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Gamow-Teller strengths near the ground states in A=110 – 120 nuclei studied by (p,n) reaction
NUCLEAR PHYSICS A
Nuclear Physics A577 (1994) 9c-12c North-Holland, Amsterdam
G a m o w - T e l l e r strengths n e a r the g r o u n d states m A = 110 - 120 nuclei studied b y (p, n) r e a c t i o n H Orlhara a, G C Zhong a, M Hosaka a, H Ishimaru a, K Itoh a, S Mlyamoto a, T Terakawa a, K Ishll a, A Narlta b, Y Fuji1 b, T Nakagawa b K Mlura c H Ohnuma d aCyclotron and Radioisotope Center, Tohoku University, Sendm 980, Japan b Department of Physics, Faculty of Science, Tohoku University, Sendm 980, Japan cTohoku Institute of Technology, Sendai 982, Japan dDepartment of Physics, Tokyo Institute of Technology, Meguro, Tokyo 152, Japan Abstract
An expenmental study of the (p, n) reactions on 11o 112, 114,116Cd and 116,118,1205nhas been carried out The GT type AJ:t=l ÷ translttons leading to the ground states or to those close to g s have been systematically observed in addition to the AJn = 0 ÷ isobaric analog transmons By testing proportionality relationship between the (p,n) cross section and the corresponding [3-decay rate, previously unknown GT matrix elements have been obtained 1. I N T R O D U C T I O N Gamow-Teiler(GT) 13-decay is one of the simple transitions carrying information about spln-lsospln excitation in nuclei
It is significant to accumulate f~-decay data through out
periodic table for our better understanding of the nuclear structure Theoretical evaluation for double [3-decay rate in l l6Cd, for example, requires such information As far as low lying nuclear states are concerned, f~-decay rates have been directly measured in many cases
In
some cases, however, such a GT type aJa=l + transition is energetically inaccessible by 13decay Recently (p,n) reactions at low and intermediate energies have been extensively used to study GT strength dlstnbution in nuclei
One can selectively excite the spin-flip components
through (p,n) reactions at intermediate energies due to the strong spln-isospln part of the effective nucleon-nucleon interaction for nuclei in almost entire region of tire periodic table with some exceptions of N = Z nuclei 1) Low energy (p,n) reactions, on the other hand, give much better energy resolution, making it possible to discuss (p,n) strength for individual nuclear levels 2) Various problems associated with the distorted-wave (DW) analysis of lowenergy (p, n) data were discussed m detail by Ohnuma et al 3) 0375-9474/94/$07 00 © 1994 - Elsevmr Science B V All nghts reserved SSDI 0375-9474(94)00339-4
10c
H Orthara et al / Gamow-Teller strengths near the ground states
Several odd-odd nuclei in A = 110 - 120 region have J~=l + ground states
The 13-decay
rates of these nuclei leading to the even-even daughter nuclei have been measured
112,114In
and 118,120Sb are such examples There are nuclei, however, m which a 1+ ground state is very close to but shghfly above the ground state with higher spin
Direct GT [3-decay rate
measurements are not possible In such a case Examples of these nuclei are 110416in and l l6Sb We are able to obtain reformation about unknown 13-decay rate in the latter case by utdlzmg proportionality between the 13-decay rates and (p,n) cross sections
We have measured cross
sections for the (p,n) reactions on 110112114116Cd and 116,118,120Sn at Ep = 35 MeV
2. EXPERIMENT The experiment was carried out using a 35 MeV proton beam from the A V F cyclotron and the time-of-flight faclhlaes 4) in the Cyclotron and Radioisotope Center at Tohoku Umverslty A beam swinger system was used to measure angular dlstnbut~ons of emitted neutrons between 0° and 80 ° (lab) Neutrons were detected by an array of twelve detectors, which were located at 44 3 m from the target and contained a total of 23 2 hters of NE213 sclntallator The targets were metalhc foils of 110,112, 114,116Cd and 116,118,120Sn with thicknesses (enrichment) of 4 64 mg/cm2(96 00 %), 6 10(97 05), 4 98(98 55), 5 11(96 53), 20 22(95 60), 5 59(97 79) and 6 27(98 00), respectively 3. R E S U L T S AND D I S C U S S I O N S Figure 1 shows an excitation energy neutron spectrum measured for the 118Sn(p,n) 118Sb reaction at 0-degrees The most prominent peak IS due to the neutrons leading to the isobaric
1500
.
.
.
.
100
.
IAS 1000
5001
118Sn(p' n ) l l s S b ~ E = 35 MeV o P ~ 0 0 deg
80
0+...~.1+ i
40
I
60
0
L)
0
15
12
9
6
3
0
-3
0
E (MeV) Figure 1 A sample energy spectrum for the 118Sn(p,n ) 118Sb reaction taken at 0 o with a fhght path of 44 3 m Energy per channel is 25 keV
H Orthara et al / Gamow-Teller strengths near the ground states
11 c
analog state m the residual nucleus In addition, a peak corresponding to the ground state of llSSb Is clearly resolved This reaction belongs to our first category, where both the 0 4 ~ 14 13-decay and (p,n) reaction are accessible Thus we are able to obtain a measure of proporaonality relationship between the 1+ ~ 0 4 13-decay rate and (p,n) cross section with these examples In figure 2, a neutron spectrum is displayed for the n°Cd(p,n)U°In reaction, belonging to the second category, where measurement of the 14 ~ 0+ 13-decay is impossible since the 1+ parent state in U°In is located slightly above the ground state The 04 ~ 14 (p, n) cross section then may give information about the 1+ --* 0 ÷ 13-decay rate of nOln from the proportionality relationship I
1000
I
I
+
10
I
>
~I00 0
1
I
IAS
4~
11°Cd(p,n)11°1 n'~~~~,
5
,
12
,
,
9
6
i
3
()
-3
E (MeV) x
Figure 2 Same as figure 1 but for the n°Cd(p,n) n ° I n reactaon As mentaoned previously, analysis of the 35-MeV (p,n) data suffers from some ambiguities, one of the dominant contributions being mixture of AL = 2 component in the AJ(AL,AS) = 1(2,1) channel Only the l(0,1) component is related to the GT 13-decay rate Thus it is needed to confirm that the dominant part of the 0+ ~ 1+ (p, n) transition is indeed AL = 0 For this purpose, we have measured the angular dlstnbulaons of emitted neutrons, and compared them with those for the IAS transitions which should be pure AL = 0 translaons Figure 3 shows angular distributions for neutrons leading to the IAS and the 1+ ground state for the case of the n4Cd(p,n)n4In reaction
The curve for the IAS transltlon is macroscopic
DWBA prediction by DWUCK-45), where optical potential parameters of Becchettl and Greenlees 6) are used for the entrance channel Those for the exit channel are self-consistent potential parameters derived by Carlson et al 7) The curve attached to the 0+ -~ 1+ transmon IS the same as that for the IAS but multlphed by a factor of 0 022 These two angular dmtnbutIons are very similar, mdlcalang that the dominant part of the 0+ -~ 1+ (p, n) transition is AL = 0
12c
H Orthara et al / Gamow-Teller strengths near the ground states
Table 1 hsts known B(GT) values and
,0-,A;
1
corresponding (p,n) cross sections at 0degrees
Also hsted are the ratios of
B(GT)/o(p,n)
Proportionality between the
GT strengths and the 0 ° (p,n) cross sections hold within about _+15 %,
GT matrix
elements previously unknown from 13-decay N
are reduced from thzs relation and hsted in
O1
Table 2 001 0
30
60
90
C.M. ANGLE (deg) Figure 3 Differential cross sections for neutrons leading to the IAS and ground 1+ state of 114In The curves are D W B A results Table 1 Comparison between B(GT) and o(p,n) at 0-degrees Transmon log ft B(GT) o(p, n) 0 ° B(GT)/o(p, n) 112Cd _ 112in 114Cd _ 114in 1~8Sn- 118Sb 12OSn - 120Sb
4 76 4 78 452 4 52
0 0685 0 0654 0 ll9 0 119
0 220 0 233 0450 0 540 0 255 _+0 037
0 295 0 272 0246 0 209
[B(GT)/o(p, n)] A~erase II The relation [gA/gv]2B(GT) = 6170/ft has been used, and corrections for Q-value and mass &fferences are taken into accounts Table 2 lo~ ft obtained from the, p,n) cross section Transition [B(GT)/o(p, n)]Av o(p, n) 0 ° B(GT)[1 ÷ ~ 0÷] ll0Cd - ll0In 116Cd - l16In l l 6 S n - 1165b
0255_+0037
0 256 0210 0470
0 0703 00546 0 130
log ft 475_+006 486_+006 4 48 _+0 06
REFERENCES 1 T N Taddeucchl et a l , Nucl Phys A469 (1987) 125 2 K Furukawaet a l , Phys Rev C36 (1987)1686 3 H Ohnuma et a l , Nucl Phys A467 (1987) 61 4 H O n h a r a e t a l , Nucl Instrum Methods A257 (1987)189 5 P D Kuntz. The code DWUCK-4, unpubhshed 6 F D BecchetU and G W Greenlees, Phys Rev 182 (1969)1190 7 J D Carlson, C D Zafiratos and D A Lind, Nucl Phys A249 (1975)29
Nuclear Physics A577 (1994) 9c-12c North-Holland, Amsterdam
G a m o w - T e l l e r strengths n e a r the g r o u n d states m A = 110 - 120 nuclei studied b y (p, n) r e a c t i o n H Orlhara a, G C Zhong a, M Hosaka a, H Ishimaru a, K Itoh a, S Mlyamoto a, T Terakawa a, K Ishll a, A Narlta b, Y Fuji1 b, T Nakagawa b K Mlura c H Ohnuma d aCyclotron and Radioisotope Center, Tohoku University, Sendm 980, Japan b Department of Physics, Faculty of Science, Tohoku University, Sendm 980, Japan cTohoku Institute of Technology, Sendai 982, Japan dDepartment of Physics, Tokyo Institute of Technology, Meguro, Tokyo 152, Japan Abstract
An expenmental study of the (p, n) reactions on 11o 112, 114,116Cd and 116,118,1205nhas been carried out The GT type AJ:t=l ÷ translttons leading to the ground states or to those close to g s have been systematically observed in addition to the AJn = 0 ÷ isobaric analog transmons By testing proportionality relationship between the (p,n) cross section and the corresponding [3-decay rate, previously unknown GT matrix elements have been obtained 1. I N T R O D U C T I O N Gamow-Teiler(GT) 13-decay is one of the simple transitions carrying information about spln-lsospln excitation in nuclei
It is significant to accumulate f~-decay data through out
periodic table for our better understanding of the nuclear structure Theoretical evaluation for double [3-decay rate in l l6Cd, for example, requires such information As far as low lying nuclear states are concerned, f~-decay rates have been directly measured in many cases
In
some cases, however, such a GT type aJa=l + transition is energetically inaccessible by 13decay Recently (p,n) reactions at low and intermediate energies have been extensively used to study GT strength dlstnbution in nuclei
One can selectively excite the spin-flip components
through (p,n) reactions at intermediate energies due to the strong spln-isospln part of the effective nucleon-nucleon interaction for nuclei in almost entire region of tire periodic table with some exceptions of N = Z nuclei 1) Low energy (p,n) reactions, on the other hand, give much better energy resolution, making it possible to discuss (p,n) strength for individual nuclear levels 2) Various problems associated with the distorted-wave (DW) analysis of lowenergy (p, n) data were discussed m detail by Ohnuma et al 3) 0375-9474/94/$07 00 © 1994 - Elsevmr Science B V All nghts reserved SSDI 0375-9474(94)00339-4
10c
H Orthara et al / Gamow-Teller strengths near the ground states
Several odd-odd nuclei in A = 110 - 120 region have J~=l + ground states
The 13-decay
rates of these nuclei leading to the even-even daughter nuclei have been measured
112,114In
and 118,120Sb are such examples There are nuclei, however, m which a 1+ ground state is very close to but shghfly above the ground state with higher spin
Direct GT [3-decay rate
measurements are not possible In such a case Examples of these nuclei are 110416in and l l6Sb We are able to obtain reformation about unknown 13-decay rate in the latter case by utdlzmg proportionality between the 13-decay rates and (p,n) cross sections
We have measured cross
sections for the (p,n) reactions on 110112114116Cd and 116,118,120Sn at Ep = 35 MeV
2. EXPERIMENT The experiment was carried out using a 35 MeV proton beam from the A V F cyclotron and the time-of-flight faclhlaes 4) in the Cyclotron and Radioisotope Center at Tohoku Umverslty A beam swinger system was used to measure angular dlstnbut~ons of emitted neutrons between 0° and 80 ° (lab) Neutrons were detected by an array of twelve detectors, which were located at 44 3 m from the target and contained a total of 23 2 hters of NE213 sclntallator The targets were metalhc foils of 110,112, 114,116Cd and 116,118,120Sn with thicknesses (enrichment) of 4 64 mg/cm2(96 00 %), 6 10(97 05), 4 98(98 55), 5 11(96 53), 20 22(95 60), 5 59(97 79) and 6 27(98 00), respectively 3. R E S U L T S AND D I S C U S S I O N S Figure 1 shows an excitation energy neutron spectrum measured for the 118Sn(p,n) 118Sb reaction at 0-degrees The most prominent peak IS due to the neutrons leading to the isobaric
1500
.
.
.
.
100
.
IAS 1000
5001
118Sn(p' n ) l l s S b ~ E = 35 MeV o P ~ 0 0 deg
80
0+...~.1+ i
40
I
60
0
L)
0
15
12
9
6
3
0
-3
0
E (MeV) Figure 1 A sample energy spectrum for the 118Sn(p,n ) 118Sb reaction taken at 0 o with a fhght path of 44 3 m Energy per channel is 25 keV
H Orthara et al / Gamow-Teller strengths near the ground states
11 c
analog state m the residual nucleus In addition, a peak corresponding to the ground state of llSSb Is clearly resolved This reaction belongs to our first category, where both the 0 4 ~ 14 13-decay and (p,n) reaction are accessible Thus we are able to obtain a measure of proporaonality relationship between the 1+ ~ 0 4 13-decay rate and (p,n) cross section with these examples In figure 2, a neutron spectrum is displayed for the n°Cd(p,n)U°In reaction, belonging to the second category, where measurement of the 14 ~ 0+ 13-decay is impossible since the 1+ parent state in U°In is located slightly above the ground state The 04 ~ 14 (p, n) cross section then may give information about the 1+ --* 0 ÷ 13-decay rate of nOln from the proportionality relationship I
1000
I
I
+
10
I
>
~I00 0
1
I
IAS
4~
11°Cd(p,n)11°1 n'~~~~,
5
,
12
,
,
9
6
i
3
()
-3
E (MeV) x
Figure 2 Same as figure 1 but for the n°Cd(p,n) n ° I n reactaon As mentaoned previously, analysis of the 35-MeV (p,n) data suffers from some ambiguities, one of the dominant contributions being mixture of AL = 2 component in the AJ(AL,AS) = 1(2,1) channel Only the l(0,1) component is related to the GT 13-decay rate Thus it is needed to confirm that the dominant part of the 0+ ~ 1+ (p, n) transition is indeed AL = 0 For this purpose, we have measured the angular dlstnbulaons of emitted neutrons, and compared them with those for the IAS transitions which should be pure AL = 0 translaons Figure 3 shows angular distributions for neutrons leading to the IAS and the 1+ ground state for the case of the n4Cd(p,n)n4In reaction
The curve for the IAS transltlon is macroscopic
DWBA prediction by DWUCK-45), where optical potential parameters of Becchettl and Greenlees 6) are used for the entrance channel Those for the exit channel are self-consistent potential parameters derived by Carlson et al 7) The curve attached to the 0+ -~ 1+ transmon IS the same as that for the IAS but multlphed by a factor of 0 022 These two angular dmtnbutIons are very similar, mdlcalang that the dominant part of the 0+ -~ 1+ (p, n) transition is AL = 0
12c
H Orthara et al / Gamow-Teller strengths near the ground states
Table 1 hsts known B(GT) values and
,0-,A;
1
corresponding (p,n) cross sections at 0degrees
Also hsted are the ratios of
B(GT)/o(p,n)
Proportionality between the
GT strengths and the 0 ° (p,n) cross sections hold within about _+15 %,
GT matrix
elements previously unknown from 13-decay N
are reduced from thzs relation and hsted in
O1
Table 2 001 0
30
60
90
C.M. ANGLE (deg) Figure 3 Differential cross sections for neutrons leading to the IAS and ground 1+ state of 114In The curves are D W B A results Table 1 Comparison between B(GT) and o(p,n) at 0-degrees Transmon log ft B(GT) o(p, n) 0 ° B(GT)/o(p, n) 112Cd _ 112in 114Cd _ 114in 1~8Sn- 118Sb 12OSn - 120Sb
4 76 4 78 452 4 52
0 0685 0 0654 0 ll9 0 119
0 220 0 233 0450 0 540 0 255 _+0 037
0 295 0 272 0246 0 209
[B(GT)/o(p, n)] A~erase II The relation [gA/gv]2B(GT) = 6170/ft has been used, and corrections for Q-value and mass &fferences are taken into accounts Table 2 lo~ ft obtained from the, p,n) cross section Transition [B(GT)/o(p, n)]Av o(p, n) 0 ° B(GT)[1 ÷ ~ 0÷] ll0Cd - ll0In 116Cd - l16In l l 6 S n - 1165b
0255_+0037
0 256 0210 0470
0 0703 00546 0 130
log ft 475_+006 486_+006 4 48 _+0 06
REFERENCES 1 T N Taddeucchl et a l , Nucl Phys A469 (1987) 125 2 K Furukawaet a l , Phys Rev C36 (1987)1686 3 H Ohnuma et a l , Nucl Phys A467 (1987) 61 4 H O n h a r a e t a l , Nucl Instrum Methods A257 (1987)189 5 P D Kuntz. The code DWUCK-4, unpubhshed 6 F D BecchetU and G W Greenlees, Phys Rev 182 (1969)1190 7 J D Carlson, C D Zafiratos and D A Lind, Nucl Phys A249 (1975)29