Sealed tube accelerator

A Kaman Nuclear Model A711 sealed-tube accelerator for the generation of 14 MEV neutrons by the deuterium-tritium reaction... 

Combination of the sealed tube accelerator and the associated alpha-particle method (ARM)... 

During the vacuum fractional distillation of bulked residues (7.2 t containing 30-40% of the bis(hydroxyethyl) derivative, and up to 900 ppm of iron) at 210-225°C/445-55 mbar in a mild steel still, a runaway decomposition set in and accelerated to explosion. Laboratory work on the material charged showed that exothermic decomposition on the large scale would be expected to set in around 210-230°C, and that the induction time at 215°C of 12-19 h fell to 6-9 h in presence of mild steel. Quantitative work in sealed tubes showed a maximum rate of pressure rise of 45 bar/s, to a maximum developed pressure of 200 bar. The thermally induced decomposition produced primary amine, hydrogen chloride, ethylene, methane, carbon monoxide and carbon dioxide. 

When the gas is kept in sealed tubes a deposit of tellurium gradually forms on the walls. This dissociation does not appear to be accelerated by light, as is the case with liquid hydrogen telluride (see before), since it occurs just as rapidly in the dark.10... 

The most common sources are based on the 3H(d, n) reaction. Deuterons are accelerated to 150 keV with currents 2.5 mA and strike a tritium target. They produce 2 x 1011 of 14-MeV neutrons/s under these conditions. The neutrons produced are widely used in fast neutron activation analysis for the determination of light elements. The tritium targets are typically metals such as Ti, which have been loaded with titanium tritide. The accelerators are usually small Cockcroft-Walton machines or small sealed-tube devices where the ion source and accelerator structure are combined to produce a less expensive device with neutron yields 108/s. 

The necessity of frequent target changes and the attendant risk of tritium contamination of personnel and laboratories 30> has led to the development of high yield sealed-tube generator systems in which the tritium supply is constantly replenished 31-32). Ordinarily these systems operate by accelerating a mixture of deuterium and tritium ions into the... 

In source development, there is a need for more compact and reliable accelerator-based neutron systems. The advantage of accelerator-based technology (as distinguished from DD or DT systems) lies in the ability to both vary the energy of the neutrons and, with kinematic focusing, limit the angles of neutron production, i.e. produce neutrons in the forward direction rather than isotropically. However, sealed tube generators, both... 

In 1913, Coolidge [COO 13] imagined another kind of X-ray source. The cathode is comprised of a tungsten filament heated by the Joule effect. According to the Edison effect, this filament emits electrons that are accelerated by an electrical field and bombard the anticathode which then emits X-rays. The entire device is placed in a sealed tube inside which the pressure must be as low as possible. A schematic view of such a tube is shown in Figure 2.3. 

It is well known that a wide variety of organic reactions are accelerated substantially by microwave irradiation in sealed tubes. These rate enhancements can be attributed to superheating of the solvent, because of the increased pressure generated when the reactions are performed in the a.m. manner. Furthermore several reports have described increased reaction rates for reactions conducted under the action of microwave irradiation at atmospheric pressure, suggesting specific or nonthermal activation by microwaves. Some of these re-studied reactions occur at... 

As previously noted, the typical high temperatures and long reaction times required for the normal electron demand Diels-Alder reactions with electron-poor indoles have rendered such approaches less attractive for the synthesis of more sensitive and highly functionalized substrates in total synthesis. Recently, there have been a few reports on attempts to accelerate these cycloaddition processes. For example, Piettre and coworkers investigated the activation of the dienophilic indoles under high pressure [33]. Thermal Diels-Alder reactions of lV-tosyl-indole-3-car-boxaldehyde (65) with dienes 66a and 66b (195°C, sealed tube, 72 h) resulted in conversions of 67% and 25%, respectively (Scheme 18). By increasing the pressure for the above reactions to 16 kbar (48 h, 50°C), the corresponding cycloadditions with dienes 66a and 66b resulted in conversions of 93% and 86%, respectively. 

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