Measurement of some gamma-ray energies suitable for routine energy calibration

The energies of several gamma-ray transitions have been measured using a Ge(Li) spectrometer. The isotopes and the corresponding transition energy measurements in keV are ¹⁴¹Ce(145.44±0.05), ¹³⁹Ce(165.85±0.05), ⁵¹Cr(320.07±0.05), ⁷Be(477.57±0.05), ⁸⁵Sr(513.95±0.07), ⁹⁵Nb(765.83±0.07), ⁵⁴Mn(834.84±0.07), ⁴⁶Sc±889.25±0.07, 1120.50±0.07), ⁸⁸Y(898.01±0.07, 1836.08±0.07), ⁹²Nb(934.51±0.07), ²⁰⁷Bi(1063.63±0.07), ⁶⁵Zn(1115.51±0.07) and ²²Na(1274.52±0.07).     

The energy levels of Al

The energies and strengths of ²⁵Mg(p, γ), ²⁵Mg(p, p₁) and ²⁵Mg(p, p₂) resonances were determined in the energy range E_p < 2 MeV. Four new (p, γ) resonances were observed at E_p = 736.2±0.7, 818.1±0.7, 834.6±0.7 and 1514.7±0.7 keV. The γ-decay of 44 resonances and 49 bound levels was established. The energies of 41 and mean lifetimes of 25 bound levels were determined. Two new levels at E_x = 4952.4±1.4 keV and 5141.7±2.0 keV were observed. Angular distributions yielded unique spins for five resonance levels. Weisskopf estimates allowed unique spin assignments for five resonances. The Q-value of the ²⁵Mg (p, γ) ²⁶Al reaction was found to be 6305.0±1.2 keV.     

The decay of 23.0 min Rb to levels in Kr

The radioactive decay of ⁷⁹Rb(23.0±0.5 min) has been studied with the aid of semiconductor radiation detectors. Both singles and coincidence spectra have been recorded. The decay energy: 3520±45 keV was determined by measuring the endpoint of the positon spectrum in coincidence with prominent γ-rays. A decay scheme is proposed incorporating most of the measured γ-rays. The following energies in keV and parities of levels are assigned: ground state ( ), , , , , 383.71±0.18, 532.82±0.33, 688.21±0.09, , 934.0±1.4, 1089.4±0.4, 1474.7±0.3. The spin and parity of the ⁷⁹Rb ground state is most probably .     

Inhibited transitions and isomeric states in the N = 50 isotones

Measured E2 transition rates in the N = 50 isotones (⁹⁰Zr–⁹⁴Ru) are satisfactorily reproduced by a shell model 0699 0 with proton configurations (p_1/2g_9/2)ⁿ. The inhibited 8⁺→6⁺ E2 transition in ⁹⁴Ru and its connection with seniority mixing is discussed. Isomeric states are predicted in ⁹¹Nb and ⁹³Tc. 0699     

Energy levels of Si

Proton energies and strengths of (p, γ), (p, p₁), (p, p₂) and (p, ₁γ) resonances of the ²⁷Al + p reaction were determined for E_p < 2.5 MeV. The γ-decay of 78 resonances and 46 bound levels was established and four new bound levels were found at E_x = 9793.8±2.0, 10513.5±1.0, 10884.1±2.0 and 11778.8±1.5 keV. The level at E_x = 11.43 MeV was found to be a doublet. Lifetimes of 25 bound levels were measured by means of the Doppler-shift attenuation technique. Angular distributions were measured at 15 resonances.     

The decay of Sc and V

The decays of ⁴⁸Sc and ⁴⁸V have been studied with Ge(Li) diodes, scintillation spectrometers and a double focussing beta-ray spectrometer. The 3507 keV level, from which originates the quadruple cascade (9.4±0.5)% in the ⁴⁸Sc decay, is also de-excited by a 1212 keV cross-over transition to the 2295 keV (4⁺) level and supports the assumption, that the 3507 keV level has a spin 6⁺. The first member of the reported triple cascade in the ⁴⁸V decay is shown to be a doublet of 928.9±0.7 (1.2±0.2)% and 944.3±0.5 keV (8.0±0.5)% gamma rays, both followed by the 1311.4–983.3 keV cascade. Evidence was found, that the 2421 keV (2⁺) level is excited by weak gamma rays from high-energy levels. The K/β⁺ ration in the ⁴⁸V decay is 0.69±0.05 The Q-values of ⁴⁸Sc and ⁴⁸V are calculated to be 3986±7 keV and if 4015±4 keV, respectively. The energy of the gamma ray of ⁴⁷Sc, which is present as an impurity, is 159.2±0.5 keV.     

Alpha decay of Cm

An enriched sample of ²⁴⁷Cm (99.4 %) has been used to investigate the -decay scheme of ²⁴⁷Cm. Seven -groups with energies and intensities 5.265 (13.8 %), 5.210 (5.7 %), 5.145 (1.2 %), 4.983 (2.0 %), 4.941 (1.6 %), 4.868 (71.0 %) and 4.818 (4.7 %) were observed. Gamma-singles and γ coincidence spectra showed the presence of 278.0, 287.5, 346.0 and 402.4 keV γ-rays. A two-parameter coincidence experiment established that the sources of the 402.4 and the 287.5 keV γ-rays were 4.868 and 4.983 MeV -groups, respectively. The multipolarity of the 287.5 keV transition was found to be M1. The K conversion coefficient of the 402.4 keV γ-ray indicates an E1 multipolarity for this transition. The levels at 287.5 and 402.4 keV have been assigned to the and Nilsson states, respectively. The half-life of ²⁴⁷Cm was found to be (1.56±0.05) ×10⁷ y from the pulse analysis and mass spectrometric analysis of the sample.     

关于93Mo中21/2+晕阱的来源(英文)

本研究通过壳模型计算研究了N=51的同中子素91Zr、93Mo和95Ru中高自旋晕态21/2+的同核异能态现象。计算发现,低角动量的p_1/2轨道上的质子是仅在93Mo中存在21/2+晕阱的主要原因。同时,本工作还研究了N=52的同中子素92Zr、94Mo和96Ru中10₁+-12₁+能级结构的系统性,发现94Mo中的10₁+-12₁+能级间隙相对最小,考虑到与93Mo的17/2₁+-21/2₁+能级相似的组态,这一结果为93Mo中出现21/2+晕阱提供了补充性的论证。Isomerism of the high-spin yrast 21/2+ states of the N=51 isotones 91Zr, 93Mo and 95Ru has been investigated using the shell model calculations. It is found that the low-j πp_1/2 is responsible for the only yrast trap in 93Mo. In addition, the relatively smaller 10₁+-12₁+ level spacing in 94Mo has been found by investigating the systematics of the 10₁+-12₁+ level structures in the N=52 isotones 92Zr, 94Mo and 96Ru. This result provides a supplementary argument to the origin of the 21/2+ yrast trap in 93Mo from the viewpoint of the similarity between the configurations of 10₁+-12₁+ states in 94Mo and those of 17/2₁+-21/2₁+ states in 93Mo.     

The decay of 91 min As

The energies and relative intensities of γ-rays following the β-decay of ⁷⁸As (and ⁷⁶As) to levels in ⁷⁸Se (and ⁷⁶Se) have been measured using an 8 cm³ Ge(Li) spectrometer. The β-decay of ⁷⁸As has been measured using a superconducting magnet beta-ray spectrometer with two 3 mm thick Si(Li) detectors. These data plus β-γ and γ-γ coincidence results have been used to construct a level scheme with 18 excited levels in ⁷⁸Se. The half-life of ⁷⁸As was measured to be 90.7±0.2 min.     

The decay scheme of Ag

The γ-radiations following the decay of ¹¹²Ag have been studied with Ge(Li) detectors. The ¹¹²Ag half-life has been measured as 3.16±0.02 h; twenty gamma radiations ranging in energy from 606.7 keV to 2829.6 keV have been observed.

Gamma-gamma coincidence measurements have been performed with Ge(Li) and NaI(Tl) detectors. A decay scheme consistent with the present data is proposed.     

Collective properties of Cr

The mean lifetimes of levels below 3 MeV excitation in ⁴⁹Cr were measured using the reaction ⁴⁹Ti(, nγ)⁴⁹Cr. The Doppler-shift attenuation method was used in a neutron-gamma coincidence measurement. The lifetime of the first excited state was determined with the recoil distance method. The results are : 272 keV, 19±5 ps; 1085 keV, 260±90 fs; 1563 keV, 590₋₁₂₀⁺³⁰⁰ fs; 1704 keV, > 5.5 ps; 1742 keV, > 4 ps; 1982 keV, > 6.5 ps; 2169 keV, > 4.5 ps; 2433 keV, > 6 ps; 2504 keV, < 12 fs; 2614 keV, 65 ±20 fs. The lifetimes of the second and third excited states in combination with known multipole mixing ratios gave evidence for spin assignments of for the 1085 keV level and for the 1563 keV level. The energies and spins of the four lowest levels as well as the B(M1) and B(E2) values of their γ-decays are in good agreement with calculations based on the strong coupling model and suggest that these levels are strongly collective. Dipole transitions of the higher levels to the ground and first excited states are highly retarded.     

Two-quasiparticle states in Ho

Thirty-one levels in ¹⁶⁴Ho have been observed up to an excitation energy of 994 keV utilizing 12 MeV deuterons and the reaction ¹⁶⁵Ho(d, t)¹⁶⁴Ho. The ground state Q-value was determined to be −1730±15 keV. The spectrum has been interpreted in terms of the coupling of the [523↑] Nilsson proton orbital with the neutron orbitals prominent in the (d, t) spectrum of ¹⁶³Dy. Based on this interpretation, the singlet-triplet splitting energies for the [523↓], [642↑], [521↑], [402↓] and [400↑] neutron orbitals coupled to the [523↑] proton orbital were determined to be −144, +67, +171, −85 and +102 keV, respectively. Theoretical calculations of these energies made for a zero-range spin-dependent central potential gave values of −248, +74, +160, −82 and +73 keV, respectively.     

The decay of Ho and Ho

The disintegration characteristics of ^164mHo and ^164gHo have been studied using a high-resolution Ge(Li) spectrometer. Radioactive samples of ^164mHo and ^164gHo were obtained through the (n, 2n) reaction on spectroscopically pure holmium oxide with 14 MeV neutrons. The isomeric cross-section ratio for the yields of the ground and metastable states has been estimated to be 1.0±0.25. Gamma rays of 37.7 and 56.1 keV energy have been assigned to the decay of ^164mHo and 73.4 and 91.5 keV γ-rays are attributed to the decay of ^164gHo by electron capture and negaton emission, respectively. The branching ratio for the electron capture decay of ^164gHo to the levels in ¹⁶⁴Dy has been estimated accurately from the analysis of X-ray intensities. The results have been incorporated into a decay scheme.     

Cross sections for several (n, 2n) reactions at 14 Mev

Precision measurements of the cross sections of the (n, 2n) reactions to produce ^44mSc, ⁸⁸Y, ⁸⁹Zr, ⁹²Nb, ¹⁵⁰Eu(35y), ¹⁶⁸Tm, ^174m+gLu and ¹⁹⁶Au were made for a range of neutron energies from 13.7 to 15.0 MeV. The samples were irradiated at various positions on the surface of a 20 cm radius sphere centered at the ²H–³H neutron source. This allowed a range of neutron energies to be obtained with good energy resolution. The ²⁷Al(n, )²⁴Na reaction was used to monitor the neutron fluence in the target samples. Particular attention was given to the accurate measurement of the (n, 2n) products, using calibrated Ge(Li) and NaI(Tl) detectors. An uncertainty of about ±5% is assigned to the results, except those for ¹⁵⁰Eu and ¹⁷⁴Lu, which have an additional uncertainty in their decay schemes.     

The Fermi matrix elements inferred from β-γ(CP) correlation measurements in Fe decay

Measurements have been made of the β-γ circular-polarization correlation paramter A for the 273 keV β-branch in the decay of ⁵⁹Fe. It has recently been established that each of the principal β-branches of ⁵⁹Fe involves ΔJ=0 and thus has a possible non-zero Fermi matrix element M_F which can be determined from the ƒt value and A. Previous β-γ (_CP) measurements on this nucleide have all employed the usual γ-ray scattering technique. This method is suitable for the 475 keV β-branch but does not produce an accurate measurement of the lower energy branch because of energy discrimination difficulties. A transmission polarimeter with γ-discrimination has been used in the present work to obtain clean data on the 273 keV β-1.29 MeV γ-cascade. Calibration with ⁶⁰Co (1.33 MeV) and ²⁸Al (1.79 MeV) yielded A = −0.154±0.023. This gives for the isospin impurity coefficient and the effective Coulomb matrix element of the 1.29 MeV state (1.1±1.4) × 10⁻³ and 9±11 keV, respectively.     

Decay of the 55 min and 12 min Te isomers

Gamma rays emitted in the decay of the ¹³³Te isomers, 55.4 min ^133mTe and 12.5 min ^133gTe, have been observed with Ge(Li) detectors. Sources were prepared by separating Sb from fission products, allowing several minutes for decay of 2.7 min ¹³³Sb and then separating the Te daughter activities. A total of 29 γ-rays between 312 and 2541 keV were attributed to decay of ^133gTe and 30 from 74 to 2050 keV to that of ^133mTe. Gamma-gamma coincidences in the decay of ^133gTe were observed with a NaI(Tl)---Ge(Li) set-up. The decay scheme of ^133gTe was constructed, involving placement of 25 of the γ-rays emitted. The decay of ^133gTe populates levels in ¹³³I at 0, 312, 720, 787, 1313, 1333, 1374, 1565, 1718, 2137, 2194 and 2541 keV. The decay of ^133mTe is very complicated, and we have not attempted construction of a complete decay scheme for it; however, levels at 913 and 1561 keV in ¹³³I are definitely populated in ^133mTe decay. The value for Q_β of ¹³³Te was measured as 3.52±0.10 MeV. The low-lying levels of the odd-mass iodine isotopes vary smoothly through the series ¹²⁵I through ¹³³I. The levels of ¹³³I are fitted rather well by predictions based on quasi-particle-phonon coupling.     

High-resolution gamma-ray spectroscopy of ΛLi

We report on the first observation of hypernuclear γ transitions using germanium detectors. Using a large-acceptance Ge detector system, we observed two γ transitions in _Λ⁷Li, the spin-flip transition at 689±4keV and the transition at 2050±2 keV (preliminary). The strength of the ΛN spin-spin interaction is derived from the energy of the former transition. As for the latter transition, B(E2) was measured to be 3.9±0.6±0.4 e²fm⁴ (preliminary), which indicates a shrinkage of the nuclear size of _Λ⁷Li from ⁶Li and confirms “glue-like role” of Λ.     

Polarisation circulaire du rayonnement gamma de Sb, Cs et Ag

The βγ circular polarization correlation of the 3⁻(β⁻ 621 keV)3⁻(γ 1692)2⁺ cascade in ¹²⁴Sb, the 4⁺(β⁻ 662)4⁺ (γ 796)2⁺ (γ 605)0⁺ in ^13Z4Cs and the 6⁺(β⁻529)6⁺ (γ 937)4⁺ (γ 885)2⁺ (γ 658)0⁺ in ^110mAg have been studied by using a Compton effect polarimeter. The measured asymmetry parameters are 0.172±0.004, −0.0702 ±0.0024 and 0.0549±0.0013 respectively.     

Quadrupole interactions in pionic and muonic tantalum and rhenium

The hyperfine splitting of pionic and muonic X-rays in natural Re has been studied using the known ratio (accurate to 1.6 parts in 10⁵) of the quadrupole moments of the two naturally occurring ¹⁸⁵Re and ¹⁸⁷Re isotopes. From the hyperfine splitting of the ⁵g → 4f and 4f → 3d pionic X-rays the effective quadrupole hyperfine constants were determined to be ¹⁸⁷A₂^eff(4f) = 1.163 ± 0.010 keV and ¹⁸⁷A₂^eff(3d) = 5.39 ± 0.63 keV, giving strong interaction quadrupole shifts ₂(4f) = 46 ± 10 eV and ₂(3d) = 1.3 ± 0.6 keV. The strong interaction monopole shifts ₀ and widths Γ₀ of the 5g, 4f and 3d levels have also been measured. For the two higher orbits, standard optical-potential calculations fit the measured shifts and widths quite well. The observed deeper-lying 3d state, however, has shifts and widths that differ by a factor of 2 or more from the predictions. From the measured quadrupole hyperfine constants of the 4f level we calculate the spectroscopic quadrupole moments to be ¹⁸⁷Q^μ(gm) = 2.09 ± 0.04 b, ¹⁸⁷Q^π = 2.07 ± 0.02 b, ¹⁸⁵Q^μ = 2.21 ± 0.04 b, and ¹⁸⁵Q^π = 2.1 addition, muonic X-rays from ¹⁸¹Ta were observed; using the same methods for determining the quadrupole moment as above, a value of ¹⁸¹Q^μ = 3.28 ± 0.06 b was obtained, in good agreement with earlier published data.