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Radioiron 59Fe activity measurement using liquid scintillators
ht. 1. Appl. Radiat. ht. 6 Per~amon Press Ltd
Vol. 35. So. 7. pp. 693-694. 1981.Printed in Great Britain
19Y-I
Table I. Radioiron j9Fe measurement efficiency obtained for different concentrations of luminophors in toluene
0020-708X:84 53.00 f 0.00
concentrations in measure sample (g.dm-‘)
Radioiron 59Fe Activity Measurement using Liquid Scintillators M. RADWAN, E. MYKOWSKA, A. PRZYBYLSKA and K. GIBAS Technical University of Poznari, Institute of Machines Technology, Isotope Laboratory, Poznati, Poland
PPO
POPOP
2.70 4.00 5.30 6.66 8.00 9.33 10.66
0.033 0.050 0.066 0.083 0.100 0.116 0.133
Measurement efficiency (“J 83.8 84.5 86.3 85.1 83.6 83.2 82.6
Table 2. Influence of some metal ion concentration in water on the efficiency of radioiron ‘9Fe activity measurement Measurement efficiency after introducing the hydrated ions
(Receified 25 Jfuy 1983) IOIl
Measurement of machine wear can be performed by measuring the radioactivity of abraded particles. The technique of liquid scintillators applied here makes possible the measurement of very low activities at any efficiency exceeding 74% for the steel labeled radioiron s9Fe. Thus, using the method described below, the measurement of mass loss of 10y9 g is possible.
The radioisotope method of wear investigation is based on determining the worn surface mass of machine components using the measured radioactivity of abraded particles. When the precise wear of particular elements is performed, it becomes necessary to determine mass in the range low9 g, and this corresponds to activities of IO-’ Bq at the activation of carbon steel and alloy steel using a neutron flux of IO” s- ’ cm-’ during the IOOh (36’ 10%). Thus, a method of measurement characterized by high efficiency is needed. This demand is met by liquid scintillators but these require specific preparation of the sample. The wear products, including radioiron ‘9Fe, were dissolved in a mixture on nitric and hydrochloric acids. When the sample had been digested and the nitrogen oxides volatilized, the solution was diluted using 5 mL (5.10 -6 m’) of distilled water. Ammonium aluminium sulphate was added to the solution; the solution was heated to a temperature of about 70°C (343 K), and an amount of ammonia, leading to the complete precipitation of iron was added. The solution was held at a temperature of 6O’C (333 K) for 1 h (3600 s). The deposition was filtered off and then dissolved on filter by hot 8 M HCl. The filter was rinsed with hot water. The water was added to the whole mixture to maintain the amount of IOOmL (I.lO-‘m3). An amount of I mL (I. IO- 6m3) of received solution of the iron chloride was collected by extraction to obtain a IOO-times reduction in content of the element being tested. To complex the iron, 5ml (5.10e6m3) of IO%-TOA (3-n-octylamine) in toluene was added each time to the liquid separator and the mixture shaken for 1min (60 s). The extraction was carried out twice. From IOmL (l.lO-$m’) of the extract obtained, a 5mL (5.10-6m3) was collected and conducted to the measuring glass containing the scintillator. Because increased measurement efficiency can be obtained using scintillation mixtures characterized by properly chosen compositions and concentrations of luminophores, several tests were carried out. AX.,.
35 7--H
(“6)
concentration (2.lO--g.dm-‘)
__ Mn
0.0
84.6 83.5 83.5 83.4 83.5 83 I
0.2
1.2 2.5 3.5 5.0
Ni
Co
Cu
Fe
Cr
84.6 84.0 83.7 83.6 83.4 X3.2
84.6 84.2 84.2 84. I 84. I 84 0
84.6 84.2 84. I 83.7 82.8 82 ?
84.6 83.1 82.7 79.7 78.2 77 7
84.6 83.3 82.9 80.3 79.2 14
n
It was found, that using a scintillation spectrometer good results are obtained with toluene as a solvent and a PPO and POPOP as luminophors. The concentration of the luminophors mentioned in the solvent was chosen on the basis of radioiron 59Fe activity measurement in the scintillator with a mass of luminophors varying from 2 to IO g PPO, and from 0.03 to 0.133 g POPOP on 1 dm3 of toluene (taking into account the toluene existing in the introduced sample). The highest measurement efficiency, equal to 86.3% was obtained with the following scintillator composition: 8.0 g dm - 3PPO and 0.1 g dm - ’ POPOP in I dm’ of mixture (see Table 1). The measurement was carried out in the energy range of the radioiron s9Fe radiation spectrum. Water, together with water-soluble salts of metals (Mn, Ni, Co, Cu, Fe, Cr) infiltrates to the active sample when the extraction process is running. The percentage of individual metal ions depends on the alloy composition.
x
co
n NI I
Mn
.
Cr
o Fe
00
I
I
I 02
I2 IOrT
I 25
concentration
I
35
I 50
(2 10-7cj.dm-3)
Fig. 1. Influence of metallic elements on radioiron s9Fe measurement efficiency.
693
691
Technical Note
A special experiment was undertaken to find the answer to the question: which metal ions and concentrations decrease the measurement efficiency? The particular metals as chlorides were introduced in succession to the scintillation mixture together with 0.05 mL (5. IO- *m’) of water and I mL (I.10 -6 m’) of methanol. The activity of the measured sample changed in this way was registered and the measurement efficiency. depending on the scintillation quenching using different concentrations of metal ions. was calculated. The results of these measurements are presented in Table 2.
After examination of the results they were compared with the measurement efficiency coefficient 0.05 mL (5. IO-’ mJ) of water. A significant scintillation quenching by the Fe and Cr ions was stated, especially in the higher concentration range. Significant influence of the presence of the hydrated ions of Co, Ni, Mn and Cu on the measurement efficiency decrease was not stated for concentrations which do not exceed 7. IO-‘g’dm-‘. The higher ion concentrations decrease measurement efficiency to an important degree (Fig. 1).
Vol. 35. So. 7. pp. 693-694. 1981.Printed in Great Britain
19Y-I
Table I. Radioiron j9Fe measurement efficiency obtained for different concentrations of luminophors in toluene
0020-708X:84 53.00 f 0.00
concentrations in measure sample (g.dm-‘)
Radioiron 59Fe Activity Measurement using Liquid Scintillators M. RADWAN, E. MYKOWSKA, A. PRZYBYLSKA and K. GIBAS Technical University of Poznari, Institute of Machines Technology, Isotope Laboratory, Poznati, Poland
PPO
POPOP
2.70 4.00 5.30 6.66 8.00 9.33 10.66
0.033 0.050 0.066 0.083 0.100 0.116 0.133
Measurement efficiency (“J 83.8 84.5 86.3 85.1 83.6 83.2 82.6
Table 2. Influence of some metal ion concentration in water on the efficiency of radioiron ‘9Fe activity measurement Measurement efficiency after introducing the hydrated ions
(Receified 25 Jfuy 1983) IOIl
Measurement of machine wear can be performed by measuring the radioactivity of abraded particles. The technique of liquid scintillators applied here makes possible the measurement of very low activities at any efficiency exceeding 74% for the steel labeled radioiron s9Fe. Thus, using the method described below, the measurement of mass loss of 10y9 g is possible.
The radioisotope method of wear investigation is based on determining the worn surface mass of machine components using the measured radioactivity of abraded particles. When the precise wear of particular elements is performed, it becomes necessary to determine mass in the range low9 g, and this corresponds to activities of IO-’ Bq at the activation of carbon steel and alloy steel using a neutron flux of IO” s- ’ cm-’ during the IOOh (36’ 10%). Thus, a method of measurement characterized by high efficiency is needed. This demand is met by liquid scintillators but these require specific preparation of the sample. The wear products, including radioiron ‘9Fe, were dissolved in a mixture on nitric and hydrochloric acids. When the sample had been digested and the nitrogen oxides volatilized, the solution was diluted using 5 mL (5.10 -6 m’) of distilled water. Ammonium aluminium sulphate was added to the solution; the solution was heated to a temperature of about 70°C (343 K), and an amount of ammonia, leading to the complete precipitation of iron was added. The solution was held at a temperature of 6O’C (333 K) for 1 h (3600 s). The deposition was filtered off and then dissolved on filter by hot 8 M HCl. The filter was rinsed with hot water. The water was added to the whole mixture to maintain the amount of IOOmL (I.lO-‘m3). An amount of I mL (I. IO- 6m3) of received solution of the iron chloride was collected by extraction to obtain a IOO-times reduction in content of the element being tested. To complex the iron, 5ml (5.10e6m3) of IO%-TOA (3-n-octylamine) in toluene was added each time to the liquid separator and the mixture shaken for 1min (60 s). The extraction was carried out twice. From IOmL (l.lO-$m’) of the extract obtained, a 5mL (5.10-6m3) was collected and conducted to the measuring glass containing the scintillator. Because increased measurement efficiency can be obtained using scintillation mixtures characterized by properly chosen compositions and concentrations of luminophores, several tests were carried out. AX.,.
35 7--H
(“6)
concentration (2.lO--g.dm-‘)
__ Mn
0.0
84.6 83.5 83.5 83.4 83.5 83 I
0.2
1.2 2.5 3.5 5.0
Ni
Co
Cu
Fe
Cr
84.6 84.0 83.7 83.6 83.4 X3.2
84.6 84.2 84.2 84. I 84. I 84 0
84.6 84.2 84. I 83.7 82.8 82 ?
84.6 83.1 82.7 79.7 78.2 77 7
84.6 83.3 82.9 80.3 79.2 14
n
It was found, that using a scintillation spectrometer good results are obtained with toluene as a solvent and a PPO and POPOP as luminophors. The concentration of the luminophors mentioned in the solvent was chosen on the basis of radioiron 59Fe activity measurement in the scintillator with a mass of luminophors varying from 2 to IO g PPO, and from 0.03 to 0.133 g POPOP on 1 dm3 of toluene (taking into account the toluene existing in the introduced sample). The highest measurement efficiency, equal to 86.3% was obtained with the following scintillator composition: 8.0 g dm - 3PPO and 0.1 g dm - ’ POPOP in I dm’ of mixture (see Table 1). The measurement was carried out in the energy range of the radioiron s9Fe radiation spectrum. Water, together with water-soluble salts of metals (Mn, Ni, Co, Cu, Fe, Cr) infiltrates to the active sample when the extraction process is running. The percentage of individual metal ions depends on the alloy composition.
x
co
n NI I
Mn
.
Cr
o Fe
00
I
I
I 02
I2 IOrT
I 25
concentration
I
35
I 50
(2 10-7cj.dm-3)
Fig. 1. Influence of metallic elements on radioiron s9Fe measurement efficiency.
693
691
Technical Note
A special experiment was undertaken to find the answer to the question: which metal ions and concentrations decrease the measurement efficiency? The particular metals as chlorides were introduced in succession to the scintillation mixture together with 0.05 mL (5. IO- *m’) of water and I mL (I.10 -6 m’) of methanol. The activity of the measured sample changed in this way was registered and the measurement efficiency. depending on the scintillation quenching using different concentrations of metal ions. was calculated. The results of these measurements are presented in Table 2.
After examination of the results they were compared with the measurement efficiency coefficient 0.05 mL (5. IO-’ mJ) of water. A significant scintillation quenching by the Fe and Cr ions was stated, especially in the higher concentration range. Significant influence of the presence of the hydrated ions of Co, Ni, Mn and Cu on the measurement efficiency decrease was not stated for concentrations which do not exceed 7. IO-‘g’dm-‘. The higher ion concentrations decrease measurement efficiency to an important degree (Fig. 1).