Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
2001-07-06
2003-04-08
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S390010
Reexamination Certificate
active
06545281
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to energetic particle detectors and is particularly directed to a coated semiconductor detector capable of detecting cold, thermal and epithermal neutrons.
BACKGROUND OF THE INVENTION
Semiconductor detectors coated with neutron reactive materials offer an alternative approach to scintillator-based neutron imaging devices for neutron radiography (normally scintillating screens coupled to photographic film or to other photorecording devices). Neutron reaction film-coated devices typically include Si, bulk GaAs, or diamond detectors, all of which have advantages and disadvantages. Si and bulk GaAs-based devices operate at moderately low voltages, whereas diamond-based films require hundreds of volts to operate. Although diamond-based films appear to be more radiation hard than GaAs, GaAs devices demonstrate superior radiation hardness to neutrons and gamma rays in comparison to Si. Neutron reactive films based on the
157
Gd(n,&ggr;)
158
Gd reaction show a higher neutron absorption efficiency than
10
B(n,&agr;)
7
Li and
6
Li(n,&agr;)
3
H-based films, however, the combined emission of low energy gamma rays and conversion electrons from
157
Gd(n,&ggr;)
158
Gd reactions make neutron-induced events difficult to discriminate from background gamma-ray events. The particle energies emitted from the
6
Li(n,&agr;)
3
H reaction are greater than those emitted from the
10
B(n,&agr;)
7
Li reaction and are much greater than observed from the
157
Gd(n,&ggr;)
158
Gd reaction. Yet, the optimized film thickness for
6
LiF is over ten times greater than needed for
10
B while producing only a slight increase in neutron detection efficiency. Background gamma rays are less likely to interact in a diamond or Si detector than in GaAs, but previous results have shown that the gamma-ray background interference for
10
B-coated GaAs detectors is low enough to discriminate between neutron and gamma-ray events. Regardless, Si, GaAs, diamond, and a variety of other semiconducting materials can be used as the detector in the present invention.
Referring to
FIG. 1
, there is shown a simplified schematic illustration of the basic components comprising a
10
B-coated semiconductor neutron detector
10
. The neutron detector
10
includes a semiconductor substrate
12
having on one surface thereof a back contact layer
14
which is coupled to a potential, depicted as neutral ground in the figure. Disposed upon the substrate
12
is a front contact
18
that forms a blocking contact upon the semiconductor substrate
12
. An active region
16
forms from either the blocking contact
18
potential or through the application of voltage
30
(shown in dotted line form in the figure), or a combination of both the blocking contact
18
and the applied voltage
30
. An energetic neutron
22
interacts with the
10
B film
20
, thereby releasing an alpha particle
24
and a
7
Li ion
26
in opposite directions. Only one particle from this interaction can enter the active region
16
of the semiconductor substrate
12
which limits detector efficiency. The active region
16
has an internal electric field that causes free charges
34
to separate and drift across the active region
16
. The motion of the free charges
34
induces a signal to appear on preamplifier circuit
28
or other sensitive electronics. The preamplifier
28
may be connected to the voltage
30
and the detector
10
through a coupling capacitor
32
. The present invention is intended to increase neutron detector efficiency, or sensitivity.
Now referring to
FIG. 2
, there is shown a simplified schematic illustration of the basic composition and configuration of a
10
B-coated self-biased high-purity epitaxial GaAs neutron detector
11
. The neutron detector
11
includes an n-type GaAs substrate
12
having on one surface thereof a back contact layer
14
which is coupled to neutral ground. The GaAs substrate
12
includes a high-purity v-type GaAs active region
16
. Disposed on a surface of the high purity v-type GaAs active region
16
is a front contact layer
18
forming a small p+ GaAs layer
36
. Disposed upon the p+ GaAs layer is a conductive contact
18
. The p+ GaAs layer may instead be replaced by a Schottky barrier contact. A built-in potential at the of the p-type/v-type GaAs junction forms an active region
16
that supplies enough voltage to operate the device. A potential source
30
(shown in dotted line form in the figure) may also be used to power the neutron detector
11
which typically provides a detection signal to a preamplifier
28
. Disposed on the front contact layer
18
is a thin layer of Boron-10 film
20
. An energetic neutron
22
interacts with the
10
B film
20
, thereby releasing an alpha particle
24
and a
7
Li ion
26
in opposite directions. Only one particle from this interaction can enter the high purity v-type GaAs active region
16
of the GaAs substrate
12
which limits detector efficiency. The present invention is intended to increase neutron detector efficiency, or sensitivity.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a neutron detector having increased efficiency for detecting cold, thermal or epithermal neutrons.
It is another object of the present invention to provide a highly sensitive energetic neutron detector which is inexpensive to fabricate, radiation hard, relatively insensitive to gamma-ray background radiation and is readily adapted for use in neutron radiography, imaging devices, or neutron imaging applications in other harsh radiation environments.
It is yet another object of the present invention to provide an energetic neutron detection device which can be operated at room temperature at low voltages and which is compact and rugged.
The present invention contemplates apparatus for detecting energetic neutrons comprising: a particle detecting semiconductor substrate having a first surface including at least one cavity extending into said semiconductor substrate; and a thin neutron responsive layer disposed on the first surface of the semiconductor substrate and responsive to energetic neutrons incident thereon for producing first and second charged reaction particles directed in opposite directions, wherein the neutron responsive layer is further disposed in said at least one cavity for increasing neutron detection efficiency by increasing the likelihood that the charged reaction particles will be directed into the semiconductor substrate.
REFERENCES:
patent: 5629523 (1997-05-01), Ngo et al.
patent: 5880471 (1999-03-01), Schelten et al.
patent: 5940460 (1999-08-01), Seidel et al.
patent: 6072181 (2000-06-01), Hassard et al.
patent: 6479826 (2002-11-01), Klann et al.
patent: 56114382 (1981-09-01), None
Klann Raymond
McGregor Douglas
Dvorscak Mark P.
Gagliardi Albert
Gottlieb Paul A.
Hannaher Constantine
Smith Bradley W.
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