The radiochemical purity of a

---

The radiochemical purity of a 

131

Cs solution used in brachytherapy is studied. After separating 

131

Cs from

the neutron irradiated targets BaO, Ba(NO

3

)

2

, and BaCO

3

, the contribution of impurities was evaluated:

0.015% for 

124

Sb and 0.012% for 

132

Cs. The contribution of the parent 

131

Ba to cesium solutions was, on

average, 0.0067% for BaO, 0.01% for Ba(NO

3

)

2

, and 0.011% for BaCO

3

.

Brachytherapeutic treatment methods for cancer are widely used in nuclear medicine. The essence of brachythera-

py lies in the fact that several tens of microsources of ionizing radiation are introduced into tissue tumors using special nee-

dles without any surgical intervention. The microsources are small titanium capsules–grains containing a radionuclide which

possesses definite nuclear characteristics, such as the presence of low-energy radiation for effective action on a tumor and

absence of high-energy radiation to prevent damage to healthy tissue. Radiation sources based on 

131

Cs were first used in

2004 in clinics in the USA and it was determined that 

131

Cs suppresses the growth of cancer cells more quickly and effec-

tively than 

125

I and 

103

Pd, which are used now [1, 2]. Radiation microsources based on 

131

Cs have proven themselves well

for treatment of various types of tumors but especially cancer of the prostate gland [1].

Radionuclides used in nuclear medicine and, specifically, brachytherapy must meet stringent requirements with

respect to radiochemical purity. The preparations used must possess high purity (99.99%) and the content of impurity

radionuclides must not exceed 0.01% [3, 4]. For this reason, the radiochemical purity of a preparation after 

131

Cs has been

separated is the main characteristic of its suitability for medical use. Detecting and qualitatively monitoring impurity radionu-

clides are special problems in obtaining 

131

Cs for brachytherapy.

It is best to obtain 

131

Cs by irradiating naturally occurring barium with thermal neutrons according to the reaction

130

Ba (n,

γ

) 

→

131

Ba 

→

131

Cs 

→

131

Xe, as a result of which 

131

Ba is formed from low-abundance (0.1%) 

130

Ba. The parent

radionuclide 

131

Ba with T

1/2

= 11.8 days forms as a result of 

β

–

decay the daughter radionuclide 

131

Cs with T

1/2

= 9.7 days,

which has only the x-ray lines K

α

= 29.65 keV and K

β

= 33.61 keV. As a result of 

β

–

decay,

131

Cs transforms into stable

131

Xe [5, 6].

Calculations were performed to evaluate the activity of radionuclides which are formed as a result of irradiating barium

targets in a nuclear reactor. As Table 1 shows, for prolonged irradiation of barium, aside from the desired 

131

Ba, more than 10

radionuclides whose half-life ranges from 2.5 min to 10.5 yr and specific activity from 1.6·10

5

to 5.9·10

10

Bq can form [6, 7].

Different barium compounds can be irradiated to obtain 

131

Cs: BaCO

3

, Ba(NO

3

)

2

, BaO, and BaCl

2

·2H

2

O. However,

prolonged irradiation of hygroscopic barium compounds damages the quartz ampul because of the elevated internal pressure.

Experiments showed that barium chloride dihydrate is similarly unsuitable. For this reason, analytically pure grade BaO,

BaCO

3

, and Ba(NO

3

)

2

were taken as the target samples.

The activity of barium and cesium solutions was determined by measuring the corresponding aliquots of the solu-

tions in high-purity germanium (V = 120 cm

3

) and germanium-lithium semiconductor detectors with GENIE 2000 (USA)

Atomic Energy, Vol. 109, No. 6, April, 2011 (Russian Original Vol. 109, No. 6, December, 2010)

UDC 543.53;546.36

Institute of Nuclear Physics, Academy of Sciences of the Republic of Uzbekistan, Tashkent, Uzbekistan. Translated

from Atomnaya Énergiya, Vol. 109, No. 6, pp. 330–332, December, 2010. Original article submitted April 30, 2010.

1063-4258/11/10906-0404

©

2011 Springer Science+Business Media, Inc.

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