Search

High-spin states in Zr89 were populated in the Se80(C13,4n) reaction, and γ-ray coincidences were measured using the Indian National Gamma Array. The level scheme of Zr89 has been extended up to spin I=49/2 with the observation of a new dipole band. Directional correlation and polarization asymmetries of the γ rays have been measured to determine spin and parity of the levels. Line shapes of several transitions have been analyzed to determine lifetimes of the levels. Possible configurations of the band have been discussed using the cranked Nilsson-Strutinsky model. The calculations suggest a triaxial shape of the nucleus at high spins, and the band may represent rotation of the nucleus about the longest axis.

The positive-parity band structure of $^{110}\mathrm{Ag}$ has been established for the first time. A new decay path to the isomeric ${6}^{+}$ state has been observed for this band. The lifetimes of the high spin levels have been measured using the Doppler-shift attenuation method. The comparison of the experimental data with the numerical results of the shears mechanism with principal axis cranking calculation indicates that this band originates due to the tilted axis rotation. On the other hand, it has already been established that the negative-parity levels in the same spin domain originate due to the principal axis rotation.

The high-spin states in $^{133}\mathrm{Cs}$, populated using the reaction $^{130}\mathrm{Te}(^{7}\mathrm{Li},4n)$ with 45-MeV beam energy, have been extended up to an excitation energy of 5.265 MeV using the Indian National Gamma Array. The observed one- and three-quasiparticle bands in $^{133}\mathrm{Cs}$, built on the $\ensuremath{\pi}{h}_{11/2},\phantom{\rule{0.28em}{0ex}}\ensuremath{\pi}{g}_{7/2}$, $\ensuremath{\pi}{d}_{5/2}$; and ${(\ensuremath{\pi}{g}_{7/2}\ensuremath{\pi}{d}_{5/2})}^{1}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}^{\ensuremath{-}2}$ configurations, respectively, have similar structure as seen in the lighter odd-$A$ Cs isotopes. The experimental level scheme has been compared with the large-scale shell model calculation without truncation using the $jj55pna$ interaction, showing a good agreement for both positive- and negative-parity states.

The positive-parity band of 106Ag has been extended up to I = 25 ¯h and the lifetimes of the high spin levels of this band have been measured. The deduced transition rates decrease with increasing spin until I = 21 ¯h. Beyond this spin, the observed transition rates are substantially small and remain nearly constant. This is a novelobservation for a shears band. The observed features have been described within the framework of the shears mechanism with a principle axis cranking calculation.

The high spin negative parity states of Ag have been investigated with the B+Mo reaction at 39 MeV beam energy using the INGA facility at TIFR, Mumbai. From the γ-γ coincidence analysis, an excited negative parity band has been established and found to be nearly degenerate with the ground state band. The spin and parity of the levels are assigned using angular correlation and polarization measurements. This pair of degenerate bands in Ag is studied using the recently developed microscopic triaxial projected shell model approach. The observed energy levels and the ratio of the electromagnetic transition probabilities of these bands in this isotope are well reproduced by the present model. Further, it is shown that the partner band has a different quasiparticle structure as compared to the yrast band. © 2013 Elsevier B.V.

The negative parity non-yrast band of $^{106}\mathrm{Ag}$ has been studied to investigate the falling trend in magnetic dipole transition rates. In this context, the level lifetimes of the excited levels of this band have been measured using the Doppler shift attenuation method. The comparison of the experimental Routhian and the transition rates with the numerical results of the shears mechanism with the principal axis cranking calculation indicates that this band is generated due to the shears mechanism involving the three proton hole configuration.

The negative-parity yrast band of 110Ag has been extended significantly and the lifetimes of the high spin levels of this band have been measured. The experimentally observed level scheme and measured electromagnetic transition rates have been compared with the theoretical predictions of a model with two quasiparticles coupled to a triaxially deformed core. This calculation successfully reproduces the energy spectra and electromagnetic transition rates beyond I π = 12 − ℏ . These observations indicate that the principal axis of rotation is responsible for the generation of high angular momentum states along the yrast cascade in 110Ag. In all the other lighter isotopes, these states are generated through titled axis rotation. Thus, 110Ag is the first nucleus where the boundary between tilted and principal axis rotation could be established.

The lifetimes for the high spin levels of the yrast band of $^{110}$Cd has been measured. The estimated B(E2) values decrease with increase in angular momentum. This is the characteristic of Anti magnetic rotation as reported in $^{106,108}$Cd. However, alignment behavior of $^{110}$Cd is completely different from its even-even neighbors. A model based on classical particle plus rotor has been used to explore the underlying systematics and develop a self consistent picture for the observed behavior of these isotopes., Comment: 18 pages including 6 figures. Accepted to be published in PLB, with some modification in the text

Effects of Quinacrine Administration on the Testicular Function of Bat (Rhinopoma kinneari wroughton)

The high spin levels of 136 Ce have been established up to a spin of 23 ℏ through the heavy ion fusion evaporation reaction 124 Sn( 16 O, 4 n ) 136 Ce. The level scheme has been constructed by using γ – γ coincidence techniques, angular correlation, and polarization asymmetry measurements. The level scheme of 136 Ce exhibits many interesting features like several Δ I = 1 bands and a highly deformed band. The B ( M1 ) / B ( E2 ) ratios, B ( M1 ) and B ( E2 ) values have been obtained for several transitions in these bands from branching ratios and lifetimes measured by using the Doppler shift attenuation method. The observations have been compared with the results of tilted axis and principal axis cranking calculations.

The characteristics of a Compton-suppressed, two-fold segmented, Clover detector have been studied in singles and add-back modes for using it in the study of heavy-ion fusion–evaporation reactions. The measurements have been performed with standard sources of 152 Eu , 60 Co and in-beam γ -rays from the fusion–evaporation reaction 28 Si on 27 Al at E lab =100 MeV . Reduction in γ -ray Doppler broadenings due to the two-fold segmentation is demonstrated through in-beam data.

Negative parity high-spin states of 107Cd have been investigated using the reaction 94Zr(18O,5n), from the γ -ray coincidence events recorded by the Indian National Gamma Array. A magnetic dipole (M1) band structure was established for the first time in this nucleus decaying to the low-spin states via several paths. Lifetimes of five in-band levels in this band have been measured using the Doppler shift attenuation method. The experimentally deduced B(M1) values are found to decrease with increasing spin. The experimental observations, interpreted by the tilted axis cranking calculations, suggest that the M1 band is developed from the shears mechanism based on the 5qp configuration π (g−2 9/2) ⊗ ν(h11/2g 7/2), which is then crossed by another 5qp configuration π (g−2 9/2) ⊗ ν(h11/2). The semiclassical model of the shears mechanism also reasonably reproduces the decreasing trend of the observed B(M1) values as a function of spin, supporting the above interpretation. The present work highlights the unique coexistence of both magnetic and antimagnetic (observed by us earlier) rotation bands in one nucleus arising from the same proton configuration, but different neutron configurations.

The Clover detectors in their addback mode are excellent tools for detecting high-energy gamma rays (⩾2 MeV ) . The characteristics of these detectors, at energies above 2 MeV , are usually determined from simulation data or from extrapolation of the empirical data. This is the first time that the characteristics of a Compton suppressed Clover germanium detector have been studied up to 5 MeV using a radioactive 66 Ga (T 1/2 =9.41 h ) source.

Lifetimes have been measured up to the I=22+ level in the yrast positive-parity band for 78Kr using the recoil distance and lineshape analysis methods. The B(E2) and Qt values obtained from these measurements show a significant drop with increasing spin. The band crossings and the observed variation in Qt are understood through cranked shell-model, TRS and configuration-dependent shell-correction calculations assuming an oblate deformation for 78Kr at low spins.

The electric quadrupole transition rates for the high-spin yrast states of ${}^{104}$Pd have been measured by using the Doppler-shift attenuation method. These values decrease with the increase of angular momentum, which can be associated with the phenomenon of antimagnetic rotation. In the present work, a numerical calculation based on the semiclassical particle plus rotor model for antimagnetic rotation has been employed, giving a good description of the experimental Routhian and the transition rates and providing conclusive evidence of antimagnetic rotation in a nucleus other than cadmium.

The lifetimes of the excited levels for the two nearly degenerate bands of $^{106}\mathrm{Ag}$ have been measured using the Doppler-shift attenuation method. The deduced $B(E2)$ and $B(M1)$ rates in the two bands are found to be similar, except around the band crossing spin, while their moments of inertia are quite different. This is a novel observation for a nearly degenerate doublet band.

The high spin structure of 108 Ag nucleus has been studied using the reaction 11 B + 100 Mo at 39 MeV with Indian National Gamma Array (INGA) at TIFR-BARC accelerator facility. From the two- and higher-fold coincidence analysis of the emitted -rays, the level structure of the nucleus is built, with addition of around ∼ 60 new transi- tions. A new positive parity dipole band has been observed and significant additions have been made in the low spin region. A pair of nearly degenerate, negative parity, dipole bands is established, which is studied using the triaxial projected shell model (TPSM).

Lifetimes of high spin states up to { $$I^\pi $$ }=22+ in the yrast positive parity bands have been measured to investigate the shape evolution with increasing spin in 72, 74Se. The Q t values derived from these measurements indicate that prolate shape stabilizes for 72Se, while a triaxial shape develops for 74Se at higher spins. Comparison of the observed trend in Q t with spin for 72, 74Se with that of the corresponding kryptones isotones emphasizes the stability provided by N=38 prolate shell gap even at high rotational frequency.

A brief description of the nuclear structure studies performed with the 14-UD pelletron at TIFR has been presented. The experimental facilities developed for these studies are described. Some of the interesting results obtained for mass 70 to 80 nuclei are presented. The development of a recoil mass spectrometer and an Indian clover array for the study of high spin states in nuclei near drip lines is discussed.

A recoil mass spectrometer (RMS) has been designed, fabricated and installed at the 15° S beam-line of the Pelletron at TIFR. The RMS consists of a quadrupole doublet just after the target chamber followed by an ‘electrostatic deflector’, a magnetic dipole and a second electrostatic deflector. The recoils produced in the 12C + 58Ni reaction using 60 MeV 12C beam were focussed with the help of electric and magnetic fields and detected in a strip detector placed at the focal plane of the RMS. Further testing of the spectrometer to obtain mass resolution and efficiency are in progress.

Lifetime of levels up to 22+, have been measured in 78Kr and an oblate shape is assigned to the ground state using the CSM and the configuration dependent shell correction calculations. Calculations further show that 78Kr is highly γ-soft nucleus. The experimental Qt values coupled with theoretical calculations indicate an oblate shape for 78Kr at low spins and triaxial shape at higher spins

A pair of degenerate dipole bands with negative parity have been established in 106 In. Projected deformed Hartree-Fock calculations were carried out in order to understand the configurations of these bands and similar structures in neighbouring odd-odd nuclei.

The lifetimes of high spin states of 75 Kr have been determined via 50 Cr ( 28 Si, 2pn) 75 Kr reaction in positive parity band using the Doppler-shift attenuation method. The transition quadrupole moments Q t deduced from lifetime measurements have been compared with 75 Br. Experimental results obtained from lifetime measurement are interpreted in the framework of projected shell model.

An array consisting of six neutron detectors has been constructed for measurement of neutron multiplicities in heavy ion reactions. The measurements are reported to demonstrate that, even with a modest array of six neutron detectors, it is possible to infer unambiguously the neutron multiplicity (upto M"4) of the reaction channel from the neutron fold distribution obtained in coincidence with c-rays, if the array is calibrated with known reaction channels. The neutron multiplicity for the 991 keV c-ray produced in the two heavy ion reactions 133Cs(12,13C, xn) has been determined from this set-up-indicating that it deexcites levels in 142Pm. This is in agreement with the excitation function measurements for the same reactions. ( 2000 Elsevier Science B.V. All rights reserved.

Clover detector has been used as a Compton polarimeter to measure the linear polarization of γ-rays produced in heavy ion fusion reaction. The polarization sensitivity of the clover detector has been measured over γ-ray energies ranging from 386 to 1368 ke V. The E1 multipolarity of the 1117 keV transition in 99Rh has been established using this polarimeter. This has resulted in the assignment of negative parity to the band head at 3710 keV in 99Rh.

A motor driven plunger has been constructed for measuring lifetimes of nuclear excited states in pico second region. An array consisting of six neutron detectors was used to clean up γ-spectra obtained with CS-HPGe detectors. Lifetimes of low excited states in neutron deficient nuclei with low production cross-section e.g.81Y,77Kr and78Rb are reported.

A hot vacuum extraction technique for the determination of hydrogen in metal and alloy samples has been standardised. After measuring the total pressure of the evolved gases, individual hydrogen and deuterium intensities are measured using an on-line quadrupole mass spectrometer. Synthetic mixtures of H2 and D2, in known concentrations, have been analysed by QMS and an analytical expression correlating the measured [D2]/[HD] intensity ratio with the mole fraction of deuterium in the synthetic mixture has been arrived at. The precision and accuracy in the measurement of hydrogen is about 10% at 50 ppmw level.

The high spin states in A = 75, Kr and Br isotopes have been populated via fusion-evaporation reaction at an incident beam energy of 90 MeV. The de-exciting γ-rays were detected utilizing the Indian National Gamma Array (INGA). Lifetime of these excited high spin states were determined by Doppler-shift attenuation method. Experimental results obtained from lifetime measurement are interpreted in the frame work of projected shell-model to get better insight into the evolution of collectivity. Comparison of the calculations of the model with transitional quadrupole moments Qt of the positive and negative parity bands firmly established their configurations.

The resolution, efficiency and summing characteristics of a clover detector obtained from Eurisys Mesures, France, have been studied in the singles and the add-back mode. The results of the measurements using 152Eu and 60Co sources are presented in this paper.

The high spin states of {sup 82}Zr have been studied through the {sup 58}Ni({sup 27}Al, p2n){sup 82}Zr reaction using a 92 MeV {sup 27}Al beam up to an excitation energy {approximately}5.2 MeV and a spin of 12{h_bar}. The electromagnetic transition probabilities were obtained from the lifetimes of nuclear states measured with recoil distance and line shape analysis methods. The measured lifetimes indicate a reduction in Q{sub t} values in going from 2{sup +} to 4{sup +} state. {copyright} {ital 1997} {ital The American Physical Society}

Lifetimes of the excited states of a pair of positive-parity $\ensuremath{\Delta}I=2$ bands of ${}^{107}$Cd have been measured by using the Doppler-shift attenuation method. The obtained $B(E2)$ transition rates significantly decrease with increasing spin, a behavior typical of antimagnetic rotation (AMR). The observed results, interpreted by the semiclassical model (SCM) calculations, confirm these bands to be AMR bands resulting from the coupling of a pair of high-$\ensuremath{\Omega}$ ${g}_{9/2}$ proton holes to aligned ${g}_{7/2}{({h}_{11/2})}^{2}$ neutron particles. This is the first evidence for two AMR bands in a single nucleus.

Multi-nucleon transfer reactions 115In(12C,X with X = 14 C , 13 C , 11 C , 12 B , 11 B, 10 B , 10 Be , 9 Be , 7 Be , 7 Li , 6 Li and 6 He have been studied at an incident carbon ion energy of 84 MeV. Absolute cross sections have been measured. Energy spectra are examined in terms of a constrained phase space approach where the observed optimum Q-value forms the constraint.

Three different methodologies are reported for circumventing the isobaric interference of 238Pu at 238U during simultaneous thermal ionization mass spectrometric analysis of U and Pu. These are as follows: (i) obtaining the 235U238U amount ratio at lower evaporation filament current and hence eliminating the need for any isobaric interference correction due to 238Pu at 238U; (ii) determining the 240Pu239Pu amount ratio at lower evaporation filament current during the optimization of the ion current of U+ and Pu+ and calculating the 238Pu239Pu amount ratio of the unknown sample; (iii) optimizing the evaporation filament heating current for simultaneous mass spectrometric analysis of U and Pu and using the 240Pu239Pu amount ratio obtained from the first 2–3 blocks to arrive at the 238Pu239Pu atom ratio required in the interfering element correction (IEC) approach. The three methodologies described are useful for either (a) completely eliminating the need to know the 238Pu239Pu amount ratio or (b) determining the 238Pu239Pu amount ratio from the same filament loading prior to performing simultaneous mass spectrometric analysis. The drawbacks and advantages of each of the methodologies are discussed with respect to the accuracy of the data and the time of analysis. It is shown that the last methodology along with the IEC approach provides a universal solution to correct for the isobaric interference of 238Pu at 238U in all the unknown samples. The studies were carried out by using the conventional method of loading nitrate solutions of U and Pu, a double rhenium filament assembly, a multicollector Faraday cup detector system and employing synthetic mixtures of SRM-200-U and SRM-947-Pu with varying UPu ratios.

vhoice Cross sections for multinucleon transfer reactions are measured at several angles in the reaction 88 Sr( 12 C,X) - X ranging from 9 Be to 14 C at an incident carbon-ion energy of 87.5 MeV. In case of single-nucleon transfer reactions, the measured angular distributions of cross sections in transition to the ground and low-lying states in the 87,89 Sr and 89 Y nuclei are described well in terms of finite-range DWBA calculations. The transfer probability obtained from the experiments to well-defined shell-model orbits forms the single-particle unit for evaluation of the mechanism in multinucleon transfer reactions. The analysis reveals a small enhancement of the transfer probability corresponding to a proton-pair stripping. The mechanism of one-step “direct” transfer of a cluster is predominant in deuteron and 3 He transfer reactions. However, the transfer of a neutron pair seems to proceed through a sequential transfer of two neutrons.

It was predicted recently by us (Int. J. Mass Spectrom. Ion Processes, 116 (1992) 87) that accurate measurements of the Li2BO2+ ion yield ratio(s) do not always imply accurate determination of the elemental isotopic abundance ratio(s). Further insight into this aspect is provided here by demonstrating that the results of the isotopic analysis of a 6Li enriched lithium sample using different pairs of isotopic Li2BO2+ ions as monitors show considerable variations, irrespective of the actual experimental errors. A theoretical explanation of the observations is presented. The present investigation provides the guidelines for selecting the proper monitor Li2BO2+ ion-pair(s) and discusses the other analytical requirements for making possible accurate isotopic analysis of lithium of any given isotopic composition. Experimental observations showing the effect of isotopic fractionation on the formation of the Li2BO2+ ions are also elaborated and discussed.

Simultaneous isotopic analysis of uranium and plutonium using thermal ionization mass spectrometer coupled to a multi-collector detection assembly with 9 Faraday cups has been reported earlier. Subsequently investigations have been carried out (1) to understand the applicability of correction methodologies available to account for the contribution of238Pu at238U and (2) to evaluate the effectiveness of these methodologies on the accuracy of235U/238U atom ratio being determined, particularly when samples containing different U/Pu atom ratios. Isotopic fractionation for both U and Pu in the simultaneous isotopic analysis has been compared with the results of the individual analysis of these elements. The different isotopic fractionation factors observed for U were attributed to different conditions of analysis. There was no significant difference in the isotopic fractionation patterns for Pu. The consideration to extend this method to actual samples from our observations on synthetic samples with diferent U/Pu atom ratios containing U and Pu isotopic reference standards is described.

Polyatomic ions, often considered as causing interference in ICP-MS, SSMS and GDMS, are useful in thermal ionisation mass spectrometry (TIMS) for determining the atomic ratios of the elements, particularly for light elements. The objective of this paper is to provide a detailed discussion on the handling of the isotopic measurement data in TIMS using polyatomic ions, a useful technique for light elements, to reduce isotope fractionation effects. Taking as an example the Li2BO2+ ion for the determination of the 6Li/7Li or 10B/11B ratio of the unknown sample, a detailed theoretical analysis is presented for optimum selection of the pair of polyatomic ions to be used to determine the isotopic ratio of the element. The theory is supported by experimental data from the literature in three different examples: (i) the isotopic analysis of natural Li samples using the SRM-951-B isotopic standard; (ii) the isotopic analysis of an enriched 6Li sample using SRM-951-B; (iii) the isotopic analysis of an enriched 10B sample using natural Li (Svec standard). It is shown that the four polyatomic peaks observed in the m/z range of 54–57 are of practical importance. A qualitative idea can be obtained about the isotopic composition of Li and B in the sample (natural or enriched) based on the intensity distribution of these four peaks in the mass spectrum. When calculating accurate atomic ratios from the observed intensities of the polyatomic peaks, a simple “rule of thumb” should be kept in mind: the polyatomic ratio that is closer to the expected atomic ratio provides an accurate value of the atomic ratio of the element in the unknown sample. Even between the two polyatomic ion ratios, better accuracy is possible in cases which do not magnify the error during calculation and show less isotopic fractionation in the ion source. It has been stressed that the two peaks of highest intensity in the polyatomic ion are not necessarily the best for arriving at atomic ratios during the analyses of unknown samples, for depleted as well as enriched 6Li and 10B samples.

Near yrast states in ${}^{89}$Zr were investigated up to high spin using the fusion evaporation reaction ${}^{80}$Se(${}^{13}$C, 4$n$) at an incident beam energy of 50 MeV. Excited levels of ${}^{89}$Zr have been observed up to $\ensuremath{\sim}$10 MeV excitation energy and spin $\ensuremath{\sim}$37/2$\ensuremath{\hbar}$ using the prompt gamma spectroscopy technique with the Indian National Gamma Array (INGA). The angular distribution, directional correlation, and polarization measurements were carried out to assign the spin and parity of the newly reported states. The structures of both the positive and negative parity states up to highest spin observed in the present experiment have been compared with shell-model calculations using two recently developed residual interactions, JUN45 and jj44b. The role of proton excitations from ${p}_{3/2}$ and ${f}_{5/2}$ orbitals to the ${g}_{9/2}$ orbital for the higher spin states has been discussed.

High spin states in $^{112}$In were investigated using $^{100}$Mo($^{16}$O, p3n) reaction at 80 MeV. The excited level have been observed up to 5.6 MeV excitation energy and spin $\sim$ 20$\hbar$ with the level scheme showing three dipole bands. The polarization and lifetime measurements were carried out for the dipole bands. Tilted axis cranking model calculations were performed for different quasi-particle configurations of this doubly odd nucleus. Comparison of the calculations of the model with the B(M1) transition strengths of the positive and negative parity bands firmly established their configurations., 10 pages, 11 figures, 2 tables

Studies have been carried out on the solubility of Pu(III) oxalate by precipitation of Pu(III) oxalate from varying concentrations of HNO3/HCl (0.5–2.0M) solutions and also by equilibrating freshly prepared Pu(III) oxalate with solutions containing varying concentrations of HNO3/HCl, oxalic acid and ascorbic acid. Pu(III) solutions in HNO3 and HCl media were prepared by reduction of Pu(IV) with ascorbic acid. 0.01–0.10M ascorbic acid concentration in the aqueous solution was maintained as holding reductant. The solubility of Pu(III) oxalate was found to be a minimum in 0.5M–1M HNO3/HCl solutions containing 0.05M ascorbic acid and 0.2M excess oxalic acid in the supernatant.

Studies are reported on the evaporation and ionisation behaviour of uranium (U) and plutonium (Pu) under conditions of their simultaneous mass spectrometric analyses using a double rhenium filament assembly, a multicollector Faraday cup detector system and a synthetic mixture of SRM-200-U and SRM-947-Pu with the U/Pu ratio as 10. The U+ and UO+ ions start appearing at an evaporation filament temperature lower than that for appearance of Pu+. However, the ion current of Pu+ is 5-10 times greater than that of U+. The coexistence of oxides of Pu and U on the evaporation filament appears to enhance the stability of UO+. Two different approaches are compared to account for Pu-238 isobaric interference at U-238 during simultaneous isotopic analyses of U and Pu from the same filament loading. The K factor values for U and Pu during their simultaneous mass spectrometric analyses are lower compared with those observed previously when U and Pu are analysed from separate filament loadings with chemically pure fractions of each.

Extraction of trivalent (Pu3+, Am3+, actinides and Eu3+, a representative of lanthanides) and tetravalent (Np4+ and Pu4+) actinides has been studied with dihexyl N,N-di-ethylcarbamoylmethyl phosphonate (DHDECMP) in combination with TBP in benzene from 2M nitric acid. The stoichiometries of the species extracted were found to be M(NO3)3·(3−n) TBP·n DHDECMP (for trivalent ions) and M(NO3)4·(2−n) TBP·n DHDECMP (for tetravalent ions) by the slope ratio method. The extraction constants evaluated (from the distribution data) indicate that for tetravalent ions (with solvation number two) the extraction constant increases when TBP (Kh=0.17) molecules are successively replaced by more basic DHDECMP (Kh=0.34) molecules. However, for trivalent ions (with solvation number three) when TBP molecules are totally replaced by DHDECMP molecules stereochemical factors appear and instead of increase, a substantial decrease in extraction constants is observed for Eu3+ and Am3+, a lesser decrease being observed for Pu3+ (larger ion).

The high spin levels in [sup 84]Sr have been populated through the [sup 59]Co([sup 28]Si, 3[ital p]) reaction using 98 MeV [sup 28]Si beam. A regular band structure was found to develop above the 12[sup +] state with a deformation parameter [beta]=0.21[plus minus]0.04 and [gamma]=8[degree][plus minus]6[degree]. The projected Hartree-Fock calculations predict a two proton and two neutron aligned configuration for this band. The predicted quadrupole moment for this configuration is also in good agreement with the experimental values obtained from the lifetime measurements. In addition, a large enhancement in [ital B]([ital M]1)/[ital B]([ital E]2) transition rates has been observed in the negative parity band above the 11[sup [minus]] state.

The high spin levels of $^{84}\mathrm{Y}$ have been established up to 12 MeV excitation energy and probable spin of ${25}^{+}$ through the reaction $^{59}\mathrm{Co}$${(}^{28}$Si,2pn${)}^{84}$Y using in-beam \ensuremath{\gamma}-ray spectroscopic techniques. The \ensuremath{\gamma} transitions in $^{84}\mathrm{Y}$ have been identified through the particle-gamma coincidences. The level scheme was constructed through the \ensuremath{\gamma}-\ensuremath{\gamma} coincidences, angular distribution, and directional correlation orientation ratios. The positive parity yrast band built on the (\ensuremath{\pi}${\mathit{g}}_{9/2}$\ensuremath{\bigotimes}\ensuremath{\nu}${\mathit{g}}_{9/2}$) configuration shows a large signature splitting and a signature inversion at I\ensuremath{\sim}11\ensuremath{\Elzxh}. The measured B(E2; I\ensuremath{\rightarrow}I-2) values give a deformation ${\mathrm{\ensuremath{\beta}}}_{2}$\ensuremath{\sim}0.17. The negative parity band shows a signature inversion at I\ensuremath{\sim}11\ensuremath{\Elzxh} and B(M1; I\ensuremath{\rightarrow}I-1) enhancement for Ig11\ensuremath{\Elzxh}. The projected Hartree-Fock and the cranked shell model calculations provide an understanding for the observed properties of the energy levels in $^{84}\mathrm{Y}$.

The proton-stripping reaction 115 In( 12 C, 11 B) 116 Sn has been studied using 84 MeV 12 C beams. Two groups of states centred at 4.2 and 5.5 MeV excitation in 116 Sn probably have configurations involving particle-hole states of ( 1 g −1 9 2 , 1 g 7 2 ) and ( 1 g − 9 2 , 1 h 11 2 ) origin. The identification is based on the published light-ion-induced proton-transfer studies as well as the shell- model calculations. The angular distributions and the excitation functions for the two groups have been measured and analysed in terms of the finite-range DWBA. The optical potentials in the entrance channel have been determined by fitting the measured elastic angular distribution data. The consistency of the normalisation constant determined indicates that the dissipation mechanism, at least, for the one-nucleon transfer stage proceeds predominantly through the direct reaction mechanism.

The isotopic analysis of boron has been carried out using different pairs of isotopic Li2BO ions as monitors. The precision of the mass spectromctric measurements of different molecular abundance ratios is roughly the same. However, the values of the 10B/11B abundance ratio calculated from the experimental ratios of different pairs of isotopic molecular ions show large variations. These variations are shown to be a logical consequence of the calculation step which leads to the magnification of measurement errors to different extents for different peak ratios. Similar arguments would apply for the isotopic analysis of any element employing the molecular ion beam technique. The effect of isotopic fractionation on the molecular abundances is also discussed. The important implication of the present investigation is that it sets the guidelines for selecting suitable monitor molecules to avoid such errors.

Problems encountered in the determination of uranium in rubidium uranium sulphate (Rb2U(SO4)3) employing isotope dilution thermal ionisation mass spectrometry (ID-TIMS) are discussed. The positive bias of 0.2 to 0.3% in the determination of uranium in Rb2U(SO4)3 by ID-TIMS with respect to the stoichiometric composition has been resolved by modifying the chemical exchange procedures. The concentration of uranium in Rb2U(SO4)3 could be determined with an accuracy better than 0.1% employing the HClO4 treatment for proper isotopic exchange between the spike and sample isotopes.