# Re: Spherical boundary for USRBDX?

From: Alberto Fasso' <fasso_at_mail.cern.ch>
Date: Fri, 4 Mar 2011 15:57:46 +0100

Dear Bertrand,

> I am wanting to score the energy and angular distribution of the
> resulting particles punching through the box shielding of a tungsten
> target when it is hit by an electron beam.

Angular distribution with respect to which direction? USRBDX gives you
a distribution around the vector normal to the surface at the point of
crossing. If the surface is flat, that vector is constant: but if it is
a spherical surface, the vector will change depending on the crossing point.
I think this is not what you want.
If you want the angular distribution around a fixed direction, you must
use USRYIELD.

> Could someone point me to an example or be kind enough to take the time
> to tell me whether my understanding of needing a non-curved surface for
> USRBDX is correct?

No, one doesn't need a non-curved surface for USRBDX, but as I have said
one gets a distribution around the normal (i.e. a particle can cross
the surface perpendicularly, or at different grazing angles, up to a
maximum of 90 degrees, i.e. particle exiting the sphere along the tangent).
That, independently of where the crossing point is.
It doesn't look like the thing you are looking for.

> Also, how would I go about measuring the angular and energy distribution
> all around the target? Should I define a boundary on each side of the
> box shielding? Or should I use two USRYIELD estimators, one for energy
> and another for angle?

Use USRYIELD if you want the distribution around a fixed direction (the
beam direction, I imagine). You don't need to define special boundaries,
the surface of the box is sufficient.
To get a whole energy-angle distribution, you need several USRYIELD
detectors (not only two, but one for each angle: for instance 15, 30,
45, 60, 75, 90, 105, 120, 135, 150, 165, 180 degrees). At each angle,
score an energy distribution with as many intervals as you wish.

> On a side note, if the energy range used by USRBDX is for the kinetic
> energy of the particles, how would one measure the fluence of photons or
> is that a non-sensical question?

For photons, kinetic energy = total energy = momentum. One just calls it
energy.
The energy range is the same as saying the photon energy range.

Alberto
Received on Fri Mar 04 2011 - 21:32:13 CET

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