SHIELD-HIT12A demo version released

Here is a little sneak-preview of the upcoming release of SHIELD-HIT12A.

Pimp my Niva... (artist's impression of SHIELD-HIT12A).

SHIELD-HIT12A is a Monte Carlo particle transport code capable of transporting heavy ions through arbitrary media. The -A fork was made in 2010 from SHIELD-HIT08, and since then we have added plenty of new features, solved many bugs, increased calculation speed and optimized the nuclear models to new data on carbon-12 fragmentation.

A free demo version where the random seed and statistics are fixed to 10.000 particles can be downloaded from the project development page. There are builds for Linux and Windows systems (32- and 64 bit). It is a beta-release, but we would like to bring this demo version to a broader community, and thereby hopefully also fix some more bugs before we release the full version.

The new features in SHIELD-HIT12A are:

• New simplified material and beam parameter parser in free format and extensible without breaking downward compability.
• Including 279 ICRU default materials and elements, it has never been so easy to specify a material.
• New beam model: divergence and focus distance can now be specified (thanks to Uli Weber from Marburg).
• Arbitrary starting beam directions now possible.
• New routine for Vavilov straggling, 5-6 times faster than the original one by Rotondi and Montagna which was used in Geant3.21. In total, this alone means a speed improvement of roughly 30-40%.
• Ripple filter has two modes of operation, Monte Carlo type or Modulus type.
• Logarithmic energy binning in SPC files for TRiP
• Full howto for generating DDD files for TRiP
• Now only three input files are needed to setup a run.
• Improved documentation.
• Scoring by zones using detect.dat (complementary to Cartesian mesh and cylindrical scoring)
• Alanine response model included, so SHIELD-HIT12A can directly calculate the dose equivalent response in alanine.
• Flat circular and square beams can be defined
• Neutron data for natural Argon was added (needed for detailed simulations of air)
• Another ton of bug fixes.

Of course SHIELD-HIT12A includes the features from SHIELD-HIT10A (which was never released):

• Totally new (parallelizable) scoring system:
• Arbitrary Mesh and Cylindrical scoring
• Lots of detectors such as energy, fluence, dose-averaged LET, track-averaged LET, average velocity (beta), dose to medium (where medium can be changed if you want to calculate stopping power ratios) etc....
• finally SHIELD-HIT10A is parallelizable
• New random number generator, which gives a massive performance boost
• New adjusted inelastic cross sections for carbon ions based on recent data
• Fine tuning of the fermi-breakup parameters
• SHIELD-HIT10A can be configured without accessing the source code anymore, so no programming knowledge required to use SHIELD-HIT10A.
• SHIELD-HIT10A is installable
• Runs on linux again, even when compiling with code optimizations, ok with GNU gfortran, Intel and Portland compilers.
• Many bug fixes

Enjoy! And please drop me a line when you find bugs in the software and errors in the manual, they are there, but we hid them well. :o)

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Making Bubbles: The Particle Way

BTI BubbleTech Industries manufacture neutron detectors intended for personal dosimetry. Theses devices contain a polymer gel holding very small droplets of a superheated gas. When a neutron interacts with these superheated droplets, a phase transition happen from liquid phase to gas phase expanding the volume dramatically - a bubble appears.

The video below demonstrates how such a detector responds to a (weak) Americium-Beryllium neutron source:



The activity of the AmBe source was 2.64E+4 neutrons per second. The detectors we had were calibrated against ICRP-60 in terms of dose equivalent, according to BTI. The sensitivity of the particular detector shown in the video above was about 0.7 bubbles / µSv dose equivalent.

The detectors come with an integrated piston which repressurizes them, so they can be reused, however not indefinitely. We used our detectors rarely, and kept them refrigerated. However, after two years the encapsulation/pressurization system leaked.

The bubble detectors can be bought with varying sensitivity ranges and BTI even offers a set of detectors which are sensitive above a varying energy threshold. Deconvoluting the counts in each detector of this set will yield a coarse energy spectrum, in e.g. 6 energy bins.

We have used the these bubble detectors in our antiproton beam line at CERN in order to get a coarse measure of the amount of fast neutrons emitted from the antiproton annihilation. We used both the personal dosimeter type and the BDS spectrometer.



The picture above show how multiple personal dosimeter detectors are places at a certain distance from the annihilation vertex.

Unfortunately we had some trouble interpreting the results from the spectrometer. The BDS spectrometer counts seemed to be simply unphysical and a spectrum could not be deconvoluted. The readings from the personal dosimeter also seemed to be off by an order of magnitude.

After some investigations we started to suspect that these bubble detectors were not only sensitive to fast neutrons, but also to charged particles, such as protons. From the antiproton annihilation we do get a similar amount of protons and a threefold multiplicity of energetic pions, which have a long range, far beyond the position of the bubble detectors.

A paper in NIM B, which was published a few years ago by us, lists our findings. Basically we conclude that the sensitivity (# of neutrons per bubble) is quite comparable to that for protons, and perhaps a bit less for pions. The proton part we could test at our storage ring, ASTRID, which we have in the basement of our Physics Department in Aarhus.

In the video you are about to see, we extract a few million protons at about 50 MeV from the synchrotron. The bubble detector here is immersed in a water bath.



The range of the protons are clearly visible. A distinct Bragg peak does not really form, the effect is primarily related to nuclear interaction cross sections.