Triple Coincidence Data Research Articles

Radiative Width of the Hoyle State from γ-Ray Spectroscopy.

The cascading 3.21 and 4.44MeV electric quadrupole transitions have been observed from the Hoyle state at 7.65MeV excitation energy in ^{12}C, excited by the ^{12}C(p,p^{'}) reaction at 10.7MeV proton energy. From the proton-γ-γ triple coincidence data, a value of Γ_{rad}/Γ=6.2(6)×10^{-4} was obtained for the radiative branching ratio. Using our results, together with Γ_{π}^{E0}/Γ from Eriksen etal. [Phys. Rev. C 102, 024320 (2020)PRVCAN2469-998510.1103/PhysRevC.102.024320] and the currently adopted Γ_{π}(E0) values, the radiative width of the Hoyle state is determined as Γ_{rad}=5.1(6)×10^{-3} eV. This value is about 34% higher than the currently adopted value and will impact models of stellar evolution and nucleosynthesis.

γ-ray spectroscopy of fission fragments produced inPb208(O18,f)

Prompt gamma-ray spectroscopy of fission fragments produced in the heavy-ion induced fusion-fission reaction $^{208}\mathrm{Pb}(^{18}\mathrm{O},f)$ at $E=90$ MeV has been performed. The relative isotopic yields of the fission fragments and the fragment mass distribution have been studied. Structures in the mass distribution have been discussed in the light of earlier results. Relative yields of several odd-$A$ isotopes of Mo, Ru, Pd, and Cd and the odd-$A$ isotones with $N=62$ and 64 have been studied along with the yields of the neighboring even-$Z$, even-$N$ fragments and correlated to nuclear structural effects. The average total neutron multiplicity during fission has been measured to be $5.48\ifmmode\pm\else\textpm\fi{}0.59$. The level schemes of the two neutron-rich nuclei $^{110}\mathrm{Pd}$ and $^{116}\mathrm{Cd}$ have been studied from $\ensuremath{\gamma}$-ray triple coincidence data. A large number of transitions, previously reported only from $\ensuremath{\beta}$-decay studies, have been observed in $^{110}\mathrm{Pd}$ for the first time. The yrast band in $^{116}\mathrm{Cd}$ has been extended up to spin $({16}^{+})$. In addition, a rotational sequence built upon an excited ${5}^{\ensuremath{-}}$ state in $^{116}\mathrm{Cd}$ has been observed up to $({13}^{\ensuremath{-}})$. The level schemes have been discussed in the context of existing results, both experimental and theoretical, in the literature.

The path to the enhanced and advanced LIGO gravitational-wave detectors

We report on the status of the Laser Interferometric Gravitational-Wave Observatory (LIGO) and the plans and progress toward Enhanced and Advanced LIGO. The initial LIGO detectors have finished a two-year long data run during which a full year of triple-coincidence data was collected at design sensitivity. Much of this run was also coincident with the data runs of interferometers in Europe, GEO600 and Virgo. The joint analysis of data from this international network of detectors is ongoing. No gravitational wave signals have been detected in analyses completed to date. Currently two of the LIGO detectors are being upgraded to increase their sensitivity in a program called Enhanced LIGO. The Enhanced LIGO detectors will start another roughly one-year long data run with increased sensitivity in 2009. In parallel, construction of Advanced LIGO, a major upgrade to LIGO, has begun. Installation and commissioning of Advanced LIGO hardware at the LIGO sites will commence at the end of the Enhanced LIGO data run in 2011. When fully commissioned, the Advanced LIGO detectors will be ten times as sensitive as the initial LIGO detectors. Advanced LIGO is expected to make several gravitational-wave detections per year.

Status of the LIGO detectors

All three LIGO gravitational wave detectors have reached their design sensitivities. A sky-averaged detection range (SNR > 8) of more than 15 Mpc for gravitational waves emitted from inspiral binary neutron stars with masses of 1.4 M⊙ has been achieved with the two 4 km instruments. The fifth LIGO science run started in November 2005 and ended in September 2007. A full year of triple coincidence data has been acquired. The duty cycle of a single instrument was between 66% and 79%. Results from previous science runs are presented.

Resolution of complex γ spectra from triple-coincidence data: Ba–Mo split in 252Cf spontaneous fission

Using triple-coincidence events of prompt fission γ rays from spontaneous fission of 252Cf, we made a new analysis of the yield matrix of coincident pairs of barium ( Z=56) and molybdenum ( Z=42) fission fragments. Branching from γ-bands ( K=2) and octupole-bands ( K=0) were also measured. From this reanalysis the previously proposed “extra-hot-fission mode” (8–10 neutrons evaporated) is much weaker than first reported. In this paper, we discuss in detail the methodology, including background subtraction for triple-coincidence data. The importance of minimal compression spectra allowing least-squares peak-fitting analysis is emphasized.

Kinematically complete final state investigations of molecular photodissociation: two- and three-body decay of laser-prepared H33 s 2 A1'

We have performed kinematically complete investigations of molecular photodissociation of triatomic hydrogen in a fast beam translational spectrometer recently built in Freiburg. The apparatus allows us to investigate laser-induced dissociation of neutral molecules into two, three, or more neutral products. The fragments are detected in coincidence and their vectorial momenta in the center-of-mass frame are determined. We demonstrate the potential of the method at the fragmentation of the 3 s 2 A 1 ′ ( N = 1, K = 0) state of triatomic hydrogen. In this state, three-body decay into ground state hydrogen atoms H+H+H, two-body predissociation into H+H 2 (v , J), and photoemission to the H 3 ground state surface with subsequent two-body decay are competing channels. In the case of two-body predissociation, we determine the rovibrational population in the H 2 (v , J) fragment. The vibrational distribution of H 2 is compared with approximate theoretical predictions. For three-body decay, we measure the six-fold differential photodissociation cross-section. To determine accurate final state distributions, the geometric collection efficiency of the apparatus is calculated by a Monte Carlo simulation, and the raw data are corrected for apparatus efficiency. The final state momentum distribution shows pronounced correlation patterns which are characteristic for the dissociation mechanism. For a three-body decay process with a discrete kinetic energy release we have developed a novel data reduction procedure based on the detection of two fragments. The final state distribution determined by this independent method agrees extremely well with that observed in the triple-coincidence data. In addition, this method allows us to fully explore the phase space of the final state and to determine the branching ratios between the two- and three-body decay processes.

Recent advances and techniques in synchrotron radiation based molecular physics

The application of synchrotron radiation to problems in molecular physics has proved highly successful, producing wide-ranging scientific data and spawning developments in experimental techniques and apparatus. As a particular example, studies of soft X-ray (0.1–1 keV) interaction with molecules are essentially not possible without access to synchrotron radiation. In this paper, we present experimental details and recent results of work carried out at the UK’s national synchrotron radiation facility, the SRS at Daresbury Laboratory. Data are shown for threshold electron spectra for SO 2 in the S 2p and O 1s core ionisation regions and triple coincidence data for ion pairs associated with threshold electron production. Recent data for Auger electron–ion–ion coincidence experiments with CO 2 are also presented, showing a strong link between Auger electron energy and final fragmentation pattern.

Pion absorption mechanism for very light nuclei.

Double- and triple-coincidence data for pion absorption on [sup 3]He and [sup 4]He are analyzed using a multistep reaction model with Monte Carlo calculations. The cross sections far from the two-nucleon absorption region could be reproduced very well using only well-known reaction mechanisms and nuclear data. Clear evidence for the two-step process is also shown.

Dynamic moment of inertia of the 192Hg superdeformed band at high rotational frequencies

The superdeformed band in 192Hg has been extended to higher transition energies from a new analysis of a large set of double and triple coincidence data. Contrary to the results of cranked shell model calculations including monopole pairing, the dynamic moment of inertia I (2) is found to continue to increase with rotational frequency.

Electroproduction of pions on the nucleon (I)

Electroproduction of pions on the nucleon is investigated with the dynamical model of Nozawa, Blankleider and Lee. The predicted cross sections are in good agreement with the inclusive p(e, e') data, and reproduce to a large extent the p(e, e'π) triple-coincidence data. Dependences of the p( e, e' π 0) cross sections on the E2 and C2 transition form factors of the γN↔ Δ excitation are presented. The model-dependence of our predictions is briefly examined by also considering the Gross-Riska approach to parameterize the electromagnetic vertices of the Born (non-resonant) term.

New pion-absorption modes observed from triple coincidences in 4He.

The first triple-coincidence data resulting from pion absorption in $^{4}\mathrm{He}$ are reported. The existence of a three-nucleon absorption component in the four-nucleon channel is established. A four-nucleon phase-space-like contribution and nucleon-nucleon final-state interactions are also identified.

Gamma spectroscopy ofFe52,Mn52, andCr52fromα+Cr50reactions

The $^{50}\mathrm{Cr}(\ensuremath{\alpha}, 2n\ensuremath{\gamma})^{52}\mathrm{Fe}$ reaction has been used at incident energies of 23.5 and 27.2 MeV to search for states in $^{52}\mathrm{Fe}$. Triple coincidence data were obtained. The first ${2}^{+}$ and ${4}^{+}$ states were located at 848.3 \ifmmode\pm\else\textpm\fi{} 0.9 and 2383.3 \ifmmode\pm\else\textpm\fi{} 1.3 keV, respectively. No $\ensuremath{\gamma}$ rays from higher spin $^{52}\mathrm{Fe}$ states were detected. A number of $\ensuremath{\gamma}$ rays associated with states populated in the ($\ensuremath{\alpha}, \mathrm{pp}\ensuremath{\gamma}$) and ($\ensuremath{\alpha}, \mathrm{np}\ensuremath{\gamma}$) reactions were observed. Two previously unreported states were located at 6452.1 \ifmmode\pm\else\textpm\fi{} 0.7 and 4163.7 \ifmmode\pm\else\textpm\fi{} 0.5 keV in $^{52}\mathrm{Cr}$ and $^{52}\mathrm{Mn}$, respectively. The relative yields of many $\ensuremath{\gamma}$ rays were consistent with compound nucleus evaporation calculations.NUCLEAR REACTIONS $^{50}\mathrm{Cr}(\ensuremath{\alpha}, X\ensuremath{\gamma})$, $E=23.5 \mathrm{and} 27.2$ MeV measured ${\ensuremath{\sigma}}_{\mathrm{rel}}(90\ifmmode^\circ\else\textdegree\fi{}, {E}_{\ensuremath{\gamma}})$ in ($\ensuremath{\gamma}, \ensuremath{\gamma}$) and ($n, n, \ensuremath{\gamma}$) coincidences, $^{52}\mathrm{Cr}$, $^{52}\mathrm{Mn}$, and $^{52}\mathrm{Fe}$ deduced levels, $J$, $\ensuremath{\pi}$. Enriched target.