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Due to low effective atomic number
organic materials in contrast to nonorganic ones are characterized by negligible back
scattering effect for the process of charged particles absorbtion. Due to high
concentration of hydrogen atoms they are used in fast neutron spectroscopy. Scintillators
on the base of organic crystals are non-hydroscopic and fast.
Anthracene (C14H10)
Traditional organic scintillator finds use in a number of special applications.
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Stilbene (C14H12)
Used for selective registration of fast neutrons (n) on the gamma radiation background in
scintillation pulse-shape discrimination techniques, as well as for alpha/beta-, n/beta-,
proton/beta-selection. It makes possible to perform neutron field spectrometry. The
largest dimension is dia. 120x100 mm.
Doped crystals of p-terphenyl (C18H14)
Undoped p-terphenyl crystals are of limited use because of their low light output.
Introduction of special dopants ensures the light output to be increased by 4-5 times.
Doped p-terphenyl crystals retain all basic advantages of organic scintillators, i.e.
short decay time (t ~ 3-4 ns), temperature-independent light output values in a wide
temperature range (-80...+150 °C).
The p-terphenyl single crystals are translucent, knotty over the whole volume, plastic,
water-insoluble, and poorly soluble in organic solvents.
Scintillators based on doped p-terphenyl crystals are used in b-radiation spectrometry,
where they are the most effective organic scintillators, a-radiation one, as well as for
fast neutrons detection on the g-radiation background in schemes for radiation
discrimination by the scintillation pulse shape. Due to short decay time, p-terphenyl can
be used in the spectrometry of high-intensity radiation. |
Selector guide.
Material |
Important properties |
Application comments |
Antracene |
Crystal anisotropy (high light
output anisotropy) |
beta radiation detection and
spectrometry |
Stilbene |
High structural perfection and
performance stability. Selection of fast neutron on the gamma radiation background |
Fast neutron spectroscopy
n/gamma, alpha/beta-discrimination |
Doped p-terphenil |
High light yield. The lowermost
light output anisotropy |
Detection and spectroscopy of
alpha-, beta-radiations |
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Physical Properties of Organic Molecular Single
Crystals
|
Antracene
(C14H10) |
Stilbene
(C14H12) |
Doped
p-terphenil
(C18H14) |
Molecular
weight |
178 |
180 |
230 |
Density,
g/cm3 |
1.25 |
1.22 |
1.23 |
H/C - ratio |
0.174 |
0.857 |
0.778 |
Melting point, °C |
216 |
124 |
214 |
Wavelength of emission maximum, nm |
445 |
390 |
420 |
Refractive index at emission maximum |
1.62 |
1.64 |
1.65 |
Light output, 104 photons/Mev |
2.0 |
1.4 |
2.7 |
Decay time, ns |
30 |
3.5 |
3.7 |
A ratio of ranges in the crystal and anthracene
for:
a) heavy charged particles
b) electrons |
1
1 |
1.002
1.014 |
0.997
1.012 |
Radiation
degradation, Mrad |
2 |
4.0 |
4.5 |
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| Pu-Be spectrum for
stibene detector dia. 80x50 mm 
137Cs spectrum for
p-terphenyl detector dia. 80x5 mm; 137Cs radionuclide sourceirradiates 125
conversion electrons per second through a collimator and 1.5 105 gamma photons
per second in 2-p geometry.
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241Am spectrum for p-terphenyl
detector dia. 20x10 mm.
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Scintillation Detectors
Detectors based on organic crystals (doped p-terphenyl, stilbene,
anthracene) are used for the detection and spectrometry of beta, gamma radiation,
discriminative n/gamma - measurements, and in phoswich detectors for discriminative
measurements of low-energy beta radiation.
Since stilbene crystals have the most stable properties, detectors with these crystals are
used as the reference ones in light output measurements.
Detectors and assemblies with organic crystals are similar in design to those with alkali
halide crystals.
In the detectors (assemblies) intended for beta radiation measurement, the input window is
made of aluminum-coated polyethylene-terephtalate film having a thickness less than 2 mg
cm -1.
Detectors with organic crystals
|
Scintillation
material |
Scintillator
sizes |
Working temp.
°C |
Relative
light output |
Energy
resolution*, % |
diam. |
height |
SDO.02,
SDO.12 |
doped
p-terphenyl |
10 to 80 |
1 to 100 |
-60 to 80 |
200 |
<10 |
SDO.04 |
stilbene |
10 to 100 |
1 to 100 |
-40 to 60 |
100 |
<10 |
SDO.08,
SDO.09 |
anthracene |
10 to 40 |
5 to 30 |
15 to 35 |
150 |
<10 |
* Cs conversion electrons |
New:
To
special orders, mosaic-type detectors with doped p-terphenil can be made up to 200 mm in
diameter. |
New:
By hot
pressing, polycrystalline large area detectors are produced with a thickness of 0.2 to 3
mm. |
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