 and 34 MeV b r e m s s t r a h l u n g d e m o n s t r a t e s little or no a l t e r a t i o n in t h e i r s h a p e s , except for an i n significant growth in the h i g h - e n e r g y portion of the s p e c t r u m produced by the 34 MeV b r e m s strahlung. Fig. 4 shows the a n g u l a r d i s t r i b u t i o n of the p r o t o n s emitted in Zr p h o t o d i s i n t e g r a t i o n brought about by b r e m s s t r a h l u n g at Eyma = 25 MeV. It i s c h a r a c t e r i z e d by a c o n s i d e r ~ t ' ~ a n i s o t r o p y and is, in fact, s y m m e t r i c towards 90 o, which should be taken to m e a n that at E y = 22 MeV the (y, p) r e s o n a n c e is of a dipoTea~hca r a c t e r . The a n g u l a r d i s t r i b u t i o n s produced by the 34 MeV b r e m s s t r a h l u n g a r e shown in fig. 5. The sharp a s y m m e t r y o b s e r v e d in the shape of a n g u l a r d i s t r i b u t i o n s i m m e d i a t e l y suggests that in the y - e n e r g y r a n g e of 25-34 MeV t h e r e is a quadrupole a b s o r p t i o n peak, which is in conf o r m i t y with the r e s u l t s of ref. 7, a c c o r d i n g to which the quadrupole a b s o r p t i o n peak for Zr m u s t o c c u r at Ey ~ 27 MeV. 1) J.H. Carver, R. B. Taylor and W. Turchinetz, Australian J. Phys. 13 (1960) 617; Yu. I. Sorokin, V.G. Shevchenko and B. A. Yur'ev, Zh. Eksp. Teor. Fiz. 43 (1962) 1600; V. G. Shevchenko, B.A. Yur'ev and B.P. Levkin, Zh. Eksp. Teor. Fiz. 44 (1963) 808; M. E. Toms and W. E. Stephens, Phys. Rev. 92 (1952) 362. 2) V.G.Shevehenko and B. A. Yur'ev, Nucl. Phys. 37 (1962) 495. 3) B.S. Ishklmnov, E.N. KorntenKo, Yu. I. Sorokin, V.G. Shevchenko and B.A.Yur'ev, Zh. Eksp. Teor. Fiz. 45 (1963) 38. 4) B.S. Ishkhanov, K.V. Shitikova and B. A. Yurtev, in press. 5) N.N. Balamatov, B.S. Ishkhanov, V.G. Shevchenko and B.A.Yurtev, Vestn. Mosk. Univ., Ser. Fiz. Astr No. 2 (1964). 6) R. M. Osokina, Conf. on Direct Interactions and Nuclear Reaction Mechanisms, Padova, 3-8 September 1962. 7) V.G.Shevchenko, N,P.Yudin and B.A.Yur'ev, Zh. Eksp. Teor. Fiz. 46 (1963) 180.