LEVELS AND TRANSITIONS IN 125Te

R. PRASAD*)

Department of Physics, Banaras Hindu University, Varanasi-221005, India

Gamma transitions and levels of 125Te following the decay of 125Sb have been studied using Ge(Li) detector and NaI(T1)--NaI(TI) sum-coincidence spectrometer incorporated with a fast- slow coincidence circuit. In all, twenty five gamma rays have been reported, out of which two weak gamma rays with energies 366.0 and 402"0 keV have been observed and confirmed for the first time. These gamma rays have been fitted by assigning a new level of 402 keV energy. An ambiguous transition of energy 122'1 keV has also been confirmed. No evidence was found for the existence of 145.9, 315.0, 489.8, and 497.4 keV transitions. The accurate intensities for various transitions have been determined.

1. INTRODUCTION

Although the decay of 1258b isotope has been extensively studied [ 1 - 1 5 ] through

various aspects of beta and gamma ray spectroscopy, yet there exists considerable difference, especially in respect of weak transitions, in the findings of various investi- gators [ 1 - 1 1 ] .

It is interesting to note that CnANORA and PANDHAR1PANDE [2] had suggested a level at 401 keV energy in order to fit the 123.0 and 80.0 keV gamma rays. They, however, suggested that these gamma rays can also be fitted by introducing a level at 444.0 keV energy depending upon whether the 80"0 keV transition follows the 123.0 keV transition or precedes it. Later on the basis of Ge(Li) spectrum, various workers [3, 4, 7] suggested a level at 443.6 keV energy fitting the 227.5, 408.1 and 443.6 keV gamma rays. This proposition is also strengthened by them by fitting 80.0 and 123.0 keV gamma rays, ruling out the level at 401.0 keV energy as proposed by CHANDKA and PANDHARIPANDE [2]. This ambiguous state of affair of 401.0 and 443.0 k e y levels needs verification.

Besides this, GUPTA et al. [10] gives a good account of other previous works on this isotope and they confirm only 172-6, 178.8 and 198.5 keV gamma rays out of all the disputed ones. Recently ARDISSON and ABDM~ZmM [11], on the basis of their singles Ge(Li) spectra studies, have proposed two new transitions of energy 315.0 and 497.4keV ,which also need confirmation. Also they have shown 145.9 keV transition with dotted lines in their decay scheme without any comment.

Thus, in view of the above ambiguities and to supplement the data further, we thought it worthwhile to reinvestigate the level scheme and transitions in 125Te employing Ge(Li) detector and sum-coincidence spectrometer referred earlier [16, 17].

*) Present address: Department of Physics, University of Dar es Salaam, P. O. Box 35063, Dares Salaam, Tanzania.

Czech. J. Phys. B 29 [1979] 7 3 7

R. Prasad: Levels and transitions in 125 Te

2. MEASUREMENTS AND RESULTS

The a/sSb isotope, in the form of antimony trichloride and antimony oxychloride in dilute HC1 solution, was obtained from BARC, Trombay, Bombay, India and it was allowed to decay for two years. For our measurements, the sources of different strengths were prepared by putting and drying few drops of active solution on small circular perspex discs. No detectable impurity was found in the sources used in our measurements.

106

o~

i

105

104

428,1 - -

O)

2• I I 160 180 200

P j

~176

~ ~176

\. "~176

~ l r

220 240 260 channel number

Fig. 1. The singles gamma ray spectrum of 125Sb in the region of interest.

The singles gamma ray spectrum was recorded with a 6 cm 3 Ge(Li) detector (resolution 3.0 keV at 1332 keV energy) in an ND 512 channel analyser. A bias-ampli- fier type BA 669 was used to account for different parts of the spectrum with ade- quate scale expansion and counting times. All the electronics used were standard ORTEC modules. The background was also taken for the same time as that of singles spectrum. No serious background was found to be present. The typical spectrum in the region of interest is shown in Fig. 1. In addition to other established gamma rays, we observed weak but clear peaks at 122-1 (not shown), 366.0 and 402.0 keV energies. Also we made careful and vigorous efforts to look for the presence of 81.8 and 111.0 keV gamma rays but on account of huge Compton background and their weak intensities they could not be resolved dearly beyond doubts. However, some indications for their presence were there. The starred peak in the spectrum corres- ponds to the laboratory background. The intensities of all the observed transitions relative to that of 428.1 keV transition were calculated and compared (Table 1) with those available in literature.

7 3 8 Czech. J. Phys. B 29 [1979]

R. Prasad: Levels and transitions in 125 Te

Table 1

Energies and Intensities of Gamma Transitions following the decay of 125Sb.

[keV] Present Ref. Ref. Ref. Ref. Work [11] [10] [9] [8]

35"5 81"8

109"7 111"0 117"3 122"1 172"0 176"7 178"8 198"4 204.3 208"9 228'7 320"9 366"0 379'5 402"0 408"8 428"1 443' 8 463-4 600.1 606"2 635-5 671"3

0.03 4- 0'01a) 0"26 -4- 0'04 b) 0"02 4- 0"01 a) 0-91 4- 0"O5 0.08 4- 0"01 0.74 4- 0.06

22.9 ~: 0.6 0.11 4- 0.01 0.06 4- 0.01 1.12 -4- 0"04 0-80 -4- 0"04 0'42 4- 0"02 1"48 4- 0"06 0'14 -t- 0"02 5"18 4- 0'2 0"12 4- 0'02 0.57 4- 0"04

100 1"06 • 0'02

35"1 4- 0.8 60"4 :k 1"1 16"6 4- 0"5 38-7 4- 0"8

6.04 :k 0"16

0"89 4- 0"04

0"65 4-4- 0'05 22"9 4- 0"7 0"10 -4- 0"02 0"055 4- 0"01 0"99 -4- 0"05 0"79 4- 0"04 0'45 4- 0"02 1-41 4- 0"07

5"15 4- 0"2

0"59 -q- 0"03 100

1"05 -4- 0"05 35"2 4- 1"0 60"1 4- 1.8 16"8 4- 0"5 38-4 • 1"1

6"02 4- 0'24

<0"02 0"18 4- 0"02

<0"01 0"85 -q- 0"05

<0"01 0"72 • 0"05

22"8 4- 0"4 0"08 4- 0.01 0"04 + 0.01 1"14 -t- 0.03 0-77 4- 0.05 0"44 4- 0"02 1.43 4- 0'04

5"12 -4- 0"1

0"55 • 0"03 100

1"05 4- 0.03 35"1 4- 0"6 60.2 4- 0"9 16.7 4- 0"3 38-5 4- 0"6 6"05 4- 0"12

M

0"045 <0 '02

1"13 4- 0"11

0"89 4- 0.1 22"7 4- 0"9

0"93 4- 0"09 0"63 4- 0'06 0"39 4- 0'04 1"52 4- 0"15

5"1 4- 0"3

0"45 4- 0"05 100

1.0 • 0.2 35"0 -4- 1.5 59.8 :k 2"5 16'4 -4- 0.8 38"4 4- 1"9

5"83 4- 0"3

19.6 -4- 2-0

O.39 • 0.04

1"13 4- 0.1

0"9 4- 0"1 24.9 4- 2.0

1"15 -t- 0.1 0.85 4- 0-08 0.44 4- 0.04 1"41 -4- 0-1

5"27 4- 0.4

0.62 q- 0.06 100

1"03 4- 0.1 35.4 4- 2.8 61-5 4- 4"9 16.4 -4- 1"2 37.3 -4- 3"0 6"0 4- 0.5

a) The gamma rays could not be resolved clearly.

b) Measured intensity depends on the state of equilibrium between 12sSb and ~25Te.

The NaI(T1)-NaI(T1)sum-coinc idence spec t rometer deve loped by PRASAD et al. [16]

was employed t o s tudy the coincidence re la t ionship o f these g a m m a rays. In o rder

to e l iminate the poss ib i l i ty of crys ta l - to-crys ta l scat ter ing [18], a 2.54 cms th ick lead

shield was p laced between the two de tec tors p laced at 90 ~ with each other . The

sum-coincidence spect ra were r ecorded at 489-7, 525.2, 639.0 and 671.6 keV gates

for several days in an air cond i t ioned room. The analysis of sum-coincidence spect ra

were m a d e af ter the sub t rac t ion o f the cor respond ing chance coincidence spect ra

f rom the or iginal ones. Whi le analys ing the spect rum, all o ther necessary precaut ions

descr ibed earl ier [16] were t aken in to account . I t is impera t ive to men t ion tha t the

Czech. J. Phys. B 29 [1979] 739

R. Prasad: Levels and transitions in ~ 25Te

laboratory background does not disturb our sum-coincidence spectrum as the background peaks do not satisfy the required sum-coincidence conditions.

The sum-coincidence spectrum at 489.7 keV sum gate (gate width 30 keV) is shown in Fig. 2. This gate will have contributions of pair of gamma rays between 642.3 and 144.7 keV and 525.2 and 35.5 keV states. The pair of peaks at 35.5 and 460, 85 and (402 + 408), 117.3 and 379.5, 122.1 and 366, 172 and 310, 176.7 and 320.9,

300

200

100

6

U~

~6

j

1 20

0 0 40

t ~

co

i ;f'! t ..: �9 . "-,," ,..

�9 .,.., I" ~ . J J I I "', i 60 80 100 120 140 160

channel number

Fig. 2. Sum-coincidence spectrum of 125Sb at the 489"7 keV gate.

178"8 and 310, 204.3 and 275.0 keV energies were observed. The pa!r of 117.3 and 379.5 keV gamma rays are well established and follow the 642.3 ~ 525.2 ~ 144.7 keV decay mode. The newly observed 366 keV gamma ray is found to be in coincidence with 122.1 keV gamma ray which can be fitted only in the 525.2 ~ 402 ~ 35.5 keV decay mode by assigning a level at 402 keV. The peaks at (402 + 408) and 85 keV correspond to the 402 and 408 keV gamma rays and the Compton contribution at 85 keV due to other coincident higher energy gamma rays. As expected, the peaks at 35.5, 172, 178.8 and 204.3 keV with their composite Compton contributions at 460, 310 and 275 keV energies have been observed.

In order to study the transitions between 525.2 and 0 keV, and 671-6 and 144-7 keV states, the sum-coincidence spectrum at 525 keV sum-gate (gate width 40 keV) was recorded as shown in Fig. 3. The pair of peaks at 122.1 and 402 keV energies suggest us a possibility of existence of 402 keV level and may follow 525-2 --* 402

7 4 0 Czech. J. Phys. B 29 [1979]

R. Prasad: Levels and transitions in ~ 2 5 Te

0 decay mode. Although 122-1 and 402 keV transitions are weak, yet in the spectrum (Fig. 3) they appear to be prominent because within the selected gate for the sum of 122.1 and 402 keV gamma rays the contributions due to other stronger cascades are comparatively weak. The other peak composites of (35.5 + 485) keV, (97 + 428.7) keV, (172 + 340) keV, (178-8 + 340) keV and (208.9 + 310) keV energies are due to Photo-Compton summings of various coincident gamma rays. The contribution due to 408 keV gamma ray and the Compton of 228 keV gamma ray, if at all present, is quite negligible.

200

6 100

0 0 20 40

l !2 El ".. ~[

!

60 80

t~

l ". ""~. " .A

I I t : . ~ d 100 120 140 160

channel number

Fig. 3. Sum-coincidence spectrum of 125Sb at the 525"2 keV gate.

The cascade transitions from 642.3 and 636.2 keV states to the ground state were studied by recording the sum-coincidence spectrum at 639.0 keV sum-gate (gate width 30 keV). As the peaks obtained in this spectrum were due to already established gamma rays only, the spectrum has not been presented.

A highest energy sum-gate at 671.6 keV was also set and the spectrum was recorded but not shown here as it does not contribute anything new. However, the presence of peaks at 228-7 and 443-8 keV energies suggested the existence of 228.7 and 443.8 keV gamma rays following the 671.6 ~ 443.6 ~ 0 decay mode and hence confirming the existence of 443.6 keV level. Other peaks obtained in the spectrum were due to well established gamma rays.

3. DISCUSSION

In addition to all the well established gamma rays we observed in our singles spec- trum weak indications of 122.1,366 and 402 keV gamma rays submerged in the huge Compton background of higher energy transitions. As this only cannot be taken

Czech. J, Phys. B 29 11979] 741

R. Prasad: Levels and transitions in 1 2 5 T e

as the confirmation for their presence, the sum-coincidence spectra at various gates were recorded. In the 525.2 keV sum gated coincidence spectrum, the 122.1 keV gamma ray was found to be in coincidence with 402 keV transition, suggesting the 525.2 --, 402 - , 0 decay mode. This confirms the presence of 402 keV gamma ray depopulating the 402 keV state. It also places the 122.1 keV gamma ray between

7 /z+ (z . - t y ) _

12 m.~ b.m

51 ,t,,-m N O . . . . . �9 . . r ~O NN r C0 G0 ~-O N __

tOl~ --

4 912"- m N

50,

58d

3 / 2 +

1/2 + I

w

u

125Te 5 2

F i g . 4. L e v e l s c h e m e o f x25,~.,

/ % _ _

671 ' 6

6 4 2 . 3

6 3 6 . 2

5 2 5 ' 2

4 6 3 . 5 4 4 3 . 6

4 0 2 , 0

3 2 1 " 1

t~

o 1 4 4 . 7

35 -5

o

525.2 and 402 keV states and not between 443 and 321 keV states as reported by MAZETS and SERGEENKOV [3] and INAMURA [4]. Had the 525.2 --* 443 -* 321 key mode been there we would have observed 80 and 443 keV gamma peaks to be present in the 525.2 keV sum-gated coincidence spectrum which we failed to do. Further check for the position of 122.1 keV gamma ray between 525.2 and 402 keV states is seen in the 489.7 keV sum-coincidence spectrum where 122.1 and 366 keV gamma rays are found to be in coincidence. This gate also confirms the presence of 366 keV gamma ray being fitted in 525.2 --* 402 --* 35.5 keV decay mode. Once the 122.1 keV gamma ray is fixed between 525.2 and 402 keV states, the 81.8 keV coincident gamma ray, if at all present, automatically on the basis of its energy consideration gets fixed between 402 and 321 keV states.

We, throughout our measurements, do not find any evidence for the presence of 489.8 keV gamma ray proposed by MAZETS and SERGEENKOV [3] and ARDISSON

7 4 2 Czech. J. Phys. B 29 [1979]

R. Prasad: Levels and transitions in 12S Te

and ABDMEZIEM [11]. Also transitions of energies 145.9, 315.0 and 497.4 keV pro- posed by ARDISSON and ABMEOZmM [11] have not been observed in any of our spectra.

The level scheme of 125Te consistent with the present measurements is shown in Fig. 4.

We are grateful to Professor P. C. SOOD for his keen interest in this work and to the Council of Scientific and Industrial Research, New Delhi, for financial support.

Received 22. 9. 1978.

References

[1] AUBLE R. L., Nucl. Data Sheets 7B (1972), 465. [2] CHANDRA G., PANDHARIPANDE V. R., Nucl. Phys. 46 (1963), 119. [3] MAZETS E. P., SERGEENKOV Yu. V., Izv. Akad. Nauk SSR. Ser. Fiz. 30 (1966), 1185. [4] INAMURA T., J. Phys. Soc. Japan 24 (1968), 1. [5] SERGOLLE H., Compt. Rend. 267 B (1968), 1042. [6] WOLCKEN K., Z. Naturforsch. 23a (1968), 788. [7] STONE N. J., FRANKEL R. B., SHIRLEY D. A., Phys. Rev. 172 (1968), 1243. [8] NAGPAL T. S., GAUCItER R. E., Can. J. Phys. 48 (1970), 2978. [9] 1VIARSOL C., ARDISSON G., Compt. Rend. Ser. 272B (1971), 61.

[10] GUPTA J. B., SINGHAL N. C., HAMILTON J. H., Z. Phys. 261 (1973), 137. [I 1] ARDISSON G., ARDMEZlEM K., Radiochem. Rad. Lett. 29 (1) (1977), 1. [12] CRUSE D. W., JOHANSSON K., KARLSON E., Nucl. Phys, A 154 (1970), 369. [13] BARRETTE J., BARRETTE M., BOUTARD A., LAMOUREUX G., MONARO S., Nucl. Phys. A 169

(1971), 101. [14] ROTS M., SILVERANS R., COUSSEMENT R., Nucl. Phys. A 170 (1971), 240. [15] BARRETTE J., BARRETTE M., HAROUTUNIAN R., LAMOUREUX G., MONARO S., Phys. Rev. 11C

(1975), 282. [16] PRASAD R., CI-IATURVEDI L., CHATIJRVFJ~I S. N., NIGAM A. K., Nucl. Phys. A 243 (1975), 317. [17] PRASAD R., Can. J. Phys. 55 (1977), 2036. [18] PRASAD R., Nucl. Instr. Methods 152 (1978), 583.

Czech. J. Phys. B 29 [1979] 743