Der Zerfall der Cäsiumisotope Cs129 und Cs130

Cs¹²⁹(T_1/2=32 h) and Cs¹³⁰(T_1/2=30 min) were produced by J¹²⁷(α,2n)Cs¹²⁹and J¹²⁷(α,n)Cs¹³⁰reactions, respectively. The γ-ray-spectra from the decays of Cs¹²⁹ and Cs¹³⁰ have been investigated using Li-drifted Ge-counters and scintillation spectrometers. In the decay of Cs¹²⁹15 γ-rays have been observed having the following energies and relative intensities: 95 keV (1.6), 177 keV (1.1), 267 keV (1.7), 278 keV (4.8), 317 keV (7.6), 371 keV (100), 410 keV (69), 511 keV (≦ 0.1), 548 keV (10.5), 587 keV (1.7), 623 keV (0.12), 660 keV (0.07), 864 keV (0.09), 907 keV (0.67) and 948 keV (0.2). The electron capture branching ratios to the ground state and excited states of Xe¹²⁹were determined; logft values for the various decay branches were derived from these ratios. In the decay of Cs¹³⁰twoγ-transitions with the following energies and intensities relative to the β⁺ emission have been found: 535 keV (11) and 585 keV (1.3). A new level at 1122 keV in Xe¹³⁰is proposed.     

Preliminary test results of LAr prototype detector

Liquid argon (LAr) is an attractive target for the direct detection of WIMPs. A LAr prototype detector was designed to study the technology and properties of LAr detectors. The prototype detector had an active volume containing 0.65 kg of liquid argon. A liquid nitrogen (LN) cooling system allowed the temperature fluctuation of the liquid argon to be controlled within less than 0.1 K during a one month run. In the ²²Na calibration run, the LAr prototype obtained 1.59±0.02 p.e./keV light yield for 511 keV gamma rays using a domestic-made argon purification system.     

Erzeugung neuer isomerer Kernzustände durch Kernphotoreaktionen am Antimon und Thallium

The systematic search for new short-lived isomeric states has been continued by irradiation of an additional 32 selected elements with 26 MeV bremsstrahlung. Isomeric transitions were detected using a conventional scintillation spectrometer. Irradiation of antimony led to the production of a new (530±50) μsec isomeric state which decays through emission of partially converted (62±2) keV and (76±3) keV gamma rays. The 530 μsec half-life is tentatively associated with the 136 keV level in Sb¹²². An apparent inconsistency in the previously proposed level scheme of Sb¹²² can be removed if the 3.5 min Sb¹²²-activity is assigned to an isomeric level in Sb¹²² lying less than 15 keV above the 136 keV isomeric state. A new measurement of the half-life of this level yielded a value of (4.1₅±0.2) min. Another new isomeric state with a (2.l±0.2) msec half-life was produced by irradiating thallium. The isomeric state decays by emission of two gamma rays of (335±8) keV and (597±12) keV which were found to be in coincidence. Irradiation of erbium led to the production of a short-lived isomeric transition which may be identical with a previously reported Ho-isomer. Results are discussed in the appendix.     

The decay of 20 min179Re

The decay of 20 min¹⁷⁹Re has been studied by means of Ge(Li) and Si(Li) detectors and a magneticβ-ray spectrometer. From the measured positon endpoint aQ-value of 2690±50 keV has been deduced. The decay scheme given is supported by coincidence relations. Fast beta transitions (logft≈5.1) to levels at 720keV and 1680 keV in¹⁷⁹W can be explained by a three quasi-particle character for these states. Nilsson assignments to these and other levels are discussed.     

PräziseQ β -Wert-Messungen mit einem Intrinsic-Germanium Detektor an leichten,neutronenreichen Spaltprodukten

An intrinsic Germanium detector of 10 mm depth and 300 mm² sensitive area has been used to determineβ-endpoint energies for Rb, Sr and Y fission products. It was calibrated with monoenergetic electrons supplied by a magnetic conversion electron spectrometer for the energy range from 1.6 to 8 MeV. The energy calibration of the detector is linear with deviations less than 2 · 10^?4, and the detector was recalibrated daily using precisely known gamma rays of⁹⁰Rb. At the on-line fission product separator OSTIS at the ILL, Grenoble the endpoints ofβ-singles-spectra have been determined andQ-values deduced if possible also from beta-gamma coincidence measurements. The obtainedQ-values are:⁸⁸Rb:(5 318±4) keV,⁸⁹Rb: (4 510 ± 8) keV,⁹⁰Rb: (6 578 ± 15) keV,⁹¹Rb: (5 857 ± 8) keV,⁹¹Sr: (2 704.5 ±3) keV,⁹²Rb: (8 111 + 15) keV,⁹³Rb:(7 485 ± 15) keV,⁹⁴Rb: (10 304 ± 30) keV,⁹⁴Sr: (3 512 ± 5) keV,⁹⁴Y: (4 920 ±5)keV,⁹⁵Rb: (8 947 ±100) keV,⁹⁵Y: (4 445±5) keV,⁹⁶Rb: (11 303±250) keV,⁹⁶Sr: (5 413±20) keV,⁹⁶Y: (7 120 ±50) keV,⁹⁷Rb: (10 020 ±50) keV.     

Radioactive decay of Os191 and Os191m

Beta and gamma spectra of Os¹⁹¹ were studied using a magnetic double-focusing beta-spectrometer and a scintillation spectrometer. The isomeric state Os^191m decays through the 74·4 ± 0·1 keV (E3/M4=50) transition with a half-lifeT _1/2=13·0 ± 0·5 hours. A continuous beta spectrum withE _max=147 ± 3 keV and the gamma transitions 41·83 ± 0·05 keV (E3), 82·5 ± 0·3 keV and 129·4 ± 0·1 keV (70%M1 + 30%E2) were observed in the decay of the ground state of Os¹⁹¹. The conversion coefficient of the last transition was determined as 1·94 ±± — 0·10. Gamma transitions with energies of 47 keV and 185·8 keV were not observed.     

Lifetimes of bound states in 15O

The lifetime values of 8.2 ± 1.0, > 3000, < 2.5, 16.0 ± 2.5 and 750 ± 200 fs for the first, second, third, fifth and sixth bound states in ¹⁵O, at 5183, 5241, 6176, 6859 and 7276 keV, respectively, were determined with the DSA method through the ¹⁴N(p, γ)¹⁵O reaction. The experimental correction factors of the nuclear and electronic stopping powers were used in the DSA analysis. In the calculations the Monte Carlo method was employed. The transition strengths are discussed in terms of shell-model calculations.     

The g-factor and lifetime of the 3− (298 keV) state in 16N

The g-factor of the 3^? (298 keV) state in ¹⁶N has been measured by observing the hyperfine modulation of the γ-ray anisotropy in one-electron ions recoiling in vacuum following the ²H(¹⁵N, p)¹⁶N reaction. From the observed spatial frequency the g-factor was deduced to be |g| = 0.532±0.020. Simultaneous lifetime determinations for this state and the 1^? (397 keV) state in ¹⁶N gave values of τm = 131.7±1.9 ps and τ_m = 5.63±0.05 ps, respectively. These and other electromagnetic observables associated with the lowest four levels in ¹⁶N are compared to shell-model calculations.     

Measurement of the electron capture branching ratio of 7Be using internal bremsstrahlung

The branching ratio in the electron capture of ⁷Be to the 478 keV excited state of ⁷Li has been measured using the internal bremsstrahlung from decays to the ground state. Comparison of the intensity of this bremsstrahlung in the region from 515–862 keV with the intensity of the 478 keV γ-ray yields a value of (10.9 ± 1.1)% for the branching ratio. This result is consistent with the accepted value of (10.38 ± 0.06)% but not with a recent measurement of (15.4 ± 0.8)%.     

A New Approach to Determining the Content and 15N Abundance of Total Dissolved Nitrogen in Aqueous Samples: TOC Analyser-QMS Coupling

Abstract

The standard method for determining the ¹⁵N abundance of total dissolved nitrogen (TDN) in aqueous samples (e.g., soil leachate, sewage, urine) is currently Kjeldahl digestion followed by steam distillation or diffusion to isolate the ammonium, and then ¹⁵N measurement using IRMS. However, this technique is both time-consuming and laborious. One way of overcoming these disadvantages could be to couple a TOC analyser to determine the TDN with a sufficient quadrupole MS to determine the ¹⁵N abundance. The highTOC analyser (Elementar Analysensysteme Hanau, Germany), which catalytically oxidises the sample's total nitrogen with a high, constant yield to nitrogen monoxide (NO), appeared particularly suitable. The quadrupole-MS ESD 100 (InProcess Instruments Bremen, Germany) proved to be a suitable mass spectrometer for the ¹⁵N determination of NO. This combination of instruments was found to provide a workable method in numerous measurements of standard and actual samples. The detection limit concerning the N amount required per analysis is 2 μg, corresponding to an N concentration of 0.7mg/l in a maximum sample volume of 3ml. Depending on the N concentration, ¹⁵N abundances starting from 0.5 at.% can be measured with the required precision of better than 3% (simple standard deviation). For example, measuring the abundance of 0.5 at.% requires about 50 μg N, whereas for 1 at.% or more only about 5 μg N is needed per analysis.     

PräziseQ β -Wert-Messungen mit einem Intrinsic-Germanium-Detektor an schweren,neutronenreichen Spaltprodukten

An intrinsic germanium detector was used to measure the beta endpoint energies of heavy fission products supplied by the on line mass separator OSTIS installed at the high flux reactor of the Institut Max von Laue-Paul Langevin, Grenoble. The endpoints of singles-spectra have been determined and, by means of beta-gamma coincidence measurements also most of theQ _β-values of the following neutron-rich nuclides could be deduced with high accuracy:¹³⁸Cs: (5388±25)keV,¹³⁹Cs: (4213±5)keV,¹³⁹Ba: (2336±25)keV,¹⁴⁰Cs: (6220±15)keV,¹⁴¹Cs: (5252+15/-60)keV,¹⁴¹Ba: (3208±35)keV.¹⁴²Cs: (7329±20)keV,¹⁴³Cs: (6287+40/-250)keV,¹⁴³Ba: (4259±40)keV,¹⁴⁴Cs: (8451±30)keV,¹⁴⁵Cs: (7358±70)keV.¹⁴⁶Cs: (9300±900)keV,¹⁴⁶Ba: (4280±100)keV.¹⁴⁶La: (6175±100)keV. The results are compared with experimental results of direct mass measurements and some predictions by mass formulae.     

The beta decay of 18N and T = 2 states of mass 18

The ¹⁸N(β^?)¹⁸O decay was observed via the ⁹Be(¹⁸O, p2α)¹⁸N reaction, utilizing helium-transport techniques and Ge(Li) spectroscopy. In addition to the previously reported β-decay to the ¹⁸O 4456 keV level (J^π = 1^?) branches were observed to levels at excitation energies (in keV) of 1982 (J^π = 2⁺). 5530(2^?), 6198(1^?). 6350(2^? or 1⁺), 6880(0^?), and 7771(2^?). The percentage β-branches, in order of increasing excitation energy, are 3.9 ± 1.5, 54.6 ± 1.0, 3.1 ± 0.4, 1.4 ± 0.2, 2.2 ± 0.3, 14.8 ± 0.8 and 5.0 ± 0.5. respectively, with 15 % assumed on the basis of calculations to proceed to non-γ-emitting states. These measurements allow definite assignments J^π = 1^? for the ¹⁸N ground state and J^π = 0^? for the ¹⁸O 6880 keV state. Additional measurements determine the ¹⁸N half-life to be T_{1 2} = 624 ± 12 ms. A shell-model calculation for mass 18 was carried out in a full 1?ω basis. The predictions for the T = 2 energy level spectrum and for ¹⁸N β-decay are discussed.     

Elektroneneinfang beim Zerfall des Ti45

Electron capture to the 718 keV, 1238 keV, 1408 keV and 1665 keV excited states of Sc⁴⁵ have been observed in the decay of Ti⁴⁵. The branching ratios were determined to be (0,4±0,04)% (0,05±0,02)%, (0,27±0,03)% and (0,08±0,01)% per decay of Ti⁴⁵ respectively.     

Phase analysis of a nitrogen implanted CrNi 18.9 steel: A cems-study

Conversion Electron Mössbauer Spectroscopy (CEMS) has been used to study the modified structure of the near surface region of a nitrogen implanted austenitic X10CrNiTi18.9 steel. The implantation dose was varied from 2 to 8*10¹⁷N⁺/cm² using an implantation temperature of 200°C and an ion energy of 100 keV. The (γ/a′)-ratio in the near surface region of the untreated material was changed by electropolishing and mechanical polishing of the surface. The results of the spectra are discussed in terms of nitrogen solid solution in the case of low nitrogen doses and precipitation of Fe-nitrides (ε-Fe₂N, ε-Fe_2+xN) with increasing implantation dose. Phase transformations referring to the Fe-nitrides and the (γ/a′)-ratio are observed with increasing nitrogen content.     

High resolutionL- andM-subshell internal conversion studies of low energy transitions in149Sm and151Eu

The internal conversion subshell intensities of the (21.529±0.014) keV transition in¹⁵¹Eu and the (22.494±0.011) keV transition in¹⁴⁹Sm have been determined in a high resolution investigation using a double-focussing iron-core spectrometer. The subshell ratios yielded unambiguousM1+E2 multipole mixtures for both transitions. δ²(E2/M1) for the 21.53 keV transition was determined to be (8.8±0.7)·10^?4 and for the 22.49 keV transition to be (5.5±1.2)·10^?3.     

A new isotope andα-lines in the Th-Np region and their production cross-sections

In the fusion reactions of^20,22Ne with²⁰⁵Tl,²⁰⁸Pb, and²⁰⁹Bi the absolute production cross-sections of the²²⁷Np,^222–224Pa,^222–224Th, and²²¹Ac isotopes were measured and the products of the xn evaporation channels and theirα-decay properties were investigated. The identified isotope is²²⁷Np (7680±10 keV). A newα-line structure of²²⁴Pa was established (7460±10 keV (25±3 %) and 7555±10 keV (75±3 %)). Fourα-lines of²²³Th were identified (7290±10 keV (41±5 %), 7320±10 keV (29±5 %), 7350 ± 15 keV (20±5 %), and 7390±15 keV (10±4 %)). The half life of²¹⁷Fr was measured to be 16±2 μs and that of²²⁰Ra was found to be 17 ±2 ms.     

对40Ca9.5—10.5MeV能区内几组核能级宽度的测量

本文介绍了用γ共振吸收法测量⁴⁰Ca 9603.9keV,10321.0keV两组能级和9864.6,9868.8keV一组双重态能级的能级宽度,选用³⁹K(p,γ)反应所放出的γ射线激发相应的⁴⁰Ca吸收核能级。对于9603.9keV,10321.0keV的能级宽度,这里给出了比较精确的结果,相应的能级宽度分别为Γ=188±47eV,Γ=91±15eV。对于9864.6,9868.8keV能级,结果为Γ=100±24eV,Γ=899±214eV,由于⁴⁰Ca 9864.6,9868.8keV两能级靠得很近,因此这里用γ共振吸收法测量它们的能级宽度与以往有所不同,将同时有两组γ射线用来激发同样两个能级而发生交叉激发。我们对相应的实验处理方法作了推广。此外,用(p,γ)共振产额法测量了⁴⁰Ca 9603.9keV,10321.0keV能级宽度,得到了与γ共振吸收法一致的结果。本文还对⁴⁰Ca 9603.9keV,10321.0keV能级的(p,γ)共振强度S_pγ、同位旋T等进行了讨论。 关键词：     

In-depth modifications of implanted amorphous carbon films

Amorphous carbon films (a-C:H) and nitrogen incorporated carbon films [a-C:H(N)] deposited by a self-bias glow discharge have been implanted with 70 keV nitrogen ions at fluences of 0.6, 1 and 2×10¹⁷ N/cm². The in-depth modifications caused by ion implantation were determined by means of nuclear techniques, such as Rutherford Backscattering Spectrometry (RBS), Nuclear Reaction Analysis (NRA) and Elastic Recoil Detection Analysis (ERDA), as well as by Auger Electron Spectroscopy (AES) and Raman scattering. ERDA profiles show that nitrogen implantation causes hydrogen depletion, the amount of which depends on the film composition and on the ion fluence. In a-C:H(N) films nitrogen loss was also measured. The induced structural modifications in both a-C:H and a-C:H(N) films were followed by both AES, using factor analysis, and microprobe Raman spectroscopy. They turn out to be related to the energy deposited by the incident ions. Our results indicate that the ion-beam bombardment causes in both a-C:H and a-C:H(N) films an increase of either the degree of disorder or the ratio between sp²/sp³ bonds across the hydrogen-depleted layer, which depends on the ion fluence.     

The study of the width for intermediate resonances in the 27Al(d,p)28Al, 27Al(d, α)25Mg, 31P(d,p)32P and 31(d, α)29Si reactions

The protons and α-particles from the reactions ²⁷Al(d, p)²⁸Al(d, α)²⁵Mg, ³¹P(d, p)³²P and ³¹P(d, α)²⁹Si were measured and analyzed with the channel cross correlation function and auto-correlation function to determine the correlating numbers N_d and average width 〈Γ_μ〉. With these values, the theoretical intermediate widths were calculated to be 119 ± 30 keV in the ²⁹Si nucleus and 249 ± 46 keV in the ³³S nucleus, which were in good agreement, within the errors, with the present experimental results of 185 ± 37 keV in ²⁹Si and 204 ± 24 keV in ³³S.