In the radiation protection test, it is often necessary to detect the X ray device in the workplace where the radiation duration is short (MS - s magnitude, or even ns - MS). Computer X - ray photography (CR) and digital X - ray photography (DR) and interventional radiography used in medical diagnosis have single irradiation time of MS - s in the mode of photography, and the single irradiation time of the pulse X - ray machine in industrial applications can even reach ns - MS. In order to obtain accurate detection results, the instrument should be selected in the case of short duration of radiation, and the instrument should be selected for response time less than ray irradiation time. Otherwise, the measurement value of the instrument should be corrected. According to the classical electronics theory, for the modified formula of the time response of the series circuit (RC circuit) composed of resistance R and capacitance C, the measurement results of the ionization chamber type instrument can be used to judge whether the radiation level in the tested workplace meets the national standard requirements. At present, there is no conclusion about the time response correction method of the radiation detection instrument. Therefore, it is very necessary to study the time of the radiation detection instrument. In this study, 4 types of detection equipment used in radiation protection detection are used to measure the duration of radiation duration of 50 - 500ms, and the time response correction formula is used to correct and discuss the measurement value of the instrument. It will help to promote the rational application of the time response correction method of the common radiation detection instruments.

Materials and methods

1. measurement object: the 4 types of dosimeters are the 6150AD6+6150AD- B dosimeter produced by German Automess company, FH40G+FHZ672E-10 type dosimeter produced by Thermo company in the United States, 451P ionization chamber dosimeter produced by Fluke company in the United States and AT1123 type dosimeter produced by Belarus ATOMTEX.

2. instrument: Brio medical X radiography equipment produced by GE company.

3. measurement method: the operating voltage 80kV, current 200mA, irradiation duration are set to 500, 200, 100 and 50ms respectively. After irradiation, the maximum equivalent rate of peripheral dose equivalent rate displayed by each dosimeter at 30cm outside the protective door is recorded, and this value is multiplied by the calibration factor of instrument to obtain the measured peripheral dose equivalent rate. For ionization chamber dosimeter, the time correction formula of RC circuit is:

D (T) =h (1-e-t/ tau)

In the formula, D (T) is the peripheral dose equivalent rate measured by the t time instrument, mu Sv/h; h is the actual peripheral dose equivalent rate of the radiation site, mu Sv/h; t is time, s; tau is the time constant of the RC circuit, s, the instrument response time is 2.197 tau.

4. quality control: 4 types of dosimeters have been calibrated or calibrated by the Metrology Research Institute of China. They are all in the period of validity of calibration or calibration.

Result

Type 1.AT1123 dosimeter: the AT1123 value dosimeter in the short time measurement mode (>30ms) is shown in Table 1 with the change of the irradiation duration. The relative standard deviation of each sample was <13% at the same irradiation time. For all 9 measurements measured by 50~500ms, the relative standard deviation of samples is <10%. The measurement is carried out in the short time measurement mode of the AT1123 dosimeter. The measurement value of the instrument is not related to the duration of the irradiation. The results of the measurement can not be corrected by the time response, which is in accordance with the instrument specification.

Type 2.451P ionization chamber dosimeter, 6150AD6+6150AD- B dosimeter and FH40G+FHZ672E-10 dosimeter: the measured values of 3 dosimeters are listed in table 2~4, and the data in the table have been deducted from the background. The range of measured values in Table 2 is 0.47~5.07 mu Sv/h, the range of measured values in Table 3 is 0.53~5.20 mu Sv/h, and the range of measured values in Table 4 is 0.64~7.76 mu Sv/h. The measured values of these 3 kinds of equipment vary with the duration of irradiation, and the difference of the measured values of the same instrument can reach one order of magnitude and the average value of the display of the ATl123. The comparison difference is close to two orders of magnitude. However, when measured under the same irradiation time, the standard deviation of samples was small and the relative standard deviation was <10%.

The response time between 3. hours was corrected: the longest duration (500ms) of type AT1123 radiation was selected (41.4 Sv/h).

In formula (1) the actual peripheral dose equivalent rate of H in the radiation site; it is necessary to point out that the 6150AD6+6150AD- B dosimeter and FH40G+FHZ672E-10 dosimeter are the plastic scintillation detectors, and this study also uses the formula (1) to correct the feasibility. The measured values (5.07, 5.20 and 7.76 mu Sv/h) of the 451P ionization chamber dosimeter, 6150AD6+6150AD- B dosimeter and FH40G+FHZ672E-10 dosimeter at the same time (5.07, 5.20 and 7.76 mu) are respectively used as D (1) substitution formula (1), and can be calculated to be 3.82, 3.72 and 2.41s respectively.

discuss

According to the above measurement and analysis, the measurement values of 451P dosimeter, 6150AD6+6150AD- B dosimeter, FH40G+FHZ672E-10 dosimeter and FH40G+FHZ672E-10 dosimeter in the case of short irradiation duration can be corrected by time response. The R values in formula (1) are 3.82, 3.72 and 2.41s. However, according to the relevant research, the R value calculated at this time is consistent with the time constant of the instrument. Further discussion is needed.

In addition, it is necessary to point out that the radiation field of this measurement is higher. When the radiation level is lower than one order of magnitude and the irradiation time is <200ms, the measurement value of the instrument will be close to the background. The statistical fluctuation of the background will have a great influence on the correction result, and can not even be corrected. For example, the actual circumference dose equivalent rate is 2.5 mu Sv/h and the irradiation time is 200ms. According to the formula (1) and the R value calculated above, it can be deduced that the measured values of the 3 instruments are only 0.15, 0.18 and 0.12 micron Sv/h, which are very close to the background value 0.10 Sv/h.

The results of this study can provide data support for the formulation and revision of the national occupational health standard radiological diagnostic radiological protection requirements. Source PDF download link

This article can be used directly in common words in abbreviations

In this article, some common words which are familiar to the following radiology workers will be allowed to be directly used in the writing and publication of their abbreviations.

Interleukin (IL)

Two ethyl pyrocarbonate (DEPC)

Leukocyte (WBC)

Polyacrylamide gel electrophoresis (PAGE)

Benzyl sulfonyl fluorine (PMSF)

Polyvinylidene fluoride (PVDF)

Alanine aminotransferase (ALT)

Streptomycin biotin complex (SABC)

Energy transfer line density (LET)

Clinical target volume (CTV)

Magnetic resonance imaging (MRI)

Phosphate buffer solution (PBS)

Propidium iodide (PI)

Three dimensional conformal radiotherapy (3D-CRT)

Gross tumor target volume (GTV)

Sodium alkyl sulfate (SDS) (SDS)

Two amino diphenyl amine (DAB)

Four methyl azazolide salt (MTT)

Two methyl sulfoxide (DMSO)

Hematoxylin eosin staining (HE)

Quinoline formic acid (BCA)

Fetal bovine serum (FBS)

4, 6- two amid based -2- phenyl indole (DAPI)

Body mass index (BMI)

Reverse transcriptional polymerase chain reaction (RT-PCR)

Aspartate aminotransferase (AST)

Interferon (IFN)

Intensity modulated radiation therapy (IMRT)

Red blood cell (RBC)

Endanger organs (OAR)

Radiosensitization ratio (SER)

Volume rotation intensity modulated radiation therapy (VMAT)

Planned target area volume (PTV)

Single photon emission computed tomography (SPECT)

Computed tomography (CT)

Fluorescein isothiocyanate (FITC)

Dose length product (DLP)

Transforming growth factor (TGF)

Dose volume histogram (DVH)

Tumor necrosis factor (TNF)