Shell model study of high spin states in theN=50 nucleus93Tc

High spin states in theN=50 nucleus⁹³Tc were reinvestigated by using the reaction⁶⁴Zn (³⁵Cl,4p 2n) at a beam energy of 140 MeV. This was done particularly with a view to observe anyγ rays upto 2.7 MeV which may have been missed in our earlier study where the experimental conditions were set to observeγ rays upto 2 MeV. We found four newγ rays of energy: 2484, 2164, 2130 and 69 keV. We have placed theseγ rays in the level scheme and it now gets extended to 49/2^?. Though there is no substantial change in the level scheme, placing theγ rays in the level scheme has resulted into two important conclusions: (1) We have performed shell model calculations for⁹³Tc nucleus within a model space which encompasses an enlarged proton configuration and allows for the excitation of the neutron across theN=50 core. The excitation of a single neutron across theN=50 core satisfactorily explains the new level scheme. (2) The energy of the 17/2^? isomeric state is now unambiguously placed at 2185 keV.     

Internal electron-positron pair production from electric monopole transitions

The yield curve of the reaction⁵⁶Fe(p,γ)⁵⁷Co has been measured over the energy rangeE _p =1,300–1,900 keV and the decay of nine resonances has been investigated. For twelve of the resonances the strengths have been determined. The angular distributions of the gamma rays have been recorded for resonances atE _p =1,599, 1,623, 1,643 and 1,649 keV, giving spin-parity assignmentsJ ^π=3/2^? for all four resonances. The resonances atE _p =1,623, 1,643 and 1,649 keV have been identified as the split analogue resonances of the 367 (J ^π=3/2^?) states in⁵⁷Fe. TheM1 transition strengths to the corresponding antianalogue states have been measured and compared with theoretical predictions.     

Study of131Ba decay

Singles and coincidence spectra of gamma rays emitted in the decay of¹³¹Ba(11.8d) have been studied with improved statistics. The existence of the level at 1342.07 keV and gamma transitions at 82.58, 461.22, 562.87, 703.53, 1046.4, 1125.97, 1170.53, 1208.43 and 1342.02 keV have been confirmed. Thirteen previously unreported gamma rays at 390.1, 474.2, 506.1, 517.5, 533.7, 596.5, 657.6, 745.5, 757.0, 785.92, 840.9, 1037.0 and 1218.30 keV have been identified and seven new coincidence relations are reported. The level at 596.4 keV is proposed based on coincidence evidence and the level at 657.6 keV is tentatively proposed on the basis of energy differences. All the 62 gamma rays observed in this study have been placed into the decay scheme.     

Verzweigungsverhältnisse und Konversionskoeffizienten von angeregten Zuständen des208Tl

The branching ratios of theγ rays of the second and fourth excited states of²⁰⁸Tl have been investigated by coincidence measurements between the α rays of²¹²Bi and subsequent 40keVγ ray. The detectors employed were a silicon surface barrier counter for α particles, and a 1.5 in ×2 mm NaJ (Tl) crystal forγ rays. It has been found that (75.6±3.7)% of all transitions of the 328 keV state and (94±7)% of all transitions of the (492 keV+473 keV) states populate the first excited state of²⁰⁸Tl. The 40 keV state is excited to (3.4±0.3)% by transitions of higher excited states relative to the direct excitation by α particles. The number of α particles with energyE _α = 6.047 MeV and the number of subsequent 40keVγ rays resulted in a conversion coefficient α(40keV)=22.55± 0.46. Similarly coincidence measurements between Tl-x rays and α particles have been used to determine theK- conversion coefficients α_K(328 keV)=0.31±0.03 and α_K(492 keV+ 473keV)=0.100±0.015. The experimental results are in good agreement with the theoretical values ofSliv.     

Spin values of the low lying nuclear levels of201Hg

Gamma-gamma directional correlations have been investigated for the cascades of 135-30 keV and 135-32 keV in²⁰¹Hg from the decay of²⁰¹Tl. A combination of NaI (Tl) and Si (Li) detectors was used for the experiments. Spin values ofI=1/2, 3/2 and 1/2 have been assigned to 1.58, 32.19 and 167.49 keV energy levels. In addition, the relative intensities of theγ rays have been measured with a Ge (Li) detector system. The results are 2.2±0.2, 2.2±0.2, 26.5±1.3, 1.6±0.1 and 100 for theγ rays of 30.60, 32.19, 135.34, 165.88 and 167.43 keV energies, respectively.     

Mn55(p,p′γ)Mn55 reaction low proton energies

Angular distributions of gamma rays following the inelastic scattering of protons from Mn⁵⁵ have been measured at proton energies below 2.50 MeV. The mixture multipole orders for the transition 983→126 keV and 1,530→0 in Mn⁵⁵ have been obtained.     

Mößbauereffekt anFe 57 nach Neutroneneinfang in Fe56

Mößbauer effect measurements with the 14.4 keV gamma rays of Fe⁵⁷ following thermal neutron capture in Fe⁵⁶ are reported. During the transition from the capture level at 7.6 MeV to the first excited state at 14.4 keV recoil energies up to 549 eV are imparted to the Fe⁵⁷ nuclei. Thus the Mößbauer gamma rays are emitted by nuclei displaced from their normal lattice positions. The measurements have been performed in order to get informations about the final position of the recoiled nuclei in metallic iron and in ordered Fe-Al alloys. Mößbauer spectra of recoil atoms in metallic iron did not show any significant deviation from the spectra of atoms on normal lattice positions. In ordered FeAl alloys of CsCl structure changes in the isomer shift due to recoil effects have been found. In a Fe₃Al alloy of DO₃ type order additional changes in the internal magnetic field have been observed. All results are discussed in terms of possible final positions for the primary recoiled iron atoms in the lattice.     

Der Zerfall des Fe53g und des Fe53m

Theγ-ray spectra from the decays of 8.5 min-Fe^53g and a new (2.51±0.02) min-Fe^53m have been investigated by means of Ge(Li)-detectors. As far as the Fe^53g -decay is concerned no other but the known 380 keV-transition (43%) has been observed indicating that the proceedingΒ ⁺-decay leads to the groundstate and first excited state of Mn⁵³ only. This contradicts formerΒ ⁺-spectroscopic results but is consistent with recent spin assignments. In the Fe^53m -decay fourγ-transitions have been found: 701 keV (100%), 1011 keV (76%), 1328 keV (76%), and 2339 keV (24%). The proposed level scheme of Fe⁵³: 0 keV (7/2^?), 1328 keV (9/2^?), 2339 keV (11/2^?), and 3040 keV (19/2^?, 2.5 min) is in agreement with results published recently byEskola. The level schemes of Mn⁵³ and Fe⁵³ are discussed in terms of the individual particle shell model.     

Der radioaktive Zerfall des Fe61

Fe⁶¹(T _1/2=5.95 min) was produced irradiating Ni⁶⁴ and natural nickelfoils with fast neutrons in the reaction Ni⁶⁴(n, α)Fe⁶¹; Fe was chemical seperated. The gamma and beta spectrum were investigated with Ge(Li)-counters, NaJ(Tl) and plastic scintillation spectrometers. Fe⁶¹ emits five gamma rays having the energies and intensities per Fe⁶¹ decay: 121 keV (0.064), 177 keV (0.027), 298 keV (0.293), 1025 keV (0.461), 1202 keV (0.539). Threeγγ-cascades could be identified: 121–177 keV, 121–1202 keV, 298–1025 keV. Inγ β-coincidence measurements the maximal beta energy was determined:E _βmax=2.86 MeV. A decay sceme Fe⁶¹-Co⁶¹ was constructed: Fe⁶¹, spin and parityJ ^π=3/2^?, decays by means of allowed beta decay to three excited states of Co⁶¹: 1323 keV (1/2^?), 1202 keV (3/2^?), 1025 keV (5/2^?). The energies and intensities per Fe⁶¹ decay of the three beta decay modes are: 2.56 MeV (0.367), 2.68 MeV (0.495), 2.86 MeV (0.138). — A 88 keV gamma ray (T_1/2=33 sec) was observed coming from the Co⁶³ decay.     

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.     

Low-lying excited states of106Ag studied with the103Rh (α,nγ)106Ag and104Pd (α,pnγ)106Ag Reactions

The level scheme of¹⁰⁶Ag has been studied using the¹⁰³Rh(α,nγ)¹⁰⁶Ag and¹⁰⁴Pd(α,pnγ)¹⁰⁶Ag Reactions. The experimental information is taken fromγ-ray coincidence data using Ge(Li)-Ge(Li) and HPGe-planar Ge(Li) configurations andγ-ray angular distributions. With these measurements 126 γ rays have been assigned to¹⁰⁶Ag with 116 deexciting 78 states below 2.26 MeV in excitation. The location of the 8.4-day 6⁺ isomer is established at 89.63±0.09 keV. Many of the low-lying states are interpreted in terms of a slightly deformed rotor model.     

Studies on the low-lying levels in192Pt and192Os populated in192Ir decay

Low-lying levels in¹⁹²Os and¹⁹²Pt are reinvestigated through¹⁹²Ir (73.831d) decay with improved system performance and counting statistics. Experiments show that gamma rays reported in literature with energies 1413, 1237, 1147, 911, 773, 629, 362 and 325 keV are not from the decay of¹⁹²Ir and gamma rays reported with energies 1200, 1056, 920, 904, 784 and 624 keV are resulted from sum-up or pile-up effects of low energy intensive gamma rays. New gamma-gamma coincidence relations are obtained with 105 cm³–110 cm³ germanium detector system. A level at 1384 keV is established in the decay scheme and four newly proposed levels at 1118.31 keV in¹⁹²Os and 1146.95, 1237.35 and 1413.76 keV in¹⁹²Pt are excluded from the decay scheme. Predictions of Interacting Boson Model on level energies andE2 absolute reduced transition probabilities are compared with experimental results.     

Investigation of multipole mixtures in gamma transitions by means of the reaction 232Th(n, n′γ)

The spectrumof gamma rays from the reaction ²³²Th(n, n′γ) induced by a beam of fast reactor neutrons and the angular distribution of the gamma rays in question with respect to this beam were measured. The multipole-mixture parameter δ was found for many gamma transitions.     

Low-lying states in112In

Low-lying states below 500 keV excitation in¹¹²In have been investigated via the¹¹²Cd(p, nγ) reaction. New levels have been established atE ^x=206.5keV and 456.1 keV from the measuredγ-ray excitation functions,γ?γ coincidences and the precision measurements of the (p, n) threshold energy of the ground state and of the 206.5 keV state of¹¹²In. Spins and parities of the 206.5 keV state (2⁺) and the 456.1 keV state (3⁺) and multipolarities and mixing ratios of the deexcitationγ-rays have been determined from the angular distributions and linear polarizations of the deexcitation γ-rays as well as the excitation functions of the residual levels. Possible configurations of the newly-found levels are discussed. Half-lives of two states have been remeasured:T _1/2=15.2±0.1 min for the ground state andT _1/2=20.9±0.1 min for the 156.4 keV (4⁺) state. The ground stateQ-value for the¹¹²Cd(p, n)¹¹² In reaction has been measured to be ?3.376±0.006 MeV.     

Gammaübergänge und Energieniveaus im49V aus der Reaktion48Ti(p, γ)49V

Deexcitation gamma rays of⁴⁹V from the⁴⁸Ti (p, γ)⁴⁹V reaction have been investigated at the resonancesE _p=1007, 1209, 1362 and 1374 keV corresponding to excited states in⁴⁹V at 7742, 7940, 8090, 8102 keV. A 4 cm²× 0.35 cm lithium-drifted germanium detector was used. The target was TiO₂ enriched in⁴⁸Ti to 99.4%. 71 gamma transitions have been observed. A level scheme of⁴⁹V is proposed involving 8 new levels in the energy range from 0 to 5.2 MeV excitation energy.     

Energy levels,decay scheme, γ-ray branching ratios and lifetimes in 55Fe from the 55Mn(p,nγ)55Fe reaction

The reaction ⁵⁵Mn(p, nγ)⁵⁵Fe has been studied at E_p = 4.0 and 6.0 MeV using a pulsed beam. From the experiments at 6.0 MeV, the energy levels of ⁵⁵Fe up to an excitation of 3810 keV, their decay scheme and the γ-ray branching ratios have been determined. Levels have been identified for the first time in the (p, nγ) reaction. The results have been compared with those available from the literature. From the 4.0 MeV experiment, the mean lifetime of the 1408 keV level has been determined to be 142.7 ± 6.6 ps by direct timing techniques.     

Multipole mixing ratios of transitions in175Lu populated from the decay of175Hf

Electron capture decay of¹⁷⁵Hf(70 d) provides a possibility for unambiguous determination of the sign and magnitude of multipole mixing ratios for 89 keV and 114 keV transitions in¹⁷⁵Lu. This is because both gamma rays are in coincidence with the 230 keV transition which is of a pureE2 character. The results of theγ —γ directional correlation measurements, in terms ofE2/M1 mixing ratiosδ, areδ ₈₉ = 0.11±0.07 andδ ₁₁₄ = 0.465±0.005. In addition the directional correlation measurements of the 89γ- 343γ and 319γ-114γ cascades yieldδ ₃₄₃ = 0.08±0.07 andδ ₃₁₉ = ?0.152±0.015.Radioactivity ¹⁷⁵Hf from¹⁷⁴Hf(n, γ); measuredγ —γ(θ) deducedδ(E2/M1); Ge(Li) detectors.     

Messung von HalbwertszeitenK-verbotener Übergänge ingg-Kernen der Seltenen Erden

The half-life of the 1,490 keV level in¹⁶²Dy has been measured in the decay of¹⁶²Ho^m (68 min) by delayed coincidences ofKX rays and (900-1,300) keV gamma radiation to be (1.94 ± 0.19) nsec. A half-life in¹⁷⁶Hf has been remeasured in the decay of¹⁷⁶Ta (8.1h) by delayed coincidences of KX rays and (1,100–1,200) keV gamma radiation to be (4.75 ± 0.25) nsec. In order to fix the level with this half-life in the level scheme of¹⁷⁶Hf, the gamma spectrum delayed to KX rays was measured. It is suggested that probably the 1,227.4 keV-level of¹⁷⁶Hf is delayed and has the spin 2^? or 3⁺.     

Decay of126m Sb and the energy levels of126Te

The decay characteristics of 19 min^126m Sb have been studied using Ge(Li) and scintillation spectrometers. The sources of^126m Sb were obtained by the (n, p) reaction on enriched¹²⁶Te. The gamma rays of energies 414.4±0.3, 666.7±0.5 and 696.1±0.5 keV were found decaying with a half-life of 19 min. The study of beta spectra employing an anthracene crystal yielded two beta groups with end-point energies of 1.9±0.15 and 2.5±0.15 MeV. The results of singles and coincidence measurements have been incorporated into a decay scheme with excited states of¹²⁶Te at 666.7, 1,362.8 and 1,777.2 keV.     

Der Zerfall des 1,5 min-Isomers Co54m

Co^54m (T _1/2=1.43 min) was produced in iron-foils by irradiation with_dE=19 MeV deuterons. The gamma ray spectrum was investigated using a NaJ(Tl) scintillation spectrometer, a coincidence circuit and a Ge(Li)-counter. There were observed three gamma rays having the following energies and intensities per Co_54m decay: 411 keV (0.97±0.07), 1130keV (0.98±0.05), 1407 keV (1.00±0.05). The directional correlation between the pairs of gamma rays were determined. These results correspond to spin and parityJ _π=2⁺ for the 1407 keV,J _π=4⁺ for the 2537 keV, andJ _π=6⁺ for the 2948 keV energy level of Fe⁵⁴. The last-mentioned level was not excited in previous scattering experiments. Our results are compatible withE=210keV andJ _π=6⁺ or 7⁺ of the isomeric state of Co^54m .