Beta Decay Research Articles

Improving instrumental neutron activation analysis detection limit using Monte Carlo simulation for lanthanides determination in Algerian phosphate

ABSTRACT Instrumental Neutron Activation Analysis (INAA) is one of the best methods to analyse Rare Earth Elements (REE) with a low detection limit in phosphate samples. Since most lanthanides emit gamma rays at the energy below 1000 keV, this energy range is affected by the Bremsstrahlung noise of beta emission produced by the 31P(n,γ)32P reaction, when the irradiation of the P2O5 composing the phosphate matrix (approximately 30%). This beta (β−) spectrum with a maximum energy of 1.71 MeV (average energy of 695 keV) affects the gamma spectrum and will reduce the detection limit significantly, other factors decrease the detection limit of lanthanides like neutron self-shielding and interference. In the present work, an analysis methodology based on optimising the measurement parameters of the INAA technique was implemented to improve the detection limits for the precise evaluation of lanthanide concentrations in Algerian phosphate deposits. The complete procedure was developed using a combination of a Monte Carlo simulation approach and experimental measurements. Two models were developed based on Monte Carlo simulation for the calibration of HPGe detector efficiency and the optimisation of type and filter thickness to reduce the beta spectrum (Bremsstrahlung) emitted by the 32P produced by neutron capture reaction 31P(n, γ) 32P. The developed model allowed a considerable improvement in the detection limit of the INAA technique and reduced the uncertainty in the lanthanide concentration. Finally, the methodology was applied to determine lanthanide elements in phosphate samples with good precision.

Production of p Nuclei from r -Process Seeds: The νr Process

We present a nucleosynthesis process that may take place on neutron-rich ejecta experiencing an intensive neutrino flux. The nucleosynthesis proceeds similarly to the standard r process, a sequence of neutron captures and beta decays with, however, charged-current neutrino absorption reactions on nuclei operating much faster than beta decays. Once neutron-capture reactions freeze out the produced r process, neutron-rich nuclei undergo a fast conversion of neutrons into protons and are pushed even beyond the β stability line, producing the neutron-deficient p nuclei. This scenario, which we denote as the νr process, provides an alternative channel for the production of p nuclei and the short-lived nucleus Nb92. We discuss the necessary conditions posed on the astrophysical site for the νr process to be realized in nature. While these conditions are not fulfilled by current neutrino-hydrodynamic models of r-process sites, future models, including more complex physics and a larger variety of outflow conditions, may achieve the necessary conditions in some regions of the ejecta. Published by the American Physical Society 2024

Lattice QCD Calculation of Electroweak Box Contributions to Superallowed Nuclear and Neutron Beta Decays

We present the first lattice QCD calculation of the universal axial γW-box contribution □γWVA to both superallowed nuclear and neutron beta decays. This contribution emerges as a significant component within the theoretical uncertainties surrounding the extraction of |Vud| from superallowed decays. Our calculation is conducted using two domain wall fermion ensembles at the physical pion mass. To construct the nucleon four-point correlation functions, we employ the random sparsening field technique. Furthermore, we incorporate long-distance contributions to the hadronic function using the infinite-volume reconstruction method. Upon performing the continuum extrapolation, we arrive at □γWVA=3.65(7)lat(1)PT×10−3. Consequently, this yields a slightly higher value of |Vud|=0.973 86(11)exp(9)RC(27)NS, reducing the previous 2.1σ tension with the CKM unitarity to 1.8σ. Additionally, we calculate the vector γW-box contribution to the axial charge gA, denoted as □γWVV, and explore its potential implications. Published by the American Physical Society 2024

Minimal seesaw and leptogenesis with the smallest modular finite group

We propose a model for leptons based on the smallest modular finite group Γ2 ≅ S3 that, for the first time, accounts for both the hints of large low-energy CP-violation in the lepton sector and the matter-antimatter asymmetry of the Universe, generated by only two heavy right-handed neutrinos. These same states are also employed in a Minimal seesaw mechanism to generate light neutrino masses. Besides the heavy neutrinos, our particle content is the same as the Standard Model (SM), with the addition of one single modulus τ, whose vacuum expectation value is responsible for both the modular and CP-symmetry breakings. We show that this minimalistic SM extension is enough to get an excellent fit to low energy neutrino observables and to the required baryon asymmetry ηB. Predictions for the neutrino mass ordering, effective masses in neutrinoless double beta decay and tritium decay as well as for the Majorana phases are also provided.

Design of high-light-collection-efficiency optical fiber for germanium detectors immersed in liquid argon

The implementation of Slicon Photon-Multipliers (SiPMs) wave-length shifting (WLS) fibers light response system in liquid argon (LAr) is a promising technology for suppressing background in rare event experiments. Moreover, it is particularly relevant for experiments that utilize high-purity germanium (HPGe) detectors directly operated in LAr, such as the direct detection of dark matter and neutrinoless double beta decay. In this work, we exhibit a designed WLS fiber for the LAr detector, verify the feasibility of the manufacturing technology, and simulation research about its light collection performance. The novel fiber incorporates two materials, styrene and 1,1,4,4-tetraphenyl-1,3-butadiene (TPB). The pre-experiments proved that the fiber has good WLS and light-conducting properties for ultraviolet light. In addition, the effect of different light collection methods on detection efficiency was assessed by Geant4 simulation. Our results show that adding optical fibers can significantly increase light collection efficiency. Compared with the design of TPB coating with commercial fiber, the new structure of WLS fiber can improve the light collection efficiency by 50%. The simulation results indicate that the new fiber structure can enhance the light collection efficiency of the LAr detection system, thereby improving the anti-coincidence system's performance in rare event experiments.

Data reduction strategy in the PandaX-4T experiment

The PandaX-4T experiment is designed for multiple purposes, including searches for solar neutrinos, weakly interacting massive particles, and rare double beta decays of xenon isotopes. The experiment produces a huge amount of raw data that needs to be stored for related physical analyses in a wide energy range. With the upgrading of the PandaX-4T experiment, the doubled sampling rate resulted in a larger data size, which challenges both the cost and the data processing speed. To address this issue, we propose a data reduction strategy by removing the noise tail of large signals and downsampling the remaining parts of them. This strategy reduces the requirement for storage by 65% while increasing data processing speed. The influences on physical analyses on different topics at different energy regions are negligible.

Cross sections of neutral-current neutrino scattering on 98,100Mo isotopes

Coherent elastic neutrino–nucleus scattering (CEνNS) is a neutral-current low-energy electro-weak reaction-channel detected recently by the COHERENT experiment at the Oak Ridge National Laboratory (ORNL), USA, in the Spallation Neutron Source facility. The extremely weak signal on the CsI detector of the first experiment and on the liquid Ar of the repeated COHERENT experiment is the energy-recoil due to the neutrino–nucleus interaction, where the nucleus is elastically scattered as a whole while simultaneously the neutrino goes out. Today, several promising nuclear detectors are on the way to be employed in designed and ongoing experiments. In our present work, we provide predictions for incoherent scattering cross sections of low-energy neutrinos on 98,100Mo isotopes obtained with the deformed shell model employed previously for similar predictions in other electroweak processes. We mention that, Mo detector medium has been used previously in the MOON and NEMO double beta decay experiments.

Theory of Majorana-Type Heavy Ion Double Charge Exchange Reactions by Pion–Nucleon Isotensor Interactions

The theory of heavy ion double charge exchange (DCE) reactions proceeding by effective rank-2 isotensor interactions is presented. Virtual pion–nucleon charge exchange interactions are investigated as the source for induced isotensor interactions, giving rise to the Majorana DCE (MDCE) reaction mechanism. MDCE is of a generic character, proceeding through pairs of complementary (π±,π∓) reactions in the projectile and target nucleus. The dynamics of the elementary processes is discussed, where the excitation of pion–nucleon resonances are of central importance. Investigations of initial and final state ion–ion interactions show that these effects are acting as vertex renormalizations. In closure approximation, well justified by the finite pion mass, the second-order transition matrix elements reduce to pion potentials and effective two-body isotensor DCE interactions, giving rise also to two-body correlations in either of the participating nuclei. Connections to neutrinoless Majorana double beta decay (MDBD) are elucidated at various levels of the dynamics, from the underlying fundamental electro-weak and QCD scales to the physical scales of nuclear MDBD and MDCE physics. It is pointed out that heavy ion MDCE reactions may also proceed by competing electro-weak charge exchange processes, leading to lepton MDCE by electrons, positrons, and neutrinos.

Superallowed Nuclear Beta Decays and Precision Tests of the Standard Model

Superallowed Nuclear Beta Decays and Precision Tests of the Standard Model

Production of [211At]NaAt solution under GMP compliance for investigator-initiated clinical trial.

The alpha emitter astatine-211 (211At) is garnering attention as a novel targeted alpha therapy for patients with refractory thyroid cancer resistant to conventional therapy using beta emitter radioiodine (131I). Herein, we aimed to establish a robust method for the manufacturing and quality control of [211At]NaAt solution for intravenous administration under the good manufacturing practice guidelines for investigational products to conduct an investigator-initiated clinical trial. 211At was separated and purified via dry distillation using irradiated Bi plates containing 211At obtained by the nuclear reaction of 209Bi(4He, 2n)211At. After purification, the 211At trapped in the cold trap was collected in a reaction vessel using 15 mL recovery solution (1% ascorbic acid and 2.3% sodium hydrogen carbonate). After stirring the 211At solution for 1h inside a closed system, the reaction solution was passed through a sterile 0.22μm filter placed in a Grade A controlled area and collected in a product vial to prepare the [211At]NaAt solution. According to the 3-lot tests, decay collected radioactivity and radiochemical yield of [211At]NaAt were 78.8 ± 6.0 MBq and 40 ± 3%, respectively. The radiochemical purity of [211At]At- obtained via ion-pair chromatography at the end of synthesis (EOS) was 97 ± 1%, and remained > 96% 6h after EOS; it was detected at a retention time (RT) 3.2-3.3min + RT of I-. LC-MS analysis indicated that this principal peak corresponded with an astatide ion (m/z = 210.988046). In gamma-ray spectrometry, the 211At-related peaks were identified (X-ray: 76.9, 79.3, 89.3, 89.8, and 92.3keV; γ-ray: 569.7 and 687.0keV), whereas the peak at 245.31keV derived from 210At was not detected during the 22h continuous measurement. The target material, Bi, was below the 9 ng/mL detection limit in all lots of the finished product. The pH of the [211At]NaAt solution was 7.9-8.6; the concentration of ascorbic acid was 9-10mg/mL. Other quality control tests, including endotoxin and sterility tests, confirmed that the [211At]NaAt solution met all quality standards. We successfully established a stable method of [211At]NaAt solution that can be administered to humans intravenously as an investigational product.

Searching for Two-Neutrino and Neutrinoless Double Beta Decay of ^{134}Xe with the PandaX-4T Experiment.

^{134}Xe is a candidate isotope for neutrinoless double beta decay (0νββ) search. In addition, the two-neutrino case (2νββ) allowed by the standard model of particle physics has not yet been observed. With the 656-kg natural xenon in the fiducial volume of the PandaX-4T detector, which contains 10.4% of ^{134}Xe, and its initial 94.9-day exposure, we have established the most stringent constraints on 2νββ and 0νββ of ^{134}Xe half-lives, with limits of 2.8×10^{22}  yr and 3.0×10^{23}  yr at 90%confidence level, respectively. The 2νββ (0νββ) limit surpasses the previously reported best result by a factor of 32 (2.7), highlighting the potential of large monolithic natural xenon detectors for double beta decay searches.

The B0→J/ψf0(1370,1500,1710)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B^0 \\rightarrow J/\\psi f_0(1370,1500,1710)$$\\end{document} decays: an opportunity for scalar glueball hunting

The scalars f0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f_0$$\\end{document} closest to 1.5 GeV contain the mesons f0(1370)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f_0(1370)$$\\end{document}, f0(1500)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f_0(1500)$$\\end{document} and f0(1710)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f_0(1710)$$\\end{document}, and the latter two ones are usually viewed as the potential candidates for the scalar glueballs. In this work, by including the important contributions from the vertex corrections, we study the decays B0→J/ψf0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B^0 \\rightarrow J/\\psi f_0$$\\end{document} within the improved perturbative QCD approach and analyze the possible scalar glueball hunting. Together with the two mixing models, namely, f0(1500)(f0(1710))\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f_0(1500) (f_0(1710))$$\\end{document} being the primary scalar glueball in model I (II), and two classification scenarios, namely, f0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f_0$$\\end{document} being the qq¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$q\\bar{q}$$\\end{document} excited (ground) states in scenario 1 (2), the branching fractions associated with their ratios for B0→J/ψf0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B^0 \\rightarrow J/\\psi f_0$$\\end{document} are evaluated comprehensively. The predictions with still large uncertainties in the considered two mixing models are roughly consistent with currently limited data, which indicates that both more rich data and more precise predictions are urgently demanded to figure out the scalar glueball clearly in the future. Moreover, several interesting ratios between the branching fractions of B0→J/ψf0(→π+π-/K+K-)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B^0 \\rightarrow J/\\psi f_0(\\rightarrow \\pi ^+ \\pi ^-/K^+ K^-)$$\\end{document} and B0→J/ψρ0/ϕ(→π+π-/K+K-)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B^0 \\rightarrow J/\\psi \\rho ^0/\\phi (\\rightarrow \\pi ^+ \\pi ^-/ K^+ K^-)$$\\end{document} that could help us to understand the nature of scalar f0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f_0$$\\end{document} are defined and predicted theoretically. These ratios should be examined in future experiments.

Revisiting Trimaximal TM2 mixing in two A4 modular symmetries

In this paper, we discuss a minimal lepton flavor model with two modular [Formula: see text] symmetries, one acting on neutrinos and the other acting on charged leptons. Two corresponding moduli fields are restricted at stabilizers. To avoid vanishing or degenerate lepton masses, the stabilizer in the charged lepton sector always preserves a [Formula: see text] symmetry, and that in the neutrino preserves a [Formula: see text] symmetry. By scanning all viable stabilizers, a unique Trimaximal TM2 mixing is predicted. However, the prediction of the lightest neutrino mass and the mass parameter in neutrinoless double beta decay, as well as two Majorana phases, are different and classified into three cases.

Evaluation of the cyclotron production of the positron emitters 43Sc, 44gSc and beta emitter 47Sc radionuclides: An emerging theranostic pair

The theranostic pair of Scandium radionuclides: 43/44Sc positron emitters along with 47Sc beta emitter, has been gaining attention in the field of nuclear medicine over the last decades. The charged particle induced reactions, namely 43Ca(p,n)43Sc, 44Ca(p,n)44Sc, 44Ca(p,2n)43Sc, 46Ti(p,α)43Sc, 48Ca(p,2n)47Sc, 41K(α,2n)43Sc,40Ca(α,p)43Sc, 41K(α,n)44gSc and 44Ca(α,p)47Sc were evaluated for the high purity production of the 43Sc, 44gSc and 47Sc radionulicdes. Three Nuclear model codes (TALYS 1.9, ALICE-IPPE and EMPIRE 3.2) were used to check the consistency and reliability of the experimental excitation functions. A comprehensive evaluation methodology was used to generate the recommended cross sections, for each production route and their corresponding radioisotopic impurities. The final recommended cross sections are at last based on the statistical fitting of the resulting combination of both experimental data and theoretical nuclear model calculations. Thick target yields were calculated by using the recommended/reference cross sections. After a careful analysis and comparison of the evaluated production routes, namely 43Ca(p,n)43Sc, 44Ca(p,n)44gSc and 48Ca(p,2n)47Sc are suggested for the high purity cyclotron production of the 43Sc, 44gSc and 47Sc radionuclide respectively.

Construction of Yemilab

The Center for Underground Physics of the Institute for Basic Science (IBS) in Korea has been planning the construction of a deep underground laboratory since 2013 to search for extremely rare interactions such as dark matter and neutrinos. In September 2022, a new underground laboratory, Yemilab, was finally completed in Jeongseon, Gangwon Province, with a depth of 1,000 m and an exclusive experimental area spanning 3,000 m3. The tunnel is encased in limestone and accommodates 17 independent experimental spaces. Over 2 years, from 2023 to 2024, the Yangyang Underground Laboratory facilities will be relocated to Yemilab. Preparations are underway for the AMoRE-II, a neutrinoless double beta decay experiment, scheduled to begin in Q2 2024 at Yemilab. Additionally, Yemilab includes a cylindrical pit with a volume of approximately 6,300 m3, designed as a multipurpose laboratory for next-generation experiments involving neutrinos, dark matter, and related research. This article provides a focused overview of the construction and structure of Yemilab.

Searches for neutrino counterparts of gravitational waves from the LIGO/Virgo third observing run with KM3NeT

The KM3NeT neutrino telescope is currently being deployed at two different sites in the Mediterranean Sea. First searches for astrophysical neutrinos have been performed using data taken with the partial detector configuration already in operation. The paper presents the results of two independent searches for neutrinos from compact binary mergers detected during the third observing run of the LIGO and Virgo gravitational wave interferometers. The first search looks for a global increase in the detector counting rates that could be associated with inverse beta decay events generated by MeV-scale electron anti-neutrinos. The second one focuses on upgoing track-like events mainly induced by muon (anti-)neutrinos in the GeV–TeV energy range. Both searches yield no significant excess for the sources in the gravitational wave catalogs. For each source, upper limits on the neutrino flux and on the total energy emitted in neutrinos in the respective energy ranges have been set. Stacking analyses of binary black hole mergers and neutron star-black hole mergers have also been performed to constrain the characteristic neutrino emission from these categories.

Towards a fiber barrel detector for next-generation high-pressure gaseous xenon TPCs

The NEXT (Neutrino Experiment with a Xenon TPC) project is an international collaboration aimed at finding evidence of neutrinoless double beta decay using gaseous xenon. The current phase of the project involves the construction and operation of NEXT-100, which is designed to hold 100 kg of xenon at 15 bar and is expected to start commissioning in the first quarter of 2024. NEXT-HD will be a tonne scale experiment following NEXT-100 and will incorporate a symmetric design, with one cathode and two anodes. For this detector, the collaboration is considering to implement a barrel of wavelength-shifting fibers read-out by silicon photomultipliers to measure the energy of the particles interacting in the gaseous xenon. In this document, we will discuss the characteristics of this approach and provide an update on the related R&D efforts.

Theoretical Advances in Beta and Double-Beta Decay

Weak interaction processes continue to be hot topics in fundamental physics research. In this paper, we briefly review some recent advances in the theoretical study of beta and double-beta decays that include both the nuclear and atomic part of these processes. On the nuclear side, we present a statistical approach for the computation of the nuclear matrix elements (NME) for neutrinoless double-beta (0νββ). A range of NME values, the most probable value for NME, and the associated theoretical uncertainty are given. Correlations with other related observables are shown as well. On the atomic side, we first briefly review the methods used to obtain the electrons’ wave functions. Further, we use them for the computation of some relevant kinematic quantities such as Fermi functions, electron spectra, and angular correlation between the emitted electrons. Then, we present applications of these calculations to the experimental data analysis related to the search of the Lorentz invariance violation in two-neutrino double-beta (2νββ) decay and description of the decay rates and decay rate ratios for allowed and unique forbidden electron capture (EC) processes.

Investigation of select radionuclides stability in urine under various conditions for liquid scintillation counting (LSC).

Liquid Scintillation Counting (LSC) gross alpha/beta screening is a valuable tool for providing rapid laboratory response for the analysis of human clinical urine samples during a large-scale radiation incident event. Verification of method performance, as required for clinical laboratory testing, is accomplished by the evaluation of routine, periodic measurements of radioactive spiked samples for quality control, performance testing, and accuracy checks. Radionuclide stability of alpha and beta emitters in urine for LSC analysis is an important consideration. The purpose of this work is to demonstrate optimal preparations and storage conditions of samples used for method verification.

Abstract 6023: 225Ac-FL-020 is a novel PSMA-targeting radionuclide drug conjugate (RDC) with superior in vivo anti-tumor activity

Abstract Despite significant developments over the last few decades, metastatic castration-resistant prostate cancer (mCRPC) remains incurable. Prostate specific membrane antigen (PSMA), a prostate cancer-specific membrane marker which directly correlates with androgen independence, metastasis, and disease progression, has been well-established as a radioligand target for the diagnosis and treatment of mCRPC. Lutetium-177 (177Lu)-PSMA-617 (PLUVICTOTM) was approved in 2022 for the treatment of progressive PSMA-positive mCRPC. However, only 30% of patients showed a radiological response in the registrational trial. Meanwhile, recent clinical experience has shown very limited efficacy in low PSMA expressing patients. These data collectively request for further improvement in the clinical benefit of PSMA-targeted radiotherapy. Actinium-225 (225Ac), an alpha emitter, is significantly more potent on cancer cell killing and has a shorter range in tissue penetration when compared to the beta emitter 177Lu. Such a profile supports the development of 225Ac based radiotherapies. Using our proprietary Clear-XTM technology platform, we developed 225Ac-FL-020, a novel 225Ac-based PSMA radioligand therapy candidate which has demonstrated prominent pre-clinical properties. We have assessed the binding affinity against PSMA of the non-labeled vector FL-020 in vitro. The in vivo biodistribution profile of FL-020 was characterized by SPECT/CT imaging and biodistribution using Indium-111 (111In)-FL-020 in PSMA high LNCaP tumor-bearing nude mice. In addition, anti-tumor activities of 225Ac-FL-020 were evaluated in the LNCaP xenograft model and directly compared to 225Ac-PSMA-617. FL-020 was found bound to LNCaP cells with an IC50 value of 51.55 nM. Meanwhile, the off-target screening showed that less than 50% inhibition of binding or activity was observed by FL-020 at 10 µM against 85 targets including receptors, ion channels, enzymes, and transporters, indicating the high selectivity of FL-020. Moreover, 111In-FL-020 displayed a very promising in vivo distribution profile with high and sustained tumor uptake and fast systemic clearance. Furthermore, 225Ac-FL-020 exhibited superior anti-tumor activity compared to 225Ac-PSMA-617 at the same dose level (10 KBq/mouse) in the LNCaP xenograft model with a favorable safety profile as indicated by body weight and hematological parameters. A mechanistic study was also conducted in 225Ac-FL-020-treated LNCaP tumor samples where DNA double-strand breaks and tumor cell apoptosis were observed, confirming the MOA of alpha emitters. Taken together, these results collectively demonstrate that 225Ac-FL-020 is a potent and selective PSMA-targeting radioligand therapy candidate with superior anti-tumor activity and a favorable safety profile warranting further clinical development. Citation Format: Fa Liu, Jiangwei Zhang, Junyu Yang, Kirstine T. Thrane, Mathias W. Hallund, Rikke V. Grønlund, Nicholas C. Wong. 225Ac-FL-020 is a novel PSMA-targeting radionuclide drug conjugate (RDC) with superior in vivo anti-tumor activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6023.