PHYSICAL REVIEW C VOLUME 27, NUMBER 1 JANUARY 1983

Determination of gamma ray energies and abundances of 229Th

S. S. Rattan, A. V. R. Reddy, V. S. Mallapurkar, R. J. Singh, Satya Prakash,and M. V. Ramaniah

Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Bombay-400 085, India(Received 21 September 1981)

Gamina-ray energies and intensities in the alpha decay of 22 Zh were precisely deter-mined using a high-resolution Ge detector. Twenty new gamma rays were observedwhereas 16 gamma rays earlier reported could not be observed. A modified energy level di-agram for 'Ra is proposed using the present results.

RADIOACTIVITY i Th; measured E„,I~ Ge d.etector. Ra de-

duced levels. Radiochemistry.

INTRODUCTION

The decay of Th has been studied by Tre-tyakov et al. ' using a low-resolution Ge(Li) detector(FWHM 5 —6 keV) and electron spectroscopy.However, their investigations yielded only crude es-timates of the gamma-ray intensities. The thoriumactivity used in Ref. 1 contained comparable activi-ties of both Th and Th. The presence of Th(Ti~2 ——1.927 yr) and of the short-lived daughterproducts (cf. Fig. 1) of Th and Th greatly com-plicates the gamma-ray spectrum. Most of the re-ported' gamma-ray abundances were calculatedfrom internal-conversion electron intensities andsuggested multipolarities, and for some of the gam-ma rays, no abundance was reported. The presentwork was undertaken to redetermine the Thgamma-ray energies and abundances.

During the preparation of this paper Dickens andMcConnell reported gamma ray intensities of

Th and its daughter products. The source used intheir work contained Th and Th along withtheir respective daughter products in equilibrium.The abundances for 18 gamma rays of Th were

reported by them, taking the 440 keV gamma ray of' Bi as standard with an abundance of 27.4%%uo.

EXPERIMENTAL

A. Purification and activity estimation of Th

Thorium along with its daughter products wasseparated from an old (-6 yr) U sample by anion exchange method using Dowex 1 g 8 in the Cl

U(i, 59xio yr)

ll

Th(7~40 yr)

U(71.&yr)

22BTh( I.9IP „r)

Ro( I4.8 d)

Ac(IO.Od)

221Fr (4.B min)

R0(~.64d)

C

RA(55. 6 s)C

P0(0. I5s)

Pb ( I 0.64h)

2I7 P 2I7At (52.&ms) Rn(0. 54ms) 2I 2

BI(60.55min)

C C

213Bi(45.59)~ Po(4.2~s)0 2I3

minC C

1~

Tl ( 2. 2 ) = Pb(5.25h)min

209BI

(STABLE)

TI(5 05

20B

( STABLE)

in) Po (0.5~s)2 I2

FIG. 1. Decay series of U and U.

form in a 6M HCl medium. The thorium was puri-fied from its daughter products by another ion ex-change method using Dowex 2&(8 in the NO3form in a 7.5M HNO3 medium. The purity of thethorium fraction was checked by gamma spec-trometry. In addition to Th, the sample wasknown to contain isotopic impurities of Th(&0.1%) and Th (&0.4%). The gamma raysdue to 2 0Th ( &0.4%) were not observed due to itsvery long half-life (7.7X 10 yr).

The purified thorium activity was used to prepare

27 327 1983 The American Physical Society

328 S. S. RATTAN et al. 27

I IOO

IOOO

XOo 900

8000

TIME (h )IO

FIG. 2. Growth of total alpha activity in the estima-tjpn pf thorium ( Th+ Th) as a fgnctjpn pf tjme.

samples for gamma counting and gross alphacounting. Three samples on polished stainless steeldisks and three samples in liquid scintillation vialswere prepared by a weight transfer method forgross alpha counting. The solid samples were fol-lowed on a gas proportional counter (efficien-cy=50.0+0.5%) and the liquid. samples on a liquidscintillation counter (efficiency & 99.5%%uo) over aperiod of 10—15 hours. Figure 2 gives a typicalplot of growth in total alpha activity with time dueto formation of alpha active daughter products.The alpha activity due to thorium ( sTh+ Th)was determined by extrapolating the growth curveto the time of purification by least squares fitting ofthe data to a quadratic equation.

An electrodeposited source of thorium was

I200—

I000—

800—hlZ'Zz

600—UJCL

Vlt-xOo +00

200—

I-gl

CV

Co

O

K

OJ

Cog)

MAlOJ

0

FOAl

~ lA

AJ

0

bJnJ

0

Mcj

IXON

0XCa0)bJ

Al

Al

0X

aoCU

AJ

X

0 y)

0tQ

Co

OJ

XcOO

OCL

FO

CV

X

M

OCL

Od

CV

4)X

CD

0 1 s s I ~ s I I s t i I s I s I a

I I 00 2 IOO 2300I 300 I 500 I 70 0 I900CHANNEL NUMBER

FIG. 3. Alpha spectrum pf Th and Th with daUghter prpdUcts in eqziljbrjpm.

2500

27 DETERMINATION OF GAMMA RAY ENERGIES AND. . . 329

prepared on platinum backing using a thorium solu-tion having the daughter products in equilibrium.The alpha spectrum of thorium (Fig. 3) was takenon a high resolution silicon surface barrier detector(resolution 20 keV at 5.486 MeV). The area underthe well-separated alpha peaks of ' Po, ' At(daughter products of Th), and ' Po (thedaughter product of Th) were used to determinethe activity ratio of Th and Th. The total al-

pha activity and the activity ratio of Th andTh were used to determine the individual activi-

ties of

B. Gamma counting and spectrum analysis

cal conditions in order to identify, through growth,the lines due to daughter products of 'Th and

Th. The total count rate was always less than1000/sec. Hence the errors due to pileup effectswere neglected.

Standard activities of Co, ' Ba, and 'Amwere used to calibrate the detector for gamma rayenergy and efficiency in the required geometry.The gamma ray spectrum analysis was carried outusing program SAMpo. The gamma ray energies of

Co, ' Ba, and 'Am and their respective peakpositions were least squares fitted to develop the en-

ergy calibration curve. The efficiency values for the

energy region above 120 keV were found to lie in astraight line on a log-log scale.

Three independent experiments were carried outfor measurements of gamma ray energies and theirabundances. In each experiment a freshly purifiedfraction of thorium of the purified stock solution

was deposited in a standard counting vial and fol-lowed for a suitable length of time with a 2 cm Gedetector (resolution 600 eV at 122 keV) coupled to a

4096 channel analyzer. Figure 4 shows a typicalgamma spectrum of the purified ' Th. After 12hours another gamma count was taken under identi-

RESULT AND DISCUSSION

The relative emission rates of the Th gammarays were determined using the developed energyversus efficiency calibration curves. The absoluteabundances of the gamma rays were then calculatedusing the estimated Th activity. Table I gives thegamma ray energies and their absolute abundancesobtained in this work, along with the reported data.

125000-GAMMA RAY OF Th

I 2500

100000— 10000

JJJ

g 75000-

OK'JJJO.

CIJ

XOD 50000-O

25000-OJJ: +

Al CJJOJ

CV

0 00

0

CV

)io

O

JCJ

Al

+

hCJJ

d—J

' g" g+IA

CO

CJJ

OOAl

OCV

+

O

0Al

+

OC4

LlAldAl

CJ

O IL'

CJJ JCJ Ncv

hl1

'IN + AJ N

CJJ

O aJC4

N

cv CJ

OCL

hl

Ol

&500

5000

2500

I I

200 400 600 800CHANNEL NUMBER

1000 1200 1400 1600

FIG. 4. Gamma spectnlm pf Th and Th.

S. S. RATTAN et al.

Present

TABLE I. Gamma ray abundances of Th.

Reported (Ref. 2)

Energy(keV)

12.33+0.04'14.81+0.02'15.25+0.02'

17.82+0.02'18.31+0.03'

28.50+0.14

31.13+0.0331.53+0.04

42.63+0.0243.96+0.0253.84+0.0956.50+0.0368.05+0.0868.80+0.0775.10+0.05

85.43+0.04'

86.35+0.0488.48+0.04'94.72+0.0299.47+0.02'

100.18+0.02'102.99+0.02'103.71+0.03107.15+0.02109.21+0.06110.38+0.03118.21+0.09120.16+0.08123.19+0.03124.59+0.02

126.76+0.09

134.33+0.08

136.99+0.03

142.97+0.03147.66+0.03148.17+0.03149.91+0.04

154.37+0.02156.41+0.02

% abundance

5.960+0.5369.381+0.781

42.480+ 1.592

17.033+0.7724.068+0.403

0.117+0.024

0.896+0.0801.692+0.085

0.188+0.0100.604+0.0200.017+0.0030.246+0.0060.052+0.0140.060+0.0130.420+0.043

9.820+0.017

2.732+0.07416.681+0.2510.232+0.0062.245+0.0703.927+0.0861.443+0.0460.451+0.0350.656+0.0090.023+0.0040.107+0.0040.015+0.0050.017+0.0030.120+0.0041.040+0.012

0.013+0.004

0.015+0.003

0.904+0.018

0.314+0.0060.183+0.0140.708+0.0170.042+0.003

0.612+0.0120.972+0.018

Energy(keV)

11.1+0.1

17.36+0.03

25.39+0.02

30.30+0.10

31.30+0.2037.80+0.1042.76+0.03

53.20+0.1056.60+0.0368.18+0.0768.90+0.0475.20+0.0775.30+0.10

86.30+0.1086.44+0.05

107.17+0.05

124.50+0.10124.70+0.10

131.97+0.05132.60+0.10134.80+0.10135.71+0.07137.03+0.06140.30+0.20142.95+0.10147.80+0.10148.30+0.20150.20+0.30151.60+0.30154.40+0.70156.48+0.04

% abundance

0.17

0.035

4.0

0.16

0.320.100.110.51

0.373.0

0.82

1.20.6

0.32

1.6

0.42

1.36

0.651.1

27 DETERMINATION OF GAMMA RAY ENERGIES AND. . . 331

Present

TABLE I. (Continued. )

Reported (Ref. 2)

Energy(keV) % abundance

Energy(keV) % abundance

158.42+0.04160.48+0.56

167.14+0.04171.59+0.07172.91+0.04179.75+0.03183.95+0.03

193.53+0.02200.81+0.03204.70+0.02210.31+0.05210.90+0.05215.16+0.08218.15+0.04221 ~ 31+0.09225.25+0.06236.31+0.06242.61+0.07

252.49+0.05259.15+0.05

'x rays of radium.

0.034+0.0030.005+0.003

0.113+0.0100.020+0.0050.093+0.0060.176+0.0050.118+0.006

3.769+0.0750.066+0.0050.495+0.0120.210+0.0332.467+0.0630.146+0.0160.149+0.0370.022+0.0030.048+0.0040.158+0.0280.065+0.007

0.089+0.0050.033+0.011

158.50+0.07161.60+0.30165.70+0.30

172.90+0.10179.80+0.20184.00+0.10190.20+0.20193.63+0.06

204.90+0.30

210.97+0.10

218.10+0.20

236.20+0.20242.60+0.30243.50+0.30

261.00+0.50290.00+0.50

0.220.500.23

4.5

3.2

0.14

0.035

Table II gives the absolute gamma ray abundancesof 2~sTh determined during the present investiga-tion, along with the reported data. Our values for

Th are in fair agreement with the literature.Table III gives a comparison of our data on Thwith those of Dickens and McConnell in which

only 18 gamma rays were reported.The earlier data' on the gamma ray energies of

229Th used for developing the energy level diagramof Ra had considerable uncertainties. Based onthe present data arid the previous measurements, ' amodified level diagram is proposed (Fig. 5). TableIV gives the gamma ray energies and their positionsin the level scheme. It is clear from the table thatmost of our data fit well in the level scheme. In thepresent work the following new gamma rays wereobserved: 28.50, 31.13, 43.96, 94.72, 103.71, 109.21,110.38, 118.21, 120.16, 123.19, 126.76, 167.14,171.59, 200.81, 210.31, 215.16, 221.31, 225.25,252.49, and 259.15 keV. Some of the earlier report-ed' transitions (25.39, 30.3, 37.8, 75.3, 124.7,131.97, 132.6, 135.71, 140.3, 151.6, 165.7, 190.2,243.5, 261.0, and 290.0 keV) were not observed. In

TABLE II. Gamma ray abundances of Th.

Energy(keV)

Reported (Ref. 8)Energy

% abundances (keV) % abundances

Present

84.29+0.05131.74+0.03166.48+0.03205.97+0.10216.00+0.06

1.351+0.0640.214+0.0040.136+0.0030.022+0.0040.285+0.002

84.5132.0167.0205.0216.0234.0

1.60.190.120.030.290.00007

some cases, this may be a result of the transitionhaving a large internal conversion coefficient. The43.96 keV garnrna ray could not be placed in thepresent level diagram. The 53.84, 68.80, 118.21,124.59, and 218.15 keV gamma rays have been

placed twice in the level diagram. Since y-y coin-cidence data are not available, the latter gammarays could not be placed unambiguously. Thegamma-ray transitions 75.10, 124.59, 154.37,210.90, 218.15, 242.61, and 259.15 keV are postulat-

332 S. S. RATTAN et al.

TABLE III. Comparison of gamma ray energies and abundances with those of Ref. 3.

27

Energy(keV)

Present data

% abundance

Dickens and McConnell data (Ref. 3)Energy(keV) % abundance

31.13+0.0331.53+0.0442.63+0.0256.50+0.0386.35+0.04

107.15+0.02124.59+0.02

Not observed136.99+0.03142.97+0.03148.17+0.031S4.37+0.02156.41+0.02172.91+0.04179.75+0.03183.95+0.03193.53+0.02204.70+0.02210.90+0.05

0.896+0.0801.692+0.0850.188+0.0100.246+0.0062.732+0.0740.656+0.0091.040+0.012

0.904+0.0180.314+0.0060.708+0.0170.612+0.0120.972+0.0180.093+0.0060.176+0.0050.118+0.0063.769+0.0750.495+0.0122.467+0.063

31.24

42.7956.5786.38

107.20124.68132.00137.06143.05148.18154.36156.45173.01179.85184.0193.59204.74210.93

1.43 +0.05

0.272+0.0110.427+0.0152.94 +0.090.95 +0.031.62 +0.050.433+0.0151.51 +0.050.532+0.0191.26 +0.041.13 +0.041.26 +0.040.130+0.0060.262+0.0100.091+0.0095.89 +0.180.75 +0.044.00 +0.13

TABLE IV. Gamma ray transitions and their position in the level scheme.

Energy ofgamma ray

(keV)

28.5031.1331.5342.63

43.9653.84

56.5068.0568.80

75.1086.3594.72

103.71107.15109.21110.38118.21

120.16123.19124.59

126.76134.33136.99142.97

Levels associatedwith the transition

272.05-243.48236.26-205.1331.55- 0.042.72- 0.00

203.62-149.91272.05-218.15236.26-179.72179.72-111.63111.63- 42.72100.47- 31.55100.47- 25.37236.26-149.91205.13-110.41321.66-218.15149.91- 42.72326.79-218.15110.41- 0.00321.86-203.62268.05-149.91392.21-272.05326.79-203.62236.26-111.63149.91- 25.37394.79-268.05284.48-149.91179.72- 42.72243.48-100.47

Energy ofgamma ray

(keV)

147.66148.17149.91154.37156.41158.42160.48

167.14171.59172.91179.75183.95193.53200.81204.70210.31210.90215.16218.15

221.31225.25236.31242.61252.49259.15

Levels associatedwith the transition

248.13-100.47179.72- 31.55149.91- 0.00179.72- 25.37268.05-111.63394.79-236.26272.05-111.63

268.05-100.47272.05-100.47284.48-111.63179.72- 0.0284.48-100.47236.26- 42.72243.48- 42.72236.26- 31.55321.86-111.63236.26- 25.37326.79-111.63243.48- 25.37218.15- 0.0321.86-100.47268.05- 42.72236.26- 0.0268.05- 25.37284.48- 31.55284.48- 25.37

27 DETERMINATION OF GAMMA RAY ENERGIES AND. . . 333

F, {A.)

600-

It)0 000 0 609

603

h

00

487

400—

300-

200-

100—

0-

Pl~~O0~ooohl

~ y

Ao~~CO

ff

0

hl

0

C4

0&Igj

I

Q

cvr ~O O'ACV

C4 ~ ye' 0 0 0 n4 0 r

OOOO~aa' 6) N O4 N QO & IC) ~

O. -o~0 OQO~O 0~0eu cv 0 0 O 0 0 0

~ ~ ~o Ap)h4r~~ &lee

h

00

00

v) ~0 ea te 0440- +roo-o o00, , ~ ~-OOOOO~

Oe &&5'~ OO ~ ~4A r~ ~~o 0 AO~~ ~e~aa M O lg)

or lo hl~ y O r 4 0r gll)CV hl~& ~OO

bl bl ~

0~ EV bO

~NOOQ

Qa

o~~cv

+ 0~ ~0C hl rhl ~ lO

OO0

b o 0 ~0

4 CV

00Wh

h

hlCV

ci ~h"~ e cv

h0 0 0 lg)

bO 'g I ~rn0~ ~'4~~ Ch

o ~~o- ~hr~oo

~ p ~ CV00 roOco OO40 Pl00OOO

QO

h ~QO

~ hlOO

~

~ Pl

41 7.394 ~ 79392.21

347..335 .326.79321.86

284 48272 ~ 05268 ~ 05

,248- 13243 ~ 48236- 2623021 8.15

g214 ~

205.13203.b2179.72

14 9.91

111 .63110.41i 00.47

4 2.72o- 31.55

25.37

0.00225 l4. 8 dRo

88 137 100 X PFIG. 5. Level scheme of 88 Ra~37. % feeding by alpha decay of Th (Refs. 2 and 9). E; is the energy of the gamma

ray in keV and A; is the absolute gamma ray abundance. y placed twice in the level scheme.

ed to populate the 25.37 keV level. However, the25.37-keV gamma ray could not be observed; we es-

timate its gamma-ray abundance to be less than0.01%%uo. Presumably this transition is of M1 mul-

tipolarity and is thus highly converted. From thelevels 609, 603, 487, 417, 347, 335, 230, and 214keV, which are quite weakly populated in the alphadecay of Th, no transition could be observed.

334 S. S. RATTAN et al. 27

E. F. Tretyakov, N. I. Tretyakova, V. F. Konyaev, Y. V.Khrudev, A. C. Beda, G. F. Kartashev, and I. N. Vish-nevskii, Izv. Akad. Nauk SSSR, Ser. Fiz. 34, 85611970) [Bull. Acad. Sci. USSR, Phys. Ser. 34, 763(1971)].

K. S. Toth, Nucl. Data Sheets 24, 263 (1978).J. K. Dickens and J. %. McConnell, Radiochem. Ra-

dioanal. Lett. 47, 331 (1981).4K. A. Kraus and F. Nelson, in Proceedings of the Inter

national Conference on Peaceful Uses of Atomic Ener

gy, Geneva, 1955 (United Nations, New York, 1956),

Vol. 7, p. 113.5L. R. Bunney, N. E. Ballou, J. Pascual, and S. Foti,

Anal. Chem. 31, 324 (1959).S. S. Rattan, A. V. R. Reddy, V. S. Mallapurkar, R. J.

Singh, and Satya Prakash, J. Radioanal. Chem. 67, 95(1981).

J. T. Routi, University of California Radiation Labora-tory Report No. UCRL-19452, 1969 (unpublished).

G. Erdtmann and W. Soyka, J. Radioanal. Chem. 26,375 (1975).

C. Maples, Nucl. Data Sheets 10, 643 (1973).