Publications (20)12.66 Total impact
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Article: Indirect nuclear physics techniques for studying nova nucleosynthesis
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ABSTRACT: Classical novae are a site of explosive nucleosynthesis where hydrogen rich material from a companion giant star accretes onto the surface of a white warf. Critical to our understanding of nova explosions are proton‐capture reaction rates involved in the nucleosynthesis. While, ideally, all of the relevant (p,γ) reactions would be measured directly, in practice, such measurements are very challenging and are only possible in a few cases. This provides considerable scope for indirect measurements including transfer reactions, mass measurements, beta‐decay and gamma‐ray spectroscopy. The latter technique, until recently largely neglected as an input in nuclear astrophysics analyses, has clear advantages in locating resonances with high energy precision and assisting in determining the spin and parity of resonances. Such information is very valuable in a complementary approach to indirect determinations of key reaction rates.AIP Conference Proceedings. 03/2009; 1098(1):82-87. -
Conference Proceeding: Heavy ion radiative capture of $^12$C + $^12$C
State of the Art in Nuclear Cluster Physics (SOTANCP2008); 11/2008 -
Article: Level structure of^{103} Ag at high spin
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ABSTRACT: High spin states in 103Ag were investigated with the Gammasphere array by using the 72Ge(35Cl,2p2n)103Ag reaction at an incident beam energy of 135 MeV. A ΔJ=1 sequence with predominantly magnetic transitions and two nearly degenerate ΔJ=1 doublet bands have been observed. The dipole band shows a decreasing trend in the B(M1) strength as function of spin, a well-established feature of magnetic bands. The nearly degenerate band structures satisfy the three experimental signatures of chirality in the nuclei; however, microscopic calculations are indicative of a magnetic phenomena.Phys. Rev. C. 12/2007; 77(2). -
Article: Recoil Beta Tagging: Application to the study of odd-odd near proton drip line nuclei, 74Rb and 78Y
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ABSTRACT: We present a study of low-spin states in 74Rb and 78Y using the new technique of Recoil Beta Tagging. This yielded new information on 74Rb and has provided the first evidence for non-isomeric T= 1 states in 78Y.The European Physical Journal Special Topics 10/2007; 150(1):147-148. · 1.56 Impact Factor -
Article: High-spin structure and Band Termination in $^{103}$Cd
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ABSTRACT: Excited states of the neutron deficient $^{103}$Cd nucleus have been investigated via the $^{72}$Ge($^{35}$Cl, p3n) reaction at beam energy of 135 MeV by use of in-beam spectroscopic methods. Gamma rays depopulating the excited states were detected using the Gammasphere spectrometer with high-fold $\gamma$-ray coincidences. A quadrupole $\gamma$-ray coincidence analysis ($\gamma^{4}$) has been used to extend the known level scheme. The positive parity levels have been established up to $J = 35/2\hbar$ and $E_{x} = 7.071$ MeV. In addition to the observation of highly-fragmented level scheme belonging to the positive-parity sequences at E$_{x}\sim$ 5 MeV, the termination of a negative-parity sequence connected by $E2$ transitions has been established at $J = 47/2 \hbar$ and $E_{x} = 11.877$ MeV. The experimental results corresponding to both the positive- and negative-parity sequences have been theoretically interpreted in the framework of the core particle coupling model. Evidence is presented for a shape change from collective prolate to non-collective oblate above the $J^{\pi} = 39/2^{-}$ (8011 keV) level and for a smooth termination of the negative-parity band.10/2007; -
Article: Coulomb shifts and shape changes in the mass 70 region
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ABSTRACT: The technique of recoil β tagging has been developed which allows prompt γ decays in nuclei from excited states to be correlated with electrons from their subsequent short-lived β decay. This technique is ideal for studying nuclei very far from stability and improves in sensitivity for very short-lived decays and for high decay Q-values. The method has allowed excited states in 78Y to be observed for the first time, as well as an extension in the knowledge of T=1 states in 74Rb. From this new information it has been possible to compare Coulomb energy differences (CED) between T=1 states in 70Br/70Se, 74Rb/74Kr, and 78Y/78Sr. The A=70 CED exhibit an anomalous behavior which is inconsistent with all other known CED. This behavior may be accounted for qualitatively in terms of small variations in the Coulomb energy arising from shape changes.Phys. Rev. C. 06/2007; 75(6). -
Article: Lifetime measurements of Triaxial Strongly Deformed bands in $^{163}$Tm
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ABSTRACT: With the Doppler Shift Attenuation Method, quadrupole transition moments, $Q_t$, were determined for the two recently proposed Triaxial Strongly Deformed (TSD) bands in $^{163}$Tm. The measured $Q_t$ moments indicate that the deformation of these bands is larger than that of the yrast, signature partners. However, the measured values are smaller than those predicted by theory. This observation appears to be valid for TSD bands in several nuclei of the region06/2007; -
Article: Evidence for particle-hole excitations in the triaxial strongly-deformed well of ^{163}Tm
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ABSTRACT: Two interacting, strongly-deformed triaxial (TSD) bands have been identified in the Z = 69 nucleus ^{163}Tm. This is the first time that interacting TSD bands have been observed in an element other than the Z = 71 Lu nuclei, where wobbling bands have been previously identified. The observed TSD bands in ^{163}Tm appear to be associated with particle-hole excitations, rather than wobbling. Tilted-Axis Cranking (TAC) calculations reproduce all experimental observables of these bands reasonably well and also provide an explanation for the presence of wobbling bands in the Lu nuclei, and their absence in the Tm isotopes.12/2006; -
Article: Spin-parity measurements in the neutron-rich N ∼ 20 34P and 36S nuclei
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ABSTRACT: Yrast and near-yrast energy levels in the neutron-rich N ∼ 20 nuclei 34P, 36S were populated using transfer/deep-inelastic processes following the 34S + 115In reaction at an incident energy of 140MeV. The use of a multi-clover array has facilitated polarization measurements of the observed γ-rays and necessitated some changes in the previously known level scheme. The observation of the negative-parity levels in these nuclei on the periphery of the “island of inversion” is indicative of the influence of the intruder orbitals on the level structure at low spins. Shell-model calculations indicate that the inclusion of the orbitals from the upper pf shell is important even for the low-lying positive-parity states.European Physical Journal A 07/2006; 29(2):151-159. · 2.19 Impact Factor -
Article: High Spin Spectroscopy of 137La
Nuclear Physics A 01/2006; 775:153. · 1.54 Impact Factor -
Dataset: Structure of odd–odd 136 La at high spin
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ABSTRACT: The high spin states in the N = 79 odd–odd 136 La nucleus have been investigated by in-beam γ -spectroscopic techniques following the 130 Te(11 B, 5n) 136 La reaction at E = 52 MeV using an array, consisting of eight Compton-suppressed clover germanium detectors. Thirty nine new γ rays have been assigned to 136 La on the basis of γ ray singles and γ γ -coincidence data. The level scheme of 136 La has been extended above the known 115 ms isomer upto an excitation energy of 4.6 MeV and spin 18 ¯ h. Thirty one new levels have been proposed and spin-parity assignments for most of the newly proposed levels have been made on the basis of the deduced asymmetry ratios and polarisation information for the de-exciting transitions. The observed positive parity yrast band has been com-pared with the theoretical calculation, done within the framework of particle rotor coupling model (PRM) where the two odd quasi-particles are coupled to an axially symmetric core. The level struc-ture has been discussed in the light of the known systematics of the neighbouring N = 79 isotonic nuclei. 2005 Elsevier B.V. All rights reserved. -
Article: High-spin states in the odd-odd nucleus 146Tb
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ABSTRACT: The odd-odd 146Tb nucleus has been investigated using the 115In(34S,3n) reaction at 140 MeV incident energy using an array of eight Compton-suppressed Clover detectors. Based on the observed γ-γ coincidences, the level structure of 146Tb has been extended up to Ex∼10 MeV. Linear polarization measurements have been combined with angular correlations of the observed γ rays to assign the electromagnetic nature to the transitions. Probable origin of a cascade of M1 transitions observed around 8 MeV excitation energy has been discussed.Phys. Rev. C. 10/2004; 70(4). -
Article: Lifetime measurements of microsecond isomers in the N= 48 nuclei^{88} Zr and^{90} Mousing recoil-isomer tagging
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ABSTRACT: The recoil-isomer tagging technique has been used to study the isomeric states of nuclei in the vicinity of the N=50 shell closure. The nuclei of interest were separated from the projectilelike nuclei and other evaporation residues and transported to the focal plane of a recoil separator. The decay of the tagged isomer was studied at the focal plane using a high-purity Ge detector. The prompt transitions feeding the isomer were detected in an array of Clover Ge detectors placed around the target. The measured half-lives of the 8+ isomers in 88Zr and 90Mo are 1.41(−0.09)(+0.12) μs and 1.17(−0.07)(+0.19) μs, respectively. The corresponding transition probabilities are in reasonable agreement with the predictions of shell model calculations. The systematics of effective charges (ep and en) for N=48 nuclei are qualitatively understood in these calculations.Phys. Rev. C. 07/2004; 70(1). -
Article: Experimental study of nuclear structure of^{91} Mo at high spin
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ABSTRACT: The high spin structure of 91Mo with neutron and proton number close to magicity has been investigated using the 63Cu(31P,xnyp) reaction at an incident beam energy of 125 MeV. The level at Ex=3811 keV has been assigned a negative parity based on our polarization measurements. In view of this change, the observed level structure for 91Mo so far does not have any negative parity sequence. More than 30 new transitions were observed and placed in the decay scheme, which has been extended up to spin of J∼39∕2ℏ and an excitation energy of Ex∼10 MeV. The energy spectrum bears signature of core breaking viz. presence of high energy (Eγ∼2 MeV) γ rays originating due to excitation of nucleons across the shell gaps. The proposed level scheme is compared with large basis spherical shell model calculations. Excitation of protons across Z=38 shell dominates the level structure up to moderate spins i.e., J∼27∕2ℏ. Configurations arising due to excitation of a single νg9∕2 across N=50 shell gap dominate the higher angular momentum J⩾35∕2ℏ states.Phys. Rev. C. 05/2004; 69(5). -
Article: A composite chiral pair of rotational bands in the odd-A nucleus 135Nd.
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ABSTRACT: High-spin states in 135Nd were populated with the 110Pd(30Si,5n)135Nd reaction at a 30Si bombarding energy of 133 MeV. Two DeltaI=1 bands with close excitation energies and the same parity were observed. These bands are directly linked by DeltaI=1 and DeltaI=2 transitions. The chiral nature of these two bands is confirmed by comparison with three-dimensional tilted axis cranking calculations. This is the first observation of a three-quasiparticle chiral structure and establishes the primarily geometric nature of this phenomenon.Physical Review Letters 10/2003; 91(13):132501. · 7.37 Impact Factor -
Article: Analog E1 transitions and isospin mixing
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ABSTRACT: We investigate whether isospin mixing can be determined in a model-independent way from the relative strength of E1 transitions in mirror nuclei. The specific examples considered are the A=31 and A=35 mirror pairs, where a serious discrepancy between the strengths of 7/2-→5/2+ transitions in the respective mirror nuclei has been observed. A theoretical analysis of the problem suggests that it ought to be possible to disentangle the isospin mixing in the initial and final states given sufficient information on experimental matrix elements. With this in mind, we obtain a lifetime for the relevant 7/2- state in 31S using the Doppler-shift attenuation method. We then collate the available information on matrix elements to examine the level of isospin mixing for both A=31 and A=35 mirror pairs.Phys. Rev. C. 78(2). -
Article: Triaxial shape coexistence and new aligned band in^{178} Os
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ABSTRACT: High spin states in 178Os were studied by means of 165Ho(20Ne,p6n)178Os fusion evaporation reaction at a beam energy of 150 MeV, using a clover detector array. Several new transitions belonging to 178Os were placed in a level scheme and a new aligned rotational band was observed in addition to earlier known bands. Spin-parity assignments for most of the proposed levels were made using the deduced directional correlation orientation and polarization measurements for the de-exciting transitions. Experimental results are compared with the projected angular momentum deformed Hartree-Fock model calculations and cranked Woods-Saxon model calculations. This nucleus is predicted to be prolate deformed in the ground state but the γ-softness at higher excitation is revealed by the cranked Woods-Saxon model and the geometrical asymmetric model calculations.Phys. Rev. C. 80(5). -
Article: Analog E1 transitions and isospin mixing
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ABSTRACT: We investigate whether isospin mixing can be determined in a model-independent way from the relative strength of E1 transitions in mirror nuclei. The specific examples considered are the A=31 and A=35 mirror pairs, where a serious discrepancy between the strengths of 7/2--->5/2+ transitions in the respective mirror nuclei has been observed. A theoretical analysis of the problem suggests that it ought to be possible to disentangle the isospin mixing in the initial and final states given sufficient information on experimental matrix elements. With this in mind, we obtain a lifetime for the relevant 7/2- state in 31S using the Doppler-shift attenuation method. We then collate the available information on matrix elements to examine the level of isospin mixing for both A=31 and A=35 mirror pairs. -
Article: THE NORTHWEST FRONTIER: SPECTROSCOPY OF N similar to Z NUCLEI BELOW MASS 100
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ABSTRACT: The spectroscopy and structure of excited states of N similar to Z nuclei in the mass 70-100 region has been investigated using two techniques. In the A similar to 70-80 region fusion evaporation reactions coupled with the recoil-beta-tagging method have been employed at Jyvaskyla to study low-lying states in odd-odd N = Z nuclei. Results from these and other data for known odd-odd nuclei above mass 60 will be discussed. In the heavier mass 90 region a fragmentation experiment has been performed using the RIS-ING/FRS setup at GSI. This experiment was primarily aimed at searching for spin gap isomers in nuclei around A similar to 96. The objectives of the latter experiment will be discussed.ACTA PHYSICA POLONICA B. 40(3):611-620. -
Article: Evidence for particle–hole excitations in the triaxial strongly-deformed well of 163Tm
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ABSTRACT: Two interacting, strongly-deformed triaxial (TSD) bands have been identified in the Z=69 nucleus 163Tm. This is the first time that interacting TSD bands have been observed in an element other than the Z=71 Lu nuclei, where wobbling bands have been previously identified. The observed TSD bands in 163Tm appear to be associated with particle–hole excitations, rather than wobbling. Tilted-axis cranking (TAC) calculations reproduce all experimental observables of these bands reasonably well and also provide an explanation for the presence of wobbling bands in the Lu nuclei, and their absence in the Tm isotopes.Physics Letters B.
Top co-authors
Top Journals
Institutions
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2007–2009
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The University of York
- Department of Physics
York, ENG, United Kingdom -
CUNY Graduate Center
New York City, NY, USA
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2006–2007
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UGC-DAE Consortium for Scientific Research
Indore, State of Madhya Pradesh, India
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