Simultaneous determination of Ra-226 and Ra-228 in water using spectrum stripping method by LSC
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Simultaneous determination of Ra‑226 and Ra‑228 in water using spectrum stripping method by LSC Ming‑Ming Xia1 · Yong‑Guang Liang2 · Guo‑Bing Yu3 · Jian‑Ping Zhu1 · Shi‑Si Cheng1 · Chao Tian1 · Tao Xu1 · Yi‑Rui Wu1 Received: 15 February 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract This paper proposes a joint measurement method of Ra-226 and Ra-228 in water. Radium was extracted from aqueous samples and analyzed by liquid scintillation counting (LSC). The spectrum and counts measured by LSC is combined with the standard spectrum, and then the activities of Ra-226 and Ra-228 can be calculated by the stripping method. Chemical yields of radium were determined by measuring the chemical analogue (barium) tracer by atomic absorption spectrometry (AAS). The accuracy of the method was verified by measuring mixtures containing varying proportions of Ra-226 and Ra-228. Keywords Ra-226 · Ra-228 · Stripping method · LSC · Yield
Introduction Ra and other alkaline metals (Ca, Sr, Ba) have similar chemical biological behaviors. Once ingested, radium is accumulated into the bones, exposing the human body to continuous internal irradiation [1, 2]. From the perspective of radiation dosimetry, it is of great significance to accurately measure Ra-226 and Ra-228 in environmental water [3]. Ra-226, α-emitting radionuclide in the uranium series (T1/2 = 1620 a). Its main energies include Eα1 = 4.781 MeV (94.5%) and Eα2 = 4.598 MeV (5.5%), while accompanied by the production of γ-photon, Eγ = 186.2 keV (3.5%) [4]. Therefore, Ra-226 can be directly measured by alpha spectrometry or gamma spectrometry [5, 6]. In addition, Ra-226 has a series of short-lived radioactive daughters (Rn-222, Po-218, Pb-214, Bi-214, Po-214). The decay scheme of Ra-226 is shown in Fig. 1. Ra-226 and its daughters can reach radioactive equilibrium after about 20 days [7], so
* Guo‑Bing Yu [email protected] 1
Science and Technology on Reactor System Design Technology Laboratory, Nuclear Power Institute of China, Chengdu, China
2
University of Science and Technology of China, Hefei, China
3
Anhui Environmental Radiation Supervision Station, Hefei, China
Ra-226 can also be measured indirectly through its daughters [8]. Ra-228, β-emitting radionuclide in the thorium series (T1/2 = 5.75 a) [9]. The energies of its β-particles are relatively low, Eβ1 = 39 keV (60%) and Eβ2 = 14.5 keV (40%) [4]. But Ra-228 is more radiotoxic than Ra-226. Ac-228, β decay, the daughter of Ra-228, has a short half-life of 6.13 h which can quickly reach radioactive equilibrium with Ra-228. Ra-228 and its isotope Ra-224 are in the same decay series. Although Ra-224 is α-emitting, there are many short-lived β-emitting radioactive species (Pb-212, Bi-212, Po-212, Tl-208), which can interfere with the measurement of Ra-228. The decay scheme of Ra-228 is shown in Fig. 2. Among them, Ra-224 and its daughters will decay completely for about 20 days. At this time, Ra-228 and Ac-228 are in radioactive equilibrium. At present, alpha spectrometry is widely used to measure
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