Things that definitely happened
Fast Neutron Spectrometer
As a part of the BEXUS (Ballon EXperiments for Students) we, a group of physics students from CAU Kiel, are building a Fast Neutron Spectrometer.
While measuring charged particles is easy, detecting neutrals is a lot harder. Different measuring principles have been tested by previous BEXUS teams from Kiel (PING, ADAM, THANOS), which helps us as we have a large heritage to build up on. So what is new about this project?
The idea is to measure fast neutrons. Doing this is additionally hard as the neutrons have to be slowed done before being captured. Our boron-doped scintillator performs both tasks of moderating and capturing the neutrons.
Neutrons are subatomic particles, meaning they are smaller than atoms and actually part of most atoms. Contrary to protons and electrons, which are the other constituents of all usual matter, neutrons are electrically neutral.
As every measurement requires interactions between a detector and the particle to be measured, their lack of electro-magnetic interactions requires special measurement principles to measure neutrons.
Neutrons outside of atomic nuclei are unstable and decay into a proton, an electron and a neutrino with a half life time of about 10 minutes. Thus all neutrons measured in the atmosphere have to be produced inside the atmosphere.
MeV means Mega Electron Volt. The electron Volt is a unit that describes an energy just like Joule, but is much smaller (19 orders of magnitude). It is used in particle physics as particles masses are many times smaller than those of everyday objects, making their kinetic engeries also far smaller.
A scintillator is a material that emits light when charged particles travel through it. A special kind of scintillator used in FaNS is the so called plastic scintillator. As the name says it is made of plastic, which is a hydrocarbon, meaning it contains large amounts of hydrogen.
As only charged particles lead to light emissions in scintillators, they cannot directly measure neutrons.
The amount of ligth emited by the scintillator is a direct measure of the charged particles energy passing through the scintillator. Still, neutrons itself are not charged. FaNS uses a combination of multiple effects to be able to measure them. Upon entering the scintillator, the neutrons may collide with the hydrogen of the plastic, losing significant parts of its energy by knocking the proton out of the molecule. This proton now carries part of the neutrons initial energy. Since protons are charged, the scintillator starts emitting light which can be measured after amplification by a photomultiplier tube (PMT).
This alone still is not sufficient to identify neutrons, as a free charged particle inside the atmosphere could do the very same. This is where the Boron-doping comes into play. Some isotopes of the Boron easily capture the now low-energy neutrons, leading to emission of additional charged particles with a specific energy.
Measuring a first light-emission, followed by a second emission with this specific energy makes sure a neutron was measured.
Neutrons, espescially fast neutrons are capable of heavily damaging human cells and genes. While there are not many humans in the given altitude, there are many fast neutrons, making it an ideal environment to test the new principle implemented in FaNS.
Once its funcionallity is proven, FaNS-like instruments may be used in more human-friendly environments.
We are fans of FaNS, so I created a FanBlog of FaNS called FaNSBlog.
I don't really know if this is necessary, but it might be cool.
Things that definitely happened
Our predecessor, also built in Kiel to measure neutrons, but using another measuring principle.
Basic concepts of FaNS developed.