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ORIGINAL RESEARCH
Year : 2012  |  Volume : 35  |  Issue : 1  |  Page : 34-42  

Study on the response of the ferrous ammonium sulfate - cupric sulfate dosimetry system of different salt concentrations at gamma chambers and radiation processing plant


1 Department of Food Technology and Biochemical Engineering, Jadavpur University, Kolkata, India
2 Department of Quality Control and Dosimetry, Radiation Processing Plant, Board of Radiation and Isotope Technology, BARC, Vashi, Mumbai, India

Date of Web Publication6-May-2013

Correspondence Address:
Sayanti Ghosh
Department of Food Technology & Biochemical Engineering, Jadavpur University, Kolkata-700032
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-0464.111408

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  Abstract 

Background and Aim: Gamma radiation is commercially used in food preservation by extending shelf life and the success of radiation preservation of food depends upon the ability of the processor of successful measurement of the radiation dose delivered to the foods. Several dosimeters are already used in radiation processing plant to measure the delivered dose. The aim of the present study was to develop a simple and appropriate chemical dosimetry system covering a wide dose range (1-30kGy) of food irradiation. Materials and Methods: The response of the ferrous ammonium sulfate (Fe(NH 4 ) 2 (SO 4 ) 2 ,6H 2 O) - cupric sulfate (CuSO 4 ,5H 2 O) dosimetry system was studied at two different gamma chambers of GC-5000 and GC-900 and at a radiation processing plant with four different salt concentrations and at the dose range of 1-30kGy. Results and Discussion: The system with highest salt concentration i.e. with 6x0.001mmol Fe(NH 4 ) 2 (SO 4 ) 2 ,6H 2 O + 6x0.01mmol CuSO 4 ,5H 2 O showed linear response in the applied dose range of 1kGy to 30kGy. Good reproducibility of the system was observed at both GC-5000 and GC-900 with different dose rate and irradiation temperature. Routine dosimetry and dose mapping at radiation processing plant with the standard Ceric-cerous dosimetry system with same salt concentration also showed good agreement with ΁5% difference. The system was stable upto 7 days before and after irradiation at 4 o C and at darkness. The estimated overall precision for the dose assessment over the dose range of interest was about ΁2% irrespective of the dose rate and irradiation temperature. Conclusion: The ferrous ammonium sulfate (Fe(NH 4 ) 2 (SO 4 ) 2 ,6H 2 O) - cupric sulfate (CuSO 4 ,5H 2 O) dosimetry system with highest salt concentration i.e. with 6x0.001mmol Fe(NH 4 ) 2 (SO 4 ) 2 ,6H 2 O + 6x0.01mmol CuSO 4 ,5H 2 O can be successfully used as chemical dosimeters in the dose range of 1-30kGy.

Keywords: Cupric sulfate, dosimetry, ferrous ammonium sulfate, radiation processing plant


How to cite this article:
Ghosh S, Khedkar K, Kashid S, Chakraborty P. Study on the response of the ferrous ammonium sulfate - cupric sulfate dosimetry system of different salt concentrations at gamma chambers and radiation processing plant. Radiat Prot Environ 2012;35:34-42

How to cite this URL:
Ghosh S, Khedkar K, Kashid S, Chakraborty P. Study on the response of the ferrous ammonium sulfate - cupric sulfate dosimetry system of different salt concentrations at gamma chambers and radiation processing plant. Radiat Prot Environ [serial online] 2012 [cited 2021 Apr 13];35:34-42. Available from: https://www.rpe.org.in/text.asp?2012/35/1/34/111408


  Introduction Top


Application of γ-irradiation is now a well-known method to eliminate/inactivate the spoilage causing and pathogenic microorganisms and to modify several physiological process for extension of shelf life with no adverse effects on nutritional and sensory quality of foods. [1] The success of radiation processing of food depends upon the ability of the processor to deliver the desired accurate radiation dose to the food materials and the successful measurement of the delivered dose. The practical uses of food irradiation have been grouped into low-, medium-, and high-dose application, and it covers the range from 30 Gy to 40 kGy. The low-dose application which is upto 1 kGy radiation dose includes inhibition of sprouting of potato, onion, garlic, ginger, disinfestations of cereals and pulses, fresh and dried fruits, dried fish and meat, and delay in ripening of fresh fruits. The medium-dose application of food irradiation is within 1-10 kGy and covers extension of shelf life of fresh fish, strawberries, mushrooms, etc., elimination of spoilage causing and pathogenic microorganisms of fresh and frozen sea foods, raw or frozen poultry and meat, and improvement of technological properties of food. On the other hand, the range of high-dose application is 10-40 kGy and includes industrial sterilization of meat, poultry, sea food, prepared foods, hospital diets, and decontamination of certain food additives and ingredients such as spices, enzyme, natural gum, etc. [2] Sterilization of medical equipments by irradiation is performed with the dose of 25 kGy and above. [3] The Standard of Codex Alimentarius Commission 2003 [4] states that in the commercial plants of food processing by gamma radiation, the minimum absorbed dose (D min ) should be sufficient to achieve the technological purpose and the maximum absorbed dose (D max ) should be less than that which would compromise consumer safety and wholesomeness of the food, and the Uniformity ratio (D max /D min ) must be successfully determined. Dosimetry assists in the proper control of process parameters in order to arrive at defined values of D min , D max , and Uniformity ratio (U). [5],[6],[7]

A simple, reliable, and reproducible routine dosimeter is important and indeed necessary in process control of food irradiation. Ferrous sulfate in acid solutions (Fricke dosimeter), a classified reference standard dosimetry system, has been extensively studied and widely utilized because of its high sensitivity to X-ray and γ-ray irradiation and 0.1% precision in measuring absorbed dose for Co-60 γ-rays irradiation process. [8],[9],[10],[11],[12] But the problem with Fricke is its limited dose range upto 400 Gy and sensitivity of response to impurities, even those present in sulfuric acid, and to irradiation temperature. [13],[14] Ceric-cerous dosimetry system, on the other hand, is another widely used reference standard dosimetry system whose recommended concentrations to measure absorbed doses from 5 to 50 kGy (high-range dosimeter) are 0.015 M ceric sulfate and 0.015 M cerous sulfate, and for 0.5-10 kGy, 0.003 M ceric sulfate and 0.003 M cerous sulfate, [15] i.e., to cover the whole dose range of food irradiation, two solutions of different concentrations are required. With the aim to develop one simple chemical dosimetry system covering a wide dose range from low dose to high dose, this study with ferrous ammonium sulfate and cupric sulfate in sulfuric acid was undertaken and the response of the system was studied in the dose range of 1-30 kGy which covers the medium-dose treatments (1-10 kGy) and a part of high-dose treatments (10-40 kGy) of food irradiation including certain fruits and vegetables, meat, poultry, fish, frozen sea food, spices, hospital meals and constituents of such meals. [16] This system is a modification of Fricke dosimetry system involving addition of cupric sulfate which was first suggested as a dosimeter in 1954 by Hart and Walsh [17] for the measurement of doses upto 70 kGy, but more frequently was used in the dose range 0.5-20 kGy. Due to the nonlinearity of the response, the system was not that popular as routine dosimeter. [18] According to the dosimetry manual of IAEA, [19] the method is most accurate for absorbed doses from 2 × 10 5 to 8 × 10 5 rad (2-8 kGy) using the spectrophotometric measurement of the ferric ion concentration at 305 nm wavelength and it can be used down to doses of 6 × 10 4 rad (600 Gy), but with decreased efficiency. It was also observed by Khan and Anwar [20] that the system showed linear response upto 7 kGy and could be used upto 14 kGy with proper calibration. But the complete studies on the response of this dosimetry system are not performed yet and this system is rather neglected by recent scientific workers. Both in Fricke and ferrous ammonium sulfate-cupric sulfate dosimetry systems, radiation-induced oxidation of ferrous ion to ferric ion is the principal reaction and the increase of concentration of ferric ion is related to the absorbed dose. In Fricke dosimetry, the depletion of oxygen at higher dose decreases the efficiency of the dosimeter solution in measuring dose above 400 Gy. In ferrous ammonium sulfate-cupric sulfate dosimetry system, cupric ion scavenges HO 2 ion and thus the absence of oxygen does not make any change in the oxidation of the ferrous ion and in measurement of dose. [21],[22]

In the case of commercial irradiation with a continuous conveyor system, the control of absorbed dose rate, source-to-product geometry, conveyor speed, cycle time, source strength, seasonal crop variation, and bulk density - all have effects in the response of dosimeters. The commercial radiation processing plant is thus different from the gamma chambers as in the latter, the radiation is much controlled due to small product volume and very compact structure of the chambers.

In this context, the response of the system with different concentrations of ferrous ammonium sulfate and cupric sulfate at different gamma chambers was studied and the dosimeter with a specific salt concentration which covers the dose range from 1 to 30 kGy was examined by routine dosimetry, dose mapping in radiation processing plant, and by comparing with standard ceric-cerous dosimetry system to establish the dosimetry system as a successful and appropriate chemical dosimeter covering the wide dose range (1-30 kGy) of food irradiation.


  Materials and Methods Top


Sample and glasswares

All the reagents were of analytical pure grade from Merck (Darmstadt, Germany) and were used without any further purification. The reagents were ferrous ammonium sulfate [Fe(NH 4 ) 2 (SO 4 ) 2 . 6H 2 O], cupric sulfate (CuSO 4 . 5H 2 O), and sulfuric acid.

The extreme low salt concentration dosimetry solution was prepared by dissolving 10−3 mol/dm 3 (0.001 mmol) ferrous ammonium sulfate and 10−2 mol/dm 3 (0.01 mmol) cupric sulfate in 5 × 10−3 mol/dm 3 (0.005 mmol) sulfuric acid. The density of the solution was measured by measuring separately the weight and volume of the solution and it was 0.9946 g/ml. The pH of the solution measured using pH meter (PH 1500, Eutech Instrument) was 2.3. Dosimetry solutions were prepared by gradually increasing the salt concentration to two times, four times, and six times of the previous one, maintaining the same molarity of sulfuric acid. The average density and pH of all the solutions was 1.003 g/ml and 2.3, respectively.

The water used to prepare the solution was triple distilled according to the standard procedures used in radiation chemistry. [23]

The dosimetry solutions were filled in dosimetry vials for irradiation. The vials were made of polypropylene with 9.5 cm height and 2 cm diameter. The vials were cleaned thoroughly with 10% nitric acid solution and doubled-distilled water before being filled up with dosimetry solutions.

Irradiation at Gamma chambers

Irradiation of all the dosimetry solutions was performed in Gamma chamber 5000 (BRIT, BARC, Mumbai, India) consisting of 60 Co as the source of gamma ray with 14 kCi power source and at 10.2 kGy/h dose rate. The dosimetry solution of extreme low and the extreme high (six times) salt concentration was also irradiated in GC-900 (made in Canada) with 3 kCi power source and at 1.76 kGy/h dose rate. For the extreme low salt concentration dosimetry solution, the dose range for irradiation was selected from 500 Gy to 5 kGy, and all the other solutions were irradiated above 1 kGy and upto 30 kGy. Average irradiation temperature was 48°C in GC-5000 and 32°C in GC-900.

All the time, the dosimeters vials were placed at the central position of the sample chamber to obtain the maximum average dose.

Irradiation of the dosimeters at radiation processing plant

Study of the response of the dosimeter in the radiation processing plant was carried out with the dosimetry solution of highest salt concentration, i.e., with the solution containing 6 × 10−3 mol/dm 3 (6 × 0.001 mmol) ferrous ammonium sulfate and 6 × 10−2 mol/dm 3 (6 × 0.01 mmol) cupric sulfate in 5 × 10−3 mol/dm 3 sulfuric acid. Irradiation of the dosimetry solutions was done at Radiation Processing Plant (two-pass gamma ray facilities), Board of Radiation and Isotope Technology, Vashi, Mumbai. It was done by performing the dose mapping by placing the dosimeters in duplicate at different positions of the tote box. The tote box had dimensions of 60 cm length, 45 cm width, and 110 cm height. The box was filled with a mixture of rice husk and saw dust as dummy materials. The weight of the box containing dummy material was 105 kg and the density of the material was 0.37 gm/cm 3 . Dosimeters were placed at aluminium sheets of 104 cm height and 60 cm length. Three aluminium sheets were used for the three planes of the tote box. Two planes were in the two sides (plane A and plane C) and one was in the central position (plane B). Dosimeters in duplicate were placed in nine different positions in each sheet, having total 27 positions in three planes of tote box [Figure 1]. Dose mapping was performed for 7 kGy and 10 kGy dose, and the irradiation temperature was 31°C for both the cases. Maximum and minimum position for dose absorption within the tote box was evaluated and the uniformity ratio was obtained by calculating D max /D min . The radiation processing plant contained 60 Co source of activity of 454.39 kCi and cycle time of 6 min.
Figure 1: Tote box with aluminium sheets showing the three planes and 27 different positions of dosimeter and the position of Dmax and Dmin

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Routine dosimetry and comparison with standard ceric-cerous dosimetry system

Ceric-cerous dosimetry system (5 mM and 15 mM) was the standard dosimetry system used in Radiation Processing Plant, BRIT, for routine dosimetry. The 5-mM ceric-cerous dosimetry system consisted of 0.005 M ceric sulfate and 0.005 M cerous sulfate in 400 mM sulfuric acid. On the other hand, the 15-mM solution contained 0.015 M of ceric sulfate and 0.015 M of cerous sulfate in 400 M sulfuric acid. [15] The evaluation of dose was done by potentiometer (MDS NORDION).

The ferrous ammonium sulfate-cupric sulfate dosimeters of highest salt concentration [(6 × 0.001 mmol) ferrous ammonium sulfate and 6 × 10−2 mol/dm 3 (6 × 0.01 mmol) cupric sulfate in 5 × 10−3 mol/dm 3 sulfuric acid] and the ceric-cerous dosimeters were attached together in duplicate and were placed at the positions of routine dosimetry, i.e., the maximum and minimum dose absorption position with the product in the tote box for dose determination and comparison with the standard ceric-cerous dosimetry system. The maximum and minimum dose absorption position is fixed for a particular plant with specific source activity, cycle time, size and volume of tote box. Different molarities of ceric-cerous dosimeters were selected according to the delivered dose.

Measurement of dose

The principle of the measurement was the oxidation of the ferrous ion (Fe 2+ ) to ferric ion (Fe 3+ ) induced by radiation. [19] The change of valence was measured by UV-Visible Spectrophotometer (U-1800 HITACHI) at 304 nm which was the wavelength of maximum absorption of Fe 3+ ions in the dosimetry solution. The change in absorbance of the irradiated sample from the non-irradiated one was directly related to the absorption of radiation dose by the solution. The average temperature for measurement was 25°C.

At high radiation dose, suitable dilution of the dosimetric solution was required before spectrophotometric measurement.

Determination of actual dose

Determination of the actual dose measured by the system was done by following the dosimetry manual, [19] with the equation D = (ΔAN/ρGεd) b/k, where "D" was the absorbed dose in grays. "ΔA" was the change in absorbance at 304 nm and at 25°C and was measured as ΔA = (Ai − Ac), where Ai and Ac were the absorbance values of the irradiated and unirradiated solutions, respectively. "N" was the Avogadro's number. "ρ" was the density of the solution. "G" was the G value of the reaction, "ε" was the molar extinction coefficient at 304 nm and at 25°C, "d" was the optical path length in the quartz cell, and "k" and "b" were the volume conversion factor and energy conversion factor, respectively.


  Results and Discussion Top


Response in gamma chambers

The response of the dosimetry system by changing the concentration of ferrous ammonium sulfate [Fe(NH 4 ) 2 (SO 4 ) 2 . 6H 2 O] and cupric sulfate (CuSO 4 . 5H 2 O) was studied in GC-5000 with a dose rate of 10.2 kGy/h. It is shown in [Table 1] that the system with lowest salt concentration [0.001 mmol Fe(NH 4 ) 2 (SO 4 ) 2 . 6H 2 O + 0.01 mmol CuSO 4 . 5H 2 O] accurately measures (±5% variation) the absorbed dose within 1-3 kGy dose range. Below 1 kGy, large variation (>20%) is observed in measurement of dose by this system. This result is similar with IAEA dosimetry manual [19] where it was reported that this system could be used down to doses of 600 Gy, but with decreased efficiency. The system also inefficiently measures the dose above 3 kGy. More than 10% variation is observed in the delivered dose and the dose as measured by the dosimeter solution (calculated dose) of 4 kGy and 5 kGy, which is different from the report of IAEA dosimetry manual [19] where it is claimed that the system is accurate for absorbed doses from 2 to 8 kGy. [Figure 2] represents the dose calibration curve of this dosimetry system obtained by plotting the delivered dose along the X-axis and the change in absorbance along the Y-axis, and the plotted curve corresponds to linear least-square fits to the experimental data. From the figure it is established that the response is linear in the observed dose range, and this is also similar with the observation of Khan and Anwar who reported the linear response of the system upto 7 kGy radiation dose. [20] The slope of the curve is 0.123, and the R 2 value of 0.994 establishes that in spite of the inaccuracy of measurement of certain doses, there is a good agreement between the delivered dose and change in absorbance.
Figure 2: Dose response graph of change in absorbance (ΔA = Ai − Ac) between irradiated (Ai) and unirradiated (Ac) dosimetric solution with delivered dose (kGy) from 0.5 kGy to 5 kGy for 0.001 mmol of Fe(NH4)2(SO4)2. 6H2O +0.01 mmol CuSO4. 5H2O salt concentrationin in GC-5000 and GC-900

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Table 1: Dose response datasheet of ΔA and corresponding delivered and calculated dose (kGy) in GC-5000 for 0.001 mmol Fe(NH4)2(SO4)2. 6H2O and 0.01 mmol CuSO4. 5H2O dosimetry solution

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[Table 2] and [Table 3] present the dose response datasheet of the dosimetry system in GC-5000 after increasing the salt concentration two times [2 × 0.001 mmol Fe(NH 4 ) 2 (SO 4 ) 2 . 6H 2 O + 2 × 0.01 mmol CuSO 4 . 5H 2 O] and four times [4 × 0.001 mmol Fe(NH 4 ) 2 (SO 4 ) 2 . 6H 2 O + 4 × 0.01 mmol CuSO 4 . 5H 2 O], respectively. It is shown in [Table 2] that the system with two times salt concentration measures the absorbed dose from 1 kGy to 5 kGy with a ± 5% variation, but more than 5% variation is observed in measuring the dose above 5 kGy. On the other hand, the dose range is extended upto 10 kGy after increasing the salt concentration four times and the dose above 10 kGy is measured with decreased efficiency. [Figure 3] establishes the linear response of the system with two times salt concentration upto 20 kGy with a good R 2 value of 0.997, and linear response upto 30 kGy is obtained with four times salt concentration with reproducible R 2 value of 0.999 [Figure 4]. The slope of the curve is 0.130 for two times and 0.135 for four times, which resembles a reproducible relationship between the change in absorbance and the increasing delivered dose.
Figure 3: Dose response graph of change in absorbance (ΔA = Ai − Ac) between irradiated (Ai) and unirradiated (Ac) dosimetric solution with delivered dose (kGy) from 1 kGy to 20 kGy for 2 × 0.001 mmol of Fe(NH4)2(SO4)2. 6H2O + 2 × 0.01 mmol CuSO4. 5H2O salt concentration in GC-5000

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Figure 4: Dose response graph of change in absorbance (ƒ¢A = Ai − Ac) between irradiated (Ai) and unirradiated (Ac) dosimetric solution with delivered dose (kGy) from 1 kGy to 30 kGy for 4 × 0.001 mmol of Fe(NH4)2(SO4)2. 6H2O + 4 × 0.01 mmol CuSO4. 5H2O salt concentration in GC-5000

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Table 2: Dose response datasheet of Δ A and corresponding delivered and calculated dose (kGy) in GC-5000 for 2×0.001 mmol Fe(NH4)2(SO4)2. 6H2O and 2×0.01 mmol CuSO4. 5H2O dosimetry solution

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Table 3: Dose response datasheet of Δ A and corresponding delivered and calculated dose (kGy) in GC-5000 for 4×0.001 mmol Fe(NH4)2(SO4)2. 6H2O and 4×0.01 mmol CuSO4. 5H2O dosimetry solution

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After increasing the salt concentration of the dosimetry solution six times, the system covers the entire desired dose range from 1 to 30 kGy and successful measurement of the absorbed dose in that range is observed [Table 4]. The curve [Figure 5] shows that the response is linear with R 2 value of 0.999 which signifies the good agreement between the change in absorbance and the delivered dose. The slope of the curve is 0.149 and it is observed that the slope increases with the salt concentration and with the accessible dose range. As a result, the response curve with six times salt concentration covering the entire 1-30 kGy dose range becomes more steeper than the previous curves and this is the ultimate relationship between the delivered dose and the radiation-induced oxidation of Fe 2+ to Fe 3+ .
Figure. 5: Dose response graph of change in absorbance (ΔA = Ai − Ac) between irradiated (Ai) and unirradiated (Ac) dosimetric solution with the delivered dose (kGy) from 1 kGy to 30 kGy for 6 × 0.001 mmol of Fe(NH4)2(SO4)2. 6H2O + 6 × 0.01 mol CuSO4. 5H2O salt concentrationin in GC-5000 and GC-900

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Table 4: Dose response datasheet of ΔA and corresponding delivered and calculated dose (kGy) in GC-5000 and GC-900 for 6×0.001 mmol Fe(NH4)2(SO4)2. 6H2O and 6×0.01 mmol CuSO4. 5H2O dosimetry solution Delivered

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The response of the system is also studied in GC-900 of 1.76 kGy/h dose rate with the lowest salt concentration [0.001 mmol Fe(NH 4 ) 2 (SO 4 ) 2 . 6H 2 O +0.01 mmol CuSO 4 . 5H 2 O] and after increasing the concentration six times [6 × 0.001 mmol Fe(NH 4 ) 2 (SO 4 ) 2 . 6H2O +6 × 0.01 mmol CuSO 4 . 5H 2 O]. Similar result as of GC-5000 is obtained with the lowest salt concentration [Table 1] covering the dose range of 0.5-5 kGy, and the linear response curve [Figure 2] is obtained with the R 2 of 0.996 and slope of 0.132. The change in absorbance (ΔA) for a specific delivered dose is close between GC-5000 and GC-900 upto 3 kGy. Considerable variation is observed above 3 kGy only due to the lack of stability of the solution in this dose range and thus inefficient measurement of the dose by the dosimeters. The subtle difference of the slope between the two chambers is also due to the inaccuracy of the system in measurement of dose below 1 kGy and above 3 kGy. The system with six times salt concentration also shows linear response in GC-900 [Figure 5] and the slope is same (0.150) with the slope of the response curve at GC-5000. The variation of change in absorbance (ΔA) at two gamma chambers above 3 kGy radiation dose as observed in [Table 1] is overcome here, and as a result, two curves coincide with each other and it indicates that the response of the system with six times salt concentration is independent of gamma chambers, applied dose rate, and of irradiation temperature also.

The exhaustion of both the salts (Fe 2+ and Cu 2+ ) due to oxidation-reduction reaction increases as the dose increases. With the lowest salt concentration, the inaccurate measurement of the dose above 3 kGy may be due to the absence of sufficient Fe 2+ and Cu 2+ salts. This is overcome by increasing the salt concentration six times and the overall range of 1-30 kGy is covered by the system.

It is noted that in the process of covering higher dose range by increasing salt concentration, any saturation point in the dose response curve is not obtained so far. This text is only concerned with the response of ferrous-cupric sulfate dosimetry in a specified 1-30 kGy dose range. Further experimentations are required to know the behavior of the system above this dose range and to get the saturation point of the dose response curve.

Therefore, the dosimetry system with six times salt concentration should successfully be used as chemical dosimeters in gamma chambers in the dose range of 1-30 kGy. But the success of a dosimetry system depends upon its successful measurement of absorbed dose in radiation processing plant.

Response in radiation processing plant

[Table 5] and [Table 6] represent the dose mapping for average 7 kGy and 10 kGy radiation dose, respectively, within the tote box by ferrous ammonium sulfate-cupric sulfate dosimetry system with six times salt concentration [6 × 0.001 mmol ferrous ammonium sulfate +6 × 0.01 mmol cupric sulfate] at 27 different positions in three planes, i.e. nine different positions in each plane. The position at which the product gets the minimum dose is in plane B for both 7 kGy and 10 kGy, whereas the position for maximum dose is at plane C for 7 kGy and at plane A for 10 kGy. The positions are shown in [Figure 1]. For both the cases, the results for the position of maximum and minimum dose are satisfactory because at the time of exposure, plane A and plane C remaining closer to the source get more dose than plane B, which being the central plane would be little bit away from the source and gets the minimum exposure. The uniformity ratio of 1.29 for 7 kGy and 1.22 for 10 kGy is also in the acceptable range of commercial food irradiation. The routine dosimetry data of absorbed dose in maximum and minimum position measures by both ferrous ammonium sulfate-cupric sulfate dosimetry system and the standard ceric-cerous dosimeter show that a variation of ±4.95% is obtained in the estimation of dose at maximum position and the variation is ±5.04% in estimation of dose at minimum position. Therefore, the response of the ferrous ammonium sulfate-cupric sulfate dosimetry system in food irradiation plant is accurate and reproducible.
Table 5: Dose mapping by ferrous ammonium sulfate (6×0.001 mmol) - cupric sulfate (6×0.01 mmol) dosimetry system at food irradiation plant for the dose 7 kGy

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Table 6: Dose mapping by ferrous ammonium sulfate (6×0.001 mmol) - cupric sulfate (6×0.01 mmol) dosimetry system at food irradiation plant for the dose 10 kGy

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Precision, pre-irradiation and post-irradiation storage effect

A precision of ±2% of the dosimeter solution with the highest salt concentration [6 × 0.001 mmol Fe(NH 4 ) 2 (SO 4 ) 2 . 6H 2 O + 6 × 0.01 mmol CuSO 4 . 5H2 O] has been obtained in the 1 kGy-30 kGy dose range. The pre-irradiation and post-irradiation storage effect on the dosimetry system with six times salt concentration is also measured. The solution is stored in the dark at 4°C temperature. The response of the dosimeter is monitored for a storage period of about 7 days before and after irradiation. The absorbance of the dosimeter solution is found to be relatively stable over the storage period.


  Conclusion Top


After studying the ferrous ammonium sulfate-cupric sulfate dosimetry systems with different salt concentrations, it is concluded that the system with six times salt concentration can be used as a chemical dosimeter in the dose range of 1-30 kGy. The system is stable upto 7 days before and after irradiation at 4°C in darkness. The estimated overall precision for the dose assessment over the dose range of interest is about ±2% irrespective of the dose rate and irradiation temperature as obtained in the gamma chambers. The response of the dosimetry system in food irradiation plant is also reproducible. Uniformity ratios of 1.29 and 1.22 are obtained in dose mapping for 7 kGy and 10 kGy radiation doses, respectively, which are in the acceptable range. Routine dosimetry with ferrous ammonium sulfate-cupric sulfate dosimetry system has also shown similar result with the dose measured by ceric-cerous dosimetry system. On an average, ±5% variation in measurement of dose with the standard ceric-cerous sulfate system is obtained. The dosimetry solutions are easy to prepare and the chemicals are cost worthy. The analysis is made by UV spectroscopy, a very accessible technique in most of the laboratories, which is a great advantage and the results show a wide range for which the dosimeter presents a linear response pattern. Therefore, the dosimetric properties of this compound are appropriate for radiation dosimetry and it appears to be an effective dosimeter in routine application in radiation processing plant.


  Acknowledgment Top


The authors gratefully acknowledge CSIR, New Delhi, Govt. of India, for financial assistance and for providing the necessary infrastructure for experimentation. They are also thankful to all the staffs of RPP, BRIT (BARC), Vashi, Mumbai, for their kind cooperation and support in completion of this work.

 
  References Top

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17.Hart EJ, Walsh PD. A molecular product dosimeter for ionizing radiations Radiat Res 1954;1:342-6.  Back to cited text no. 17
    
18.Bjergbakke E, Sehested K. The ferrous - cupric dosimeter. In: Radiation Chemistry. Adv Chem Ser 1968;81:579.  Back to cited text no. 18
    
19.IAEA. Manual of food irradiation dosimetry. Vienna: 1977. p. 96-8.  Back to cited text no. 19
    
20.Khan HM, Anwar M. Stability of response of ferrous-cupric sulfate dosimeter at different temperatures. Journal of Radioanalytical and Nuclear Chemistry, Letters, 1993;175:199-206.  Back to cited text no. 20
    
21.Hotta H. Oxidation of ferrous ions in the aqueous Ferrous - cupric system. I. Effect of Cobalt - 60 gamma rays. Radiat Res 1959;33:442-5.  Back to cited text no. 21
    
22.Feng PY. High-intensity radiolysis of aqueous ferrous sulfate - cupric sulfate - sulfuric acid solutions. J Phys Chem 1970;74:1221-7.  Back to cited text no. 22
    
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]



 

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Abstract
Introduction
Materials and Me...
Results and Disc...
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Acknowledgment
References
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