Under construction
I have never tested at NSRL before. Where do I start?
[Work in progress]
If I send my test article to NSRL, can you irradiate it for me?
[Work in progress]
How do I convert between the units of flux that NSRL uses—ions/cm2/spill—and ions/cm2/second?
This is a somewhat difficult question with multiple answers depending on the the calculation or comparison you’re trying to make. As explained in the temporal characteristics section of this guide, the beam is not delivered continuously like a cyclotron, but rather in spills.
If an average flux over time is desired, the flux value we report (which is the fluence in ions/cm2 for one spill) can be divided by the current supercycle length. For example, if the supercycle length is 6.6 seconds and we report the flux as 1.0e4 ions/cm2/spill, that represents an average flux of 1.5e3 ions/cm2/second over time. This would be the quantity to use when estimating the length of time needed to achieve a particular fluence.
In some circumstances, the instantaneous flux is the parameter of interest. Because the average flux calculation above takes into account the “beam off” time (which is generally much longer than the “beam on” time) the instantaneous flux is much higher. An accurate calculation of this quantity can be difficult, as the spill has many different time structures. However a reasonable approximation can be made by dividing the the flux value we report (which is the fluence in ions/cm2 for one spill) by the length of the “beam on” time for that spill. For example, If that spill length is 400 ms and we again report the flux as 1.0e4 ions/cm2/spill, the instantaneous flux would be approximately 2.5e4 ions/cm2/second during that spill. The spill length varies by ion species and energy, but is generally between 300-600 ms.
I see that the SEE Library beam list only shows LETs in silicon up to 28. Does that mean 28 is the highest LET NSRL can do?
No. NSRL can deliver an LET in silicon of up to 100 MeV-cm2/mg, which is the peak LET for our heaviest ion, bismuth.
The LETs listed for the SEE Library base energy beams are surface LETs, i.e., the LET at the incident surface of a part which is assumed to be bare silicon. Any ion will slow down as it passes through the particular stack up of materials before it reaches the region of interest, and will continue to slow down through that region. The LET, dependents only on the ion species and energy, increases as the ion slows.
The SEE Library beam energies were selected so that intermediate energies could be achieved by passing the beam through a configurable thickness of polyethylene from a binary filter. The 147 MeV/u bismuth base energy beam can be slowed with the binary filter to decrease its energy and thus increase its LET.
How much air (and other materials) does the beam pass through before it gets to my sample? I want to determine the energy at the surface of my sample.
While a list of effective material thicknesses of beamline equipment is listed here, experimenters almost certainly do not need to do this.
The beam energy quoted by NSRL is, unless explicitly specified otherwise, in reference to the upstream test position—38.00 inches (96.52 cm) from the vacuum window. The beam’s energy loss through stripping foils, the vacuum window, the QC1 primary monitor ion chamber, and the column of air, have already been accounted for.
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