A-Emitters

Radon-222 [14859-67-7] Rn, is a naturally occuriing, iaert, radioactive gas formed from the decay of radium-226 [13982-63-3] Ra. Because Ra is a ubiquitous, water-soluble component of the earth s cmst, its daughter product, Rn, is found everywhere. A major health concern is radon s radioactive decay products. Radon has a half-life of 4 days, decayiag to polonium-218 [15422-74-9] Po, with the emission of an a particle. It is Po, an a-emitter having a half-life of 3 min, and polonium-214 [15735-67-8] Po, an a-emitter having a half-life of 1.6 x lO " s, that are of most concern. Polonium-218 decays to lead-214 [15067-28A] a p-emitter haviag = 27 min, which decays to bismuth-214 [14733-03-0], a p-emitter haviag... 

The discovery of plutonium-238, an a-emitter having a half-life, 0, of 87.7 years, by G. T. Seaborg and co-workers (9,10) was achieved by bombardment of uranium using deuterons, (eqs. 1 and 2) ... 

The principal ha2ards of plutonium ate those posed by its radioactivity, nuclear critical potential, and chemical reactivity ia the metallic state. Pu is primarily an a-emitter. Thus, protection of a worker from its radiation is simple and usually no shielding is requited unless very large (kilogram) quantities are handled or unless other isotopes are present. 

Elaborate precautions must be taken to prevent the entrance of Pu iato the worker s body by ingestion, inhalation, or entry through the skin, because all common Pu isotopes except for Pu ate a-emitters. Pu is a P-emitter, but it decays to Am, which emits both (X- and y-rays. Acute intake of Pu, from ingestion or a wound, thus mandates prompt and aggressive medical intervention to remove as much Pu as possible before it deposits in the body. Subcutaneous deposition of plutonium from a puncture wound has been effectively controlled by prompt surgical excision followed by prolonged intravenous chelation therapy with diethylenetriaminepentaacetate (Ca " —DTPA) (171). 

Neutron radiation is emitted in fission and generally not spontaneously, although a few heavy radionueleides, e.g. plutonium, undergo spontaneous fission. More often it results from bombarding beryllium atoms with an a-emitter. Neutron radiation deeays into protons and eleetrons with a half-life of about 12 min and is extremely penetrating. 

The final member of the group, actinium, was identified in uranium minerals by A. Debieme in 1899, the year after P. and M. Curie had discovered polonium and radium in the same minerals. However, the naturally occurring isotope, Ac, is a emitter with a half-life of 21.77 y and the intense y activity of its decay products makes it difficult to study. 

Cl is an efficient, and relatively mild, method of ionization which takes place at a relatively high pressure, when compared to other methods of ionization used in mass spectrometry. The kinetics of the ion-molecule reactions involved would suggest that ultimate sensitivity should be obtained when ionization takes place at atmospheric pressure. It is not possible, however, to use the conventional source of electrons, a heated metallic filament, to effect the initial ionization of a reagent gas at such pressures, and an alternative, such as Ni, a emitter, or a corona discharge, must be employed. The corona discharge is used in commercially available APCI systems as it gives greater sensitivity and is less hazardous than the alternative. 

Calorimetry. Radioactive decay produces heat and the rate of heat production can be used to calculate half-life. If the heat production from a known quantity of a pure parent, P, is measured by calorimetry, and the energy released by each decay is also known, the half-life can be calculated in a manner similar to that of the specific activity approach. Calorimetry has been widely used to assess half-lives and works particularly well for pure a-emitters (Attree et al. 1962). As with the specific activity approach, calibration of the measurement technique and purity of the nuclide are the two biggest problems to overcome. Calorimetry provides the best estimates of the half lives of several U-series nuclides including Pa, Ra, Ac, and °Po (Holden 1990). 

Schoeters G, Van Den Heuvel R, Vanderborght O. 1985. The study of damage to bone marrow cells as a biological dosimeter after contamination with osteotropic a emitters. EUR 9250 51-61. 

The plutonium concentration in marine samples is principally due to environmental pollution caused by fallout from nuclear explosions and is generally at very low levels [75]. Environmental samples also contain microtraces of natural a emitters (uranium, thorium, and their decay products) which complicate the plutonium determinations [76]. Methods for the determination of plutonium in marine samples must therefore be very sensitive and selective. The methods reported for the chemical separation of plutonium are based on ion exchange resins [76-80] or liquid-liquid extraction with tertiary amines [81], organophosphorus compounds [82,83], and ketones [84,85]. 

By 1930 experiences of the earliest workers with radioisotopes, especially a emitters, had offered dramatic evidence of their dangers. It... 

Fig. 8.7. FD probe, (a) Emitter holder of a JEOL FD probe tip, (b) a drop formed of 1-2 pi analyte solution placed onto the activated emitter by means of a microliter syringe.

The only isotope of Np suitable for chemical work is Np, which has a very long Tj/2 of 2.14 x 10 years. It is an a-emitter with some penetrating y radiation, and is available in kilogram amounts. The isotope is formed in nuclear reactors from both and and also results from the a-decay of Am. Although it is the least toxic of the common transuranic isotopes, it is about 1000 times more radioactive than U and should always be handled in gloved boxes. 

Because of the multivalent nature of the actinide ions, understanding the radiation-induced change of the valence-state of the actinide in solutions under self-irradiation or external irradiation is a challenge in radiation chemistry. Some of the ions are strong a-emitters. It is also important from a practical viewpoint that the solution chemistry of actinide ions is closely related to the storage and the repository of the wastes. Much work combined with experiment and simulation has been conducted and reviews were summarized [136,140-144]. 

For X-ray generation, other radionucleides such as 241 Am (r = 430 years) can be used. This nucleus emits a radiation accompanied by b photons of 60 keV energy. Finally, it is possible to mix a / -emitter and a second element, which is used as a target and plays the role of the anticathode in an X-ray tube. For example, the source 147Pm/Al (r — 2.6 years) emits a decelerating radiation between 10 and 200 keV. 

Small neutron sources containing an a emitter (a few pg of 241 Am or 124Sb) inserted in a beryllium envelope have been developed to avoid the above limitations. The nuclear reaction generating the neutrons is the following ... 

Actinides, unlike lanthanides, are a emitters. Tests made with 243Am, 241Am, and 244Cm, which have a radiation intensities (or a decay constants) in the ratio 1 17 435, gave very similar results in regard to both target elution and product yield. Therefore, if a radiation is responsible for the difference, the effect is independent of a intensity. 

---