Decay of the very neutron-deficient isotope 131Pm

The decay of ¹³¹Pm has been investigated by means of γ-ray spectroscopy. The ¹³¹Pm nuclei were produced by fusion-evaporation reaction of ¹⁰⁶Cd(³²S,3p4n) at the beam energy of 170 MeV. A helium-jet technique and a tape transport system were used to collect the activities and transfer them to a detecting position for X and γ rays measurement. Two γ rays of 185.0 and 220.0 keV were unambiguously identified to follow the β⁺ decay of ¹³¹Pm by results of X-γ and γ–γ coincidence. A growth-decay feature of the decay curve for 87.8 keV γ-ray of ¹³¹Nd confirmed the production of ¹³¹Pm nuclei. The half-life of ¹³¹Pm was measured to be 6.3 ± 0.8 s. A partial decay scheme of ¹³¹Pm is proposed on the basis of X-γ and γ–γ coincidence data in this experiment and the known structure information deduced from in-beam experiments of the daughter nucleus ¹³¹Nd. Received: 11 January 1999 / Revised version: 20 May 1999     

ESR studies of sepiolites

The electron spin resonance (ESR) spectra for each beige and brown sepiolites from Polatli-Ankara, Turkey, a clay mineral of Mg₈Si₁₂O₃₀(OH)₄(OH₂)₄(H₂O)₈, at 77 K have their own single characteristic peak atg ≈ 1.99, which begins to anneal from 437 and 536°C, respectively. The sextet lines of Mn²⁺ were also observed in addition to two peaks (g = 4.4 and 5.0) associated with Fe³⁺. A high-quality sepiolite called “meerschaum” from Sepetci-Eskisehir, Turkey, has two characteristic peaks atg ≈ 1.99, which begins to anneal from 419°C, and atg ≈ 2.03. ESR intensities of the signal atg ≈ 1.99 for beige, brown sepiolites and meerschaum are enhanced by γ-ray irradiation to give equivalent dosesD _E = 11.8 ± 3.4, 4.7 ± 2.3 and 4.6 ± 1.2 kGy, respectively. The ESR ages obtained by assessing the annual dose rate from the content of²³⁸U,²³²Th and⁴⁰K determined by γ-ray spectroscopy are 1.8 ± 0.8, 0.7 ± 0.5 and 0.9 ± 0.2 Ma, respectively, falling into the Pliocene Epoch in geological time scale in agreement with the stratigraphy.     

Shift in the angular distributions of γ quanta accompanying <Superscript>235</Superscript>U fission by polarized thermal neutrons

The angular dependence of the γ-ray asymmetry relative to the plane formed by the directions of fission-fragment separation and longitudinal polarization of the thermal neutrons inducing ²³⁵U(n, f) fission was investigated. The results obtained confirm the existence of γ-ray emission asymmetry and the dependence of its coefficient on the angle between the axes of the fission-fragment and γ-ray detectors, revealed for the first time by the ITEP group at the FRM-II reactor in Munich. The observed T-odd effect of around ∼2 × 10⁻⁴ can be explained by the angular anisotropy of the γ-ray emission from fission fragments with large angular momenta oriented relative to the fission axis.     

Terrestrial gamma-ray flashes and neutron pulses from direct simulations of gigantic upward atmospheric discharge

Gamma-ray pulses are calculated from 2D numerical simulations of upward atmospheric discharge in a self-consistent electric field using the multigroup approach to the kinetics of relativistic runaway electrons. Thecalculated numbers and spectra of γ-rays are consistent with the data on terrestrial γ-ray flashes observed aboard spacecraft. The calculated runaway electron flux is concentrated mainly within the domain of the blue jet fluorescence. This proves that exactly this domain is a source of the γ-ray flashes. One γ-ray flash generates ∼10¹⁴-10¹⁵ photonuclear neutrons. The text was submitted by the authors in English     

Atmospheric gamma-ray and neutron flashes

Gamma-ray pulses are calculated from 2D numerical simulations of an upward atmospheric discharge in a self-consistent electric field using the multigroup approach to the kinetics of relativistic runaway electrons (REs). Computed γ-ray numbers and spectra are consistent with those of terrestrial γ-ray flashes (TGFs) observed aboard spacecrafts. The RE flux is concentrated mainly within the domain of the Blue Jet fluorescence. This confirms that exactly the domain adjacent to a thundercloud is the source of the observed γ-ray flashes. The yield of photonuclear neutrons is calculated. One γ-ray pulse generates ∼10¹⁴–10¹⁵ neutrons. The possibility of the direct deposition of REs to the detector readings and the origin of the lightning-advanced TGFs are discussed. The text was submitted by the authors in English.     

Measurement of the K shell X-ray production cross-sections and fluorescence yields for Nd,Eu, Gd,Dy and Ho using radioisotope X-ray fluorescence in the external magnetic field

The effect of external magnetic field on the K_α and K_β X-ray production cross-sections and K shell fluorescence yields for ferromagnetic elements Nd, Gd and Dy and paramagnetic elements Eu and Ho have been measured at the excitation energy of 59.5 keV γ -rays from ²⁴¹Am radioactive source of strength 100 mCi in the external magnetic field of intensities ±0.75 T. Furthermore, I_Kβ /I_Kα intensity ratios for these elements have been measured in the external magnetic field. The K X-rays from different targets were detected using a high resolution Si(Li) semiconductor detector. For B = 0, the measured K X-ray production cross-sections, K shell fluorescence yields and the I_Kβ /I_Kα intensity ratios were compared with the experimental and theoretical data in literature. The results have shown that the fluorescence parameters as photoionization cross section, fluorescence yield, radiation rates and spectral linewidth can change when the irradiation is conducted in a magnetic field.     

γ -ray spectroscopy study of 11 ΛB and 12 ΛC

In this paper, a preliminary result from the latest hypernuclear γ -ray spectroscopy experiment (KEK-E566) is presented together with a short discussion. The experiment was performed at the KEK-PS K6 beam line in 2005. In this experiment, the ¹²C(π⁺, K ⁺)¹² _ΛC reaction was employed to populate ¹² _ΛC/¹¹ _ΛB hypernuclei. A germanium detector array, Hyperball2, was constructed to detect γ -rays emitted from the hypernuclei produced. Three hypernuclear γ -ray peaks were observed and assigned.     

Radical formation in lithium trifluoromethane-sulfonate for ESR dosimetry

Lithium trifluoromethane-sulfonate (Li-TFMS:CF₃SO₃Li) irradiated by γ-rays showed an electron spin resonance (ESR) powder spectrum having the rhombicg-factor ofg _xx = 2.0259 ± 0.0005,g _yy = 2.0112 ± 0.0005 andg _zz = 2.0025 ± 0.0005 and a triplet hyperfine coupling constant ofA _xx/gβ= 0.8 ± 0.15 mT.A _yy andA _zz are not obtained because of the broadened spectrum. The energy levels,g-factor,A _xx/gβ and optical absorption spectrum of several conceivable radicals such as C^⋅F₂SO₃Li, CF₃-S-O^⋅ and CF₃-S-O-O^⋅ have been calculated by softwares MOPAC-V2 and Gaussian-98 based on ROHF (Restricted Hatree-Fock for open shell molecule). The most probable radical was ascribed to CF₃-SO^⋅ from both calculated and experimental results. The response to γ-ray dose and the thermal stability have been studied in addition to the effect of UV illumination for possible use of the signal intensity in ESR dosimetry. The obtained number of free radicals per 100 eV (G-value) was 1.23 ± 0.40.     

Study of the Mo-Ba partition in 252Cf spontaneous fission

Measurements of fission fragment yields and neutron multiplicities have been carried out for the Mo-Ba fragment pairs in the spontaneous fission of ²⁵²Cf, using the γ-ray spectroscopy technique to analyze γ-γ-γ coincidence data. Prompt γ -ray multiplicities were also measured as a function of the number of neutrons emitted in the fission process leading to the Mo-Ba partition. We do not observe the enhancement in the yields of events with high neutron emission multiplicity (ν_n > 7) that has been associated to a second fission mode leading to the production of hyperdeformed Ba fragments, as reported in some earlier studies. The average γ-ray multiplicity is found to be rather weakly dependent on the number of neutrons emitted in the fission process. Received: 21 July 1999 / Revised version: 19 November 1999     

Search for 100 TeV gamma-rays from SN 1987 A

Summary We present the results of a search for very high energy γ-rays (E _γ≈100 TeV) from SN 1987A between August 1987 and May 1988. No counting rate excess from the source is observed. The larger enhancement is seen in January 1988, but is statistically not significant (1.4 s.d.). The derived upper limits to the γ-ray and proton luminosities of the SN areL _γ≤1.9·10⁴⁰ erg/s andL _p≤1.2·10⁴² erg/s. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

Isospin symmetry breaking in ρ→πγ decay

In terms of effective field theory and mixed-propagator approach, we show that there is a larger hidden effect of isospin breaking in ρ→πγ decay due to a ω exchange, ρ→ω→πγ. The branching ratio is predicted as B(ρ→πγ) = (11.67±2.0)×10^-4, which is much larger than Particle Data Group's datum (6.8±1.7)×10^-4 and one of charged mode, B(ρ^±→π^±γ) = (4.5±0.5)×10^-4. Received: 7 January 2002 / Accepted: 2 April 2002     

Study of analogue states in52Cr through proton capture by51V

γ-Ray yield function has been studied for the proton capture by vanadium in the proton energy range 720–1300 keV. Isobaric analogues of low lying states in⁵²V have been identified. At two resonances theγ-decay andγ-ray angular distributions have been obtained and the branching ratios and the multipole mixing ratios have been deduced. The analogue-antianalogue M1 transition in⁵²Cr is found to be strongly hindered as in other f_7/2 nuclei. TheQ-value obtained for this reaction is (10500±2.8) keV and the Coulomb displacement energy is (8.06±0.01) MeV. An upper limit of 2 meV has been obtained for theα- decay strength of the 11.395 MeV state in⁵²Cr.     

Recoil-fission tagging of the transfermium nucleus 252No

An in-beam study of the transfermium nucleus ²⁵²No has been performed using the JUROSPHERE II array of germanium detectors coupled to the gas-filled recoil separator RITU. A new technique of recoil-fission tagging was used to extract tagged γ-ray data. Having significant spontaneous fission and α-decay branches, ²⁵²No is an ideal candidate for a comparative study. In a similar manner to α-decay tagging the fission events can be used to obtain γ-ray data. The recoil-fission tagged γ-ray spectrum showed a similar structure to the α-decay tagged γ-ray spectrum. By comparing the α-tagged and fission-tagged spectra and decay curves, it was shown that the spontaneous fission originates from the same initial state as the α decay. This extension of the tagging method allows in-beam spectroscopic data to be obtained from heavy nuclei with significant spontaneous-fission branches.     

Observation of the 7 MeV excited spin-flip and non-spin-flip partners in 16 ΛO by γ -ray spectroscopy

We have observed three γ -ray transitions in _Λ ¹⁶ O from both 7MeV excited spin-flip and non-spin-flip partners ( 2^-, 1^- ₂ to the ground-state doublet ( 1^- ₁, 0^- via the ¹⁶O(K ^-,π^-) reaction. The 7MeV excitation energies of the spin-doublet members ( 2^-, 1^- ₂ were determined to be 6784±4±4 keV and 6562±1±2 keV, respectively, and thus the spacing was obtained to be 222±4±5 keV. This is the first observation of the spin-flip state directly populated by the ( K ^-,π^- reaction. Moreover, such directly populated spin-flip and non-spin-flip partners were resolved for the first time.     

Searches for gamma-quanta from local sources by a wide-angle imaging telescope

Summary A new Cherenkov imaging telescope SHALON equipped with a very high-definition camera (144 pixels, imaging 7.2⁰×7.2⁰) takes data since 1993 at a mountain altitude of 3338 m. We discuss some results of the observations of the indicated gamma-ray sources and the discrimination methods between gamma-rays and protons. Selection of showers produced by gamma-quanta from a background of showers produced by protons has been made according to the following criteria: 1) alpha<20⁰; 2) length/width>1.6 for γ; 3) Cherenkov light intensity in pixels with max light to the light in the light pixels near around is >0.2 for γ and <0.6 for p; 4) Cherenkov light intensity in pixels with max light to all light in imaging excluding in centre is >0.8 for γ and <0.8 for p; 5) distance for γ is <3.5 pixels.I _Crab=(0.95±0.18)·10⁻¹² cm⁻²c⁻¹.I _Mark421=(0.98±0.36)·10⁻¹² cm⁻²c⁻¹. Paper presented at the Special Session on ground-based gamma-ray astronomy of the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Experimental determination of the chemical changes in the electron density on indium nuclei by the γ‐spectrometric ΔIγ/Iγ method

The γ‐spectrometry method for determination of the relative change Δλ_EC/λ_EC in the partial probability λ_EC for the ^114mIn decay branch by the electron capture (EC), when the nucleus is in different chemical environments, was developed. The method is based on an experimental determination of the relative change ΔI_γ/I_γ in the intensity of the γ‐radiation which is emitted by the excited daughter ¹¹⁴Cd nuclei after EC. The ^114mIn decay by EC in indium metal, In₂O₃ and InAs was compared. The largest ΔI_γ/I_γ=(2.5±0.8)·10⁻⁴ has been found for InAs relatively to In₂O₃. The chemical changes in the electron density on the indium nucleus corresponding to the measured ΔI_γ/I_γ values have been determined. This revised version was published online in July 2006 with corrections to the Cover Date.     

In-beam study of 145Tb

The high-spin states of ¹⁴⁵Tb have been studied in the ¹¹⁸Sn(³²S, 1p4n) reaction at ³²S energies from 161 to 175 MeV using techniques of in-beam γ-ray spectroscopy. Measurements of γ-ray excitation functions and γ-γ-t coincidences were performed with 12 BGO(AC)HPGe detectors. Based on the measured results of γ-γ coincidences, γ-ray anisotropies and DCO ratios, a level scheme for ¹⁴⁵Tb was established for the first time. The observed excited states show typical irregular pattern in a spherical nucleus, and the low-lying levels have been interpreted qualitatively with a particle-core coupling. Received: 21 September 2001 / Accepted: 9 November 2001     

High-spin isomers in 183Os

High-spin states in ¹⁸³Os have been studied by means of in-beam γ-ray spectroscopy. Two isomers with I ^π= ((43/2)⁻) and (43/2)⁺ have been identified at excitation energies of E _x = 5.068 and 5.168 MeV. The half-lives are determined as T _1/2= 27 ± 3 and 24 ± 2 ns. Received: 22 December 1997     

Amplitude analysis of high statistics results on γγ→π+π- and the two photon width of isoscalar states

We perform an amplitude analysis of the world published data on γγ→π⁺π^- and π⁰π⁰. These are dominated in statistics by the recently published results from Belle on the charged pion channel. Nevertheless, having only limited angular information, a range of solutions remain possible. We present two solutions with Γ(f₀(980)→γγ)=0.42 and 0.10 keV, and Γ(f₂(1270)→γγ)=3.14±0.20 and 3.82 ± 0.30 keV, respectively: the former being the solution favoured by χ², the latter at the edge of acceptability. Models of the structure of the f₀(980) predict two photon widths to be between 0.2 and 0.6 keV, depending on its composition as mainly K̄K, s̄s or qq̄qq. Presently available data cannot yet distinguish unambiguously between these predictions. However, we show how forthcoming results on γγ→π⁰π⁰ can not only discriminate between, but also refine, these classes of partial wave solutions.     

High spin states and evidence for octupole correlations in 117Xe

High-spin states of ¹¹⁷Xe were investigated by means of in-beam γ-ray spectroscopic techniques via the reaction of ²⁸Si bombarding a ⁹²Mo target at beam energies of 100-120 MeV. A positive-parity rotational band decaying into the yrast negative-parity band by a series of enhanced E1 transitions was observed for the first time, implying the existence of octupole correlations in ¹¹⁷Xe. The B(E1) values increase with spin. The νd_5/2 band was firmly established up to 27/2⁺ and the B(M1)/B(E2) ratios were extracted from the relative intensities of γ-rays in this band. The previously known νh_11/2 and νg_7/2 [413]5/2⁺α=−1/2 bands were confirmed and extended up to high spins and two bandcrossings are observed in the latter at ħω=0.33 and 0.44 MeV, respectively. The bandcrossings and configurations of these bands are discussed by TRS and CSM calculations. In a γ–γ–t measurement, the 11/2⁻ and 7/2⁻ levels were identified as two isomers with half-lives of 59.4±20 ns and 16.5±8.0 ns, respectively. Received: 17 June 1997 / Revised version: 29 September 1997