The level scheme of 112Cd

Girgis, R. K. Van Lieshout, R. 1959

Physica 25 1200-1210

T H E L E V E L SCHEME OF ll2Cd b y R. K. G I R G I S * and R. VAN L I E S H O U T Instituut voor kernphysisch Onderzoek, Amsterdam, Nederland

Synopsis The level scheme of ll2Cd has been investigated by studying the gamma ray spectrum from the decay of ll2Ag which excites levels in this'nucleide. A source of l l 2 p d - l l 2 A g in equilibrium was used. Gamma rays of 615, 690, 785, 855, 980, 1090, 1210, 1310, 1400, 1490, 1620, 1810, 1930, 2110, 2240, 2300, 2520, 2540, 2680, 2710, 2830, 2950, 3100 and 3280 keV were found to follow the decay of ll2Ag. The summing spectrum was examined using a well type NaI(T1) crystal with the source in different geometries; summing peaks of 3560, 3300, 3130, 2830, 2710, 2450, 2230, and 2050keV were observed. Gamma-gamma coincidences were performed using a conventional fastslow coincidence circuit. The results of these coincidence measurements are listed in table I. A level scheme for 119Cd, based on the intensity values of the various gamma rays following the decay of ll2Ag and on the summing and gamma-gamma coincidence measurements is presented in fig. 6.

1. Introduction. The first and second 2 + levels in ll2Cd have been observed in Coulomb excitation work performed b y S t e 1s o n and M c G o w a n 1) ; these levels were found to lie at 610 and 1295 keV respectively. N u s s b a u m, W a p s t r a , S t e r k and K r o p v e l d 2) studied the gamma rays following the decay of ll2Ag which excites levels in ll2Cd. No transitions corresponding to the deexcitation of the second 2+ level were reported. The present authorsS) investigated the decay of the l12In isomers, which also excites levels in 112Cd. A gamma ray of 617 keV was found to show a growth and decay curve consistent with the parent-daughter relation between a 22 minute n2In isomeric state and an ~ 11 minute positon emitting l12In ground state. Another weak peak at 710keV was found to disappear at approximately the same rate as the 617 keV peak, but it was masked by the comparatively strong l16In spectrum which was present in the source, preventing a precise determination of its half-life. In order to obtain more definite information about the deexcitation of the second 2+ level in ll2Cd, the gamma ray spectrum following the decay of 112Ag was therefore reexamined with the improved experimental techniques now available at our Institute. t On leave of abseJice from the Faculty of Sciel~cc, University of Cairo, Giza, Eg.vpt, U.A.R.

-

-

1200

-

-

THE LEVEL SCHEME OF l l 2 C d

1201

2. Production and Chemical Procedure. It is convenient to study the decay of ll2Ag using a source of ll2pd-ll2Ag in equilibrium due to the longer half-life of ll2pd (21 hours) compared to that of ll~Ag (3.2 hours). The llZpd activity present in the source does not contribute to the ll2Ag spectrum in the region of interest 2), since its total decay energy is < 300 keV 4). Sources of ll2pd were obtained through fission of thorium, bombarded with 25-MeV deuterons in the synchrocyclotron of this Institute. Targets of thorium metal were dissolved in 3N HC1. A few milligrams of tellurium and a few micrograms of silver and palladium were added as carriers. S02 was passed through the solution which was then centrifuged. The precipitate of tellurium and palladium was washed with 1N HC1 and dissolved in HN03. The solution was evaporated down to a small volume. Perchloric acid was added and the solution was diluted with water. The tellurium and palladium were separated with an ion exchanger (Dowex 50). The palladium was taken out of the column with 0.05-0.5 N HC1. A precipitate of palladium (a few milligrams) was made with dimethylglyoxime and then dried. The gamma ray spectrum was examined about one day after the end of the irradiation, when equilibrium between ll~Ag and ll2pd was established.

3. Measurements and results. 3.1. D i r e c t g a m m a r a y s p e c t r u m. The gamma ray spectrum was examined using a cylindrical NaI(T1) crystal 105

615

690 IO4 (~/7858S5

I0 ~

' ','

,3,o]

I

I

,'o 2o 3'o 4o s'o Chonn¢l

I

7'0 ;o 9'o

number

Fig. 1. T h e g a m m a r a y s p e c t r u m f r o m ll~-Ag in a n energy region f r o m ~ 400 t o 1500 keV.

1202

R. K. GIRGIS AND R. VAN LIESHOUT

(diameter 25 mm, height 25 mm) optically coupled to a 6292 Dumont photomultiplier. This crystal-photomultiplier combination was experimentally calibrated for efficiency over a region from ~ 22 keV to 3000 keV. The spectra were displayed on a R I D L 100 channel analyzer. Care was taken to suppress summing effects by placing the sources m 8 cm above the crystal. The spectrum of ll2pd-n2Ag was examined in an energy region from ~400 to 4000 keV. Figs. 1 and 2 show the various parts of the spectrum. I0 5

L~ '° ~ L

2,.0

,o 4

1930

I1 I ~

"

2950c'~0 I~

0

i'I

,d

,] ~\

,0

2830

I

103

/ "";~ f" \3280

,5 2'0 3'0 .,5 s'o ..'0 7b 8'0 9'0 ,60 Chonn¢l

number

Fig. 2. The g a m m a r a y s p e c t r u m from ll2Ag in all e n e r g y region from ~ 1 2 0 0 to 4000 keV.

The analysis of the spectrum was performed in the manner mentioned in previous publications s), which will be explained in detail in a forthcoming article 6). Sources of 37S, ThC", 24Na, 38K, ssy, 42K, 22Na' 65Zn' eoTBi' 54Mn, 137Cs and 85Sr were available. The characteristic lines of these sources were used to interpolate the line shapes of the various peaks resolved in 112Ag spectrum; in addition they were used for energs~ calibrations. Table I gives the various gamma rays resolved in the spectrum. The relative intensities are normalized to a value of I00 for the 615 keV gamma ray. The

T H E I E V E L SCHEME OF l l 2 C d

1203

results obtained by N u s s b a u m e . a . 2 ) . are also listed in this table. The agreement between the two sets of results is very satisfactory. Many complex gamma rays reported by the ]a st authors could be resolved in the present work. In the energy between the 1310 keV and 690 keV peaks there are probably more gamma rays than those mentioned in table I, but at all events, these are still weaker than the listed ones. The importance of the contribution of the bremsstrahlung of negatons in this region makes a decision about the correct energy of these weak peaks, if present, rather difficult. Only those peaks which show up in the direct spectrum as visual bumps, are reported in the table. TABLE I Energies and relative intensities of various g a m m a rays found to follow the decay of naAg. Results obtained by N u s s b a u m et al. 2) are included. The intensity of the 615 keV g a m m a ray has been normalized to 100 Nussbaum el al. 2) scin

present w o r k * ) scin

Energy (keV)

Relative Intensity

l'ne rgy (keV)

618 :~ 5

100

615 ± 5 690 4- 10 785 ± 15 855 4 - 1 0 980 ± 20 20 1090 1210 =[: 30 1310 :[- I0 1400 4 - 1 0 1490 ~_ 30 1620 ± 2O 1810 -~ 20 1930 =- 20 2 l l O ± 20 2240 :L 30 2300 ! 40 a) 40 a) 2520 2540 J: 20 2680 ~: 40") 2710 j- 30 2830 i 30 4O 2950 5O 3100 3280 ± 50

1110 =~: 50

1390 : 40

20

1620 :L 60 1830 4- 60

9 6

2110 !: 40

2510 L 60 2 7 9 0 : 5 80

Relative Intensity

I00 11.5 2.3 4 3 3 1.5 3.6 13.3 3 8 4 2.0 8 2.0

~E 1.5 =E 0.6 ::El ±1 4-0.7 4- 0.7 1.5 -~1 El ±I 0.6

:! 0.5

2.5

~0.5

0.9 1.5 0.17 0.10 0.06

:5 ± ± ± ±

0.3 0.4 0.05 0.04 0.02

a) ol)served in the coincidence spectrum only. *) (_~alllUla-gaulllla coincidences (615 keV 7) (690, 785,855,980, 1090, 121 O, 1400, 1490, 181 O, 1930, 211 O, 2240, 2300, 2520, 2680 keV 7)

Sources of ll2pd were extremely pure in the region of interest ( >/500 keV,) this was shown by following the decay of the individual peaks in the spectrum. The decay of these peaks, followed for more than 6 days, yielded a half-life of 21.0 ± 0.5 hours. The presence of other Pd activities (lnpd, l°gPd, 107pd) in the sources did not distort the spectrum in this region since

1204

R. K. GIRGIS AND R. VAN LIESHOUT

none of these isotopes have gamma rays with an energy higher than 500 keV. No important summing is expected to be present in the spectrum in the geometry applied. The g a m m a rays corresponding to the deexcitation of the second 2+ level in ll2Cd were observed, the 690 keV peak is visible as a bump on the high energy side of the strong 615 keV peak, while the 1310 keV gamma ray lies on the low energy side of the 1400 keV peak. 3.2 S u m m i n g s p e c t r u m . A cylindrical well-type NaI(T1) crystal of 62 mm × 62 mm external size having a hole of 9 mm diameter and 31 mm depth was used for summing studies. The hole was provided with a copper tube of 2 mm thickness, enough to stop beta particles of ~ 4 MeV energy. The crystal was optically coupled to a 6363 DuMont photomultiplier. The summing spectrum due to ll2Ag was examined in an energy region extending to ~ 4 MeV. The sources were placed in different geometries with the aim of differentiating between summing peaks resulting from cascades of two or more than two gamma rays T). Fig. 3 shows the summing spectrum IO" 1400 1620

.o.o ,o.

V',\ A

t,-,," , 2.o

"~ /i \ 24so

t ;~ \2830

',,j,

"

I0'~

0

•-

~300

-

!

io:

~s6o

I I I

,o

,'o ~o 3'o ,,% s'o go ~b ~'o Channel

number

Fig. 3. S u m m i n g s p e c t r u m f r o m n 2 A g in a n e n e r g y region f r o m 1000 to 4000 keV. T h e d a s h e d line r e p r e s e n t s t h e d i r e c t s p e c t r u m in t h i s region.

THE

LEVEL

SCHEME

OF

ll2Cd

1205

obtained when the source was placed inside the well. The various summing peaks observed are listed in table II together with their possible origin. TABLE

II

S u m m i n g peaks and their interpretation S u m m i n g peak (keV) 3 5 6 0 ± 50 3 3 0 0 ~ `50 3 1 3 0 ± 40 2830 zk 3 0 2 7 1 0 ± 30

"

24.50 :~ 40 2 2 3 0 4- 30 2050 ± 30*)

possible origin t) 2300 ztz 40 + 29`50 -- 40 + 2680 ,-4- 40 + 1810 i 20 + 2`520 ± 40 + 1490 Jz 30 + 2240 i 30 2,_ 1400- 10-k 2110 Jz 20 + 1810 ~ 20 + 1620 ~ 20 + 1400 ± 10 +

1310 615 615 1310 61S 1310 61,5 1310 61'5 61'5 61'5 615

± ~ -+~ 2': ~ ~ zL j: 5z + gz

10 5 5 I0 5 10 S 10 5 .5 ,5 '5

~') T h e results of ganmla-gamma coincidences mentioned in table 1 are taken into consideration. *) T h e e n e r g y value does not match too well with the energy sum of the proposed components, probably because this peak is overlapped b y the 2110 keV peak in the spectrum.

The 2.71 MeV summing peak is certainly partially due to cascades composed of more than two components, since its intensity drops very quickly when the source is placed on top of the crystal T). No definite conclusions can be mentioned with regard to the other peaks owing to the complexity of the spectrum and also due to the fact that some of these summing peaks overlap with real peaks in the direct spectrum (e.g. the 2050 keV summing peak and the 21 I0 keV real peak, the 2450 keV summing peak and the 2540 keV real peak). The 1310 keV peak appears as a visual peak in the summing spectrum, when the strong 1400 keV peak in its neighbourhood is diminished by being summed. This confirms that the 1310 keV peak corresponds to the cross over transition from the second 2+ level in ll2Cd having this energy. 3.3 G a m m a - g a m m a c o i n c i d e n c e s . Gamma-gamma coincidences were performed using a conventional fast-slow coincidence circuit having a resolving time of 2T = 17 ns. Two NaI(T1) crystal of 25 × 25 mm were employed. Only measurements of the coincidences with the 615 keV gamma ray were carried out. Fig. 4 and fig. 5 give the coincident spectrum obtained in the two energy regions examined in the direct spectrum. The results are reported in table I. The 615 keV peak which appears in the coincident spectrum is entirely due to coincidence with the compton distribution of the high energy gamma rays. This was confirmed experimentally by selecting the valley of the 615 keV peak in the single channel analyzer and examining coincidences in the two energy regions mentioned above. The valley of the

1206

R. K. GIRGIS AND R. VAN LIESHOUT

1400 keV peak in the coincident spectrum becomes deeper owing to the absence of the 1310 keV peak in the coincident spectrum (see fig. 5). This gives certainty to the assignment of this peak to the cross-over transition from the second 2+ level in Cd.

,o 3

>.

¢

,o:

t

[ 20

tO

I t I ' I 30 40 50 60 Chonnll number

I 70

i 80

Fig. 4. Spectrum coincident with the 615 keV peak in the low energy, region (400 to 1500 keV). The peak at 615 keV was found to be entirely due to coincidences with the compton distribution from the higher energy gamma rays.

,o4 1400

~

l

O

l

O

v

/2240

~300

Z _c

io2

I0

~ o

f

I

I0

20

I I

I

30 40 50 Chonnel number

I

60

I ~

70

I

80

Fig. 5. Spectrum coincident with the 615 keV peak in the high energy region (1200 to 4000 keV).

Three peaks, not resolved in the direct spectrum, were found in the coincident spectrum. These peaks are at 2300 ± 40, 2520 ___40 and 2680 40 keV. The first is probably very weak in the direct spectrum and masked

THE LEVEL SCHEME OF l l 2 C d

1207

by the relatively strong 2540 keV peak. The other two peaks are very close in energy to peaks resolved in the direct spectrum. This means that both the 2710 and the 2540 keV peaks are double. The sharp drop in the intensity of the 2540 keV peak in the coincident spectrum also points in this direction. The 2520 keV gamma ray is probably on top of the 615 keV level, since no summing peaks > 3.6 MeV were observed. The 2680 :[: 40 keV peak found in coincidence with the 615 keV gamma ray could be the same as the 2710 __+_30 keV peak resolved in the direct spectrum. However, the presence of a strong summing peak having this energy suggests a level at 2710 keV which may deexcite by a ground state transition; this therefore probably means t h a t the 2680 keV peak found in coincidence with the 615 keV gamma ray is not identical with the 2710 keV peak. 4. Discussion. A tentative decay scheme of 112Ag is presented in fig. 6. Levels at 615, 1310, 2020, 2230, 2430, 2540, 2710, 2830, 3120, 3280 and 3580 keV are rather certain. The first two levels follow from Coulomb excitation results 1), while the rest follows from the summing measurements reported above. These levels are shown in the decay scheme as full lines. The level at 1310 keV deexcites by two transitions: 690 and 1310 keV. The intensity ratio between the cross-over and stop-over transitions from this level was found to be 0.31 -¢- 0.08. The agreement between this value and the different values obtained for the same branching ratio from the second 2 + level in 114Cd, is excellent (The ratio between the energies of the second 2+ level to the first 2 + level in both cases has been taken into consideration). These values as found by different authors s)9) are 0.28 and 0.29. In the ll2Cd case, according to the level scheme proposed above, the 1310 keV transition can be fitted between various levels, which may mean that the ratio of the cross-over to the stop-over transition has been over-estimated but the summing measurements and the gamma-gamma coincidence measurements reported in this work show that only a small part of the 1310 keV transition may belong elsewhere. The levels at 1400, 1460 and 1600 keV are very tentative (they are shown on the decay scheme, fig. 6, in dashed line); they are proposed by analogy with the level scheme of llaCd, but their existance is compatible with the results of the gamma-gamma coincidence measurements. The presence of summing peaks at these energies could not be confirmed since two of those peaks (1400, 1600 keV) coincide with real peaks found in the direct spectrum. The valley between the 1620 and the 1400 keV peaks gains in height in the summing spectrum, which may indicate the presence of a summing peak at 1460 keV. The level at 1810 keV is also tentative. Gamma rays of 1210 and 1810 keV can originate at this level. If this level has the same character as the corresponding 1850 keV level in ll4Cd (J = 3 + or 4+), a cross-over transition

] 208

R.

K.

GIRGIS

AND

R.

VAN

LIESHOUT

should b e absent. T h i s agrees w i t h g a m m a - g a m m a coincidence m e a s u r e m e n t s in which t h e 1810 keV p e a k was f o u n d to b e in coincidence w i t h t h e 615 keV g a m m a r a y . I t also agrees w i t h t h e results of s u m m i n g m e a s u r e m e n t s , where t h e height of t h e 1810 k e V p e a k w a s f o u n d to diminish in this s p e c t r u m which m e a n s t h a t a t least p a r t of this p e a k is s u m m e d o u t w i t h coincident C2~)

""

•.)h 112 A. 47 "'J .65

o

_o_io I

o o*¢

-'2 ~

ol ~t i

i I i

I

J

,

1 I

1 :

"-i

I

I

I

I

I

I

~,-oT~- T I -I

,----:~T-~-.

I

,{.- - - - - - - - - , ~ :, : ,

':

r-J

, '

II ',

]

I

,;; ~

1I

,I

I I

I , ;

I

' , ,

,

....

1810 ~/,,'

~--

....

L,'/ 1600

F - r ~-

1

:

....

L

-.

I

3.44

-

, 1

-

....

-

14 >/(O+4+) "- I-4~ , (4~0+) R+

1I i I I I

2+

1I I I t

I I t

o+

112 Stabl~ 48 Cd 64

Fig. 6. A tentative level scheme of ll"Cd as found from the decay of x12 Ag. The levels drawn as dashed lines are uncertain. The energies of the various transitions axe given on the decay scheme. The beta ray branches from ll~Ag as found by J e n s e n 1°) are given on the scheme. Also the beta branches from llg-In as could be inferred from the work of the present authors 3) are given. p e a k s ( p r o b a b l y the 6 1 5 k e V p e a k ; the 1 2 1 0 k e V g a m m a r a y does n o t c o n t r i b u t e s t r o n g l y to the s u m m i n g , owing to its low intensity). T h e level at 1810 keV is also suggested b y t h e presence of a b e t a b r a n c h of 2.3 MeV wh{ch m a y fit a t this level, b u t this b r a n c h can equally well be the r e s u l t a n t of a n u m b e r of n e g a t o n groups.

THE LEVEL SCHEME OF

ll2Cd

1209

Tile level at 2020 keV is suggested from summing measurements. The only transition which deexcites this level is the 1400 keV gamma ray, but the 1400 keV peak does not seem to originate completely at this level (see below). The level at 2230 keV can be deexcited b y both the 1620 keV gamma ray and the 2230 keV gamma ray, b u t the fact that the 2230 keV peak was found to be in coincidence with the 615 keV peak indicates that only part of the 2230 keV peak corresponds to the ground state transition from the level at 2240 keV. The 2430 keV level can be deexcited b y a 1810 keV transition to the first excited state and a 1090 keV transition to the second excited state, in agreement with the coincidence measurements. The 2540 keV level is proposed from the absence of the major part of the peak having the same energy in the coincident spectrum with the 615 keV gamma ray. T h e absence of a strong summing peak with an energy value of 2540 keV suggests that this level is not deexcited b y strong cascades. The 1930 keV gamma would fit as a transition from this level to the 615 keV level. The intensity of this peak is only 2% of that of the 615 keV peak. A 2710 keV level is certainly populated from the decay of ll2Ag since a strong peak of this energy was observed in the summing spectrum. The summing results demonstrate that this level is deexcited b y cascades with more than 2 components. Gamma rays of 1400 keV and 2110 keV would match in energy between this level and the 1310 and 615 keV levels respectively; this also agrees with gamma-gamma coincidence measurements. The 1400 keV transition is the only one which may form part of a triple cascade. It is unlikely that the 1400 keV transition should be placed entirely between the 2710 and the 1310 keV level, since its intensity (13.3 4- 1.5 units) is practically equal to that of the transitions deexciting the 1310 keV level (15.1 -t- 1.7 units), leaving no place for any other transition to populate the second 2 + state. This corraborates the assumption that part of the 1400 keV transition takes place between the 2020 and 615 keV levels. The presence of a ground state transition from the 2710 keV level is uncertain, unless the 2680 keV peak, found in the spectrum coincident with the 615 keV peak, is different from the 2710 keV peak. Levels at 2830, 3120, 3280 and 3580 keV are suggested from the summing measurements. These levels can be deexcited in the modes shown on the decay scheme, which was constructed to be consistent with the gamma-gamma coincidence measurements and with energy value relations. The above decay scheme accommodates all gamma rays resolved in the direct spectrum and also those found in the spectrum coincident with the 615 keV peak. The deexcitation of some of these levels is uncertain due to the fact that many peaks in the direct spectrum seem to be composite as Physica 25

1210

T H E L E V E L S C H E M E OF

ll2Cd

discussed above; thus the intensity of the beta branches feeding each level cannot be calculated. The beta branches following the decay of ll2Ag resolved b y J e n s e n and cited in the Nuclear Data Sheets lo) are shown on the decay scheme. The 2.3 MeV group seems to be the sum of numerous branches feeding levels from 1310 keV up to the 2240 keV level. Also the 1.4 MeV beta branch must be a composite of many negaton groups, the major part of which feed the level at 2710 keV. The authors wish to thank Prof. Dr. P. C. G u g e l o t for his interest in this work and Prof. Dr. A. H. W. A t e n Jr. and Prof. Dr. A. H. W a p s t r a for valuable criticism. They are also indebted to Mrs. A. F u n k e - K l o p p e r for performing the many chemical separations and to the staff of the cyclotron for the irradiations. This work forms part of the, research program of the "Stichting voor Fundamenteel Onderzoek der Materie (F.O.M.)", which is financially supported b y the "Nederlandse Organisatie voor ZuiverWetenschappelijk Onderzoek (Z.W.O.)". One of the authors (R.K.G.) is indebted to the Egyptian Atomic Energy Commission for a grant. Received 25-8-59 REFERENCES 1) S t e l s o n , P. H. and M c G o w a n , F. K., Bull. Am. Phys. Soc. 2 (1957) 267 L2. 2) N u s s b a u m , R. H., W a p s t r a , A. H., S t e r k , IVl. J. and K r o p v e l d , R. E. W., Physiea " !

(1955) 77. 3) G i r g i s , R. K. and V a n L i e s h o u t , R., Physiea 2.5 (1959) 597. 4) N u s s b a u m , R. H., W a p s t r a , A. H., V e r s t e r , N. F. and C e r f o n t a i n , H., Physica 19 (1953) 385. 5) G i r g i s , R. K. and V a n L i e s h o u t , R., Physica 25 (1959) 133. 6) G i r g i s , R. K., R i c c i , R. A. and V a n L i e s h o u t , R., to be published. 7) G i r g i % R. K. and V a n L i e s h o u t , R., Nuclear Physics 12 (1959) 204. 8) M o t z , H. T., Plays. Rev. 104 (1956) 1353. 9) A d y a s e v i c h , B. P., G r o s h e v , B. D. and D e m i d o v , A. M., Conf. Acad. Sci, USSR on Peaceful Use of Atomic Energy, Phys. Math. Sci. p. 270, J u l y (1955); Consultants Bureau Transl. p. 195. I0) Nuclear Data Sheets, NRC 58-5-62.