Bachelor in Physics

Investigation of neutron moderators with spherical voids

This is the web page connected to the bachelor project of Mads Bertelsen and Pia Jensen (now Pia Jensen Ray) from the Niels Bohr Instutute under the University of Copenhagen. Here it is possible to download the project, the source codes, and some of the figures from the project with larger quality. The download section is at the bottom of this page.


The project was a study of moderator geometry, working with both theory, simulation and experiments. A simple simulation was written in order to model a box neutron moderator with a concave void, investigating the flux increase from the void, as compared to the flux from a similar flat box moderator. A gain of about 3.5 was found in both the experiments and the simulation, after addition of absorption in the simple model.

Paraffin neutron moderator block with a spherical void

The sph1 moderator used during the experiment.

Regular downloads

Below is the report, all the source codes shown in the report, and the measurements taken during the experiment.

We have given speeches about the project several times, and the used slides can be downloaded from below (in order of appearances).

Figure downloads

Below are first the most important figures to see in large resolution. Simply clicking the thumbnail brings you to the larger image. Note that there are links to these images in the table below as well (and to MATLAB FIG files for some of them).

Below are all the figures shown in the report (except the flow-charts), saved in high resolution PNG files. Some of the figures can also be downloaded as MATLAB FIG files, which are plots that can be opened in MATLAB and seen as if you plotted them yourself.

NumberDescriptionDownload link(s)
2.1(a)Scattering coordinate system definitionPNG
2.1(b)Rotation of scattering coordinate systemPNG
2.2(a)Distribution of thetaPNG
2.2(b)Distribution of alphaPNG
2.3Alpha as a function of theta and theta'PNG
2.4Illustration of the "source volume"PNG
2.5Illustration of the focus effectPNG
3.2(a)Neutron intersecting voidPNG
3.2(b)Neutron ending in voidPNG
3.3The mirror routinePNG
3.4(a)Flux 1 mm over flat moderatorPNG / FIG
3.4(b)Flux 1 mm over sph2 moderatorPNG / FIG
3.4(c)Flux 1 mm over sph1 moderatorPNG / FIG
3.4(d)Flux 13 mm over flat moderatorPNG / FIG
3.4(e)Flux 13 mm over sph2 moderatorPNG / FIG
3.4(f)Flux 13 mm over sph1 moderatorPNG / FIG
3.4(g)Flux 25 mm over flat moderatorPNG / FIG
3.4(h)Flux 25 mm over sph2 moderatorPNG / FIG
3.4(i)Flux 25 mm over sph1 moderatorPNG / FIG
3.4(j)Flux 37 mm over flat moderatorPNG / FIG
3.4(k)Flux 37 mm over sph2 moderatorPNG / FIG
3.4(l)Flux 37 mm over sph1 moderatorPNG / FIG
3.5(a)Divergence diagramPNG
3.5(b)Divergence calculationPNG
3.6(a)Divergence of neutrons from sph1 voidPNG / FIG
3.6(b)Divergence of neutrons from sph2 voidPNG / FIG
3.7(a)r_old's from flat moderatorPNG / FIG
3.7(b)r_old's from sph1 moderatorPNG / FIG
3.7(c)r_old's from sph2 moderatorPNG / FIG
4.1Moderator wood boxPNG
4.2Neutron counter electronicsPNG
4.3Measured dataPNG / FIG
5.1Energy distribution from primary moderatorPNG
5.2Measured data and simulated dataPNG / FIG
5.3Neutron scalar flux for two casesPNG
5.4Measured data and simulated data w./w.o. abs.PNG / FIG
F.1Neutron detector and housingPNG
F.2(a)Exact measurements of flat moderatorPNG
F.2(b)Exact measurements of sph1 moderatorPNG
F.3Overview of radioactive sourcePNG
G.1(a)r_old's from flat moderator (more energies)PNG / FIG
G.1(b)r_old's from sph1 moderator (more energies)PNG / FIG
G.1(c)r_old's from sph2 moderator (more energies)PNG / FIG
G.2(a)Measured data and simulated dataPNG / FIG
G.2(b)Measured data and thermal simulated dataPNG / FIG
G.2(c)Measured data and simulated data w. absorptionPNG / FIG
G.3Overview of the Farnsworth-Hirsch fusorPNG
G.4(a)Typical short path of a neutron from the simulationPNG
G.4(b)Typical long path of a neutron from the simulationPNG
H.2Scattering cross section data from NNDCPNG

Photographs from the experiments

Finally, during the project several photos were taken, to document all the fun we had. These are shown below with small explanations. For larger size images, simply click the thumbnails.