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This is the final progress report resulting from 55 consecutive years of support as a Principle Investigator supported by the Atomic Energy Commission, the Energy Research and Development Administration and the Department of Energy. Included in various accomplishments are publications issued and experiments conducted.
Current fieldable spectroscopy techniques often use single detector systems heavily impacted by interferences from intense background radiation fields. These effects result in low-confidence measurements that can lead to misinterpretation of the collected spectrum. To help improve interpretation of the fission products and short-lived radionuclides produced in a composite sample, a coincidence-database is being developed in support of a robust portable and X-ray coincidence detector system concurrently under development at the Pacific Northwest National Laboratory for in-field deployment. Hitherto, no database exists containing coincident γ–γ and γ–X-ray branching-ratio intensities on an absolute scale that will greatly enhance isotopic identification for in-field applications. As part of this project, software has been developed to parse all radioactive-decay data sets from the Evaluated Nuclear Structure Data File (ENSDF) archive to enable translation into a more useful JavaScript Object Notation (JSON) formats that more readily supports query-based data manipulation. The coincident database described in this work is the first of its kind and contains coincidence γ–γ and γ–X-ray intensities and their corresponding uncertainties, together with auxiliary metadata associated with each decay data set. The new JSON format provides a convenient and portable means of data storage that can be imported into analysis frameworks with relatively low overhead allowing for meaningful comparison with measured data.
The β decay of the neutron-rich 134 In and 135 In was investigated experimentally in order to provide new insights into the nuclear structure of the tin isotopes with magic proton number Z=50 above the N=82 shell. The β-delayed γ-ray spectroscopy measurement was performed at the ISOLDE facility at CERN, where indium isotopes were selectively laser-ionized and on-line mass separated. Three β-decay branches of 134 In were established, two of which were observed for the first time. Population of neutron-unbound states decaying via γ rays was identified in the two daughter nuclei of 134 In, 134 Sn and 133 Sn, at excitation energies exceeding the neutron separation energy by 1 MeV. The β-delayed one- and two-neutron emission branching ratios of 134 In were determined and compared with theoretical calculations. The β-delayed one-neutron decay was observed to be dominant β-decay branch of 134 In even though the Gamow-Teller resonance is located substantially above the two-neutron separation energy of 134 Sn. Transitions following the β decay of 135 In are reported for the first time, including γ rays tentatively attributed to 135 Sn. In total, six new levels were identified in 134 Sn on the basis of the βγγ coincidences observed in the 134 In and 135 Inβ decays. A transition that might be a candidate for deexciting the missing neutron single-particle 13/2 + state in 133 Sn was observed in both β decays and its assignment is discussed. Experimental level schemes of 134 Sn and 135 Sn are compared with shell-model predictions. Using the fast timing technique, half-lives of the 2 + , 4 + , and 6 + levels in 134 Sn were determined. From the lifetime of the 4 + state measured for the first time, an unexpectedly large B(E2;4 + → 2 + ) transition strength was deduced, which is not reproduced by the shell-model calculations.
We propose a theory framework to study the isospin-symmetry breaking correction 𝛿 C in superallowed nuclear 𝛽 decays, crucial for the precise determination of |𝑉 𝑢𝑑 |. Based on a general assumptions of the isovector dominance in isospin-symmetry breaking interactions, we construct a set of functions 𝐹 𝑇 𝑧 which involve nuclear matrix elements of isovector monopole operators and the nuclear Green's function. Via the functions 𝐹 𝑇 𝑧 , a connection of 𝛿 C to measurable electroweak nuclear radii is established, providing an experimental gauge of the theory accuracy of 𝛿 C . Here, we outline a strategy to perform ab initio calculations of 𝐹 𝑇 𝑧 based on the Lanczos algorithm, and discuss its similarity with other nuclear-structure-dependent inputs in nuclear 𝛽 decays.
The CGMF code implements the Hauser-Feshbach statistical nuclear reaction model to follow the de-excitation of fission fragments by successive emissions of prompt neutrons and γ rays. The Monte Carlo technique is used to facilitate the analysis of complex distributions and correlations among the prompt fission observables. Starting from initial configurations for the fission fragments in mass, charge, kinetic energy, excitation energy, spin, and parity, Y(A,Z,KE,U,J,π), CGMF samples neutron and γ-ray probability distributions at each stage of the decay process, conserving energy, spin and parity. Nuclear structure and reaction input data from the RIPL3 library are used to describe fission fragment properties and decay probabilities. Characteristics of prompt fission neutrons, prompt fission γ rays, and independent fission yields can be studied consistently. Correlations in energy, angle and multiplicity among the emitted neutrons and γ rays can be easily analyzed as a function of the emitting fragments. Finally, in its current version, CGMF is limited to certain spontaneous fission reactions on Pu and Cf isotopes, as well as neutron-induced fission reactions up to 20 MeV on U, Np, and Pu isotopes.
Recent studies have completed the A=16 isospin quintets for states with J π =0 + and 2 + . The dependence of their masses as a function of isospin projection shows evidence for deviations from quadratic behavior indicating isospin violation beyond the expectation from two-body forces. The deviation is most pronounced for the 2 + states. Predictions from the shell model embedded in the continuum (SMEC) allow us to explain that this isospin violation is associated with a modification of the nuclear structure due to the open-quantum-system nature of the proton-rich members of the quintet. In particular, the 0 + and 2 + states in 16 Ne and the 2 + state in 16 F are threshold resonances located just above a proton-decay threshold where s-wave coupling to the continuum is expected. The measured deviations of these threshold states from the quadratic behavior of the remaining members of the multiplets makes it possible to obtain information on the magnitude and the energy dependence of the continuum-coupling energy correction. Finally, continuum coupling is also indicated for the ground state of 8 C, but this time through p-wave coupling
Code framework to perform simulations of nuclear reactions with incident particles including gammas, protons, neutrons, deuterons, tritons, helium-3, and alphas to develop nuclear data libraries and study nuclear reaction phenomona. The code can model nuclear reactions or initial populations specified by the user. The decays principally follow the compound-nucleus hypothesis and the statistical decay of Hauser and Feshbach. The code models nuclear decays with a Monte Carlo process that tracks the decay of each state. Data libraries are produced that can be translated into GNDS (generalized Nuclear Data Structure). YAHFC can also be used as an event generator, with individual decays written to disk for offline analysis. Both serial and MPI versions are provided. YAHFC does NOT perform transport of nuclear reactions through materials, only the primary reaction with a target material.
Excited structures in 104 Mo were populated by β decays of the ground and isomeric states in the neutron-rich nucleus 104 Nb. The beams were produced by the CARIBU facility at Argonne National Laboratory, re-accelerated by the ATLAS accelerator and implanted on a moving-tape system in the middle of the GAMMASPHERE array. Separate decay schemes for the two β-decaying states in 104 Nb were constructed for the first time. The structure of the isomers are discussed in the framework of the deformed Nilsson model and systematics of known quasiparticle structures in neighboring nuclei.
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The nuclear gamma-ray lines emitted when Co-57 decays to Fe-57 should be detectable for several years following Galactic supernovae, and the time structure of their intensity relative to those emitted following the Ni-56 and Co-56 decays can reveal the structure of the exploding star. An analysis of a simplified analytic model is presented as an example.
The semi-magic 110-122 Sn isotopes display signs of shape coexistence in their excited 0 + states, which, in contrast to the spherical 0+ ground states, are deformed. Here, this paper investigates the nuclear structure of 114 Sn using the competing β + decay and electron capture of a radioactive beam of 114 Sb produced at the TRIUMF-ISAC facility using the GRIFFIN spectrometer. This study will allow for an in-depth understanding of the excited 0 + states in 114 Sn, by focusing on their decay patterns. In the present experiment, transitions at 856.2-keV and 1405.0-keV, which were observed in an earlier β + decay study but not placed in the 114 Sn level scheme, have been Physics, assigned to the level scheme in connection to the 0$^+_3$ level at 2156.0-keV. Properly assigning these transitions refines the level scheme and enhances our understanding of the nuclear structure in 114 Sn.
Here, the double-beta (2 β )-decay is the rarest nuclear physics process, and its experimental half-lives (T 1/2 ) exceed the age of the Universe from nine to fourteen orders of magnitude. Double-beta decay was observed, and its half-life was measured in 14 parent nuclei using direct, radiochemical, and geochemical methods. The decay observables are analyzed using the Evaluated Nuclear Structure Data File (ENSDF) procedures, and the recommended T 1/2 were deduced. Using the calculated values of phase factors, the effective nuclear matrix elements were extracted and compared with available data. Thousands of theoretical and experimental works have been dedicated to these topics in the last 85 years, and we present two data sets of recommended values to encapsulate the results.
The double-beta (2β)-decay is the rarest nuclear physics process, and its experimental half-lives (T 1/2 ) exceed the age of the Universe from nine to fourteen orders of magnitude. Double-beta decay was observed, and its half-life was measured in 14 parent nuclei using direct, radiochemical, and geochemical methods. The decay observables are analyzed using the Evaluated Nuclear Structure Data File (ENSDF) procedures, and the recommended T 1/2 were deduced. Using the calculated values of phase factors, the effective nuclear matrix elements were extracted and compared with available data. Thousands of theoretical and experimental works have been dedicated to these topics in the last 85 years, and we present two data sets of recommended values to encapsulate the results.
Two-neutrino double-β decay of certain nuclear isotopes is one of the rarest Standard Model processes observed in nature. Its neutrinoless counterpart is an exotic lepton-number nonconserving process that is widely searched to determine if the neutrinos are Majorana fermions. In order to connect the rate of these processes to the Standard Model and beyond the Standard Model interactions, it is essential that the corresponding nuclear matrix elements are constrained reliably from theory. Lattice quantum chromodynamics (LQCD) and low-energy effective field theories (EFTs) are expected to play an essential role in constraining the matrix element of the two-nucleon subprocess, which could in turn provide the input into ab initio nuclear-structure calculations in larger isotopes. Focusing on the two-neutrino process $nn\rightarrow pp(ee\bar{v}_{e}\bar{v}_e)$, the amplitude is constructed in this work in pionless EFT at next-to-leading order, demonstrating the emergence of a renormalization-scale independent amplitude and the absence of any new low-energy constant at this order beyond those present in the single-weak process. Most importantly, it is shown how a LQCD four-point correlation function in Euclidean and finite-volume spacetime can be used to constrain the Minkowski infinite-volume amplitude in the EFT. The same formalism is provided for the related single-weak process, which is an input to the double-β decay formalism. The LQCD-EFT matching procedure outlined for the double-weak amplitude paves the road toward constraining the two-nucleon matrix element entering the neutrinoless double-β decay amplitude with a light Majorana neutrino.
We report an exploratory study of the 𝒪(𝛼) structure-dependent electromagnetic radiative corrections to unique first-forbidden nuclear beta decays. We show that the insertion of angular momentum into the nuclear matrix element by the virtual or real photon exchange opens up the decay at vanishing nuclear recoil momentum which was forbidden at tree level, leading to a dramatic change in the decay spectrum not anticipated in existing studies. We discuss its implications for precision tests on the standard model and searches for new physics.
We report on the masses and hyperfine structure of ground and isomeric states in 114,116,118,120 Ag isotopes, measured with the phase-imaging ion-cyclotron-resonance technique (PI-ICR) with the JYFLTRAP mass spectrometer and the collinear laser spectroscopy beamline at the Ion Guide Isotope Separator On-Line facility, Jyväskylä, Finland. We measured the masses and excitation energies, electromagnetic moments, and charge radii, and firmly established the nuclear spins of the long-lived states. A new isomer was discovered in 118 Ag and the half-lives of 118 Ag long-lived states were reevaluated. We unambiguously pinned down the level ordering of all long-lived states, placing the inversion of the 𝐼 = 0 − and 𝐼 = 4 + states at 𝐴 = 118 (𝑁 = 71). As a result, we compared the electromagnetic moments of each state to empirical single-particle moments to identify the dominant configuration where possible.
We report beta-decay spectroscopy of the 187 Ta ground state was performed at the KEK Isotope Separation System. β-delayed γ rays corresponding to the previously reported in-beam transitions were observed. The β-decay half-life of the 187 Ta ground state was determined to be 283(10) s by analyzing a time spectrum of β-γ coincidence events. The β-decay branching ratio and log(ft) values were evaluated for the first time. Based on the newly evaluated log(ft) values of >6.0 and a decay scheme, spin-parity values of I π = 7/2 + originating from the odd-proton orbit π7/2[404] were assigned with high confidence, which is consistent with the systematics of neighboring odd-A nuclides.
We report the Hauser-Feshbach fission-fragment decay (HF 3 D) model is extended to calculate the prompt fission neutron spectrum (PFNS) for the thermal-neutron-induced fission on 235 U, where the evaporated neutrons from all possible fission-fragment pairs are aggregated. By studying model parameter sensitivities on the calculated PFNS as well as nonstatistical behavior of low-lying discrete level spin distribution, we conclude that discrepancies between the aggregation calculation and the experimental PFNS seen at higher neutron emission energies can be attributed to both the primary fission-fragment yield distribution and the possible high spin states that are not predicted by the statistical theory of nuclear structure.