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14C data from AMS measurements need to be corrected for isotopic fractionation using the δ13C values. Whether to use the δ13C values obtained from the AMS stable isotope measurements as they reflect any additional isotopic fractionation or to use Isotope Ratio Mass Spectrometry (IRMS) δ13C values due to their high precision and accuracy is the question that finds supporting arguments on either side. In this article, we present our observations by examining the data from the two AMS units at CAIS: a 500 kV CAMS and a 250 kV SSAMS. Offline δ13C values resulted in the fraction modern values of standards that are in excellent agreement with the consensus values for both machines. In the case of SSAMS, beyond a certain value, the high energy 12C beam current is found suppressed and skewed the δ13C. In general, the 13C+/12C+ ratio on SSAMS is more susceptible to beam current variation than it is on CAMS. But 14C+/13C+ ratios are nearly independent of beam current variations on both machines. Our analysis shows that online δ13C works well for CAMS, but results are not satisfactory for SSAMS. But we have found that using pre-acceleration 12C− instead of post-acceleration 12C+ for stable isotope ratio calculation substantially improves the online δ13C for SSAMS.

It is known that 12C beam transmission through the accelerator decreases at high beam currents. This effect depends on machine design and varies across different types of AMS instruments. For beam currents of about 100 μA, the effect is small on the 500 kV tandem CAMS unit, whereas beam saturation is observed for similar high beam currents on the 250 kV SSAMS unit. While this effect is very evident for high 12C beam currents, we have also observed that even the 13C beam is found to suffer modest transmission loss with beam current. As a result, the 13C/12C ratio does not remain constant with beam current. By correcting for the effects of 12C beam saturation and decreased 13C transmission, we have obtained online δ13C values that are more accurate and precise at moderately high beam currents for SSAMS.

In 2018 Pearson et al. published a new sequence of annual radiocarbon (14C) data derived from oak (Quercus sp.) trees from Northern Ireland and bristlecone pine (Pinus longaeva) from North America across the period 1700–1500 BC. The study indicated that the more highly resolved shape of an annually based calibration dataset could improve the accuracy of 14C calibration during this period. This finding had implications for the controversial dating of the eruption of Thera in the Eastern Mediterranean. To test for interlaboratory variation and improve the robustness of the annual dataset for calibration purposes, we have generated a replicate sequence from the same Irish oaks at ETH Zürich. These data are compatible with the Irish oak 14C dataset previously produced at the University of Arizona and are used (along with additional data) to examine inter-tree and interlaboratory variation in multiyear annual 14C time-series. The results raise questions about regional 14C offsets at different scales and demonstrate the potential of annually resolved 14C for refining sub decadal and larger scale features for calibration, solar reconstruction, and multiproxy synchronization.

The NEC 250 kV single stage AMS accelerator (SSAMS) was installed two years ago at the Center for Applied Isotope Studies (CAIS), University of Georgia. The accelerator is primarily being used for radiocarbon measurements to test the authenticity of natural and bio-based samples while all other samples such as geological, atmospheric, marine and archaeological. are run on the 500 kV, NEC 1.5SDH-1 model tandem accelerator, which has been operating since 2001. The data obtained over a six months period for OXI, OXII, ANU sucrose and FIRI-D are discussed. The mean value of ANU sucrose observed to be slightly lower than the consensus value. The processed blanks on SSAMS produce lower apparent age compared to the tandem accelerator as expected.

A gravity core SK-221 recovered from the southeastern Arabian Sea near Laccadive–Chagos Ridge was examined to identify the sources of detrital clay minerals and to decipher paleoenvironmental changes for the last 30 kyr. The clay mineral assemblages predominantly consist of illite, kaolinite and chlorite with small amounts of smectite. Quartz, feldspar and occasionally gibbsite are the clay-sized non-clay minerals present in the examined section. The detrital clay minerals primarily originated from the hinterland and were supplied to the present site by the numerous small rivers draining western India during preglacial and Holocene periods, and partly by the strong reworking of Indian continental shelf during glacial period. The low values of humidity proxies (kaolinite content, kaolinite to illite and smectite to illite ratios) and better illite crystallinity indicate relatively weak summer monsoon condition that resulted in reduced chemical weathering during glacial period, which was interrupted by a discrete event of winter monsoon intensification at ∼20–17 ka. The increased kaolinite content, higher values of humidity indices and poorer illite crystallinity reflect high humidity that resulted in strong hydrolysis activity during the preglacial and Holocene periods. The increased CaCO3 during above periods also indicates less terrigenous dilution and intensified southwest monsoon-led upwelling which result in higher surface biogenic productivity. The characteristic clay mineral associations broadly suggest dry to semi-drier conditions during Heinrich Events H1, H2, and H3 and also during Younger Dryas. The low values of biogenic carbonate and organic carbon also indicate low productivity associated with weak summer monsoons during Heinrich Events. Abrupt increased humidity was recorded at 15–12.7 ka (Bolling/Allerod Event) sandwiched between two lows of Heinrich Events. Cycles of millennial timescale variations 2300, 1800, 1300 and 1000 yr have been observed from the clay mineralogical data. All the cycles observed in the monsoonal climate appear to be part of global oscillations.

The center for applied isotope studies has developed a protocol for the measurement of radiocarbon in the range 0.01–0.3 mg of carbon. We analyzed a series of radiocarbon-free and modern standards using the same sample preparation procedure as for unknown samples. We have studied the size dependency of 12C and 13C beam currents and 14C/13C ratios from cathodes containing less than 1 mg of carbon. The iron catalyst used for graphite preparation contains some carbon with activity about 60 pMC and the level of contamination varies between batches from the same supplier. The cathodes in the range smaller than 50 μg showed a very significant dependency between current and the sample size. In this range the current increased by about fifteen-fold; between 50 and 100 μg the current increased two-fold. Samples larger than 300 μg have shown negligible current variation. The 14C/13C ratio was significantly affected only for the samples less than 50 μg. Larger samples have shown very little variation in the 14C/13C ratio. For the measurement of ultra-small unknown samples in the range of 10–50 μg, we have found it to be important to use blanks and modern standards with exactly the same amount of carbon, which makes it possible to apply a mass-balanced correction.

A new 250kV single stage AMS accelerator (SSAMS) was installed at the Center for Applied Isotope Studies, University of Georgia. The accelerator is intended to be used primarily for radiocarbon measurements of natural and bio-based samples, while all other samples such as marine, geological, atmospheric and archaeological samples are measured on the decade-old 500kV compact tandem accelerator (CAMS). The new AMS system is equipped with a 134-cathode MC-SNICS ion source. In this article, we show the results of the tests carried out on standards and blanks and compare the performance of the new machine with that of the CAMS unit. We have also compared the stable isotope data from AMS measurements to the conventional isotope ratio mass spectrometers (IRMS) data. DOI: 10.2458/azu_js_rc.55.16292

Radiocarbon and stable isotope determination in foods, flavors, and beverages, for the authentication of source material and process of formation, is a well-established method of identity used in industry. New methods of provenance determination, using stable isotopes of oxygen and hydrogen, have added to the host of other isotopic methods used for characterizing natural or botanically derived products. The unambiguous determinant of a product's fossil fuel origin be it from petroleum, natural gas, or coal, is through the measurement of its 14C content. The 14C content can also be used to determine the fraction dilution of recently grown and harvested material with that derived from fossil fuel, and even confirms the vintage of agricultural products based on the well-established decrease of bomb-produced atmospheric 14C. This paper documents 14C measurements at the University of Georgia's Center for Applied Isotope Studies accelerator mass spectrometry and stable isotope laboratories, over the last 3 yr, for 10 important flavoring compounds. By establishing an accurate and current level of 14C in botanically derived products, we were able to confirm a particular source for vanilla production, the most popular consumer flavor in the marketplace. Over the years, vanilla extract has been produced less and less from vanilla beans (Vanilla planifolia), particularly those from Madagascar and the Comoros Islands, and more from other botanical precursors such as ferulic acid, clove oil, and guaiacol. We report isotopic data to support this precursor for vanilla production based on high 14C levels accumulated during the tree's life, incorporated in the tree rings and their associated stable isotope abundances.

In a span of 10 years, the University of Georgia’s Center for Applied Isotope Studies (CAIS) has transformed itself from principally a liquid scintillation counting (LSC) laboratory to one conducting thousands of accelerator mass spectrometry (AMS) and stable isotope ratio analysis (SIRA) annually. After receiving the first of the NEC compact AMS units in the United States, the CAIS began to meet the demand for 14 C analysis outside the normal realm of most radiocarbon dating laboratories. With industry’s support, isotope research continued on an already developing natural products program to authenticate materials origin and process of formation. The CAIS’s AMS allowed for the detection of synthetic materials in milligram quantities rather than gram quantities required by LSC and allowed new compound specific SIRA techniques to be directed toward compound specific 14 C measurement. By 2005 the CAIS was one of only a few laboratories accredited to determine bio-base content in industrial fuels and products by both AMS and LSC following ASTM D6866-10 [1] . Since 2001, when our first sample was analyzed by AMS method, both radiocarbon and natural products sample numbers have increased steadily. The advantages of AMS analysis in overall efficiency, cost savings, accuracy, and precision, are detailed here in a review of analytical precision for radiocarbon and natural products analyzed over 10 years of AMS operation. Comparisons are made between natural products and bio-based materials analyzed by both AMS and LSC. Although high precision is not required to authenticate natural products, for the purpose of product comparison with regard to degree of naturalness accurate and precise 14 C measurement is shown to be achievable by both methods.

After the 2004 Sumatra–Andaman tsunamigenic earthquake, waters from the ocean moved upstream along rivers, bays, harbors, and lagoons and inundated many coastal and inland locations in the southern, eastern, and northern parts of Sri Lanka. The tsunami waters were observed to move upwards inland and then recede downwards to the ocean after varying inundation periods in different coastal areas. Subsequent massive tsunami waves came with the wave height varying from 3 to 8 m inland with speed of about 30–40 kmph. The oceanic waves carrying heterogeneous sediments with water deposited them in coastal as well as inland locations about 1 km from the present coastline. Given the chaotic nature of tsunami oceanic waves, pre-tsunami deposits, such as beach sands, debris from coral reefs and buildings, parts of vehicles and ships, and tree trunks are found incorporated in authentic tsunami sediments. Thus, the texture, structure, and composition of sediments deposited by tsunami waters differed from one location to another. Therefore, in identifying paleo-tsunami sediments, care was taken to compare them with diagnostic unmixed uncontaminated recent tsunami sediments having characteristic textures and marine microfossil assemblages, such as foraminifera, radiolarians, and diatoms where preserved in coastal depressions. The radiocarbon ages of the carbonate and the organic fractions of these sediments are stratigraphically inconsistent, indicating mixing of sediments by the tsunami waves. The concentrations of organic carbon and nitrogen and their isotopic signatures confirm marine origin of these sediments.

Right from the time of the Painted Grey Ware (PGW) culture, dating to c. 1200–600 bce, more than 210 archaeological sites in India have provided evidence of glass, but there has been no attempt to date the glass-yielding layers by radiometric techniques. This has hampered the establishment of a chronology for the beginning and evolution of glass-making in India. The site of Kopia was excavated by the first author for three seasons from 2004 to 2006 to understand the history, development and technology of glass production in India. The excavation produced evidence of a long period of occupation, covering the Fine Grey Ware (FGW), Northern Black Polished Ware (NBP), Sunga–Kushana and Gupta periods. Twenty accelerator mass spectrometry (AMS) and radiocarbon dates, all derived from charcoal samples and processed independently by three laboratories, are available from the site. The dates range in their calibrated form on average from the ninth to the second century bce in locality I and from the second century bce to the second century ad in locality II.

Down-core variations of granulometric, geochemical and mineral magnetism of a 70-cm long sediment core retrieved from the eastern Bay of Bengal abyssal region were studied to understand sedimentation pattern and sediment provenance during the last ∼ 12 kyr BP. Based on down-core physical and elemental variations, three units were identified: unit 3 (70–43 cm) is a ∼ 30 cm thick clayey silt organic carbon-rich (0.5–0.92%) turbidite probably delivered by the Brahmaputra River during the late Quaternary period. Units 2 (43–24 cm) and 1 (24–0 cm) represent enhanced and reduced supply of coarse-grained detrital sediments from the Ganges River during early and late Holocene period, respectively. Increased terrigenous supply dilutes calcium carbonate (CaCO3) and biogenic elements (P, Ba and Cu) in units 3 and 2. On the contrary, a reduction in detrital input enhances CaCO3 and biogenic elements in unit 1. Lithogenic elements (Ti, Al, K and Rb) and shale-normalized REE patterns in all three units suggest terrigenous source. The shift in provenance from the Brahmaputra to the Ganges derived sediments is evident by a sharp increase in sediment grain size, increased concentration and grain size assemblages of magnetic minerals, lithogenic elements concentration and Lan/Ybn ratio. This study highlights terrigenous dilution on biogenic sedimentation in the eastern Bay of Bengal sediments.

Radiocarbon was measured in the surface seawater dissolved inorganic carbon (DIC) of the Bay of Bengal during November 2006. A meridional transect of the Δ14C in DIC was obtained from measurements in closely spaced samples collected roughly along 88°E. The Δ14C of these samples ranged from 44‰ to 57.7‰ (mean 51.8 ± 1.1‰, n = 12), and 38‰ at one station in the northern Bay of Bengal. The overall pattern of 14C distribution in DIC of surface Bay of Bengal during 2006 was roughly similar to that during the WOCE expedition of 1995. These results indicate a Δ14C decline rate of ∼4‰ per decade since WOCE in the surface Bay of Bengal, which is much smaller compared to a decline rate of ∼25‰ per decade observed in the 2 decades between the GEOSECS and WOCE expeditions, due to the smaller atmosphere-ocean Δ14C gradient.

Extensive field investigations were carried out for the first time in the meizoseismal area of the great 1950 Assam Earthquake aimed at exploring the paleoseismic history of the NE Indian region through documentation of liquefaction features and radiocarbon (14C) dating. Trenching at more than a dozen locations along the Burhi Dihing River valley and within the alluvial fans adjoining the Brahmaputra and Dibang Rivers resulted in the identification of more than a dozen very prominent liquefaction features (sand dykes, sills, sand blows etc.) as evidences of large to great earthquakes. 14C dating of the organic material associated with some of the features indicates a paleoseismic record of about 500 yrs archived by the sediments in this region. Compelling geological evidence(s) of the great 1950 earthquake are well constrained by 14C dating. Out of the two historically reported seismic events (1548 AD and 1697 AD) from this region, 14C dating could constrain the 1548 AD event though not distinctly. Further studies using combined 14C and OSL dating may better constrain the seismo-chronology of the study region.

The great Indian Ocean earthquake of December 26, 2004 caused significant vertical changes in its rupture zone. About 800 km of the rupture is along the Andaman and Nicobar Islands, which forms the outer arc ridge of the subduction zone. Coseismic deformation along the exposed land could be observed as uplift/subsidence. Here we analyze the morphological features along the coast of the Andaman and Nicobar Islands,in an effort to reconstruct the past tectonics, taking cues from the coseismic effects. We obtained radiocarbon dates from coastal terraces of the island belt and used them to compute uplift rates, which vary from 1.33 mm $yr^{-1}$ in the Little Andaman to 2.80 mm $yr^{-1}$ in South Andaman and 2.45 mm $yr^{-1}$ in the North Andaman. Our radiocarbon dates converge on \sim 600 yr and \sim 1000 yr old coastal uplifts, which we attribute to the level changes due to two major previous subduction earthquakes in the region.

The radiocarbon AMS facility at Institute of Physics, Bhubaneswar is based on a 3 MV tandem accelerator. In this paper, we present the recent improvements to the AMS system at this general purpose accelerator facility. We report an effective method of overcoming terminal voltage instability often met with in switching between AMS and other modes of operation of the accelerator. We report the radiocarbon measurements made on connate groundwater samples from the Bhadrak district of Orissa state (eastern India) to identify the regions that require artificial recharge.

Heavy ion impact has been known to cause a loss of light elements from the near-surface region of the irradiated sample. One of the possible approaches to a better understanding of the processes responsible for the release of specific elements is to irradiate shallow-implanted samples, which exhibit a well-known depth distribution of the implanted species. In this work, the samples studied were produced by implantation of Si wafers with 11B at implantation energies of 250 and 500 eV and fluence of 1.0×1015 atoms/cm 2. Elastic Recoil Detection Analysis was applied to monitor the remnant boron fluence in the sample. Irradiation of the samples by a 14.2 MeV 19F 4+ beam resulted in a slow decrease of boron remnant fluence with initial loss rates of the order of 0.05 B atom per impact ion. Under irradiation with 12 MeV 32S 3+ ions, the remnant boron fluence in Si decreased exponentially with a much faster loss rate of boron and became constant after a certain heavy ion irradiation dose. A simple model, w...

Stopping powers of energetic Si and P ions are measured in thin GaAs films. A new technique derived from molecular beam epitaxy (MBE) was developed to prepare near stoichiometric GaAs films on thin carbon layers for use in transmission ion beam experiments. The GaAs films were characterized using X-ray photoelectron spectroscopy (XPS) and particle induced X-ray emission (PIXE). Stopping power data are presented for the first time for Si and P in GaAs.

The compound semiconductor GaN has become the electronic material for many semiconductor applications because of its high-power, high-temperature and high-frequency characteristics. The introduction of impurities to GaN, either by direct doping or by contamination of unwanted impurities during fabrication leads to changes in its electronic properties [CAARI 2002: 17th International Conference on the Application of Accelerators in Research and Industry, American Institute of Physics, Vol. 680, 2002, p. 369]. There are a number of techniques routinely used to analyze the depth profiles of impurities in semiconductor substrates, but they lack the sensitivity required for today's applications. For example, secondary ion mass spectrometry (SIMS) has molecular interferences which obscure analysis of some elements. Trace element accelerator mass spectrometry (TEAMS), which is a combination of accelerator mass spectrometry (AMS) and SIMS, removes molecular interferences by breaking apart the molecules in an accelerator. Like SIMS, secondary ions are sputtered from a target, the negative ions are then extracted and injected into a 3 MV tandem accelerator. As they pass through a gas at the center of the terminal, molecular breakup is achieved via a coulomb explosion due to electron stripping. The ions are then passed through momentum/charge and energy/charge filters, which are used to separate out many of the unwanted interferences. In most cases, TEAMS is a complimentary technique to SIMS and can eliminate the interferences that may not be resolvable by SIMS. The purpose of this work is to examine the depth profiles and detection limits of various impurities implanted into a GaN substrate.

The 3 MV tandem Pelletron accelerator facility at the Ion Beam Laboratory of the Institute of Physics (IOP), Bhubaneswar is being augmented by the installation of a fast bouncer system for routine 14 C measurements. The old injector involving a single cathode SNICS source and a 45° bending magnet has been replaced by a new system consisting of a 40 cathode MC-SNICS source and a 90° analyzing bending magnet. The system is being tested for transmission. The status of the facility with test results is presented.

We have measured alpha-particle spectra at different laboratory angles from the fusion reaction Si-28+V-51 at 140 MeV. These spectra deviate at higher energies from the statistical model calculations using rotating liquid drop model values of the moment of inertia. In order to explain the experimental spectra, changes were required in the moments of inertia corresponding to deformation, which suggests dynamical effects on the deexcitation process for charged-particle emission. The comparison of decay times with formation times implies that light charged particles are preferentially emitted prior to the full relaxation of the compound nucleus. Statistical models and dynamical calculations have been employed in an attempt to interpret the experimental data. The results were compared with the Si-28+Al-27 system studied earlier in order to understand the symmetric and asymmetric entrance channel effects in the formation of the compound system.

Fission fragment angular distributions and fission excitation functions have been measured for ${}^{11}\mathrm{B}$, ${}^{12}\mathrm{C}$, and ${}^{14}\mathrm{N}{+}^{209}\mathrm{Bi}$ systems at near-barrier energies. The measured fission fragment anisotropies are in agreement with the predictions of the standard saddle point statistical model. For these systems, there is no evidence for any ``anomalous'' behavior of the anisotropies as a function of both energy and entrance channel mass asymmetry. The present results combined with the data available for ${}^{16}\mathrm{O}$, ${}^{19}\mathrm{F}{+}^{208}\mathrm{Pb}$, and ${}^{16}\mathrm{O}{+}^{209}\mathrm{Bi}$ systems and for deformed actinide targets systems are consistent with the conjecture that target deformation plays a strong role in the observed anomalous anisotropies in actinide targets.

A comparison was made between various radiocarbon measurement techniques for the purpose of quantifying each methods capability for the proper apportionment of biobase-derived additives to gasoline. Measurement techniques include (1) direct liquid scintillation counting, (2) carbon dioxide absorption followed by liquid scintillation counting, (3) conversion to benzene followed by liquid scintillation counting and (4) accelerator mass spectrometry. In addition, stable isotope ratios of carbon and hydrogen were determined to assist in the authentication of a fuels source with regard to petrochemical or biobase origin is required for the confirmation of minimum anti-knock components, consumer awareness and proper assessment for regulatory taxation. Accelerator mass spectrometry was found to be the most precise technique followed by conversion of fuel to benzene with liquid scintillation counting and direct counting by liquid scintillation counting. Finally, liquid scintillation counting of absorbed carbon dioxide was found to be the least precise and should not be used for this analysis. The high to low precisions correlate with the high to low cost of equipment and support required by each of these methods except for direct liquid scintillation counting. Therefore, laboratories interested in developing capability to perform such authentication can use this data to consider the economics of the optimum technique to use for radiocarbon measurement.

The intensity of the Indian monsoon has varied greatly over the past glacialinterglacial cycles as well as on shorter time scales (Duplessy, 1982; Van Campo, 1986; Clemens et al., 1991; Sirocko et al., 1993; Reichart et al., 1998; Von Red et al., 1999). It is well known that seasonal variation in the heating of the southern Asian continent produces a semiannual reversal in wind direction over the northern Indian Ocean (Wyrtki, 1973). In summer (June-September), the intense SW monsoon winds cause strong mixing of the water column and upwelling which eventually promotes high productivity in the Arabian Sea. In contrast, during winter, reversal of weak and NW wind direction relatively lowers the productivity in the Arabian Sea (Quasim, 1977). It was demonstrated that biological productivity and terrigenous supply in the Arabian Sea is strongly linked to the intensity of the monsoon, although the lowest biological productivity was noticed during inter-monsoon period in the Arabian Sea.

The entrance channel dynamics in a heavy-ion fusion reaction is followed by solving the Langevin equations of motion for the elongation and mass asymmetry degrees of freedom. Thermal diffusion over the conditional barrier in early stages of the dynamics is shown to result in a small number of fission-like reaction events having a memory of the entrance channel mass asymmetry. Evidence for such a component arising from the precompound nucleus phase of the reaction is shown to exist in the measured data on the yield of binary fragments in the reaction {sup 232}Th+{sup 12}C reported earlier. {copyright} {ital 1996 The American Physical Society.}

A conventional tandem Van de Graaff accelerator is used to produce charged carbon cluster beams. The unique capability of the method for studying highly charged clusters unaccessible to other methods of producing cluster beams is demonstrated.

The electronic properties of one-dimensional clusters of N atoms or molecules have been studied. The model used is similar to the Kronig-Penney model with the potential offered by each ion being approximated by an attractive delta function. The energy eigenvalues, the eigenstates and the density of states are calculated exactly for a linear cluster of N atoms or molecules. The dependence of these quantities on the various parameters of the problem show interesting behavior. Effects of random distribution of the positions of the atoms and random distribution of the strengths of the potential have also been studied. The results obtained in this paper can have direct applications for linear chain of atoms produced on metal surfaces or artificially created chain of atoms by using scanning tunneling microscope or in studying molecular conduction of electrons across one-dimensional barriers., A shorter version of this paper to be published in Physica B

Continuous miniaturization of integrated circuits requires narrower dopant profile depth in the Si channel and consequently the use of ultra‐shallow implants in the manufacturing process. Secondary Ion Mass Spectroscopy (SIMS) is routinely used to measure the boron depth concentration profiles. However, due to the altered nature of the near‐surface sputtering process inherent to SIMS, it underestimates the B implanted doses for implantation energies below 2 keV. Alternate ion beam methods for absolute dose measurements of ultra‐shallow implanted As and B in Si are presented in this study. The dopant implant energies ranged from 250 eV, to 5 keV for boron and from 500 eV to 5 keV for arsenic. Implanted doses for both B and As varied from 2 × 1013 to 1 × 1015 atoms/cm2. The arsenic implants were studied with Rutherford Backscattering Spectrometry (RBS) using 2 MeV carbon ions. The absolute arsenic implanted doses were measured to an accuracy of better than 5%. The 1 keV arsenic implants were extensively studied for radiation damage with a 12C beam. No appreciable arsenic dose loss was observed during C irradiation for an integrated charge of ⩽ 80 μC, which was the maximum used for these studies. For the B implants, Elastic Recoil Detection (ERD) was used with 14 MeV F4+ ions. A 9.4 μm Mylar foil was found to adequately stop the scattered 19F ions and give good energy separation for the 11B recoiled ions. The absolute dose measurements are ∼ 5% for the 5 keV 11B implants. Significant radiation damage was observed for the ultra shallow implants and the measured B dose has been obtained by extrapolation to the zero integrated charge of the beam. The absolute boron dose measurements of the ultra shallow (250 eV) implants were determined with an accuracy better than 10%.

GaN is one of the most promising electronic materials for applications requiring high-power, high frequencies, or high-temperatures as well as opto-electronics in the blue to ultraviolet spectral region. We have recently measured depth profiles of Mg, Si, and Zn implants in GaN substrates by the TEAMS particle counting method for both matrix and trace elements, using a gas ionization chamber. Trace Element Accelerator Mass Spectrometry (TEAMS) is a combination of Secondary Ion Mass Spectrometry (SIMS) and Accelerator Mass Spectrometry (AMS) to measure trace elements at ppb levels. Negative ions from a SIMS like source are injected into a tandem accelerator. Molecular interferences inherent with the SIMS method are eliminated in the TEAMS method. Negative ion currents are extremely low with GaN as neither gallium nor nitrogen readily forms negative ions making the depth profile measurements more difficult. The energies of the measured ions are in the range of 4-8 MeV. A careful selection of mass/charge ratios of the detected ions combined with energy-loss behavior of the ions in the ionization chamber eliminated molecular interferences.

A simple formula for conditional fission barriers of rotating nuclei is proposed based on an extension of Swiatecki`s dimensionless expressions for conditional barrier energies. The calculated barrier heights are compared with the measured values. The utility of the present formula in the analysis of experimental results in a typical heavy ion fusion reaction is discussed.

DOI = 10.3126/hjs.v5i7.1290 Himalayan Journal of Sciences Vol.5(7) (Special Issue) 2008 p.97