J.-C. Roy

On the transport of chernobyl radioactivity to eastern Canada

Abstract A large number of radionuclides released by the Chernobyl nuclear reactor were detected in air and river water samples collected in the Quebec region of eastern Canada. Analysis of the data supports the view that three waves of airborne radioactivity entered eastern Canada between 6 May 1986 and the end of June 1986. The first two waves would have followed an Arctic route and arrived over Quebec on 6 May and around 14 May respectively. The third wave would have been carried by the prevailing westerly winds across the Pacific Ocean and arrived over Quebec around 25–26 May. On 25 June and thereafter, Chernobyl radioactivity was undetectable in our airfilters but was still being detected in the St Lawrence river in March 1987.

A very sensitive sampling method for the measurement of radioactivity in waters from various sources

Abstract A sampling method to detect weapons fallout, natural radioactivity, 7 Be, and activation products in water is described. It consists in collecting the floc in the alum coagulation unit used in a water treatment plant. It lowers the detection level by at least a factor of 100 over the usual procedures. Gamma spectra are shown and applications are discussed.

On the identification of gamma rays from the 232Th decay

Abstract A planar germanium detector was used to study the γ-rays emitted in the disintegration of 232 Th. The samples were four different thorium salts on which radiochemical purifications were carried out. Two γ-rays at 63.9 and 140.8 keV were observed in those purified salts and assigned to 232 Th. The emission probabilities are: P γ (63.9) = (0.255 ± 0.017)% and P γ (140.8) = (0.026 ± 0.003)%. This finding leads to a re-evaluation of the decay scheme of 232 Th; the energies of the first and second excited states of 228 Ra become 63.9 and 204.7 keV while the energies of the second and third alpha groups which populate these states become 3948 and 3807 keV respectively.

Partitioning and transport of lead-210 in the Ottawa river watershed

The partitioning of 210Pb between dissolved and the suspended sediment phases of the Ottawa River waters has been studied. The results indicate high affinity of the radionuclide for particulates (Kd, 1.9 × 105 mL g−1). Companion studies on the precursor 226Ra give an average (Kd value of 7.8 × 103 mL g−1). Nearly 77% of the total 210Pb (i.e., dissolved plus particulate) and 99% of the total 226Ra are transported through the system in the dissolved form. The suggestion is made that the low availability of particulates in the system promotes the export of 210Pb in the dissolved form. The conventional approach gives a mean residence time of about 2000 yr for the atmospherically-derived 210Pb in the watershed. However, if the flux of this 210Pb falling directly on the rivers surface is taken into account, a mean residence time of about 6200 yr is inferred for this radionuclide in the area soils. This aspect of the study is largely applicable to metals with geochemical behavior similar to that of 210Pb for the radionuclide itself has a mean life of only 32.2 yr.

A study of the indium and germanium photopeaks in the background spectra of Ge spectrometers with a passive shield

Cosmic ray neutron interactions with indium, used as electrical contact within a Ge diode, the diode itself and the surrounding materials can give rise to a large number of photopeaks in the 50 to 1300 keV region of background spectra of Ge spectrometers with a passive shield. The nuclear processes and decays involved in the production of these photopeaks are discussed. These cosmic ray produced photopeaks are compared with those due to primordial radionuclides. Some useful information can be drawn from these measurements on the contribution of the cosmic rays on the background of Ge detectors with a passive shield.

Measurements with a planar germanium detector of low energy γ and X-ray emitters in waters sampled by the floc method

Abstract A planar germanium detector was used to study the low energy γ and X-ray emitters in floc samples collected in different municipal water filtration plants located on the St. Lawrence river and its tributaries. The experimental techniques are described and the radiation spectra of different samples are given and discussed. Thirty-seven peaks corresponding to forty-seven radiations could be observed between 10 and 160 keV; they are distributed about equally between γ and X-rays and are due to fallout and natural radioactivity. Twenty-one different emitters which are linked to seventeen different radionuclides could be associated with these radiations. Of special interest are the naturally occurring radionuclides 210 Pb, 228 Th, 230 Th, 238 U along with the fallout fission products, 127m Te, 129m Te and 155 Eu; it appears that these three fallout fission products have been identified for the first time in the canadian environment. The 59.5 keV γ-ray seen in some of the samples is assigned to 241 Am which would arise from the decay of 241 Pu, a fallout product of recent origin from nuclear weapons testing. The potential of a planar Ge detector as a tool to study the radioactivity in surface waters is discussed along with the results.

A study of γ-rays from the 238U decay

Abstract A planar germanium detector was used to study the γ-rays following the α-decay of 238U. A γ-ray at 113.5±0.1 keV with an emission probability of (0.0102±0.0015)% was identified in the decay of 238U samples in which a radiochemical separation of the thorium isotopes was performed. It is attributed to the photon going from 4+ to the 2+ level of 234Th; it follows that the energy of the 4+ level of 234Th is 163.0±0.1 keV. The emission probability of the well known γ-ray at 49.55 keV going from the 2+ to 0+ states of 234Th was found to be (0.064±0.008)%, a value much lower than the one which seems to be accepted in the literature. From these emission probabilities and the theoretical total internal conversion coefficients for E2 transitions, the α-branchings to the 4+ and 2+ states of 234Th in the decay of 238U are calculated to be (0.078±0.012)% and (21.2±2.7)% respectively; on the basis of these values, the α-branching to the ground state of 234Th becomes (78.8±2.7)

Fallout of 58Co, 60Co and 54Mn in eastern Canada from nuclear weapons testing

Fallout of the 58 Co, 60 Co and 54 Mn radionuclides was observed in a small river located in eastern Canada. These activities were found in sludge samples collected at a water filtration plant. They were attributed to the Chinese thermonuclear test of November 17, 1976. Their relative formation rates would indicate that they were induced by 14-MeV neutron activation of a bomb casing material with a high nickel content.

On the transport and trajectories of the chernobyl debris across Canada and the arctic

A scenario is presented for the transport of the Chernobyl radioactive debris across Canada and the Arctic. It is based on the analysis of the103Ru/137Cs ratios in terms of the Chernobyl release pattern. The ratios which ranged from 0.2 to more than 4.0 were associated with four different phases of the Chernobyl emissions which lasted 10 days, from April 26 to May 6, 1986. Debris from the initial phase /ratios of 0.2 to 0.5/ and the last phase /ratios above 2.5/ would have entered Canada on a very broad front extending from northern Quebec to the North West Territories by way of Greenland and the Arctic; debris from the second phase /ratios of 0.5 to 2.0/ and the third phase /ratios of 2.0 to 2.5/ would have entered Canada from the west after travelling by way of northern Siberia and the Bering Sea.

On the depletion of235U and234U in commercially available uranium compounds: A survey using low energy γ-ray spectrometry

A survey of the situation regarding depletion of235U and234U in nine commercially available uranium compounds is reported. It was done by using a low energy γ-ray counting method, based on peak area ratio and dilute uranium solution. This survey shows that in Canada and USA there may be a large inventory of uranium compounds inadequately labelled regarding their isotopic composition; this situation is likely to be prevalent in many other countries.