Showing papers on "Linear particle accelerator published in 1974"

Experimental and calculated bremsstrahlung spectra from a 25-MeV linear accelerator and a 19-MeV betatron

Abstract: The bremsstrahlung spectra from a 25‐MeV linear accelerator and a 19‐MeV betatron have been measured using a NaI(Tl) spectrometer system. The spectra show a low energy cut‐off at 0.6 and 0.4 MeV, respectively, and the maximum photon energies were 26.8 and 19 MeV, respectively. Cross sections, thin‐ and thick‐target photon spectra and total electron energy losses (collision and radiative) were computed using a digital computer for tungsten ( Z = 74 ) and platinum ( Z = 78 ) targets. The measured spectra were compared to the calculated spectra for thin and thick targets using electron kinetic energies of 26.75 and 19 MeV. The photon spectra from the two therapy units are different; however, depth dose data (10 × 10 cm, 100 cm TSD) are approximately the same. In addition, narrow‐beam attenuation coefficients in lead for the two machines were measured. The effective energy derived from the first HVL was 8.1 MeV for the linear accelerator and 7.8 MeV for the betatron.

Design of x-ray targets for high energy linear accelerators in radiotherapy

Abstract: The 25 MeV electron beam was extracted from a Varian Clinac-35 linear accelerator and made to produce x-rays in thick targets of different materials. The x-ray beams were flattened by filters of various materials.We have found that an aluminum thick target gives a more penetrating beam in the forward direction than does a lead or tungsten target.The x-ray yield in the forward direction from 0-5° is essentially the same for both aluminum and lead targets. At angles larger than 10°, a lead target shows a higher x-ray yield and a more penetrating beam than an aluminum target.The flattening filter material is important. A more penetrating beam is produced if the flattening filter is made of aluminum rather than tungsten or lead.With an aluminum target and an aluminum flattening filter, we obtain the same depth dose distribution from our linear accelerator as we do from our betatron unit operating at the same energy. In the betatron unit, the radiation is produced in a thin target of tungsten and filtered by a...

Linear particle accelerator system having improved beam alignment and method of operation

Abstract: A linear particle accelerator having detection apparatus for detecting the presence of and correcting for beam misalignment. The linear accelerator includes a charged particle accelerator system and deflection coils for changing both the positional and angular displacement of a charged particle beam. A target is disposed in the particle beam path for emitting X-rays upon being struck by the charged particles. The photon field pattern developed by the target takes the form of a forward-peaked lobe configuration extending from the target. An arrangement of radiation responsive electrodes is disposed in the radiation field for developing electrical signals responsive to changes in the lobe pattern. The signals developed by the radiation responsive electrodes are applied to differential servo circuitry for applying signals to the deflection coils to correct for both positional and axial misalignment of the particle beam.

Linear acceleration system for high energy electrons with preacceleration and main acceleration means

Abstract: A linear acceleration system composed of a high energy field emission source and two linear accelerators connected in sequence to accelerate electrons emitted by the source, the first accelerator shifting the electron pulses from the source by 180° relative to phase and the second accelerator accelerating the electrons in a pulse whose energies differ from the lowest energy electrons by an amount which is less than the acceleration imparted to the lowest energy electrons and which differs therefrom by an amount proportional to such energy difference, whereby the electrons at the output of the second accelerator have a highly uniform energy level.

Comparison of electron beams from the Siemens betatron and the Sagittaire linear accelerator.

Abstract: Electron beams from two high-energy machines, a Sagittaire linear accelerator and a Siemens betatron, were compared. The linear accelerator has two stationary accelerating sections and a rotating magnetic deflection system, uses a scanning magnet for beam flattening and movable jaws for a collimator, and produces 7–31 MeV electrons in steps of 3 MeV. The betatron uses scattering foils of different materials and thicknesses for beam flattening and cones for a collimator and produces electrons in a range of 6–18 MeV. Appreciable differences in beam energy, dose distribution, beam flatness, surface dose, dmax position, and fall-off slope were found.

High speed linac-beam analyzer

Abstract: A device for analyzing a charged particle beam developed by an accelerator device having an RF driving signal is provided. The particle beam passes through a transparent medium, developing light of intensity proportional to the intensity of the particle beam. A photocathode is aligned to detect the light and thereby generate an electron beam of intensity proportional to the intensity of the light. The RF driving signal is coupled via a phase-varying network to an X-axis deflection system and, after a phase shift of 90*, to a Y-axis deflection system. The electron beam is directed through the X-axis and Y-axis deflection system, thereby causing the electron beam to precess about an axis and describe a circular trace in a plane perpendicular to the axis. Means are provided to measure the intensity of the beam along a particular narrow arc of the circular trace as the phase of the RF signal applied to the X and Y deflection systems is varied from 0* to 360*.

Interaction of nuclear environment with MNOS memory device

Abstract: This paper reports on the results of an investigation of the interaction of a nuclear environment with a metal-gate, silicon nitride, silicon dioxide, silicon-on-sapphire memory device. The test device was a 63-bit (7 words by 9 bits) three-terminal device. The tests were as follows: (1) transient photocurrent, (2) transient annealing, (3) total dose, (4) survivability, and (5) neutron tests. Facilities at AFCRL were used in the first four tests and at the Aberdeen Pulse Reactor for the last test. Samples were irradiated under power. Both interrogated and passive words containing “1” and “0” states were investigated. Transient photocurrent and annealing data were obtained with the Linac operating in the electron mode. Electron energy was 10 MeV and pulse widths of 20 nanoseconds and 4. 5 microseconds were used. Total dose data was obtained with a cobalt-60 source as well as the reactor. A Flash X-ray generator operating in the electron mode (20-nanosecond pulse) was used to determine survivability rates.

Electron diffraction instrument using the high energy beam of LINAC

Abstract: A preliminary experiment was conducted for the purpose of using the linear accelerator (LINAC) as a high energy electron source, instead of a Cockcroft-Walton type accelerator. Since LINAC acceleration is easier at high energies, the duty factor and the energy distribution of the linac beam were the main problems; both were solved by this new method. A pulse-slicer was developed to make particularly high power pulses (130 kV, 12.5 MW) even. It allowed a pulse flatness of 5*10-4 (pulse width 1 mu s) to be obtained. An automatic control circuit was used for the pulse power to get a stability of 1*10-3 min-1.

Simulation for radiation effects in electronics

Abstract: Adequate simulation testing for radiation effects requires knowledge of radiation effects mechanisms to relate test environments to operational environments. In order to scale the effect with radiation type, spectrum, or time dependence, the response must be separated into different radiation effects, The basic separation is into displacement, charge-transfer, and ionization effects. Within each category short-lived and long-term responses must be considered. Specific simulation facilities can be used to produce particular combinations of effects. Pulsed and steady-state neutron sources (reactor or accelerators), flash X-ray machines, and electron linear accelerators are particularly useful for producing the effects of the radiation from a nuclear explosion. Steady-state electron and proton accelerators are especially appropriate for simulating space radiation. In the first case the problem is to produce the high radiation rates; in the second to qualify accelerated testing. Many other simulation problems fall between these two limits.

Comparison of electron beam characteristics from Siemens betatron 6 to 18 MeV and Sagittaire linear accelerator 7 to 32 MeV radiotherapy machines

Abstract: The linear accelerator has two stationary accelerating sections and a rotating magnetic deflection system which allows the beam to be used at any angle, and also uses a scanning magnet for beam flattening and moveable lead and aluminium jaws as collimator. This machine is designed to produce 25 MV photons and electrons in the range 7-32 MeV in steps of 3 MeV. The betatron uses scattering foils of different material and thickness for beam flattening and brass cones of fixed dimensions as collimator and produces 19 MV photons and electrons in the range 6-18 MeV. Appreciable differences were found in beam energy, dose distribution, flatness, surface dose, position of d-matrix and slope of fall-off were described.

Medical linac design possibilities

Abstract: During the last five years, a dramatic expansion of the use of accelerator generated radiations in medicine became possible. The application of resonant standing wave accelerator technology to conventional medical linac systems brought them within the reach of hundreds of cancer treatment centers throughout the country. In addition, the construction of meson factories will allow the use of secondary particle beams for cancer therapy. A brief discussion of the LAMPF linear accelerator is provided, including the properties of the side coupled accelerator system. Some design criteria for possible dedicated meson producing accelerator systems for hospital use are described.

Superconductivity, Cryogenics, and Vacuum Technology for Linear Accelerators

Abstract: The conventional, 10-8 Torr-range, ion-pumped vacuum system of the SLAC 3.2-km linear accelerator is briefly described, along with typical performance data. Since polarized electron sources are of increasing importance to high-energy research, the necessary physical environments for such sources are given, and differential pumping and/or isolation systems capable of maintaining those conditions while protecting both source and accelerator are discussed. The development of microwave superconducting linear accelerators is summarized. Emphasis is on vacuum and materials processing techniques necessary to the maintenance of low surface resistance and high electric and magnetic fields. Problems remaining and prospects for their solution are briefly described, along with details of the physical processes taking place at the vacuum-metal interface.

The karlsruhe fast neutron time-of-flight facility

Abstract: Although the area of resonance neutron spectroscopy is presently dominated by pulsed neutron sources based on electron linacs, the highest instantaneous neutron intensities are provided by acceleration of positive charged particles to high energies. While advanced types of circular and linear accelerators hold great promise for the future, this concept has not in general been realized because of technological problems such as heat transfer, etc. Certain existing machines do, however, permit us to partially realize this concept already at present. A high energy proton linear accelerator to be used as a high intensity neutron source will be described by Dr. Moore in an other invited talk of this conference. Of the circular accelerators the sector-focussed cyclotron is currently best able to take advantage of this capability. This machine combines both, high beam intensity and narrow pulse width of a few nanoseconds. For proper use of this machine additional equipment is necessary because sector-focussed cyclotrons run continuously with a microstructure pulse recurrence frequency of 10–30 MHz which is far too high in view of frame overlap problems. It is obvious that for long flight paths the time interval of 30–100 nsec between two subsequent pulses is so short that slow neutrons from a preceeding pulse can be overtaken by fast neutrons from the following pulse. A reduction of the recurrence frequency by suppression of most of the microstructure pulses would entail a tremendous sacrifice in intensity.