Journal of Nuclear and Radiochemical Sciences, Vol. 19, pp. 1-7, 2019

ArticlesRadiochemical purification of 144Ce from its in-grown daughter 144Pr and other fission
products
G.V.S. Ashok Kumar, R. Kumar* and M. Joseph
Materials Chemistry and Metal Fuel Cycle Group, Indira Gandhi Centre for Atomic Research, HBNI, Kalpakkam,
Tamil Nadu-603102, India.
Received August 21, 2018; Accepted December 26, 2018: Published online February 8, 2019
144
Ce-144Pr is one of the radionuclide generators used for demonstration of radioactive equilibrium, an importantconcept in radioactive decay kinetics for pedagogic activities in nuclear physics and chemistry practicals. This
work describes the method of purification of 144Ce from mixed oxide fuel dissolver solution of FBTR by ionexchange chromatography using Dowex resin followed by solvent extraction using di-(2-ethylhexyl)phosphoricacid (HDEHP). The daughter nuclide 144Pr was purified by extraction chromatographic technique using HDEHP
coated XAD-7 resin. The purified 144Ce was used to demonstrate radioactive equilibrium concept from thegrowth of its daughter nuclide 144Pr.

1. Introduction
The phenomenon of radioactive equilibrium is described
extensively in the literature [1-4]. Radioactive equilibrium is acondition in which the ratio of the parent and its daughter
activities remains constant whenever the daughter’s half-life isshorter than that of the parent. However, there is no possibilityof achieving the equilibrium condition if the parent half-life isshorter than that of the daughter. Further, there exist two
types of equilibria i.e. secular and transient. A radioactive
equilibrium between the parent and the daughter is referred aseither transient or secular equilibrium, depending upon the relative half-lives of the parent and daughter in a pair. For a secular equilibrium, half-life of the parent is greater than half-lifeof daughter by at least an order of magnitude. However for atransient equilibrium, the ratio of the half-life of the parent tothat of the daughter is about or less than 10. Various parentdaughter pairs which are in radioactive equilibrium are shownin the Table 1 [5-11].
In a radioactive equilibrium, the daughter always appears to
decay with the half-life of the parent as long as it is present in
the mixture but decays with its own half-life when separated
from its parent. This observation is explained from the factthat the daughter is continuously produced from the parent
when it is in equilibrium with the latter. In the case of secularequilibrium, the activity ratio of parent to daughter tends
towards a constant value i.e. unity in this case. Further, theactivity of parent remains apparently constant over the periodof measurement because of its relatively very long half-life incomparison with that of daughter and hence its activity showsno significant or negligible change during the period of measurement. However, the activity of the daughter increases
continuously until the rate of formation of the daughter equals
to the rate of decay of the parent. Hence, the secular equilibrium phenomenon can be defined as a condition in which theratio of activities of the parent and daughter radionuclides
becomes a constant i.e. unity with no significant or observablechange in the parent activity during the period of observation[4]. Similarly, the ratio in the transient equilibrium is also a
constant, but less than unity depending upon the decay constants of parent and daughter nuclides.
Among them, the pair 144Ce-144Pr was chosen to demonstrate
the concept of radioactive equilibrium in general and secularequilibrium in particular in this work for a practical convenience even though some of the other pairs also can be used
for the same. Among the known pairs which are in secularequilibrium as shown in table 1, the 90Sr-90Y has the disadvantage of having relatively a long lived daughter with a half-lifeof 2.7 d, which demands the observation period of more thanabout two weeks for the convenient demonstration of the phenomenon of secular equilibrium. The other pair 137Cs-137m Ba
has a relatively short half-life for its daughter i.e. 2.55 min
which is convenient to establish the secular equilibrium phenomenon in a relatively short observation time but limits theaccuracy in the measurement of the half-life of the daughter
nuclide owing to the practical delay between the purificationof the parent nuclide and the starting of the assay of the total
activity using a detector. However, the pair 144Ce-144Pr which

TABLE 1: Parent-Daughter pairs which are in radioactive equilibrium
Type ofequilibrium
SecularParent-Daughter
pair
137

Cs-137mBa
Ce-144Pr90
Sr-90Y99
Mo-99mTc
166
Dy-166Ho72
Se-72As
144

TransientHalf-life of Parent(T1/2(P))

Half-life of Daughter(T1/2(D))

Ratio
T1/2(P) / T1/2(D)

30 y
285 d
28.8 y2.75 d3.4 d
8.4 d

2.55 min17.3 min
2.7 d
6.0 h
1.117 d1.08 d

6.2×106
2.37×104
3.9×102
11.0
3.04
7.77

*Corresponding author. E-mail: rkumar@igcar.gov.in© 2019 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 02/08/2019

J. Nucl. Radiochem. Sci., Vol. 19, 2019

2

R. Kumaris in secular equilibrium has reasonable half-lives providing a
convenient observation time of establishing the secular equilibrium phenomenon (~ 2 h) as well as the measurement ofhalf-life accurately.
In order to profile the growth of the daughter with a better
accuracy, in a demonstration experiment, it is necessary tohave a pure source of the parent, 144Ce, free from its in-growndaughter of 144Pr in this case. The only viable source for the
production of 144Ce is the nuclear fission. The chain yields ofthe mass number 144 are 5.38% and 3.82% for the thermal
neutron induced fission of 235U and 239Pu, respectively; but thesame are 5.34%, 4.65% and 3.73% for the fast fission of 235U,
238
U and 239Pu, respectively [12]. The decay chain for the isobaric series corresponding to the mass number 144 is as follows.
144

1.2 s

Xe
144

Ce

144

Cs

284.9 d1.01 s

144

Pr

144

Ba

17.29 m11.4 s

144

Nd

144

La

2.29x1015 y

40.7 s140

CeFigure 1. Decay scheme of 144Ce and 144Pr [13, 14].

The decay chain rapidly accumulates in to the long-lived
Ce. Thus, the presence of 144Ce and its daughter (144Pr) are
the only observable radionuclides practically because of thefact that all the precursors of 144 Ce are short-lived. Decay
schemes of 144Ce and 144Pr are depicted in Fig. 1 [13, 14]. The
parent nuclide 144 Ce decays in to its daughter nuclide 144Pr
through β - emission which again decays into 144Nd by a beta
emission. The half-lives of 144 Ce and 144Pr are 284.9 d and17.29 min, respectively. Some of the important decay characteristics of the parent 144Ce and its daughter 144Pr are shown in
the Table 2.
As the daughter nuclide 144Pr is short-lived, the generator
would be used many times a day with the maximum activity of
144
Pr which allows repeated studies. The special feature of thisnuclide is having well-spaced gamma photons of 696, 1489
and 2185 keV, which enables information of the depth distribution of 144Pr labelled tracer in extended volumes [15]. The separated 144 Ce-144Pr pair is having several other applications.
The purified 144Ce source can be used as a radioactive tracer inchemical and biochemical application studies to track the pathof cerium [16]. It can be used as energy and efficiency calibration source for the gamma spectrometric studies like HPGe
detector [17]. It is also being tested as a potential candidate forthe interstitial and intravascular brachytherapy applications
due its relative long half-life [18, 19]. The 144Ce-144Pr pair isalso widely used for the demonstration of secular equilibrium
to explain the radioactive equilibrium concept to students [8].
The present study deals with the usage of pure 144Ce parent
towards the demonstration of radioactive secular equilibrium.
To demonstrate the secular equilibrium behaviour using
144
Ce-144Pr, it is preferred to start with a pure parent 144Ce followed by assaying it by a suitable counting technique and thus
the in-growth of daughter with the parent is profiled until theequilibrium or steady state is reached. Several methods werereported for the separation of 144Pr from 144Ce, particularly
towards the development of its radio nuclide generator [7, 8].
However, reports on the source preparation of 144Ce for thedemonstration of secular equilibrium concept were limited.
Walter et al. [7] studied the absorption of 144Ce from 144Pr on
manganese dioxide coated alumina and elution of 144Pr under
different conditions. Semmelrogge et al.[8] carried out thestudies on secular equilibrium of 144Ce-144Pr in which 144Ce
was separated by solvent extraction followed by its precipitation on a planchet. Tompkins et al. studied the separation of144
Pr from 144Ce using a cation-exchange resin, Dowex 50 with
a 5% citrate complexing solution (pH=3.0) as the eluant [20].
But McDonald et al. [21] studied the same using an anion
exchange resin, Dowex l (100-200), and 9 M HNO3 containing
0.5 N NaBrO3 as an eluant. Bradley et al. [22] separated 144Ce
144

TABLE 2: Decay characteristics of the parent and daughter

144

Ce

144

Pr

Gamma energy(keV)%
Intensity

β –max(keV)%
Intensity

133.5
80.1
53.4
696.5
1489.22185.710.83%
1.4%
0.1%
1.4%
0.28%
0.73%

185.1
238.5
318.6
811.8
2301
2997.5

19.2%
3.9%
76.9%
1.02%
1.12%
97.85%

from 144Pr as an insoluble iodate salt of Ce in the oxidation
state +4.
All these methods describe either the separation of 144Pr
from 144Ce, or precipitation of 144Ce, a time consuming and a
relatively clumsy process which is a matter of concern especially while demonstrating the secular equilibrium concept ina normal chemistry laboratory where the radiochemical processing is carried out very carefully observing all the safety
precautions to avoid contamination. In order to establish thesecular equilibrium and to determine the half-life of daughter
nuclide, it is important to obtain a sample of parent nuclide144
Ce with as much purity as possible, so that the profiling ofdaughter nuclide before reaching the radioactive equilibrium
can be accomplished conveniently as accurately as possible.
To follow the kinetics more proficiently, the time gap between
the separation of 144Ce and its counting should be as short as
possible. Hence, a rapid solvent extraction method was demonstrated in this work in which the pure parent (144Ce) was
obtained and assayed very immediately after its separation.
Extraction chromatographic studies were also carried out toseparate pure 144Pr and subsequently follow its half-life bywhich its purity was ascertained clearly and indirectly, forreporting its half-life unambiguously. The present work
describes a simple and rapid separation procedure to obtain apure 144Ce by using solvent extraction and pure 144Pr by using
extraction chromatography. This procedure is established to
be a simple and a practically convenient technique for a demonstration experiment in any educational institution with minimum or no possibility of any spread of contamination.
2. Experimental Details
2.1. Materials and Instruments. All chemicals used inthis work were only of analytical grade unless mentioned oth-Radiochemical purification of 144Ce from its in-grown daughter 144Pr anderwise. Di-(2-ethylhexyl) phosphoric acid (HDEHP) was
obtained from BDH Chemicals, England while Amberlite
XAD-7 (20-60 mesh) and Dowex 50W×8 (100-200 mesh) cation exchange resins were obtained from Sigma Aldrich Co.,
France. Nitric acid and n-hexane were obtained from Loba
Chemie, India. The assay of the gamma emitting radionuclides was accomplished by gamma spectrometry using an
HPGe detector with 30% efficiency and having resolution of
1.85 keV at 1332 keV of 60Co along with an associated 8k multichannel analyser (MCA) system (Canberra Eurisys; Aptec
spectra software). Energy calibration of the HPGe detector
was established using 241Am, 137Cs, 133Ba and 152Eu as standard
sources (Amersham, Inc.). The detection efficiency was established previously as a function of gamma-ray energy from 244
to 1408 keV using 152Eu standard source before the assay of thesamples having same dimensions of the standard in the reproducible geometry. A well-type NaI (Tl) detector with a resolution of 8% at 661.6 keV of 137Cs was procured from The
Harshaw Chemical Co., (Division of Kewanee Co., USA) was
also used to assay the total activity of 144Ce-144Pr. The stock
fuel dissolver solution was obtained by dissolving the Fast
Breeder Test Reactor (FBTR)-irradiated mixed oxide ((U, Pu)
O2) pellets in 12 M nitric acid with its associated burn-up of
112 GWd/t. An initial inventory of the stock fuel dissolver
solution of the major radionuclides along with their half-lives
is shown in Table 3.
2.2. Separation of 144Ce-144Pr from the fuel dissolver solution by using ion-exchange chromatography.
Measurement of Distribution ratios
In order to standardize the procedure for the purification of
144
Ce-144Pr fraction from other activated and fission products
by ion-exchange chromatography, the distribution ratio wasmeasured for the Dowex 50W×8 (100-200 mesh) resin as afunction of acidities using simulated solution containing thefission products as that of the dissolver solution described in
the previous section. The simulated solution of 5 mL for the
long-lived fission products i.e. 144Ce, 137Cs and 90Sr as well as
the activated products i.e. 60Co and 54Mn was prepared using
their respective tracers in the range of kBq to MBq. Their distribution ratios were determined for Dowex resin over a rangeof nitric acid concentrations. A known amount (ca. 100 mg) of
Dowex 50W×8 (100-200 mesh) resin was taken with therequired amount of simulated solution of the tracers in test
tubes containing nitric acid of different concentrations i.e. 0.5,
1, 2, 4 and 6 M. The above mentioned tubes were equilibrated
for a period of 4 h using a rota-spin. The solution-resin mixture in the tubes was subjected to the centrifugation for aperiod of 10 min with speed of 10000 rpm and relative centrifugal force of 1700 × g, subsequently. The aliquot of the clear
solution was sampled out and assayed by gamma spectrometry
using HPGe detector.
Separation of 144Ce-144Pr from Fuel Dissolver Solution
An aliquot of the stock solution of the above referred fueldissolver solution was taken in a small beaker and was dried
under IR lamp. The residue was taken into a 1 mM nitric acid
which became the feed for the ion exchange column used in
the subsequent separation studies. The Dowex 50W×8 (100200) resin of 1 g in 1 mM HNO3 medium soaked over-night
was made into a slurry. The same was loaded into a chromatographic glass column of the dimension of 25 cm length and 0.8
cm ID forming a bed height of about 4 cm. The column was
initially conditioned using 1 mM nitric acid. The feed solution
was introduced into the column and the elution was carried out
initially using 80 mL of 1 M nitric acid followed by further
elution of about 20 mL of 6 M nitric acid. A flow rate of 0.40.5 mL/min was maintained throughout this experiment. The
samples of the uniform size of 10 mL were collected during

J. Nucl. Radiochem. Sci., Vol. 19, 2019

3

TABLE 3: Activities of fission and activation productspresent in the stock fuel dissolver solution
No.
1
2
3
4
5
6
7
8

Fission / Activation
Product
106
Ru-106Rh
125
Sb
134
Cs
137
Cs
144
Ce-144Pr
154
Eu
54
Mn
60
Co

Half-life (y) Activity (kBq)
1.02
2.76
2.06
30.1
0.78
8.59
0.86
5.27

780
400
280
11300
4300
66
14
3.7

the elution and the same were assayed using HPGe detector.
2.3. Purification of 144Ce from its in-grown-daughter-inequilibrium 144Pr by using Solvent Extraction. The extractant HDEHP was used in the present study to purify the 144Ce
fraction obtained from the above separation from its in-growndaughter-in-equilibrium 144Pr as well as from the other minor
impurity of 154Eu. While the pure HDEHP is a clear colourlesssolvent, it is amber in case of commercial HDEHP. The purification of the commercial HDEHP was accomplished throughthe selective precipitation of its copper complex [23].
Approximately 1M HDEHP in cyclohexane was saturated withcopper (II), by equilibrating the above organic phase with anaqueous solution of CuSO4 mixed with NaOH. Acetone wasadded, on stirring, to the organic phase separated from theabove mixture which resulted into the precipitation of
Cu-HDEHP complex.

Cu OH 2

2HDEHP org

Cu DEHP 2 org

2H 2O

The Cu(DEHP) 2 precipitate was filtered subsequently;
washed with acetone, air dried and converted back to pure
HDEHP by contacting it with 0.5 M hydrochloric acid andmillipore water. The acid washings with HCl were repeated toremove all the copper from the HDEHP phase. The clear
HDEHP phase was contacted with millipore water three tofour times to remove the dissolved acid. Further, the water
was evaporated off from the purified fraction of HDEHP using
a rotary evaporator at about 60 °C. The purified HDEHP wasused for the subsequent separation studies.
The 144Ce-144Pr sample fraction with the trace impurities of154
Eu obtained as described above was evaporated to the dryness under IR lamp. The dried residue was taken into 5 mL ofconcentrated HNO3 to which a 30 mL of 1 M potassium bromate in 9 M HNO3 was added. From this stock solution, a 10mL fraction was taken into a separating funnel along withfreshly prepared 1 M KBrO3 in 9 M HNO3 and 0.7 M HDEHP
in n-heptane of 5 mL each. The mixture was equilibrated
manually for about 5 minutes and allowed to stand for about aminute for its phase separation. The samples of the organic
phase of about 2 and 5 mL were sampled out for an immediateassay of the total activity using NaI (Tl) as well as HPGe
detectors, respectively for the assay of parent 144Ce and the ingrown daughter 144Pr.
2.4. Demonstration of Secular Equilibrium behaviour of
Ce-144Pr. The sample assay was carried out using a welltype NaI (Tl) scintillation detector in an integral mode. The
total activity of the sample was recorded by counting it in regular intervals for a period of about two hours. The initialcountings were noted for a counting period of 30 s with a gapof the same duration between the successive countings for a144

4

J. Nucl. Radiochem. Sci., Vol. 19, 2019

R. Kumarperiod of first 20 min beyond which the gap was increased
from 1 to 5 min maintaining the same counting period of 30 s
for the duration of next 100 min again. Further, the 5 mL
sample was also assayed simultaneously using HPGe detector
to monitor the growth of the daughter 144Pr for the comparisonand confirmation. The decay curve was plotted for the total
activity data obtained from NaI (Tl) detector as a function oftime on a semi-log graph paper.
2.5. Purification of the daughter nuclide 144Pr by using
extraction Chromatography. A measured quantity ofAmberlite XAD-7 beads were washed with 4 M HNO3, distilled water and acetone successively after which the same wasdried at 40 °C in vacuum [24]. The purified XAD-7 resin was
weighed accurately and taken with the appropriate amount of
HDEHP corresponding to 40% (w/w) HDEHP/XAD7 resins ina reagent bottle containing the diluent n-hexane. This mixture
was equilibrated for 2 h in a mechanical shaker. After theequilibration, the diluant, n-hexane was evaporated using arota-evaporator and the resin was further dried at 60 °C forabout an hour. Mass balance for the coated resin with respect
to the initial weight (XAD7+HDEHP) was observed to bearound 95% - 100%.
About 5 g of the above HDEHP coated XAD-7 resin in
n-hexane in its slurry form was loaded into a glass column
with the dimension of 25 cm length and 1 cm ID that resulted
into a resin bed height of 10 cm. The column was conditioned
using 1 M KBrO3 in 9 M HNO3 medium. The mixture solution containing 144Ce-144Pr in 1 M KBrO3 - 9 M HNO3 medium
was loaded in to the column. The immediate elution was initiated using 1 M KBrO3 in 9 M HNO3 at a flow-rate of 0.8-0.9
mL/min. Sample fractions of 15 mL were collected andassayed for its activity using HPGe detector. At the end of theelution, the chromatographic column was washed with 9 M
HNO3 in order to maintain the column completely free fromthe eluant KBrO3.

Figure 2. Variation of the distribution ratios with the nitric acidconcentration in the DOWEX 50W×8 (100 –200 mesh) resin.
(Amount of resin in each tube: 50 mg; Volume of the HNO3 solution:
5 mL; Equilibration time: 4 h; Assay: Gamma Spectrometry using
HPGe detector).

3. Results and Discussion
3.1. Separation of 144Ce-144Pr from the fuel dissolver solution by using ion-exchange chromatography.
Measurement of Distribution ratios
All the equilibrated samples from batch studies wereassayed by HPGe detector and the distribution ratios (DM)were calculated using the following equation.

(A0 A)V
M
where A0 and A are the activities (cps) of the elements in the
aqueous phase before and after equilibration with the resin,
respectively; V is the volume of the solution kept for equilibration (mL) and M is weight of the resin (g). The distribution
ratios for the different radio tracers, representing various fission and activated products present in the dissolver solution
were determined as function of nitric acid concentration for
the Dowex resin. The data obtained are plotted as shown in
Fig. 2. It is observed from the graph that the DM values of all
the tracers decreased exponentially with the increased concentration of nitric acid in the range of study. The decrease in DM
values of metal ions at increased nitric acid concentration isowing to the higher competition of H+ ions towards the functional sites of resin. It was also observed that the DM values of
Ce were always higher than that of the other tracers over arange of nitric acid concentration i.e. up to 4 M nitric acid
which is due to its higher ionic potential.
This observation may be attributed to the relatively stronger
interaction of Ce with cation exchange resin in comparison
with the other fission products in the simulated solution owing
to its relatively higher ionic potential i.e. charge to radius ratio.

Figure 3. Elution profile for the separation of 144Ce from fission andactivation products using cation exchange chromatography. (Amountof Dowex resin: 1 g; Column Dimensions: 0.8 cm ID, 25 cm lengthand 4 cm bed height; Conditioning: 1 mM Nitric acid; Feed: Fission
product solution in 1 mM HNO3; Flow rate: 0.4-0.5 mL/min; Assay:
Gamma Spectrometry using HPGe detector).

DM

Even though, the distribution ratio and the separation factor
were observed to be higher and comparable for Ce at both 0.5
M as well as 1 M HNO3, the latter concentration was chosen as
the same yielded a baseline separation of Ce from other fission
products by ion-exchange chromatography, in a relatively lessvolume of eluant.
Separation of 144Ce-144Pr from Fuel Dissolver Solution
The separation profile for the fission products using Dowex
resin column was established and the elution profile is shownin Fig. 3. It is observed that the fission products such as 137Cs,
134
Cs, 125Sb, 106Ru-106Rh and more importantly the activation
products 54Mn and 60Co were all eluted in the initial fractions
with 1 M nitric acid as the eluting agent. This is due to thelower distribution ratio values of these metal ions at the eluant
concentration of 1 M HNO3. Cerium was eluted last owing to
its very high distribution ratio and collected in a small fraction
using 6 M HNO3 along the other lanthanides i.e. in-grown 144Pr
and traces of 154Eu impurity. Thus, a lanthanide group separation from other fission products is performed initially followed
by a specific isolation of cerium from the lanthanide group toRadiochemical purification of 144Ce from its in-grown daughter 144Pr andJ. Nucl. Radiochem. Sci., Vol. 19, 20195

be carried out to demonstrate the secular equilibrium behaviour subsequently.
3.2. Purification of 144Ce from its in-grown-daughter-inequilibrium 144Pr by Solvent Extraction. The secular equilibrium phenomenon was demonstrated conveniently using thepure fraction of 144Ce including its purification from its ingrown daughter product 144Pr. The variation in the total countsof the pure 144Ce fraction was profiled using NaI (Tl) detector
that included the associated growth of the daughter product144
Pr there on. Purification of 144Ce from its in-grown daughter product, 144Pr is a challenging task owing to the fact thatthey both belong to the same lanthanide series and their separation is made difficult by the nature of their inherent complicated separation chemistry owing to the similar oxidation stateof +3 as well as their similar chemical behaviour due to thephenomenon of lanthanide contraction. However, Cerium also
has another stable oxidation state of +4 [15, 24] which facilitates its separation both from the other lanthanides as well as
the fission products. Initially, the lanthanides i.e. 144Ce-144Pr
and 154Eu were separated from the other fission products byion-exchange chromatography followed by the individual separation of 144Ce (IV) from the lanthanide fraction using solvent
extraction technique. Separated fraction of pure 144Ce (IV)gets quickly contaminated with its in-grown daughter nuclide144
Pr and hence requires fresh purification every time to obtaina pure fraction of the parent nuclide 144Ce. The purification of
the parent fraction from its daughter 144Pr is carried out byadding 1 M KBrO3 solution that converts all the Ce (III) into asingle and uniform oxidation state of Ce (IV) and facilitates its
efficient extraction by the extractant HDEHP from the otherlanthanides as well [24-25], which is shown below.

KBrO3 6Ce(NO3 )3 6HNO3
KBrO3 5KBr 6HNO3

6Ce(NO3 ) 4

Figure 4. Demonstration for secular equilibrium using 144Ce-144Pr
pair. (Sample details: 2 mL of pure 144Ce fraction separated by solvent extraction using HDEHP & the total activity assay by using NaI(Tl) scintillation detector).

KBr 3H 2 O

3Br2 3H 2O 6KNO3

144

Ce was extracted into the organic phase (HDEHP) while thedaughter product 144 Pr was retained in aqueous phase.
HDEHP exists as a dimer in dilute organic medium as(HDEHP)2. The nature of the extracted species depends on
the nature of the acid in the aqueous phase and its concentration [26]. The extraction of cerium (IV) from nitric acidmedium to the organic phase is represented as follows [27-29].

Ce 4

4 HDEHP 2

Ce H DEHP 2 4 4H

The purified 144 Ce in the organic phase was assayed byusing a NaI (Tl) detector to demonstrate the secular equilibrium phenomenon.
3.3. Demonstration of Secular Equilibrium behaviour of
Ce-144Pr. The time interval between the end of separationof pure 144Ce and to the beginning of assay in the experimentmust be as short as possible to precisely profile the variation of
the total activity as well as the growth of the daughter 144Pr.
The pure parent sample was counted by well type NaI (Tl)scintillation detector and the total activity there on was monitored periodically for a period of about two hours. The initialdelay of seven minutes to assay the purified fraction was dueto the practical delay in bringing the sample to the detector
after its separation. The total activity was observed toincrease initially which remained apparently constant aftersome time. The initial increase in the total activity was due tothe in-growth of the daughter nuclide 144Pr from its pure parent
144
Ce. The total activity remained apparently constant due tothe subsequent achievement of radioactive equilibrium.
The total activity of 144Ce-144Pr pair from the NaI (Tl) detector was plotted as a function of time (curve a) using a semi-log
144

Figure 5. Gamma spectrum of 144Ce-144Pr secular equilibrium pairby HPGe detector. (Sample details: 5 mL of pure 144Ce fraction separated by solvent extraction using HDEHP and assay by using HPGe
detector).

graphical pattern as shown in Fig. 4. As there was some shorttime delay between the separation of pure 144Ce and its initialcounting, the missing data points during this period wereobtained by back-extrapolating the total activity data to theY-axis. By using this plot, individual profiles i.e. profiles ofthe parent decay, daughter growth in parent and daughter
decay were resolved (Fig. 4).
‘Parent decay’ profile (curve b) was obtained by drawing astraight line parallel to the linear portion of the total activity
from the point of total activity at zero time. ‘Daughter growthin parent’ (curve c) line was obtained by subtracting parent
activity curve from the ‘Total activity’ (curve a). ‘Daughter
decay’ (curve d) was profiled by subtracting daughter growthin parent curve (curve c) from parent activity curve (curve b).
This corresponds to the independent decay profile of daughter
activity, separated from the parent in-equilibrium. The halflife of the daughter 144Pr was determined using its decay curve
which was found to be 17.14 ± 0.17 min and agreed well withthe reported value of 17.29 min [13, 14].
The 144 Ce-144Pr pair which is in secular equilibrium wasanalysed by high resolution gamma spectrometry using HPGe
detector. The gamma spectrum of the same sample is shownin Fig. 5. The spectrum indicated the presence of parent 144Ce
which was extracted in its pure form into organic phase andJ. Nucl. Radiochem. Sci., Vol. 19, 2019

6

R. Kumar144

the in-grown daughter Pr from the same. The long lived
144
Ce parent shows no significant change in decay rate except
the variation due to the statistics during the period of experiment, while the daughter 144Pr grows in to a constant value.
The rate at which the daughter 144Pr grows to this constantvalue depends on its half-life and not on that of parent 144Ce.
This experiment demonstrates the parent-daughter relationship in the phenomenon of secular equilibrium satisfactorily.
3.4. Determination of half-life using the pure fraction of
Pr obtained by extraction chromatography. The extraction chromatographic studies were carried using 40% (w/w)
HDEHP-XAD7 resin. The column was conditioned with
KBrO3 to maintain the Ce oxidation state in +4, so that it binds
strongly to the resin. The gamma spectrometric analysis of
the eluted fractions in the medium of 1 M KBrO3 in 9 M
HNO3 showed the presence of 144Pr only, indicating that all the144
Ce was held strongly with the resin. The purified 144Pr fraction was assayed continuously by HPGe detector to obtain its
corresponding decay curve.
The pure 144Pr fraction was assayed regularly by high resolution gamma ray spectrometry using HPGe detector for 75
min and obtained its corresponding decay profile (Fig. 6). The
half-life obtained from the decay profile was found to be 17.32± 0.64 min and was in good agreement with the reported valuei.e. 17.29 min [13, 14]. The half-life value of the daughter
nuclide 144Pr obtained from the pure fraction yielded a moreaccurate value compared to the value (17.14 min) obtained by
secular equilibrium graph as discussed earlier, indicating thepurity of the daughter nuclide.
144

4. Conclusion
144

Ce-144Pr pair was purified from fission products and activation products in the FBTR irradiated (U, Pu) O2 fuel dissolver solution in nitric acid medium using ion-exchange
chromatography. The separation of pure parent (144Ce) fromthe 144Ce-144Pr pair was accomplished by solvent extraction
method using 0.7 M HDEHP/n-heptane as the extractant. The
pure 144Ce fraction was assayed continuously for a particularduration using well type NaI (Tl) solid scintillation detector.
The total activity due to both parent 144Ce and its in-growndaughter 144Pr was profiled as a function of time using a semilog paper. The curve was resolved into its individual components such as parent decay, daughter growth in its parent andindependent decay of daughter. The daughter nuclide 144Pr
was purified from its parent in-equilibrium 144Ce by extraction
chromatographic technique using HDEHP impregnated XAD7
resin with KBrO3-HNO3 as the eluant. Half-life of 144Pr was
obtained from this graph and found to be 17.32 ± 0.64 min
which is in agreement with the value obtained from secularequilibrium graph i.e. 17.14 ± 0.17 min. Thus the half-life values obtained from pure fraction 144Pr as well as equilibrium
curve were in agreement with the reported value, namely,
17.29 min. Thus the phenomenon of secular equilibrium wasdemonstrated using the pure fraction of 144Ce satisfactorily.
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Figure 6. Decay profile of 144Pr. (Amount of resin: 5 g of 40% w/w
HDEHP coated XAD7; Column Dimensions: 10 mm ID, 25 cm
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