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BORON LOADED

EJ-254

 

EJ-254

 

This blue-emitting plastic scintillator contains natural boron at concentrations up to 5% by weight. It is a clear, stable plastic with physical properties similar to those of the standard Eljen plastic scintillators. Its principal applications are fast neutron spectrometry and thermal neutron detection. The primary function of the boron is to provide a unique scintillation signal for low energy neutrons. The standard formulation contains 5% boron, and practical boron concentrations down to 1% are available.

The isotopic fraction of 10B in natural boron is 19.9%, meaning that the 5% loaded plastic contains nearly 1% of 10B. The neutron capture reaction on the boron 10B(n,αγ)7Li  has a Q value of 2.78 MeV of which 2.34 MeV is shared by the alpha and lithium particles. This energy is fully captured in the plastic to produce a scintillation signal approximately equivalent in amplitude to that of a 76 keV electron. For delayed coincidence timing of the capture of fast neutrons, the time delay from the prompt recoil-proton pulse is typically 2.7 µs for 5% B-nat plastics. This delay is inversely proportional to the boron loading.

Reference: D.M. Drake et al., Nucl. Instr. & Meth., A247, 576-582 (1986)

 

PROPERTIES EJ-254-5%
EJ-254-2.5%
EJ-254-1%
Light Output (% Anthracene) 48 56 60
Scintillation Efficiency (photons/1 MeV e-) 7,500 8,600 9,200
Wavelength of Maximum Emission (nm) 425 425 425
Rise Time (ns)
0.85 0.85 0.85
Decay Time (ns) 1.51 1.51 1.51
Pulse Width, FWHM (ns) 2.24 2.24 2.24
No. of H Atoms per cm3 (x1022) 5.18 5.17 5.16
No. of C Atoms per cm3 (x1022) 4.44 4.55 4.62
No. of 10B Atoms per cm3 (x1020) 5.68 2.83 1.14
No. of Electrons per cm3 (x1023) 3.33 3.33 3.33
Density (g/cc) 1.026 1.023 1.021
Polymer Base Polyvinyltoluene
Refractive Index 1.58
Softening Point 75°C
Vapor Pressure Vacuum-compatible
Coefficient of Linear Expansion 7.8 x 10-5 below 67°C
Light Output vs. Temperature
At 60°C, L.O. = 95% of that at 20°C
No change from 20°C to -60°C
Temperature Range -20°C to 60°C

 

Chemical Compatibility
Attacked by: Aromatic solvents, Chlorinated solvents, Ketones, Solvent bonding cements, etc.
Stable in: Water, Dilute acids and alkalis, Lower alcohols, and Silicone greases.
It is safe to use most epoxies with this scintillator.

 

EJ-254 Emission Spectrum