CN101738626A - Method for confirming thickness and clearance rate of gamma dosemeter compensating filter - Google Patents

Abstract

The invention relates to a radiation measurement technology, in particular to a method for confirming the thickness and clearance rate of a gamma dosemeter compensating filter. By a method similar to a least square method, a subtracted value of the energy response of a compensated gamma dosemeter and 1 trends to the minimum, thereby obtaining a simultaneous equation which can be solved to confirm the optimal values of the thickness t and the clearance rate p of the compensating filter. The method does not need to carry out the manufacture of a plurality of physical models; and compared with actual measurement data, the obtained data is more ideal.

Description

Definite method of the thickness of gamma dosimeter compensating filter and voidage

Technical field

The present invention relates to radiometric technique, be specifically related to a kind of thickness of gamma dosimeter compensating filter and definite method of voidage.

Background technology

When gamma dosimeter being carried out the energy response compensation with the partly shielding effect method, usually use the compensating filter that ray is had the material of strong screening ability, be enclosed within outside the probe, allow ray before arriving probe earlier after filtration, made originally low energy is responded too high instrument, its energy response becomes smooth.In the prior art, for the energy response that makes instrument becomes smooth, normally make the large quantities of different thickness t and the compensating filter of voidage p proportioning at a certain shielding material, be enclosed within outside the probe one by one successively, from experimentally measuring various t, better person is selected in the energy response of instrument under the p proportioning thus.Because this method need expend a large amount of time and efforts and carry out the making of model, not only workload is very big, and is difficult to find required optimum value.

For different ray energies, the corresponding series of equations formula of the energy response of the gamma dosimeter after compensation,

$(1-p)e^{-{\mathrm{\μ}}_{1}t}\·k_1+{\mathrm{pk}}_1$

$(1-p)e^{-{\mathrm{\μ}}_{2}t}\·k_2+{\mathrm{pk}}_2$

$......$

$(1-p)e^{-{\mathrm{\μ}}_{n}t}\·k_n+{\mathrm{pk}}_n$

The optimum value of the thickness t of compensating filter and voidage p is to draw under all equations all equal 1 situation.Theoretically, it is impossible that above-mentioned all equations all equal 1, only may make any two equations equal 1, and all the other equations all relatively approach 1.In order to look after all energy, can make above-mentioned all equations be equal to 1 and add a decimal δ _i, and make Be tending towards thickness t and voidage p under the minimizing situation, be optimal selection.But lacking a kind of theoretical calculation method again at present to determine the thickness t of compensating filter and the optimum value of voidage p by some given datas.

Summary of the invention

The objective of the invention is at problems of the prior art, a kind of thickness of gamma dosimeter compensating filter and definite method of voidage are provided, this method need not carried out a large amount of experiment measurings, just can be compensated comparatively accurately filtrator parameter to be determined.

Technical scheme of the present invention is as follows: definite method of a kind of thickness of gamma dosimeter compensating filter and voidage, this method at first record the primary energy response K of the corresponding different ray energy of the preceding gamma dosimeter of not compensated ₁, K ₂... K _n, and used compensating filter shielding material is to the linear attenuation coefficient μ of various ray energies ₁, μ ₂... μ _n, then by following associating equation, the thickness t of the compensating filter of definite this shielding material of use and the optimum value of voidage p:

$\left\{\begin{array}{c}\underset{i}{\mathrm{\Σ}}(1-p){\mathrm{\δ}}_i{\mathrm{\μ}}_i{K}_i{e}^{-{\mathrm{\μ}}_{i}t}=0\\ \underset{i}{\mathrm{\Σ}}{\mathrm{\δ}}_i{K}_i(1-e^{-{\mathrm{\μ}}_{i}t})=0\end{array}\right.$

${\mathrm{\δ}}_i=(1-p)e^{-{\mathrm{\μ}}_{i}t}{k}_i+{\mathrm{pk}}_i-1$ i＝1、2......n。

Further, definite method of the thickness of aforesaid gamma dosimeter compensating filter and voidage, wherein, the primary energy response K of the ray energy that the gamma dosimeter correspondence is different before the not compensated ₁, K ₂... K _nValue, be in secondary standard dosimeter laboratory, filter a series of line matter of x reference radiation with the narrow pedigree row that meet the ISO4037 requirement, respond known secondary standard dosemeter and the quantimeter to be compensated of calibration factor with method of substitution at identical position difference irradiation energy one by one, try to achieve by the reading that compares them.

Further, definite method of the thickness of aforesaid gamma dosimeter compensating filter and voidage, wherein, the compensating filter shielding material is to the linear attenuation coefficient μ of various ray energies ₁, μ ₂... μ _nValue, be the even book sheet that this material is pressed into different-thickness, record its thickness, use the line matter identical then with the response of above-mentioned measurement gamma dosimeter primary energy, record half thickness HVL under each energy successively with absorption process, then by formula Try to achieve.

Beneficial effect of the present invention is as follows: for different ray energies, the corresponding series of equations formula of the energy response of the gamma dosimeter after compensation, the optimum value of the thickness t of compensating filter and voidage p is to draw under all equations all trend towards 1 situation, the present invention is by being similar to the method for least square method, the value that the energy response and 1 of the gamma dosimeter of order after compensation is subtracted each other is tending towards minimizing, thereby obtain the associating equation that to find the solution, determine the thickness t of compensating filter and the optimum value of voidage p with this.This method need not carried out a large amount of mock-up making, and the gained data are compared desirable more with measured data.

Embodiment

Below in conjunction with specific embodiment the present invention is described in detail.

Two parameters to be asked of compensating filter are thickness t and voidage p.If the response of the primary energy of gamma dosimeter is K before the not compensated ₁, K ₂... K _n＞1,

It is right to represent ⁶⁰The gamma-ray response normalizing of Co, wherein 1,2 ... the ray energy that n is corresponding different.When applying parameter is thickness t, and after the compensating filter of voidage p, its energy response just becomes:

$(1-p)e^{-{\mathrm{\μ}}_{1}t}\·k_1+{\mathrm{pk}}_1$

$(1-p)e^{-{\mathrm{\μ}}_{2}t}\·k_2+{\mathrm{pk}}_2$

$......$

$(1-p)e^{-{\mathrm{\μ}}_{n}t}\·k_n+{\mathrm{pk}}_n---\left(1\right)$

μ in the system of equations (1) ₁, μ ₂... μ _nBe the linear attenuation coefficient of used compensating filter shielding material to corresponding ray energy, K in the formula ₁, K ₂... K _nAnd μ ₁, μ ₂... μ _nAll can be recorded by known experimental technique, have only t, the p binomial is a unknown number to be asked.

The primary energy of gamma dosimeter response K before the not compensated ₁, K ₂... K _nValue, be in secondary standard dosimeter laboratory (SSDL), filter a series of line matter of x reference radiation with the narrow pedigree row that meet the ISO4037 requirement, respond known secondary standard dosage (rate) instrument and the quantimeter to be compensated of calibration factor with method of substitution at identical position difference irradiation energy one by one, try to achieve by the reading that compares them.And the linear attenuation coefficient μ of compensating filter shielding material ₁, μ ₂... μ _nValue, be the even book sheet that this material is pressed into different-thickness, record its thickness, use then and the identical line matter of above-mentioned measurement gamma dosimeter primary energy response with weighing and measuring area-method, record half thickness HVL under each line matter (being energy) successively with absorption process, then by formula Try to achieve.

In theory, it is impossible making in the top system of equations (1) all equations be equal to 1.On the mathematics, only may make any two equations equal 1, all the other equations all are not equal to 1.In order to look after all energy, make above-mentioned each equation all relatively approach 1, can make

$(1-p)e^{-{\mathrm{\μ}}_{n}t}\·k_n+{\mathrm{pk}}_n-1={\mathrm{\δ}}_n$ n＝1、2......

And make $s=\underset{n-1}{\mathrm{\Σ}}{\mathrm{\δ}}_n^2$ Be tending towards minimal value,

Like this, just, the available method that is similar to least square method is found the solution:

Get $\frac{\∂s}{\∂t}=0,$ $\frac{\∂s}{\∂p}=0$

Can get the associating equation that another group only contains two unknown numbers:

$\left\{\begin{array}{c}\underset{i}{\mathrm{\Σ}}(1-p){\mathrm{\δ}}_i{\mathrm{\μ}}_i{K}_i{e}^{-{\mathrm{\μ}}_{i}t}=0\\ \underset{i}{\mathrm{\Σ}}{\mathrm{\δ}}_i{K}_i(1-e^{-{\mathrm{\μ}}_{i}t})=0\end{array}\right.---\left(2\right)$

${\mathrm{\δ}}_i=(1-p)e^{-{\mathrm{\μ}}_{i}t}{k}_i+{\mathrm{pk}}_i-1$ i＝1、2......n

Just can solve t and two unknown numbers of p by above-mentioned simultaneous equations (2).It is to look after the unknown number t of all equations in the above-mentioned system of equations (1) and the optimal selection of p.

Said method, represent to be with mathematical usual method:

Suppose that two unknown numbers of x, y (waiting to ask) will satisfy following n equation n＞2.

......

$\left\{\begin{array}{c}{f}_1(x.y)=0\\ f_2(x.y)=0\\ f_3(x.y)=0\end{array}\right.---\left(3\right)$

Then can establish f ₁(x.y)=δ ₁

f ₂(x.y)＝δ ₂

......

Order $s=\underset{i}{\mathrm{\Σ}}{\mathrm{\δ}}_i^2,$ Ask again $\frac{\∂s}{\∂x}=0,$ $\frac{\∂s}{\∂y}=0$

Just can get another group simultaneous equations

$\left\{\begin{array}{c}F(x,y)=0\\ G(x,y)=0\end{array}\right.---\left(4\right)$

The x that solves thus, y are the optimal selections of separating of above-mentioned system of equations (3).

With GJ-III personal stereo dosemeter is example, this instrument with the J-613 counter tube as detecting element.Its primary energy response is:

Energy kev	??47	??65	??86	??104	??123	??170
							To H p(10) response	??5.54	??5.66	??4.69	??3.59	??2.46	??1.42

In order to improve its energy response, former before this in the counter tube outsourcing the thick sheet lead of one deck 1mm, make a call to 30% hole on the sheet lead with the drill bit of φ 2, (being that voidage is 30%), under such compensation condition, the energy response of instrument obtains part and improves, but the low energy place still than ⁶⁰The response of Co exceeds 2-3 doubly.In order further to improve its energy response, use the optimization compensation principle, use tin (S instead _n) make shielding material, selecting thickness is t=1.5mm, and getting voidage is p=0.18, and the energy response of GJ-III personal stereo dosemeter is further improved greatly, and result of calculation sees the following form:

Timing ∑ δ _i ²Only be 0.0687.

On the implementing process, to originally on lead, punch, change tin sheet into 1.5mm, make three rings, be enclosed within on the counter tube, stay a crack between per 2 rings, the width of three rings, two seams account for 18% of counter tube effective length, do like this, can make instrument rotate howsoever in the φ direction that to remain voidage be 0.18.Owing to technologic reason, actual energy response does not have the so good of Theoretical Calculation, but can remain on basically ± 30% in.

Method of the present invention is not limited to the embodiment described in the embodiment, and those skilled in the art's technical scheme according to the present invention draws other embodiment, belongs to technological innovation scope of the present invention equally.

Claims (3)

1. definite method of the thickness of a gamma dosimeter compensating filter and voidage is characterized in that: this method at first records the primary energy response K of the corresponding different ray energy of gamma dosimeter before the not compensated ₁, K ₂... K _n, and used compensating filter shielding material is to the linear attenuation coefficient μ of various ray energies ₁, μ ₂... μ _n, then by following associating equation, the thickness t of the compensating filter of definite this shielding material of use and the optimum value of voidage p:

$\left\{\begin{array}{c}\underset{i}{\mathrm{\Σ}}(1-p){\mathrm{\δ}}_i{\mathrm{\μ}}_i{K}_i{e}^{-{\mathrm{\μ}}_{i}t}=0\\ \underset{i}{\mathrm{\Σ}}{\mathrm{\δ}}_i{K}_i(1-e^{-{\mathrm{\μ}}_{i}t})=0\end{array}\right.$

${\mathrm{\δ}}_i=(1-p)e^{-{\mathrm{\μ}}_{i}t}{k}_i+p{k}_i-1$ i＝1、2......n。

2. definite method of the thickness of gamma dosimeter compensating filter as claimed in claim 1 and voidage is characterized in that: the primary energy response K of the ray energy that the gamma dosimeter correspondence is different before the described not compensated ₁, K ₂... K _nValue, be in secondary standard dosimeter laboratory, filter a series of line matter of x reference radiation with the narrow pedigree row that meet the ISO4037 requirement, respond known secondary standard dosemeter and the quantimeter to be compensated of calibration factor with method of substitution at identical position difference irradiation energy one by one, try to achieve by the reading that compares them.

3. definite method of the thickness of gamma dosimeter compensating filter as claimed in claim 1 or 2 and voidage is characterized in that: described compensating filter shielding material is to the linear attenuation coefficient μ of various ray energies ₁, μ ₂... μ _nValue, be the even book sheet that this material is pressed into different-thickness, record its thickness, use and measure the identical line matter of gamma dosimeter primary energy response then, record half thickness HVL under each energy successively with absorption process, then by formula

Try to achieve.