CN101162269A - Germanium crystal dimension automatic regulation method for high-purity germanium detector passive efficiency scale division - Google Patents

Abstract

The invention relates to radiation measuring technical field, specifically to a germanium crystal size automatic adjustment method with souceless efficiency calibration used in high-purity germanium detector, wherein, a plurality of measuring values of gamma radial omnipotence peak testing efficiency of different Ei energies can be obtained at one testing position, and then the computing valves of all gamma radial omnipotence peak testing efficiency of different Ei can be attained through Monte Carlo analog computation according to the original size of crystal provided by the product instruction of the detector; and error analysis is performed on the efficiency computing value and the measuring value, an efficiency influence formula of the crystal sizes T, R, L on E-energy gamma radial can be calculated under the present crystal sizes through Monte Carlo calculation; a computational efficiency expecting change percentage is set, and an equation group is built to get the size of a new crystal, a final result can be got by repeating the above procedures. The invention can automatically, quickly, accurately determine a high-purity germanium crystal and the size of the sensitive area to effectively ensure the realization of quick Monte Carlo souceless efficiency calibration for high-purity germanium detector.

Description

The germanium crystal dimension automatic regulation method of high purity germanium detector passive efficiency scale

Technical field

The present invention relates to the radiometric technique field, be specifically related to a kind of germanium crystal dimension automatic regulation method that is used for the high purity germanium detector passive efficiency scale.

Background technology

HpGe (HPGe) detector is one of detector that is most widely used in the actinometry.In actinometry, need carry out efficiency calibration to used detector usually.Utilizing Monte Carlo method that high purity germanium detector is carried out passive efficiency scale at present, generally all is accurately to obtain directly to carry out analog computation after the crystalline size data.Wherein the most key crystal sensitive volume size is general difficult definite, common a kind of way is in conjunction with experimental result crystal sensitive volume size to be carried out manual setting to obtain comparatively satisfied accuracy in computation, but the influence of manual setting process human factor is bigger, and spended time is also longer.

Summary of the invention

The objective of the invention is to provides a kind of germanium crystal dimension automatic regulation method of high purity germanium detector passive efficiency scale at the more doubt problem of high purity germanium detector crystal sensitive volume size.

Technical scheme of the present invention is as follows: a kind of germanium crystal dimension automatic regulation method of high purity germanium detector passive efficiency scale comprises the steps:

(1), measures and obtain different E more than three or three at place, a measuring position _iEnergy gamma-rays full energy peak detection efficiency measured value η _Mea(E _i);

(2) set that crystal dead band thickness is that T, crystal radius are that R, crystal length are L in the HpGe crystalline size parameter, the crystal original size T that provides according to the high purity germanium detector product description ₀, R ₀, L ₀, carry out Monte Carlo simulation and calculate, obtain corresponding each E in the step (1) _iEnergy gamma-rays full energy peak detection efficiency calculated value η _Cal(E _i);

(3) if each E _iEnergy gamma-rays efficiency calculation value η _Cal(E _i) and corresponding E _iEnergy gamma-rays efficiency measurement value η _Mea(E _i) between relative error do not reach requirement, then with current crystal dead band thickness T _nBe initial value, change crystal dead band thickness T=T one by one _n+ N* Δ t, wherein n since 0 for integer, Δ t be step-length, N be integer, this moment R _nAnd L _nRemain unchanged, at different E _iEnergy carries out Monte Carlo Calculation respectively and obtains a series of and the corresponding different E of crystal dead band thickness T _iEnergy gamma-rays efficiency calculation value η _Cal(E _i, T); Adopt line fitting method, obtain current crystalline size T _n, R _n, L _nDown, crystal dead band thickness T is to different E _iEnergy gamma-rays efficiency calculation value influence formula δ η _Cal(E _i)=f _{T, Ei}(T);

(4) in like manner obtain crystal radius R to different E _iEnergy gamma-rays efficiency calculation value influence formula δ η _Cal(E _i)=f _R.Ei(R), crystal length L is to different E _iEnergy gamma-rays efficiency calculation value influence formula δ η _Cal(E _i)=f _{L, Ei}(L); Thus, draw at current crystalline size T _n, R _n, L _nDown, crystal dead band thickness T, crystal radius R, crystal length L are to different E _iTotal formula δ η that influences of energy gamma-rays efficiency calculation value _Cal(E _i)=f _{T, Ei}(T)+f _{R, Ei}(R)+f _{L, Ei}(L);

(5) to different E _iEnergy settings δ η _Cal(E _i) be current E _iEnergy gamma-rays efficiency calculation value and corresponding E _iEnergy gamma-rays efficiency measurement value η _Mea(E _i) between the negative of relative error, with the different E of above-mentioned steps (4) gained _iTotal formula δ η that influences of energy gamma-rays efficiency calculation value _Cal(E _i)=f _{T, Ei}(T)+f _R.Ei(R)+f _{L, Ei}(L) combine and be built into system of linear equations, can obtain crystal size T the n+1 time _N+1, R _N+1, L _N+1

(6) with new crystalline size T _N+1, R _N+1, L _N+1Carry out the Monte Carlo efficiency calculation, obtain each new E _iIf energy gamma-rays efficiency calculation value is each new E _iEnergy gamma-rays efficiency calculation is worth its corresponding E _iThe error of energy gamma-rays efficiency measurement value does not also reach requirement, and then repeating step (3) is to step (5), until new different E _iEnergy gamma-rays efficiency calculation is worth its corresponding E _iThe error of energy gamma-rays efficiency measurement value in allowed band, this moment end operation, thereby obtain the fit value of crystal dead band one-tenth-value thickness 1/10 T, crystal radius value R, crystal length L.

Effect of the present invention is: utilize Monte Carlo method that high purity germanium detector is carried out passive efficiency scale, generally all be accurately to obtain directly to carry out analog computation behind HpGe crystal and the sensitive volume dimensional data thereof, the present invention can determine HpGe crystal and sensitive volume size thereof automatically, quickly and accurately, thereby high purity germanium detector is realized that quick Monte Carlo passive efficiency scale provides effective assurance.

Description of drawings

Fig. 1 is a method flow diagram of the present invention.

Fig. 2 is radioactive source experiment location arrangements synoptic diagram of the present invention.

Embodiment

The present invention is described in further detail below in conjunction with instantiation.

The present invention is after accurately obtaining HpGe crystal and sensitive volume size thereof, utilizes Monte Carlo method directly to carry out analog computation, thereby realizes the high purity germanium detector passive efficiency scale.The key factor that influences the result of calculation accuracy is HpGe crystal and sensitive volume size thereof, and wherein of paramount importance be following three parameters: crystal dead band thickness T, crystal radius R, crystal length L.Fig. 1 is HpGe crystal of the present invention and sensitive volume size algorithm flow chart thereof, and Fig. 2 is radioactive source experiment location arrangements synoptic diagram of the present invention.

(model: passive efficiency scale GEM30P4) is an example with the P of Ortec company type high purity germanium detector below, after accurately obtaining HpGe crystal and sensitive volume size thereof by the present invention, utilize Monte Carlo method directly to carry out analog computation, thereby realize the high purity germanium detector passive efficiency scale.

Adopt following steps:

(1) 65cm place, i.e. (z on the center probe line _o=65cm, ρ _o=0cm), measure and obtain four different E _iEnergy (is respectively E ₁=1.332MeV, E ₂=0.662MeV, E ₃=0.344MeV, E ₄=0.122MeV) gamma-rays full energy peak detection efficiency measured value η _Mea(E _i), be respectively η _Mea(E ₁), η _Mea(E ₂), η _Mea(E ₃), η _Mea(E ₄).

(2) the crystal original size (original size that detector manufacturer provides: T that provides according to the high purity germanium detector product description ₀=0.7mm, R ₀=34.4mm, L ₀=39.5mm) carry out Monte Carlo simulation to calculate, obtain above-mentioned different-energy E _i(be respectively E ₁=1.332MeV, E ₂=0.662MeV, E ₃=0.344MeV, E ₄=0.122MeV) gamma-rays full energy peak detection efficiency calculated value η _Cal(E _i), be respectively η _Cal(E ₁), η _Cal(E ₂), η _Cal(E ₃), η _Cal(E ₄).

(3) because different E _iEnergy gamma-rays efficiency calculation value η _Cal(E _i) and corresponding E _iEnergy gamma-rays efficiency measurement value η _Mea(E _i) between relative error do not reach requirement, then with current crystal dead band thickness T ₀Be initial value, change crystal dead band thickness T=T one by one ₀+ N* Δ t (wherein Δ t be step-length, N be integer, this moment R ₀And L ₀Remain unchanged), at different E _iEnergy carries out Monte Carlo Calculation respectively, obtains a series of and the corresponding different E of crystal dead band thickness T _iEnergy gamma-rays efficiency calculation value η _Cal(E _i, T), adopt the line fitting method analysis to obtain current crystalline size (T ₀, R ₀, L ₀) under, T is to different E _iEnergy gamma-rays efficiency calculation value influence formula δ η _Cal(E _i)=f _{T, Ei}(T).

(4) in like manner obtain R to different E _iEnergy gamma-rays efficiency calculation value influence formula δ η _Cal=f _{R, Ei}(R); L is to different E _iEnergy gamma-rays efficiency calculation value influence formula δ η _Cal=f _{L, Ei}(L).Thus, draw current crystalline size (T ₀, R ₀, L ₀) under, crystal dead band thickness T, radius R, length L are to different E _iTotal formula δ η that influences of energy gamma-rays efficiency calculation value _Cal(E _i)=f _{T, Ei}(T)+f _{R, Ei}(R)+f _{L, Ei}(L).Below with E ₁=1.332MeV energy is an example, and T is to E ₁The formula that influences of energy gamma-rays efficiency calculation value is f _{T, 1.332}=-13.83T+9.78; R is to E ₁The formula that influences of energy gamma-rays efficiency calculation value is f _{R, 1.332}=7.828R-269.85; L is to E ₁The formula that influences of energy gamma-rays efficiency calculation value is f _{L, 1.332}=2.8053L-111.04 obtains E thus ₁Total formula δ η that influences of energy gamma-rays efficiency calculation value _Cal(1.332)=-13.83T+7.828R+2.8053L-371.11 (dimensional units: mm).Calculate gained crystal dead band thickness T, radius R, length L to different E _iEnergy (is respectively E ₁=1.332MeV, E ₂=0.662MeV, E ₃=0.344MeV, E ₄=0.122MeV) gamma-rays efficiency calculation value influences formula and always influences formula and see Table 1.

(5) to different E _iEnergy settings δ η _Cal(E _i) be current E _iEnergy gamma-rays efficiency calculation value and corresponding E _iEnergy gamma-rays efficiency measurement value η _Mea(E _i) between the negative of relative error, promptly set different E respectively _iThe expectation of energy gamma-rays efficiency calculation value changes number percent, for example E ₁=1.332MeV energy gamma-rays efficiency calculation value is more higher 22.45% than its corresponding efficiency measurement value, then can set E ₁The change expectation value of energy gamma-rays efficiency calculation value is-22.45%, with the different E of above-mentioned steps (4) gained _iTotal formula δ η that influences of energy gamma-rays efficiency calculation value _Cal(E _i)=f _{T, Ei}(T)+f _{R, Ei}(R)+f _{L, Ei}(L) combine and be built into system of linear equations, system of equations is as shown in the formula shown in (1), can separate to ask to obtain crystalline size and adjust result of calculation T the 1st time ₁=0.708mm, R ₁=32.149mm, L ₁=37.961mm, concrete result of calculation sees Table 2.

$\left\{\begin{array}{c}{\mathrm{\δ\η}}_{\mathrm{cal}}\left(1.332\right):-13.83T+7.828R+2.8053L-371.11=-22.45\\ {\mathrm{\δ\η}}_{\mathrm{cal}}\left(0.662\right):-13.95T+7.1315R+1.8884L-309.342=-18.76\\ {\mathrm{\δ\η}}_{\mathrm{cal}}\left(0.334\right):-13.31T+6.704R+0.8244L-253.898=-16.32\\ {\mathrm{\δ\η}}_{\mathrm{cal}}\left(0.122\right):-23.97T+5.8754R-184.24=-12.28\end{array}\right.$ Formula (1)

(6) with new crystalline size (T ₁, R ₁, L ₁) carry out the Monte Carlo efficiency calculation, obtain new different E _iEnergy gamma-rays efficiency calculation value is because new different E _iThe error that energy gamma-rays efficiency calculation is worth its corresponding gamma-rays efficiency measurement value does not also reach requirement, repeats (3) step and obtains at crystalline size (T ₁, R ₁, L ₁) under, crystal dead band thickness T, crystal radius R, crystal length L are to different E _iThe influencing formula and always influence formula of energy gamma-rays efficiency calculation value, concrete result of calculation is listed in table 3.Repeating step (4) is set different E respectively then _iThe expectation of energy gamma-rays efficiency calculation value changes number percent (E for example ₁=1.332MeV energy gamma-rays efficiency calculation value is more on the low side 2.59% than corresponding efficiency measurement value, then can set E ₁The change expectation value of energy gamma-rays efficiency calculation value is 2.59%), with the different E of gained _iEnergy gamma-rays efficiency calculation value total influences formula and combines and be built into system of linear equations, and system of equations is as shown in the formula shown in (3), can separate to ask to obtain crystalline size and adjust result of calculation T the 2nd time ₂=0.845mm, R ₂=33.149mm, L ₂=36.921mm, concrete result of calculation sees Table 4.

$\left\{\begin{array}{c}{\mathrm{\δ\η}}_{\mathrm{cal}}\left(1.332\right):-14.55T+8.6841R+3.1431L-389.01=2.59\\ {\mathrm{\δ\η}}_{\mathrm{cal}}\left(0.662\right):-14.59T+8.2622R+2.6300L-354.49=4.15\\ {\mathrm{\δ\η}}_{\mathrm{cal}}\left(0.344\right):-14.88T+7.6813R+1.7556L-303.16=3.70\\ {\mathrm{\δ\η}}_{\mathrm{cal}}\left(0.122\right):-25.23T+6.5548R-191.834=4.12\end{array}\right.$ Formula (2)

Calculate gained crystalline size (T owing to adjust for the 2nd time ₂, R ₂, L ₂) carry out the Monte Carlo efficiency calculation after, the different E that obtain _iThe relative error that energy gamma-rays efficiency calculation is worth its corresponding efficiency measurement value reaches error requirements less than 2%, and concrete outcome sees Table 5, finishes the crystalline size adjustment process, obtains suitable crystal dead band thickness T simultaneously ₂, crystal radius R ₂, crystal length L ₂

(z, detection efficiency scale ρ) need not to carry out experimental measurement again, but directly utilize last crystal to adjust size (T to be in other positions for radioactive source ₂, R ₂, L ₂) carry out Monte Carlo simulation and calculate.

As checking, shown in table 6 and table 7, for other positions, different E _iThe relative error that energy gamma-rays efficiency calculation is worth its corresponding efficiency measurement value generally in ± 2%, thereby realize quick passive efficiency scale to high purity germanium detector.

When radioactive source is nearer to detector distance z, promptly this distance z and detector entrance window are to the distance of crystal when suitable, if counting yield and conventional efficient deviation are bigger, should consider whether need to adjust the distance of detector entrance window to crystal this moment, if need to adjust, then closely needing energy of experimental point of increase to get final product (is E _i, i 〉=4), adjustment algorithm is identical with said process.

Table 1 crystal original size (T _o, R _o, L _o) under the effectiveness affects formula

The 1st calculated value of table 2 crystalline size

Table 3 crystal is adjusted size (T the 1st time ₁, R ₁, L ₁) under the effectiveness affects formula

The 2nd calculated value of table 4 crystalline size

Table 5 crystalline size the 2nd is adjusted back (T ₂, R ₂, L ₂), the contrast of 65cm place efficiency calculation value and measured value on the detector center line

Table 6 crystalline size is adjusted back (T for the 2nd time ₂, R ₂, L ₂), the contrast of efficiency calculation value and measured value

Table 7 crystalline size the 2nd is adjusted back (T ₂, R ₂, L ₂), the contrast of efficiency calculation value and efficiency measurement value

Claims (1)

1. the germanium crystal dimension automatic regulation method of a high purity germanium detector passive efficiency scale comprises the steps:

(1), measures and obtain different E more than three or three at place, a measuring position _iEnergy gamma-rays full energy peak detection efficiency measured value η _Mea(E _i);

(2) set that crystal dead band thickness is that T, crystal radius are that R, crystal length are L in the HpGe crystalline size parameter, the crystal original size T that provides according to the high purity germanium detector product description ₀, R ₀, L ₀, carry out Monte Carlo simulation and calculate, obtain corresponding each E in the step (1) _iEnergy gamma-rays full energy peak detection efficiency calculated value η _Cal(E _i);

(3) if each E _iEnergy gamma-rays efficiency calculation value η _Cal(E _i) and corresponding E _iEnergy gamma-rays efficiency measurement value η _Mea(E _i) between relative error do not reach requirement, then with current crystal dead band thickness T _nBe initial value, change crystal dead band thickness T=T one by one _n+ N* Δ t, wherein n since 0 for integer, Δ t be step-length, N be integer, this moment R _nAnd L _nRemain unchanged, at different E _iEnergy carries out Monte Carlo Calculation respectively and obtains a series of and the corresponding different E of crystal dead band thickness T _iEnergy gamma-rays efficiency calculation value η _Cal(E _i, T); Adopt line fitting method, obtain current crystalline size T _n, R _n, L _nDown, crystal dead band thickness T is to different E _iEnergy gamma-rays efficiency calculation value influence formula δ η _Cal(E _i)=f _{T, Ei}(T);

(4) in like manner obtain crystal radius R to different E _iEnergy gamma-rays efficiency calculation value influence formula δ η _Cal(E _i)=f _{R, Ei}(R), crystal length L is to different E _iEnergy gamma-rays efficiency calculation value influence formula δ η _Cal(E _i)=f _{L, Ei}(L); Thus, draw at current crystalline size T _n, R _n, L _nDown, crystal dead band thickness T, crystal radius R, crystal length L are to different E _iTotal formula δ η that influences of energy gamma-rays efficiency calculation value _Cal(E _i)=f _{T, Ei}(T)+f _{R, Ei}(R)+f _{L, Ei}(L);

(5) to different E _iEnergy settings δ η _Cal(E _i) be current E _iEnergy gamma-rays efficiency calculation value and corresponding E _iEnergy gamma-rays efficiency measurement value η _Mea(E _i) between the negative of relative error, with the different E of above-mentioned steps (4) gained _iTotal formula δ η that influences of energy gamma-rays efficiency calculation value _Cal(E _i)=f _{T, Ei}(T)+f _{R, Ei}(R)+f _{L, Ei}(L) combine and be built into system of linear equations, can obtain crystal size T the n+1 time _N+1, R _N+1, L _N+1

(6) with new crystalline size T _N+1, R _N+1, L _N+1Carry out the Monte Carlo efficiency calculation, obtain each new E _iIf energy gamma-rays efficiency calculation value is each new E _iEnergy gamma-rays efficiency calculation is worth its corresponding E _iThe error of energy gamma-rays efficiency measurement value does not also reach requirement, and then repeating step (3) is to step (5), until new different E _iEnergy gamma-rays efficiency calculation is worth its corresponding E _iThe error of energy gamma-rays efficiency measurement value in allowed band, this moment end operation, thereby obtain the fit value of crystal dead band one-tenth-value thickness 1/10 T, crystal radius value R, crystal length L.

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