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Neutron dosimetry based on fission reactions: Preliminary results
Conference
Distribution Ecosystem
of Radionuclides in a Forest of the French Southern Alps
G. BARCI-FUNEL, Laboratoire
391
Abstracts
de Radiochimie,
J. DALMASSO
Universiti:
and G. ARDISSON
de Nice Sophia-Antipolis,
06108 Nice Cedex 2, France
After the reactor accident at Chernobyl, high levels of fission products were observed in rain and air as well as in terrestrial radioactive bioindicators, in South Eastern France. Samples of soil, moss, lichen (parmeliu furfuracea, usnea barbatu) and fern were collected in a particularly contaminated area: the forestal massif of Boreon, 30 km north of Nice (Barci-Funel et al., 1988, 1992). Activity concentrations as high as 42.8, 9.4 and 3.8 kBq . md2, respectively, were measured in humic soils for ‘37Cs, ‘34Cs and “‘(‘Ru. r2’Sb, “OrnAg and “‘Eu were also detected. Activity concentrations were found to be higher between 1400 and 1700 m altitude. This was probably due to higher rainfall in this zone, moreover at the highest altitudes soil was still covered by snow at the end of April and the melting snow could have carried down some of the fallout, this altitude also corresponds to a dense forest. An indirect determination of 24’Pu in soil by measurement of the in situ ingrown 24’Am permitted an estimate of the activity ratio 241Pu/137Cs of (0.3-l) 10M2 and subsequently a ratio 239+240Pu/‘37Csof about 4. IO-‘. ‘34Cs, 13’Cs and “OrnAg activity concentrations were measured in mushrooms of different species. The activity ratio “omAg/‘37Cs in Lepista nuda was found to be about 50 times higher than in Chernobyl fallout.
References Barci-Funel Barci-Fuel
G., Dalmasso G., Dalmasso
J. and Ardisson J. and Ardisson
G. (1988) Sci. Total Enuir. 70, 373. G. (1992) J. Radioanal. NW/. Chem., Left. 164, 157.
Neutron Dosimetry Based on Fission Reactions: Preliminary Results G. BIGAZZI,’
J. C. HADLER NETO,’ P. IUNES,2 M. ODDONE
S. MELONI-’
and
‘lstituto di Geocronologia e Geochimica Isotopica, CNR, Pisa, Italy, %stituto de Fisica “Gleb Wataghin”, UNICAMP, Campinas SP, Brazil, ‘Centro di Radiochimica e Analisi per Attivazione, CNR, Dipartimento di Chimica Generale, Universiti di Pavia, Pavia, Italy and 4Dipartimento di Chimica Generale, Universita di Pavia, Pavia, Italy Age determination using the fission track technique depends upon an accurate neutron fluence measurement. Potential sources of systematic error may be found in the metal foil activation technique, such as the determination of the absolute efficiency of the counting system, differences in the geometrical arrangements in the comparison with the standard sources, possible self-shielding. An important starting point is the employment of neutron dosimeters which operate on the 235U(n,f) reaction and for which the natural uranium quantity can be determined independently of any parameter related to the neutron irradiation. When such dosimeters and a mineral to be dated are irradiated together, any anomaly that occurs during neutron irradiation, has the same effect on both. In the present paper the use of natural uranium dosimeters is described. Data are comparated with fluence values obtained by using NIST glass standards and the traditional activation foils. Irradiations were performed in the TRIGA MARK II nuclear reactor of the University of Pavia. Two irradiation facility were selected, characterized by different nominal thermal neutron flux and cadmium ratio: (a) rotatory specimen rack, (b) thermalizing column. Induced radioactivity was measured by gamma-ray spectrometry using a Ge(Li) detector coupled to a computer assisted multichannel analyser. Fission track density measurement was carried out by standard optical methods. Neutron fluences in the rotatory specimen rack and in the thermahzing column are reported and discussed. Individual data are given together with the standard deviation deriving only from counting statistics. Reported data indicate that fluence measurements obtained using metallic dosimeters are in agreement, usually within 5%, for both irradiation facilities; fluence measurements obtained by fission track densities, using NIST 962a glass dosimeters provide reliable results as well.
Distribution Ecosystem
of Radionuclides in a Forest of the French Southern Alps
G. BARCI-FUNEL, Laboratoire
391
Abstracts
de Radiochimie,
J. DALMASSO
Universiti:
and G. ARDISSON
de Nice Sophia-Antipolis,
06108 Nice Cedex 2, France
After the reactor accident at Chernobyl, high levels of fission products were observed in rain and air as well as in terrestrial radioactive bioindicators, in South Eastern France. Samples of soil, moss, lichen (parmeliu furfuracea, usnea barbatu) and fern were collected in a particularly contaminated area: the forestal massif of Boreon, 30 km north of Nice (Barci-Funel et al., 1988, 1992). Activity concentrations as high as 42.8, 9.4 and 3.8 kBq . md2, respectively, were measured in humic soils for ‘37Cs, ‘34Cs and “‘(‘Ru. r2’Sb, “OrnAg and “‘Eu were also detected. Activity concentrations were found to be higher between 1400 and 1700 m altitude. This was probably due to higher rainfall in this zone, moreover at the highest altitudes soil was still covered by snow at the end of April and the melting snow could have carried down some of the fallout, this altitude also corresponds to a dense forest. An indirect determination of 24’Pu in soil by measurement of the in situ ingrown 24’Am permitted an estimate of the activity ratio 241Pu/137Cs of (0.3-l) 10M2 and subsequently a ratio 239+240Pu/‘37Csof about 4. IO-‘. ‘34Cs, 13’Cs and “OrnAg activity concentrations were measured in mushrooms of different species. The activity ratio “omAg/‘37Cs in Lepista nuda was found to be about 50 times higher than in Chernobyl fallout.
References Barci-Funel Barci-Fuel
G., Dalmasso G., Dalmasso
J. and Ardisson J. and Ardisson
G. (1988) Sci. Total Enuir. 70, 373. G. (1992) J. Radioanal. NW/. Chem., Left. 164, 157.
Neutron Dosimetry Based on Fission Reactions: Preliminary Results G. BIGAZZI,’
J. C. HADLER NETO,’ P. IUNES,2 M. ODDONE
S. MELONI-’
and
‘lstituto di Geocronologia e Geochimica Isotopica, CNR, Pisa, Italy, %stituto de Fisica “Gleb Wataghin”, UNICAMP, Campinas SP, Brazil, ‘Centro di Radiochimica e Analisi per Attivazione, CNR, Dipartimento di Chimica Generale, Universiti di Pavia, Pavia, Italy and 4Dipartimento di Chimica Generale, Universita di Pavia, Pavia, Italy Age determination using the fission track technique depends upon an accurate neutron fluence measurement. Potential sources of systematic error may be found in the metal foil activation technique, such as the determination of the absolute efficiency of the counting system, differences in the geometrical arrangements in the comparison with the standard sources, possible self-shielding. An important starting point is the employment of neutron dosimeters which operate on the 235U(n,f) reaction and for which the natural uranium quantity can be determined independently of any parameter related to the neutron irradiation. When such dosimeters and a mineral to be dated are irradiated together, any anomaly that occurs during neutron irradiation, has the same effect on both. In the present paper the use of natural uranium dosimeters is described. Data are comparated with fluence values obtained by using NIST glass standards and the traditional activation foils. Irradiations were performed in the TRIGA MARK II nuclear reactor of the University of Pavia. Two irradiation facility were selected, characterized by different nominal thermal neutron flux and cadmium ratio: (a) rotatory specimen rack, (b) thermalizing column. Induced radioactivity was measured by gamma-ray spectrometry using a Ge(Li) detector coupled to a computer assisted multichannel analyser. Fission track density measurement was carried out by standard optical methods. Neutron fluences in the rotatory specimen rack and in the thermahzing column are reported and discussed. Individual data are given together with the standard deviation deriving only from counting statistics. Reported data indicate that fluence measurements obtained using metallic dosimeters are in agreement, usually within 5%, for both irradiation facilities; fluence measurements obtained by fission track densities, using NIST 962a glass dosimeters provide reliable results as well.