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Search for the anomalous beta-gamma directional correlation in Au198
Vo~ur~e 1 e ~ l ~ r 7
PHYSICS L E T T E R S
the "2,40 M e W y-ray is that it proceeds to the sharp level at 5,16 MeV. If third' is the ease, grave doubts a r i s e as to the correctness o~ t!~e aBsigtlmeat of,F: = 2+, T ~ 1 to this "latter level 2,3), •~h!ch beh~wes, so f a r as i t s subsequent 7~decay 5) i s concerned, as though it were the T = 1 analogue Of the 2 + f i r s t excited state of Be 10. These probIems have been discussed more fully by Meads and
~
MeV state, The deuteron b e a m was obtained from the liarwell tandem etectr°static generater and the reaction produe~s were. observed with a broad range spectregraph. A brief explanation of the e,~erhnental a r -
~ 200 ~ 150 ~ ~ 100
e m ~ l on target enriched in B 10 was bombarded with 16.44 M e V deuterons, and the Inelae~tlcally scattered deuterons were detected at ~ laboratory observation angle of 60 °. A region of the B I0 m o meslan'~ spectrum, recorded on a nuclear emulsion plate is shown ~ the figure. The number of tracks for ½ m m of emulsion is plotted against position on the p i ~ e . Peaks a r e v i s i b l e a r i s i n g from the excitation of the 4.77 MeV and 6.11 MeV levels in B t0, as also i s a broad dtztribution at 5.18 MeV. It i s apparent that the 5.11 MeV peak is s~perimpesed o~ the br~ad 5.18 MoV peak. The cause of the high ~ e k g r o u n d on the low energy side of the peak i s not understood, but i s i s conceivably due to the presence of another broader state at an energy greater t I ~ 6.2 MeV. There i s no trace of a narrow pe~& attrfvutable to the 5.16 MeV T = 1 level, . ~ t e r careful subh'aeLion el the 5.11 M e V peak the centre of m a s s width o~ the 6~1t MeV state was measured te be I10 ~ I0 keV. 'During the period of the p r e s e n t worK, the existence of the 5.18 M e V level in B ~o has been confirmed by Dearnaley eL aL 6) with Lib(a, z)Li6, They foue ~ the width of t!'e state to be 105 keV. The ag* ~ement between these r e s u l t s suggests
SEARCH
I Jiffy 1962 Deuteron energy (MeV} 3.8 3.6
4.0 "--
300
B10(4"7~
'~,.4 -~']
[ t / [ B10(5.11)
i0(5.04) J i
BI0(s.18) t~.~.~':
llx
t
1/2
~(
.] -'-: . "~ 31 29 27 25 23 Distance along plate (cras) Fig. I. Sppetrum of deuterons obtained by bembardLug a ~fi0 target with 10.44 MeV deuter as. The energies in MeV of the excited states corresponding to the outgoteg deuteron groups are sbevm. 33
•
strongly that the width of the level was o v e r e s t i mated by Sprenkel e t a l . , ~mclthere is no reason to doubt that lhe "2.40 M e ~ ' gamma ray from the 7.5S M e V level populates the 5.16 M e V level.
References 1) E, C. Sprenkel, J.W. Olness and R. E. Segel, Phys. Rev. Letters 7 (1961) 174. 2) B.K.Armitage and R.E. Meads, Nuclear Physics 33 (t962) 494. 3) N.W. Tanner and S.S. ~ , Nuclear Physis~ 23 (Z9Sl) 319. 4) R. E. Meads a,-~J. E. G. McI1dowie, Nuclear Physics 33 (1962) 502. 5) L. Meyer-Seh~tzmeister and S. S. Hanna, Phys. Rev. I08 (1957) 1506. 6) G. Dearnaley, D, S. Gemmel and S. S. Hanna, to be published.
FOR THE ANOMALOUS BETA-GAMMA C O R R E L A T I O N IN Au 198 *
DIRECTIONAL
B. -G. '~ET : E R S S O N * % W. L. C R O F T and J. H. H A M I L T O N Physie~ Department, Vanderbflt University, Nnsh~il!e, Tennessee Received id June Recent studies of the 960-keV, 2" - 2+ beta * York supported in part by a ~rant from the National Science F~u~iation° ~* On leave from the University o~ Uppsala, Sweden.
1962
group in Au 198 indicate that both the longitudinal uolarization 1) of the beta r,artinles and the beta~ ' n m a directional correlation 2) exhibit a strong energy dependence for electron energies below abSut 125 keV. • 285 : : ::
Volume I, number 7
PHYSICS LETTERS
The longitudinal polarization w a s f i r s t found to d~,op f r o m ~ V/C at 400 keV to - (0.82 ± 0.05) V/C at 145 keV /. M o r e recently Avakyan et al, 1.) r e ported polarizations of - (0.74 + 0,07) V/C, - (C.(;6 :k 0:06) V/C, and - (0.56 .~ 0.00) V/C at 120, 9 0 and 60' keV respectively. The b s t a - g a m m a directlcnal correlation in this low beta energy region w a s s~udled by E l - N e s t et al. 2) to s e a r c h f o r effects which might be correlated to the unusual effect in the beta polarisation. They found the anlsotropy in the b e t a - g a m m a directional cor~elatiou to decrease to a m i n i m u m around 150 keV, and then increase again at .~ower electron energies. The behu polariz~.tlon and b e r n - g a m m a d~ectlonal correL~tfon for once, forbidden, noaunique t r a n s i t i o n s ~n the Konopinskl-Uhlenbeck approximation 4) a r e related to the shape of the h e m spectrum. Re.cent careful studies of the shape factor 5) show a definite de;'~ation f r o m the statistical shape f o r electrons with energies below about 350 keV. The shape factor i n c r e a s e s about 15% f r o m 350 to 100 keV 5). The d e c r e a s e in the beta polarization i s at least qua2itstively explained by the r i s e in the shape factor, i I c ~ e v e r , %he i n c r e a s e in the anisotrepy ~i the b e t a - g a m m a directinnRl correlation belov: 1~0 keV i s in the opposit~ direction f r o m that expected on the b a s i s of the shape factor ~.one and in fact is miexplainable in the ~-xpprorArnation or the K~U approximation. A magnetic tens s p e c t r o m e t e r 6) adapted f o r elecJron-gamma directional correlation m e a s u r e m~c~s has been used to ~tudy the beta-gamma directional correL%tion in Au !9g, The experLmental se~ up has been extensively tested by s t ~ y i n g the iso+ropic b e t a - ~ m m a d i r e c t i o n ~ c o r r e h t i o n in CO60. /u:~r~ent~/~nAsotropies have bee,l shown to be less than 0.1%. T w o sources of A u 198 were prepared by thermal e~poratlon in vaeunm, qFne source thicknesses were definitely less than 40 ~g/cm 2, T w o dJ:~ferent ah, a n i n ~ bacMnge, one thick, 1,5 m g / c m g, and one thin, 0.i4 m ~ / c m 2 , were used to !ook for possible s c a ~ e r m g ~-fects in the backing, Tat)!e 1 shows fl~e r e s u l t s of our m e a s u r e m e n t s at four beta e n e r ~ e s for the b~o s o u r c e s which guve the same rem, lt. Our restflts are also compared in table 1 i~ the d~R of E1-Nesr et RL ~') obtained w i ~ a magnetic !ens s p e c t r o m e t e r f'.r the beva momentan~ ~.nalysis and of S~effen 7) ob~ ,ed w ~ . a scmtilIat!cn crystal f o r the beta enerc.
286
I July 1962
Table 1 The A2 term de~ ~ n e d ta the l:~ta-gam~,~ dfreetion~l correlatI~ _~~u168 as a function of energy.
I
70
I ~0
I 0.020 ~ 0.004
[ 0.00,~±0.00~1
1
---
---
10.003 _+o.oog,
lo.o099~o.~o~t
J 400 ] o.oz4_+.+,').~4 ~0.014±0.0oI~o.010
[ 6oo6oo I~ o..o9s~:0.004 ~ o~ o + o,o0~Io.o~
±o.oo~
_+o~oo,3
analysis. Our datl do not support the data of ElNest et aL 2). %~,e difference in our data and that of EI-Nesr et al, cannot be explalned in terms of back scattered electrons from the source backing. The sha~es of the b?ta spectra obtained with co,utwo sources were compared with that of I-lamiltoa et aL 5), and a g r e e m e n t within about 5% was obtained for the thin backed source and an increase of about 15% f r o m backscattering wa~ observed at 70 keV for the thick backed source. As expected, this amount of backseattering did not m e a s u r a b l y influence the correlation even at this low energy a s m e a s u r e ~ v'ith the two sources. Oct- m e a s u r e d a n i sotropy should not be significantly attenUatc~ ( d ~ i nitely < 5% reduction at 70 keY) by source thickness effects on the b a s i s of the work of G~mmi et al. g). At high beta e n e r g i e s our r e s u l t s ~-re consisteut with the e a r l i e r data reported by Steffen 7). As a result of the s m e l l anisotropy a detailed comparison of the anisotropy and the shape factor is not possible at this time. Our data r e m o v e , howev;.r, the reported anoma!ie 2) ~ d a r e consistent w~th either the ~ or K - U approxirn~,tions. Refore.noes !} R.O.Avakyau et ai., J. E~pt' Theorct phv~ 41 (l:.~J~ 681; t~t~]a~on: Soviet Phy~c~ JZTP ~4 (~932} 4~1. L) M.S.EI--Nesr et ~! , Z, ftlr Phys~k 166 (1962~ 119. 3) A.I. Alikba~iov, ~:~'.P. Ellseev an'J V.A. Lyubimov, J. Expd, Theoret. Phys. B0 (!0SO) ,587;Zransla' ,,~: Soviet Physic8 d'~TP 12 (1001} 414. 4) T, Kotani, Phys. Bey. 114 (1959) 7~5. 5) J.H.Hazsilton, R V.Stoekendal. D.C.Camp, L.M, Langer ~ d D. R. Smih~, Nu~lear;,hy~les, in press. 6) W, L. Croft, J. H, Hamilton. T. 5!. George, J,H. ~istler ~.ud B.-G, Pe~terssen, Bull. Am. Phys. Soc.? (1982), in press. 7) B.M,S~ffen, Phys. Bey. 118 (19~;9)763. F.Ginlrni, E.Heer aatl P.Seherrer, Heir. Physlca Aeta 29 (1959) 147.
PHYSICS L E T T E R S
the "2,40 M e W y-ray is that it proceeds to the sharp level at 5,16 MeV. If third' is the ease, grave doubts a r i s e as to the correctness o~ t!~e aBsigtlmeat of,F: = 2+, T ~ 1 to this "latter level 2,3), •~h!ch beh~wes, so f a r as i t s subsequent 7~decay 5) i s concerned, as though it were the T = 1 analogue Of the 2 + f i r s t excited state of Be 10. These probIems have been discussed more fully by Meads and
~
MeV state, The deuteron b e a m was obtained from the liarwell tandem etectr°static generater and the reaction produe~s were. observed with a broad range spectregraph. A brief explanation of the e,~erhnental a r -
~ 200 ~ 150 ~ ~ 100
e m ~ l on target enriched in B 10 was bombarded with 16.44 M e V deuterons, and the Inelae~tlcally scattered deuterons were detected at ~ laboratory observation angle of 60 °. A region of the B I0 m o meslan'~ spectrum, recorded on a nuclear emulsion plate is shown ~ the figure. The number of tracks for ½ m m of emulsion is plotted against position on the p i ~ e . Peaks a r e v i s i b l e a r i s i n g from the excitation of the 4.77 MeV and 6.11 MeV levels in B t0, as also i s a broad dtztribution at 5.18 MeV. It i s apparent that the 5.11 MeV peak is s~perimpesed o~ the br~ad 5.18 MoV peak. The cause of the high ~ e k g r o u n d on the low energy side of the peak i s not understood, but i s i s conceivably due to the presence of another broader state at an energy greater t I ~ 6.2 MeV. There i s no trace of a narrow pe~& attrfvutable to the 5.16 MeV T = 1 level, . ~ t e r careful subh'aeLion el the 5.11 M e V peak the centre of m a s s width o~ the 6~1t MeV state was measured te be I10 ~ I0 keV. 'During the period of the p r e s e n t worK, the existence of the 5.18 M e V level in B ~o has been confirmed by Dearnaley eL aL 6) with Lib(a, z)Li6, They foue ~ the width of t!'e state to be 105 keV. The ag* ~ement between these r e s u l t s suggests
SEARCH
I Jiffy 1962 Deuteron energy (MeV} 3.8 3.6
4.0 "--
300
B10(4"7~
'~,.4 -~']
[ t / [ B10(5.11)
i0(5.04) J i
BI0(s.18) t~.~.~':
llx
t
1/2
~(
.] -'-: . "~ 31 29 27 25 23 Distance along plate (cras) Fig. I. Sppetrum of deuterons obtained by bembardLug a ~fi0 target with 10.44 MeV deuter as. The energies in MeV of the excited states corresponding to the outgoteg deuteron groups are sbevm. 33
•
strongly that the width of the level was o v e r e s t i mated by Sprenkel e t a l . , ~mclthere is no reason to doubt that lhe "2.40 M e ~ ' gamma ray from the 7.5S M e V level populates the 5.16 M e V level.
References 1) E, C. Sprenkel, J.W. Olness and R. E. Segel, Phys. Rev. Letters 7 (1961) 174. 2) B.K.Armitage and R.E. Meads, Nuclear Physics 33 (t962) 494. 3) N.W. Tanner and S.S. ~ , Nuclear Physis~ 23 (Z9Sl) 319. 4) R. E. Meads a,-~J. E. G. McI1dowie, Nuclear Physics 33 (1962) 502. 5) L. Meyer-Seh~tzmeister and S. S. Hanna, Phys. Rev. I08 (1957) 1506. 6) G. Dearnaley, D, S. Gemmel and S. S. Hanna, to be published.
FOR THE ANOMALOUS BETA-GAMMA C O R R E L A T I O N IN Au 198 *
DIRECTIONAL
B. -G. '~ET : E R S S O N * % W. L. C R O F T and J. H. H A M I L T O N Physie~ Department, Vanderbflt University, Nnsh~il!e, Tennessee Received id June Recent studies of the 960-keV, 2" - 2+ beta * York supported in part by a ~rant from the National Science F~u~iation° ~* On leave from the University o~ Uppsala, Sweden.
1962
group in Au 198 indicate that both the longitudinal uolarization 1) of the beta r,artinles and the beta~ ' n m a directional correlation 2) exhibit a strong energy dependence for electron energies below abSut 125 keV. • 285 : : ::
Volume I, number 7
PHYSICS LETTERS
The longitudinal polarization w a s f i r s t found to d~,op f r o m ~ V/C at 400 keV to - (0.82 ± 0.05) V/C at 145 keV /. M o r e recently Avakyan et al, 1.) r e ported polarizations of - (0.74 + 0,07) V/C, - (C.(;6 :k 0:06) V/C, and - (0.56 .~ 0.00) V/C at 120, 9 0 and 60' keV respectively. The b s t a - g a m m a directlcnal correlation in this low beta energy region w a s s~udled by E l - N e s t et al. 2) to s e a r c h f o r effects which might be correlated to the unusual effect in the beta polarisation. They found the anlsotropy in the b e t a - g a m m a directional cor~elatiou to decrease to a m i n i m u m around 150 keV, and then increase again at .~ower electron energies. The behu polariz~.tlon and b e r n - g a m m a d~ectlonal correL~tfon for once, forbidden, noaunique t r a n s i t i o n s ~n the Konopinskl-Uhlenbeck approximation 4) a r e related to the shape of the h e m spectrum. Re.cent careful studies of the shape factor 5) show a definite de;'~ation f r o m the statistical shape f o r electrons with energies below about 350 keV. The shape factor i n c r e a s e s about 15% f r o m 350 to 100 keV 5). The d e c r e a s e in the beta polarization i s at least qua2itstively explained by the r i s e in the shape factor, i I c ~ e v e r , %he i n c r e a s e in the anisotrepy ~i the b e t a - g a m m a directinnRl correlation belov: 1~0 keV i s in the opposit~ direction f r o m that expected on the b a s i s of the shape factor ~.one and in fact is miexplainable in the ~-xpprorArnation or the K~U approximation. A magnetic tens s p e c t r o m e t e r 6) adapted f o r elecJron-gamma directional correlation m e a s u r e m~c~s has been used to ~tudy the beta-gamma directional correL%tion in Au !9g, The experLmental se~ up has been extensively tested by s t ~ y i n g the iso+ropic b e t a - ~ m m a d i r e c t i o n ~ c o r r e h t i o n in CO60. /u:~r~ent~/~nAsotropies have bee,l shown to be less than 0.1%. T w o sources of A u 198 were prepared by thermal e~poratlon in vaeunm, qFne source thicknesses were definitely less than 40 ~g/cm 2, T w o dJ:~ferent ah, a n i n ~ bacMnge, one thick, 1,5 m g / c m g, and one thin, 0.i4 m ~ / c m 2 , were used to !ook for possible s c a ~ e r m g ~-fects in the backing, Tat)!e 1 shows fl~e r e s u l t s of our m e a s u r e m e n t s at four beta e n e r ~ e s for the b~o s o u r c e s which guve the same rem, lt. Our restflts are also compared in table 1 i~ the d~R of E1-Nesr et RL ~') obtained w i ~ a magnetic !ens s p e c t r o m e t e r f'.r the beva momentan~ ~.nalysis and of S~effen 7) ob~ ,ed w ~ . a scmtilIat!cn crystal f o r the beta enerc.
286
I July 1962
Table 1 The A2 term de~ ~ n e d ta the l:~ta-gam~,~ dfreetion~l correlatI~ _~~u168 as a function of energy.
I
70
I ~0
I 0.020 ~ 0.004
[ 0.00,~±0.00~1
1
---
---
10.003 _+o.oog,
lo.o099~o.~o~t
J 400 ] o.oz4_+.+,').~4 ~0.014±0.0oI~o.010
[ 6oo6oo I~ o..o9s~:0.004 ~ o~ o + o,o0~Io.o~
±o.oo~
_+o~oo,3
analysis. Our datl do not support the data of ElNest et aL 2). %~,e difference in our data and that of EI-Nesr et al, cannot be explalned in terms of back scattered electrons from the source backing. The sha~es of the b?ta spectra obtained with co,utwo sources were compared with that of I-lamiltoa et aL 5), and a g r e e m e n t within about 5% was obtained for the thin backed source and an increase of about 15% f r o m backscattering wa~ observed at 70 keV for the thick backed source. As expected, this amount of backseattering did not m e a s u r a b l y influence the correlation even at this low energy a s m e a s u r e ~ v'ith the two sources. Oct- m e a s u r e d a n i sotropy should not be significantly attenUatc~ ( d ~ i nitely < 5% reduction at 70 keY) by source thickness effects on the b a s i s of the work of G~mmi et al. g). At high beta e n e r g i e s our r e s u l t s ~-re consisteut with the e a r l i e r data reported by Steffen 7). As a result of the s m e l l anisotropy a detailed comparison of the anisotropy and the shape factor is not possible at this time. Our data r e m o v e , howev;.r, the reported anoma!ie 2) ~ d a r e consistent w~th either the ~ or K - U approxirn~,tions. Refore.noes !} R.O.Avakyau et ai., J. E~pt' Theorct phv~ 41 (l:.~J~ 681; t~t~]a~on: Soviet Phy~c~ JZTP ~4 (~932} 4~1. L) M.S.EI--Nesr et ~! , Z, ftlr Phys~k 166 (1962~ 119. 3) A.I. Alikba~iov, ~:~'.P. Ellseev an'J V.A. Lyubimov, J. Expd, Theoret. Phys. B0 (!0SO) ,587;Zransla' ,,~: Soviet Physic8 d'~TP 12 (1001} 414. 4) T, Kotani, Phys. Bey. 114 (1959) 7~5. 5) J.H.Hazsilton, R V.Stoekendal. D.C.Camp, L.M, Langer ~ d D. R. Smih~, Nu~lear;,hy~les, in press. 6) W, L. Croft, J. H, Hamilton. T. 5!. George, J,H. ~istler ~.ud B.-G, Pe~terssen, Bull. Am. Phys. Soc.? (1982), in press. 7) B.M,S~ffen, Phys. Bey. 118 (19~;9)763. F.Ginlrni, E.Heer aatl P.Seherrer, Heir. Physlca Aeta 29 (1959) 147.