CN1948996A - Passive efficient graduating method of radiation detector - Google Patents

Abstract

The invention relates to high pure germanium zinc cadmium telluride radiation measurement detector efficiency graduating method. It doesn't need to exactly gain crystal size and sensitive volume size, only needs to roughly give the crystal size according to detector specification, combines efficiency carry over factor based on Monte-Carlo direct calculating to fast and exactly realize passive efficiency graduation for the detector.

Description

The method of radiation detector passive efficiency scale

Technical field

The invention belongs to the radiometric technique field, be specially the efficiency calibration method of radiation measuring detectors such as a kind of HpGe, cadmium zinc telluride.

Background technology

Usually need carry out efficiency calibration to used detector in actinometry, efficiency calibration generally can be divided into experiment scale and two kinds of methods of passive efficiency scale.Laboratory scale expense is big, the time is long, the scope of application is little; The passive efficiency scale method has obtained extensive attention in recent years because of having advantages such as speed is fast, applied widely.About the passive efficiency scale problem of detector, study both at home and abroad more, as efficient experimental formula, Monte Carlo simulation calculating etc.Utilize Monte Carlo method that semiconductor detectors such as HpGe, cadmium zinc telluride are carried out efficiency calculation at present, generally all be accurately to obtain directly to carry out analog computation after the crystalline size data, the key that direct modeling is calculated is accurately to obtain crystal and sensitive volume size thereof, but the sensitive volume size generally is difficult to determine, and spended time is also long; It relatively is suitable for the efficiency calculation of specific detector, if change detector, then needs again the new detector cost plenty of time is determined its crystal accurate dimension.So direct calculation method is poor for applicability, spended time is long.From practical experience, direct calculation method generally needed for two thoughtful times all around could finally determine rational crystalline size.

Summary of the invention

The object of the present invention is to provide a kind of Monte Carlo efficient transmission factor method that realizes the radiation detector passive efficiency scale quickly and accurately.

This method comprises the steps:

(1) at measuring position (x _o, y _o, z _o) locate, be that the gamma-rays of E carries out a normal experiment and measures to energy, obtain conventional efficient value ε _Mea. (E, x _o, y _o, z _o);

(2) with above-mentioned conventional efficient value ε _Mea.(E, x _o, y _o, z _o) and Monte Carlo direct counting yield value ε _MC.(E, x _o, y _o, z _o) compare, obtain the gamma-ray efficient transmission factor of this E energy κ _E,

${\mathrm{\κ}}_E=\frac{{\mathrm{\ϵ}}_{\mathrm{Mea}.}(E,x_o,y_o,z_o)}{{\mathrm{\ϵ}}_{\mathrm{MC}}(E,x_o,y_o,z_o)};$

(3) for these other positions of E energy gamma-rays (x, y, detection efficiency z), direct counting yield ε in the Monte Carlo _MC(E, x, y, stack efficient transmission factor κ on basis z) _E, that is: ε (E, x, y, z)=κ _Eε _MC(y z), just can realize the passive efficiency scale of this energy exactly for E, x.

Method provided by the present invention does not need accurately to obtain crystalline size and sensitive volume size, and only need according to the crystalline size that provides roughly on the detector instructions, directly calculate joint efficiency transmission factor on the basis in the Monte Carlo, can realize the passive efficiency scale of detector quickly and accurately.It has advantages such as method is easy, applicability is strong, only needs several hrs can finish the passive efficiency scale problem of detector, is particularly suitable for the passive efficiency scale of detector in batches.

Description of drawings

Fig. 1 is radioactive source experiment location arrangements synoptic diagram.

Embodiment

For the gamma-ray efficiency calibration of particular energy (E), only need at certain (x of place, measuring position _o, y _o, z _o) carry out experiment measuring one time, with conventional efficient value ε _Mea.(E, x _o, y _o, z _o) and Monte Carlo direct counting yield value ε _MC.(E, x _o, y _o, z _o) compare, obtain the gamma-ray efficient transmission factor of this energy (E) κ _E:

${\mathrm{\κ}}_E=\frac{{\mathrm{\ϵ}}_{\mathrm{Mea}.}(E,x_o,y_o,z_o)}{{\mathrm{\ϵ}}_{\mathrm{MC}}(E,x_o,y_o,z_o)}---\left(1\right)$

(detection efficiency z) does not then need the measurement that experimentizes again for x, y, but at direct counting yield ε for these other positions of E energy gamma-rays _MC(E, x, y, stack efficient transmission factor κ on basis z) _E, promptly

ε(E，x，y，z)＝κ _E·ε _MC(E，x，y，z) (2)

For other energy (as E ₂) efficiency calibration of ray, similar with said process; Also only need ad-hoc location is carried out experiment measuring one time, obtain this ENERGY E ₂Efficient transmission factor κ _E2, can realize the passive efficiency scale of this energy quickly and accurately.

Be example with the passive efficiency scale of HpGe (HPGe), cadmium zinc telluride (CZT) detector respectively below, Monte Carlo efficient transmission factor method is verified.Confirm that Monte Carlo efficient transmission factor method can realize the passive efficiency scale of actinometry semiconductor detectors such as HpGe, cadmium zinc telluride quickly and accurately.

1. high purity germanium detector passive efficiency scale

With 344keV, 662keV, 1332keV energy gamma-rays is example, and Monte Carlo efficient transmission factor method is verified in the application of HPGe detector passive efficiency scale;

Fig. 1 is radioactive source experiment location arrangements figure, and d is the axial distance of radioactive source to detector, and the R radioactive source is to the radial distance of detector; The HPGE detector is the GEM30P4 of an Ortec company product, and product description provides the HPGE crystal data and is: crystal dead band thickness 0.7mm, crystal diameter 68.8mm, crystal length 39.5mm.

For 1332keV energy gamma-rays, at d=25.0cm, the R=0.0cm position is carried out experiment measuring one time, obtains this position conventional efficient and is: 3.93E-04, the direct counting yield in Monte Carlo is 4.78E-04, this energy efficiency transmission factor κ ₁₃₃₂=0.822.Detection efficiency for other positions then can be passed through efficient transmission factor κ ₁₃₃₂Be superimposed upon on the direct result calculated of efficient and obtain.Table 1 is for introducing the contrast of efficient transmission factor front and back counting yield and conventional efficient.

Obtain efficient transmission factor κ for the 662keV energy ₆₆₂=0.834.Table 2 is the contrast of other position efficiency calculation values and experiment value.Equally, obtain efficient transmission factor κ for the 344keV energy ₃₄₄=0.860.Table 3 is the contrast of other position efficiency calculation values and experiment value.

Introduce the efficient transmission factor as can be seen from table 1, table 2, table 3 after, the detection efficiency calculated value is more near experiment value.

Table 1 is introduced the contrast of efficient transmission factor κ front and back 1332keV energy counting yield and conventional efficient

R(cm)	d(cm)	Conventional efficient ε Mea.	Direct calculation method		Efficient transmission factor method
							Counting yield	With experimental bias	Counting yield	With experimental bias
			0	25	3.93E-04	4.78E-04					21.62％	3.93E-04	0.00％
35	2.09E-04	2.56E-04					22.45％	2.10E-04	0.65％
				65	6.45E-05	7.86E-05				21.87％	6.46E-05	0.17％
10	25	3.42E-04					4.14E-04	20.93％	3.40E-04				-0.59％
			35	1.92E-04	2.37E-04	23.29％				1.95E-04	1.34％
	65	6.25E-05					7.67E-05	22.68％	6.30E-05			0.84％
			20	25	2.45E-04	2.97E-04				21.50％	2.44E-04		-0.13％
35	1.57E-04	1.94E-04					23.28％	1.60E-04	1.34％
				65	5.85E-05	7.14E-05				22.00％	5.87E-05	0.28％

Table 2 is introduced the contrast of efficient transmission factor κ front and back 662keV energy counting yield and conventional efficient

R(cm)	d(cm)	Conventional efficient ε Mea.	Direct calculation method		Efficient transmission factor method
							Counting yield	With experimental bias	Counting yield	With experimental bias
			0	25	7.27E-04	8.71E-04					20.87％	7.27E-04	0.00％
35	3.93E-04	4.67E-04					19.69％	3.89E-04	-0.96％
				65	1.18E-04	1.42E-04				18.91％	1.19E-04	1.03％
10	25	6.28E-04					7.48E-04	19.08％	6.24E-04				-0.68％
			35	3.60E-04	4.31E-04	19.67％				3.59E-04	-0.19％
	65	1.16E-04					1.39E-04	19.51％	1.16E-04			-0.33％
			20	25	4.39E-04	5.31E-04				19.88％	4.43E-04		0.80％
35	2.91E-04	3.48E-04					18.76％	2.90E-04	-0.18％
				65	1.08E-04	1.29E-04				21.13％	1.08E-04	-0.83％

Table 3 is introduced the contrast of efficient transmission factor κ front and back 344keV energy counting yield and conventional efficient

R(cm)	d(cm)	Conventional efficient ε Mea.	Direct calculation method		Efficient transmission factor method
							Counting yield	With experimental bias	Counting yield	With experimental bias
			0	35	7.29E-04	8.48E-04					16.32％	7.29E-04	0.00％
65	2.22E-04	2.60E-04					16.65％	2.23E-04	0.32％
				10	35	6.64E-04				7.79E-04	17.31％	6.70E-04	0.88％
65	2.19E-04	2.51E-04	14.84％				2.16E-04	-1.24％
					20	35			5.42E-04	6.32E-04	16.69％	5.43E-04	0.35％
65	2.04E-04	2.34E-04	14.92％	2.02E-04			-1.17％

2. cadmium zinc telluride detector passive efficiency scale

With 59.5keV, 662keV, 1332keV energy gamma-rays is example, and efficient transmission factor method has been carried out experimental verification in the application of CZT detector passive efficiency scale.The CZT detector is the CZT500 of RITEC company (S) product, and it is 10 * 10 * 5mm that product description provides the CZT crystalline size ³

For 59.5keV energy gamma-rays, at d=10.0cm, the R=0.0cm position is carried out experiment measuring one time, obtains this position conventional efficient and is: 6.08E-04, the direct counting yield in Monte Carlo is 6.32E-04, this energy efficiency transmission factor κ _59.5=0.963.Detection efficiency for other positions then can be passed through efficient transmission factor κ _59.5Be superimposed upon on the direct result of calculation of efficient and obtain.Table 4 is for introducing the contrast of efficient transmission factor front and back counting yield and conventional efficient.

Equally, obtain efficient transmission factor κ for the 662keV energy ₆₆₂=0.918.Table 5 is the contrast of other position efficiency calculation values and experiment value.Introduce the efficient transmission factor as can be seen from table 4, table 5 after, the detection efficiency calculated value is more near experiment value.

What deserves to be explained is that the efficient transmission factor that detector obtains waits the conditional situation of shielding also suitable equally after adding collimating apparatus for detector under exposed condition.

With 1332keV energy gamma-rays is example, and at d=11.0cm, the R=0.0cm position obtains this energy efficiency transmission factor κ under the exposed condition of detector ₁₃₃₂=0.847; As shown in table 6, add passive efficiency scale after the collimating apparatus, efficient transmission factor κ for detector ₁₃₃₂=0.847 still is suitable for.

Table 4 is introduced the contrast of efficient transmission factor κ front and back 59.5keV energy counting yield and conventional efficient

d(cm)	R(cm)	Conventional efficient ε Mea.	Direct calculation method		Efficient transmission factor method
							Counting yield	With experimental bias	Counting yield	With experimental bias
			10	0	6.08E-04	6.32E-04					3.84％	6.08E-04	0.00％
5	5.25E-04	5.53E-04					5.33％	5.33E-04	1.43％
				10	3.15E-04	3.26E-04				3.60％	3.14E-04	-0.23％
15	1.74E-04	1.84E-04					5.53％	1.77E-04	1.62％
				20	1.05E-04	1.11E-04				5.35％	1.07E-04	1.45％
25	6.72E-05	7.26E-05					7.99％	6.99E-05	3.99％
				22	0	1.33E-04				1.34E-04	0.94％	1.29E-04	-2.80％
5	1.30E-04	1.34E-04	3.32％				1.29E-04	-0.50％
					10	1.16E-04			1.20E-04	3.71％	1.16E-04	-0.13％
15	9.43E-05	9.86E-05	4.53％				9.49E-05	0.66％
					20	7.30E-05			7.62E-05	4.35％	7.34E-05	0.49％
25	5.56E-05	5.81E-05	4.41％				5.59E-05	0.54％

Table 5 is introduced the contrast of efficient transmission factor κ front and back 662keV energy counting yield and conventional efficient

d(cm)	R(cm)	Conventional efficient ε Mea.	Direct calculation method		Efficient transmission factor method
							Counting yield	Counting yield	Counting yield	With experimental bias
			10	0	2.32E-05	2.53E-05					8.93％	2.32E-05	0.00％
5	1.85E-05	2.08E-05					12.39％	1.91E-05	3.18％
				10	1.20E-05	1.33E-05				10.93％	1.22E-05	1.83％
20	4.74E-06	5.44E-06					14.67％	4.99E-06	5.27％
				22	0	5.19E-06				5.43E-06	4.58％	4.98E-06	-3.99％
5	4.63E-06	5.16E-06	11.48％				4.74E-06	2.34％
					10	4.57E-06			4.80E-06	5.01％	4.41E-06	-3.60％
15	3.46E-06	3.65E-06	5.58％				3.35E-06	-3.08％
					20	2.69E-06			3.05E-06	13.28％	2.80E-06	3.99％
25	2.19E-06	2.43E-06	11.21％				2.23E-06	2.09％

Table 6 is introduced the contrast of efficient transmission factor κ front and back 1332keV energy counting yield and conventional efficient

d(cm)	R(cm)	Conventional efficient ε Mea.	Direct calculation method		Efficient transmission factor method		Remarks
								Counting yield	With experimental bias	Counting yield	With experimental bias
			8	0	8.51E-06	1.01E-05						18.66％	8.55E-06	0.51％	The collimating aperture of collimating apparatus is opened
5	4.30E-07	4.89E-07					13.55％	4.14E-07	-3.82％
				10	4.34E-08	5.53E-08				27.38％	4.68E-08	7.89％
15	5.35E-08	6.54E-08					22.26％	5.54E-08	3.56％
				24	0	9.78E-07				1.26E-06	29.04％	1.07E-06	9.30％
5	7.27E-07	8.45E-07	16.26％				7.16E-07	-1.53％
					10	1.46E-07			1.58E-07	8.18％	1.34E-07	-8.37％
15	5.29E-08	5.79E-08	9.39％				4.90E-08	-7.34％
					8	5			2.18E-07	2.63E-07	20.63％	2.23E-07	2.18％	Collimating aperture stops up
15	5.35E-08	6.45E-08	20.49％	5.46E-08			2.06％

Claims (1)

1. the method for a radiation detector passive efficiency scale comprises the steps:

(1) at measuring position (x _o, y _o, z _o) locate, be that the gamma-rays of E carries out a normal experiment and measures to energy, obtain conventional efficient value ε _Mea. (E, x _o, y _o, z _o);

(2) with above-mentioned conventional efficient value ε _Mea. (E, x _o, y _o, z _o) and Monte Carlo direct counting yield value ε _MC(E, x _o, y _o, z _o) compare, obtain the gamma-ray efficient transmission factor of this E energy κ _E,

${\mathrm{\κ}}_E=\frac{{\mathrm{\ϵ}}_{\mathrm{Mea}.}(E,x_o,y_o,z_o)}{{\mathrm{\ϵ}}_{\mathrm{MC}}(E,x_o,y_o,z_o)};$

(3) for these other positions of E energy gamma-rays (x, y, detection efficiency z), direct counting yield ε in the Monte Carlo _MC(E, x, y, stack efficient transmission factor κ on basis z) _E, that is: ε (E, x, y, z)=κ _Eε _MC(y z), just can realize the passive efficiency scale of this energy exactly for E, x.