All 2 entries tagged Irradiation
No other Warwick Blogs use the tag Irradiation on entries | View entries tagged Irradiation at Technorati | There are no images tagged Irradiation on this blog
April 06, 2022
How To Irradiate Your Samples
Following some of the successes and pitfalls at the DCF facility we now have all the irradiations completed thanks to the dedicated staff at the Dalton Cumbrian Facility. Since the energies in this round of experiments were sufficiently below the threshold of activation, samples were dispatched in the post.
The next stage will be to clean and mount sample for cross-sectional imaging, hardness testing, EBSD and TEM but that will be discussed in a later entry since much of that work will be for publication.
So how does one get to irradiate samples in the first place? And what has this specific experiment got to do with the first goal of the Radiation Dense Materials concept?
First of all as with any new science experiment, you have to talk to people first, in person, online or by email. This is critical to ensure that you can flesh out the proposed experiment and see how feasible it is or isn't. By discussing the planned irradiation schedule with the staff at the Dalton Facility we were able to acertain that ambient and non-ambient irradiation was possible with the proton beam and the gamma irradiator.
One of the inherent difficulties of current irradiation facilities is that generally samples can only be irradiated by one type of radiation at one time, unless placed in a test reactor. This is similar to reproducing a painting but with only one brush and one pigment. Hence, it is important to state the limitations of irradiation testing on samples with this in mind.
So, how are samples actually irradiated? This depends on the method and the radiation used. For the gamma irradiator it is simply a case of tracking the face closest to the 60Co source and placing it in a low-activation borate glass. The 60Co irradiator is shown below:
For low-temperature (77K) irradiations, samples were placed in a dewar full of LN2. Since oxygen liquifies at 85K this forms a pool in the dewar which under gamma irradiation transforms to O3 which is solid at LN2 temperatures. Solid O3 is an explosion hazard and thus nescessitates emptying and renewing the LN2 every 5 kGy. The low-temperature high-dose gamma sample had 90 kGy in total.
For proton beam irradiation, sample preparation is more involved. Samples need to be mounted with a heat-resistant conductive adhesive (silver paste) and need alignment such that the beam energy and radiation time can be computed, the exact figures depending on the dosage and the target temperature. Samples mounted for proton-beam irradiation are shown below:
Since protons are charged particles, total proton dosage can be computed from the charge accumulated from the beam current. Alongside sample irradiation, other data from samples such as emissivity can be obtained from proton irradiation at elevated temperatures.
Data analysis is at the earliest stages with the following planned sequence (1) Cross-sectional imaging (2) microhardness measurements (3) EBSD and (4) TEM (specifics to be determined following from EBSD and HV measurements).
Ultimately, this work will form the outline for subsequent radiation work as this is a first for both cWC and RSB materials.
March 30, 2022
First irradiation studies of RSBs at the Dalton Facility
Writing about web page https://www.dalton.manchester.ac.uk/research/facilities/cumbria-facilities/
Last week was a first in the field of Radiation Dense Materials in that samples of Reactive Sintered Borides (RSBs) and cemented Tungsten Carbide (cWC) were irradiated for the first time by proton beam and gamma irradiation at the Dalton Cumbrian Facility in the Westlakes Science Park during some truly beautiful springtime weather.
Much work on simulating the radiation response and attenuating properties of a cWC, cWC-RSB and tungsten boride shielding concepts has occured during the 2010s onward [C.G. Windsor et al 2015 Nucl. Fusion 55 023014,C.G. Windsor et al 2018 Nucl. Fusion 58 076014], however, data on the radiation response of cWCs [Shielding materials in the compact spherical tokamak https://doi.org/10.1098/rsta.2017.0443] is very sparse due to their recent adoption as candidate shielding materials. No data on radiation response exists for RSBs due to their novelty so this will be the first time any practical data will be obtained from irradiated RSB materials.
The planned experimental work at DCF fell into two main topics: Proton irradiation and gamma irradiation. Each type of radiation would take place at two different intensities and at two different temperatures.
Proton radiation most closely resembles the conditions at or near the plasma-facing component of a tokamak reactor and hence was to take place at ambient and at 600oC.
Gamma radiation will be significant at all parts of a tokamak reactor but particularly near the superconducting magnets. These irradiations were performed at -196oC (77K) and at ambient. Each experiment consisted of three samples: cWC, RSB and W metal alloy with eight different irradiation conditions with a 9th sample set to sit in the gamma irradiator for long-term irradiation studies.
So....how did the work go and what happened over last week? Read on.
The gamma irradiation mostly went to plan. Low dose gamma irradiation was set to 30 kGy for both the 77K and ambient irradiation. High dose gamma radiation samples was set to 240 kGY for ambient and 90 kGY for 77k. The lower dose at 77K is a result of the different sample positioning due to the dewar and the requirement to change the N2 the dewar every 5 kGy to prevent excessive ozone formation, which is an explosion hazard. All gamma irradiated samples except the long-term samples have been returned.
Proton irradiation was less straightforward. The high dose ambient proton irradiation was successful, with a steady state temperature of 125oC and a total dose equivalent to 1.66 x 1018 protons. Subsequent proton irradiation attempts were unsuccesful, mostly due to the plasma failing the strike and therefore enable the proton beam to irradiate the samples. However, these sample will be irradiated this week and sent by post.
This is one of the many hazards of experimental work in that failure is always an option but nevertheless this work on completion will provide an important first step in realizing the cWC-RSB concept as practical radiation shielding materials whatever the damage or lack of is present on analysis.
This work would not be possible without the dedication of the staff and researchers at the DCF who make this possible.