Weak Γ-rays Research Articles

On the Energetics of a Possible Relativistic Jet Associated with the Binary Neutron Star Merger Candidate S190425z

Abstract Advanced LIGO and Virgo (AdvLIGO/VIRGO) detectors reported the first binary neutron star merger candidate in the third observing run, S190425z , on 2019 April 25. A weak γ-ray excess was reported nearly coincidentally by the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) satellite, which accidentally covered the entire localization region of AdvLIGO/VIRGO. Electromagnetic follow-up in longer wavelengths has not lead to the detection of any associated counterparts. Here we combine the available information from gravitational wave measurements and upper limits of fluence from INTEGRAL to show that the observations are completely consistent with a relativistic Gaussian structured jet and a typical short duration gamma-ray burst (GRB) being produced in the merger. We obtain posterior bounds on the on-axis isotropic equivalent energy of the associated GRB under different prior distributions. This study demonstrates that even limited gravitational wave and electromagnetic information could be combined to produce valuable insights about outflows from mergers. Future follow-ups may help constrain the jet structure further, especially if there is an orphan afterglow detection associated with the candidate.

Revised level structure of 127Xe

Excited states of 127Xe were populated via fusion-evaporation reaction. A level at 2306.7 keV has been established instead of the previously reported two different levels at 2307 keV. has been assigned to this level on the basis of the DCO ratio and linear polarization asymmetry of decaying γ-rays. A weak γ-ray of 840.2 keV, decaying from this state to the state, has also been identified. Results are compared with neighboring Xe isotopes.

Measuremets of presolar grain in meteorite using neutron activation analysis with multi-parameter coincidence method

Neutron activation analysis with multi-parameter coincidence method was developed at the Japan Atomic Energy Agency (JAEA) and a non-destructive, ultra-high sensitive multi-elemental determination has been realized. The multi-parameter coincidence method is carried out with an array of 19 germanium detectors, GEMINI-II. Using this system, very weak γ-rays emitted from trace amounts of elements can be detected. The presolar grains were extracted from the Allende meteorite. Trace elements in the presolar diamonds were measured by neutron activation analysis with multi-parameter coincidence method.

High-sensitive elemental analysis using multi-parameter coincidence spectrometer: GEMINI-II

In this study, using neutron activation analysis with multi-parameter coincidence method which was developed at Japan Atomic Energy Agency (JAEA), a non-destructive, ultra-high sensitive multi-elemental determination has been realized. The multi-parameter coincidence method is carried out with an array of 19 germanium detectors, GEMINI-II. Using this system, very weak γ-rays emitted from trace amounts of elements can be detected. The iridium concentration has been determined by means of neutron activation analysis with multi-parameter coincidence method for Cuban sediment samples across the K/T boundary strata.

Simple source preparation and disintegration rate measurement of 56Co and its use for efficiency calibration

In order to precisely determine the γ-ray detection efficiencies in the energy region above 1500 keV, sources of 56Co, which emit many γ-rays with well determined emission probabilities in that energy region, have been prepared and used. After proton irradiation of natural iron foils, thin foils with 10- μm thickness were sandwiched with two metallised VYNS films and thick foils were treated by ion exchange after dissolving. Although 55Fe was produced by a secondary reaction, the disintegration rates of 56Co sources were successfully determined by means of the 4 πβ– γ coincidence method. The absolute detection efficiency was determined and the emission probabilities for four weak γ-rays of 56Co were measured.

Radiochemical analysis of 129I in radioactive waste streams

129I is the longest lived of the volatile radionuclides produced in the nuclear fuel cycle. This radionuclide emits soft β-particles, a weak γ-ray and X-rays. Since the half-life of 129I is 1.57 × 10 7 y, the evaluation of optimum waste management practices, for this radionuclide, has received special consideration. This work proposes an analytical method for 129I in radioactive ion exchange resins and evaporator concentrates based on two methods. The first method consists in direct measurement, without chemical separation, by low energy γ-ray spectrometry. The achieved detection limit of 129I, with 60 h of counting time, is 0.2 Bq. The second method is based on a radiochemical separation process consisting in two precipitation steps of the β—γ emitters present in the samples and 129I measurement by low energy γ-rays spectrometry. The achieved detection limit of 129I with 5 h of counting time, is 0.02 Bq, ten times lower than those achieved with the direct measurement method.

Confirmation of the l-forbidden Gamow-Teller decay branch of 39Ca

A search for Gamow-Teller decay branches of 39Ca to excited states in 39K was conducted with a large HPGe detector which observed the decays of 39Ca samples delivered by a helium-jet transport system. A pair of plastic scintillators in front of the HPGe detector were used to reject events due to bremsstrahlung from the 39Ca positrons. With this setup, weak γ-rays could be observed with a degree of sensitivity not previously achieved. The l- forbidden 1 d 3 2 → 2 s 1 2 transition to the first excited state in 39K, was observed with a branching ratio of (2.50 ± 0.27) × 10 −5. This result agrees with but is more accurate than the only previous measurement. Thus, the ratio of the l-forbidden Gamow-Teller and isovector M1 matrix elements in mass-39 nuclei continues to disagree with theoretical values obtained by Towner and Khanna from calculations involving core-polarization and meson-exchange currents. This leaves very few possibilities to explain the discrepancy between theory and experiment.

Eurogam and superdeformation in A = 150 nuclei

The EUROGAM array has recently completed its first experiments. The results of these will be described together with an assessment of the performance of the array in terms of its Resolving Power and its improvement of the peak/background ratio for weak γ-rays associated with superdeformed bands.

Observation of Coulomb excitation of unstable nuclei utilization of a secondary beam

An experimental technique to detect γ-rays from secondary-beam Coulomb excitation was developed. A secondary beam of 76Kr produced by the inverse reaction 9Be( 70Ge, 3n) was Coulomb excited by a 208Pb target. Weak γ-rays from the secondary-beam Coulomb excitation were discriminated from those of a primary beam by measuring triple coincidences of primary γ-rays, scattered particles and emitted γ-rays from the second target. Coulomb excitation of the unstable nucleus was observed for the first time in the medium heavy mass region. The observed yield of the 2 + → 0 + transition in 76Kr is consistent with that which is estimated from the known B(E2: 0 + → 2 +) for this nucleus.

Lifetime of the long-lived isomer of 236Np from α-, β- and electron-capture decay measurements

Abstract The half-life of long-lived 236Np, due to α, β and electron-capture decay, was found to be 1.55 × 105 yr. Of all decays, 88% populate excited states in 236U and 12% populate levels in 236Pu. Lifetimes measured by growth of the ground states of 236U and 236Pu agree with values from corresponding γ de-excitations in these daughter nuclei. Therefore, nearly all the electron-capture decays populate the 6+ level of the ground-state band in 236U. Similarily, essentially all the β− decay populates an analogous 6+ level in 236Pu, which de-excites through a previously unreported transition of 158.3 keV. If a very weak γ-ray at 894 keV can be ascribed to a level in 232U populated by β decay of 232Pa, its existence establishes a 0.2% α-branching decay in 236Np.

The decays of 21.55 min 162gTm and 24.3 s 162Tm (a new isomer)

The decay of the 21.55 min ground state and of the 24.3 s isomeric state of 162Tm was investigated with semiconductor detectors. The γ-ray spectrum was investigated with a Compton-suppression Ge(Li)-NaI(Tl) arrangement. A Si (Li) detector, mounted in an electron transport solenoid, was used to investigate the conversion electron spectrum. Three-dimensional coincidence measurements were performed with large-volume Ge(Li) detectors. The 162Tm ground state has spin-parity 1 − and Nilsson assignment p[411]↓− n[521]↑. An allowed β-transition (log ft ≈ 6.4) was observed to a 2 −, 2 octupole vibrational level at 1572.84 keV. The Q-value determined from positon-gamma coincidence measurements is 4705 ± 70 keV. The discrepancy of the experimental K / β + ratio with theoretical predictions might possibly be explained by a large number of unobserved weak γ-rays besides the total of 315 stronger ones observed in this study. The average β-strength function was calculated to be 1.2 × 10 −5. Among the 50 levels observed in the decay, the 2 +, 4 + and 6 + members of the ground-state band, the 2 +, 3 + and 4 + members of the γ-band, several 0 + and 2 + members of the K = 0 β-bands and 1 −, 2 − and 3 − octupole vibrational levels were identified. Parameter values Z γ (0) and Z γ (2) determining the mixing between the γ-band and the ground-state band, allow no conclusive evidence about unequalness of the intrinsic quadrupole moments of the ground states and the γ-band. The Z(0) parameters, determining the mixing between the β-bands and the ground-state band, and X parameters determining the ratio of E0 to E2 transition probabilities, were deduced. A previously unreported 24.3 sec isomer in 162Tm was observed to decay in 10% of the cases by an allowed unhindered (log ft = 4.7) β-ray transition to a level at 1712.20 keV in 162Er. The Nilsson configurations assigned to the isomeric and 1712.20 keV levels are p[523]↑ + n[521]↑ 5+ and n[523]↓ + n[521]↑ 4+ respectively. The isomeric level decays in 90% of the cases by an E3 transition ( E IT < 125 keV) to a p[404]↓ −n[521]↑ 2− level at 66.90 keV in 162Tm, which decays by an (M1+ < 40 % E2) to the 21.55 min 162Tm 1 − ground state.

Energy levels of 82Kr populated by 82Br decay

The γ-rays following the β-decay of 82Br have been investigated using a 220 mm 3 Ge(Li) detector, an anti-Compton NaI(Tl) spectrometer and a two-dimensional coincidence arrangement. The 82Br was produced by thermal neutron activation of ammonium bromide. The presence of eight, well-known and 11 weak γ-rays has been established. It has been shown through half-life measurements that the newly identified γ-rays belong to 82Br decay and that the high-energy peaks are not to summing effects. All the reported transitions have been incorporated in a level scheme of 82Kr by introducing levels at 0, 776, 1474, 1820, 1953, 2093, 2426, 2554, 2647 and 2828 keV. Limits on probable spin and parity values for the newly-introduced levels have been established. The level introduced at 2828 keV on the basis of a 1008–1043 keV γγ-coincidence must be fed by a weak β-branch of 82Br with an end-point energy of 263 keV and log ft of approximately 6.1.

The metastable [formula omitted] hole state in 47Sc

With a Ge(Li) detector, we have studied the γ-ray spectrum of 47Sc (populated by β-decay of 47Ca). The results obtained were (i) two weak γ-rays (0.5324±0.0007 and 0.7640±0.0007 MeV were observed in the singles spectrum; (ii) the intensities of the γ-transitions were determined to be (0.17±0.02) % of the total transition rate from the 1.2945 MeV level; (iii) from the delayed coincidence spectrum, the 0.7640 MeV line was found to be the only transition deexciting the metastable state; (iv) from the time-to-pulse-height spectrum, the half-life was more accurately measured to be 270±12 nsec. In addition, the technique of applying the Ge(Li) detector to coincidence work in spectroscopic studies is described.

Decay of the new 2.5 min201Pt

The radiations from 2.5 min201Pt are investigated by scintillation and coincidence techniques.201Pt was produced by204Hg(n, α)201Pt from natural mercuric oxide irradiated in a reactor. The end point of the β-spectrum was found to be (2660±50) keV. A strong γ-ray of energy (1760 ±20) keV was observed. The half-life of this activity was measured more accurately by following the decay of the 1760 keV y-ray and it was found to be (2.5±0.1) min. A β-γ coincidence study showed the presence of weak γ-rays of energy (70±5), (150±10) and (230±20)keV. A tentative decay scheme based on these observations is proposed. The crosssection for204Hg(n, α)201Pt reaction was estimated to be 2.5 mb.

Conversion-gamma angular correlation measurements in Gd152 populated by the beta decay of Eu152

Angular correlation measurements were carried out between the K conversion electrons of the 344 keV transition and the gamma particles de-exciting all the upper levels in Gd152 populated by the 13y Eu152 disintegration. The coincidence gamma spectrum was recorded simultaneously on a multichannel pulse-height analyser at the angles 270°, 180° and 90°, where the information was accumulated for 4 cascades. The anisotropies derived from the present measurements combined with the data of the conversion coefficients yielded the spin assignment 2+, 3− and 2− for the levels 755 keV, 1124 keV, and 1614 keV, respectively. The 2+ 755 keV level together with the 615 keV 0+ state comprise two members of the two phonon vibration excitation triplet. Some evidence is obtained for a weak γ-ray around 500 keV, and it is suggested that perhaps this is the 4+ missing member of the triplet. A tentative 3− spin assignment for 1444 keV level, on the basis of the present anisotropy measurement and the β feeding to the level, is also proposed.

Radioactivation Analysis of Niobium in Tantalum by Irradiation with Protons in a Cyclotron

CONSIDERABLE work has been done in the past decade on the separation and determination of relatively small amounts of tantalum and niobium. However, no adequate method for the determination of these elements seems to have been devised. Although neutron activation analysis has provided a good tool for the determination of many elements, no satisfactory results have been obtained for niobium in tantalum. The reasons are as follows: (1) small cross-section for the 93Nb(n, γ)-94mNb reaction (1.1 ± 0.1 barn); (2) 94mNb has a short half-life (6.6 min) and emits a weak γ-ray (0.0415 MeV); (3) chemical similarity of these elements.

Radioactive decay of 103Ru

The decay of 103Ru has been investigated with a scintillation spectrometer, a β-ray lens spectrometer, and by β-γ absorption coincidence measurements. With the scintillation spectrometer the X-ray and two strong γ-rays were found with the following energies and relative intensities: 20 keV (9.1%), 498 keV (100%) and 611 keV (7.8%). In addition three very weak γ-rays were observed at 53 keV (0.4%), 295 keV (0.4%) and 357 keV (0.25%). With the β-ray spectrometer the K conversion coefficient of the 611 keV γ-ray was found as (0.06 ± 0.02)%, which characterizes this transition as E1. Also the intensity of the weak β-component with an endpoint of 702 keV was measured as 2.9%. Absorption measurements of the β−-particles in coincidence with the 611 keV γ-ray show that there exits a third β-ray branch with an endpoint of 145 ± 35 keV, in addition to the known β-ray branches with endpoints of 217 and 702 keV. No coincidences were found between the 702 keV β-ray branch and the 53 keV γ-ray, showing that the half life of the 53 keV level is greater than 10 μsec. The 103Rh level scheme deduced from these measurements is in agreement with that given by Cork et al., except for the spin of the 611 keV level and of 103Ru. There are strong arguments that both are J = ½+. Also the levels found from Coulomb excitation by Heydenburg and Temmer at 295 keV (J = 3/2−) and 357 keV (J = 5/2−) have been confirmed from the 103Ru decay.