Addtives: Scintillator and WLS

``Additives'' are adjunct materials that can be added to normal media (described in the MEDA titles banks). By adding and additive to a normal medium, SNOMAN can be used to simulate

• Scintillation
• Wavelength-shifter
• Simple absorber

Additives can be assigned to media by using the ADMX ("admixture") bank. Each row in this bank sets the additives for a different medium. (Note that adding additive to a medium, you change the medium everywhere in the detector.) In this bank, you set the media code, the fractional concentration (between 0 and 1) and the type of the additive. Multiple addtives can be assigned to any material, although the need for this should be rare.

The 'type' refers to the bank ID of the associated SCNT bank, which holds the additive properties:

Quantum Efficiency

This refers to how much light will be made when an ionizing particle passes through the medium, i.e. scintillation. Units are Photons/MeV.

Birk's constant

This parameter gives the saturation of the scintillator to heavy particles (i.e. protons). Units are cm/MeV.

Decay time

It is assumed that if the additive is luminescent (either by scintillation or fluorescence) that the intensity of light falls off with an exponential decay time, or with multiple exponentials, characterized in ns.

Emmission Spectrum

If luminiescent, the spectrum of emmitted light (in nm).

Absorption Spectrum

If the addtive is not completely transparent, the absoption spectrum should be specified (in attenuation lengths) just as it is for a medium.

WLS Quantum Efficiency

If the additive is flourescent, this quantum efficiency gives the number of emitted photons per absorbed photon. At present, this is assumed to be less than unity. Typically, this property is used to simulate wavelength shifting.