The decay of 214Pb and other 226Ra daughters

Nuclear Physics A133 (1969) 630----647; (~) North-Holland Publishiny Co., Amsterdam Not to be reprodueodby photoprintor microfilmwithout written permissionfrom the publisher

T H E D E C A Y OF 2t4Pb A N D O T H E R 226Ra D A U G H T E R S E. W. A. LINGEMAN, J. KONIJN, P. POLAK and A. H. WAPSTRA

Instituut voor Kernphysisch Onderzoek, Amsterdam Received 21 October 1968 (Revised 20 May 1969) Abstract: Energies and relative intensities of gamma radiations following the decay of 226Ra and its short-lived daughters have been measured using Ge(Li) detectors. A special study of the decay scheme of 2~4pb was made using a zl*Pb source from which the Bi daughter was eluted continuously. Earlier intensity discrepancies in its decay were solved. An improved scheme is also given for the decay of 2X4Bi.

El

RADIOACTIVITy 21"pb' 2~*Bi [natural activity]; measured ET' I~" 2l*Bi' 21*P°

I

deduced levels, J, ~. Ge(Li) detectors. 1. Introduction The decays of 26.8 min 214pb and its daughter 19.7 min 214Bi (RaB and RaC) have been studied very extensively 1). The intensity balance is not satisfactory; 100 decays of 214Bi appear to be preceded by only 85 decays of 214pb (the number 79 given in ref. 1) is a misprint). The presence of several weak y-rays corresponding to conversion electrons observed by Mladenovi6 and Sl~itis 2) cannot explain the difference. We have measured 2x#pb g a m m a rays using a source from which its daughter 2X4Bi, which emits very many 7-rays, is continually eluted, and will show below that their total intensity is not high enough. We therefore have very carefully measured the energies and intensities of the y-rays in the decay of a sample containing 214pb and 214Bi in radioactive equilibrium and also of pure 214Bi samples. Using sum relations, we have extended the earlier proposed decay scheme in order to make a meaningful check of the intensity balance. The present results are believed to be considerably more precise than the Ge(Li) values reported recently by Buschman and Lauterjung a), Hultsch and Liihrs 4) and the beautiful Oe(Li) pair-spectrometer study of Maria and Ardisson 5). 2. Source preparation The 214pb and 214Bi sources were milked from their ancestor 222Rn by liquifying and solidifying radon with methane (as carrier) at - 195°C (b.p. methane - 161.5°C; m.p. methane - 182.5°C; b.p. radon -61.8°C). The liquified methane is left for about one hour in a cold finger, which can be detached from the rest of the apparatus. After 63o

631

214pb AND 2~4Bi DECAY

this period, during which the lead and the bismuth activities grow in and are deposited on the wall of the vessel, the methane is distilled off. The activities are dissolved by rinsing the glass wall with 0.1 M dilute nitric acid; carriers are not required. Using ion-exchange methods, we isolated the lead and the bismuth, respectively. The continuous separation for measuring 214pb without its daughter 2t 4Bi is based on the work of Taketatsu 6) and Khopkar and De 7) quoted by Samuelson s). The ion exchange column (see fig. 1) is filled with Dowex 50W-x 8, 400 mesh in the am-

THIS COLUMN MOVED

UP

CAN BE AND

DOWN

50 mm

DOWEX 50 W x 8 Gt(Li} DETECTOR

Fig. 1. Measurement of 26.8 min 214Pb(RaB) free from its daughter 19.7 min Z~4Bi(RaC). monium form. The column length is 65 mm, the diameter 6 mm. Eluting agent is a solution of 0.001 M EDTA (disodium salt) and 0.1 M NH4NO3 (this helps to prevent possible hydrolysis) adjusted t o p H = 1.5 with ammonia. The active solution is passed through the column at a flow rate of 30 mm (1 ml) per rain under a pressure of 0.25 atm. By choosing a p H = 1.58+0.02 (D~ni = 1, D~b = 60_+ 10), an optimum separation is obtained under which the Pb travels downwards at a rate of less than 0.5 mm per min. By moving the column upwards at the same rate, the activity is kept before the hole of a collimator during the measurement. Thus, the ratio of measured Pb to Bi y-rays is increased by about a factor 40. The remaining small 214Bi peaks were subtracted afterwards using a pure 214Bi source. The preparation of pure 214Bi was carried out on an anion exchange resin with 6 M hydrochloric acid.

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3. Gamma-ray measuring procedure The gamma-ray spectra were measured with 20 cm 3 and 30 cm 3 Ge(Li) detectors, both Nuclear Diodes coaxial types with a resolution from 1.8 keV at 100 keV to 3.4 keV at 3 MeV. The spectra recorded in a 4096-channel Laben pulse-height analyser were analysed both by hand and by a computer program (run on the Electrologica X8 computers of this Institute and of the Mathematical Centre, Amsterdam) t The energy values given by Muller et al. 9) for the 53, 242, 295, 352 and 609 keV lines (table 2) were used for calibration. More energy values were obtained by meaTABLE 1

Energies (in keV) for S6Co~,-rays, from ref. 22) 846.764-0.05 1037.97 4-0.07 1238.344-0.09 1771.574-0.10 2035.03 4-0.12

2598.80 4-0.12 3202.25 4-0.19 3253.824-0.15 3273.384-0.18 3452.18 4-0.22

suring 226Ra together with a 56Co source. The energies given in table 1 were adopted for the v-rays of the last nucleide; in addition, values 1460.9 +_0.2 and 2614.47 +__0. l0 keV were adopted for the 4°K and T h C " lines present in the spectrum as background lines. Within the errors, these energies fitted a quadratic calibration curve. This curve was used to determine best values for several of the stronger R a C y-rays. In measurements with pure Ra, RaB or R a C sources, the last values were used for further calibration. Intensity calibration was obtained using many absolutely calibrated sources obtained from the I A E A at Vienna, and sources like s 6Co and l a omHf' which contain several v-rays with accurately known intensity ratios. Corrections were made for summing tt. The photopeak efficiency curve obtained at a sufficient distance from the detector is a power function (log s = a + 1.507 log E) between 0.2 and 3.5 MeV within an average deviation of about 3 ~ without obvious systematic deviation. By comparing relative intensities of pair peaks and photopeaks, some lines appear to be only partly due to pair peaks. We thus believe to have determined energies and intensities of the stronger RaB and R a C lines with the best instrumentation and methods currently available.

4. Comparison with earlier results The spectra measured in the present work are shown in fig. 2. The resulting energies and intensities are collected in table 2 both for the equilibrium sample and for the pure RuB measurement. Some low-energy R a C lines are seen only in a measurement t We thank the Mathematical Centre for permission to use its facilities. ?t We thank Miss H. M. Cardoso for help in this intensity calibration.

TABLE 2 Gamma-ray energies (in keV) and intensities (in parts per 100 decays) in 226Ra in radioactive equilibrium and in its daughter 214pb(RaB)

E~,

Intensity Ra,q

(46.52) 7.3(RaD) (53.23) Kcc 18.9 4-2.0 K/~ 4.5 ±0.8 137.454-0.3 141.3 4-0.6 186.0 4-0.1 3.9(Rn) 196.3 4-0.5 (205.59) (238.4) (241.92) 7.8 4-0.8 258,824-0.10 0.6 4-0.1 273.5 +0.5 a) 0.08 4-0.04 a) 274.804-0.10 0.5 4-0.1 281.1 4-0.6 0,06 4-0.03 286.9 ±0.6 0,03 (295.22) 19.4 4-2.0 (298.76) 303 4-1.5 0.08 4-0.02 305.4 4-0.5 314.2 4-0.4 0,10 4-0.02 324.3 4-0.5 0.03 4-0.01 334.3 4-0.5 ") 0.06 4-0.02 a) 338.5 4-0.6 0.04 (351.99) 36.3 q-4 386.8 4-0.8 a) 0.31 4-0.12 a) 388.8 4-0.8 a) 0.37 4-0.12a) 396.3 + 0 . 6 a) 0.03 ~) 405.9 4-0.4a) 0.15 4-0.04~) 426.5 4-0.5 a) 0.I0 4-0.03 a) 440.4 +0.6 ") 0.03 a) 455.0 4-0.3 0.28 4-0.05 462.1 4-0.2 0.21 4-0.05 470.0 4-0.3 0.13 4-0.04 470.6 4-0.8 474.6 4-0.3 0.07 4-0.03 480.504-0.20 0.30 4-0.07 487.254-0.20 b) 0.35 4-0.08 b) 511.0 4-0.4 0.10 533.804-0.20 0.17 4-0.04 536.6 +0.8 a) 0.04 ~) 538.7 4-0.4 543.5 4-0.4 0.10 4-0.03 544.0 +0.3 546.8 4-0.5 0.03 4-0.01 572.6 4-0.4 0.06 4-0.02 580.304-0.20 0.32 4-0.06 (609.37) 42.8 ±4.0 615.8 4-0.6 0.09 -4-0.03

Intensity RaB

2.2 17.3 4.3 0.06 0.04

4-0.4 -4-2.0 -4-0.8 10.02

0.05 -4-0.02 <0,015 <0.015 7.6 4-0.8 0.8 4-0.2 0.7

4-0.2

18.9 4-2.0 <0.02 0.03 4-0.01 0.08 4-0.02 0.02 4-0.01

(36.3)

0.17 4-0.03 0.0104-0.005 0.34 0.33 0.03 0.17

4-0.03 4-0.03 4-0.01 4-0.02

0,005 0.06 4-0.02

0.36 4-0.04

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Racq

633.6 ! 0 . 4 0.05 4-0.02 639 ± 1 b) 0.03 b) 649.4 ± 0 . 4 0.05 ±0.02 665.6 4-0.2 1.4 +0.2 683.3 4-4-0.5 0.08 4-0.02 693.3 4-0.8 0.03 698.4 4-0.4 0.07 4-0.02 703.1 4-0.2 0.47 4-0.06 710.8 4-0.6 0.06 4-0.03 719.9 4-0.2 0.38 4-0.05 727 4-1 b) 0.05 b) 734.3 4-0.6 0.03 4-0.01 753.0 ±0.3 0.11 4-0.03 766.0 4-0.4 768.4 4-0.2 785,954-0.20 1.05 4-0.15 786.1 4-0.4a) 0.29 4-0.08 a) 798.2 4-0.6 0.03 806.2 4-0.2 1.1 4-0.2 815 4-1 b) 0.04 4-0.02 b) 821.2 4-0.3 0.16 5:0.04 826 4-1 b) 0.13 +0.06 b) 832.0 4-0.6 0.03 4-0.01 839.204-0.20 0.59 4-0.08 904.1 4-0.5 0.07 4-0.03 934.0 4-0.2 3.1 -4-0.3 964.1 4-0.3 0.37 4-0.05 1032.5 4-0.6 0.07 4-0.02 1052.0 4-0.3 0.33 4-0.04 1070.0 4-0.3 0.26 4-0.04 II04.0 4-0.4 0.16 4-0.03 1120.4 4-0.2 15.0 4-I.5 I133.8 4-0.3 0.25 4-0.05 1155.3 4-0.2 1.7 4-0.2 1172.9 4-0.6 0.03 4-0.01 1207.8 4-0.3 0.47 4-0.06 1238.2 4-0.2 6.1 4-0.6 1281.1 4-0.2 1.5 4-0.2 1303.8 4-0.4 0.II 4-0,03 1317.1 4-0.3 0.07 4-0.02 1377.7 -I-0.2 4.3 4-0.5 1385.4 5:0.3 0.8 4-0.15 1401.6 4-0.3 1.5 4-0.2 1408.0 4-0.2 2.6 4-0.3 (1415,7) <0.03 (1447) <0.03 1479.2 4-0.7 0.05 4-0.02 1509.3 ±0.3 2.2 4-0.2 1538.7 4-0.3 0.53 4-0.06

RaB

0.08 ±0.02 0.864-0.09

0.594-0.06

2t'*pb AND 21"~BiDECAY

637

Table 2 (continued) Intensity Ey

Raeq

1543.3 4-0.4 0.34 ±0.08 1583.3 4-0.3 0.73 4-0.07 1594.8 4-0.4 0.30 4-0.09 1599.5 4-0.4 0.34 4-0.09 (1605.5) 1661.4 4-0.2 1.16 4-0.12 1684.1 4-0.3 0.24 4-0.04 1729.8 4-0.2 3.2 4-0.04 1764.6 4-0.2 16.7 4-1.6 1782.1 4-1.0 0.015 4-0.005 1838.6 4-0.3 0.37 4-0.05 1847.6 4-0.3 2.3 4-0.3 1873.4 4-0.3 0.22 4-0.05 1890.4 4-0.4 0.10 4-0.03 1896.7 4-0.4 0.18 4-0.04 1936.6 4-1.5 b) ~0.05 b) 1994.7 -4-1.5 0.005 4-0.003 2011.0 4-0.6 0.037 -4-0.006 2016.0 ±1.0 0.016 4-0.003 (2016.7) 2053.2 4-0.3 0.07 4-0.02 2084.2 4-1.2 0.010 4-0.003 2089.7 4-0.7 0.05 4-0.01 2110.4 4-0.3 0.10 4-0.02 2118.7 4-0.3 1.3 4-0.15 2147.7 4-1.0 0.012 4-0.003 2192.5 4-0.5 0.07 4-0.02 2204.3 4-0.3 5.3 4-0.5 2260 4-1 ~0.005 4-0.002

Intensity

Ey

RaB

2266.4 2293.7 2312.5 2331.7 2377.2 2423.7 2448.0 (2479) 2505.6 2695.1 2699.5 2719.4 2770.3 2786.1 2827.6 2880.7 2893.7 (2918) 2922.2 2940.0 (2963) 2979.0 2988.7 3000.1 3054.0 3081.7 3142.5 3161.2 3182.8

10.6 4-0.3 4-1.0 4-0.4 4-0.5 4-0.6 4-0.3 4-0.4 4-0.4 4-1.0 4-1.0 4-0.4 4-0.4 4-1.0 4-0.4 4-0.4 4-0.4 4-1.0 4-0.4 4-1.0 4-0.4 4-0.4 4-0.4 4-0.7 4-1.0 4-1.0

Ra,q

RaB

0.015 4-0.003 0.33 4-0.04 0.009 4-0.003 0.021 4-0.004 0.006 4-0.002 0.006 4-0.002 1.65 4-0.18 <0.016 0.007 4-0.002 0.031 -4-0.04 0.005 4-0.002 0.00154-0.0005 0.026 -4-0.004 0.005 4-0.001 0.00214-0.0005 0.008 4-0.0015 0.006 4-0.0015 <0.0015 0.016 4-0.003 0.00154-0.0005 <0.0010 0.014 4-0.003 0.00104-0.0003 0.010 4-0.002 0.021 4-0.003 0.005 4-0.002 0.00104-0.0004 0.00054-0.0002 0.00054-0.0002

a) Seen in a separate measurement of the daughter 214Bi(RaC). b) Obtained after correction for nearly coincident pair lines. on a p u r e source. The best earlier energy values, except those o f M u l l e r et aL 9) are derived f r o m the p h o t o g r a p h i c b e t a - r a y s p e c t r o m e t e r w o r k o f M l a d e n o v i 6 a n d Sl~itis [ref. 2)]. T h e a g r e e m e n t with the present energy values is a l m o s t perfect (see fig. 3). C o n s i d e r i n g the s o m e w h a t worse a g r e e m e n t for the 1238 M-, 1281 L- a n d 1378 Llines we note t h a t the c o r r e s p o n d i n g K-lines check very well with the present energy values; the 1207 a n d 1848 K-lines are m e m b e r s o f n a r r o w doublets. I n the last cases a n d for the 1730 K - a n d 2119 K-lines, the present values check very well in energy s u m relations, which is n o t true for the values o f M l a d e n o v i 6 a n d Sl~itis. Fig. 3 shows also the differences with the values o f M a r i a a n d A r d i s s o n . The agreem e n t is very satisfactory. The errors assigned b y B u s c h m a n n a n d L a u t e r j u n g 3) to their values are so large t h a t c o m p a r i s o n is n o t very useful. Intensities d e t e r m i n e d b y several earlier a u t h o r s ( m o s t l y t a k i n g a value 100 for the 2204 k e V line) are c o m p a r e d with the present results in table 3. T h e first g r o u p in

E. W. A. LINGEMANet al.

638

TABLE 3 Comparison o f gamma-ray intensities A. Transitions to 2t'tPo ground state Method E7 (keY)

Compton Dzhelepov refs. lo-x2)

Ewan ref. 14)

Ge(Li) Buschmann ref. 3)

Present work

Maria ref. 5)

609

859

786

690

818

811

1377 1416

90

82

78

82

80

1543

13

1661

23

1730 1765

50 305

285

1848 2119 2204 2294 2448 other b)

32 25 (100)

(100)

33

33

sum a)

1561

1479

6.3

Pair Mayer ref. is)

102

7.2

20

22

21

58 300

60 318

57 313

29 284

52 26 (100) 6.2 32

43 24 (100) 6.2 31.4 10.4

39 24 (100) 7.0 35

50 21 (100)

1525

1504

1407

1542

34

") Including intensities 12, 8 and 1 for the 609, 1416 and 1764 keV conversion electrons, and present intensities for unobserved lines. b) The intensity o f all 7-rays above 1400 keV not placed in the decay scheme is 10.4 units. B. Other RaC lines with intensity above 10 units (0.5 %) Method E~, (keV) 666 768 806 934 1120 1155 1238 1281 1385 1402 1408 1509 1583

Compton Dzhelepov refs. lo-12) 46 103 31 68 305 40 88 33 32 46 46 19

Ewan ref. J,)

Ge(Li) Buschmann ref. 3) 40 60

258

32

34 208 69 61 26

48 33 14

Present work 27 92 24 60 285 32 116 29 15 28 49 42 14

Maria ref. 5) 30 93 23 56 220 35 132 33 20 28 44 38 13

Pair Mayer ref. 13)

115 23

56 25

2t4pb AND 21ZtBi DECAY

639

C. RaB lines

Method Compton E~, Dzhelepov (keV) refs. ~o-12)

Ge(Li) Ewan Buschmann ref. t4) ref. 3)

242 295 352 462 480 487 580 786 839

126 318 604

90 270 480

19 }

29 24 15

Present work

Maria ref. 5)

149 370 690 4.0 5.7 6.7 6.0 20 11.2

75 315 683

Scint Nielsen ref. 21)

Crystal Muller ref. 9)

(150)

96 280 510

9.0 11

6

21 10 10 if I(609) -- (820)

table 3 contains all ~-rays that we ascribe to transitions to the ground state in 21+po. According to Daniel and Nierhaus 1s), their total intensity should be 8 1 % (in sufficient agreement with several earlier 1) less accurate measurements). Then, the sum of their intensities (including that of their conversion lines) indicates that the reference intensity of the 2204 keV line is 5.25 % per disintegration. This result is used to obtain +2

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2.5

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Fig. 3. Energy differences with Mladenovi6 and Sltttis (open points) and with Maria (lines indicating error in the present results; those reported by Maria are about three times larger.) the absolute intensities given in table 2. It will be shown in sect. 8 that then the intensity balance in the decay of RaB is very satisfactory. Table 3 shows, moreover, that all other authors report a total intensity of the ground state transitions in satisfactory agreement with the present work. The second part of table 3 shows the same comparison for all other RaC lines with intensities above 0.5 ~o; again, the agreement is satisfactory in almost all cases. It is therefore rather amazing that the sum of our intensity values for the three strong RaB lines (third part of table 3) is larger than all earlier ones, even the recent results of Maria 5). Though this difference does indeed solve the problem of the defective intensity balance stated in sect. 1, we have repeated the measurement some five times under rather different conditions. We feel confident that the present results should be more dependable than the earlier ones.

640

E.W.A. LINGEMANet

al.

5. Long-range ~-particles Various levels in 21,po decay by ~-emission 17, ~s) to 21 opb" Decay to the ground ~tate is only possible if the spin-parity of the initial level is 0 +, 1 -, 2 + etc. In earlier interpretations ~), six of the 14 long-range groups were interpreted as transitions to higher excited states. Since ~-ray transition probabilities increase exceedingly fast with increasing transition energy, non-ground state transitions should never be expected to compete seriously with ground state transitions. Their observation should, therefore, be considered a strong argument for assigning opposite spin-parity combinations to the initial states. They also should be expected to be much more difficult to observe than ground state transitions. We therefore consider it an improvement that we can now reduce their number to three. Two of them, if interpreted as ground state transitions, would imply levels at 756 and 1283 keV in 21"po, where according to systematics in doubly even nuclei and to theoretical models, no levels should be expected. The new assignments and the spin-parities assignments based on their existence are collected in table 4 and depicted in the decay scheme (fig. 5).

6. Conversion data for 214Bi Ltihrs and Mayer-B6ricke 16) used their electron line intensity measurements for multipolarity assignments. These can be partly corrected and amended using the present gamma-ray intensities. For this purpose, the relative electron line intensities are converted to absolute values adopting an intensity of 0.64 ~o for the 609 keV E2 transition from a theoretical 19) K-conversion coefficient 0.0149. The resulting Kconversion coefficients have been plotted in fig. 4. We agree with Maria's conclusion [ref. 5)] that the 1730 keV y-ray should be assigned E2 character rather than M1 as given by Liihrs and Lauterjung. The conversion coefficients for the 703, 1208, 1509, 1848 and 2294 keV transitions not given by Liihrs and Lauterjung are derived from complex electron lines by subtracting the parts due to other transitions; these parts have been estimated from other electron line intensities using systematics of conversion ratios. Conversion coefficients for the members of the 824 and 786 keV doublets could be given separately due to separation of the corresponding y-rays in the present work. For unknown reasons, Liihrs and Mayer-B6ricke do net give the conversion coefficient or multipole assignment for the 1661 keV transition. The E2 assignment following from fig. 5 combined with the dependable M 1 assignment of the 786.1 keV transition would prevent to consider the E1 2448 keV transition as a cross-over of a cascade formed by the first two transitions. Neither Ltihrs and Mayer-B6ricke nor Maria 2) give multipole information on the 666 keV transition, presumably since Mladenovi6 and Sl/itis report an electron line which could correspond to a 661 keV y-ray not seen separated from the 666 keV one. According to the present results, the last y-ray can only have a very small fraction of the intensity of the 666 keV y-ray. Though we find indications for a weak 2017 keV gamma ray, its assignment to the

214"pb AND 214Bi DECAY

641

same tran,,ition as the 2016 K-conversion line reported by L hrs and Laut riung would imply a conversion coefticient 0.28_ 0.14, which is far larger than possible for a n y reasonable multipolarity. Thus, the original E0 assignment for the conversion electrons is confirmed. The several cases where the above conclusions differ from those of Maria, because of the additional information found in the present experiments, have been carefully considered. 7. The decay scheme of ~t4Bi-at4Po

Table 4 displays the data discussed in sects. 5 and 6, condensed sum-rule information and the resulting consequences for the existence of levels and their spin-parity assign6.

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2.5

E~.

Fig. 4. Conversion coefficientsof RaC lines compared with theory for pure multipolarities. merits. Since no yet unobserved levels are expected below the 1414 keV 0 ÷ state (with possible exception of the 4 + state of the Goldhaber triplet) and since the total decay energy is 3280 4- 13 keV [ref. Zo)], all y-rays with energies above about 2600 keV have to be ground state transitions, those between this value and 1800 keV can also feed the 609 keV level, and no y-ray below 1420 keV can feed the ground state. Taken together, this means that only a very small uncertainty exists in the absolute intensity calibration in sect. 4. The resulting decay scheme is given in fig. 5. Since y-transitions between levels with spin 0 are strictly forbidden and pure M2 transitions cannot compete with El, E2 and MI transitions, observation of a ground-state gamma transition limits the level spin-parity assignment to 1+, 1- and 2 +. Table 4 and fig. 5 only display spin-parity values if additional information is known.

TABLE 4 N e w levels a n d s p i n - p a r i t y i n f o r m a t i o n for 214po Ex (keV)

New level

1543 1661

a c

1730 1765 1782 1848 1890 1995 2011 2018 2053 2089 2119

a a n a n n n a a n a

2148 2193 2204 2209 2237 2294 2405 2448 2457 2482 2506

n n a n 0 a 0 a 0 n a

2695 2699 2720 2771 2786 2828 2881 2894 2922 2940 2961 2979 2987 3000 3054 3082 3142 3161 3183 3221

n a n a n n a n n n 0 n n n a n a n n 0

New sum rule

New multipolarity

Long-range New

n

n c

1661 E2, 1 787 M1 1730 E2

Spin-parity

Old

New

a

tX756

1+

o~1663

2448

1-, 2 +

c~1722

2506

2+ 1+

(I +)

2+

(2 + )

C

Old

,(3 +)

(I +)

n

n n

1848 E2, 1 1281 M1

a

(X1846

(1,2) +

n

n

1401 (M1)

C

(I, 2 +) a

0c2ols

0+

~1286

none

(I +) I+

0t2145

3221

(I -, 2 +) (I, 2) + I+

(0 +, 2 +)

n C

c

2118 M I 1509 M I 703 M1

n

n n

1583 M1 826 M1

(I +)

n

n

2448 E1

a 0

~2440 ~1663

a

~2509

0

~1722

1-

n n

~2692 0

~2692

a

~2871

a

~2261

0

~2145

0: p r e v i o u s i n f o r m a t i o n or i n t e r p r e t a t i o n believed to be w rong, a: p r e v i o u s i n f o r m a t i o n or i n t e r p r e t a t i o n accepted. c: p r e v i o u s i n f o r m a t i o n or i n t e r p r e t a t i o n confirmed. n: n ew i n f o r m a t i o n or i n t e r p r e t a t i o n . n u m b e r s in c o l u m n 6: level f r o m which l o n g - r a n g e c~-particle w a s a s s u m e d to c ome in p r e v i o u s w o r k .

214Pb

AND

214Bi

643

DECAY

The information about the parity of the 1661 keV level is conflicting. We consider the conversion coetticients of the 1661 keV line to be the weakest evidence. Though it is attractive to assign the 666 keV E1 transition between the 2448 keV 1 - state and the proposed 1782 keV level, the intensity balance can then only be made to fit by assuming a low-energy highly converted transition from the last level to the 1765 keV level. The relative intensities of the 1402 and 1408 K-lines as reported by Mladenovi~ and Sl~tis and of their gamma rays as found in the present work suggest that the second transition is E2 in agreement with the decay scheme, but the first transition is M 1. The present decay scheme places 83 7-rays (four of them twice). The total intensity of the 16 unplaced ?-rays (the existence of eight of them is considered doubtful) is only 2.0 ~o per decay; almost all this intensity will occur between levels above 1300 keV.

oo

~

(1-)

llkll m

3182a 3141.~ 3142,5 3o81.7 ~o~4.o

o

]ooo.I 2986.9 2979.0 2940,4 2922.2 2093.6

: u

2880.7 2627.6

^

2786.0 2770.4 2719.~ 26 g 9 . 5

m

~

2694.9 ~os.e

Gel

3.1"1.

6.3

1.07

1.7"1.

7.0

1.08

5.7./.

24e2.7 244e.o 2293,6 2~o9.o 2~4,3 2192.6 2148.0 2118.7 2068*2 zoe3.o

1.26

2.7 "1,

7.1

1.27

1.7"1,

7.3

1.43

A6.I.

69

1.52

18.7"/°

6.5

1.~5

17.6"/°

6.7

ao17.6 2011.0 1995.0 1690.4 1847.6 1782.3 ~764.6 ~729.8 1661.4

1.74

2.0"/,

7.9

1.86

0.7"/.

8.4

~843.4 1416.6

1.90

7.9 "/o

7.3

1377.7

2.19 < 4 . i , > 8 . 1 3.2e

21.1.

609.4

7.8

o

Miv

82Pb,~° Fig. 5a.

(RaD)

644

E.W.A.

oo.

LINGEMAN

et aL

o,

8

I

0 >1

#*C

o~.~ s~ s

>1

- - 2

Fc~

:~

>1

4 F

g-

F

"%1 ,

I°

~

~

E~ ~

.

''2,

~

~.~ ~ ~'~

~=

~ ~.~ ~.

I[--

~0

>t

41

@o i

~ ~.~ -N

•7

._~

~ ~,.~

214pb A N D

214Bi D E C A Y

645

8. The decay scheme of 214Pb The present data confirm the decay of all earlier levels i) in 214Bi except the highcst with significant sum-rule chccks. The new cnergy values suggest that the 90.96 and I 15.38 keV electron lines reported by Mladenovid and SI~itis2) should be interpreted as K-lines of 181.50 and 205.92 keV transitions, and the 40.30 keV elcctron line as L1-1ine of a 56.84 LI transition, that could fit in the decay scheme (shown dotted). The gamma-ray intensities of the first two transitions are so low that the reported conversion linc intensities would indicatc a strong E0 admixture in both transitions. Theoretical conversion coefficients 19) have been used for deriving transition intensities for the three strongest lines. Thc total intensity of the K-lines, i.c. 5.3 % + 7.6 %+9.0 %+0.7 % = 22.6 % for the 242, 295 and 352 keV transitions and all other K-lines together, agrees very nicely with the value 21.9 % from the K X-ray intensity given in table 2. This is significant in view of the fact that all intensity values measured by Nielsen et al. 21) (4.5___0.4 %, 6.2+0.5 % and 7.9+0.6 % for the separate strong lines) are a little smaller than the values above. Our calculated total intensity of the electron lines of the three strongest transitions is 27.2 %. Nielsen et al. give 23 %, Mladenovid and S1/itis 37.3 % (recalculated to an intensity 0.64 % for the 609 K-line as mentioned in sect. 6). We thus believe the present electron intensities are dependable. The intensity of the conversion electrons of the 53 keV transition is 24.6 % as derived from Mladenovid and Sl~itis, thus confirming that their intensities for lowenergy transitions are somewhat high. The ratio with the 242 K-line of Nielsen et al. [ref. 21)] and our intensity value for the last line, give the total intensity of the 53 keV transition shown in fig. 6. This somewhat unprecise intensity value is only used here in checking the intensity balance at the 53 keV level. We cannot confirm the reported 777 keV 7-ray, which should originate in an 831 keV level. Instead, the 786 and 831 keV y-rays earlier assigned 1) to RaC are now demonstrated to belong to RaB. Together with several more sum rules and the earlier 1) demonstration of coincidences between 53 and ~ 780 keV v-rays, they prove the existence of a new level at 839 keV, which is fed by an allowed beta transition (logft = 4.8) from 214pb and therefore has spin-parity 1 +. The 786 keV transition has E1 character. Even if E2, its K-conversion line would have been stronger than the 3 keV lower-K conversion line of the 786 keV M1 transition in RaC (see sect. 7) and therefore, could not have been missed in the Mladenovic-Sl~itis measurements. They also did not see the 839 keV K-line, which again suggests El character but with less certainty, since it should be only slightly stronger than the 825 K-line seen by Liihrs and Mayer-B6ricke 16) but not by the first authors. (Ltihrs and Mayer-B6ricke could not separate the 839 K-line from the stronger 768 L-lines.) Yet, taken together and combined with the undisputed M1 character 1) of the 53 keV transition, these new data prove that the ground state of z xaBi has negative parity. Since, on the other hand, the discussions in sect. 7 now yield spins 2 for the levels at 1730 and 1848 keV in 21,tpo ' which are strongly fed in its beta decay (logfi = 6.8 and 6.7), the ground state

646

E.W.A.

LINGEMAN e t aL

spin of 214Bi cannot have spin O. Since spin 2 has been excluded already earlier x), the present data finally prove the suggested x) spin-parity 1- for this level. 0 +

1042 214~

b

8 2 {'~

26.8 m

132

9 ~o'~o9 ~ o , ~.eo. o

1+

839.1 0

,o' ,?.

A,r°~Q~

203

2.3"/J

4.8

506

1.6 "/,

6.4

690

47.1 "/,

5.2

747

4 2 . 8 "I,

5.4

797 969 1042

766.0

~o ,9 ,~.,oo

<0.15"/~ > 7.8 < 2 "1, • 7.1 (6.2"/,) 6.5

533,6

..~"

351.99 0.49

~. ~ .

2 9 5 . 2 0 0.10 41,7

"7"

~

i

0.12 1.22

1.0

--

T 1 7 . . ?

-

+1 214

88.46

.

8 3 E ~ 1131

Fig. 6. D e c a y scheme o f 214pb(fl,7)2'4Bi. D a s h e d lines are considered uncertain. If only electron lines are observed, or if only a limit on the intensity is known, the transitions are s h o w n as dotted lines.

214pb AND 214Bi DECAY

647

The 766 keV level suggested in fig. 6 is tentative, and four of the 20 observed gamma lines have not been placed. The intensity of the strongest line at 462 keV is only 0.2 % (though if the electron line 2) at 121.06 keV is interpreted as a 137.46 L1 line, the transition intensity of the 137.4 keV transition, which is then evidently M 1 converted, may be about 0.3 %). Thus, these uncertainties do not influence the intensity balance appreciably. From the intensity balances at the excited states, it is then calculated that the intensity of the transition between the ground states of 214pb and 214Bi is 6.2 % with an estimated uncertainty of about 5 %. Since this value agrees very well with the value 6 % measured by Daniel and Nierhaus ~5), the discrepancy mentioned in sect. 1 no longer exists. We thank Professor Dr. R. van Lieshout for his interest in this work, which is part of the research program of the Institute for Nuclear Physics Research (I.K.O.); it was made possible by financial support from the Foundation for Fundamental Research on Matter (F.O.M.) and the Netherlands Organization for the Advancement of Pure Research (Z.W.O.). References 1) 2) 3) 4) 5)

A. H. Wapstra and N. B. Gove, Nucl. Data BI-5 (1967) 7 M. Mladenovi6 and H. Slitis, Ark. Fys. 8 (1954) 65 H. T. Buschmann and K. H. Lauterjung, Z. Phys. 207 (1967) 411 I-L Hultsch and G. Liihrs, Z. Phys. 190 (1966) 378 H. Maria and G. Ardisson, Compt. Rend. 265A (1967) 789; H. Maria, Compt. Rend. 265A (1967) 1138 6) T. Taketatsu, J. Chem. Soc. Japan 78 (1957) 148 7) S. M. Khopkar and A. R. De, Talanta 7 (1960) 7 8) O. Samuelson, Ion Exchange Separations in Analytical Chemistry (Almqvist and Wiksell, Stockholm, (1963)) p. 406 9) D. E. Muller, H. C. I-Ioyt, D. J. Klein and J. W. M. DuMond, Phys. Rev. 88 (1952) 775 10) B. S. Dzhelepov, N. N. Zhukovskii, S. A. Shestopalova and J. F. Uehevatkin, Nucl. Phys. 8 (1958) 250 11) J. D. Vitman, B. S. Dzhelepov and A. H. Karan, Izv. Akad. Nauk USSR (ser. fiz.) 25 (1961) 201; Columbia Techn. Transl. 25 (1962) 194 12) B. S. Dzhelepov, S. Shestopalova and J. Uchevatkin, Nucl. Phys. 5 (1958) 413 13) C. Mayer-B0ricke, Z. Naturf. 14A (1959) 609 14) G. T. Ewan and A. J. Tavendale, Can. J. Phys. 42 (1964) 2286 15) H. Daniel and R. Nierhaus, Z. Naturf. l l A (1956) 212 16) G. Lfihrs and C. Mayer-B6ricke, Z. Naturf. 15A (1960) 939 17) W. B. Lewis and B. V. Bowden, Proc. Roy. Soc. 145A (1934) 235 18) C. F. Leang, Compt. Rend. 260 (1965) 3037 19) S.A. Sliv and J. M. Band, Coefficients of Internal Conversion of Gamma Radiation (LeningradMoscow, 1956, 1958); R. S. Hager and E. C. Seltzer, Nucl. Data 4 (1968) 1 20) A. H. Wapstra, C. Kurzeck and A. Anisimoff, Proc. Int. Conf. on Nuclear Masses, Winnipeg (1967) 21) R. O. Nielsen, O. B. Nielsen and M. A. Waggoner, Nucl. Phys. 2 (1956) 476 22) J. B. Marion, Nucl. Data 4A (1968) 301