The coordinates of the starting point of the track. This would usually be a set of 3 numbers. If you omit the z-coordinate, 0 is assumed. [No default, in cm.]
The coordinates of the end point of the track. If the particle undergoes multiple scattering or energy loss (HEED model), then the end point merely serves to compute the initial direction of the particle. When both TO is used and DIRECTION and RANGE, then the information provided with TO is taken. This would usually be a set of 3 numbers. If you omit the z-coordinate, 0 is assumed. [No default, in cm.]
The direction in which the particle starts moving from the starting point. When using DIRECTION, you must also use RANGE. You should not use TO however in this case, since TO overrules the information from DIRECTION and RANGE. This would usually be a set of 3 numbers. If you omit the z-coordinate, 0 is assumed. [No default, in cm.]
This is the maximum distance the particle is allowed to travel from the starting point. The range is measured by projection onto the DIRECTION, i.e. the additional length that results from multiple scattering is not taken into account. The RANGE should be chosen sufficiently large to avoid having the particle cut prematurely, but not too large either - this would cause overflow in HEED's internal buffers. [No default, in cm.]
Requests the simple model in which a fixed number of electrons or ions is generated at equally spaced points along the track. The track is straight in this model. Since this the only model that doesn't depend on external information, this is the initial default.
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Requests a model in which the number of clusters generated along a straight track is always exactly mean * length where "mean" is the mean number of clusters per cm as entered with the PARAMETER statement in the gas section and where "length" is the distance between the start and end points of the track. The clusters are deposited with a constant spacing. The cluster size distribution is respected. This model can only be selected if the mean number of clusters and the cluster size distribution have been entered in the gas section.
Requests a model in which the number of clusters generated along a straight track is Poisson distributed with a mean of: mean * length where "mean" is the mean number of clusters per cm as entered with the PARAMETER statement in the gas section and where "length" is the distance between the start and end points of the track. The spacing between the clusters is exponentially distributed. The cluster size distribution is respected. This model can only be selected if the mean number of clusters and the cluster size distribution have been entered in the gas section.
This model generates single electron or ion deposits (i.e. no clusters) at positions that follow a user specified distribution. The model can be used to simulate certain background conditions. The deposits are generated in random sequence.
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A single cluster is generated on each track. The cluster size is taken from the information entered in the gas section. This model differs from FIXED-NUMBER with a number of samples set to 1 in that the cluster in SINGLE-CLUSTER is at a random location while it would be in the middle of the track when using FIXED-NUMBER. This model can be seen as a rough approximation to photon from e.g. an Fe 55 source, provided an adequate cluster size distribution is entered.
This option calls the Heed program to take care of cluster generation. This program simulates the ionisation of the gas molecules by a particle. The particle knock an electron out of an atom. The electron may have sufficient energy to cause further ionisations (in that case we speak of a delta electron) or it may start drifting towards the anode. The atom returns to its ground state by either emitting an Auger electron or by fluorescence photons. The Auger electrons are treated like the ionisation electrons. The photons can be absorbed in other atoms. When using the Heed interface, you must define the gas mixture to Heed in the gas section. Then, you should specify on the TRACK statement what kind of particle traverses the chamber. Clustering information entered in the gas section through the PARAMETER and CLUSTER statements is not used.
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