Search for an isomer in94Rb

Measurements of theβ-ray half-life,γ-ray and X-ray spectra andγ-ray half-lives have been done with a plastic scintillation detector, a high resolution Ge(HP) detector and a 142 cm³ Ge(Li) detector to search for an isomeric state in⁹⁴Rb. Mass-separated activities of⁹⁴Rb were obtained from the He-jet type on-line mass-separator at the Kyoto University reactor. No isomeric transition was found in theγ-ray and X-ray measurements with the upper limits of 3×10^?4 and 8×10^?5, respectively, as compared with the 836.9 keV transition. Half-lives obtained from theγ-ray decay measurements are discussed in the light of classification given byQ _β -value measurements.     

The decay of 33 70 Se37

The decay of⁷⁰Se was studied using a 75 cm³ Ge(Li) detector, placed in an anti-compton shield, and a low-energy detector. Of the 36γ-rays observed 31 are placed in a levelscheme of⁷⁰As, based on coincidence- and sumrelations. Conversion electrons of two low energy transitions were observed in order to determine their multipolarity. The halflife is measured (41.1 min). Spins and parities of the excited levels were deduced and compared with shell model predictions and logft values of theEC/β ⁺ branches were calculated.     

Remeasurement of capture to positron decay ratios in22Na and65Zn and comparison with theory

In the decay of²²Na theEC/β ⁺ ratio for theβ-transition to the 1275 keV-level was measured to beEC/β ⁺=0.1050 (29). Single and coincidence counting was performed using a 16% Ge(Li) and an NaI well-type detector. For⁶⁵Zn theK/β ⁺ ratio for the ground state transitionK ₁/β ⁺=30.3 (10) was obtained using the same apparatus and in addition a 10 mm diam. × 5.4 mm Si(Li) detector. The results are compared with earlier experiments and with theory.     

The spectroscopy of 22Al: a βp, β2p and βα emitter

In an experiment at the LISE3 facility of GANIL, we produced the proton-rich isotope ²²Al by the fragmentation of a ³⁶Ar primary beam at 95 MeV/nucleon. After implantation in a detector telescope, the decay of ²²Al via β-delayed proton emission, β-delayed two-proton emission as well as, for the first time, via β-delayed α emission has been studied. An α peak has been observed at (3.27 ± 0.04) MeV with a branching ratio of (0.31 ± 0.09) %. The comparison of the different decay channels to those of the mirror nucleus ²²F and to shell-model calculations favor a 3⁺ state as being the ground state of ²²Al. A half life of T_1/2 = (59 ± 3) ms has been measured.     

Status of an experiment aimed at laboratory searches for the electron-antineutrino magnetic moment at a level of μ ν ≤3±10− μ B

An experiment aimed at directly detecting antineutrino-electron scattering by using a 40-MCi tritium β-active source will make it possible to lower the present-day laboratory limit on the neutrino magnetic moment by two orders of magnitude. The experiment brings together novel unique technologies in studying rare processes of neutrino-electron scattering: (i) an artificial source of antineutrinos from tritium decay of 40-MCi activity with the antineutrino flux density of about 6×10¹⁴ cm^?2 s^?1 and (ii) new types of detectors capable of detecting electrons of energy down to about 10 eV, namely, a silicon cryogenic detector based on the ionization-into-heat conversion effect and a high-pure germanium detector with an internal signal amplification in the electric field. A compact installation located at a specially equipped underground laboratory (≤100 mwe) will provide favorable background conditions for running the experiment. With a background level of about 0.1 event/(kg keV d) and detector assembly masses of 3 and 5 kg for the silicon and germanium ones, respectively, a limit of μ _ν ≤3±10^? μ _B on the electron-antineutrino magnetic moment will be obtained within 1 to 2 years of data acquisition. The status of the experiment and the state of the art are presented.     

L X-ray-gamma angular correlations following the decay of139Ce

A reinvestigation of theL X-ray-gamma angular correlations following the decay of¹³⁹Ce is made by using a Si(Li) semiconductor detector asL X-ray detector. Coincidence measurements at five different angles were made between the 166-keV gamma ray and theL X-ray spectrum. The data were handled in two different ways: (i) the counts under theL _l +L _α+L _β+L _γ peaks were taken; (ii) the counts under theL _l +L _α+L _β peaks were only considered. Chance coincidences as well as coincidences background were taken into account. The results indicate that no anisotropy is to be found within a margin of error of 6×10^?3.     

A note on60Co decay

Theγ-rays from⁶⁰Co have been studied with a 30 cm³ Ge(Li) detector. Gamma rays of energies 826.4 and 2,158.9 keV which are expected on the basis of the⁶⁰Co decay scheme were sought but not observed. Their intensities are <0.02% and <0.002%, respectively, of the⁶⁰Co disintegrations. Any direct feeding from the (5⁺)⁶⁰Co ground state to the (2⁺) 2,159 keV level is <0.022%, yielding a logft>12.3 for the 664 keV second-forbidden uniqueβ-transition. Radioactivity⁶⁰Co; measuredE _γ,I _γ.⁶⁰Ni deduced levels, logft. Ge(Li) detector.     

2<Emphasis Type="Italic">π</Emphasis> proportional counting chamber for large-area-coated <Emphasis Type="Italic">β</Emphasis> sources

Detection system for measuring absolute emission rate from large-area-coated β sources has been indigenously developed. The system consists of a multiwire-based proportional counter with gas flow and a source mounted within the sensitive volume of the detector. Design of the counter enables efficient counting of emissions in 2π solid angle. A provision is made for change of the source and immediate measurement of source activity. These sources are used to calibrate the efficiency of contamination monitors at radiological facilities. Sensitive area of the detector covers 165^° solid angle nearing 2 π of emission from the source of size 100 × 150 mm. Performance of the chamber is tested using collimated ⁵⁵Fe X-ray source and ⁹⁰Sr / ⁹⁰Y coated β sources of various activities. The activity measurement system is established as a national primary standard for calibration of coated β sources at Radiological Laboratory at BARC. Design and performance of the chamber are presented.     

β-delayed neutron emission studies

The study of β-delayed neutron emission plays a major role in different fields such as nuclear technology, nuclear astrophysics and nuclear structure. However the quality of the existing experimental data nowadays is not sufficient for the various technical and scientific applications and new high precision measurements are necessary to improve the data bases. One key aspect to the success of these high precission measurements is the use of a very pure ion beam that ensures that only the ion of interest is produced. The combination of the IGISOL mass separator with the JYFLTRAP Penning trap is an excellent tool for this type of measurement because of the ability to deliver isobarically and even isomerically clean beams. Another key feature of the installation is the non-chemical selectivity of the IGISOL ion source which allows measurements in the important region of refractory elements. This paper summarises the β-delayed neutron emission studies that have been carried out at the IGISOL facility with two different neutron detectors based on ³He counters in a polyethylene moderator: the Mainz neutron detector and the BEta deLayEd Neutron detector.     

Time-resolved Mössbauer spectra obtained after 57Mn implantation in Si

A new detector system for the coincidence technique between Mössbauer γ-rays and energetic β-rays originating from ⁵⁷Mn has been developed for in-beam Mössbauer spectroscopy using ⁵⁷Mn implantation. This system enables time-resolved Mössbauer measurements of ⁵⁷Fe at various elapsed times after β ^?-decay of ⁵⁷Mn with sufficient quality. We applied this system to the time-dependent measurement of the site distributions of dilute Fe atoms in n-type Si. It was suggested that Fe atoms were already located at substitutional and interstitial positions in Si within a time of about 100 ns after the β ^?-decay of ⁵⁷Mn, and that the occupancy ratio between these positions was hardly dependent on the elapsed time after the β ^?-decay.     

The decay of115 mIn

The decay of^115m In has been investigated using accurate counting methods. The emission rate of conversion electrons plusβ ^?-particles was determined with a 4π proportional flow counter. The total andK-shell internal conversion coefficients of the 336 keVγ-ray in¹¹⁵In were measured by the electron X-ray coincidence method using combinations of a Si surface barrier with a NaI(Tl) detector and of a magneticβ-spectrometer with a high energy resolution Si(Li) detector, respectively. The conversion ratioR=K/(L+M+...) was deduced from electron spectra recorded with the magneticβ-spectrometer. The 336 keVγ-ray emission rate of all used sources was determined with a calibrated NaI(Tl)γ-ray spectrometer. A Ge(Li) detector has been used to determine the relative intensity of the 497 keVγ-ray in¹¹⁵Sn. As results have been deduced the 336 keVγ-ray emission per decay (N _γ1/N ₀=(45.9 ± 0.1)%), the total internal conversion coefficient (α=1.073 ± 0.014), theK-shell internal conversion coefficient (α _K=0.843±0.012), the conversion ratioR=3.63±0.07, theβ ^?-transition per decay going to the ground state (N _β1/N ₀=(5.0 ± 0.7)%) and to the first excited level in¹¹⁵Sn¹¹⁵Sn(N _β2/N ₀=(0.047 ± 0.002)%), and the 497 keVγ-ray emission (N _γ2/N _γ1=(0.103 ± 0.004)%). From the obtained internal conversion data it follows that the 336 keVγ-ray transition is ofM4 character with anE5 admixture of less than (3.5±1.5)%. The half-life of the isomeric state¹¹⁵ mIn has been determined with four different methods. The result isT _1/2=(4.486±0.004) h.     

Isomerism,total decay energies,and absolute γ-ray intensities of the heavy Pd and Ag isotopes

The decays of^{113, 114, 115g, 115m, 116}Pd have been studied with an emphasis on the determinations of total decay energies and absoluteγ-ray intensities. The experiments also provided improved data on these quantities for the decays of^{114, 115g, 115m, 116m}Ag. A search for isomeric transitions using a high resolution electron detector resulted in the identification of isomericE3 transitions in¹¹⁵Pd and^{113, 115, 116, 117}Ag. The isomeric branching was determined in all cases. TheQ _β-values of^113–116Pd and^113–116Ag have been measured using aβγ-coincidence method.     

The beta branching ratio and conversion coefficients in the137Cs decay

The decay of¹³⁷Cs has been reinvestigated using several precision counting methods. The emission rate ofβ-particles plus internal conversion electrons was measured by the 4π-proportional counter method using vacuum evaporated sources free of self-absorption and checked by the liquid scintillation method. TheK-conversion coefficient was determined by the electron X-ray coincidence method using a magnetic spectrometer and a high resolution Si(Li) detector. TheK/(L+M+...) conversion ratio and a second less accurate value for the β-branching ratio were obtained from the recorded electron spectra. Theγ-ray emission rate of all sources was determined to within ±0.14%, on the average, with a calibrated NaI(Tl) crystal detector. As results the intensity of theβ-decay to the ground state of¹³⁷Ba could be determined to (5.4±0.3)% of the¹³⁷Cs decays, theK-conversion coefficient to 0.0916±0.0004, and theK/(L+M+...) conversion ratio to 4.41±0.04. From these values the γ-ray emission intensity is (85.1±0.4)% of the¹³⁷Cs decays and theK X-ray emission intensity is (8.13±0.10)% of the emittedγ-rays. All errors are discussed in detail.     

The alpha-branching ratios of the188,190,192Pb isotopes

Theα-branching ratios (b _α ) of^192,190,188Pb are measured using mass-separated sources. Different experimental set-ups are used — one detector as well as two detector set-ups — thereby detecting theα particles from the parent and/or viaα decay formed daughter nuclei, theβ-delayed gamma radiation from the parent and/or viaβ decay formed daughter nuclei and the Tl KX rays from electron capture decay. Values forb _α of 6.2(6) 10^?5 and 4.0(4) 10^-3 were found for^192,190Pb respectively. For¹⁸⁸Pb, limits on theb _α values were obtained: 0.03<b _α <0.10. A careful analysis of the previously reportedb _α values showed that the discrepancies in theb _α values were not due to inadequate correction procedures, as was suggested, but to experimental uncertainties in the efficiency determination of the different detection set-ups and to an unreliableβ-decay scheme for¹⁸⁸Pb. Theb _α obtained in this work show that the leadα decay is not faster than the Hgα decay and that there is no need to assume a disappearance of theZ=82 shell closure halfway betweenN=82 andN=126.     

Search for charginos,neutralinos and gravitinos in e+e− interactions at s=183 GeV

An update of the searches for charginos and neutralinos is presented, based on a data sample corresponding to the 53.9 pb⁻¹ recorded by the DELPHI detector in 1997, at a centre-of-mass energy of 183 GeV. No evidence for a signal was found. The lower mass limits are 4–5 GeV/c² higher than those obtained at a centre-of-mass energy of 172 GeV. The (μ,M₂) domain excluded by combining the neutralino and chargino searches implies a limit on the mass of the lightest neutralino which, for a heavy sneutrino, is constrained to be above 29.1 GeV/c² for tanβ≥ 1.     

Investigation ofβ + β + andβ +/EC decay of106Cd

A low background scintillation detector with a CdWO₄ crystal of 1.046 kg was used to search forβ ⁺ β ⁺ andβ ⁺/EC processes in¹⁰⁶Cd. For the neutrinoless mode the limits T_1/2(0νβ ⁺ β ⁺)≥2.2·10¹⁹ y and T_1/2(0νβ ⁺/EC)≥5.5·10¹⁹ y were obtained with 90% C.L. For the possible two neutrino decay limits of T_1/2(2νβ ⁺ β ⁺)≥9.2·10¹⁷ y and T_1/2(2νβ ⁺/EC)≥2.6·10¹⁷ y have been determined with 99% C.L.     

Random coincidence of 2<Emphasis Type="Italic">ν</Emphasis>2<Emphasis Type="Italic">β</Emphasis> decay events as a background source in bolometric 0<Emphasis Type="Italic">ν</Emphasis>2<Emphasis Type="Italic">β</Emphasis> decay experiments

Two-neutrino double β decay can create an irremovable background even in high energy resolution detectors searching for neutrinoless double β decay due to random coincidence of 2ν2β events in the case of poor time resolution. Some possibilities for suppressing this background in cryogenic scintillating bolometers are discussed. It is shown that the present bolometric detector technologies enable one to control this form of background at the level required to explore the inverted hierarchy of the neutrino mass pattern, including the case of bolometers searching for the neutrinoless double β decay of ¹⁰⁰Mo, which is characterized by a relatively short two-neutrino double β decay half-life.     

Studies on the energy levels of153Eu following the β−-decay of153Sm

The level scheme of¹⁵³Eu was investigated by observing the gamma-rays following theβ ^?-decay of the 47 h¹⁵³Sm using a high purity Ge(HPGe) detector and a Ge(Li)-Nal(Tl) fast-slow coincidence spectrometer. The energies and relative intensities of about fifty six gamma-ray transitions were determined. Five of them at energies of 124.91, 431.65, 443.24, 487.75 and 623.73 keV were observed and confirmed for the first time in the present singles and/or gamma-gamma coincidence measurements. These new transitions could be fitted into a proposed level scheme of¹⁵³Eu. Theβ ^?-decay branching ratios as well as the log (ft) values were obtained.