Organization of the Laboratory and Personnel Protection When Working with a Betatron

G. P. GARTANEEV, V. A. MOSKALEV, B. M. YAKOVLEV

(Presented by the scientific seminar of the Faculty of Physics and Technology)

To ensure safety when working with accelerator installations, it is necessary to know the spatial distribution of radiation and the doses received by personnel.

Working with a betatron with a maximum energy of 11 MeV, we carried out approximate measurements using a type “B” installation. The data obtained on this installation with the use of γ- and β-counters made it possible to qualitatively assess the level of scattered radiation at various points of the betatron laboratory by comparing the number of counts of the instrument with the level of the natural background.

Quantitative measurements of doses at the laboratory workstations were carried out using a “Mak” type microdosimeter, calibrated against a radioactive preparation.

The results of measurements of scattered radiation obtained using the type “B” installation showed that the most intense radiation is observed during operation of the betatron in adjacent rooms in the plane of the equilibrium orbit of the electrons and especially in the direction of the radiation maximum characteristic of the spatial distribution of the betatron rays. When the counters were displaced upward and downward relative to the indicated plane, the radiation intensity decreased, and in measurements in the rooms of the second floor, including the room located directly above the betatron, the magnitude of the radiation exceeded the level of the natural background by no more than a factor of 2.

Quantitative measurements showed that, on average over an 8-hour working day, at the control panel (position 1, Fig. 1), separated from the apparatus by a brick wall 90 cm thick, the dose was 0.0288 r, i.e., almost 4 times lower than 0.1 r and 2 times lower than 0.05 r, which are officially recognized as permissible. Under the same conditions, in position 2 (Fig. 1) this dose was 0.46; in position 3—0.135 r; in position 4—0.307 r. In position 2, when the dosimeter chamber was located 1.3 m below the plane of the equilibrium orbit, the average dose over the working day was 0.115 r. In the rooms of the second floor, radiation was not detected by the “Mak” dosimeter while the betatron was operating.

Since the energy of the gamma quanta of our betatron exceeded the threshold of photonuclear reactions for a number of elements, activation of objects exposed to irradiation by betatron rays was observed. Measurements showed,

that at all points of the apparatus room the radiation background exceeded the natural level. Measurements carried out on August 28, 1953, showed that in the center of the apparatus room the excess over the natural background averaged 20–25%. This excess was somewhat greater when the counter was placed near the wall, at the place where the beam struck. The presence of radio-

Fig. 1. Plan of the laboratory and arrangement of the equipment.

active isotopes in the apparatus room is also indicated by the fact that, with the closed iron doors leading into the apparatus room, in the adjacent room where the control panel is installed, at position 1 the γ- and β-counters showed no excess over the natural background level. With the doors open, this excess averaged 11% of the natural background level. In the remaining rooms of the laboratory, no induced activity was observed.

The phenomenon of activation of surrounding objects during operation of the betatron is, of course, considerably intensified at higher radiation energies (20–30 MeV), at which the beam of ultrahard rays of the betatron is accompanied by a sufficiently intense flux of fast and slow neutrons, arising both in the betatron target and in the parts that form the beam of rays (collimator, equalizing filter, etc.). The neutron flux can contribute to the induction of artificial activity of elements with a long half-life.

The constant irradiation of laboratory personnel that occurred in the case under discussion led to the manifestation of separate symptoms of chronic radiation sickness.

For example, in employee B., before the start of work, the leukocyte count was 3800 per mm³. During the work, B. was at the control panel (position 1, Fig. 1) for 2 hours. Analyses carried out directly at the control panel showed that the leukocyte count by the end of the first hour had increased to 4950 per mm³, and by the end of the second—to 5850. Studies carried out over the subsequent 4 hours after work gave the following series of figures: 3050, 4200, 6650, and 7950 leukocytes per mm³. After 24 hours, there were 4250 leukocytes per mm³.

Examination of employee G. under the same conditions gave similar results.

Analyses of hemograms carried out in absolute numbers often show an increased number of lymphocytes with reduced numbers of neutrophils. The acute reaction, examples of which we have given above, is characterized by neutrophilic leukocytosis with a left nuclear shift and by the intactness or decrease in the number of lymphocytes.

Hemoglobin and erythrocyte values change more slowly than the number of leukocytes; therefore it is especially important that studies be carried out over time. Under conditions of chronic irradiation, a decrease in erythrocytes and hemoglobin is usually observed, which may sometimes continue even after work has ceased, for several days. Then recovery of these values begins; they may reach high levels at the time of prolonged rest (Fig. 2).

Fig. 2. Curves of the erythrocyte count and hemoglobin percentage.

In studying blood smears, we noted a number of morphological changes, which on some days of examination either increased in intensity or disappeared completely. In neutrophils, the presence of toxic granulation in the protoplasm was noted fairly often, as were areas of pyknosis in the nuclei of individual cells; in lymphocytes, atypical nuclei of some cells and often increased basophilia of the protoplasm. Among deviations in the red blood, the rather infrequent appearance of erythroblasts may be noted.

Among other general phenomena observed in the personnel, one may note slight fatigability, irritability, increased sweating, brief attacks of dizziness, headaches, sleep disturbance, pain in the region of the heart, and a number of other symptoms.

Consequently, if one takes into account that symptoms of chronic radiation sickness are observed at doses of scattered radiation below the officially permissible limits (0.05–0.1 r per working day), the question must be raised of lowering the latter. In all probability, this dose for high-energy radiation should be reduced to values close to the natural background.

To reduce the scattered-radiation background to such a level is possible either by constructing special barite-concrete walls or, taking into account the peculiarities of the spatial distribution of the scattered radiation of the betatron, by placing the accelerator in a special basement room in such a way that the plane of the equilibrium orbit of the electrons is 2–3 meters below the floor level of the remaining rooms when the beam of rays propagates horizontally. In any other case (including a rotatable betatron), the plane of the equilibrium orbit must not intersect adjacent rooms where people are present.

Taking into account the induced activity and the presence of a radioactive target, it is necessary to provide the laboratory room with effective supply-and-exhaust ventilation, to create in the zone where the beam falls a so-called “extinction pit,” and to ensure ease of mechanical cleaning of the walls and floor.

premises and, if necessary, ease of replacement of the facing material.

For such a laboratory, no fewer than two rooms are required, since the betatron must be controlled only from other premises.

In our view, placing the betatron in special basement rooms is the most advantageous solution, both in terms of the effectiveness of protection and in terms of saving resources.

When working with animals, it is necessary to take into account the possibility of induced activity in their tissues; accordingly, the housing and care of the animals must be the same as for animals into which a radioactive substance has been introduced internally.