Evidence for violation of the Gallagher-Moszkowski rules in154Pm

The existence of two radioactive species of154Pm (1.8 min ground state and 2.65 min isomer) is established. The Nilsson model configurations assigned to these states give evidence against the validity of the Gallagher-Moszkowski coupling rules in154Pm.

Isomeric states (T½ ≥ 10−10 s) listed according to increasing half-life

Values of some 700 half-lives of isomeric states, ranging from 10−10 seconds to 106 years, are presented in order of increasing half-life.

Asymmetric linear Ge(Li)Ge(Li) sum-peak coincidence spectrometer

Abstract An asymmetric linear Ge(Li)Ge(Li) sum-peak coincidence spectrometer configuration has been designed and tested. In this system, the ratio of the gains of two detector-amplifier chains is chosen around 1.2 to 1.3, and the pulse amplitudes or addresses due to coincident events are summed. The simple method introduced involving a single run which results in two spectra (separated according to which detector records the larger energy) appears to be quite useful in γγ coincidence and directional correlation measurements, especially in laboratories where no event-by-event data acquisition hardware are available.

A combination magnetic plus Si(Li)-Si(Li) sum-coincidence technique for in-beam studies of internal pair transitions

Abstract An intermediate-image magnetic plus Si(Li) combination pair spectrometer featuring an excellent energy resolution and a pair-line efficiency of 10 −3 , recently presented and demonstrated, has been made more universally applicable by reducing the background underlying the pair lines. The best background reduction is achieved by using two standard Si(Li) detectors and a sum-coincidence method. An experimental coincidence pair-line efficiency of 2.1 × 10 −4 for the 1911 keV E0 pair line in 64 Zn is achieved. In this typical case, the high-energy background (mainly caused by β + activity) is reduced by a factor of about 200 as compared with the direct spectrum of a single detector.

Solution of controversy over 1583-keV levels inPb204

Data from {sup 204}Pb({ital p},{ital p}{prime}){sup 204}Pb conversion-electron and gamma-ray experiments, together with previous results, prove the existence of two levels (0{sup +} and 2{sup +}) at 1583-keV excitation energy in {sup 204}Pb. Modified values (limits) of the {rho}{sub 21}{sup 2} and {ital X}{sub 211} are 0.0013{lt}{rho}{sub 21}{sup 2}{lt}0.015 and {ital X}{sub 211}{gt}0.073. New experimental evidence indicates that all the three observed excited {ital O}{sup +} states in {sup 204}Pb can be explained as belonging to the four-neutron-hole valence space and, therefore, there is no clear candidate for the proton 2p-2h intruder state in this nucleus.

Decay of 14.6 h90Nb

The disintegration of 14.6 h90Nb produced by bombarding natural Zr with 13 MeV protons was investigated by methods of γ-ray spectrometry. Results from singles, coincidence and anti-Compton spectrometer measurements are reported. A decay scheme is proposed including excited states in90Zr at 1761, 2186.4, 2319.1, 2739.4, 2747.9, 3077.0, 3448.2, 3589.5, 3977.1, 4232.4, 4319.5, 4375.4, 4541.6, 5060.0, 5164.6 and 5432.9 keV. Over 10 γ-ray transitions and several levels proposed in an earlier investigation are shown to be in error.

The use of the integral-bias summing coincidence spectrometer in directional correlation measurements

Abstract The performance of the integral-bias summing coincidence spectrometer (the sum-peak spetrometer) in measurements of directional correlations of gamma rays has been tested. As compared with the conventional method, the sum-peak spectrometer is easier to use and seems to yield results which agree with those obtained with the ordinary method. Because of the complex shapes of response functions of gamma rays above about 3 MeV, the new method is best suited to the study of cascading transitions below this energy, where the two methods appear to complement each other. The analysis of the sum-peak spectra in the present work is based on a simple graphical method which seems to yield satis…

Cross Sections of232Th (p,xn+yp) Reactions at Ep= 6.8 to 20.2 MeV

Cross-sections for the (p, n), (p, 2n), (p, 3n) and (p, pn) + (p, d) reactions on 232Th targets were measured, by comparison with the K-shell ionization cross-section, for proton energies between 6.8 and 20.2 MeV. The results are compared with the predictions of the statistical and the pre-equilibrium model. For the (p, pn) reaction, the "clean knock-out" model is also considered.

Decay of 0 2 + states in88,92,94Zr andE0 systematics of Zr isotopes

Branching ratios ofE0 andE2 transitions depopulating the 0 2 + states of88, 92, 94Zr have been determined using conversion-electron and γ-ray spectroscopy. Two different lifetime-measurement methods were applied in the remeasurement of the half-lives of the 0 2 + states in92, 94Zr, yielding consistent results ofT 1/2(0 2 + ,92Zr)=85(15) ps andT 1/2(0 2 + ,94Zr)=280(40) ps. The monopole strengths extracted areρ 2(92Zr)=8.4(17) ×10−3 andρ 2(94Zr)=11.9(20)×10−3. The proton configurations of the 0 2 + states are discussed in view of these values and proton transfer data.

A walk-free centroid method for lifetime measurements with pulsed beams

Abstract A delayed-coincidence lifetime measurement method based on a comparison of walk-free centroids of time spectra is presented. The time is measured between the cyclotron rf signal and the pulse from a plastic scintillation detector followed by a fixed energy selection. The events to be time-analyzed are selected from the associated charge-particle spectrum of a silicon detector which is operated in coincidence with the scintillator, i.e. independently of the formation of the signal containing the time information. With this technique, with the micropulse fwhm of typically 500 to 700 ps, half-lives down to the 10 ps region can be measured. The following half-lives are obtained with th…

A method for high-resolution in-beam studies of internal pair transitions

Abstract A combination intermediate-image magnetic plus Si(Li) electron spectrometer has been adapted to internal pair formation measurements of cyclotron-induced reactions. The system is especially intended for the study of E0 transitions in the energy range from 1.5 to 8.6 MeV and to measurements of coincidences between internal pairs and heavy particles. The method is based on the fact that the electron and the positron spiral from the target to the detector simultaneously, the sense of rotation being of opposite sign. The energies of the particles are summed in a high-resolution cooled Si(Li) detector. Calculations of the spectrometer pair-line efficiency for E0 transitions versus trans…

Systematic study of low-spin states in even Cd nuclei.

Low-lying low-spin collective states in even $^{106\mathrm{\ensuremath{-}}112}\mathrm{Cd}$ and $^{116}\mathrm{Cd}$ were investigated using in-beam and off-beam \ensuremath{\gamma}-ray and conversion-electron spectroscopy. New spin assignments and decay branching ratios for the levels in $^{106}\mathrm{Cd}$, $^{108}\mathrm{Cd}$, $^{110}\mathrm{Cd}$, and $^{112}\mathrm{Cd}$ were obtained. The present results essentially complement the level systematics from $^{106}\mathrm{Cd}$ to $^{120}\mathrm{Cd}$. From the new data, it is inferred that two sets of low-lying ${0}^{+}$ states having different excitation characteristics cross between $^{114}\mathrm{Cd}$ and $^{116}\mathrm{Cd}$. No correspondi…

A Ge(Li)Ge(Li) sum-peak (summing coincidence) spectrometer

Abstract The sum-peak spectrometer (also called the integral-bias summing coincidence spectrometer) arrangement earlier developed with NaI(Tl) detectors is extended to Ge(Li) detectors. The integral-bias method in sorting sums of coincident pulse amplitudes is replaced by a set of pulse-height selection windows, which simply and more effectively aid in the analysis of sum-peak complexities associated with the symmetric linear summing procedure employed. A large part of the original information lost in summing of the pulse amplitudes can be retained by simultaneous sorting of the total spectrum into suitable subgroups. The arrangement represents in effect a real-time totalizing spectrometer …

AbsoluteE0 andE2 transition rates and collective states in116Sn

AbsoluteE0 andE2 transition rates in116Sn have been measured using several newly developed techniques. ManyE2 transitions are observed to have a collective character withB(E2) values of up to 60 W.u. The presence of deformed excited states in116Sn is discussed in view of the results obtained.

E0study of0+states near 5 MeV in208Pb

Strong E0 lines from the 4866 and 5237 keV ${0}^{+}$ states in $^{208}\mathrm{Pb}$ have been identified using a new high-energy conversion-electron spectrometry technique in the study of the $^{207}\mathrm{Pb}$(d,p${)}^{208}$Pb and $^{208}\mathrm{Pb}$(p,p'${)}^{208}$Pb reactions at ${E}_{\mathrm{d}=10}$ MeV and ${E}_{\mathrm{p}=17.3}$ MeV, respectively. No evidence for an E0 transition from the expected third ${0}^{+}$ state was found.

Corrections for positon annihilation in flight in nuclear spectrometry

Abstract Theories of positon single- and two-quanta annihilation in flight, the Fermi beta-decay theory, and theories of positon energy loss are used in calculations of total probabilities of annihilation in flight of positons in continuous spectra. The results are given in a nomogram useful in correcting for positon annihilation in flight in various nuclear-spectrometry experiments. Confirmation of the theoretical basis employed was obtained by comparing total absolute probabilities for annihilation in flight of 62 Cu positons in Perspex, copper, cadmium and lead, using a new differential method. The agreement with the theory was found to be excellent. A method for obtaining “correct” posi…

The role of target geometry in 14 MeV neutron capture cross-section measurements

Abstract Some activation capture cross sections of 14.5 MeV neutrons have been measured by systematically varying the target geometry. In all cases, the results are found to strongly depend on the geometrical conditions, which implies that a large part of the activation capture cross sections reported earlier are in error. An investigation of a number of materials shows that aluminium gives rise to a fairly small fraction of secondary low-energy neutrons and is, therefore, suitable material for target holders. A thin air-cooled target head specially designed for reliable activation cross-section measurements has been constructed and tested.

A test of the feasibility of γp-coincidence techniques in conjunction with the (t, pγ) reaction

Abstract A setup has been tested for γp coincidence measurements in conjunction with the (t, pγ) reaction. The γ-rays were detected by a Ge(Li) detector and protons with an annular Si(Au) detector placed at forward angles, elastically scattered tritons being removed with an absorber.

Levels in208Pb populated in the decay of208Tl(ThC″)

Gamma rays in the disintegration of208Tl(ThC″) have been studied with Ge(Li)-Na I(Tl) anti-Compton and coincidence spectrometers. Several new transitions are reported most of which are placed in a decay scheme incorporating excited states in208Pb at 2,614.5, 3,197.6, 3,475.0, 3,708.3, 3,919.8, 3,960.9, 3,998.5, 4,125.3, 4,180.4, 4,296.1 and 4,480.0 keV. According to the present data, the recently reported intensity of 4.5±1.5% of beta groups feeding levels near 4.3 MeV is far too large.

New features in systematics of low-spin states in even106?120Cd

Low- spin states in even106–112Cd and116Cd were investigated by in-beam and off-beam γ-ray and conversion electron spectroscopy. New spin assignments and decay branching ratios for the levels in106Cd,108Cd and110Cd were obtained. From the new systematical data for the even106–120Cd, it is inferred that two sets of low-lying 0+ states cross between114Cd and116Cd. One of these sets appears to have features of both intruder and two-quadrupole-phonon states.

A simple two-detector method for precision intercomparisons of source strengths

Abstract A two-detector method for comparing source strengths which largely eliminates errors due to uncertainties of geometric character is described. The simplest version of the method is based on the fact that, when a symmetric face-to-face geometry is being used, the change of the counting rate of one detector caused by the change of the position of the source is approximately compensated for by the change of the counting rate of the other detector. In a more versatile geometry, in which the axes of the detectors are slightly misaligned, the sum and the ratio of the two counting rates can be used in a simple manner to virtually eliminate uncertainties due to the shapes and horizontal po…

A semiconductor detector telescope electron spectrometer

Abstract A simple d E d x+E type semiconductor detector telescope electron spectrometer featuring high detection efficiency and effective discrimination against γ-rays and heavy particles is described. The line shape of the spectrometer is better than that of a single detector of corresponding size; at 1 MeV, the peak-to-total ratio is approximately 0.8. The device is suited to the study of beta-ray spectra and conversion electron lines at energies above about 0.4 MeV.

Electron-transporter spectrometer for on-line isotope separator

Abstract ELLJ — a conversion-electron and beta-ray spectrometer for an on-line isotope separator - is described. The instrument is a broad-range, high-transmission device consisting of a two-coil magnetic transporter plus a cooled Si(Li) detector. The spectrometer was designed to perform several kinds of coincidence measurements. A number of representative spectra of fission-product activities separated on-line at the IGISOL facility demonstrate the performance of the spectrometer.

A combination intermediate-image magnetic plus Si(Li) electron spectrometer for in-beam experiments

Abstract A magnetic lens plus Si(Li) combination in-beam beta spectrometer with focusing properties and field shape similar to those of an intermediate-image spectrometer is described. A high transmission and a large momentum band-width are achieved by placing both the target and the detector in a high magnetic field inside the lens. The beam enters the lens axially, and the Faraday cup is placed inside the lens. The spectrometer is well suited to singles conversion-electron spectroscopy, to electron-heavy particle coincidence measurements, to lifetime measurements and to studies of internal-pair transitions.

A swept-current magnetic lens plus Si(Li) electron spectrometer with simultaneous momentum and energy selection

Abstract A combined swept-current magnetic lens plus Si(Li) electron spectrometer with simultaneous momentum and energy selection is presented. The spectrometer is intended for in-beam measurements of conversion electron lines up to several MeV in energy and for nanosecond lifetime determinations, as well as for off-beam studies of continuous beta-ray spectra and conversion lines from short-lived activities. The sweeping of the lens current is automatized and the energy selection, synchronously with the momentum, is performed using a simple digital window arrangement. The performance of the spectrometer is demonstrated in conversion electron and continuous spectrum measurements. Different v…

Comparison of experimental and calculated K/L ratios of E0 transitions in some heavy nuclei

A comparison of the experimental and theoretical K/L conversion-intensity ratios of E0 transitions in the lead region is presented. No major differences were found, the overall agreement being better than 7%. However, with the present data, a systematic 5% deficiency of the measured values, as compared with the calculated ones, can not be ruled out.

Levels of118Sn populated in the decay of118In and118Sb isomers

Gamma-rays in the disintegration of 5.0 s (1+), 8.5 s (7−, 8−), and 4.4 min (4+, 5+)118In isomers and of 3.5 min (1+) and 5.1 h (8−)118Sb isomers have been investigated using Ge(Li) detectors and Ge(Li)-NaI(Tl) coincidence spectrometers. The decay schemes of these isomers have been constructed incorporating 17 levels in the product nucleus,118Sn, at the following energies (in keV): 0 (0+), 1229.5 (2+), 1757.5 (0+), 2043.1 (2+), 2056.4 (0+), 2280.3 (4+), 2321.3 (5−), 2326.4 (1+, 2+), 2402.7 (4+), 2488.8 (4+), 2496.5 (0+), 2575.2 (7−), 2677.3, 2733.7 (2+), 2929.8, 2963.5 (4+), and 3137.1 (0+). The structure of118Sn is briefly discussed in view of results from recent quasiparticle-model calcul…

Collective states in 116Sn

Determination of ion-induced K-shell ionization cross sections by comparison with nuclear Coulomb excitation

Abstract A new method for the determination of cross sections for K-shell ionization of heavy atoms by charged particles is proposed. The method is based on a comparison of photon lines due to K X-rays and low-energy γ-rays, the latter ones being produced in nuclear Coulomb excitation with accurately known cross sections. This procedure applies within a limited energy range to the study of targets comprising deformed even nuclei, but can also be extended to other targets having Z≳30. A test of the new technique has been carried out for Gd, W, Th and U natural targets irradiated by 4.75 MeV protons. For Th, also energies of 6.80–10.10 MeV were used. The results are briefly discussed with ref…

Electromagnetic properties of low-spin states in102, 104Pd

Electromagnetic transitions from low-lying 0+, 2+, 4+ and 3− states in102, 104Pd have been studied using (p, 2n) and (p, p′) reactions and Coulomb excitation. TheE2 transition probabilities from the 0 3 + state in102Pd (13 W.u.) and from the 02/+ state in104Pd (14 W.u.) are somewhat low for two-phonon states. Generally, theE2 transition rates are reasonably well reproduced by the IBA-2 and by the boson-expansion description. The intruding 0 2 + state (t1/2=14.3 ns) in102Pd is connected to the 22/+ and 2 3 + states via strong E2 transitions: B(E2; 0 2 + → 2 2 + )=96±40 W.u.; B(E2; 2 3 + → 0 2 + =17±11 W.u.

Decay characteristics of 0 2 + and 0 3 + states in112Cd and114Cd

Absolute rates ofE0 andE2 transitions depopulating 0 2 + and 0 3 + states in112Cd and114Cd have been determined using conversion-electron andγ-ray spectroscopy, and double Coulomb excitation. The collectivity of these states is established and discussed.

New Features in the Systematics of Low‐Spin States in Even 106‐120Cd

Low‐spin states in even 106‐112Cd and 116Cd were investigated by in‐beam and off‐beam γ‐ray and conversion‐electron spectroscopy. New spin assignments and decay branching ratios for the levels in 106Cd,108Cd,110Cd and 112Cd were obtained. From the new systematical data for the even 106‐120Cd, it is inferred that two sets of low‐lying 0+ states cross between 114Cd and 116Cd. One of these sets appears to have features of both intruder and two‐quadrupole‐phonon states.

Directional correlations of some γ-ray cascades in200Hg

Directional correlation functions of 10 γ-ray cascades in200Hg have been measured using a200Tl source and a Ge(Li)-NaI(Tl) coincidence spectrometer arrangement. Values of the mixing parameter δ for several transitions are determined, and the spin assignments for the following levels in200Hg are established (level energies are given in keV): 1029.4 (0+), 1254.2 (2+), 1573.7 (2+), 1593.4 (2+), 1641.5 (2+), 1730.9 (2+) and 1775.6 (3+).