CN103018765A - Method for synchronously measuring concentrations of 222Rn and 220Rn by utilizing low-pressure single scintillation chamber - Google Patents

Abstract

The invention relates to a method for synchronously measuring concentrations of 222Rn and 220Rn by utilizing a low-pressure single scintillation chamber, which comprises the specific steps of: opening a first electromagnetic valve and a second electromagnetic valve in a measuring system, opening a sampling pump, and flowing air including 222Rn and 220Rn in the loop of the measuring system at a certain flow velocity for 5-20 minutes, so that 222Rn and 220Rn in the low-pressure single scintillation chamber and 222Rn and 220Rn in the measurement environment are balanced; after filtering daughters of air including 222Rn and 220Rn through a high-efficiency filter at a certain flow velocity, entering the air into the low-pressure single scintillation chamber; adjusting air pressure in the low-pressure single scintillation chamber through an adjusting valve in the measuring system, so that the range of an alpha particle decayed and discharged by 222Rn is more than the maximum distance between any two points in the scintillation chamber; and synchronously closing the first electromagnetic valve and the second electromagnetic valve after sampling for 2-20 minutes, simultaneously, closing the sampling pump, keeping the air pressure in the low-pressure single scintillation chamber constant at this time, then, beginning to measure, and obtaining concentrations of 222Rn and 220Rn by utilizing measured counts according to the radioactive decay law.

Description

Utilize the single scintillation chamber of low pressure pair 222Rn, 220The method of Rn concentration synchro measure

Technical field

The present invention relates to a kind of nuclear radiation detection technology, particularly a kind of single scintillation chamber of low pressure pair of utilizing ²²²Rn, ²²⁰The method of Rn concentration synchro measure.

Background technology

In the environment ²²²Rn is the main source of human suffered natural radiation, in recent years, and to environment ²²⁰The interest of Rn Survey of level is obvious ascendant trend, and investigation is found in some environment ²²⁰Rn concentration is higher, and in China's soil ²³²The content of Th and world's average are apparent in view higher.The current scintillation chamber's synchro measure that utilizes ²²²Rn, ²²⁰The method of Rn concentration all needs complicated experiment or calculates scintillation chamber pair ²²⁰The calibration factor of Rn and scintillation chamber all need to measure background before measurement, described background refers to not introduce from external environment contain ²²²Rn, ²²⁰The counting of the unit interval of scintillation chamber during the air sample of Rn.

Summary of the invention

The present invention seeks to disclose a kind of single scintillation chamber of low pressure pair of utilizing ²²²Rn, ²²⁰The method of Rn concentration synchro measure.

Technical scheme of the present invention is: a kind of single scintillation chamber of low pressure pair of utilizing ²²²Rn, ²²⁰The method of Rn concentration synchro measure, its concrete steps are as follows:

Open the first solenoid valve and the second solenoid valve in the measuring system, open sampling pump, will contain ²²²Rn, ²²⁰The air of Rn contains with certain flow velocity mobile 5-20min in the measuring system loop ²²²Rn, ²²⁰The air of Rn flows into from the draft tube of flowmeter, discharges from the gas outlet of sampling pump, thereby makes in the single scintillation chamber of low pressure ²²²Rn, ²²⁰In Rn gas and the measurement environment ²²²Rn, ²²⁰Rn gas reaches balance, contains ²²²Rn, ²²⁰The air of Rn enters the single scintillation chamber of low pressure with certain flow velocity after high efficiency particulate air filter filters out daughter.Because the sampling pump flow rate is larger, by the air pressure in the single scintillation chamber of the adjusting of the variable valve in measuring system low pressure, so that the air pressure in the single scintillation chamber of low pressure is lower than an atmospheric pressure.Suppose that any point in the single scintillation chamber of low pressure is L to the scintillator zinc sulphide surface ultimate range of the inside surface coating of scintillation chamber, the air pressure in the reduction low pressure list scintillation chamber, ²²²Rn, ²²⁰The α particle that Rn and daughter disintegration thereof are emitted has different energy, and corresponding range is also different.Wherein ²²²The alpha-particle energy that the Rn decay is emitted is minimum, and range is also minimum.Adjustable pressure so that ²²²The α particle that Rn decay is emitted under this air pressure range greater than L, like this so that low pressure list scintillation chamber is under low pressure right ²²²Rn, ²²⁰The α particle that Rn and daughter disintegration thereof are emitted has identical detection efficiency.Detection efficiency represents with two kinds of methods, and a kind of is an average alpha-decay, can measure η counting, represents detection efficiency with η; Another kind is average K alpha-decay, can measure 1 counting, represents detection efficiency with K.Represent detection efficiency with η among the present invention.

Sample after 2-20 minute, close synchronously the first solenoid valve and the second solenoid valve are closed sampling pump simultaneously, and the air pressure in the single scintillation chamber of low pressure this moment remains unchanged, and then begins to measure, and utilizes the counting that measures to obtain according to Law of radioactive decay ²²²Rn, ²²⁰The concentration of Rn.

Finish and measure the moment of beginning in sampling, be located in the single scintillation chamber of low pressure ²²²Rn and daughter RaA thereof ( ²¹⁸Po), RaB ( ²¹⁴Pb), RaC ( ²¹⁴Bi) activity is respectively A _Rn1, A _RaA1, A _RaB1, A _RaC1Disintegration constant is respectively λ _Rn, λ _RaA, λ _RaB, λ _RaCBecause RaC ' ( ²¹⁴Po) half life period only has 164 μ s, and its half life period is very short, so people often are summed up as the radioactivity of RaC ' radioactivity of RaC.Because ThA ( ²¹⁶Po) half life period very short, with ²²⁰Rn reaches balance very soon, is located in the single scintillation chamber of low pressure ²²⁰Rn and daughter ThA thereof ( ²¹⁶Po) activity is A _Th, ²²⁰The Rn disintegration constant is λ _Th, background activity is A ₀, do not consider other long-life daughters, then have according to Law of radioactive decay:

$A_{\mathrm{Rn}}\left(t\right)=A_{\mathrm{Rn}1}{e}^{-{\mathrm{\λ}}_{\mathrm{Rn}}t}---\left(1\right)$

${\mathrm{dA}}_{\mathrm{RaA}}\left(t\right)/\mathrm{dt}=A_{\mathrm{Rn}}\left(t\right){\mathrm{\λ}}_{\mathrm{RaA}}-A_{\mathrm{RaA}}\left(t\right){\mathrm{\λ}}_{\mathrm{RaA}}---\left(2\right)$

${\mathrm{dA}}_{\mathrm{RaB}}\left(t\right)/\mathrm{dt}=A_{\mathrm{RaA}}\left(t\right){\mathrm{\λ}}_{\mathrm{RaB}}-A_{\mathrm{RaB}}\left(t\right){\mathrm{\λ}}_{\mathrm{RaB}}---\left(3\right)$

${\mathrm{dA}}_{\mathrm{RaC}}\left(t\right)/\mathrm{dt}=A_{\mathrm{RaB}}\left(t\right){\mathrm{\λ}}_{\mathrm{RaC}}-A_{\mathrm{RaC}}\left(t\right){\mathrm{\λ}}_{\mathrm{RaC}}---\left(4\right)$

$A_{\mathrm{Th}}\left(t\right)=A_{\mathrm{Th}1}{e}^{-{\mathrm{\λ}}_{\mathrm{Th}}t}---\left(5\right)$

$A_{\mathrm{ThA}}\left(t\right)\≈A_{\mathrm{Th}1}{e}^{-{\mathrm{\λ}}_{\mathrm{Th}}t}---\left(6\right)$

$A_0\left(t\right)=A_0---\left(7\right)$

After formula (2), (3), (4) are found the solution, obtain total alpha activity activity over time rule be:

$A_{\mathrm{Rn}}\left(t\right)+A_{\mathrm{RaA}}\left(t\right)+A_{\mathrm{RaC}}\left(t\right)+2A_{\mathrm{Th}}\left(t\right)+A_0=f(A_{\mathrm{Rn}1},A_{\mathrm{RaA}1},A_{\mathrm{RaB}1},A_{\mathrm{RaC}1},A_{\mathrm{Th}1},A_0,t)---\left(8\right)$

Because the single scintillation chamber of low pressure is identical to the alpha-particle detection efficient of different-energy, is η all, has

$n\left(t\right)=\mathrm{\ηf}(A_{\mathrm{Rn}1},A_{\mathrm{RaA}1},A_{\mathrm{RaB}1},A_{\mathrm{RaC}1},A_{\mathrm{Th}1},A_0,t)---\left(9\right)$

The counting that n (t) measures for scintillation chamber's measurement mechanism is rule over time.

Adopt the method for scintillation chamber's measurement mechanism measurement count to have two kinds:

A, short time interval measurement: the Measuring Time T of each measuring period is 1-5 minute, measuring period quantity more than or equal to 6, the counting of each measuring period is n (i), i is measuring period.

Computing method take short time interval T as measuring period have two kinds:

A, try to achieve the average counter of the unit interval of i measuring period according to the counting n (i) of i measuring period, this average counter with this measuring period mid point the pass of totalαradioactivity activity be:

$n\left(i\right)/T=\mathrm{\ηf}(A_{\mathrm{Rn}1},A_{\mathrm{RaA}1},A_{\mathrm{RaB}1},A_{\mathrm{RaC}1},A_{\mathrm{Th}1},A_0,(i-\frac{1}{2})T)---\left(10\right)$

Utilize formula (10) that the data of n (i)/T are carried out nonlinear fitting, can obtain A _Rn1, A _RaA1, A _RaB1, A _RaC1, A _Th1, A ₀Value, then try to achieve according to formula (11), (12) ²²²Rn, ²²⁰The concentration of Rn:

$C_{\mathrm{Rn}}=\frac{A_{\mathrm{Rn}1}{P}_0}{\mathrm{VP}}---\left(11\right)$

C in the formula _RnFor ²²²The concentration of Rn; V is the volume of the single scintillation chamber of low pressure; P is the air pressure in the single scintillation chamber of low pressure; P ₀Be ambient pressure.

$C_{\mathrm{Tn}}=\frac{A_{\mathrm{Tn}1}{P}_0}{\mathrm{VP}}---\left(12\right)$

C in the formula _ThFor ²²⁰The concentration of Rn.

B, ask the integration of totalαradioactivity activity i measuring period:

$A_{\mathrm{\α}}\left(t\right)=A_{\mathrm{Rn}}\left(t\right)+A_{\mathrm{RaA}}\left(t\right)+A_{\mathrm{RaC}}\left(t\right)+2A_{\mathrm{Th}}\left(t\right)+A_0---\left(13\right)$

A in the formula _α(t) be totalαradioactivity activity.Obtain according to formula (8):

$A_{\mathrm{\α}}\left(i\right)={\∫}_{(i-1T)}^{\mathrm{iT}}f(A_{\mathrm{Rn}1},A_{\mathrm{RaA}1},A_{\mathrm{RaB}1},A_{\mathrm{RaC}1},A_{\mathrm{Th}1},A_0,t)\mathrm{dt}---\left(14\right)$

A in the formula _α(i) be the integration of totalαradioactivity activity i measuring period.

The application least square method is found the solution, and introduces residual error R _A:

$R_A=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{w}_i{(n\left(i\right)-\mathrm{\η}{A}_{\mathrm{\α}}\left(i\right))}^2---\left(15\right)$

W in the formula _iBe the weight factor of i counting section, the introducing of weight factor is to consider that the counting statistics error difference of each measuring period is to the error effect of fitting result.

According to principle of least square method, so that residual error R _AGet minimum value, can obtain A _Rn1, A _RaA1, A _RaB1, A _RaC1, A _Th1, A ₀Value, then try to achieve according to formula (11), (12) ²²²Rn, ²²⁰The concentration of Rn.

B, long-time interval measurement: the measurement time t of each measuring period ₁, t ₂, t ₃, t ₄, t ₅, t ₆Be respectively 5-60 minute, be 6 measuring period, and the counting of six measuring periods is respectively n (1), n (2), n (3), n (4), n (5), n (6).

$n\left(1\right)=\mathrm{\η}{\∫}_0^{t_1}{A}_{\mathrm{\α}}\left(t\right)\mathrm{dt}---\left(16\right)$

$n\left(2\right)=\mathrm{\η}{\∫}_{t_1}^{t_1+t_2}{A}_{\mathrm{\α}}\left(t\right)\mathrm{dt}---\left(17\right)$

$n\left(3\right)=\mathrm{\η}{\∫}_{t_1+t_2}^{t_1+t_2+t_3}{A}_{\mathrm{\α}}\left(t\right)\mathrm{dt}---\left(18\right)$

$n\left(4\right)=\mathrm{\η}{\∫}_{t_1+t_2+t_3}^{t_1+t_2+t_3+t_4}{A}_{\mathrm{\α}}\left(t\right)\mathrm{dt}---\left(19\right)$

$n\left(5\right)=\mathrm{\η}{\∫}_{t_1+t_2+t_3+t_4}^{t_1+t_2+t_3+t_4+t_5}{A}_{\mathrm{\α}}\left(t\right)\mathrm{dt}---\left(21\right)$

$n\left(6\right)=\mathrm{\η}{\∫}_{t_1+t_2+t_3+t_4+t_5}^{t_1+t_2+t_3+t_4+t_5+t_6}{A}_{\mathrm{\α}}\left(t\right)\mathrm{dt}---\left(21\right)$

Formula (16), (17), (18), (19), (20), (21) are found the solution, can obtain A _Rn1, A _RaA1, A _RaB1, A _RaC1, A _Th1, A ₀Value, then try to achieve according to formula (11), (12) ²²²Rn, ²²⁰The concentration of Rn.

The measuring system that said method adopts by flowmeter, sampling pump, the first solenoid valve, vacuum meter, the single scintillation chamber of low pressure, the second solenoid valve, ²²²Rn, ²²⁰Rn daughter filtrator, variable valve and scintillation chamber's measurement mechanism form.By pipeline successively with the single scintillation chamber of flowmeter, sampling pump, the first solenoid valve, vacuum meter, low pressure, the second solenoid valve, ²²²Rn, ²²⁰Rn daughter filtrator and variable valve are together in series and form a measuring circuit, wherein: an end of sampling pump is connected with an end of the first solenoid valve by pipeline, the other end of the first solenoid valve is connected with an end of vacuum meter by pipeline, the other end of vacuum meter is connected by the end of pipeline with the single scintillation chamber of low pressure, the other end of the single scintillation chamber of low pressure is connected with an end of the second solenoid valve by pipeline, the other end of the second solenoid valve by pipeline and ²²²Rn, ²²⁰One end of Rn daughter filtrator connects, ²²²Rn, ²²⁰The other end of Rn daughter filtrator is connected with an end of variable valve by pipeline, and the other end of variable valve is connected with an end of flowmeter by pipeline.

The present invention compared with prior art has following features:

Utilize the single scintillation chamber of low pressure pair ²²²Rn, ²²⁰The measuring system that the method for Rn concentration synchro measure adopts is simple, Measuring Time is short and realize that easily robotization, especially the method do not need to measure background before measurement, can reduce and measure setup time.

The invention will be further described below in conjunction with the drawings and specific embodiments.

Description of drawings

Accompanying drawing 1 is measuring system schematic diagram of the present invention, and the P1 among the figure represents air inlet, and P2 represents to give vent to anger.

Embodiment

A kind of single scintillation chamber of low pressure pair of utilizing ²²²Rn, ²²⁰The method of Rn concentration synchro measure, its concrete steps are as follows:

Open the first solenoid valve 3 and the second solenoid valve 6 in the measuring system, open sampling pump 2, will contain ²²²Rn, ²²⁰The air of Rn contains with certain flow velocity mobile 5-20min in the measuring system loop ²²²Rn, ²²⁰The air of Rn flows into from the draft tube of flowmeter 1, discharges from the gas outlet of sampling pump 2, thereby makes in the single scintillation chamber 5 of low pressure ²²²Rn, ²²⁰In Rn gas and the environment ²²²Rn, ²²⁰Rn gas reaches balance, contains ²²²Rn, ²²⁰The air of Rn enters the single scintillation chamber 5 of low pressure with certain flow velocity after high efficiency particulate air filter 7 filters out daughter.Because sampling pump 2 flow rates are larger, by the air pressure in the single scintillation chamber 5 of variable valve 8 adjusting low pressure in the measuring system, so that the air pressure in the single scintillation chamber 5 of low pressure is lower than an atmospheric pressure.Suppose that the single scintillation chamber of low pressure 5 interior any point are L to the scintillator zinc sulphide surface ultimate range of the inside surface coating of scintillation chamber, reduce the air pressure in the single scintillation chamber 5 of low pressure, ²²²Rn, ²²⁰The α particle that Rn and daughter disintegration thereof are emitted has different energy, and corresponding range is also different.Wherein ²²²The alpha-particle energy that the Rn decay is emitted is minimum, and range is also minimum.Adjustable pressure so that ²²²The α particle that Rn decay is emitted under this air pressure range greater than L, like this so that low pressure list scintillation chamber 5 is under low pressure right ²²²Rn, ²²⁰The α particle that Rn and daughter disintegration thereof are emitted has identical detection efficiency.Detection efficiency represents with two kinds of methods, and a kind of is an average alpha-decay, can measure η counting, represents detection efficiency with η; Another kind is average K alpha-decay, can measure 1 counting, represents detection efficiency with K.Represent detection efficiency with η among the present invention.

Sample after 2-20 minute, close synchronously the first solenoid valve 3 and the second solenoid valve 6 are closed sampling pump 2 simultaneously, and the air pressure in the single scintillation chamber 5 of low pressure this moment remains unchanged, and then begins to measure, and utilizes the counting that measures to obtain according to Law of radioactive decay ²²²Rn, ²²⁰The concentration of Rn.

Finish and measure the moment of beginning in sampling, be located in the single scintillation chamber 5 of low pressure ²²²Rn and daughter RaA thereof ( ²¹⁸Po), RaB ( ²¹⁴Pb), RaC ( ²¹⁴Bi) activity is respectively A _Rn1, A _RaA1, A _RaB1, A _RaC1; Disintegration constant is respectively λ _Rn, λ _RaA, λ _RaB, λ _RaCBecause RaC ' ( ²¹⁴Po) half life period only has 164 μ s, and its half life period is very short, so people often are summed up as the radioactivity of RaC ' radioactivity of RaC.Because ThA ( ²¹⁶Po) half life period very short, with ²²⁰Rn reaches balance very soon, is located in the single scintillation chamber 5 of low pressure ²²⁰Rn and daughter ThA thereof ( ²¹⁶Po) activity is A _Th, ²²⁰The Rn disintegration constant is λ _Th, background activity is A ₀, do not consider other long-life daughters, then have according to Law of radioactive decay:

$A_{\mathrm{Rn}}\left(t\right)=A_{\mathrm{Rn}1}{e}^{-{\mathrm{\λ}}_{\mathrm{Rn}}t}---\left(1\right)$

${\mathrm{dA}}_{\mathrm{RaA}}\left(t\right)/\mathrm{dt}=A_{\mathrm{Rn}}\left(t\right){\mathrm{\λ}}_{\mathrm{RaA}}-A_{\mathrm{RaA}}\left(t\right){\mathrm{\λ}}_{\mathrm{RaA}}---\left(2\right)$

${\mathrm{dA}}_{\mathrm{RaB}}\left(t\right)/\mathrm{dt}=A_{\mathrm{RaA}}\left(t\right){\mathrm{\λ}}_{\mathrm{RaB}}-A_{\mathrm{RaB}}\left(t\right){\mathrm{\λ}}_{\mathrm{RaB}}---\left(3\right)$

${\mathrm{dA}}_{\mathrm{RaC}}\left(t\right)/\mathrm{dt}=A_{\mathrm{RaB}}\left(t\right){\mathrm{\λ}}_{\mathrm{RaC}}-A_{\mathrm{RaC}}\left(t\right){\mathrm{\λ}}_{\mathrm{RaC}}---\left(4\right)$

$A_{\mathrm{Th}}\left(t\right)=A_{\mathrm{Th}1}{e}^{-{\mathrm{\λ}}_{\mathrm{Th}}t}---\left(5\right)$

$A_{\mathrm{ThA}}\left(t\right)\≈A_{\mathrm{Th}1}{e}^{-{\mathrm{\λ}}_{\mathrm{Th}}t}---\left(6\right)$

$A_0\left(t\right)=A_0---\left(7\right)$

After formula (2), (3), (4) are found the solution, obtain total alpha activity activity over time rule be:

$A_{\mathrm{Rn}}\left(t\right)+A_{\mathrm{RaA}}\left(t\right)+A_{\mathrm{RaC}}\left(t\right)+2A_{\mathrm{Th}}\left(t\right)+A_0=f(A_{\mathrm{Rn}1},A_{\mathrm{RaA}1},A_{\mathrm{RaB}1},A_{\mathrm{RaC}1},A_{\mathrm{Th}1},A_0,t)---\left(8\right)$

Because the alpha-particle detection efficient of the 5 pairs of different-energies in the single scintillation chamber of low pressure is identical, is η all, has

$n\left(t\right)=\mathrm{\ηf}(A_{\mathrm{Rn}1},A_{\mathrm{RaA}1},A_{\mathrm{RaB}1},A_{\mathrm{RaC}1},A_{\mathrm{Th}1},A_0,t)---\left(9\right)$

The counting that n (t) measures for scintillation chamber's measurement mechanism 9 is rule over time.

Adopt the method for scintillation chamber's measurement mechanism 9 measurement count to have two kinds:

A, short time interval measurement: the Measuring Time T of each measuring period is 1-5 minute, measuring period quantity more than or equal to 6, the counting of each measuring period is n (i), i is measuring period.

Computing method take short time interval T as measuring period have two kinds:

A, try to achieve the average counter of the unit interval of i measuring period according to the counting n (i) of i measuring period, this average counter with this measuring period mid point the pass of totalαradioactivity activity be:

$n\left(i\right)/T=\mathrm{\ηf}(A_{\mathrm{Rn}1},A_{\mathrm{RaA}1},A_{\mathrm{RaB}1},A_{\mathrm{RaC}1},A_{\mathrm{Th}1},A_0,(i-\frac{1}{2})T)---\left(10\right)$

Utilize formula (10) that the data of n (i)/T are carried out nonlinear fitting, can obtain A _Rn1, A _RaA1, A _RaB1, A _RaC1, A _Th1, A ₀Value, then try to achieve according to formula (11), (12) ²²²Rn, ²²⁰The concentration of Rn:

$C_{\mathrm{Rn}}=\frac{A_{\mathrm{Rn}1}{P}_0}{\mathrm{VP}}---\left(11\right)$

C in the formula _RnFor ²²²The concentration of Rn; V is the volume of the single scintillation chamber 5 of low pressure; P is the air pressure in the single scintillation chamber 5 of low pressure; P ₀Be ambient pressure.

$C_{\mathrm{Tn}}=\frac{A_{\mathrm{Tn}1}{P}_0}{\mathrm{VP}}---\left(12\right)$

C in the formula _ThFor ²²⁰The concentration of Rn.

B, ask the integration of totalαradioactivity activity i measuring period:

$A_{\mathrm{\α}}\left(t\right)=A_{\mathrm{Rn}}\left(t\right)+A_{\mathrm{RaA}}\left(t\right)+A_{\mathrm{RaC}}\left(t\right)+2A_{\mathrm{Th}}\left(t\right)+A_0---\left(13\right)$

A in the formula _α(t) be totalαradioactivity activity.

$A_{\mathrm{\α}}\left(i\right)={\∫}_{(i-1T)}^{\mathrm{iT}}f(A_{\mathrm{Rn}1},A_{\mathrm{RaA}1},A_{\mathrm{RaB}1},A_{\mathrm{RaC}1},A_{\mathrm{Th}1},A_0,t)\mathrm{dt}---\left(14\right)$

A in the formula _α(i) be the integration of totalαradioactivity activity i measuring period.

The application least square method is found the solution, and introduces residual error R _A:

$R_A=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{w}_i{(n\left(i\right)-\mathrm{\η}{A}_{\mathrm{\α}}\left(i\right))}^2---\left(15\right)$

W in the formula _iBe the weight factor of i counting section, the introducing of weight factor is to consider that the counting statistics error difference of each measuring period is to the error effect of fitting result.

According to principle of least square method, so that residual error R _AGet minimum value, can obtain A _Rn1, A _RaA1, A _RaB1, A _RaC1, A _Th1, A ₀Value, then try to achieve according to formula (11), (12) ²²²Rn, ²²⁰The concentration of Rn.

B, long-time interval measurement: the measurement time t of each measuring period ₁, t ₂, t ₃, t ₄, t ₅, t ₆Be respectively 5-60 minute, be 6 measuring period, and the counting of six measuring periods is respectively n (1), n (2), n (3), n (4), n (5), n (6).

$n\left(1\right)=\mathrm{\η}{\∫}_0^{t_1}{A}_{\mathrm{\α}}\left(t\right)\mathrm{dt}---\left(16\right)$

$n\left(2\right)=\mathrm{\η}{\∫}_{t_1}^{t_1+t_2}{A}_{\mathrm{\α}}\left(t\right)\mathrm{dt}---\left(17\right)$

$n\left(3\right)=\mathrm{\η}{\∫}_{t_1+t_2}^{t_1+t_2+t_3}{A}_{\mathrm{\α}}\left(t\right)\mathrm{dt}---\left(18\right)$

$n\left(4\right)=\mathrm{\η}{\∫}_{t_1+t_2+t_3}^{t_1+t_2+t_3+t_4}{A}_{\mathrm{\α}}\left(t\right)\mathrm{dt}---\left(19\right)$

$n\left(5\right)=\mathrm{\η}{\∫}_{t_1+t_2+t_3+t_4}^{t_1+t_2+t_3+t_4+t_5}{A}_{\mathrm{\α}}\left(t\right)\mathrm{dt}---\left(21\right)$

$n\left(6\right)=\mathrm{\η}{\∫}_{t_1+t_2+t_3+t_4+t_5}^{t_1+t_2+t_3+t_4+t_5+t_6}{A}_{\mathrm{\α}}\left(t\right)\mathrm{dt}---\left(21\right)$

Formula (16), (17), (18), (19), (20), (21) are found the solution, can obtain A _Rn1, A _RaA1, A _RaB1, A _RaC1, A _Th1, A ₀Value, then try to achieve according to formula (11), (12) ²²²Rn, ²²⁰The concentration of Rn.

The measuring system that said method adopts by flowmeter 1, sampling pump 2, the first solenoid valve 3, vacuum meter 4, the single scintillation chamber 5 of low pressure, the second solenoid valve 6, ²²²Rn, ²²⁰Rn daughter filtrator 7, variable valve 8 and scintillation chamber's measurement mechanism 9 form.By pipeline successively with the single scintillation chamber 5 of flowmeter 1, sampling pump 2, the first solenoid valve 3, vacuum meter 4, low pressure, the second solenoid valve 6, ²²²Rn, ²²⁰Rn daughter filtrator 7 and variable valve 8 are together in series and form a measuring circuit, wherein: an end of sampling pump 2 is connected by the end of pipeline with the first solenoid valve 3, the other end of the first solenoid valve 3 is connected with an end of vacuum meter 4 by pipeline, the other end of vacuum meter 4 is connected by the end of pipeline with the single scintillation chamber 5 of low pressure, the other end of the single scintillation chamber 5 of low pressure is connected by the end of pipeline with the second solenoid valve 6, the other end of the second solenoid valve 6 by pipeline and ²²²Rn, ²²⁰One end of Rn daughter filtrator 7 connects, ²²²Rn, ²²⁰The other end of Rn daughter filtrator 7 is connected with an end of variable valve 8 by pipeline, and the other end of variable valve 8 is connected with an end of flowmeter 1 by pipeline.

Claims (1)

1. one kind is utilized the single scintillation chamber of low pressure pair ²²²Rn, ²²⁰The method of Rn concentration synchro measure is characterized in that: its concrete steps are as follows:

Open the first solenoid valve and the second solenoid valve in the measuring system, open sampling pump, will contain ²²²Rn, ²²⁰The air of Rn contains with certain flow velocity mobile 5-20min in the measuring system loop ²²²Rn, ²²⁰The air of Rn flows into from the draft tube of flowmeter, discharges from the gas outlet of sampling pump, thereby makes in the single scintillation chamber of low pressure ²²²Rn, ²²⁰In Rn gas and the measurement environment ²²²Rn, ²²⁰Rn gas reaches balance, contains ²²²Rn, ²²⁰The air of Rn enters the single scintillation chamber of low pressure with certain flow velocity after high efficiency particulate air filter filters out daughter; Because the sampling pump flow rate is larger, by the air pressure in the single scintillation chamber of the adjusting of the variable valve in measuring system low pressure, so that the air pressure in the single scintillation chamber of low pressure is lower than an atmospheric pressure; Suppose that any point in the single scintillation chamber of low pressure is L to the scintillator zinc sulphide surface ultimate range of the inside surface coating of scintillation chamber, the air pressure in the reduction low pressure list scintillation chamber, ²²²Rn, ²²⁰The α particle that Rn and daughter disintegration thereof are emitted has different energy, and corresponding range is also different, wherein ²²²The alpha-particle energy that the Rn decay is emitted is minimum, and range is also minimum; Adjustable pressure so that ²²²The α particle that Rn decay is emitted under this air pressure range greater than L, like this so that low pressure list scintillation chamber is under low pressure right ²²²Rn, ²²⁰The α particle that Rn and daughter disintegration thereof are emitted has identical detection efficiency;

An average alpha-decay can measure h counting, represents detection efficiency with h;

Sample after 2-20 minute, close synchronously the first solenoid valve and the second solenoid valve are closed sampling pump simultaneously, and the air pressure in the single scintillation chamber of low pressure this moment remains unchanged, and then begins to measure, and utilizes the counting that measures to obtain according to Law of radioactive decay ²²²Rn, ²²⁰The concentration of Rn;

Finish and measure the moment of beginning in sampling, be located in the single scintillation chamber of low pressure ²²²The activity of Rn and daughter RaA, RaB, RaC is respectively

,

,

, Disintegration constant is respectively

,

, , Because the half life period of RaC ' only has 164 μ s, its half life period is very short, the radioactivity of RaC ' is summed up as the radioactivity of RaC, because the ThA half life period is very short, with ²²⁰Rn reaches balance very soon, is located in the single scintillation chamber of low pressure ²²⁰The activity of Rn and daughter ThA thereof is

, ²²⁰The Rn disintegration constant is , background activity is A ₀, do not consider other long-life daughters, then have according to Law of radioactive decay:

（1）

（2）

（3）

（4）

（5）

（6）

（7）

After formula (2), (3), (4) are found the solution, obtain total alpha activity activity over time rule be:

（8）

Because the single scintillation chamber of low pressure is identical to the alpha-particle detection efficient of different-energy, is h all, has

（9）

The counting that measures for scintillation chamber's measurement mechanism is rule over time;

Adopt the method for scintillation chamber's measurement mechanism measurement count to have two kinds:

A, short time interval measurement: the Measuring Time T of each measuring period is 1-5 minute, measuring period quantity more than or equal to 6, the counting of each measuring period is

, i is measuring period;

Computing method take short time interval T as measuring period have two kinds:

A, according to the counting of i measuring period Try to achieve the average counter of the unit interval of i measuring period, this average counter with this measuring period mid point the pass of totalαradioactivity activity be:

（10）

Utilize formula (10) right

Data carry out nonlinear fitting, can obtain

,

,

,

,

, Value, then try to achieve according to formula (11), (12) ²²²Rn, ²²⁰The concentration of Rn:

(11)

In the formula

For ²²²The concentration of Rn; V is the volume of the single scintillation chamber of low pressure; P is the air pressure in the single scintillation chamber of low pressure; P ₀Be ambient pressure;

(12)

In the formula For ²²⁰The concentration of Rn;

B, ask the integration of totalαradioactivity activity i measuring period:

（13）

In the formula

Totalαradioactivity activity;

(14)

In the formula

The integration of totalαradioactivity activity i measuring period;

The application least square method is found the solution, and introduces residual error

:

（15）

W in the formula _iBe the weight factor of i counting section, the introducing of weight factor is to consider that the counting statistics error difference of each measuring period is to the error effect of fitting result;

According to principle of least square method, so that residual error

Get minimum value, can obtain

,

, ,

,

,

Value, then try to achieve according to formula (11), (12) ²²²Rn, ²²⁰The concentration of Rn;

B, long-time interval measurement: the measurement time t of each measuring period ₁, t ₂, t ₃, t ₄, t ₅, t ₆Be respectively 5-60 minute, be 6 measuring period, and the counting of six measuring periods is respectively

,

, , , ,

（16）

（17）

（18）

（19）

（20）

（21）

Formula (16), (17), (18), (19), (20), (21) are found the solution, can obtain ,

, ,

,

,

Value, then try to achieve according to formula (11), (12) ²²²Rn, ²²⁰The concentration of Rn;

The measuring system that said method adopts by flowmeter, sampling pump, the first solenoid valve, vacuum meter, the single scintillation chamber of low pressure, the second solenoid valve, ²²²Rn, ²²⁰Rn daughter filtrator, variable valve and scintillation chamber's measurement mechanism form; By pipeline successively with the single scintillation chamber of sampling pump, the first solenoid valve, vacuum meter, low pressure, the second solenoid valve, ²²²Rn, ²²⁰Rn daughter filtrator, variable valve and flowmeter are together in series and form a measuring circuit, wherein: an end of sampling pump is connected with an end of the first solenoid valve by pipeline, the other end of the first solenoid valve is connected with an end of vacuum meter by pipeline, the other end of vacuum meter is connected by the end of pipeline with the single scintillation chamber of low pressure, the other end of the single scintillation chamber of low pressure is connected with an end of the second solenoid valve by pipeline, the other end of the second solenoid valve by pipeline and ²²²Rn, ²²⁰One end of Rn daughter filtrator connects, ²²²Rn, ²²⁰The other end of Rn daughter filtrator is connected with an end of variable valve by pipeline, and the other end of variable valve is connected with an end of flowmeter by pipeline.

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