Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Particle Accelerators”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6Linked to original sources
PubMed2000

The X-Ray Emission of the Centaurus A Jet.

The extended nonthermal X-ray emission of extragalactic jets like Centaurus A can only be explained by in situ particle acceleration. The only energy source in the entire jet region is the magnetic field. Magnetic reconnection can convert the free energy stored in the helical configuration to particle kinetic energy. In the collisionless magnetized jet plasma, the inertia-driven reconnection is operating in a highly filamentary magnetic flux rope, and this results in a continuously charged particle acceleration. The synchrotron radiation of these particles can cause the observed X-ray emission in Centaurus A.

Journal Article↗
PubMed2002

Length scales of acceleration for locally isotropic turbulence.

Length scales are determined that govern the behavior at small separations of the correlations of fluid-particle acceleration, viscous force, and pressure gradient. The length scales and an associated universal constant are quantified on the basis of published data. The length scale governing pressure spectra at high wave numbers is discussed. Fluid-particle acceleration correlation is governed by two length scales: one arises from the pressure gradient, the other from the viscous force.

Journal Article↗
PubMed1993

Chaotic scattering and acceleration of particles by waves.

Relativistic charged particles in a uniform magnetic field and traveling waves of large amplitude can be accelerated limitlessly. Since much of phase space is chaotic the process can be viewed as chaotic scattering on waves. For multiple waves an explicit map arises with unusual properties. It contains infinite island chains around nonperiodic orbits and it is also an example of transient chaos in a Hamiltonian system.

Journal Article↗
PubMed1991

Therapeutic radionuclides: production and decay property considerations.

The development of effective therapeutic radiopharmaceuticals requires careful consideration in the selection of the radionuclide. The in vivo targeting and clearance properties of the carrier molecule must be balanced with the decay properties of the attached radionuclide. Radionuclides for therapeutic applications fall into three general categories: beta-particle emitters, alpha-particle emitters, and Auger and Coster-Kronig-electron emitters following electron capture. Alpha particles and Auger electrons deposit their energy over short distances with a high LET that limits the ability of cells to repair damage to DNA. Despite their high levels of cytotoxicity, the relatively short range of alpha particles requires binding of the carrier molecule to most cancer cells within a tumor in order to be effective. Because of the extremely short range of Auger electrons, the radionuclide must be carried directly into the nucleus to elicit high radiotoxicity, making it necessary to deliver the radionuclide to every cell within a tumor cell population. These characteristics impose rigid restrictions on the nature of the carrier molecules for these types of particle emitters but successful targeting of these types of radionuclides could result in high therapeutic ratios. Most beta-emitting radionuclides are produced in nuclear rectors via neutron capture reactions; however, a few are produced in charged-particle accelerators. For radionuclides produced by direct neutron activation, the quantities and specific activities that can be produced are determined in large part by the cross-section of the target isotope and the flux of the reactor. Many applications (e.g., therapeutic bone agents, radiolabeled microspheres, radiocolloids) do not require high-specific activities and can therefore utilize the wide range of radionuclides that can be produced in sufficient quantity by direct neutron activation. Other applications (e.g., MAb labeling) require high-specific activity radionuclides in order to deliver a sufficient number of radionuclide atoms to the target site without saturating the target or compromising the integrity of the carrier molecule. Most radionuclides, produced at NCA levels in reactors, are produced via indirect reactions. High-specific activity beta emitters can also be obtained from radionuclide generator systems where the longer-lived parent radionuclide may be obtained from direct neutron activation, as a fission product, or from charged-particle accelerators. It is essential that the half-life of a radionuclide used in RNT be compatible with the rates of localization in target tissues and clearance of the carrier molecule from normal tissues. This consideration is especially important for the various MAbs and their fragments that are currently under investigation as carrier molecules to RIT.(ABSTRACT TRUNCATED AT 400 WORDS)

Half-Life↗
PubMedDate not supplied

[The cytogenetic effects of low doses of accelerated charged particles in human blood lymphocytes in vitro].

The aim of the investigation was the study of cytogenetic effects in human blood lymphocytes of low doses of ionizing radiation in vitro. The analysis of unstable chromosome aberrations in human lymphocytes after irradiation by the accelerated ions 12C with the energy 500 MeV/nucleon and LET 10.7 keV/microm was carried out. Blood samples were irradiated on Nuclotron of the High Energy Laboratory of the Joint Institute for Nuclear Research. The doses of irradiation were in the range from 0.05 up to 1.0 Gy. Was shown that the frequency of unstable chromosome aberrations depends from the dose of ionizing radiation and can be described by linear function. At the doses 0.25-0.50 Gy the dose-independent curve was obtained for dicentrics and centric rings. The frequencies of dicentrics and centric rings as markers of the radiation action were slightly different for different donors that could be explained by different radiosensitivity. Using the calibration curve obtained earlier for gamma-rays coefficients of relative biological efficiency of accelerated 12C with the energy 500 MeV/nucleon were defined: they varied from 1.0 at the doses (0.5-1.0 Gy) up to 3.2 at the lower doses (0.05-0.25 Gy).

Carbon Radioisotopes↗
PubMed2001

A comparison of mutations induced by accelerated iron particles versus those induced by low earth orbit space radiation in the FEM-3 gene of Caenorhabditis elegans.

The fem-3 gene of Caenorhabditis elegans was employed to determine the mutation frequency as well as the nature of mutations induced by low earth orbit space radiation ambient to Space Shuttle flight STS-76. Recovered mutations were compared to those induced by accelerated iron ions generated by the AGS synchrotron accelerator at Brookhaven National Laboratory. For logistical reasons, dauer larvae were prepared at TCU, transported to either Kennedy Space Center or Brookhaven National Laboratory, flown in space or irradiated, returned to TCU and screened for mutants. A total of 25 fem-3 mutants were recovered after the shuttle flight and yielded a mutation frequency of 2.1x10(-5), roughly 3.3-fold higher than the spontaneous rate of 6.3x10(-6). Four of the mutations were homozygous inviable, suggesting that they were large deletions encompassing fem-3 as well as neighboring, essential genes. Southern blot analyses revealed that one of the 25 contained a polymorphism in fem-3, further evidence that space radiation can induce deletions. While no polymorphisms were detected among the iron ion-induced mutations, three of the 15 mutants were homozygous inviable, which is in keeping with previous observations that high LET iron particles generate deficiencies. These data provide evidence, albeit indirect, that an important mutagenic component of ambient space radiation is high LET charged particles such as iron ions.

Animals↗
PubMed2004

Development of an accelerometer-based underwater acoustic intensity sensor.

An underwater acoustic intensity sensor is described. This sensor derives acoustic intensity from simultaneous, co-located measurement of the acoustic pressure and one component of the acoustic particle acceleration vector. The sensor consists of a pressure transducer in the form of a hollow piezoceramic cylinder and a pair of miniature accelerometers mounted inside the cylinder. Since this sensor derives acoustic intensity from measurement of acoustic pressure and acoustic particle acceleration, it is called a p-a intensity probe. The sensor is ballasted to be nearly neutrally buoyant. It is desirable for the accelerometers to measure only the rigid body motion of the assembled probe and for the effective centers of the pressure sensor and accelerometer to be coincident. This is achieved by symmetric disposition of a pair of accelerometers inside the ceramic cylinder. The response of the intensity probe is determined by comparison with a reference hydrophone in a predominantly reactive acoustic field.

Journal Article↗
PubMed1986

Detection of infrasound by the Atlantic cod.

Below about 50 kHz the level of ambient noise in the sea increases continuously towards lower frequencies. In the infrasound range the spectral slope is particularly steep. This low-frequency noise may propagate long distances with little attenuation, causing a directional pattern of infrasound in the sea. Using a standing-wave acoustic tube, we have studied the sensitivity of cod to infrasound down to 0.1 Hz by means of the cardiac conditioning technique. The threshold values, measured as particle acceleration, showed a steady decline towards lower frequencies below 10 Hz, reaching a value close to 10(-5)ms-2 at 0.1 Hz. The spectrum level at 0.1 Hz in the sea ranges between 120 and 180 dB (re 1 microPa), with corresponding particle accelerations from less than 10(-6) to more than 10(-4)ms-2. The sensitivity of cod is thus sufficient to detect the highest levels of ambient infrasound, and we put forward the hypothesis that fish may utilize information about the infrasound pattern in the sea for orientation during migration, probably in addition to an array of other sensory inputs.

Acoustic Stimulation↗
PubMed2001

Analytical calculation of the longitudinal space charge and resistive wall impedances in a smooth cylindrical pipe.

The longitudinal space charge and resistive wall impedances have been investigated in a smooth cylindrical beam pipe. At any point from the beam axis, we obtained an expression for the total impedance, which at the beam surface r=a for infinite pipe wall conductivity gives the expression for the total impedance that was derived by Zotter and Kheifets in studying the impedance of uniform beams in concentric cylindrical wall chambers, when a single cylindrical chamber is considered [B. W. Zotter and S. A. Kheifets, Impedances and Wakes in High-Energy Particle Accelerators (World Scientific, Singapore, 1998), Chap. 6]. A fitting formula for the space-charge impedance at the beam surface (r=a), which is valid for arbitrary wavelengths, is given. Rather than calculating the impedance with the field on the axis [Joseph J. Bisognano, Fifth European Particle Accelerator Conference (EPAC96), edited by S. Myers, A. Pacheco, R. Pascual, Ch. Petit-Jean-Genaz, and J. Poole (Institute of Physics, Bristol, 1996), Vol. 1, p. 328], the fitting formula is obtained by averaging over the transverse beam distribution. We also give another approach for the calculation of the resistive wall impedance using the flux of the Poynting vector at the pipe wall and then compare it with the expression obtained from the volume integral over the beam distribution.

Journal Article↗
PubMed2000

Global dynamics of the advanced light source revealed through experimental frequency map analysis.

Frequency map analysis was first used for the dynamical study of numerical simulations of physical systems (solar system, galaxies, particle accelerators). Here it is applied directly to the experimental results obtained at the Advanced Light Source. For the first time, the network of coupling resonances is clearly visible in an experiment, in a similar way as in the numerical simulation. Excellent agreement between numerical and experimental results leads us to propose this technique as a tool for improving numerical models and actual behavior of particle accelerators. Moreover, it provides a model-independent diagnostic for the evaluation of the dynamical properties of the beam.

Journal Article↗
PubMed2006

Laser-plasma acceleration of quasi-monoenergetic protons from microstructured targets.

Particle acceleration based on high intensity laser systems (a process known as laser-plasma acceleration) has achieved high quality particle beams that compare favourably with conventional acceleration techniques in terms of emittance, brightness and pulse duration. A long-term difficulty associated with laser-plasma acceleration--the very broad, exponential energy spectrum of the emitted particles--has been overcome recently for electron beams. Here we report analogous results for ions, specifically the production of quasi-monoenergetic proton beams using laser-plasma accelerators. Reliable and reproducible laser-accelerated ion beams were achieved by intense laser irradiation of solid microstructured targets. This proof-of-principle experiment serves to illuminate the role of laser-generated plasmas as feasible particle sources. Scalability studies show that, owing to their compact size and reasonable cost, such table-top laser systems with high repetition rates could contribute to the development of new generations of particle injectors that may be suitable for medical proton therapy.

Journal Article↗
PubMed2005

Multi-GeV energy gain in a plasma-wakefield accelerator.

A plasma-wakefield accelerator has accelerated particles by over 2.7 GeV in a 10 cm long plasma module. A 28.5 GeV electron beam with 1.8 x 10(10) electrons is compressed to 20 microm longitudinally and focused to a transverse spot size of 10 microm at the entrance of a 10 cm long column of lithium vapor with density 2.8 x 10(17) atoms/cm3. The electron bunch fully ionizes the lithium vapor to create a plasma and then expels the plasma electrons. These electrons return one-half plasma period later driving a large amplitude plasma wake that in turn accelerates particles in the back of the bunch by more than 2.7 GeV.

Journal Article↗
PubMed1989

Inheritance and expression of foreign genes in transgenic soybean plants.

DNA-coated gold particles were introduced into meristems of immature soybean seeds using electric discharge particle acceleration to produce transgenic fertile soybean plants. The lineages of integrated foreign DNA in two independently transformed plants were followed in the first (R(1)) and second (R(2)) generation of self-pollinated progeny. One plant (4615) was transformed with the Escherichia coli genes for beta-glucuronidase and neomycin phosphotransferase II; the other (3993) was transformed only with the gene for beta-glucuronidase. Segregation ratios for the introduced gene(s) were approximately 3:1 for plant 4615 and 1:1 for plant 3993 in the R(1) generation. DNA analysis showed 100% concordance between presence of the foreign gene sequences and enzyme activity. Moreover, all copies of the foreign genes are inherited as a unit in each plant. Plant 3993 segregated in a 1:1 ratio in the R(2) generation. R(1) plants derived from plant 4615, which expressed both genes, gave either 100% or 3:1 expression of both genes in the R(2) generation, demonstrating recovery of both homozygous and heterozygous R(1) plants. Our results show that foreign DNA introduced into soybean plants using electric discharge particle acceleration can be inherited in a Mendelian manner. Results also demonstrate cotransformation of tandem markers and show that both markers are inherited as closely linked genes in subsequent generations. These results indicate that whole plants can be derived from single transformed cells by a de novo organogenic pathway.

Journal Article↗