Polonium Source Research Articles

Forensic Aspects in Polonium-210 Poisoning

The human body is exposed to radiation resulting from the presence and degradation in the environment of natural radionuclides like uranium and thorium. In laboratories, several radioactive isotopes are being used: uranium-235, iodine-131, cobalt-60, and carbon-14. These radioactive isotopes are useful in scientific (dating human skeletal remains) and medical purposes (radiotherapy/radiodiagnosis), but they are also used in criminal context. Polonium 210 (Po-210) is a natural radioisotope occurring in the natural environment as consequence of uraniu-238 decay chain. The current paper presents a less known subject of lethal poisoning with Po-210 radioisotope, in order to underline the methods used for Po-210 identification in forensic samples. The authors performed a literature review of the scientific researchers published in the last years concerning polonium sources and its use as a poison. Polonium�s effectiveness as a poison relies on its chemical characteristics only to the extent that they determine the isotope�s distribution and retention in organs and tissues; the alpha particles are responsible for the lethal effect. Po-210 poisoning is particular, as it doesn�t leave traces, it can be easily transported, and is not detected by airport scanners. Identifying this compound during a medico-legal autopsy is very difficult, as the post-mortem examination will not yield characteristic aspects, the forensic pathologist being forced to consider this as a potential cause of a rapid death, with significant visceral damage.

Biomembranes research using thermal and cold neutrons

In 1932 James Chadwick discovered the neutron using a polonium source and a beryllium target (Chadwick, 1932). In a letter to Niels Bohr dated February 24, 1932, Chadwick wrote: “whatever the radiation from Be may be, it has most remarkable properties.” Where it concerns hydrogen-rich biological materials, the “most remarkable” property is the neutron’s differential sensitivity for hydrogen and its isotope deuterium. Such differential sensitivity is unique to neutron scattering, which unlike X-ray scattering, arises from nuclear forces. Consequently, the coherent neutron scattering length can experience a dramatic change in magnitude and phase as a result of resonance scattering, imparting sensitivity to both light and heavy atoms, and in favorable cases to their isotopic variants. This article describes recent biomembranes research using a variety of neutron scattering techniques.

Rapid Preparation of Polonium Counting Sources for Alpha Spectrometry Using Copper Sulfide Microprecipitation

Thin-layer polonium (Po) sources for alpha spectrometry counting can be rapidly prepared using copper sulfide (CuS) microprecipitation. Polonium was coprecipitated with CuS, filtered onto Eichrom Resolve filters, and counted. This simple procedure is faster, cheaper, and more convenient than traditional spontaneous plating on metallic discs, and similar yields were obtained (80-90%). The experimental conditions for the microprecipitation technique were optimized (0.05 mg of Cu(2+) in 10 mL of 1 M HCl); these compare advantageously with conventional preparation and purification procedures for polonium samples (0.1 to 1 M HCl). The results showed that the most likely potential radionuclide interferences (Ra, Th, U, Np, Pu, and Am) for long-lived polonium isotopes ((208)Po, (209)Po, (210)Po) are effectively removed during processing. The effects of several transition metals (Cu(2+), Ag(+), Fe(3+), Fe(2+), Pb(2+), and Ni(2+)) on the yield and the resolution of the alpha peaks obtained were also assessed. Little interference was found, demonstrating the versatility of the present microprecipitation technique for environmental and biological matrices. The procedure has been successfully applied to different amounts of (210)Po using (209)Po as a yield tracer.

1932, a watershed year in nuclear physics

The consequences, for good and ill, of that annus mirabilis of discovery and invention are still very much with us.

A new version of a portable polonium source for the non-destructive PIXE (particle induced X-ray emission) analysis in the cultural heritage field

A new version of the portable polonium source, named L-PIXE (large-particle induced X-ray emission), to be used for the non-destructive analysis in the Cultural Heritage field, was realised in the framework of a collaboration between the Italian LNS-INFN (Laboratori Nazionali del Sud-Istituto Nazionale di Fisica Nucleare) and IBAM-CNR (Istituto per i Beni Archeologici e Monumentali-Consiglio Nazionale delle Ricerche).The new source presents a compact geometry and it was designed to operate with large area SDD (silicon drift detector) detectors. In particular, the L-PIXE source was coupled to a 50mm² SDD detector and tested by measuring geochemical reference materials.Results evidenced a gain factor, in terms of counting statistics in the measured X-ray spectra, equal to 11–12 with respect to the previous versions of the source. A preliminary evaluation of the MDL (minimum detection limit) of the new experimental set-up evidenced the possibility of using the new L-PIXE source for identifying the presence of minor and, in some cases, trace elements composing samples under investigation.

Testing the stand-alone microbeam at Columbia University

The stand-alone microbeam at Columbia University presents a novel approach to biological microbeam irradiation studies. Foregoing a conventional accelerator as a source of energetic ions, a small, high-specific-activity, alpha emitter is used. Alpha particles emitted from this source are focused using a compound magnetic lens consisting of 24 permanent magnets arranged in two quadrupole triplets. Using a 'home made' 6.5 mCi polonium source, a 1 alpha particle s(-1), 10 microm diameter microbeam can, in principle, be realised. As the alpha source energy is constant, once the microbeam has been set up, no further adjustments are necessary apart from a periodic replacement of the source. The use of permanent magnets eliminates the need for bulky power supplies and cooling systems required by other types of ion lenses and greatly simplifies operation. It also makes the microbeam simple and cheap enough to be realised in any large lab. The Microbeam design as well as first tests of its performance, using an accelerator-based beam are presented here.

A microbeam irradiator without an accelerator

The stand-alone microbeam, under development at RARAF, presents a novel approach to biological microbeam irradiation studies. Foregoing a conventional accelerator as a source of energetic ions, we propose to use a small, high-specific-activity, alpha emitter. Alpha particles emitted from this source are focused using a compound magnetic lens consisting of 24 permanent magnets arranged in two quadrupole triplets.Using a “home made” 6.5mCi Polonium source, a 1 alpha particle/s, 10μm diameter microbeam can be realized. As the alpha source energy is constant, once the microbeam has been set up, no further adjustments are necessary apart from a periodic replacement of the source. The use of permanent magnets eliminates the need for bulky power supplies and cooling systems required by other types of ion lenses and greatly simplifies operation. It also makes the microbeam simple and cheap enough to be realized in any large lab.

A novel technique for the simultaneous determination of 210Pb and 210Po using a crown ether

A simple radiochemical procedure has been developed to separate lead and polonium simultaneously from different environmental and biological materials. After adding 208Po tracer and lead carrier samples are decomposed using mineral acids. Lead and polonium are selectively retained from 2 m HCl solution by the bis-4,4′(5′)- t-butyl-cyclohexano-18-crown-6-ether; polonium is stripped with 6 m HNO 3 while lead is stripped with 6 m HCL solution. A polonium source is prepared by spontaneous deposition onto a silver disk. The activity concentration of 210Po is determined by isotope dilution alpha spectrometry. Lead is precipitated as oxalate; the chemical recovery is determined by gravimetry. The activity concentration of 210Pb is calculated from the liquid scintillation spectrum.

The radiation chemistry of aqueous solutions - I. The effect of changing linear energy transfer along a polonium α -particle track

Absolute G values for chemical change when various aqueous solutions are irradiated with α -particles from an external polonium source have been determined for different fractions ( x ) of the α -particle track spent within the solution. G(Fe 3+ ) for an aerated solution containing 1 mM ferrous ions and 0.1N sulphuric acid decreases from 5.0 at x =0.02 through a minimum value 3.65 at 0.11 x 0.01 and then increases to 5.94 at x = 0.525. The local value G(Fe 3+ ), defined as G(Fe 3+ ) for an element of track length a distance x R from the end of the track, where R is the range of the whole track in water, shows a similar but more pronounced dependence on x which is strongly reminiscent of the inverted Bragg curve for l. e. t. plotted against x in this medium, having a minimum of 3.2 5 ± 0.1 5 at x= 0.085±0.015. As x is increased G(Ce 3+ ) for an aerated 200 μM solution of ceric sulphate in 0.1 N sulphuric acid shows no minimum but increases from 1.0 at x =0.04 to 3.0 at x=0.25 and 4. 05 at x = 0.525. Thallous ions have no effect on G(Ce 3+ ) for x ≤ 0.45. G(H 2 O 2 ) for aerated water was found to be 1.22 ±0.06. It is concluded that very few hydroxyl radicals are available and that the intra-track reactions between H 2 O 2 and H as well as OH are very important and vary in extent as x is varied.

Alpha-Particle Ionization in Polyatomic Gases and the Energy Dependence ofW

A series of measurements by three different methods is carried out to determine the variation of W, the average energy to make an ion pair in the gases N/sub 2/ and C/sub 2/H/sub 4/ as a function of the energy of the ionizing alpha particle. In one method, the ionization ratios are determined in the two gases for single alpha particles from two collimated polonium sources, the particles from one source belng reduced in energy by passage through a succession of interchangeable mlca windows. The corresponding energy ratios are determined by auxiliary measurements in pure argon, the W values in argon being assumed constant. W values for alphas of lnitial energy up to 9 Mev are also obtained by a comparison in C/sub 2/H/sub 4/ and N/sub 2/ of the relative ionization from single alpha particles from (Po/sup 210/ + U/sup 212/) and P/sup 210/ + Po/sup 212/) sources. These experiments lndicate a continuous decrease in W values in C/ sub 2/H/sub 4/ and N/sub 2/ wlth lncreasing alpha energy over a range from 1 to 9 Mev. The differential w (defined as the ratio of energy increment deg E to ionization increment deg I at any point on themore » alpha path) also decreases similarly and seems to approach but never quite reach, within the limits of alpha energy so far investigated, the corresponding W value for beta particles. No explanation of this contlnuous decrease with energy of the W values can at present be advanced. (auth)« less

Multiple Scattering of Low-Energy Alpha Particles in a Gas

Alpha particles from a polonium source were slowed down and allowed to enter a cloud chamber containing a mixture of hydrogen, water, and ethyl alcohol at pressures of 12.25 cm, 1.50 cm, and 2.25 cm, respectively, during the sensitive time. Eighty-four sharp tracks of particles which stopped in the illuminated part of the chamber and which did not show any sharp bends due to single scattering were selected for study. Starting at the termini of the projected tracks, the angles between successive chords of three millimeters length were measured, the energies at the first three intersections of the chords being approximately 18, 45, and 85 kev. The magnitudes of the angles at which the tails of the distributions could be distinguished from the Gaussian parts were determined to be 10\ifmmode^\circ\else\textdegree\fi{}, 6\ifmmode^\circ\else\textdegree\fi{} to 8\ifmmode^\circ\else\textdegree\fi{}, and 4\ifmmode^\circ\else\textdegree\fi{}, respectively. The total standard deviations (which included the experimental error of 2.2\ifmmode^\circ\else\textdegree\fi{}) for the Gaussian part of the distributions at these energies were 8.0\ifmmode^\circ\else\textdegree\fi{}, 4.3\ifmmode^\circ\else\textdegree\fi{}, and 3.0\ifmmode^\circ\else\textdegree\fi{}, respectively, so that the standard deviations due to multiple scattering were, respectively, 7.7\ifmmode^\circ\else\textdegree\fi{}, 3.7\ifmmode^\circ\else\textdegree\fi{}, and 2.0\ifmmode^\circ\else\textdegree\fi{}.

An apparatus giving an -particle microbeam for the irradiation of living cells

A microscope fitted for phase contrast observation is modified so that a biological specimen in the centre of the field of view may be irradiated with α-particles. A beam of α-particles is obtained from a polonium source by a glass capillary collimating tube of 15 μ internal diameter, the source and collimator being mounted in a tube passing axially through the optical condenser. The irradiation rate is of the order of 1 particle/min and 70% of the particles lie within a circle of 30 μ diameter in the focal plane of the objective. A statistical method is used to calculate the probability of irradiation of a target of known size which is irradiated for a known time.

Radiation induced by Alpha-Particles in Thin Films

WE have examined spectrographically the light emitted by thin films bombarded by α-particles1. The films were built up by evaporation on quartz slides to a thickness small compared with the range of the α-particles. The slides were mounted in front of the slit of a Hilger f/4 quartz spectrograph and exposed to a 25-mC. polonium source. Representative spectra, photographed on Eastman Kodak type II-0 spectroscopie plates, are shown in the accompanying photograph.

Energy Levels inC12fromBe9(α,n)C12

A thin polonium source and thin beryllium target have been used to investigate energy states in ${\mathrm{C}}^{12}$. The neutron spectrum was determined from proton tracks in Eastman NTA emulsions. By investigating the neutrons emitted in the forward and backward directions, neutrons associated with the transition to the ground state of ${\mathrm{C}}^{12}$ were detected, and excited levels in ${\mathrm{C}}^{12}$ were identified at 4.2 and 7.5 Mev above the ground state.

Investigation of the -Rays from Polonium

A method of standardizing polonium sources by measurement of the number of γ-rays is described. The hard γ-radiation of 0.773 MeV. energy emitted in the decay of 210Po has been found to have an intensity of 1.8±0.14 × 10-5 quanta per α-particle The internal conversion of this line to the extent of 6.7±1.7% gives rise to K X-radiation of lead. No other soft radiation was detected. The decay scheme of polonium is discussed.

Energy Levels inC12fromBe9(α,n)C12

A thin polonium source and thin beryllium target have been used to investigate energy states in ${\mathrm{C}}^{12}$. The neutron spectrum was determined from proton tracks in Eastman NTA emulsions. By investigating the neutrons emitted in the forward and backward directions, neutrons associated with the transition to the ground state of ${\mathrm{C}}^{12}$ were detected, and excited levels in ${\mathrm{C}}^{12}$ were identified at 4.2 and 7.5 Mev above the ground state.

Relative Yields of Ions Produced by α- Particles in Air and Water Vapour

IN continuation1 of the examination of the radiological properties of water, the yield of ion-pairs in water vapour under the action of α- particles has been compared with the yield in air. A sector-shaped parallel-plate ionization chamber containing either water vapour at 95° C. or air has been exposed to a semi-collimated beam of 5·0-MeV.α- particles derived from a polonium source. A low collecting field (about 50 volts/cm.) is sufficient to produce complete saturation in both gases at pressures of 10–20 cm. of mercury, and several determinations of the relative yield of ions1 have been made. These have a mean value IH3o/Iair =1·139 ± 0· 006. Making allowance for possible systematic errors, the corresponding ratio for the energy expenditure per ion pair is taken to be the reciprocal of this figure, = 0· 878 ± 0·02. If the value of Wair for 5-MeV. α-particles is 34·7 ± 0·5 eV.2, the value for water vapour is therefore = 30·5 ± 0·8 eV.

Angular Distribution of Protons Ejected in the Disintegration of Nitrogen by ?-Particles

USING a powerful polonium source and an especially well-defined geometry, we have recently obtained 850 expansion-chamber photographs showing 90 proton tracks produced on the disintegration of nitrogen by ?-particle bombardment. Our arrangement, therefore, gave on the average one disintegration for every ten photographs, thus greatly reducing both the expense of the photographic materials used and the labour of the examination of the photographs.

Electrostatic Deflection Studies of Alpha-Particles; the Alphas fromLi6(p,α)He3

A technique is described for studying nuclear reactions in which short range alpha-particles are produced with a yield that is too small for the direct application of the electrostatic deflector. In preliminary experiments a strong polonium source is used to supply alpha-particles to the deflector, and a group of these alphas, homogeneous in energy, passes through the deflector and enters a variable pressure absorption cell and ionization chamber. Cut-off pressures determined for various alpha-particle energies result in a calibrated cell which can then be used to determine the alpha-particle energies in nuclear disintegrations. Application of this method to ${\mathrm{Li}}^{6}(p,\ensuremath{\alpha}){\mathrm{He}}^{3}$ results in a $Q$ value of 3.94\ifmmode\pm\else\textpm\fi{}0.08 Mev. The calibration, extending in alpha-particle energy from 1 to 1.8 Mev, is also used to determine the slope of the range energy curve. The average value of the slope found for this region is 200 kv per mm range.

On the Preparation of Polonium Sources

On the Preparation of Polonium Sources