High-energy radiation has been utilized for decades, however, the role of low-energy electrons created during irradiation has only recently begun to be appreciated Nuclear decay is one of the most extreme processes and is central to a range of fields including energy, medicine, imaging, labelling, archaeology and sensing. Radiation in the form of alpha particles, beta particles and gamma rays have fundamentally different interactions with matter and therefore exhibit different mean-free paths (∼1 μm, 1 mm and 1 cm, respectively). These forms of primary radiation deposit their energy over the course of their trajectory by ionizing their surroundings and producing non-thermal secondary electrons. Only very recently has the ability of low-energy secondary electrons to induce chemical reactions and biological damage begun to be appreciated 1 , because they have energies below the typical ionization threshold of organic matter. For example, low-energy electrons (3-20 eV) have been shown to be effective at causing DNA cleavage 2,4,7 . This ability stems from their high cross-section for breaking chemical bonds, and as a consequence they have a very short meanfree path of ∼1-10 nm in solution 8,9 . Furthermore, hot electrons that are not captured by surrounding molecules become thermalized as solvated electrons which are known to be chemically and biological active [9][10][11][12] . To harness these unique properties, the design of radioactive materials that increase and localize the flux of short-range lowenergy electrons to target sites is crucial for their application in targeted cancer therapies that minimize damage to healthy cells. Thus far, it has not been possible to design atomically precise radioactive materials that maximize these effects due to self-destruction arising from nuclear recoil, Coulomb explosion and self-irradiation [13][14][15][16] . We report a straightforward method for synthesizing monolayer films of radioactive 125 I atoms on gold-coated mica substrates under ambient conditions, and characterize their composition and their electron emission. Despite being synthesized from radioactive 125 I (> 99.9% purity) they are robust with respect to self-destruction, and provide well-defined, intense planar sources of secondary electrons. 125I decays by electron capture (EC) of a core shell electron to produce a nuclear excited state of 125 Te (Figure 1a), the majority of which eject another core
A new gate drive for high-voltage, high-power IGBTs has been developed for the SLAC NLC (Next Linear Collider) Solid State Induction Modulator [1]. This paper describes the design and implementation of a driver that allows an IGBT module rated at 800A/3300V to switch up to 3000A at 2200V in 3µS with a rate of current rise of more than 10000A/µS, while still being short circuit protected. Issues regarding fast turn on, high de-saturation voltage detection, and low short circuit peak current will be presented. A novel approach is also used to counter the effect of unequal current sharing between parallel chips inside most high-power IGBT modules. It effectively reduces the collector-emitter peak current, and thus protects the IGBT from being destroyed during soft short circuit conditions at high di/dt.
The Next Linear Collider accelerator proposal at SLAC requires a high efficiency, highly reliable, and low cost pulsed-power modulator to drive the 500 KV, 260A X band klystrons. With a pulse width of less than 1.5 microseconds, it is difficult for the present SLAC type modulator with conventional pulse transformer to have a high efficiency due primarily to the inherently slow rise and fall time of the video pulse. The proposed induction modulator utilises a pulse transformer similar to an induction accelerator driven by Solid State high voltage IGBTs. The performance of the IGBTs, induction cores and a low voltage model will be discussed as well as the design and construction of a prototype modulator capable of driving up to 8 of the X band klystrons Design consideration efficiency, availability & costThe major problem with the conventional PFN type modulator use at SLAC and around the world for the Next Linear Collider (NLC) is the efficiency of the modulator for short pulse operation. The leakage inductance for the pulse transformer and the stray inductance of the switching circuit inherently limit the rise and fall time of the klystron voltage waveform. To reach the efficiency goals of > 75% for the modulator for the NLC it is necessary to have a rise and fall time of the klystron voltage pulse of less than 200 ηsec. With the high voltage of the NLC klystron of 500 kV and large stray capacitance of > 100 ρfd per klystron (RC time constant of 200 ηsec.) it is difficult to obtain a fast rise time with a matched impedance PFN modulator. The operational availability of the standard SLAC type modulator is limited by the failure rate of hydrogen thyratron used for switching. In addition thyratron are subject to a high incidents of spontaneous triggering, which effects the overall accelerator availability. The peak power of thyratron and circuit & PFN impedance limits the practical peak power of a SLAC type modulator to about 300 megawatts peak, or capability of driving more than two NLC klystron at one time. This makes the cost of modulators >100k$ per klystron for the conventional SLAC modulator expensive to build.
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