CN103336296A - Neutron detector - Google Patents

Abstract

The invention relates to the nuclear radiation detection field and especially relates to a neutron detector which detects slow neutrons and thermal neutrons. The neutron detector comprises a diamond film, a borated film and a combined electrode. A detected neutron is converted by the borated film into electriferous alpha particles, the alpha particles realizes ionization of the diamond film, a current signal is generated on the combined electrode, so neutron detection is realized. Compared with a helium medium neutron detector in the prior art, the neutron detector has advantages of obviously-reduced cost and improved detection efficiency.

Description

A kind of neutron detector

Technical field

The present invention relates to the nuclear radiation detection field, relate in particular to a kind of boron material and diamond of utilizing neutron is converted into the detection slow neutron of electric signal and the neutron detector of thermal neutron.

Background technology

The neutron detection technology is a kind of nuclear radiation detection technology.Because neutron is not charged, so neutron can not directly cause ionization in material.Therefore detected neutron will be in two steps: the first step utilize neutron and nuclear certain be used for producing charged particle or γ photon; Second step utilized nuclear detector to survey these charged particles or γ photon.The method of detected neutron mainly contains: the method for nuclear recoil, nuclear reaction method, nuclear fission method, activation probe method.Detection slow neutron and the most frequently used method of thermal neutron are the nuclear reaction method in these four kinds of methods, namely select certain nuclear reaction that can produce charged particle, record these charged particles then.

What employing was maximum in the nuclear reaction method is following three kinds of reactions: (1)

(2)

(3)

Widespread use at present ³The He neutron detector adopts ³He (n, p) ³The T reaction.But the energy minimum that it is emitted, detector is not easy to remove the g background.And in the natural He gas ³The content of He is very low by (about 1.4 10 ^-4%), ³The He isotope is purified very difficult, thereby makes preparation ³The He price is very expensive.This detection method has 40 years of development history, but owing to there are not enough reliabilities and stable for a long time, application is restricted.Therefore, it is extremely urgent developing novel material for detector and device.In the natural lithium ⁶The content of Li has only 7.5%, has therefore limited its application as the neutron detection material. ¹⁰B (n, a) ⁷The Li reaction is to use the most at present.Main cause is that the reaction energy of emitting is big, and detector is removed the g background easily.And boron material obtains easily, in the natural boron ¹⁰The content of B is about 19.8%, in order to improve detection efficiency, in the mill during sub-detector many with concentrate boron ( ¹⁰The concentration of B is more than 96%), and the acquisition of concentrated boron is not difficult.

Use for Homeland Security, restriction neutron false alarm rate is had strict requirement.According to USDOE's report in 2009, in present adoptable Detection Techniques, BF ₃Proportional detector, boron serve as a contrast proportional detector, carry ⁶Li scintillation glass fiber detector and non-flicker plastic optical fibre detector are ³The substitute that the He technology is potential, but these Detection Techniques based on gas proportional chamber or scintillator still are not so good as the solid Detection Techniques at aspects such as sensitivity, size, weight, power consumption, processing safety, transportation and costs.And the solid Detection Techniques be considered to size little, can be portable, low voltage operating, technology be simple, and safety, power consumption are little.

The present invention proposes to adopt ¹⁰B (n, a) ⁷Li reacts to obtain detectable a particle (its energy is 1.47 MeV), and with the adamas detector as follow-up detector at a particle.At present a particle detector of widespread usage mainly contain gas proportional counter (as ³He standard neutron detector) and scintillator detector etc.But these detectors exist obviously not enough at aspects such as sensitivity, size, weight, power consumption, processing safety, transportation and costs, particularly these detectors mostly can not be operated in high temperature and the rugged surroundings (as ³He standard neutron detector can only be operated in about 100 ° of C), and the energy resolution ability of detector, response speed are obviously not enough.

Semiconductor probe device has broad application prospects in military affairs, industry, agricultural, environmental protection, medical science and fields such as particle detection and radiation owing to the advantage that volume is little, energy resolution is high, power is low, cost is low.In order to be operated in extremely under the rugged environment, material for detector must have wideer energy gap.In the research of wide bandgap semiconductor detector, mainly concentrate on natural Π type adamas [on materials such as diamond film.Wherein the diamond film detector becomes one of the most attractive research topic, and adopts the chemical vapor deposition (CVD) method can realize that quality is near the film of natural diamond at present.Show from the comparison of some physical properties of material and current research level, adopt the detector of diamond film preparation will have more superior performance.(1) adamantine forbidden band is 5.5eV, down can trouble free service at high temperature (greater than 600 ° of C), and the detector leakage current is extremely low, it is reported that its leakage current is 100pA/cm only in the thick adamas sample of 500mm ²And ³He standard neutron detector can only be operated in about 100 ° of C.(2) carrier mobility height (electronics: 1800cm ²V ^-1s ^-1, hole: 1200cm ²V ^-1s ^-1), detector has high response speed (can reach the ns level), faster than ³6 ~ 7 orders of magnitude of He standard neutron detector.(3) adamantine atomic number little (Z=6) has reduced high energy cascade process and multiple scattering, can guarantee that it has lower susceptibility to the gamma-rays in the neutron irradiation, and have quite low irradiation damage.Though signal is little, (because leakage current is extremely low) fully can improve by signal processing technology.(4) producing an electronics-hole in the adamas is 13eV to required energy, and for gas detector (as ³He standard neutron detector) produces a pair of " signal charge carrier " institute energy requirement and be about 30eV.The energy resolution that shows the adamas detector apparently higher than ³He standard neutron detector.(5) the adamas detector has good chemical stability, frequency stability and good temperature stability, guarantees that under long-time particle irradiation steady operation, performance are constant, and particularly aspect the particle detection of space, this point is particularly important.And ³The shortcoming that He standard neutron detector is fatal is: do not have enough reliabilities and stable for a long time.(6) thermal conductivity is the highest (20W/cm.K) in all substances, is a kind of best heat conductor.Can guarantee that like this heat that produces at work in time distributes.

The present invention proposes based on the CVD diamond film ¹⁰B (n, a) ⁷Li nuclear reaction neutron detection technology.Adopt boron film and diamond surface to be compounded to form boron/adamas laminated film double-decker.Wherein the effect of boron film is a particle that the neutron of incident is converted into 1.47MeV, and namely neutron-a particle conversion coating adopts the CVD adamas that a particle is surveyed then, the final detection that realizes low-energy neutron.

Summary of the invention

A kind of neutron detector of the present invention is characterized in that: utilizing boron substance is the isotope of boron ¹⁰B produces nuclear reaction with being detected neutron, and utilizes adamas to survey the α particle that transforms; Its reactional equation is:

；

The preparation method of neutron detector is as follows:

A. the preparation of diamond thin

Adopt (100) mirror polish silicon chip as deposition substrate; The bortz powder foot couple silicon substrate mechanical lapping of use 100nm particle diameter 5 ~ 15 minutes; Put into the reaction chamber of microwave plasma CVD (MPCVD) device after the cleaning; Feed methane and hydrogen, the flow of methane and hydrogen is respectively 10～60 standard ml/min and 10 ~ 200 standard ml/min; The air pressure of reaction chamber is set at 0.3KPa～1kPa; Substrate bias is set at 50 ~ 150V; Underlayer temperature control is at 600 ~ 800 ° of C; Microwave power is set at 1200W ~ 2000W; 50 ~ 500 hours film growth time; Use the method for hydrofluorite chemical corrosion that the silicon substrate corrosion is gone, obtain diamond thin;

B. the preparation of boron substance film

Ready-made diamond thin substrate is carried out photo etched mask, use magnetron sputtering at diamond film surface deposition boron substance film afterwards; System's base vacuum 5 * 10 ^-4~ 1 * 10 ^{~ 3}Pa; Feed high purity argon, argon flow amount 10 to 15 standard ml/min, total gas pressure 0.3 ~ 1Pa; Be raw material with pure boron target or boron carbide target, regulate 50 ~ 150 watts of sputtering powers, substrate is to 50 ~ 100 millimeters of target distances, sputtering time 1 ~ 6 hour; Obtain 0.5 ~ 2 micron of boron substance film thickness;

C. the preparation of combination electrode

Adopt the Ti target, use dc magnetron sputtering method splash-proofing sputtering metal Ti on diamond thin, the base vacuum 2 * 10 of system ^{~ 4}To 5 * 10 ^{~ 4}Pa; The working gas of sputter is Ar gas, and the flow of Ar is 10 to 15 standard ml/min; Total gas pressure is at 0.3 ~ 0.8Pa; Sputtering power is generally 100 ~ 300W; Sputtering time is 12 ~ 15 minutes; The Ti layer thickness is 30 ~ 60nm; Adopt the Pt target again, use the ion sputtering method at Ti layer preparation metal level Pt; In the sputter procedure, operating air pressure is 0.5 ~ 1Pa, ion stream 1 ~ 5mA, and sputtering time is 5 ~ 15 minutes, Pt layer thickness 30 ~ 60nm; After sputter is finished, adopt the Au target again, by identical technological parameter sputter Au on the Pt layer, sputtering time is 20 ~ 40 minutes, and the thickness of Au layer is 100 ~ 150nm.

Description of drawings

Fig. 1 is neutron detector structural drawing of the present invention.

Embodiment

After now specific embodiments of the invention being described in.

Embodiment

Concrete preparation process and step in the present embodiment are as described below:

One, diamond thin preparation

1) silicon substrate pre-service: adopt (100) mirror polish silicon chip as deposition substrate; Adopt HF acid ultrasonic cleaning 10 minutes, to remove the silicon oxide layer on surface; In order to increase the nucleation density of nanocrystalline diamond film, the bortz powder foot couple silicon substrate mechanical lapping of use 100nm particle diameter 15 minutes; With the ultrasonic cleaning 20 minutes in the acetone soln that is mixed with the 100nm bortz powder of the silicon chip after grinding; Again silicon chip is used deionized water and acetone ultrasonic cleaning respectively at last, until the silicon chip surface cleaning, put into the reaction chamber of microwave plasma CVD (MPCVD) device after the oven dry;

2) diamond thin preparation: with vacuum pump reaction chamber is evacuated to 7Pa earlier, with molecular pump reaction chamber is evacuated to 10 then ^-2Below the Pa, feed reacting gas (mixed gas of methane and hydrogen), the flow of regulating methane and hydrogen is respectively 40 standard ml/min and 160 standard ml/min; The air pressure of reaction chamber is set at 1kPa; Substrate bias is set at 100V; Underlayer temperature control is at 650 ° of C; Microwave power is set at 1500W; 200 hours film growth time;

3) use the method for hydrofluorite chemical corrosion that the silicon substrate corrosion is gone, obtain self-supporting diamond thin film.

Two, boron membrane preparation

Ready-made diamond thin substrate is adopted acetone and alcohol, and ultrasonic cleaning is after 15 minutes successively, and mask is carried out in oven dry, puts into the magnetron sputtering cavity afterwards; Earlier with vacuum pump the magnetron sputtering cavity is evacuated to 7Pa, with molecular pump reaction chamber is evacuated to 1 * 10 then ^-3Pa feeds high purity argon, and argon flow amount 15 standard ml/min are regulated air pressure to 0.3Pa.Be raw material with pure boron target, regulate 150 watts of sputtering powers, substrate is to 70 millimeters of target distances, and sputtering time 3 hours makes boron membrane thickness reach 1 micron.

Three, combination electrode preparation

1) preparation of metal Ti: adopt the Ti target, use dc magnetron sputtering method splash-proofing sputtering metal Ti on diamond thin, the base vacuum 4 * 10 of system ^-4Pa; The working gas of sputter is Ar gas, and the flow of Ar is 10 standard ml/min; Total gas pressure is 0.5Pa; Sputtering power is 100W; Sputtering time 15 minutes; The Ti layer thickness is 50nm.

2) preparation of metal Pt layer and Au layer: adopt the Pt target, prepare metal level Pt by the ion sputtering method at Ti.In the sputter procedure, operating air pressure 0. 8Pa, ion stream 1.8mA, sputtering time is 15 minutes, Pt layer thickness 50nm.After sputter is finished, adopt the Au target again, by identical technological parameter sputter Au on the Pt layer, 30 minutes time, the thickness of Au layer is 150nm.

Fig. 1 is neutron detector structural representation of the present invention.As seen, prepare the film that contains boron substance at the upper surface of diamond thin among the figure, be converted into the α particle in order to the incident neutron that will be detected; The upper surface of diamond thin has also prepared titanium platinum combination electrode.Simultaneously, the lower surface at diamond thin also prepares titanium platinum combination electrode.

Claims (1)

1. neutron detector, it is characterized in that: utilizing boron substance is the isotope of boron ¹⁰B produces nuclear reaction with being detected neutron, and utilizes adamas to survey the α particle that transforms; Its reactional equation is:

The preparation method of neutron detector is as follows:

A. the preparation of diamond thin

Adopt (100) mirror polish silicon chip as deposition substrate; The bortz powder foot couple silicon substrate mechanical lapping of use 100nm particle diameter 5 ~ 15 minutes; Put into the reaction chamber of microwave plasma CVD (MPCVD) device after the cleaning; Feed methane and hydrogen, the flow of methane and hydrogen is respectively 10～60 standard ml/min and 10 ~ 200 standard ml/min; The air pressure of reaction chamber is set at 0.3KPa～1kPa; Substrate bias is set at 50 ~ 150V; Underlayer temperature control is at 600 ~ 800 ° of C; Microwave power is set at 1200W ~ 2000W; 50 ~ 500 hours film growth time; Use the method for hydrofluorite chemical corrosion that the silicon substrate corrosion is gone, obtain diamond thin;

B. the preparation of boron substance film

Ready-made diamond thin substrate is carried out mask, use magnetron sputtering at diamond film surface deposition boron substance film afterwards; System's base vacuum 5 * 10 ^-4~ 1 * 10 ^{~ 3}Pa; Feed high purity argon, argon flow amount 10 to 15 standard ml/min, total gas pressure 0.3 ~ 1Pa; Be raw material with pure boron target or boron carbide target, regulate 50 ~ 150 watts of sputtering powers, substrate is to 50 ~ 100 millimeters of target distances, sputtering time 1 ~ 6 hour; Obtain 0.5 ~ 2 micron of boron substance film thickness;

C. the preparation of combination electrode

Adopt the Ti target, use dc magnetron sputtering method splash-proofing sputtering metal Ti on diamond thin, the base vacuum 2 * 10 of system ^{~ 4}To 5 * 10 ^{~ 4}Pa; The working gas of sputter is Ar gas, and the flow of Ar is 10 to 15 standard ml/min; Total gas pressure is at 0.3 ~ 0.8Pa; Sputtering power is generally 100 ~ 300W; Sputtering time is 12 ~ 15 minutes; The Ti layer thickness is 30 ~ 60nm; Adopt the Pt target again, use the ion sputtering method at Ti layer preparation metal level Pt; In the sputter procedure, operating air pressure is 0.5 ~ 1Pa, ion stream 1 ~ 5mA, and sputtering time is 5 ~ 15 minutes, Pt layer thickness 30 ~ 60nm; After sputter is finished, adopt the Au target again, by identical technological parameter sputter Au on the Pt layer, sputtering time is 20 ~ 40 minutes, and the thickness of Au layer is 100 ~ 150nm.

Images