Charged particle measuring apparatus

Details Charged particle measuring apparatus Charged particle measuring apparatus

2002-12-27

2004-03-23

Lee, John R. (Department: 2881)

Radiant energy

With charged particle beam deflection or focussing

With detector

C250S305000

Reexamination Certificate

active

06710352

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a charged particle measuring apparatus for measuring the types and energy of charged particles in a field where a plurality of charged particles (e.g., electrons, protons, &agr; particles, and so on) exist together, such as in space and in a space ship.
2. Description of the Related Art
Conventionally, charged particles have been measured for types and energy by using a telescope type measuring apparatus having a plurality of detectors in layers. In order to measure the total energy of a high-energy charged particle incident on the detectors, it has been considered necessary for the detectors to have sufficient thicknesses so that the total energy of the incident changed particle is absorbed within the detectors. For this reason, there have been developed &Dgr;E telescope type charged particle measuring apparatuses in which a plurality of detectors and absorbers are arranged in combination, and improved &Dgr;E·E telescope type charged particle measuring apparatuses.
FIG. 9
shows a block diagram of a conventional &Dgr;E telescope type charged particle measuring apparatus which measures electrons, protons, and &agr; particles for energy.
FIG. 10
shows theoretical calculations of the relationship between the energy which charged particles lose to form electron-hole pairs in the detectors (hereinafter, referred to as loss energy) and the total energy of the charged particles prior to incidence (hereinafter, referred to as particle energy) for situations where the charged particles are incident on the &Dgr;E telescope type charged particle measuring apparatus shown in FIG.
9
.
FIG. 11
is a conceptual diagram showing the configuration of detectors in a conventional &Dgr;E·E telescope type charged particle measuring apparatus.
FIG. 12
shows a block diagram of the conventional &Dgr;E·E telescope type charged particle measuring apparatus. With reference to
FIGS. 9 and 10
, description will first be given of the conventional &Dgr;E telescope type measuring apparatus.
In
FIG. 9
, the reference numeral
1
represents a charged particle, and
201
-
203
absorbers for absorbing the energy of the charged particle. The absorber
201
is made of aluminum of 0.1 mm in thickness. The absorber
202
is made of copper of 2 mm in thickness. The absorber
203
is made of tantalum of 2 mm in thickness. The reference numerals
204
-
207
represent detectors, each of which is a silicon semiconductor detector of 0.2 mm in thickness. The reference numerals
208
represent amplifying units,
209
a trigger generating unit,
210
a three-channel pulse-height discriminating unit, and
211
a data processing unit.
When the charged particle
1
is incident on the &Dgr;E telescope type charged particle measuring apparatus, the detectors
204
-
207
generate electron-hole pairs if the charged particle
1
passes therethrough or impinges thereon. The amplifying units
208
detect these electron-hole pairs and convert them into analog pulse signals proportional to the number of electron-hole pairs generated.
The electron-hole pairs generated by the detector
204
are converted by the amplifying unit
208
into an analog pulse signal for output. The output is applied to the three-channel pulse-height discriminating unit
210
. The three-channel pulse-height discriminating unit
210
discriminates the incident charged particle among an electron, a proton, and an &agr; particle. The result is output as an address
1
to the data processing unit
211
.
Now, the method of discriminating a charged particle in the three-channel pulse-height discriminating unit
210
will be described with reference to FIG.
10
.
In
FIG. 10
, the axis of ordinates on the left shows the loss energy of the incident charged particle
1
on a logarithmic scale in units of mega-electron volts (MeV). The axis of abscissas shows the particle energy of the incident charged particle on a logarithmic scale in units of MeV.
L1, L2, and L3 shown on the right axis of ordinates in
FIG. 10
are 0.05 MeV, 0.4 MeV, and 6 MeV, respectively, which are values predetermined for discriminating the types of charged particles. The curves designated by S1-S4 are ones obtained from theoretical calculations of the relationship between the loss energy and particle energy of charged particles detected by the detectors
204
-
207
, respectively. The curves are classified into three curve groups which represent the types of incident charged particles, namely, electron, proton, and &agr; particle. If the loss energy of the charged particle concerned falls between L1 and L2, the incident charged particle is discriminated as an electron. If the loss energy of the charged particle concerned falls between L2 and L3, the incident charged particle is discriminated as a proton. If the loss energy of the charged particle concerned exceeds L3, the incident charged particle is discriminated as an &agr; particle. When the charged particle is a proton, the rising parts of the curves S1-S4 lie in the electron area below L2. Charged particles detected in this area are discriminated as electrons even if they are protons. However, such occasions are extremely rare and will thus be left ignored. The same also holds for the rising parts of the curves S1-S4 when the charged particle is an &agr; particle.
The output, or the analog pulse signal, converted by the amplifying unit
208
from the electron-hole pairs detected by the detector
204
is applied to the trigger generating unit
209
. If the output applied exceeds a threshold value for noise distinction which is set in the trigger generating unit
209
, the trigger generating unit
209
generates a trigger signal and applies the trigger signal to the data processing unit
211
.
The three-channel pulse-height discriminating unit
210
contains the values of analog pulse signals corresponding to L1, L2, and L3 of
FIG. 10
above. The three-channel pulse-height discriminating unit
210
compares the values of analog pulse signals corresponding to L1, L2, and L3 with the output, or the analog pulse signal, converted by the amplifying unit
208
from the electron-hole pairs generated by the detector
204
, and thereby discriminates the type of the charged particle. As described above, the result is output as the address
1
to the data processing unit
211
.
The detectors
205
-
207
generate electron-hole pairs when the charged particle
1
passes therethrough or impinges thereon. The amplifying units
208
apply analog pulse signals proportional to the number of electron-hole pairs to the data processing unit
211
.
In response to the trigger signal from the trigger generating unit
209
, the data processing unit
211
determines up to what detectors generate the analog pulse signals, based on the inputs of the analog pulse signals proportional to the number of electron-hole pairs generated by the detectors
205
-
207
. Take, for example, a case where the discrimination of the charged particle
1
by the three-channel pulse-height discriminating unit
210
results in a proton, and the detectors
204
and
205
generate analog pulse signals while the detector
206
does not. From
FIG. 10
, it is determined that the particle energy of this proton falls within the range of 6.1 MeV, which is shown by the rising part of the curve S2 of the proton group, and 20 MeV, which is shown by the rising part of the curve S3 of the proton group (hereinafter, the sections of particle energy range will be referred to as energy channels). The result of determination is an address
2
.
Using the address
1
and the address
2
, or the output from the three-channel pulse-height discriminating unit
210
and the outputs from the amplifying units
208
of the detectors
204
-
207
, the data processing unit
211
cumulatively adds the frequencies of occurrence of the events that charged particles are measured for the respective energy channels, with respect to each type of the charged particles. The frequencies are accumulated into memories of those addresses

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