Dear Alex,
in USRYIELD
-plain double differential yield d2 N / d x1 d x2 counts the number of
particles that cross the border between the "upstream"(what(4)) and
"downstream" (what(5)) regions.
Only particles going from upstream to downstream are counted. Thus,
changing the order will change the distribution.
There is no dependence on where the particles were generated, or
scattered, or reflected: only the direction at the boundary matters. If
one of the scoring quantities is the angle, this angle is measured with
respect to the direction of the beam. Direction of the beam is the one in
the BEAMPOS card, or the z axis by default. It can be changed with the
USRYIELD...BEAMDEF card.
-double differential fluence yield 1/cos (theta) d2 N / d x1 d x2
measures the fluence of particles at same boundary.
Fluence is a measure of the radiation field, or in other words of the
density of particle tracks. According to the ICRU definition, fluence is
the number of particles, ΔN which enter an (infinitesimal) sphere of
cross-sectional area a, such that Φ=ΔN/Δa. It has a direct connection to
the "effect" of the radiation field, because the number of interactions
within a volume V is given by the product fluence*crosssection*volume.
It can be shown (see
https://agenda.infn.it/event/20624/contributions/105895/attachments/68619/85014/AdvancedScoring2019.pdf)
that fluence can be measured on a surface by counting the particles
crossing it with a weight equal to 1/cos(theta), where now theta is the
angle between the direction of the particle and the normal to the surface.
( it is as one would orient the surface to be perpendcular to the
particle's direction, and rescale the area of the surface) In this way,
the evaluation of fluence is independent on the orientation in space of
the surface. ( while current, dN/dx, depends on the orientation of the
surface)
USRYIELD measures fluence in this way.
If used to measure fluence, and one of the variables is angle, this angle
is measured with respect to the normal to the surface defining the
boundary
If no angular boundaries are give, the interval 0-pi is assumed, which means
that particles going in both directions (upstream-->downstream and
downstream->upstream) are counted. That's why changing the order of
regions the result does not change.
Hope this helps
Paola
> Dear experts,
> Would it be possible for someone to describe a little bit more in detail
the difference between USRYIELD WHAT(12) plain double differential yield
d2 N / d x1 d x2 and double differential fluence yield 1/cos (theta) d2
N
> / d x1 d x2? I have no previous experience in using these quantities. I
am
> trying to figure out how I could evaluate the photon scattering in
heterogenous environment with regions of different density. For this I
want to employ USRYIELD/ polar angle/ Ekin.
> My problem is that as I never worked with this before, I have a hard
time
> to visualize - its very important for me - and interpret this. I
understand the basics of usryield card but I don't get the
> upstream/downstream regions and what exact photons it counts. Does it
measure the photons at which angle they crossed the boundary between
upstream/downstream regions ? I also noticed that swapping
> upstream/downstream regions does not change the fluence yield while the
plain yield changes.
> I made a test simulation where an iron cube is in water environment. I
run
> usryield polar angle/Ekin plain yield WATER>IRON, usryield plain yield
IRON>WATER and usryield plain fluence WATER>IRON.
> In case 1_WATER-IRON, I see typical Compton scattering curve, so does it
represent photons scattered inside IRON ?
> In case 2_IRON-WATER, does it represented photons reflected from IRON,
or
> transmitted through IRON and then scattered in WATER?
> In case 3, fluence yield ,does it represent the scattered photons in
both
> regions?
> Any clarifying comments in layman terms would be highly appreciated,
especially any kind of simple schematics
> Rgds
> Alex
Paola Sala
INFN Milano
tel. Milano +39-0250317374
tel. CERN +41-227679148
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Received on Thu Apr 02 2020 - 16:18:45 CEST