What is being assumed when you run SNOMAN 5_03
The detector is divided into regions and the geometry defining these regions
is an embedding geometry- that is regions of higher priority are embedded in
regions of lower priority eg the acrylic chimney is considered to be a solid
cylinder of acrylic, the region ACRC_OVL (OVL standing for outer volume)
in which a cylinder of D2O, ACRC_IVL, is embedded. (For more information
on how the geometry is handled in SNOMAN see the user's manual
geometry .)
Regions and media are each given region and media codes and these are listed in
regions and
media .
The shape, size, position and medium of each region are given in the file:
geometry.dat . (The format for the
information in this file is defined in the `titles' files
GEDP and
GEDS .)
The default detector regions
There are many regions
defined, eg for calibration sources, and only those describing the detector in
detail with just D2O and no calibration sources are enabled by default:
ie heavy water inside the acrylic vessel, with belly plates, ropes and a
chimney, surrounded by light water then the PSUP, with the
PMT panels and the PMT+concentrators, more light water and finally above the
counting room and enclosing all the rock cavity.
These regions are:
Region No Region Medium No Medium
100 D2O 200 Heavy water
201 ACRV_TILE 400 Acrylic
211 ACRV_OVL 403 Acrylic (Poor)
212 ACRV_IVL 200 Heavy water
300 H2O 100 Light water
310 BLY_PLATE 400 Acrylic
315 BLY_GROOVE 100 Light water
320 BLY_ROPE 1000 Kevlar
400 PAN_ZONE 100 Light water
410 HEX_EMPTY 100 Light water
422 PMT_OVL 100 Light water
423 PMT_GLASS 700 Glass
424 PMT_VACUUM 1 Vacuum
425 PMT_PETAL 602 Petals
426 PMT_ABS 1300 Water/ABS sludge
427 PMT_PINOUT 700 Glass
428 PMT_BASE 1300 Water/ABS sludge
431 PMT_STACK_OVL 603 Dynode stack
432 PMT_STACK_OVL_T 1 Vacuum
433 PMT_STACK_IVL 1 Vacuum
455 ABS_SKIRT 1300 Water/ABS sludge
500 INNER_DARK 100 Light water
550 Counting_room 800 Air
570 Urylon 1700 Polyethylene
580 SHOTCRETE 1800 Concrete
600 ROCK 300 Norite
Optical properties of media
The optical properties of all the media in SNOMAN are given in
media.dat . (The format for the
information in this file is explained in the `titles' file
MEDA .)
The properties listed are: the mean refractive index (real and
imaginary); the variation in refractive index and the absorption coefficient
as a function of wavelength; the Rayleigh scattering parameters and data on
any specular and diffuse reflection/transmission.
Properties of media assumed in the transport of electrons and gammas
The information on media used for the simulation of the transport of electrons
and gammas using EGS4 is given in
PEGS . The properties listed are: whether the medium is an element, a
compound or a mixture; the composition, atomic numbers and atomic weights
of the elements; the density and various energy thresholds that are
applied in EGS4. (The actual information used by SNOMAN can be found in the
very long file pegs4_10.dat )
Neutron cross sections
The data files giving the cross-sections for neutron interactions are described
in neutron files . Where the
atomic number is not given the cross-section is for the natural abundance
of isotopes. The cross-sections included in SNOMAN are for:
H, D, HE3, HE4, B10, B11, C, N14, N15, O16, O17, F19, Na23, Mg, Al27,
Si, S, Cl, Ar, K, Ca, Cr50, Cr52, Cr53, Cr54, Mn55, Fe54, Fe56, Fe57,
Ni58, Ni60, Ni61, Ni62, Ni64, Cu63, Cu65, I127, Cs137, Ba138, Pb206
and Pb208
When tracking a neutron SNOMAN finds out what region and hence what medium the
neutron is in. Given the medium the code in the routine
neutron_media_query.for first uses the information in
pegs4_10.dat to find out what
nuclei are in the medium. If in the D2O, the heavy water is assumed to
have a light water fraction of 0.8888% by weight and an isotopic abundance of
O17 as a fraction of O16 of 0.055% (cf the normal 0.038%). The data file
neutron_control.dat then identifies what neutron table, either the
particular isotope table, the natural elemental abundance table or the
most abundant isotope table, will be used for each nucleus. For O18 the O16
table is used which introduces negligible error as the isotopic fraction (~0.6%
in D2O, 0.2% in H2O) is so small and the scattering and capture
cross-sections are comparable to those of O16.
The main detector elements
Heavy water
For the heavy water the optical absorption lengths in the wavelength range
254nm to 578nm are all set equal to 1000 metres
and the scattering is assumed to equal twice Rayleigh scattering (an isothermal
compressibilty of 4.92e-10 N^-1 m^2 is assumed) (see
media.dat .) The transport of electrons
and gammas assumes the heavy water is pure D and O16 with a density of 1.105
(see PEGS ) .
For neutrons the heavy water is assumed to have a light water fraction
of 0.8888% by weight defined in
neutron_heavy_water.dat
and an isotopic abundance of O17 as a fraction of
O16 of 0.055% defined in
neutron_impurities.dat ,
the format for these files being in
neutron files .
(NOTE almost all of the hydrogen in the heavy water is in the
form HDO and the use of H-in-H2O and D-in-D2O thermal tables introduces a
small error estimated as less than 1% (Jeremy Lyon's thesis p100).)
Heavy water plus salt (sodium chloride)
Salt has to be added using the commands given in the symbol table . SNOMAN assumes the optical properties
of the heavy water are unaffected by the addition of salt. The density though
is corrected as well as adding sodium and chlorine nuclei to the heavy water
in the routine neutron_media_query.for .
Acrylic vessel
The acrylic vessel is made up from acrylic tiles and belly plates, whose
absorption lengths are given in
opt_variations.dat , and an
acrylic chimney made from acrylic (Poor). The acrylic glue between the tiles
is made from acrylic (bad 4-inch).
NOTE: the various types of acrylic listed in
media.dat only differ in their
absorption lengths.
Any diffuse transmission or reflection at the surface of the acrylic is
assumed to be ZERO and the probability of specular reflection
and refraction is calculated according to Fresnel coefficients.
Light water
For the light water the scattering is also assumed to be twice Rayleigh
but the absorption is based on measurements in the 500-700nm range and is
estimated to be (see media.dat ):
1000m at 250nm, 1000m at 350nm, 767m at 400nm, 50m at 500nm,
17m at 548nm and 11m at 578nm.
PMTs
The modelling of the PMTs is a full 3D simulation. (For information on the
modelling in SNOMAN see
PMT modelling .)
(The PMT efficiencies and concentrator reflectivities are currently
assumed all the same in SNOMAN.)