GB 14883.8-2016National Food Safety Standard -- Determination of radioactive substances plutonium - 239 and plutonium - 240 in foods (English PDF)

3.1 Reagents

3.1.1 hydrochloric acid (HCl).

3.1.2 hydrofluoric acid (HF).

3.1.3 nitric acid (HNO3).

3.1.4 Ammonium nitrate (NH4NO3).

3.1.5 hydroxylamine hydrochloride (NH2OH · HCl).

3.1.6 Sodium nitrite (NaNO2).

3.1.7 sodium hydroxide (NaOH).

3.1.8 Hydrogen peroxide (H2O2).

3.2 Reagent preparation

3.2.1 hydrochloric acid - a mixture of hydrofluoric acid. hydrochloric acid solution will 180mL1mol L/poured into 500mL volumetric flask, add 20mL0.26mol/L Hydrofluoric acid solution and diluted with water to the mark.

3.2.2 hydrochloric acid - a mixture of nitric acid. hydrochloric acid was poured into 500mL to 333mL volumetric flask, add 9.4mL nitric acid and diluted with water to the mark.

3.2.3 Ammonium nitrate - nitric acid mixture. 5 by volume 0.1mol/L solution of nitric acid and three volumes of 0.4mol/L ammonium nitrate solution mixed.

3.2.4 nitric acid solution. 1mol/L, 3mol/L, 7mol/L, 7.5mol/L and 10mol/L.

3.2.5 sodium hydroxide solution. 6mol/L.

3.2.6 2mol/L hydroxylamine hydrochloride solution. Weigh 139g of hydroxylamine hydrochloride, dissolved in an appropriate amount of water, diluted with water to 1L.

3.2.7 2mol/L sodium nitrite solution. Weigh 138g of sodium nitrite, dissolved in an appropriate amount of water, diluted with water to 1L.

3.2.8 251 × 8 trimethylamine polystyrene strong base anion exchange resin. 180µm ~ 250µm. The appropriate amount of resin is poured into 1L burn Cup, soaked in water for 24h, decanted upper layer of water. Poured into 10% sodium hydroxide solution, and the solution above the resin of about 2cm, stirring occasionally. About 2h After the liquid was decanted, washed once. After washing the decanted solution was poured into 1mol L hydrochloric acid solution/the solution above the resin of about 2cm, stirring occasionally.

2h after the acid was decanted, washed repeatedly with water until no chlorine ions in solution, dried spare.

Recycled resin. first with 10mL of hydrochloric acid - hydrofluoric acid mixed solution (3.2.1) with 1mL/min flow rate through the column, and then 20mL 7.5mol/L nitric acid through the column at the same flow rate, the standby.

3.3 Standard

239Pu standard solution. radioactive intensity of about 10 decays/(min · mL) magnitude, 0.5mol/L nitrate system.

5.1 Low background alpha spectrometer preparations

May refer to GB/T 16141 Recommended methods spectrometer working state selection, scale and energy efficiency calibration before measuring samples should the instrument background measurement.

5.2 Preparation of sample and assay

5.2.1 Sampling and pretreatment according to the provisions of GB 14883.1.

5.2.2 Weigh 5g ~ 10g (accurate to 0.001g) ash sample dissolved in 100mL porcelain evaporating dish, add 3mL ~ 5mL10mol/L nitrate Fluid wetted surface covered dish, on a hot plate heated slowly added dropwise 1mL of hydrogen peroxide, evaporated to near dryness. Coolish after adding 1mL ~ 2mL10mol/L solution of nitric acid and hydrogen peroxide 1mL, heated and evaporated to dryness. This repeated process several times until white or gray ash white.

5.2.3 to ash added 25mL7mol/L nitric acid solution, heated to dissolve the soluble fraction then slowly heated 10min, after cooling switch Transferred to a centrifuge tube and centrifuged 5min at 3000r/min. With 25mL7mol/L solution of nitric acid leaching is repeated once by centrifugation. Then 25mL hot 7mol/L nitric acid solution was washed raw evaporating dish and the residue was centrifuged, all supernatant was combined, insolubles were discarded.

5.2.4 plus 0.4mL2mol/L hydroxylamine hydrochloride solution into the clear liquid, placing added 0.4mL2mol/L sodium nitrite solution after 10min.

After standing 10min, the solution was heated to 50 °C, added 1.5g been handled well anion exchange resin (3.2.8), stir on the magnetic stirrer Mix 30min.

5.2.5 The solution was charged together with ion exchange resin columns (4.4), the flow rate of 1 drop/s ~ 2 drops/s through. Followed by 20mL Hydrochloric acid - nitric acid mixed solution (3.2.2), 25mL7mol/L nitric acid solution, 3mL3mol/L nitric acid solution, 1mL1mol/L nitric acid solution Column leaching rate of 1 drop/2s, discarded all the leachates.

5.2.6 The 10mL hydrochloric acid - hydrofluoric acid mixture (3.2.1) heated to about 50 °C, 2 drops/min ~ 3 drops a flow rate of desorption of plutonium/min., Originally collected effluent 7mL desorption solution.

5.2.7 desorption solution evaporated slowly to prevent splashing the samples, so as not to reduce the recovery. With 1mL1mol/L nitric acid solution to dissolve the dry matter, the Solution was transferred to the electrodeposition bath. 7mL with ammonium nitrate - nitric acid, (3.2.3) the container was washed 3 times, combined eluate into the electrodeposition bath.

5.2.8 at a voltage of 24V, 350mA current conditions electrodeposition 2h, before terminating added 1mL6mol/L hydroxide 1min when Sodium. Remove the stainless steel sheet, water rinse, dry 239 240Pu measuring radioactivity in the low background alpha spectrometer.

5.2.9 After measuring the sample surface immediately with 239Pu source counting efficiency standards, reagent blanks and instrument background measurement.

5.3 Determination of radiochemical recovery

Accurately weighed sample and sample measurement and other quality ash added 1.00mL239Pu standard solution (236Pu or 242Pu standard solution acceptable) 5.2.2 ~ 5.2.8 by the same operating procedures, after the measurement according to equation (1) calculate the radiochemical recovery.

EA0

Where.

R --- 239Pu radiochemical recovery;

N '--- radiochemical recovery measured in the corresponding channel region 239Pu net count rate measured in units of counts per minute (cpm);

N --- sample source 239Pu corresponding channel region of the net count rate measured in units of counts per minute (cpm);

E --- alpha spectrometer detection efficiency of 239Pu standard surface sources;

A0 --- radiochemical recovery added 239Pu amount measured in units of decays per minute (dpm).

5.4 Determination of the reagent blank value

Measure 200mL7mol/L nitric acid solution, according to 5.2.4 - 5.2.8 operating prepare a measurement sample reagent blank value in the sample after measurement Measurements.

9.1 Reagents

9.1.1 TOA extraction agent. Industrial pure. Before use purified by distillation under reduced pressure, mixed in equal volumes and xylene.

9.1.2 polychlorotrifluoroethylene (Kel-F). 150µm ~ 180µm.

9.1.3 nitric acid (HNO3).

9.1.4 Ammonia (NH4 · H2O).

9.1.5 oxalic acid (H2C2O4).

9.1.6 hydrochloric acid (HCl).

9.1.7 acetone (CH3COCH3).

9.1.8 Ethanol (C2H6O).

9.2 Reagent preparation

9.2.1 8mol/L nitric acid solution. 65% 552mL amount of nitric acid, diluted to 1L.

9.2.2 oxalic acid - nitric acid, (A). concentrations of nitric acid and oxalic acid, respectively 0.4mol/L and 2mol/L.

9.2.3 oxalic acid - nitric acid mixed solution (B). concentrations of nitric acid and oxalic acid were 0.05mol/L and 0.3mol/L.

9.2.4 2mol/L sodium nitrite solution. Weigh 138g of sodium nitrite, dissolved in an appropriate amount of water, diluted with water to 1L.

9.2.5 10mol/L hydrochloric acid solution. Measure 833mL of hydrochloric acid, diluted to 1L.

9.2.6 nitro hydrochloric acid. one volume of hydrochloric acid and nitric acid is mixed with 3 volumes, also known as aqua regia.

9.3 Standard

239Pu standard solution. Same as 3.3.

11.1 Low background alpha spectrometer preparations

With 5.1.

11.2 Sample preparation and assay

11.2.1 Sampling and pretreatment according to the provisions of GB 14883.1.

11.2.2 Weigh 1g ~ 2g (accurate to 0.001g) in 35mL sample gray porcelain evaporating dish with a small amount of hydrochloric acid nitro soaked, steamed slowly heating to date no mist, and then burned in a muffle furnace 450 °C 0.5h. Ignition temperature not exceeding 500 °C, in order to avoid the formation of insoluble plutonium oxide.

11.2.3 After cooling in ml 8mol/L nitric acid solution was heated leaching filtered residue was washed 2 times with the same solution of nitric acid, 1mL/Ci ~ 2mL/times. The combined filtrate 25mL centrifuge tube.

11.2.4 take leaching solution was added a few drops of 2mol/L sodium nitrite solution, heated to regulate and stabilize the positive tetravalent plutonium in a water bath. Rush to make two Oxide after cooling.

11.2.5 leach solution at a flow rate of 0.3mL/min ~ 0.5mL/min through a chromatographic column (10.4). Then successively with the same flow rate 10mL8mol/L nitric acid solution and 15mL10mol/L hydrochloric acid solution was washed chromatographic column, discard the effluent.

11.2.6 with 10mL oxalic acid - a mixture of nitric acid (A) (9.2.2) eluting plutonium flow rate above. Effluent collected 35mL porcelain evaporating dish.

11.2.7 eluent evaporated low heat until all the oxalic acid decomposition of volatile power deposition.

11.2.8 with 8mL oxalic acid - nitric acid mixture (B) (9.2.3) Fractional the dry matter immersion, equipped transferred into the treated stainless steel sheet Electrodeposition tank (10.5), add 2 drops of ammonia, the full mix.

11.2.9 platinum wire as the anode, a stainless steel sheet as a cathode power. Electrodeposition at a voltage of 24V, 400mA current conditions 2h.

11.2.10 before the end of plating, concentrated ammonia is added 1mL, continue electrodeposition 1min. Disconnect the power, discard the electrolyte, washed with water electrolyzer.

After removing the stainless steel sheet, followed by acetone, ethanol, washed with water, dried under an infrared lamp, electric stove burning 3min ~ 5min, cooled in a low background alpha Measured on the spectrometer.

11.2.11 After the sample measurement surface immediately with 239Pu source counting efficiency standards, reagent blanks and instrument background measurement.

11.3 Determination of radiochemical recovery

Accurately weighed sample and sample measurement and other quality ash added 1.00mL239Pu standard solution (236Pu or 242Pu standard solution acceptable) 11.2.2 - 11.2.10 by the same operating procedures, after the measurement according to equation (1) calculate the radiochemical recovery.

11.4 Determination of the reagent blank value

Measure 200mL7mol/L nitric acid solution, according to 11.2.4 - 11.2.10 operation to prepare a measurement sample reagent blank value in the sample survey After the measurement volume.