B. Sethi

Lifetimes of excited levels and electromagnetic transition rates in 147Pm and 199Hg

Abstract The lifetimes of the 687.4, 531.9 and 91.03 keV levels in 147 Pm and the 158.2 keV level in 199 Hg are measured by the delayed coincidence technique using a time-to-amplitude converter. The results are: T 1 2 (687.4 keV level , 147 Pm ) = 0.25±0.10 ns , T 1 2 (531.9 keV level , 147 Pm ) = 0.133±0.030 ns , T 1 2 (91.03 keV level , 147 Pm ) = 2.57±0.02 ns) , T 1 2 (158.2 keV level , 199 Hg ) = 2.49±0.03 ns . The energies and relative intensities of γ-rays in the decays of 147 Nd and 199 Au are determined using high-resolution Ge(Li) detectors. The γ-ray transition probabilities for M1 and E2 multipolarities are deduced from the above results.

The decay of 164Ho

Abstract 164 Ho activity is produced by bombarding natural holmium with 14 MeV neutrons. Two beta groups of 875±20 and 965±20 keV are measured using a lithium drifted silicon detector. Photons of 36, 46, 51, 72 and 90 keV are found and the decay of each is followed with a scintillation spectrometer. The β-γ, γ-γ and x-γ coincidence experiments are performed. A metastable state is found in 164 Ho. The half-lives of the metastable and ground states of 164 Ho are found to be 39.0±0.5 and 23.9±0.5 min, respectively. The cross sections for the production of the two states by the (n, 2n) reaction at 14 MeV neutron energy are estimated to be 1050±100 and 730±100 mb, respectively. The 51 and 36 keV gamma rays belong to the decay of 164m Ho.

Decay of 68mCu(3.75 min) and 68gCu(30 sec)

Abstract The existence of the isomer of 68 Cu is confirmed and its half-life measured as 3.75±0.05 min. The 68m,g Cu activities have been produced by irradiation of enriched targets of 68 Zn (99.3 %) and 71 Ga (98.1 %), as well as spectroscopically pure ZnO targets, with 14 MeV neutrons. The 3.75 min 68m Cu is found to decay to the 30 sec ground state of 68 Cu with the emission of γ-rays whose energies (keV) and relative intensities (given in parentheses) are: 84.6±0.4 (95±5), 110.4±0.7(24.5±1.7), 525.7±0.4(100) and 635.9±0.7(16.5±1.5). The decay of the 30 sec 68 Cu was re-examined. A 4.60 MeV β-group (37 %) corresponding to the transition from the ground state of 68 Cu to the ground state of 68 Zn is observed. The energies (keV) and relative intensities of the 68 Zn γ-rays observed in these studies are 577.6±1.0(2.9±0.5), 805.7±1.0 (3.0±0.6), 1077,7±0.5(82.4±3.0), 1261.8±0.8(17.5±1.5), 1744.9±1.5(2.7±0.5), 1883.7±1.5 (1.8±0.5) and 2339.5±1.5(1.1±0.7). β-γ and γ-γ coincidence experiments were performed. A decay scheme is proposed for 68m Cu with energy levels in 68 Cu at 84.6, 610.3 and 720.7 keV. The cross sections for the production of the metastable and ground states of 68 Cu by the reaction 68 Zn(n, p) 68m,g Cu at 14 MeV neutron energy have been measured and found to be 4.5±0.8 and 6.5±1.3 mb, respectively.

Band structure of 79Br

Abstract High-spin states of 79Br have been studied in the reaction 76 Ge( 7 Li , 4nγ) at 32 MeV. A gamma-detector array with twelve Compton-suppressed HPGe detectors was used. The positive-parity yrast states, interpreted as a rotationally aligned g 9 2 proton band, and the negative-parity ground state band have been extended to spins of ( 33 2 + ) and ( 25 2 − ), respectively. Lifetime measurements indicate that both bands have a similar quadrupole deformation of β2 ∼ 0.2. The positive-parity α = −1 2 band has been identified. Several new inter-band transitions are observed. A cranked-shell model analysis shows that the νg 9 2 alignments occur in the positive-parity and the negative-parity bands at rotational frequencies of ℏω ∼ 0.6 and 0.4 MeV, respectively. The level energies and the electromagnetic properties of the g 9 2 band can be well reproduced by a particle-rotor model calculation with an axially symmetric core.

Doppler shift attenuation measurements on57Fe and57Co

SummaryLifetime measurements by the Doppler shift attenuation method for levels in the nuclei57Fe and57Co, populated via the reactions55Mn(α, pnγ)57Fe and55Mn(α, 2nγ)57Co, respectively, are reported. The relative γ-ray intensities and the branching ratios for levels in the two nuclei are also presented. In57Fe, mean lifetime values of τ=(0.20±0.09) ps and (0.26±0.10) ps are obtained for the levels at 1007.0 keV and 1356.8 keV, respectively, for which no lifetime information existed previously and values of τ=0.08±0.03, 0.54−0.15+0.30 and (0.16±0.06) ps are determined for the levels at 2355.7, 3269.1 and 6185.6 keV, respectively, for which only the limits of lifetimes were reported earlier. For the 2455.2 keV level in57Fe a lower limit of 2 ps is obtained for its mean life. In57Co lifetimes of eight levels withJπ≤19−/2 have been measured and compared with the earlier reported values. The results of lifetime measurements and reduced transition probabilities for both the nuclei are discussed and compared with the available shell model calculations.RiassuntoSi riportano le misure di vita media mediante il metodo di attenuazione dello spostamento Doppler per livelli nei nuclei57Fe e57Co popolati mediante le reazioni55Mn(α, pnγ)57Fe e55Mn(α, 2nγ)57Co, rispettivamente. Si presentano anche le intensità relative dei raggi γ e i rapporti di diramazione nei due nuclei. Per57Fe si ottengono i valori di vita media di τ=(0.20±0.09) ps e (0.26±0.10) ps per i livelli a 1007.0 keV e 1356.8 keV, rispettivamente, per i quali non esistevano precedentemente informazioni sulla vita media, e si determinano i valori di τ=0.08±0.03, 0.54−0.15+0.30 e (0.16±0.06) ps per i livelli a 2355.7, 3269.1 e 6185.6 keV, rispettivamente, per i quali si erano stati riportati precedentemente solo i limiti di vita media. Per il livello a 2455.2 keV nel57Fe si ottiene per la sua vita media un limite inferiore di 2 ps. Nel57Co le vite medie degli otto livelli conJπ≤19−/2 sono state misurate e confrontate con valori riportati precedentemente. Si discutono i risultati delle misure di vita media e le probabilità di transizione ridotte per entrambi i nuclei e si confrontano con i calcoli disponibili del modello a strati.

Decay of the 46.6 s75Gem

SummaryThe decay of the 46.6 s isomer of75Ge is investigated by gamma-spectroscopic measurements using an enriched76Ge target and highresolution X-ray Ge(Li) and 32.2 cm3 Ge(Li) detectors. New γ-rays have been found at energies 61.92, 77.86, 121.15, 136.01, 279.48 and 400.20 keV, in addition to a strong γ-ray at 139.68 keV, which was previously known to occur in the decay of75Gem. TheK conversion coefficient of the 139.68 keV transition has been measured and found to be 1.40 ± 0.07, supporting anE3 multipolarity assignment for this transition in75Ge. A decay scheme for the 46.6 s75Gem is proposed which shows for the first time a β-decay to75As, populating a level at 400.60 keV, and a cascade of γ-rays of energies 77.86 and 61.92 keV in75Ge in addition to a cross-over transition of 139.68 keV, populating the ground state of75Ge. The half-life of the 139.68 keV level in75Ge has been determined. The intensity and logft of the new β-group, and the spins and parities of the levels in75Ge are given and the results are discussed.RiassuntoSi è studiato il decadimento dell’isomero di 46.6 s del75Ge mediante misurazioni spettroscopiche gamma usando un bersaglio di76Ge arricchito e rivelatori Ge(Li) di raggi X ad alta risoluzione e Ge(Li) di 32.2 cm3. Si sono trovati nuovi raggi γ ad energie di 61.92, 77.86, 121.15, 136.01, 279.48 e 400.20 keV, in aggiunta ad un forte raggio γ a 139.68 keV, che si sapeva già occorrere nel decadimento del75Gem. Si è misurato il coefficiente di conversioneK della transizione di 139.68 keV e si è trovato essere 1.40 ± 0.07, che dà sostegno ad assegnazione di multipolaritàE3 per questa transizione nel75Ge. Si propone uno schema di decadimento per il75Gem di 46.6 s che mostra per la prima volta un decadimento β a75As, the popola un livello a 400.60 keV ed una cascata di raggi γ di energie 77.86 e 61.92 keV in75Ge in aggiunta ad una transizione d’incrocio di 139.68 keV, che popola lo stato fondamentale di75Ge. Si è determinata la vita media del livello di 139.68 keV in75GeV. Si dà l’intensità ed il logft del nuovo gruppo β e gli spin e le parità dei livelli in75Ge e si discutono i risultati.РеэюмеИсследуется распад иэомера75Ge со временем 46.6 с, с помошью гамма-спектроскопич еских иэмерений, испольэуя обогашенную мищень76Ge и рентгеновский детектор Ge(Li) с высоким раэрещением и 32.2 cm2 Ge(Li) детектор. Обнаружено γ-иэлучение при знергиях 61.92, 77.86, 121.15, 136.01, 279.48 и 400.20кзB, в добавление к интенсивному γ-иэлучению при 139.68 кзB, которое было ранее обнаружено при распаде75Gem. Был иэмерен козффициентK-конверсии для перехода 139.68 кзВ. Этот козффициент равен 1.40±0.07, что подтверждает приписываниеE3 мультипольности зтому переходу в75Ge. Предлагается схема распада для75Gem со временем 46.6 с, которая обнаруживает β-распад в75As, эаселяюший уровень при 400.60 кзB, и каскад γ-лучей с знергиями 77.86 и 61.92 кзB в75Ge, в добавление к переходу 139.68 кзB, эаселяюшему основное состояние75Ge. Определяется период полураспада уровня 139.68 кзB в75Ge. Приводятся величины интенсивности и logft для новой β группы, а также спины и четности уровней в75Ge. Проводится обсуждение полученных реэультатов.

A semiempirical method based on the LSS formalism for estimating electronic energy loss

Abstract A modified semiempirical expression for the LSS parameter ξe valid for ions with nuclear charge ⩽ 92 is presented and its applicability for predicting electronic stopping powers is discussed.

Decay of the 83 min ground state of75Ge

SummaryThe decay characteristics of the 83 min75Ge produced by the (n, 2n) reaction with 14.7 MeV neutrons on enriched76Ge target have been studied by using 32.2 cm3 Ge(Li) and 7.6 cm×7.6 cm NaI(Tl) γ-detectors. The study shows the presence of a 270.2 keV γ-ray confirming a recent report, but does not show any 136 keV γ-ray (intensity <0.007) and hence rules out the recently proposed β-feeding (the unique 1st forbidden) to the well-established 5/2+ state at 400.6 keV in75As. Two new γ-rays have been found with energies 279.7±0.4 and 338.0±0.4 having relative intensity of 0.05±0.01 and 0.04±0.01, respectively, relative to 100 for the 264.6 keV γ-ray. In all 10 observed γ-rays have been fitted in a revised decay scheme of the 83 min75Ge. The results are discussed and compared with those known from the 120 d75Se decay. Moreover, the isomeric (n, 2n) cross-section ratio for the production of the 46 s and 83 min isomers of75Ge has been determined, giving σm/(σm + σg) = 0.71 ± 0.04.RiassuntoLe caratteristiche di decadimento del75Ge di 83 min prodotto dalla reazione (n, 2n) con neutroni di 14.7 MeV su bersaglio arricchito di76Ge sono state studiate usando detettori γ di Ge(Li) di 32.2 cm3 e di NaI(Tl) di 7.6 cm×7.6 cm. Lo studio mostra la presenza di un raggio γ a 270.2 keV confermando un recente resoconto, ma non mostra nessun raggio γ a 136 keV (intensità <0.007) e quindi esclude il recentemente proposto β-feeding (l’unico primo vietato) per il ben definito stato 5/2+ a 400.6 keV in75As. Si sono trovati due nuovi raggi γ con energie 279.7±0.4 e 338.0±0.4 aventi intensità relative di 0.05±0.01 e 0.04±0.01, rispettivamente, rispetto a 100 per il raggio γ a 264.6 keV. In tutto 10 raggi γ osservati sono stati approssimati in uno schema di decadimento rivisto per il75Ge di 83 min. Si discutono i risultati e li si confronta con quelli conosciuti per il decadimento di75Se di 120 giorni. Inoltre il rapporto isomerico delle sezioni d’urto (n, 2n) per la produzione di isomeri di75Ge di 46 s e 83 min è stato determinato, dando σm/(σm + σg) = 0.71 ± 0.04.РезюмеИсследуются характеристики распада 83 м75Ge, образованного в реакции (n, 2n) нейтронами с энергией 14.7 МэВ на мишени, обогащенной76Ge, используя γ детекторы 32.2 см3 Ge(Li) и 7.6 cm×7.6 cm NaI(Tl). Исследование указывает на наличие γ-лучей с энергией 270.2 кэВ. Однако, не обнаружено γ-лучей с энергией 136 кэВ (интенсивность <0.007) и, следовательно, исключается недавно предложенный β-«фидинг» в хорошо установленное состояние 5/2+ при 400.6 кэВ в75As. Обнаружены две линии γ-лучей с энергиями 279.7±0.4 и 338.0±0.4, которые имеют относительные интенсивности 0.05±0.01 и 0.04±0.01, соответственно, по сравнению с 100 для γ-излучения с энергией 264.6 кэВ. Все 10 наблюденных линий γ-лучей удовлетворяют уточненной схеме распада 83 м75Ge. Обсуждаются полученные результаты и проводится сравнение с результатами для распада 120 д75Se. Определяется также отношение изомерных поперечных сечений (n, 2n) для рождения изомеров 46 с и 83 м75Ge, которое равно σm/(σm + σg) = 0.71 ± 0.04.

A technique for precision monitoring of target-stopper separation in recoil-distance lifetime measurements

Abstract An r.f. technique is described for measurement of absolute target-stopper separation in recoil-distance lifetime measurements of excited nuclear states. It is shown that the technique is suitable for precision monitoring of the target-stopper distance. The technique is sensitive enough to detect changes as small as 9 × 10−7 cm in the distance.

Weak transitions in160Tb decay

SummaryThe decay scheme of the 72.3d160Tb and γ-transitions in160Dy has been studied by γ-ray spectroscopy with high-efficiency Ge(Li) and HPGe detectors. The intensity of the 1004.8 keV γ-ray is measured to be 0.04±0.01 relative to 30 for the 879.353 keV γ-ray. Gamma-rays of energies 707.6 and 239.70 keV with relative intensities 0.010±0.005 and 0.002±0.001 are observed and assigned to160Dy. The energies and relative intensities of all other γ-rays are remeasured to remove anomalies in the previous reports. A new β-group of intensity (0.032±0.012)% and logft 11.2±0.2 is proposed to feed the 1288.6 keV level in160Dy. The total conversion coefficient of the 197.008 keV transition in160Dy is measured to be 0.22±0.08. The total andK-shell conversion coefficients of the 86.796 keV transition in160Dy are remeasured and the results obtained are 4.71±0.20 and 1.54±0.12, respectively. The results of the branching ratios of β and γ transitions are discussed. The band-mixing parametersz2 for160Dy is determined and it is observed that the measured γ-ray branching ratios do not lead to a unique value ofz2 for160Dy.RiassuntoSi studia lo schema di decadimento di 72.3d160Tb e le transizioni γ in160Dy con la spettroscopia dei raggi γ con rivelatori ad alta efficienza Ge(Li) e HPGe. L’intensità misurata del raggio γ a 1004.8 keV è 0.04±0.01 relativa a 30 per il raggio γ a 879.353 keV. Sono stati osservati e assegnati a160Dy raggi γ d’energia 707.6 e 239.70 keV con intensità relative 0.010±0.005 e 0.002±0.001. Sono state misurate nuovamente le energie e le intensità relative di tutti gli altri raggi γ per rimuovere le anomalie riscontrate in precedenti lavori. Si propone un nuovo gruppo β di intensità (0.032±0.012)% e logft 11.2±0.2 per alimentare il livello 1288.6 keV in160Dy. Il coefficiente misurato di conversione totale della transizione a 197.008 keV in160Dy risulta di 0.22±0.08. Si misurano nuovamente i coefficienti di conversione totale e dello stratoK della transizione a 86.796 keV in160Dy e i risultati ottenuti sono, rispettivamente, 4.71±0.20 e 1.54±0.12. Si discutono i risultati dei rapporti di diramazione delle transizioni β e γ. Si determina il parametroz2 di mescolamento di banda per160Dy e si osserva che i rapporti di diramazione dei raggi gamma non portano ad un unico valore diz2 per160Dy.