SHiPGeometry::HeliumPiece Struct Reference

The innermost free region of the SBT, and the helium that fills it. More...

#include <SBTEnvelope.h>

Public Attributes
double	z_lo_mm = 0.0
double	z_hi_mm = 0.0
double	dx_lo_mm = 0.0
	half-width in X at z_lo
double	dx_hi_mm = 0.0
	half-width in X at z_hi
double	dy_lo_mm = 0.0
	half-height in Y at z_lo
double	dy_hi_mm = 0.0
	half-height in Y at z_hi

Detailed Description

The innermost free region of the SBT, and the helium that fills it.

The helium decay region must fill the space inside the SBT exactly: it may not protrude into any steel or scintillator, and it may not leave an arbitrary safety margin behind either. That makes its size a consequence of where the SBT material is, never an independent parameter.

This header therefore derives the helium purely from the placement primitives on SBTConfig — the same ones SBTStructureBuilder and SBTSensorBuilder place their volumes with. Change a placement rule and the helium follows automatically; there is no second copy of the arithmetic to forget to update.

Two properties of the SBT make this non-trivial, and both are handled here:

• The X envelope is not linear in Z. Side containers are split at the column front-flange edge (SBTConfig::zSplitOffset()) and the upstream piece has a flat outer face frozen at the sub-frustum's entrance half-width, so it does not clash with the column. The inner surface is therefore a sawtooth, dipping inward by up to xGrowth()*zSplitOffset() relative to the frustum. A single linear GeoTrap cannot follow it.
• The innermost material in Y is steel, not scintillator. The top and bottom longitudinal beams straddle the scintillator plane and their inner flange hangs below it, into the decay region. It sits deeper than the cells by (hbeam_height - flange_thickness) - container_thickness
  • sensor_clearance, and it — not the scintillator — bounds the helium.

Consequently the helium is built as a stack of GeoTraps, two per sub-frustum, each exactly filling the envelope over its Z span. One Z slab of the helium: a GeoTrap with rectangular faces at z_lo/z_hi.

Member Data Documentation

dx_hi_mm

double SHiPGeometry::HeliumPiece::dx_hi_mm = 0.0

half-width in X at z_hi

dx_lo_mm

double SHiPGeometry::HeliumPiece::dx_lo_mm = 0.0

half-width in X at z_lo

dy_hi_mm

double SHiPGeometry::HeliumPiece::dy_hi_mm = 0.0

half-height in Y at z_hi

dy_lo_mm

double SHiPGeometry::HeliumPiece::dy_lo_mm = 0.0

half-height in Y at z_lo

z_hi_mm

double SHiPGeometry::HeliumPiece::z_hi_mm = 0.0

z_lo_mm

double SHiPGeometry::HeliumPiece::z_lo_mm = 0.0

---

The documentation for this struct was generated from the following file:

• subsystems/DecayVolume/include/DecayVolume/SBTEnvelope.h