Engineering topics

Copp, P.

Publications and source records attributed to Copp, P..

15 records

DOE OSTI2024

Nuclear structure of 157 Sm via 𝛽−decay of 157 Pm

Excited states of the neutron-rich nucleus 157 Sm were populated through the 𝛽−decay of 157 Pm , which has a tentatively assigned ground-state spin and parity of 𝐽 𝜋 =(5/2 − ). Over 30 levels have been observed, 16 of which are new, and over 45 new 𝛾-ray transitions have been placed in the level scheme. An evolution in the ground-state configurations for 𝑁 = 95 nuclei from 5/2 − ⁢[523] (Er/Yb), to 5/2 + ⁢[642] (Dy), to 3/2 − ⁢[521] (Sm/Gd) can be explained based on increasing deformation from 𝑍 = 70 to 𝑍 = 62 and the fact that these three orbitals are energetically close to each other at deformations near 𝛽 2 ≈ 0.25–0.3. Finally, tentative spin and parity assignments are made for most of the states below 1500 keV based on the decay properties of the levels and using excitation-energy systematics of the various orbitals observed in 𝑁 = 95 nuclei.

beta decay↗

DOE OSTI2024

Nuclear structure of 157 Sm via β – decay of 157 Pm

Excited states of the neutron-rich nucleus 157 Sm were populated through the β – decay of 157 Pm, which has a tentatively assigned ground-state spin and parity of J π = (5/2 – ). Over 30 levels have been observed, 16 of which are new, and over 45 new γ-ray transitions have been placed in the level scheme. An evolution in the ground-state configurations for N = 95 nuclei from 5/2 – [523] (Er/Yb), to 5/2 + [642] (Dy), to 3/2 – [521] (Sm/Gd) can be explained based on increasing deformation from Z = 70 to Z = 62 and the fact that these three orbitals are energetically close to each other at deformations near β 2 ≈ 0.25 – 0.3. Tentative spin and parity assignments are made for most of the states below 1500 keV based on the decay properties of the levels and using excitation-energy systematics of the various orbitals observed in N = 95 nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2024

Precise measurements of the γ -ray intensities following the β decay of Ce 144 and Nd 147

For many fission products, the γ rays emitted following β decay provide an easily detectable signature that can be used to identify their quantities and distributions in a sample. As a result, γ-ray spectroscopy is often exploited to study fission-product yields, provided sufficiently accurate information on the γ-ray intensities is available. Further, in many cases, the uncertainties in the existing nuclear data are large enough that they compromise the precision achievable for modern experiments and applications. In this paper, we present high-precision results for the absolute γ-ray emission intensities for the most intense transitions in the β decays of 144 Ce and 147 Nd. We measured these intensities to ≲1% accuracy by producing radiopure samples with fission-product beams at CARIBU and detecting the emitted radiation with a 4⁢πβ counter and a meticulously efficiency-calibrated high purity germanium detector at Texas A&M University.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2024

Investigation of the $\gamma $-ray Properties of the $2^+$ States in $^{14}$C

The properties of the 2$^+_1$ and 2$^+_2$ excited states in 14 C were studied in an experiment conducted at Argonne National Laboratory. A 9 Be( 6 Li,pγ) fusion-evaporation reaction and the GRETINA-ORRUBA setup were employed to populate states of 14 C and detect γ-particle coincidence events. Finally, the precise determination of the 2$^+_1$ level energy, complemented by the estimation of the γ-ray branch of the 2$^+_2$ near-threshold state, will serve as a benchmark to test the Shell Model Embedded in the Continuum calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2024

The LSU-Argonne conversion electron spectrometer: A new detector for the X-Array and SATURN decay station

In this study, a new conversion electron detector has been commissioned at the ATLAS/ CARIBU facility at Argonne National Laboratory. The LSU-Argonne Conversion Electron Spectrometer (LACES) is a LN 2 -cooled Si(Li) detector system designed to be incorporated into a decay station that comprises the dedicated HPGe clover array with a box geometry (X -Array) and the Scintillator and Tape Using Radioactive Nuclei (SATURN) device. This integration enables simultaneous measurements of conversion electrons and gamma-rays in decay experiments, yielding novel information on transition multipolarities, electric monopole transitions, and isomeric states that decay mostly via conversion electrons. A measurement of the energy resolution of LACES yielded 2.3-keV FWHM at 975 keV for electrons and 1.3-keV FWHM at 75 keV for X-rays. A detailed study of the absolute detection efficiency (at 5 mm from the source) was performed, where this quantity was determined experimentally in the range of electron transition energies between 25.5 keV and 1047.8 keV and subsequently simulated using the GEANT4 code. Measurement and simulations are found to be in excellent agreement. A precise characterization, for this type of detector system, of the absolute detection efficiency for such a wide energy range is reported for the first time.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2024

Structure of the high-spin, 𝛽-decaying state in the neutron-rich nucleus 146 La

Excited structures in 146 Ce were populated in 𝛽 decay of the high-spin state in the neutron-rich nucleus 146 La. The beam was produced by the Californium Rare Isotope Breeder Upgrade (CARIBU) facility at Argonne National Laboratory, reaccelerated by the ATLAS accelerator, and implanted on a moving-tape system in the middle of the GAMMASPHERE array. The decay scheme of the high-spin, 𝛽-decaying state in 146 La was revised with respect to previous studies and evaluated nuclear data. Here, the structure of 146 La is discussed in the framework of the deformed Nilsson model and systematics of known quasiparticle structures in the region.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2024

Structure of the high-spin, β-decaying state in the neutron-rich nucleus 146 La

Excited structures in 146 Ce were populated in β decay of the high-spin state in the neutronrich nucleus 146 La. The beam was produced by the Californium Rare Isotope Breeder Upgrade (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. The decay scheme of the high-spin, β-decaying state in 146 La was revised with respect to previous studies and evaluated nuclear data. The structure of 146 La is discussed in the framework of the deformed Nilsson model and systematics of known quasiparticle structures in the region.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2022

Decay spectroscopy of the blocked fission product 130 $\mathrm{I}$

We report numerous applications rely on the identification and quantification of fission products with the activation technique, where γ-rays emitted in the decay are used to estimate the initial activity of the radionuclide of interest. 130 I is a so-called blocked fission product, which can be produced only directly through fission, a property that makes it particularly attractive for nuclear forensics. A source of 130 I was produced using a (p,n) reaction on enriched 130 Te at the Brookhaven Tandem Van de Graaff and its decay was studied with Gammasphere at Argonne National Laboratory. Two new levels were identified, and over 25 transitions were added, removed or re-placed in the level scheme, with intensity measurements made down to I γ = 0.00066 per 100 decays. The uncertainty on the intensities of the strongest transitions, those that are commonly used to quantify the activity of the radionuclide, was improved by a factor of 2 compared to the previous best assessment and discrepancies in the literature values were resolved. A detailed angular correlation analysis further permitted the determination of a number of spin assignments for excited levels and mixing ratios for γ-ray transitions

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2022

Discovery of the new isotope 251 Lr and the α-decay fine structure in 253 L

The products of the 203, 205 Tl ( 50 Ti, 2n) fusion-evaporation reactions were studied using the recently commissioned Argonne Gas-Filled Analyzer at Argonne National Laboratory. Two α-decay activities with energies of 9210(19) and 9246(19) keV and half-lives of $42^{+42}_{-14}$ and $24.4^{+7.0}_{-4.5}$ ms were observed which were followed by the known α decays of 247 Md and 243 Es . They are interpreted as originating from the 1/2 ⁻ [521] and 7/2 ⁻ [514] single-proton Nilsson states in the hitherto unknown isotope 251 Lr . From the measured Q α values the 1/2 ⁻ level was placed 117(27) keV above the 7/2 - level in 251 Lr in contrast to 255 Lr where the 1/2 ⁻ level is the lowest. Also, the α decay of 253 Lr was studied in more detail and a new α line at 8660(20) keV was found and a new half-life value of 2.46(32) s for an isomeric state in 253 Lr was measured. The 251, 253, 255 Lr Q α values were compared with predictions of various mass models. The relative energies of the 1/2 ⁻ [521] and 7/2 ⁻ [514] single-proton Nilsson states in 251, 253, 255 Lr isotopes were compared with results of the cranking shell model with pairing treated using the particle-number-conserving method. The level separation and, in particular, the level order change between 251 Lr and 255 Lr was reproduced only when the hexacontetrapole deformation ϵ 6 was included in the calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2022

Identification of excited states in Bi 188 and Po 188

The neutron-deficient 188 Bi and 188 Po isotopes have been studied by γ-ray spectroscopy using the recoil-decay tagging technique with the Argonne Gas-Filled Analyzer. A new 0.25(5)-μs isomeric state and a prompt cascade formed by 319-, 366-, and 462-keV γ rays have been established on top of the (10¯) α -decaying isomer in 188 Bi. The first excited (2 + ) state in 188 Po was identified, its excitation energy of 242(2) keV continues the nearly constant trend for the first 2 + states in 190, 192,194 Po. Here, the state is most likely a member of a prolate rotational band built on the ground state, albeit mixing with other coexisting configurations cannot be excluded. The new results obtained in the present work provide new information to shape coexistence in bismuth and polonium isotopes near the neutron midshell at N = 104 . In this mass region, a reduction in the prompt γ-ray yield obtained with recoil decay tagging was observed for a few nuclides, and the possible reasons are presented.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2022

First observation of a shape isomer and a low-lying strongly-coupled prolate band in neutron-deficient semi-magic 187 Pb

Prompt and delayed gamma-ray spectroscopy of the neutron-deficient, semi-magic isotope 187Pb has been performed using the recoil-decay and isomer-decay tagging techniques at the Argonne Gas-Filled Analyzer. A new 5.15(15)-mu s isomeric state at only 308 keV above the spherical 3/2 - ground state is identified and classified as a shape isomer. A strongly-coupled band is observed on top of the isomer, which is nearly identical to the one built on the prolate 7/2 - [514] Nilsson state in the isotone 185 Hg. Based on this similarity and on the result of the potential-energy surface calculations, the new isomer in 187 Pb is proposed to originate from the same configuration. The retarded character of the 308-keV (7/2( - )→ 3/2$_{gs}^{-}$ transition with a deduced B(E2) = 5.6(2) x 10 -4 W.u. can be well explained by the significant difference between the prolate parent and spherical daughter configurations, leading to the shape isomerism. The excitation energy of the isomer is surprisingly low, being roughly half of the excitation energies of the known 0 + intruder bandheads in the neighboring 186,188 Pb isotopes. The combined results of the present work and the previous alpha-decay and laser spectroscopy studies present evidence for triple shape coexistence at low energy in the negative-parity configurations of 187 Pb, which is well reproduced by the potential-energy surface calculations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2021

New approach to precisely measure γ-ray intensities for long-lived fission products, with results for the decay of 95 Zr

For many fission products, the rays emitted following decay provide an easily-detectable signature that can be used to identify their quantities and distributions in a sample. As a result, γ-ray spectroscopy is often exploited to study fission-product yields, provided sufficiently accurate information on the γ-ray intensity is available. However, in many cases, the uncertainties in the existing nuclear data are large enough that they compromise the precision achievable for modern experiments and applications. To address this need, we have developed a new experimental method that is well suited to precisely measure absolute γ-ray intensities in the β decay of long-lived fission products. The approach involves the production of a radiopure sample by implantation of a mass-separated ion beam from the CAlifornium Rare Isotope Breeder Upgrade (CARIBU) facility on a thin carbon foil. The emitted β-decay radiation is detected with a 4π gas proportional counter and a meticulously efficiency-calibrated high-purity germanium (HPGe) detector. As a first measurement to demonstrate the approach, we studied the absolute γ-ray intensities of the strongest transitions following the β decay of 95 Zr and its decay-daughter 95 Nb, and determined them to fractional precisions of better than 1–2%. In addition, with a larger sample of activity produced through neutron irradiation of an isotopically-enriched Zr foil, we performed a high-precision measurement of the relative γ-ray intensities following the decay of 95 Zr with just the HPGe detector. Here, the sample-production method at CARIBU and the coincidence detection approach demonstrated here can be applied to study fission products with half-lives longer than a day, which includes isotopes important not only for nuclear-energy and national-security applications, but also for medical-isotope research and environmental monitoring.

4π↗

DOE OSTI2021

Ground-state and decay properties of neutron-rich 106 Nb

The ground-state properties of neutron-rich 106 Nb and its β decay into 106 Mo have been studied using the CARIBU radioactive-ion-beam facility at Argonne National Laboratory. Niobium-106 ions were extracted from a 252 Cf fission source and mass separated before being delivered as low-energy beams to the Canadian Penning Trap, as well as the X-Array and SATURN β-decay-spectroscopy station. The measured 106 Nb ground-state mass excess of –66202.0(13) keV is consistent with a recent measurement but has three times better precision; this work also rules out the existence of a second long-lived, β-decaying state in 106 Nb above 5 keV in excitation energy. The decay half-life of 106 Nb was measured to be 1.097(21) s, which is 8% longer than the adopted value. Here, the level scheme of the decay progeny, 106 Mo, has been expanded up to ≈ 4 MeV. The distribution of decay strength and considerable population of excited states in 106 Mo of J ≥ 3 emphasizes the need to revise the adopted J π = 1 – ground-state spin-parity assignment of 106 Nb; it is more likely to be J ≥ 3.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2020

High- K , two-quasiparticle states in Gd 160

Excited states in Gd 160 were populated via β decay from the low- and high-spin isomers in Eu 160 . The high-spin, K π = 5 - state feeds several two-quasiparticle levels, as well as a sequence associated with a γ vibration and a K π = 4 + , hexadecapole vibrational structure. The decay scheme was significantly improved with the observation of new transitions and states when compared with the two competing level schemes from over four decades ago. Configuration assignments for some of the multiquasiparticle levels have been suggested, based upon decay properties, systematics from neighboring nuclei, and comparisons with theoretical calculations. Finally, in addition, 15 new low-spin states and approximately 60 new transitions were observed resulting from the decay of the low-spin Eu 160 isomer.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2020

Longitudinal Wobbling Motion in Au 187

The rare phenomenon of nuclear wobbling motion has been investigated in the nucleus 187Au. A longitudinal wobbling-bands pair has been identified and clearly distinguished from the associated signature-partner band on the basis of angular distribution measurements. Theoretical calculations in the framework of the particle rotor model are found to agree well with the experimental observations. This is the first experimental evidence for longitudinal wobbling bands where the expected signature partner band has also been identified, and establishes this exotic collective mode as a general phenomenon over the nuclear chart.

150 ≤ A ≤ 189↗