Ground State Decay Research Articles

Half-life determination of the ground state decay of 167Tm and 168Tm

Precise determination of half-lives of 167Tm and 168Tm are important for their application in nuclear medicine diagnostics, nuclear forensics, and other nuclear data measurements. We produced 167Tm and 168Tm sources using an α-particle beam bombarded 165Ho target and a series purification steps. A series of 173 measurements was performed over a period of 44 days using a high-purity germanium (HPGe) detector to track the count rate change as a function of time by following the 207.8 keV and 531.5 keV γ-lines to determine the radioactive decay half-life of 167Tm. The measurement of half-life of 168Tm ground state has been performed using the same HPGe γ-ray spectrometer to observe γ-lines at 198.3 keV, 816.0 keV, 184.3 keV, 741.4 keV and 914.9 keV. Weighted least-squares fits of exponential decay curves were performed for the dataset of each γ-ray emission, with final determined half-lives of 9.250(15) d and 93.41(12) d for 167Tm and 168Tm, respectively. The uncertainty budgets are presented and discussed in detail. Our result of 167Tm half-life is consistent with the Evaluated Nuclear Structure Data File (ENSDF) recommended half-life of 9.25(2) d. The outcome of 168Tm half-life determination is longer than the ENSDF recommended half-life of 93.1(2) d. Further independent measurements would be ideal to resolve the discrepancy.

Prompt neutron emission in 250No spontaneous fission associated with ground and isomeric state decays

Abstract The complete-fusion reaction 204Pb(48Ca,2n)250No was used to study two activities of 250No with distinct half-lives. A total of 1357 events were observed in the SFiNx neutron detection system. The average number of neutrons emitted per spontaneous fission of 250No was determined to be . The unusually symmetrical shape of the prompt neutron multiplicity distribution was restored and presented for the first time. Statistical tests were performed to compare the prompt neutron multiplicity distributions associated with the ground state and K-isomer state decays.

On dilation analyticity and spatial exponential decay of atomic ground states in non-relativistic QED

We consider the ground state and the ground state energy of an atom with spinless electrons in the framework of non-relativistic quantum electrodynamics. We show that the ground state energy as well as the ground state depend analytically on the parameters of the group of dilations, the parameter of a group of spatial dependent phase changes, and on the minimal coupling constant. As a corollary we obtain spatial exponential decay of the ground state as well as of its dilation analytic extension. No infrared regularization is needed for the result. Our result is based on operator theoretic renormalization.

Study of various ground state decay mechanisms of Actinide nuclei* *Financial support from the Department of Science and Technology (DST), New Delhi, India in the form of a research project grant (CRG/2021/001144) is gratefully acknowledged.

The special property of the actinide mass region is that nuclei belonging to this group are radioactive and undergo different ground state processes, such as alpha decay, cluster radioactivity (CR), heavy particle radioactivity (HPR), and spontaneous fission (SF). In this study, the probable radioactive decay modes of the heavy mass region (Z = 89−102) are studied within the framework of the preformed cluster model (PCM). In the PCM, the radioactive decay modes are explored in terms of the preformation probability () and penetration probability (P) at the turning point , where the penetration of fragments is initiated [R = R (touching state) + (neck length parameter)]. First, the alpha decay half-lives are calculated for light and heavy nuclei, and points are obtained by optimizing the neck length parameter. These points are further employed to fix the Q-value dependent turning point ((Q)). Then, using the ((Q)) relation, the decay half-lives are computed, and the calculated results are compared with the available theoretical and experimental data. The isotopical trend of and P is studied with respect to the mass number of the parent and daughter nucleus, respectively. The CR and HPR channels are also explored, and a comparison of calculated data is conducted with the available literature. Comparative analysis of the fragmentation potential and preformation probability is carried out for alpha decay and SF. The mass distribution of the nuclei is studied as a function of fragment mass (A ) by considering the spherical and hot-compact deformation of the decaying fragments. Finally, the most probable fission fragments are identified using the fragmentation structure, and the corresponding fission fragment total kinetic energy of the identified fragments is calculated and compared with available data, wherever applicable.

High event rate analysis technique for the dual-axis duo-lateral position-sensitive silicon detectors of FAUST

The dual-axis duo-lateral (DADL) position-sensitive silicon detector was developed to obtain precise position and energy information for detected charged particles. The Forward Array Using Silicon Technology (FAUST) is currently equipped with 68 DADL detectors backed by CsI(Tl) scintillators for the study of charged particle correlations in heavy-ion collisions where precise position and energy information is essential. When conventional signal processing electronics were used for the DADL detectors, a position dependence of the measured energy as well as distortions in the calculated particle positions were observed. In previous work, waveforms from the detector after preamplification were studied to better understand the features that give rise to these distortions; therein, a waveform analysis technique was developed to improve the energy resolution and linearity in position reconstruction. However, the reading and writing of waveforms for an entire detector array limits data collection rates and adds significant burden in data storage and analysis speed. In this work, the integrators of a Struck SIS3316 ADC were utilized to process 228Th source data to develop and optimize a new analysis method that captures the benefits of the waveform analysis technique while circumventing the waveform writing requirement. This integrator method – capable of 59keV (FWHM) energy resolution – was used in the collection of 35 MeV/nucleon 28Si + 12C collision data using FAUST to investigate exotic decays of highly excited highly deformed nuclei. In this data, a position resolution of 0.4mm (FWHM) was obtained for 25MeV α-particles; for α-particles near this energy that originate from 8Be ground state decays, a 8Be ground state width of 30keV (FWHM) was obtained. The impact of the energy-dependent DADL position resolution emergent from electronic noise on the quality of excited state measurement was modeled and compared to the experimental data.

Ground state solutions and decay estimation of Choquard equation with critical exponent and Dipole potential

<p style='text-indent:20px;'>In this paper, we study a class of Choquard equations with critical exponent and Dipole potential. We prove the existence of radial ground state solutions for Choquard equations by using the refined Sobolev inequality with the Morrey norm, and show that any nonnegative weak solutions of Choquard equations have additional decay properties in terms of ground state representation.</p>

Model-independent determination of the dipole response of Zn66 using quasimonoenergetic and linearly polarized photon beams

[Background] Photon strength functions are an important ingredient in calculations relevant for the nucleosynthesis of heavy elements. The relation to the photoabsorption cross section allows to experimentally constrain photon strength functions by investigating the photo-response of atomic nuclei. [Purpose] We determine the photoresponse of $^{66}$Zn in the energy region of 5.6 MeV to 9.9 MeV and analyze the contribution of the "elastic" decay channel back to the ground state. In addition, for the elastic channel electric and magnetic dipole transitions were separated. [Methods] Nuclear resonance fluorescence experiments were performed using a linearly-polarized quasi-monoenergetic photon beam at the High Intensity $\gamma$-ray Source. Photon beam energies from 5.6 to 9.9 MeV with an energy spread of about 3% were selected in steps of 200-300 keV. Two High Purity Germanium detectors were used for the subsequent $\gamma$-ray spectroscopy. [Results] Full photoabsorption cross sections are extracted from the data making use of the monoenergetic character of the photon beam. For the ground-state decay channel, the average contribution of electric and magnetic dipole strengths is disentangled. The average branching ratio back to the ground state is determined as well. [Conclusions] The new results indicate lower cross sections when compared to the values extracted from a former experiment using bremsstrahlung on $^{66}$Zn. In the latter, the average branching ratio to the ground state is estimated from statistical-model calculations in order to analyze the data. Corresponding estimates from statistical-model calculations underestimate this branching ratio compared to the values extracted from the present analysis, which would partly explain the high cross sections determined from the bremsstrahlung data.

Role of Skyrme forces in cluster radioactivity of parent nuclei with even ( A,Z )

We investigate the role of different Skyrme forces (SIII, SkI4, and SAMi) in the ground state decay of various radioactive parent nuclei such as Ra, Th, U, and Pu. The daughters of these nuclei are either doubly magic $^{208}\mathrm{Pb}$ or a nearby isotope of Pb. Using spherical choice of cluster and daughter, calculations are performed within the framework of the preformed cluster model (PCM), where the preformation probability ${P}_{0}$ and penetration probability $P$ of decaying fragments are used to obtain the half-lives of cluster emission. The considered forces modify the barrier characteristics and consequently the penetration path, as the scattering potential at the first turning point of the barrier is lowest with the SkI4 force (lowest penetrability) and highest with the SIII force (highest penetrability). However, the preformation probability of decaying clusters is highest for the SkI4 force followed by SAMi and SIII Skyrme forces. To look for the possible role of the spin-orbit effect on the cluster radioactivity, the half-lives of emitted clusters are calculated with and without the inclusion of spin-orbit potential ${V}_{J}$. In addition, the $\ensuremath{\alpha}$-decay half live are also calculated to extract an inclusive picture of the dynamics involved.

β −p and β−α decay of the 11Be neutron halo ground state

Beta-delayed proton emission from the neutron halo ground state of 11Be raised much attention due to the unusually high decay rate. It was argued that this may be due to the existence of a resonance just above the proton decay threshold. In this letter, we use the lenses of real-energy continuum shell model to describe several observables including the Gamow–Teller rates for the β −-delayed α and proton decays, and argue that, within our model, the large β −p branching ratio cannot be reconciled with other data.

Search for fission from a long-lived isomer in No250 and evidence of a second isomer

In the present work, a $K$ isomeric state in $^{250}\mathrm{No}$, which is more stable against fission than the ground state, was experimentally studied. The aim was to measure the fission branch of this isomeric state. In total, 780 fission events attributed to the decay of $^{250}\mathrm{No}$ were detected. Among them 133 cases were attributed to the ground-state decay with a half-life of 4.0(4) $\ensuremath{\mu}\mathrm{s}$, which was populated by the deexcitation of the isomeric state via electromagnetic transitions with a half-life of 23(4) $\ensuremath{\mu}\mathrm{s}$. In addition, in two more cases, this long-lived isomeric state was populated in the deexcitation of a hitherto unknown, yet higher-lying and short-lived isomeric state with a half-life of $0.{7}_{\ensuremath{-}0.3}^{+1.4}\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{s}$. No direct fission from the long-lived isomeric state, i.e., with a lifetime of longer than 40 $\ensuremath{\mu}\mathrm{s}$, was identified. This results in an upper limit of 0.035 for the branching ratio for fission. This is a significantly more strict limit than the previously known value of 0.5. Nonobservation of fission branching of the long-lived isomer is discussed relative to theoretical predictions and within various semiempirical ways, which resulted in an attribution of a lower limit of ${10}^{4}$ for the fission-hindrance factor, caused by the $K$ quantum number. The presences of multiple high-$K$ isomeric states seemingly is a widespread phenomenon in deformed heavy nuclei.

Macroscopic–microscopic calculations of the ground state properties of Z = 120 isotopes and their α-decay chains

One of the substantial successes achieved in nuclear physics in the last two decades was the synthesis of dozens of isotopes of new elements up to [Formula: see text]Og, which closed the seventh row of the periodic table and inspired the ambition of adding more elements. This work aims to study extensively the ground state structure and decay properties of proposed [Formula: see text] isotopes. We employed Macroscopic–microscopic scheme based on the Skyrme energy density functional, the Woods–Saxon single-particle potential and Strutinsky’s method to find the structure properties, in a multidimensional deformation space. The same nucleon–nucleon potential is used to find the [Formula: see text]-decay half-life, within the Preformed Cluster Model. For 45 [Formula: see text]120 isotopes, the total energy surfaces, ground state masses, binding energy, deformations and fissionability are determined. The [Formula: see text]-values of the different competing decays and [Formula: see text]-decay half-lives are investigated based on the obtained structure. The results indicate the [Formula: see text]120 isotopes to be the most bound among the studied isotopes. The smallest fission barriers are indicated for the [Formula: see text]120 isotopes. The [Formula: see text]120 isotopes showed the longer half-lives against [Formula: see text]-decay, with an order of [Formula: see text]. The longest half-lives are estimated for the [Formula: see text]120 ([Formula: see text] and [Formula: see text]120 ([Formula: see text] isotopes. The longest full decay chain ending with the stable [Formula: see text]Pb nucleus is anticipated for the [Formula: see text]120 isotope. The shortest decay chain of [Formula: see text]120 terminates after three [Formula: see text]-decays by the spontaneous fission of [Formula: see text]Fl.

H6 states studied in the H2(He8,He4) reaction and evidence of an extremely correlated character of the H5 ground state

The extremely neutron-rich system $^{6}$H was studied in the direct $^2\text{H}(^8\text{He},{^4\text{He}})^{6}$H transfer reaction with a $26 A$ MeV secondary $^{8}$He beam. The measured missing mass spectrum shows a broad bump at $\sim 4-8$ MeV above the $^3$H+$3n$ decay threshold. This bump can be interpreted as a broad resonant state in $^{6}$H at $6.8(5)$ MeV. The population cross section of such a presumably $p$-wave state (or may be few overlapping states) in the energy range from 4 to 8 MeV is $d\sigma/d\Omega_{\text{c.m.}} \simeq 190^{+40}_{-80}$ $\mu$b/sr in the angular range $5^{\circ}<\theta_{\text{c.m.}}<16^{\circ}$. The obtained missing mass spectrum is practically free of the $^{6}$H events below 3.5 MeV ($d\sigma/d\Omega_{\text{c.m.}} \lesssim 5$ $\mu$b/sr in the same angular range). The steep rise of the $^{6}$H missing mass spectrum at $\sim 3$ MeV allows to derive the lower limit for the possible resonant-state energy in $^{6}$H to be $4.5(3)$ MeV. According to the paring energy estimates, such a $4.5(3)$ MeV resonance is a realistic candidate for the $^{6}$H ground state (g.s.). The obtained results confirm that the decay mechanism of the $^{7}$H g.s.\ (located at 2.2 MeV above the $^{3}$H+$4n$ threshold) is the "true" (or simultaneous) $4n$ emission. The resonance energy profiles and the momentum distributions of fragments of the sequential $^{6}$H$ \,\rightarrow \, ^5$H(g.s.)+$n\, \rightarrow \, ^3$H+$3n$ decay were analyzed by the theoretically-updated direct four-body-decay and sequential-emission mechanisms. The measured momentum distributions of the $^{3}$H fragments in the $^{6}$H rest frame indicate very strong "dineutron-type" correlations in the $^{5}$H ground state decay.

Cluster decay half-lives of Ba112–122 isotopes from the ground state and intrinsic excited state using the relativistic mean-field formalism within the preformed-cluster-decay model

Background: The cluster radioactivity from the neutron-deficient trans-tin region of the nuclear landscape has given immediate attention in the nuclear structure studies. Recent prediction of the emitting clusters from the ground and intrinsic excited states of proton-rich Ba isotopes opens the direction to explore the corresponding decay characteristics. A theoretical probe is necessary for understanding the cluster decays of Ba isotopes.Purpose: In the present study, cluster-decay half-lives are calculated and their decay characteristics are investigated for even-even $^{112--122}\mathrm{Ba}$ isotopes in both ground and intrinsic excited states along the proton drip line.Method: The preformed-cluster-decay model (PCM) is employed for estimating the decay half-lives. The preformation probability $({P}_{0})$ of the cluster decay from the parent nuclei is calculated by using the well-known phenomenological formula of Blendowske and Walliser [Phys. Rev. Lett. 61, 1930 (1988)], supplemented with the newly proposed $Q$-value-based preformation factor for the cluster with mass ${A}_{c}&gt;28$. The penetration probability is calculated from the interaction potential using the Wentzel-Kramers-Brillouin (WKB) approximation. The nucleon-nucleon ($NN$) potential and individual binding energy (BE) of the cluster and daughter nuclei are estimated from the microscopic relativistic mean-field formalism (RMF) and compared with those from experiments and the finite-range-droplet model for the estimation of the $Q$ values of the cluster decays. The nonlinear RMF Lagrangian from which the effective relativistic R3Y $NN$ potential is derived using the $\mathrm{NL}{3}^{*}$ parameter set is employed for the calculation of the nuclear matter densities. The R3Y and well-known M3Y potential are employed to obtain the cluster-daughter interaction potential using the double-folding procedure along with their corresponding RMF densities. The total potential along with their respective cluster decay $Q$ values are used as input in the PCM to obtain the half-lives (${T}_{1/2}$) of $^{112--122}\mathrm{Ba}$ isotopes in their ground and intrinsic excited states.Results: The calculated half-lives (${T}_{1/2}$) for relativistic R3Y $NN$ potential and $Q$ values are found to deviate slightly compared to the ones from the M3Y due to the difference in their barrier characteristics. We notice that at elongated neck configuration a minimum neck-length parameter $\mathrm{\ensuremath{\Delta}}R=1.0\phantom{\rule{4.pt}{0ex}}\text{fm}$ is required for R3Y potential due to its repulsive nature, whereas the value is $0.5\phantom{\rule{4.pt}{0ex}}\text{fm}$ is suitable for the M3Y case. However, the estimated decay half-lives for both the potentials are in reasonably good agreement with the experimental lower limit of $^{114}\mathrm{Ba}$. In contrast with the ground-state decays, the inclusion of intrinsic excitation reduces the corresponding half-life values considerably but does not rule out the role of magicity.Conclusions: The sensitivity of the decay half-lives to $Q$ values and neck-length parameter has also been demonstrated. The decay half-lives are predicted for various cluster decays from neutron-deficient Ba isotopes. Since none of the experimental half-lives for the examined clusters is precisely known yet, further studies with available observed half-lives will be needed to substantiate our findings.

Proton decay spectroscopy of S28 and Cl30

States in S28 and Cl30 have been studied using one- and two-proton decay spectroscopies. In the first spectrometer setting, states in S28 were populated following one-neutron knockout from a fast S29 beam. Three new states are observed in S28 from one- and two-proton decays. For the two-proton case the nature of the decay was investigated and found to proceed via sequential two-proton emission. For the second setting, states in Cl30 were populated via one-proton knockout from a fast Ar31 beam. The decay energy of the ground and first excited state were measured with the ground-state decay energy found to be in disagreement with a previous measurement. The spin and parity of these two Cl30 states were inferred from shell-model calculations.Received 2 February 2022Accepted 5 April 2022DOI:https://doi.org/10.1103/PhysRevC.105.044321©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasNuclear spin & parityProton emissionUnstable nuclei induced nuclear reactionsProperties20 ≤ A ≤ 38Nuclear Physics

Цөмийн үндсэн ба өндөр өдөөгдсөн төлөвийн альфа задрал

The alpha decay of ground and high excited states is considered from the view-point of statistical model as two independent processes: perforation of alpha particle on the nucleus and penetration of the alpha panicle through centrifugal and Coulomb barriers. The reformation and penetration factors are calculated for the alpha decay of the ground and high excited states. The alpha decay of the ground and high excited states of Nd-144 nucleus was analyzed using the cluster model and performed alpha particle model. It was showed that the results obtained by these models are different.

Determination of the 161Tb half-life

There is significant interest in the use of terbium radioisotopes for applications in cancer therapy and diagnosis. Of these, 161Tb, as a medium energy beta-emitter, is being investigated as a potential alternative to 177Lu. The relatively high proportion of conversion electron and Auger electron emissions per decay make 161Tb an attractive targeted therapeutic. As a product of nuclear fission, 161Tb is also of importance to nuclear forensics. The standard uncertainty of the current evaluated half-life of 6.89(2) d contributes significantly to the standard uncertainty of any decay corrected activity determination made. Furthermore, the accuracy of this evaluated half-life has been called into question by measurements reported in 2020 at the Institute of Radiation Physics (IRA), Switzerland, who reported a half-life of 6.953(2) d. In the current work, the half-life of the 161Tb ground state decay has been measured at three independent laboratories located in the United Kingdom and the United States of America for a total of six determinations using three independent measurement techniques; gamma-ray spectrometry, ionisation chamber measurement and liquid scintillation counting. The half-life determined for 161Tb of 6.9637(29) d confirms the observed 1% relative increase observed by IRA, though the reported half-lives in this work and at IRA are significantly different (ζ-score = 3.1).

Exploring the ground state bulk and decay properties of the nuclei in superheavy island

The α-decay half-lives of 204 superheavy nuclei covering the range 114≤Z≤126 have been investigated using the relativistic mean-field model (RMF) for NL3⁎ parameter set. The ground state bulk properties such as binding energy, quadrupole deformation parameter (β2), and root-mean-square charge radii for these nuclei are analyzed. Four different semi-empirical formulae, namely, the universal decay law (UDL), the Viola-Seaborg (VSS) formula, the modified universal decay law (MUDL), and the modified Brown formula (MBrown), are used to obtain the α-decay half-lives for the considered nuclei. To examine the applicability of relativistic mean-field model within NL3⁎ parametrization, the α-decay energies, and the half-lives of a few known superheavy nuclei within the range 102 ≤ Z ≤ 118 are calculated and the results are compared with the experimental data along with the theoretical predictions. The α-decay energies (Q-values) are estimated from the binding energies of the parent, and daughter from the RMF (NL3⁎) parameter set. The calculated results are compared with macroscopic-microscopic Finite-Range-Droplet-Model (FRDM), Global Nuclear Mass Model (WS3, WS4), Weizsacker-Skyrme mass model (WS⁎) predictions, and the experimental data, wherever available. The possible standard deviations are also estimated for experimental and various theoretical predictions. We find a good consistency for the experimental-to-UDL, FRDM-to-UDL, and WS4-to-UDL estimates of the decay energy and corresponding half-life. The present analysis provides the theoretical predictions within the microscopic model for the upcoming experiments on the superheavy region.

Nuclear Data Sheets for A=48

Experimental nuclear structure data from various reactions and decays are compiled and evaluated for all known nuclides with mass number A=48 (S, Cl, Ar, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni). For each nuclide, detailed evaluated nuclear structure information is presented for each individual reaction and decay, and the best values combining all available data are recommended for spectroscopic properties, such as level energies, half-lives, γ-ray energies and intensities, decay radiations. No excited states have been identified in 48S, 48Cl, 48Co and 48Ni, among which the first three even have no measured ground-state half-lives and decay modes. For 48Fe, a level scheme with a sequence of excited states was established for the first time from a recent one-neutron removal measurement by 2021Ya33. Data for excited states in 48Ar, 48K and 48Mn remain limited; no decay scheme has been measured for 48Ar and 48K yet, while the decay scheme for 48Ni is incomplete due to unobserved levels. 48Ti is the most studied nuclide through various reactions and decays, followed by 48V, 40Ca, 48Sc, and 48Cr, among which no decay event to 48Sc has been observed and the decay schemes for 48V and 48Cr are considered as incomplete. This work supersedes the previous full evaluations of A=48: 2006Bu08, 1993Bu04, 1985Al14, 1978Be01.

First Observation of the Four-Proton Unbound Nucleus Mg18

Mg18 was observed, for the first time, by the invariant-mass reconstruction of O14+4p events. The ground-state decay energy and width are ET=4.865(34) MeV and Γ=115(100) keV, respectively. The observed momentum correlations between the five particles are consistent with two sequential steps of prompt 2p decay passing through the ground state of Ne16. The invariant-mass spectrum also provides evidence for an excited state at an excitation energy of 1.84(14) MeV, which is likely the first excited 2+ state. As this energy exceeds that for the 2+ state in Mg20, this observation provides an argument for the demise of the N=8 shell closure in nuclei far from stability. However, in open systems this classical argument for shell strength is compromised by Thomas-Ehrman shifts.Received 30 August 2021Revised 18 October 2021Accepted 16 November 2021DOI:https://doi.org/10.1103/PhysRevLett.127.262502© 2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasLifetimes & widthsNuclear structure & decaysProton emissionRare & new isotopesProperties6 ≤ A ≤ 19TechniquesRadioactive beamsNuclear Physics

Production and measurement of fission product noble gases

Gaseous fission products have been produced via thermal neutron irradiation of a highly-enriched uranium target and extracted using a custom gas processing system for measurement on a prototype, high-resolution β − γ coincidence detection system. The gas was extracted and measured in two stages in order to measure the prompt and β−–delayed fission products. This paper presents an overview of the system used to produce gaseous fission products, and the results of the advanced coincidence spectrometry techniques used to identify and quantify decays from the radionuclides produced, including the noble gases 85Kr, 85mKr, 88Kr, 133Xe, 135Xe, 133mXe and 135mXe, as well as 133I and 88Rb. The measurements were validated by determination of the nuclear decay half-lives, specifically for the ground state decay of 135Xe, which was found to be 9.15(49) hours and consistent with the literature value. This work demonstrates the UK capability to produce gaseous radionuclides for quality assurance and calibration purposes in Radionuclide Laboratories supporting the Comprehensive Nuclear-Test-Ban Treaty (CTBT).