The Cherenkov effect provides a reliable radiometric approach for detecting high-energy β emitters, yet its efficiency for α-emitting radionuclides such as 210Po is inherently limited, since α particles do not exceed the threshold velocity required for Cherenkov photon generation in aqueous media. Nevertheless, the detection of 210Po can be achieved indirectly similarly to 210Pb and daughter isotope 210Bi, whose β– emission produces measurable Cherenkov radiation. Recent studies [1, 2] have demonstrated that doping the detection medium with sodium salicylate (NaC₇H₅O₃) significantly increases the detectable Cherenkov signal. This enhancement originates from two complementary mechanisms: (I) a modest increase in the effective refractive index of the solution, obtained by slightly lowering the Cherenkov threshold and modifying photon yield, and (II) the wavelength-shifting property of sodium salicylate, which absorbs the ultraviolet radiation of Cherenkov photons (λ ≈ 280–320 nm) re-emitting in the visible region (λ ≈ 410–420 nm), where photomultiplier tubes and solid-state detectors exhibit maximal quantum efficiency. Additionally, sodium salicylate is water-soluble, non-volatile, and comparatively non-toxic, offering a sustainable alternative to conventional organic scintillation cocktails that employ aromatic solvents such as toluene or pseudocumene [3].
In the present study, we investigated the feasibility of doping the medium typically used for the elution of 210Po from SrSPEC and DGA-N/B resins (0.05 M HNO₃) with increasing amounts of sodium salicylate, in order to determine the alpha emissions of radionuclide by triple-to-double coincidence ratio liquid scintillation counting (TDCR-LSC).
The comparison between the liquid scintillation emission spectra of doped and undoped 210Po solutions shows a clear enhancement in the former. In Figure 1, the emission spectra are reported in logarithmic scale. In contrast to the classic Cherenkov emission, the doped sample displays a pronounced alpha-emission component that is clearly separated within the overall spectrum. As well as in beta spectrum [1], alpha emission counting efficiency is enhanced too, passing from zero up to about 50%, with a minimum tested activity of 30 Bq.
This type of technique, named Doped-Cherenkov-Alpha-Detection (DCAD), represents a promising candidate for the determination of alpha-emitting radionuclides through Cherenkov-based emission. Compared with conventional liquid scintillation counting, the DCAD approach offers a considerably more environmentally friendly, or “green,” alternative, owing to the absence of aromatic organic solvents, and the use of water-based, low-toxicity dopants such as sodium salicylate.
Looking ahead, the principle of Cherenkov enhancement by optical wavelength conversion could be extended beyond salicylate systems. Matrix-Assisted Laser Desorption/Ionization (MALDI) matrices—such as 2,5-dihydroxybenzoic acid or α-cyano-4-hydroxycinnamic acid—exhibit strong UV absorption and radiative re-emission in the visible range, and may act as efficient Cherenkov wavelength shifters or hybrid scintillators when dissolved or dispersed in aqueous media. The structural similarity of these aromatic acids to sodium salicylate suggests that MALDI-type matrices could serve as next-generation, environmentally benign dopants for Cherenkov-based radiometric assays, enabling higher sensitivity and broader spectral compatibility in radionuclide determination.
Yadong Wang, Yonggang Yang, et al., Effects of sodium salicylate on the determination of Lead-210/Bismuth-210 by Cerenkov counting, Applied Radiation and Isotopes 139 (2018) 175–180, https://doi.org/10.1016/j.apradiso.2018.05.013
G. A. Peck, J. D. Smith, et al., Enhanced counting efficiency of Cerenkov radiation from bismuth-210, Journal of Radioanalytical and Nuclear Chemistry, Vol. 238, Nos 1 2 (1998) 163 165
K. Kossert a,n, A.GrauCarles b, et al., Improved Čerenkov counting techniques based on a free parameter model, Applied RadiationandIsotopes86(2014)7–12, http://dx.doi.org/10.1016/j.apradiso.2013.12.022