Monitoring of radiocarbon (C14) in carbon dioxide is demonstrated using mid-infrared spectroscopy and a quantum cascade laser. The measurement is based on cavity ring-down spectroscopy, and a high sensitivity is achieved with a simple setup. The instrument was tested using a standardized sample containing elevated levels of radiocarbon. Radiocarbon dioxide could be detected from samples with an isotopic ratio C14/C as low as 50 parts-per-trillion, corresponding to an activity of 5 kBq/m(3) in pure CO(2), or 2 Bq/m(3) in air after extraction of the CO(2) from an air sample. The instrument is simple, compact, and robust, making it the ideal tool for on-site measurements. It is aimed for monitoring radioactive gaseous emissions in a nuclear power environment, during the operation and decommissioning of nuclear power plants. Its high sensitivity also makes it the ideal tool for the detection of leaks in radioactive waste repositories.
By tailoring the wavefront of the laser pulse used in a laser-wakefield accelerator, we show that the properties of the x-rays produced due to the electron beam's betatron oscillations in the plasma can be controlled. By creating a wavefront with coma, we find that the critical energy of the synchrotron-like x-ray spectrum can be significantly increased. The coma does not substantially change the energy of the electron beam, but does increase its divergence and produces an energydependent exit angle, indicating that changes in the x-ray spectrum are due to an increase in the electron beams oscillation amplitude within the wakefield.
A laser pulse traveling through a plasma can excite large amplitude plasma waves that can be used to accelerate relativistic electron beams in a very short distance-a technique called laser wakefield acceleration. Many wakefield acceleration experiments rely on the process of wavebreaking, or selfinjection, to inject electrons into the wave, while other injection techniques rely on operation without self-injection. We present an experimental study into the parameters, including the pulse energy, focal spot quality and pulse power, that determine whether or not a wakefield accelerator will selfinject. By taking into account the processes of self-focusing and pulse compression we are able to extend a previously described theoretical model, where the minimum bubble size kpr b required for trapping is not constant but varies slowly with density and find excellent agreement with this model.
We report a photoacoustic spectroscopy setup with a high-power mid-infrared frequency comb as the light source. The setup is used in broadband spectroscopy of radiocarbon methane. Due to the high sensitivity of a cantilever-enhanced photoacoustic cell and the high power light source, we can reach a detection limit below 100 ppb in a broadband measurement with a sample volume of only a few milliliters. The first infrared spectrum of 14 CH 4 is reported and given a preliminary assignment. The results lay a foundation for the development of optical detection systems for radiocarbon methane.
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