Search

The vector and tensor analysing powers in deuteron-proton elastic scattering have been measured in the forward hemisphere at deuteron kinetic energies of 1.2 GeV and 2.27 GeV using the ANKE spectrometer at the COSY storage ring. The results are compared with other experimental data and with predictions made within the framework of Glauber multiple scattering theory., Comment: 11 pages with 8 figures. To be submitted for publication

The search for He 4 - η bound states was performed with the WASA-at-COSY facility via the measurement of the excitation function for the d d → He 3 n π 0 and d d → He 3 p π − processes. The deuteron beam momentum was varied continuously between 2.127 GeV/c and 2.422 GeV/c, corresponding to the excess energy for the d d → He 4 η reaction ranging from Q = − 70 MeV to Q = 30 MeV . The luminosity was determined based on the d d → He 3 n reaction and the quasi-free proton–proton scattering via d d → p p n s p e c t a t o r n s p e c t a t o r reactions. The excitation functions, determined independently for the measured reactions, do not reveal a structure which could be interpreted as a narrow mesic nucleus. Therefore, the upper limits of the total cross sections for the bound state production and decay in d d → ( He 4 - η ) b o u n d → He 3 n π 0 and d d → ( He 4 - η ) b o u n d → He 3 p π − processes were determined taking into account the isospin relation between the both of the considered channels. The results of the analysis depend on the assumptions of the N ⁎ (1535) momentum distribution in the anticipated mesic- He 4 . Assuming, as in the previous works, that this is identical with the distribution of nucleons bound with 20 MeV in He 4 , we determined that (for the mesic bound state width in the range from 5 MeV to 50 MeV) the upper limits at 90% confidence level are about 3 nb and about 6 nb for n π 0 and p π − channels, respectively. However, based on the recent theoretical findings of the N ⁎ (1535) momentum distribution in the N ⁎ - He 3 nucleus bound by 3.6 MeV, we find that the WASA-at-COSY detector acceptance decreases and hence the corresponding upper limits are 5 nb and 10 nb for n π 0 and p π − channels respectively.

Various theoretical calculations based on QCD or hadronic interactions predict that in addition to the recently observed dibaryon resonance d⁎(2380) with I(JP)=0(3+) there should also exist a dibaryon resonance with mirrored quantum numbers I(JP)=3(0+). We report here on a search for such a NN-decoupled state in data on the pp→ppπ+π+π−π− reaction. Since no clear-cut evidence has been found, we give upper limits for the production cross section of such a resonance in the mass range 2280–2500 MeV., This work has been supported by DFG (CL 214/3-1), STFC (ST/L00478X/1) and by the Polish National Science Center through grants Nos. DEC-2013/11/N/ST2/04152 and 2011/03/B/ST2/01847

We report on the experimental search for the bound state of an eta meson and He-3 nucleus performed using the WASA-at-COSY detector setup. In order to search for the eta-mesic nucleus decay, the pd ...

Charge symmetry breaking (CSB) observables are a suitable experimental tool to examine effects induced by quark masses on the nuclear level. Previous high precision data from TRIUMF and IUCF are cu ...

The deuteron tensor analysing power t_{20} of the d(pol) p --> 3He eta reaction has been measured at the COSY-ANKE facility in small steps in excess energy Q up to Q = 11 MeV. Despite the square of the production amplitude varying by over a factor of five through this range, t_{20} shows little or no energy dependence. This is evidence that the final state interaction causing the energy variation is not influenced by the spin configuration in the entrance channel. The weak angular dependence observed for t_{20} provides useful insight into the amplitude structure near threshold.

The transverse spin correlations A x , x and A y , y in the n → p → → d π 0 reaction have been measured for the first time in quasi-free kinematics at the COSY-ANKE facility using a polarised deuteron beam incident on a polarised hydrogen cell target. The results obtained for neutron energies close to 353 MeV and 600 MeV are in good agreement with the partial wave analysis of data on the isospin-related p p → d π + reaction, though the present results cover kinematic regions that are largely absent from existing data sets.

The charge-exchange break-up of polarised deuterons d → p → { p p } s n , where the final { p p } s diproton system has a very low excitation energy and hence is mainly in the S 0 1 state, is a powerful tool to probe the spin-flip terms in the proton–neutron charge-exchange scattering. Recent measurements with the ANKE spectrometer at the COSY storage ring at 1.6, 1.8, and 2.27 GeV have extended these studies into the pion-production regime in order to investigate the mechanism for the excitation of the Δ ( 1232 ) isobar in the d → p → { p p } s X reaction. Values of the differential cross section and two deuteron tensor analysing powers, A x x and A y y , have been extracted as functions of the momentum transfer to the diproton or the invariant mass M X of the unobserved system X. The unpolarised cross section in the high M X region is well described in a model that includes only direct excitation of the Δ isobar through undistorted one pion exchange. However, the cross section is grossly underestimated for low M X , even when Δ excitation in the projectile deuteron is included in the calculation. Furthermore, direct Δ production through one pion exchange only reproduces the angular dependence of the difference between the two tensor analysing powers.

The presently world largest data sample for π 0 → γ e + e − decays studies containing nearly 5 × 10 5 events was collected using the WASA detector at COSY. A search for a dark photon U produced in the π 0 → γ U → γ e + e − decay from the p p → p p π 0 reaction was carried out. An upper limit on the square of the U − γ mixing strength parameter ϵ 2 of 5 × 10 − 6 at 90% CL was obtained for the mass range 20 MeV M U 100 MeV . This result together with other recent experimental limits significantly reduces the M U vs. ϵ 2 parameter space which could explain the presently seen deviation between the Standard Model prediction and the direct measurement of the anomalous magnetic moment of the muon.

The PAX Collaboration has successfully performed a spin-filtering experiment with protons at the COSY-ring. The measurement allowed the determination of the spin-dependent polarizing cross section, that compares well with the theoretical prediction from the nucleon-nucleon potential. The test confirms that spin-filtering can be adopted as a method to polarize a stored beam and that the present interpretation of the mechanism in terms of the proton-proton interaction is correct. The outcome of the experiment is of utmost importance in view of the possible application of the method to polarize a beam of stored antiprotons. (C) 2012 Elsevier B.V. All rights reserved.

The differential cross section d σ / d Ω and analysing power A y of the p → p → { p p } s π 0 reaction have been measured at COSY-ANKE at 353 MeV. The final proton pair was detected at very low excitation energy, leading to an S -wave diproton, denoted here as { p p } s . The angular dependence of both d σ / d Ω and A y can be described in terms of s - and d -wave pion production. By using phase information from elastic pp scattering, unique solutions are derived for the corresponding amplitudes only as a result of the combined analysis of both experimental observables. The large d -wave term thus obtained is important for the tests of the current state-of-the-art chiral perturbation theory approach. The amplitudes will also help towards determining the isospin dependence of pion production in nucleon–nucleon collisions with diproton formation.

In order to test chiral perturbation theory and establish links between p-wave pion production in nucleon–nucleon collisions and low energy three-nucleon scattering, an extensive programme of experiments on pion production is currently underway at COSY-ANKE. The final proton pair is measured at very low excitation energy, leading to an S-wave diproton, denoted here as {pp}s. By using a deuterium target we have obtained data on the differential cross section and analysing power of the quasi-free p→n→{pp}sπ− reaction at 353 MeV. The spectator proton psp was either measured directly in silicon tracking telescopes or reconstructed using the momentum of a detected π−. Both observables can be described in terms of s-, p-, and d-wave pion production amplitudes. Taken together with the analogous data on the p→p→{pp}sπ0 reaction, full partial wave decompositions of both processes were carried out.

An exclusive measurement of the decay eta -> pi(+) pi(-) gamma has been performed at the WASA facility at COSY. The eta mesons were produced in the fusion reaction pd -> He-3 X at a proton be ...

COSY has a history of highly successful operation of cooled beams and internal targets both with and without polarization and as such it constitutes a unique facility for hadronic probes on a world-wide scale. Starting from meson production and nucleon-nucleon scattering more and more experience in polarized beam/target manipulation and polarimetry is gained. Extending polarization physics to antiprotons requires pre-studies at COSY to be continued at the antiproton decelerator AD at CERN. As a long-term perspective, the search for electric dipole moments of the proton, deuteron, and 3He in a dedicated storage ring could provide a new method to push the limits in the quest for CP violation searches beyond the Standard Model.

The cross sections for the p p → p p K + K − reaction were measured at three beam energies 2.65, 2.70, and 2.83 GeV at the COSY-ANKE facility. The shape of the K + K − spectrum at low invariant masses largely reflects the importance of K K ¯ final state interactions. It is shown that these data can be understood in terms of an elastic K + K − rescattering plus a contribution coming from the production of a K 0 K ¯ 0 pair followed by a charge-exchange rescattering. Though the data are not yet sufficient to establish the size of the cusp at the K 0 K ¯ 0 threshold, the low mass behaviour suggests that isospin-zero production is dominant.

The p p → { p p } s π 0 differential cross section has been measured with the ANKE spectrometer at COSY-Julich for seven proton beam energies T p between 0.51 and 1.97 GeV. By selecting proton pairs with an excitation energy of less than 3 MeV it is ensured that the final { p p } s system is in the S 0 1 state. In the measured region of θ p p cm ≲ 18 ° , the data reveal a forward dip for T p ⩽ 1.4 GeV whereas a forward peaking is seen at 1.97 GeV. The energy dependence of the forward cross section shows a broad peak in the 0.6–0.8 GeV region, probably associated with Δ ( 1232 ) excitation, and a minimum at 1.4 GeV. Some of these features are similar to those observed for the spin–isospin partner reaction, p p → d π + . However, the ratio of the forward differential cross sections of the two reactions shows a significant suppression of single pion production associated with a spin-singlet final nucleon pair.

The pp ! pK + Y 0 reaction has been studied for hyperon masses m(Y 0 ) � 1540MeV/c 2 at COSY-Julich by using a 3.65GeV/c circulating proton beam incident on an in- ternal hydrogen target. Final states comprising two protons, one positively charged kaon and one negatively charged pion have been identified with the ANKE spectrom- eter. Such configurations are sensitive to the production of the ground stateand � 0 hyperons as well as the � 0 (1385) and �(1405) resonances. Applying invariant- and missing-mass techniques, the two overlapping excited states could be well sep- arated, though with limited statistics. The shape and position of the �(1405) distri- bution, reconstructed cleanly in the � 0 � 0 channel, are similar to those found from other decay modes and there is no obvious mass shift. This finding constitutes a challenging test for models that predict �(1405) to be a two-state resonance.

The observed variation of the total cross section for the dp -> He-3 eta reaction near threshold means that the magnitude of the s-wave amplitude falls very rapidly with the eta centre-of-mass momentum. It is shown here that recent measurements of the momentum dependence of the angular distribution imply a strong variation also in the phase of this amplitude. Such a behaviour is that expected from a quasi-bound or virtual eta He-3 state. The interpretation can be investigated further through measurements of the deuteron or proton analysing powers and/or spin-correlations. (C) 2007 Elsevier B.V. All rights reserved.

Inclusive K + production in proton–proton collisions has been measured at a beam energy of 2.16 GeV using the COSY-ANKE magnetic spectrometer. The resulting spectrum, as well as those corresponding to K + p and K + π + correlated pairs, can all be well described using consistent values of the total cross sections for the p p → K + p Λ , p p → K + p Σ 0 , and p p → K + n Σ + reactions. While the resulting values for Λ and Σ 0 production are in good agreement with world data, our value for the total Σ + production cross section, σ ( p p → K + n Σ + ) = ( 2.5 ± 0.6 stat ± 0.4 syst ) μb at an excess energy of e = 129 MeV , could only be reconciled with other recently published data if there were a highly unusual near threshold behaviour.

The pp → ppπ 0 differential cross section has been measured with the ANKE spectrometer at COSY–Julich for pion cms angles between 0 ◦ and 15.4 ◦ at a proton beam energy of 0.8 GeV. The selection of diproton pairs with an excitation energy Epp < 3 MeV ensures that the final pp system is dominantly in the spin-singlet 1 S0 state. The kinematics are therefore very similar to those of pp → dπ + but with different spin and isospin transitions. The cross sections are over two orders of magnitude smaller than those of pp → dπ + and show a forward dip that is even stronger than that seen at lower energies. The results should provide a crucial extra test of pion production models in nucleon–nucleon collisions.

New data on ϕ -meson production in pp collisions have been obtained at the ANKE facility of COSY-Julich. These data will provide the energy dependence of the total cross section down to an excess energy of 19 MeV above threshold. In combination with the existing SPES-III and COSY-TOF results on ω -meson production the ϕ / ω production ratio at this low excess energy will be extracted. As an exciting new aspect an enhancement in the invariant ϕp mass spectrum is observed at a mass around 1.965 GeV / c 2 .

The reaction pp->pK+Y has been studied with the ANKE spectrometer at COSY-Juelich in order to investigate heavy hyperon production. The missing mass spectra MM(pK+) have been analyzed and compared with Monte Carlo simulations. Indications for a hyperon resonance Y0*(1480) have been found., Baryons2004 Proceedings, 4 pages, 6 figures

A study of the deuteron breakup reaction $pd \to (pp)n$ with forward emission of a fast proton pair with small excitation energy $E_{pp}, Comment: 17 pages including 6 figures and 1 table v2: minor changes; v3: minor change of author list; v4: changes in accordance with referee remarks

The spectrometer ANKE has been put into operation at the accelerator COSY of the Forschungszentrum Julich in spring 1998. An initial scientific goal is to study K + -production in pA collisions at subthreshold energies far below the free NN-threshold at T p =1.58 GeV. This requires the identification of K + -mesons in a background of pions and protons, about 10 6 times more intense. In this paper the sophisticated detection system and the software procedures for kaon identification are described. With the help of TOF, energy-loss and range measurements as well as the track information from wire chambers, it is possible to measure d 2 σ/ d Ω d p for deep subthreshold K + production at beam energies down to T p =1.0 GeV.

ANKE is a new experimental facility for the spectroscopy of products from proton-induced reactions on internal targets. It has recently been implemented in the accelerator ring of the cooler synchrotron COSY of the Forschungszentrum Julich (FZ-Julich), Germany. The device consists of three dipole magnets, various target installations and dedicated detection systems. It will enable a variety of hadron-physics experiments like meson production in elementary proton–nucleon processes and studies of medium modifications in proton–nucleus interactions.

The new spectrometer ANKE has been put into operation at the accelerator COSY of the Forschungszentrum Julich. An initial scientific goal is to study K+-production in pA collisions at subthreshold energies below the free NN-threshold of T = 1.58 GeV. First measurements of double differential cross sections in p12C collisions at emission angles around 0° have been performed at T = 1.0, 1.2 and 2.0 GeV. The challenge is to identify the kaons in a huge background of pions and protons, since the signal to background ratio decreases to about 10−6 at T = 1.0 GeV. For background suppression detectors and a trigger system based on energy-loss and time-of-flight measurements have been developed. In the analysis the decay of kaons (τ = 12.4 ns) stopped in the detection system into μ+ and π+ is exploited as well as the track information from the wire chambers.

Within transport calculations we study the production and decay of $\omega$-mesons in $pA$ reactions at COSY energies including elastic and inelastic ${\omega}N$ rescattering, the $\omega{\to}\pi^0\gamma$ Dalitz decay as well as $\pi^0 N$ rescattering. The resulting invariant $\pi^0 \gamma$ mass distributions indicate that in-medium modifications of the $\omega$-meson may be observed experimentally.

Coherent and incoherent pi(0) photoproduction off the deuteron has been measured for incident quasi-monoenergetic photons in the energy range from pi(0) threshold up to 300 MeV using the TAPS setup together with the Glasgow tagger at MAMI. Integral and differential cross sections over the full angular range have been obtained. Coherent and incoherent production are found to exhibit very different angle and energy dependences. The sum of both processes, the total pi(0) production off the deuteron is quantitatively extremely well described by a pure quasifree model, whereas the data for coherent and incoherent channels necessitate strong FSI effects for their description. Finally upper limits for the production of dibaryon resonances in this reaction have bees obtained.

Optical properties of large size lead fluoride (PbF 2 ) crystals of three different manufacturers and their degradation caused by 60 Co γ-radiation have been investigated. Transmission losses have been systematically studied at absorbed energy doses between 0.1 and 7 kGy. Several radiation induced absorption bands have been observed. Optical bleaching with light of wavelengths ≳365 nm has been found very effective to restore the original characteristics even after repeated irradiations. This observation together with the high density and the ultraviolet extended transmission make PbF 2 an excellent choice for high rate and high resolution e.m. calorimetry.

New high-precision measurements of p( γ , π) and p( γ , γ) cross sections and beam asymmetries have been combined with other polarization ratios in a simultaneous analysis of both reactions. Compton scattering has provided two important new constraints on the photo-pion amplitude. The E2/M1 mixing ratio for the N → Δ transition extracted from this analysis is EMR = -3.0% ± 0.3 (stat + sys) ± 0.2 (model).

A fast analog trigger processor is being developed for the measurement of the parity violating asymmetry of the cross section of elastically scattered polarized electrons on unpolarized protons. The total event rate expected is about 100 MHz in the whole detector which consists of 1022 PbF 2 crystals. This requires fast cluster recognition, spatial and temporal pile-up rejection and fast data storage. First results of a prototype are discussed.

The impact-parameter dependence of π o - and η-meson production is reported for the system 40 Ar+ nat Ca at a beam energy of 800 A MeV. Scaling of the meson abundances with the transverse mass is observed. The experimental results are compared to calculations within the BUU model.

The photoproduction of two neutral pions off the proton has been studied for incident photon energies between E γ = 309 MeV (threshold) and 792 MeV with the TAPS photon spectrometer at the Mainz Microtron MAMI. Both 3γ- and 4γ-events have been analysed in order to deduce the total p ( γ , 2 π 0 ) p cross section. The total cross section is less than 300 nb between threshold and ⋍ 460 MeV, beyond which it starts to rise to a maximum value of about 11 μb at around 750 MeV. For the highest energies it starts to decrease again. The 4γ-sample has been used to reconstruct 2 neutral pions from the above reaction channel by an invariant mass and a missing mass analysis. After reconstruction of the unobserved proton, a Dalitz-plot of m π 0 π 0 2 vs. m pπ 0 2 has been obtained, which indicates that the decay chain includes the Δ(1232)-resonance as an intermediate state.

Total and differential cross sections for photoproduction of eta mesons from C-12, Ca-40, Nb-93 and Pb-nat have been obtained up to 790 MeV incident photon energy at the Mainz Microtron (MAMI) with the TAPS spectrometer. The absorption cross section sigma(eta N)(abs) = (30 +/- 2.5 +/- 6) mb of eta mesons in nuclear matter and the absorption length lambda(eta) = (2.0 +/- 0.2 +/- 0.4) fm are extracted. No significant depletion of the S(1)1(1535) strength in the eta photoproduction on nuclei is observed.

Differential and total cross sections for the photoproduction of neutral pions from the proton have been measured for incident photon energies from 140–270 MeV, using the photon spectrometer TAPS at the tagged photon beam of the 855 MeV Mainz Microtron. The energy dependence of the s- and p-wave multipoles close to threshold was deduced from a multipole fit and a multipole analysis. The extracted s-wave amplitude E 0+ at threshold is found to be significantly smaller than the prediction of the classical low energy theorems, but is in reasonable agreement with the chiral perturbation theory.

Absolute differential and integrated-over-angle cross sections for the reactions 12 C( γ , π 0 ) 12 C and 13 C( γ , π 0 ) 13 C leaving the residual nuclei in the ground state have been measured with tagged bremsstrahlung photons in the near threshold region (170.1 MeV ≤ E γ ≤ 176.8 MeV). This reaction mechanism is sensitive to the whole nuclear volume and the coherent processes which occur are revealed by comparing the extracted cross sections for both isotopes with each other and with theoretical calculations.

The Two Arm Photon Spectrometer TAPS - comprising 384 plastic-BaF2 scintillator telescopes - was tested with monochromatic photons in the energy range between 45 and 790 MeV. The energy resolution for a collimated photon beam hitting the central detector module was determined to sigma/E = 0.59% X E(gamma)-1/2 + 1.9% (E, given in GeV). For the the fast scintillation component alone sigma/E = 0.79% X E(gamma)-1/2 + 1.8% has been measured. The position resolution of the point of impact amounts to DELTAx = 2 cm (FWHM) at the highest energies which corresponds to 30% of the diameter of an individual module. Monte Carlo simulations using the code GEANT3 are in good agreement with the experimental results.

We measured cross sections for the subthreshold production of antiprotons and K − mesons in nucleus-nucleus collisions for the systems Ne+NaF, Cu, Sn, and Bi, and recently also Ni+Ni, using 20 Ne and 58 Ni beams from the heavy ion synchrotron (SIS) at GSI with energies between 1.6 GeV/u and 2.0 GeV/u. π − production cross sections were also determined. The dependency of the measured cross sections on the incident energy, the size of the system and the momentum of the detected particle is discussed.

Manitoba, Winnipeg, Manitoba, Canada R3T 2N2 Communicated by P. Roquette Received December 28, 1988; revised October 3, 1989 We determine all possible torsion groups of elliptic curves E with integral j-invariant over pure cubic number fields K. Except for the groups Z/22, Z/32 and Z/22 @ Z/22, there exist only finitely many curves E and pure cubic fields K such that E over K has a given torsion group E,, (K), and they are all calculated here. The curves E over K with torsion group E roOR( K) r Z/22 0 Z/22 have j-invariants belonging to a finite set. They are also calculated. A preliminary report on the results obtained was given by H. H. Miiller, H. Stroher, and H. G. Zimmer (in “Proceedings, Intern. Numb. Th. Conference at Lava1 University, Quebec, Canada, 1987” (J.-M. DeKoninck and C. Levesque, Eds.), pp. 671-698, de Gruyter, Berlin/ New York, 1989).

The half-life of the 238U shape isomer and its yield ratio in a (γ, γ') reaction have been measured by pulsed beam techniques at a bremsstrahlung endpoint energy of 12 MeV. From the results (T12 = 146 ± 22 ns, Yiso/Ypr = (6.6 ± 1.0) × 10−6) the isomeric fission cross section has been deduced. Combining this information with the results of a previous 238U(γ, xnγ) study, an upper limit for the branching ratio Γγ/Γf|II < 13 for the decay of 238mU can be obtained. The decay properties of the 236U and 238U shape isomers are discussed.

Absolute cross sections for electron- and positron-induced fission of 238 U have been measured in the energy range 10–35 MeV. The cross sections were compared with the corresponding photo-fission cross sections using DWBA virtual-photon spectra. The reliability of the virtual-photon formalism to extract E2 strength from inclusive electrodisintegration experiments is critically discussed.

Absolute cross sections and angular distributions for the production of neutral pions from 12 C by monochromatic photons have been measured near threshold. The contribution of incoherent pion production is found to be less than 10% for E γ ⩽168 MeV. Both the absolute cross section and the angular distribution indicate that a quantitative analysis requires final-state interactions of the produced π 0 with the surrounding nucleons to be taken into account.

Angular and multiplicity distributions for the γ-decay of 164 Er compound nuclei have been measured with the Darmstadt-Heidelberg Crystal Ball. Combining this information with the fusion cross section of (500 ± 50)mb, a compound nuclear spin distribution has been derived which almost exhausts the unitarity limit for lower partial waves. Near the limiting angular momentum of (52 ± 2)ℏ the distribution of partial wave cross sections exhibits a steeper fall-off than predicted by barrier fluctuation and coupled channel calculations.

The preparation of large area uranium layers (diameter 65 mm) with a thickness of 2–3 mg/cm 2 by electrolysis on Al foils is described. The layers are used in a multiple parallel plate avalanche detector with 30 counter gaps for photofission experiments. The performances and applications of this detector set-up are discussed.

A π 0 spectrometer is described which has been installed at the Glasgow-Mainz tagging spectrometer at the Mainz Microtron. It consists of 176 lead glass detectors arranged in two blocks of 8 × 11 detectors. It is employed to investigate neutral pion production off the proton and off complex nuclei with monochromatic photons between threshold and ≈175 MeV.

Absolute electrofission cross sections for 182,184,186 W, nat Pt, and 209 Bi have been measured using solid-state track detectors and parallel-plate avalanche counters for the detection of the fission fragments. The measured cross sections — together with others known from literature — have been analyzed within an extended statistical model to deduce fission barriers and compared with theoretical calculations. From the derived barrier height for platinum, it is concluded that the pairing strength G most likely does not change with deformation ( G = const). All experimental fission barriers agree very well with theoretical predictions for G = const.

The half-lives and yield ratios for the two 241 Pu fission isomers have been measured in the 242 Pu(γ, n) reaction. The observed half-life for the long-lived isomer (T 1 2 = 20.5 ± 2.2 μs) is in agreement with previous data, and the existence of a short-lived 34 ± 7 ns isomer in 241 Pu could be confirmed. The measured yield ratios are Y iso / Y pr = (9.2 ± 0.8) × 10 −5 and Y iso / Y pr = (3.7 ± 0.7) × 10 −5 , respectively. From a statistical model analysis of the isomeric fission yield ratio, Y long iso / Y short iso = 2.5 ± 0.6, a spin assignment for the two isomers is attempted. Possible spin combinations are compared with single-particle shell-model calculations and with available spectroscopic data for the other even-odd Pu isotopes.