JP2535786B2 - High energy-Integrated dose monitor for particle beam- - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an integrated dose monitor for high energy particle beams. More specifically, the present invention provides high energy useful for dosimetry (dose spatial distribution measurement) and integrated dose measurement for environmental monitoring in a high-energy particle beam environment such as a nuclear reactor, space environment, or accelerator. The present invention relates to an integrated dose monitor for particle beams.

[0002]

2. Description of the Related Art Conventional reactors, accelerators,
Or, in a facility that uses gamma rays, etc., measuring their radiation dose with various types of equipment is essential for performance evaluation and safety inspection of equipment,
Although various measuring methods have been devised for that purpose, it is still not so easy to measure the spatial distribution of radiation dose and evaluate it.

For example, conventionally, when measuring the radiation dose in a nuclear reactor, the cumulative dose is indirectly estimated from the change in physical properties such as swelling (bulging) of the material and the measurement of the nuclear reaction product, and from the reactor physical calculation. The radiation dose distribution is determined by comparison with the estimated value of. Further, for example, in the case of measuring the radiation dose in the accelerator, if the ion species and energy are known, the particle dose is determined from the current (charge amount), etc. Accurate monitoring of distribution is very difficult with current technology.

In contrast to such a conventional radiation measuring method, for example, the fact that the electric conductivity of a metal or a semiconductor material is increased by point defects generated by high energy particle beam irradiation is utilized to make an element having a small volume. It has also been pointed out that it is possible to measure dose. However, in such a method, the change is continuous and gradual, and as a result, accurate dose measurement is not yet possible.

On the other hand, as an example of a material whose dose can be easily measured and exhibits a clear change, an ionic crystal which produces a color center is known. This ionic crystal is colored by generation of color centers (a type of defect) when a high dose of high energy radiation reaches a certain dose. Furthermore, in the dose measurement method using this ionic crystal, a small volume of Since only a sample is required, high spatial resolution measurement is possible.

However, in this method, it is not easy to electrically monitor the coloring phenomenon, and the critical dose at which the color center is generated is peculiar to the material and cannot be controlled. The present invention solves the drawbacks of the conventional techniques as described above, and it is possible to accurately measure the dose even in a high energy particle beam environment.
The purpose is to provide a new high energy particle beam integrated dose monitor.

[0007]

Means for Solving the Problems The present invention is, in order to solve the above problems, an integrated dose monitor in which energetically shallow impurities are added in an amount of 10 ¹⁵ to 10 ¹⁷ / cm ³ in semiconductor silicon. The free charge supplied from the impurities compensates for the irradiation defect generated by high-energy radiation, thereby reducing the free charge trapping ability of the irradiation defect and maintaining the electric conductivity at a constant value up to the critical dose. Provided is a cumulative dose monitor for high-energy particle beams, which is characterized by rapidly changing the degree above the critical dose and controlling the critical dose by adding impurities.

[0008]

The present invention has the constitution as described above, but the definition of "energy is shallow" is an energy level close to the conduction band for n-type impurities supplying electrons. This means that the energy level is close to the valence band for p-type impurities that supply holes. On the contrary, “energy deep” means that the n-type electronic state that supplies electrons is an energy level away from the conductor, and the p-type electronic state that supplies holes is Means that the energy level is far from the valence band, that is, the energy level near the center of the forbidden body.

That is, the present invention adopts semiconductor silicon doped with energetically shallow impurities as an electric conduction type element, so that it has an optimum criticality for dose measurement in a high energy particle beam environment, which has been difficult until now. It gives specific electrical characteristics and enables simple dose detection.
In the present invention, semiconductor silicon to which n type or p type energetically shallow impurities are added by 10 ¹⁵ to 10 ¹⁷ / cm ³ is used. If the impurity is less than 10 ¹⁵ / cm ^3, the compensation effect of irradiation defect is a insufficient, also, 10 ¹⁷
If it exceeds / cm ³ , the dose detection performance is rather deteriorated, which is not preferable. Further, in the present invention, it is desirable that the semiconductor material is provided with a parallel (planar) type electrode having an ohmic characteristic, and a DC electric field is applied to this element to measure electric conductivity during or after irradiation with high energy particle beam. You can At this time, it was found that when the dose exceeded a certain level, the electrical conductivity drastically decreased and exceeded the critical dose, and the large sensitivity coefficient enables the dose to be evaluated with relatively high accuracy.

In the integrated dose monitor for high-energy particle beams of the present invention, as described above, an irradiation defect generated by high-energy radiation by adding an energy-shallow impurity to an electrically conductive element to supply a free charge, By compensating for the free charge, the free charge trapping ability of the irradiation defect is diminished to maintain a constant electric conductivity up to a certain amount of particle dose (the critical dose at which the number of irradiation defects competes with the impurity concentration).
Then, with respect to the dose or more, a rapid decrease in electrical conductivity occurs.

Therefore, in the state where the irradiation defect is introduced, the free charge fills (compensates) the defect, so that the electric conduction characteristic is not rapidly deteriorated, and the electric conductivity is almost constant up to the critical dose. When the number of irradiation defects exceeds the impurity concentration sufficiently, the free charge is suddenly depleted and a critical change occurs. More specifically, in the present invention, energetically shallow impurities such as n-type P and Sb, or energetically shallow impurities such as p-type B and Ga, 10 ¹⁵
The electric conductive element added to ~ 10 ¹⁷ / cm ³ from room temperature to -73 ℃
It is desirable to use it in some degree.

FIG. 1 shows the operating principle of the integrated dose monitor for high energy particle beams according to the present invention. That is, as also shown in FIG. 1, the irradiation defect generated by high-energy radiation generally forms an energetically deep level in the semiconductor material and immediately captures thermally excited charges and the like to generate electricity. It reduces the conductivity. On the other hand, in the integrated dose monitor for high-energy particle beams according to the present invention, a relatively large amount of energetically shallow impurities are added to supply free charges, and irradiation defects generated by high-energy radiation are compensated for to capture irradiation defects. Diminish ability. Therefore, in the state where the irradiation defect is introduced, the free charge compensates for the defect, so that the electric conduction characteristic is not rapidly deteriorated, and is superior to the conventional non-added electric conduction element. It will exhibit electrical conduction characteristics.

It is desirable that the electric conduction element constituting the present invention uses a direct current or alternating current electric conduction method, and the electric conduction element has a parallel (planar) type electrode having ohmic characteristics, and a portion other than the electrodes. Alternatively, an etching treatment may be performed, or an electrode may be coated with an etching protective agent such as nail polish, dried, and surface-etched with a hydrofluoric acid-based etching solution such as CP4.

For the integrated dose monitor for high-energy particle beams according to the present invention, a conventionally known electrode manufacturing technique may be appropriately used. As the metal material for the electrode, impurities such as Au and Al are basically used. N to add
Vacuum deposition using a material containing Sb, P, etc. as an additive for type silicon and 0.1 to 1% B, Ga, etc. for p-type silicon as an evaporation source. Depending on the apparatus, it is possible to deposit approximately 50 nm to 1 μm.

Then, the number of impurities is expanded so that impurities can be added. Furthermore, in the integrated dose monitor of the present invention, element cooling technology, DC power supply, potentiometer,
Also, as the ammeter and the like, appropriate ones may be used, including conventionally known ones. Examples will be shown below to describe the high-energy particle beam cumulative dose monitor of the present invention in more detail.

[0016]

EXAMPLE First, about 1 × 10 6 B as a p-type impurity is added.
A semiconductor silicon wafer containing ¹⁵ / cm ³ (sample number: P1E15) (a thickness of about 200 microns) and a semiconductor silicon wafer containing P as an n-type impurity of about 4 × 10 ¹⁵ / cm ³ (sample number: N4E15) ( A thickness of about 200 microns) was cut into a strip shape with a width of about 4 mm and a length of about 7 mm.

A central portion of the strip-shaped silicon wafer having a width of about 1 mm was used as a measured portion, and a planar type ohmic electrode was formed in the remaining portion to obtain an electric conduction element. This ohmic electrode is a Ga-added A for a p-type sample.
For the u and n type samples, Sb-added Au was vapor-deposited, and the sample was prepared by thermal diffusion treatment (500 ° C. × 10 minutes). As shown in FIG.
An electric field of about 1 to 10 V is applied between the electrodes, at room temperature or below zero.
It is cooled to 73 ℃. Electrical conductivity is evaluated by measuring the current and voltage drop across the device. The high-energy particle beam was irradiated with 17 MeV protons, and the influence on the electric conduction property was examined.

As shown in FIG. 3, the electric conductivity of the element constituting the dose monitor of the present invention is the standard material P1E13 (p-type impurity 1 × 10 ¹³ / cm ³ ) containing almost no impurities.
Compared with, there is less change with respect to particle beams. That is, while the electrical conductivity of the standard material sharply decreases immediately after the start of irradiation, the electrical conductivity of P1E15 and N4E15 is 2.5 × 10 ¹³ ion / cm ² (1.3 × 10 ^-7 dpa), respectively. , And an almost constant value is obtained up to a dose of 8 × 10 ¹³ ion / cm ² (4 × 10 ⁻⁷ dpa). Meanwhile, during that time, the standard material P1
The electrical conductivity of E13 decreased by about 5 digits. Like this P1E1
5 and N4E15's electrical conductivity is stable up to the critical dose, and drops sharply beyond the critical dose. This critical dose has a constant ratio with the impurity concentration, and the critical dose can be controlled by controlling the amount of impurities.

[0019]

As described in detail above, according to the present invention, the electric conductivity of the high energy particle beam can be increased to 17 by irradiation of the high energy particle beam.
Since the critical dose value, which is dependent on the MeV proton irradiation dose, changes greatly, the dose can be determined by a simple method such as a tester using a small test piece. Further, the large change can be used for an alarm of the radiation environment and the like. The high-energy particle beam dose monitor of the present invention can be widely applied as a new integrated dose monitor for a severe radiation environment such as a nuclear reactor.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing the principle of the present invention.

FIG. 2 is a schematic configuration diagram showing the present invention.

FIG. 3 is a relationship diagram showing the dependency of the electrical conductivity of the present invention and the conventional integrated dose monitor on the 17 MeV proton irradiation dose. Here, the unit dpa on the horizontal axis (upper) means the irradiation defect generation amount (specific concentration) corresponding to the ion density (ion / cm ² ).

Claims (1)

(57) [Claims] 1. A cumulative dose monitor in which energetically shallow impurities are added to semiconductor silicon in an amount of 10 ¹⁵ to 10 ¹⁷ / cm ³ , and irradiation defects generated by high-energy radiation in which free charges supplied from the impurities are generated. By compensating for the irradiation charge, the free charge trapping ability of the irradiation defect is reduced, the electric conductivity is maintained at a constant value up to the critical dose, and the electric conductivity is rapidly changed above the critical dose. Integrated dose monitor for particle beam.