Gamma-gamma Directional Correlation Research Articles

Nuclear structure of30S and its implications for nucleosynthesis in classical novae

The uncertainty in the 29P(p,gamma)30S reaction rate over the temperature range of 0.1 - 1.3 GK was previously determined to span ~4 orders of magnitude due to the uncertain location of two previously unobserved 3+ and 2+ resonances in the 4.7 - 4.8 MeV excitation region in 30S. Therefore, the abundances of silicon isotopes synthesized in novae, which are relevant for the identification of presolar grains of putative nova origin, were uncertain by a factor of 3. To investigate the level structure of 30S above the proton threshold (4394.9(7) keV), a charged-particle spectroscopy and an in-beam gamma-ray spectroscopy experiments were performed. Differential cross sections of the 32S(p,t)30S reaction were measured at 34.5 MeV. Distorted wave Born approximation calculations were performed to constrain the spin-parity assignments of the observed levels. An energy level scheme was deduced from gamma-gamma coincidence measurements using the 28Si(3He,n-gamma)30S reaction. Spin-parity assignments based on measurements of gamma-ray angular distributions and gamma-gamma directional correlation from oriented nuclei were made for most of the observed levels of 30S. As a result, the resonance energies corresponding to the excited states in 4.5 MeV - 6 MeV region, including the two astrophysically important states predicted previously, are measured with significantly better precision than before. The uncertainty in the rate of the 29P(p,gamma)30S reaction is substantially reduced over the temperature range of interest. Finally, the influence of this rate on the abundance ratios of silicon isotopes synthesized in novae are obtained via 1D hydrodynamic nova simulations.

Gamma-gamma directional correlation measurements in130,132Xe following thermal neutron capture by natural xenon

Directional correlations of gamma-ray cascades in 130,132Xe have been measured following thermal n capture by a pressurised natural xenon gas target. Gamma-ray singles spectra were measured up to 5.5 MeV and the coincidence correlation data were obtained for the energy range 0.2-2.5 MeV. Decay schemes were developed on the basis of the coincidence measurements. The data spin-parity assignments to be made to most levels lying below 3.5 MeV in the 132Xe and the multiple mixing ratios to be evaluated for the more intense transitions. The results are fitted to IBM-1 and IBM-2 and are also compared with the prediction of the dynamic deformation model of Kumar (1983). The 23+ level at 1985 keV in 132Xe is considered to be a mixed-symmetry state with B(M1; 23+ to 21+)=0.29 mu N2.

Evidence for entrance channel effects in neutron and high-energy gamma-ray emission

Gamma-gamma directional correlation and neutron-gamma coincidence measurements give evidence for precompound neutron and precompound high-energy gamma-ray emission in nuclear fusion reactions with 12 C projectiles. The precompound neutrons emanate from the hot collision zone mainly formed in central collisions. The precompound gamma rays contribute to the gamma-ray spectrum at somewhat lower energies than the giant dipole resonance and are associated with the formation of nuclear “molecular” configurations of the beam and target nuclei.

Dominance of stretched E1 transitions in statistical gamma decay

The gamma transitions in the energy range 2–8 MeV following 113,115In( 12 C, x n) reactions at E lab ≈ 100 MeV have been studied by gamma-gamma directional correlation and linear polarization measurements. Electric dipole transitions are found to dominate, of these approximately 80% are stretched. The average spin removed in each transition is 0.7(2)ħ.

Decay studies of131Ba

The electron-capture decay of131Ba (T1/2=11.7 d) to excited levels of131Cs has been studied using high resolution semiconductor detectors. The presence of 1046.9 keV gamma-ray in between 1170.6 and 123.8 keV levels, in addition to 1047.6 keV gamma-ray from 1047.6 keV level to ground state of131Cs is confirmed through gamma-gamma coincidence measurements. TheK-capture probabilities to 1047 keV, 696 keV and 620 keV levels are measured usingX-gamma coincidence method. The gamma-gamma directional correlation measurements of the cascades 496-123, 240-133, 486-133, 404-216, 480-216 and 832-216 keV are carried out and spins and multipolarities of the levels and transitions involved are studied.

Gamma-gamma directional correlations: Simplifications at high spin

We derive simplified expressions, valid at high spin, for the gamma-gamma directional correlation function. With only four directional distribution coefficients to characterize the coincident transitions, close agreement is obtained with the exact result already at spin 20 h ̵ .

Study of the radioactive decay of192Ir

Theβ − and electron capture decays of192Ir to the levels of192Pt and192Os respectively have been investigated to verify the existence of some of weak gamma transitions reported earlier. Gamma-gamma directional correlation measurements have been done for 13-cascades. Multipole admixture of 201, 283, 485 keV gamma transitions in192Os and 296, 308, 416, 604 keV gamma transitions in192Pt have been deduced. A spin value of 4+ has been reaffirmed on the basis of almost zero intensity of 1201 keV gamma ray (4+→0+) and 416→(468)→316 keV cascade directional correlation measurements.

Nuclear quadrupole interaction at133Cs in some barium compounds

Nuclear quadrupole interaction frequencies at133Cs following the electron-capture decay of133Ba for BaSO4, Ba/BrO3/2 and Ba/NO3/2 were obtained by measuring the perturbation of 356–81 keV cascade of133Ba. Nuclear quadrupole interaction frequencies for BaSO4 and Ba/BrO3/2 are 17.2 Mrad sec−1 and 14.6 Mrad sec−1, respectively, while no perturbation of 356–81 keV cascade was observed in case of Ba/NO3/2. Further the possibility of any after-effects of electron-capture decay is ruled out through the measurement of 276–161 keV gamma-gamma directional correlation.

Density dependent resonance behaviour of a perturbed gamma-gamma directional correlation in a magnetic field

Using pure gaseous H275Se sources with densities between 1.9×1015/cm3 and 3.8·1017/cm3, the directional correlation of the 121.1–279.5 keV gamma-gamma cascade of75As was measured as a function of the strength of an external magnetic field. The anisotropy shows a resonance behaviour around zero magnetic field with a broadening of the curves for increasing density. A comparison with the theory of Leisi was possible for the source with the lowest density. Using the stochastic model of Bosch and Spehl, the theory of Leisi was extended to describe the broadening of the curves. The measured half widths of the curves were fitted to the theory yielding a cross section of 1.6 ×10−13 cm2 for charge transfer collisions in the eV energy region between As ions and H2Se molecules.

Gamma-Gamma Directional Correlations in 160Dy

The gamma-gamma directional correlation coefficients of 16 cascades in 160 Dy following the decay of 160 Tb ( t 1/2 =72.1 d) have been measured using a Ge(Li)-NaI(Tl) coincidence set-up (2 τ≈6 n sec). Out of these, the correlation coefficients of the 310-962, 338-962, 392-(879)-87, 1003-(197)-87, 1103-(197)-87 and 1115-197 keV cascades have been measured for the first time. From these correlation measurements the spin value of 4 - has been confirmed for the 1386.5 keV level. The multipole mixing ratios of the 1003, 1103, 1115, 1200 and 1312 keV transitions in 160 Dy have been determined for the first time.

A program for calculating gamma-gamma directional correlation coefficients and angular distribution coefficients for gamma rays of mixed multipolarities from partially aligned nuclei

A program for calculating gamma-gamma directional correlation coefficients and angular distribution coefficients for gamma rays of mixed multipolarities from partially aligned nuclei

A program for calculating gamma-gamma directional correlation coefficients and mixing pations

A program for calculating gamma-gamma directional correlation coefficients and mixing pations

Gamma-gamma directional correlation measurements in144Nd

Gamma-gamma directional correlations have been measured for cascades in 144Nd following thermal-neutron capture by 143Nd. Unique multipole mixing ratios have been assigned to 12 transitions. Coincidence relations established from 18 coincidence gates have enabled an extensive decay scheme to be constructed. The results are compared with the predictions of the interacting boson approximation and some agreement is found. The 2+ assignment to the 1560 keV state is confirmed, which is in conflict with existing averaged resonance capture data.

Gamma-gamma directional correlation measurements in146Nd following thermal-neutron capture

The directional correlations of cascade gamma rays in 146Nd formed following thermal-neutron capture have been measured. The coincidence information allows the authors to extend the decay scheme while the correlation data provide unique spin-parity assignments to many levels and also the multipolarity of 25 transitions. The experiment also indicates several levels that should have been seen in the neutron averaged resonance capture experiment if the primary gamma rays were dipole. The data are examined within the framework of the IBA model.

Nature of the 153 and 270 keV Transitons in119Sb from119mTe

The 153 and 270 keV transitions in 119 Sb have been investigated for the presence of any anomalous conversion through conversion electron intensity and conversion-electron gamma and gamma-gamma directional correlation measurements. The resulting subshell ratios and particle parameters have been analysed for the accurate determination of mixing ratios for the transitions. The results are δ 153 =±0.0025 and δ 270 =0.10± 0.03 0.20 . The conversion process has been found to be normal in both cases.

Gamma-gamma directional correlation study of model membranes

Measurements of the perturbed gamma-gamma directional correlation were made for the 173-247 keV cascade in 111Cd at the In ion site in dipalmitoylphosphatidylcholine liposomes. A time-dependent electric quadrupole interaction was observed. Below the order in equilibrium fluid phase transition temperature the exponential damping coefficient was lambda 2 = 0.033 +/- 0.007 ns-1. Above the transition temperature the coefficient was lambda 2 = 0.015 +/- 0.006 ns-1 indicating a twofold increase in molecular mobility in the disordered phase. Absolute values for the motional correlation time, tau c, were estimated to be on the order of a few nanoseconds. The presence of cholesterol was found to cause no significant difference in the molecular mobility of the phosphatidylcholine head groups in the ordered and fluid states.

Gamma-Gamma Directional Correlation in the Decay of 168Tm

Time-integral and time-differential gamma-gamma directional correlation measurements were performed for cascades in 168 Er populated from the decay of 168 Tm (90d.). The mixing parameters of most of the intense gamma-rays have been determined more precisely than ever. Some ambiguities concerning to the directional correlation coefficients of the 447–198 keV and 447–830 keV cascades were well removed. The directional correlation coefficients of these cascades were determined as A 22 =0.009 ±0.003 and -0.067 ±0.008, respectively, and A 44 ≈0 for both. The mixing parameters of the 198-, 447- and 830-keV gamma-rays were determined as δ(198)=0.13 ±0.02, δ(447)=0.09 ±0.01 and δ(830)=0.05 ±0.03, respectively. The transition probabilities of the gamma-rays deexciting the 1094-keV level are deduced on the basis of this work.

Determination of solid angle corrections for precise gamma-gamma directional correlation experiments with Ge-detectors

An experimental method is described to determine angle dependent attenuation factors due to the finite solid angle in gamma-gamma directional correlations with Ge-detectors. The correction factors have been calculated a.o. for the 622-512 keV (0 +−2 +−0 +) cascade in 106Pd. Data from a correlation experiment on this cascade have been fitted to the factors and produced A 2 and A 4 anisotropy coefficients within 1% of the theoretical values. Angle independent correction factors obtained from Monte-Carlo calculations and from a horizontal scan method have been used in a comparison with the mentioned results. This comparison has shown that differences of more than 10% can arise by using these methods. An extended measurement yielded A 2 and A 4 coefficients for the (0 +−2 +−0 +) cascade in 106Pd. The values are: A 2 = 0.356(2) and A 4 = 1.143(3), very close to the theoretical ones.

Gamma-gamma directional correlation measurements in 162,164Dy following thermal neutron capture

Gamma-gamma directional correlation measurements in ^162,164Dy following thermal neutron capture

Level Structure of82Kr

The level structure of 82 Kr, from the decay of 35.3 h 82 Br, has been investigated using a 64.1 cc Ge(Li) detector (FWHM≈2.1 keV at 1.33 MeV) in singles mode and Ge(Li)–NaI(Tl) (64.1 cc and 3''×3'' respectively) detector set-up in coincidence mode (2τ=6 nsec). These measurements confirmed the existence of 129.22, 180.5, 280.8, 332.5, 470.28, 735.7, 1 173.3, 1427.2 and 1871.7 keV weak gamma ray transitions, while the 345.65, 599.5, 625.5, 692.7, 726.8 and 932.1 keV gamma rays reported earlier, could not be observed. The gamma-gamma directional correlation measurements have been done on 15 cascades, out of which the 221–(606)–1044, 273–1014, 606–1044 and 221–1650 keV cascades have been attempted for the first time. Based on these measurements, the spin 3 + has been confirmed for the 2426.79 keV level in 82 Kr. Also the multipole admixtures in the 221.34, 273.45, 606.30, 619.07, 698.32, 827.81, 1007.57, 1043.98, 1317.46 and 1650.28 keV gamma transitions have been evaluated.