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.     

Beta and gamma decays of J π = 1+, 24mAl state

A β-γ spectroscopy of the J ^π , 426 keV isomeric state of ²⁴Al (^24m Al) has been carried out by using a ²⁴Al secondary beam with high purity and high isomeric ratio. From the absolute γ-ray and β-particle intensities observed in the decay of the isomeric state, the branching ratio R _B of the isomeric γ decay from ^24m Al to the J ^π = 4⁺, ground state of ²⁴Al have been derived. The obtained R _B value of 69.6(7)% is much smaller than the previously accepted value of 82.5(30)%. The precise half-life for the isomer decay, T _1/2 ^m = 130.9(13) ms, has been also determined in this experiment. Accordingly, the M3 γ-decay strength B(M3) of the ^24m Al decay becomes smaller and the total β-decay branching ratio becomes larger. In particular, the β-decay branching ratio to the ground state of ²⁴Mg becomes 24.3(9)%, which is 2.4 times larger than the previous value of 10.1(28)%. By combining the branching ratio and the half-life, the Gamow-Teller (GT) transition strength B(GT) of 0.0194(7) is deduced for the GT transition from ^24m Al to the J ^π = 0⁺, ground state of ²⁴Mg. This value is in good agreement with the values derived from charge-exchange reactions.     

High-spin states in106Cd

Levels of¹⁰⁶Cd, populated by¹⁰⁴Pd(α, 2nγ)¹⁰⁶Cd have been studied measuring direct and delayedγ-ray spectra,γ-γ coincidences andγ-ray angular distributions. A decay level scheme is proposed including states up to 4659.8 keV. IntenseE2 transition cascades have been observed. The half-life of an isomeric level located at 4659.8 keV has been measured:T _1/2= 62±6ns. Nuclear Reactions ¹⁰⁴Pd(α, 2nγ),E _α=31MeV; measuredE _γ,I _γ,γ-γ coinc, σ(θ)T _1/2.¹⁰⁶Cd deduced levels,J, π, Enriched targets. Ge(Li) detectors.     

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.     

In beam gamma spectroscopy of62Zn

The decay scheme of⁶²Zn has been investigated by studying the yield functions, angular distributions and coincidence relation-ships of theγ-rays emitted in the⁶³Cu(p, 2nγ) and⁶⁰Ni(α, 2nγ) reactions. Spins up to7? were assigned to the observed states. Nuclear Reactions ⁶⁰Ni(α, 2nγ)⁶²Zn,E _α=28–35 MeV and⁶³Cu(p, 2nγ)⁶²Zn,E _p = 22–31 MeV; measuredE _γ,I _γ(θ),I _γ(E _p , andI _γ,E _α-γ coincidences,⁶²Zn deduced decay scheme. Enriched target, Ge(Li) detectors.     

Evidence for anI=1 isomeric state in96Rb

Aβ-RADOP (β-Radiation Detected Optical Pumping) experiment on the short lived (T _1/2=203 ms)⁹⁶Rb isotope has been performed at the on line mass separator for fission produced alkali isotopes at the TRIGA reactor in Mainz. Irradiation of r.f. onto the polarized sample to induce Zeeman transitions resulted in two signals for nuclear spinsI=2 andI=1. The previously undetermined component withI=1 is interpreted as evidence for an isomeric state in⁹⁶Rb.     

Gamma and Alpha decay from the 2.1-msec isomer213m Ra

The isomer^213mRa was produced by the reaction²⁰⁹Bi(¹⁰B, 6n), as well as by bombardments of¹²C on Pb isotopes,¹⁴N on Bi, and¹⁶O on natural Hg, with projectile energies in the range 60–100 MeV. The isomer decays with a halflife of 2.1 ms both via gamma internal transitions and via alpha branching to levels in²⁰⁹Rn. A level scheme is proposed in which the isomeric state is assigned as either 17/2^? or 13/2⁺ with shell-model configurations either of theh _9/2 protons coupled to ap _1/2 neutron hole, or of an uncoupledi _13/2 neutron hole. On the basis of alpha decay rate predictions from the new Fliessbach theory, the 17/2^? isomeric assignment is to be preferred. Phys. Abstracts classifications 4.200–4.375 E [Radioactivity^213m Ra [from²⁰⁹Bi(¹⁰B, 6n),^204-6Pb(¹²C, 3n–5n) etc.,E=60–100 MeV]; measuredE _α ,E _γ ,I _α ,I _γ ,I _x ,γγ-coin,xγ-coin,α _K,T _1/2.²¹³Ra,²⁰⁹Rn deduced levels,J, π,γ-multipolarity.]     

High spin states in77Se populated by the74Ge(α,n γ) reaction

⁷⁷Se has been investigated by the reaction⁷⁴Ge(α,nγ) at 14 MeV. Gamma singles spectra, gamma angular distributions and gamma-gamma coincidences have been taken. A level scheme has been established, spins and parities have been assigned. States of a rotational band on the 1/2^? ground state, a rotational band on the 5/2^? 249.7 keV state and an anormal band have been identified. Nuclear Reaction ⁷⁴Ge(α,n γ)E _α=14 MeV; measuredE _γ ,I _γ ,γ-γ-Coin.,γ-ang. distr.⁷⁷Se deduced levels,J, π. Enriched target, Ge (Li).     

Spin assignment for the 4.28 MeV level in48Ca by means of the48Ca (p,p′γ) reaction

The gamma decay mode and the possible spin values of the second excited state of⁴⁸Ca (E _x =4.28 MeV) were investigated by studying the⁴⁸Ca(p, p′γ) reaction at an incident proton energy of 10.30 MeV. No ground state gamma transition was observed. The analysis of thep ₂ -γ angular correlation — using method II of Litherland and Ferguson — supports the spin assignmentI=0 for this level and excludes all spin values higher thanI=1.     

The Q-value and decay properties of114Ag

The decay of mass separated¹¹⁴Ag has been studied withβ- andγ-ray spectroscopy. The totalβ-decay energy has been accurately determined to (5.16±0.11) MeV using aβγ-coincidence technique. A detailed decay scheme has been constructed.     

Reinvestigation of the decay scheme of the short-lived isomeric states in112In

The two short-lived isomeric states in¹¹²In have been reinvestigated by means of the¹¹²Cd(d, 2n) and¹⁰⁹Ag (α, n) reactions. Measurements of delayed X- andγ-ray, lifetime and TDPAD spectra have been performed. A 6.32(3) keVγ-ray has been identified in the isomeric decay and anM1 multipolarity has been assigned to it on the basis of the measured internal conversion coefficients:α _L =196(39) andα _tot=231(35). TheE1+M2(δ =+0.24(4)) andE2 multipolarities have been determined for the 263 and 188 keV transitions deexciting the 8^?(T _1/2=2.82(2) μs) and 7⁺ (T _1/2=0.93(2) μs) isomeric states, respectively. A revised isomeric decay scheme is presented.     

Der Zerfall des125m Xe,des127m Xe und des127g Xe

The decay of^125m Xe produced by the reaction¹²²Te(α, n)^125m Xe using a target enriched in¹²²Te (95.4%) and the decay of^127m Xe produced by the reaction¹²⁷J(d, 2n)^127m Xe have been investigated: ^125m Xe decays with a half-life ofT _1/2=(56±3) sec by ayy- cascade withE _γ1=(140.4 ±0.5) keV andE _γ2=(110.5 ±0.5) keV. The experimental conversion coefficients yield multipolarities ofE3 for the 140.4 keV isomeric transition and predominantlyM1 for the 110.5 keV-transition. ^127m Xe decays with a half-life ofT _1/2=(71±2) sec. The decay also proceeds by aγγ-cascade with an isomeric E3 transition ofE _γ1=(172.5±0.3) keV and a predominantlyM1 transition ofE _γ2=(124.6±0.3) keV. In the decay of^127g Xe an additional branching of the electron capture to a level at (618.1±0.3) keV was observed. The relative probability forK-captureP _K618/P_K375=0.40 ±0.07 yields a total transition energyQ _EC=(664 ±4)keV. A spin of 1/2⁺ was assigned to the ground state.     

Levels in154Eu populated by thermal neutron capture

The level scheme of¹⁵⁴Eu has been investigated by means of thermal neutron captureγ-rays and conversion electrons. The high energyγ-ray spectrum from thermal neutron capture in enriched¹⁵³Eu has been studied in the energy range of 5700 to 6500 keV. Low energyγ radiation has been observed with Ge(Li) and Si(Li) detectors from 5 to 300 keV and conversion electrons have been measured from 15 to 300 keV. Low energy (n, γγ) coincidences and half lives of transitions have been measured. The data, combined with three very recent studies of the 8^? isomer decay in¹⁵⁴Eu has led to the construction of a level scheme with 12 excited levels. Nuclear Reaction¹⁵³Eu(n, γ),E _n =thermal, measuredE _γ ,I _γ ,E _ce ,I _ce ,γγ-coincidence, halflives,¹⁵⁴Eu deduced levels.     

The decay scheme of the 3-s Isomer of100Nb and the properties of levels in100Mo

Theβ ^? decay of the longer-lived isomer in¹⁰⁰Nb has been studied at the fission-product separator JOSEF. Measurements ofγ-ray singles spectra, ofγ-γ coincidences and ofγ-γ angular correlations have been performed. A value oft _1/2=2.99(11)s has been determined for the isomer which probably hasI ^π=4⁺ or 5⁺. A scheme of the levels of¹⁰⁰Mo which are populated in the decay of this isomer has been established. Information on the spins of several states of¹⁰⁰Mo has been obtained. Thus,I=0 levels have been identified at 1,505, 2,038 and 2,087 keV. The mixing ratios have been determined for the 2₂ ⁺→2₁ ⁺ and 2₃ ⁺→2₁ ⁺ transitions. The results provide evidence for a vibrational structure of¹⁰⁰Mo with separate bands based on the ground state and on the first excited 0⁺ level.     

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.     

The level structure of69Ge

Theγ-ray decay of the states in⁶⁹Ge has been studied using the reaction⁶⁶Zn(α, nγ)⁶⁹Ge atE _α =13 and 19 MeV. The level scheme and spin assignments were established by means of coincidence measurements, angular distributions and excitation functions. 27 new levels could be found or confirmed. It is suggested that⁶⁹Ge is a further example for the weak coupling phenomenon in the medium mass nuclei. Nuclear Reactions: ⁶⁶Zn(α, nγ)⁶⁹Ge,E _α =13–22 MeV, measuredE _γ ,I _γ ,I _γ (θ),E _γ =f(E _α ),γ-γ coincidences,⁶⁹Ge deduced levels,J, enriched target.     

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 ± 70keV. 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.     

Possible evidence for shape isomeric γ-decay in μ− atoms of 238U

A search for the γ-decay of the shape isomer in muonic ²³⁸U excited by radiationless transitions has been performed. Seven delayed transitions in the energy region of 700 to 3200 keV have been observed with a large Ge(Li) detector. Two transitions with E_γ = 2215 and 3131 keV have been attributed to the decay of the shape isomeric state into levels in the first well. The isomeric shift of the second minimum E₁₁ ≈ 600 keV in the presence of the muon and the decrease of the lifetime of the shape isomer to τ = 12 ± 2 ns give arguments in favour of the connection of shape isomerism with large quadrupole deformations.     

Zur Gamma- und Röntgenstrahlung von Holmium-164

The photon spectrum in the decay of¹⁶⁴Ho was investigated using a high resolution solid state detector separating theK-X-rays of Dy, Ho and Er. The two γ-rays depopulating the 3⁺ and 2⁺ levels in¹⁶⁴Ho were found to have energies of 56.6 and 37.3 keV. The 91.4 keV radiation of Er from our sample seems to have a non resolved high energy component with about 2.5% intensity. It may be due to the cross-over transition 3⁺→1⁺ or a sum line. The half-life of the isomeric state of¹⁶⁴Ho was found to be 36.7 ± 1 min. The total transition rates between different levels were calculated from the measured photon intensities. The fraction 0.27 found in the branching of thee ^?-capture feeding the 2⁺-state of Dy has nearly the same value as the analog branching in the β^?-decay. Combining the measured complex ground state decay curve and the transition intensities of the isomeric and of the ground state the ground state half-live can be deduced and was found to be (28.1 ± 1.0) min. The corresponding ratio of the ground state and the isomeric state production rates is 2.8₄:1. A ratio of 0.04 was found for the cross section of¹⁶⁵Ho (γ, 3n),¹⁶²Ho and¹⁶⁵Ho (γ,n)¹⁶⁴Ho for a 90 MeV bremsspectrum.     

Gamma-ray spectroscopy of short-lived fission products using the recoil separator “Lohengrin”

γ-spectra and half-lives of⁹⁰Br,⁹⁵Rb,⁹⁶Rb,⁹⁶Sr,⁹⁶Y,¹³²Sb and¹³²Sn have been measured using the unslowed fission fragment separator “Lohengrin”. Preliminary decay schemes for⁹⁰Kr,⁹⁵Sr,⁹⁶Sr and⁹⁶Y are given.