Due to the progress of nuclear detection technology and electronic science and technology, one instrument and one sample can simultaneously measure α and β radioactivity, which saves manpower and material resources and brings convenience to work.

Experience has proved that making samples of 0.05 ~ 0. 18 mg/mm2 (generally 0. 1mg/mm2) can not only meet the requirements of measuring α in thick layers (saturated layers greater than the effective thickness) but also meet the requirements of measuring β in thin layers (less than the maximum sampling amount).

For different substances to be tested, the requirement of 0. 1mg/mm2 is not fixed. For example, it is difficult to produce a large amount of solid residues in relatively pure drinking water (although some water samples can be treated with a little more sulfuric acid and precipitated with barium chloride, and more water samples can be taken). Can be relaxed to 0.05mg/mm2 according to the specific situation. For samples with rich sources, the sampling amount can be increased from 0. 15 to 0. 18 mg/mm2, or even 0.3mg/mm2.

Under the condition of pH4, radioactive substances in drinking water samples were precipitated and adsorbed by barium sulfate and activated carbon, and the precipitate was burned to make a sample source of 0.05mg/mm2. Biological sample: the burnt sample ash is made into a sample source of 0.05mg/mm2; Soil sample: Take 0. 1mg/mm2 of treated soil as the sample source, and put it on a low background α and β measuring instrument to measure α and β radioactivity.

It is important to note that when calibrating (calibrating) the instrument (measuring the efficiency of the standard source), the quality of the standard source must be consistent with it, otherwise it will increase the uncertainty of determination.

tool

Low background α, β measuring instrument.

reagent

Sulfuric acid.

muriatic acid

Barium chloride solution (100g/l).

EDTA solution (10g/L).

α source natural uranium powder standard source (specific activity 10Bq/g) or 24 1Am powder standard source (specific activity 10.2Bq/g) and natural uranium (or 239Pu) check the non-point source.

Beta source potassium chloride powder standard source (specific activity 14.4Bq/g) and 90Sr-90Y inspection surface source.

Activated carbon 20g of activated carbon was soaked in 200mLEDTA solution or 200mL( 1+99)HCl, stirred and left overnight. Pour out the supernatant, then filter, wash the activated carbon with water to neutrality, put it in a drying oven and dry it at 105℃.

Sample collection and pretreatment

(1) water sample

Sample collection:

1) When collecting river water, surface water (the first residential water intake point) and main drainage water samples, they should be collected at a certain depth below the water surface; If the water is deep, samples of different depths should be collected at the same time; When the water surface is wide, a few samples should be taken from the left, middle and right of the estuary.

2) Select representative industrial water, tap water and upstream water as control points, and collect samples at the same time.

3) Samples collected from polluted water bodies should be representative, and the collection methods can be divided into three types according to wastewater discharge, wastewater properties, analysis requirements and monitoring purposes: instantaneous collection method, average collection method and individual collection method.

4) The sampling tool can be a glass bottle without radioactive pollution (it is best to use a plastic bucket as the container for water samples), and the sampling bottle (bucket) can be washed with water for many times at the collection site before collection.

5) When collecting in shallow water, be careful not to stir the mud at the bottom of the water.

6) Sampling bottles (barrels) must have fixed numbers and be earmarked for special purposes to prevent cross-contamination.

7) The sampling amount (volume) depends on the analysis item, generally 2 ~ 10L, and the gap of110 should be ensured in the container; Under no circumstances can the container be filled with water samples.

Sample pretreatment:

Sampling records and sample labels should be filled in when sampling, and the collected water samples should be acidified with nitric acid or hydrochloric acid immediately (acidification pH ≤ 2); After standing for 24 hours, the supernatant was taken for analysis (except radon measurement).

If the water sample is turbid, it should be filtered before acidification.

(2) Soil samples

Sample collection:

Soil sampling sites should be selected in a flat place and distributed appropriately according to needs. Diagonal sampling method and plum blossom sampling method should be adopted when sampling. According to different monitoring purposes, the sampling depth is 5cm. When sampling, draw a square of 10cm× 10cm with a knife, and take out the soil sample with a vertical depth of 5cm; Take the soil below 20cm for the deep soil.

In order to collect contaminated soil samples, the natural conditions, agricultural production environment, soil properties and pollution history of the investigation area were investigated at first. On this basis, sampling points are set as needed to represent the pollution situation of a certain area, and an unpolluted area is selected as a control.

Samples of river bottom silt should be collected in the same place as water samples for comparison.

Sample pretreatment:

Wrap the soil (river bottom mud) samples collected on site with cleaning paper (plastic bag) or put them in other clean containers, and indicate the sampling time, place, sampling area, depth and the surrounding conditions of the sampling point.

Natural drying of soil samples in the laboratory, or drying at 1 10℃, removing impurities such as stones and grass, and weighing.

Put the dried soil sample on a clean flat plate and grind it into a square with a thickness of 1 ~ 2 cm. Draw a crosshair along the diagonal of the square and divide the sample into four parts. Draw a square with the intersection of intersecting lines as the center, and remove all the soil outside the square. Repeatedly eliminate until the residual soil sample reaches about 300g, put the soil sample into a high-temperature furnace and burn it at 500℃ for1~ 2 hours. After cooling, it is ground in a mortar, sieved with a 40 ~ 100 mesh sieve, mixed evenly, and bottled for inspection.

(3) Biological samples

Vegetables:

Remove the roots of the collected vegetable samples, wash them, and weigh the fresh samples after the surface moisture is completely dried or dried. Chop fresh samples, air-dry or put them in a blast drying box, put the dried samples in a porcelain evaporating dish and carbonize them in an electric furnace. In the process of carbonization, prevent the sample from catching fire, so that some ash particles in the sample are taken away by hot air and cause losses. And then transferred to a high-temperature furnace, the temperature is gradually increased from low to 400-450 DEG C, and the sintering is often observed to prevent. Completely ashed ash powder should be gray and loose. If the ash powder is still black, it should be taken out, cooled, wetted and evaporated with 6mol/LHNO3 or 6mol/LNaNO2 solution, and then ashed again.

Put the completely ashed sample at room temperature, weigh the ash mass and save it for later use.

Rice:

In the morning and evening harvest season, the paddy fields that must be monitored are selected, and about 500g mixed samples are collected from different parts to understand the situation of irrigation and fertilization (especially potassium fertilizer) in paddy fields. Remove impurities from the collected rice samples, weigh fresh samples, moisten the samples with 30g/LNaAc solution, put them in a porcelain evaporating dish, carbonize them in an electric furnace, and then transfer them to a high-temperature furnace for ashing at 450℃. The completely ashed ash powder should be grayish white. If the ashing is not complete, 6 mol/L nano _ 2 solution can be used to treat the vegetable samples, re-ashing and storing for later use.

Fish samples:

Dissect fish samples captured in polluted river sections (or control points), remove scales and internal organs, wash, dry or dry in the sun, and weigh a certain amount of fish meat and bones from each fish (if there are only small fish, it is not necessary to analyze fish meat and bones separately).

Chop the dried fish samples respectively, put them into a weighed porcelain evaporating dish, carbonize them on an electric furnace, and then transfer them to a high-temperature furnace when there is no smoke. Gradually raise the temperature, and finally keep it at about 450℃ until it becomes loose gray ash. After cooling to room temperature, weigh the ashes and keep them for later use.

Meat samples:

After removing bones and internal organs, make samples according to the preparation method of fish samples for later use.

Sample preparation, measurement and result calculation

Water sample: the prepared solid residue powder was weighed as 0.05mg/mm2.

Soil sample: the weight of the treated powder is 0. 1mg/mm2.

Biological sample: weigh the prepared ash to 0.05 mg/mm2.

Spread the above-mentioned weighed samples evenly in the sample tray, and then make formal measurement after checking the instrument with surface standard source. Measure the α and β counting rates, measure the background, and find out their respective net counting rates. According to different quality requirements, find out the standard source efficiency of corresponding quality and calculate α and β radioactivity.

Result calculation

The total α and β radioactivity in water, soil and living things are calculated by formulas [(66.60), (66.63)], [(66.6 1), (66.65)] and [(66.62), (66.66)] respectively.

When the total beta radioactivity in mineral water is greater than 1.0Bq/L, the total beta radioactivity in food (organism) should be reduced by 40K, and the calculation method is shown in formula (66.64).

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This chapter was written by Guo Dongfa (Analysis and Testing Center of Beijing Institute of Geology, Nuclear Industry).

Li Yaping, Ni Chuanzhen, Li Jiasheng, Deng Xiuwen and Yan Shidong (Guangdong Institute of Mineral Application).