Transport of ?-Radiation Through a Barrier with Finite Transverse Dimensions
Abstract Generated abstract
The paper examines gamma radiation transport through barriers whose transverse dimensions are comparable to the incident radiation field, a situation relevant to radiation monitoring of hot rolled products. Using a Monte Carlo statistical trials calculation on a BESM-4 computer, the authors model Co-60 gamma radiation passing through a 200 mm thick and 200 mm wide iron barrier, analyzing 25,000 particle histories and normalizing results to one incident quantum. The study reports angular and energy distributions of radiation emerging from the lateral face and shows that side-face flux is not negligible, being comparable in magnitude to reflected flux. It emphasizes that shielding calculations for such geometries should include the hard spectral component and angular anisotropy of lateral radiation.
Full Text
TRANSPORT OF $\gamma$-RADIATION THROUGH A BARRIER WITH LIMITED TRANSVERSE DIMENSIONS
G. Sh. Pekarskii, Yu. Ya. Katsman
(Presented by the scientific seminar of the Scientific Research Institute of Electrical Measurements)
The practice of radiation monitoring is associated with the passage of radiation through barriers with limited transverse dimensions, with the width of the incident-radiation field being equal to or close to the width of the barrier. The available data on the albedo of $\gamma$-radiation from point sources [1] do not make it possible to calculate protection against radiation that has passed through the lateral faces of the product being monitored.
In developing the shielding for a radiation-monitoring system for hot-rolled products at the Izhevsk Metallurgical Plant, the transport of Co$^{60}$ $\gamma$-radiation through iron barriers 200 mm thick was investigated. The calculation of $\gamma$-radiation transport was carried out on a BESM-4 computer by the method of statistical trials, using statistical weights and conditional probabilities, for a barrier 200 mm wide with an incident-radiation field width of 200 mm. The results were obtained on the basis of an analysis of 25,000 histories and normalized to one incident $\gamma$-quantum.
The angular distribution of the radiation emerging through the lateral face is shown in Fig. 1; the angle $\Theta$ is measured from the direction of incidence of the radiation. The results are integrated within the limits $\Delta \varphi$ indicated in the figure by the numbers next to the curves. Figures 2 and 3 present the energy distribution of the $\gamma$-radiation emerging through the lateral face.
Fig. 1. Angular distribution of the radiation emerging through the lateral face of the barrier.
Fig. 2. Energy distribution of the radiation from a line source that emerged through the side face:
—— \(\cos\Theta > 0\);
— — — \(\cos\Theta < 0\).
Fig. 3. Energy distribution of the radiation from a point source that emerged through the side face:
—— \(\cos\Theta > 0\);
— — — \(\cos\Theta < 0\).
The energy distribution of \(\gamma\)-radiation, differential in \(\varphi\), that emerged into a unit solid angle through the side face is presented in the table.
Table
Energy distribution, differential in \(\varphi\), of \(\gamma\)-radiation that emerged into a unit solid angle through the side face \((\times 10^{-4})\)
| Energy interval, MeV | \(\cos\Theta>0\), \(\varphi\): \(0^\circ\div15^\circ\) | \(\cos\Theta>0\), \(\varphi\): \(15^\circ\div45^\circ\) | \(\cos\Theta>0\), \(\varphi\): \(45^\circ\div90^\circ\) | \(\cos\Theta<0\), \(\varphi\): \(0^\circ\div15^\circ\) | \(\cos\Theta<0\), \(\varphi\): \(15^\circ\div45^\circ\) | \(\cos\Theta<0\), \(\varphi\): \(45^\circ\div90^\circ\) |
|---|---|---|---|---|---|---|
| 0.1–0.16 | 41.3 | 34 | 15 | 32 | 26.9 | 10.3 |
| 0.16–0.23 | 59.5 | 49.8 | 22 | 92.8 | 80.3 | 36.2 |
| 0.23–0.31 | 68.2 | 56.4 | 20.9 | 118.5 | 122.8 | 39.5 |
| 0.31–0.39 | 101 | 66.9 | 29.3 | 78.7 | 71.4 | 25.3 |
| 0.39–0.47 | 133.7 | 105 | 36.1 | 22.6 | 25.7 | 9.6 |
| 0.47–0.55 | 79.6 | 78.8 | 29.5 | 1.1 | 3.4 | 4.0 |
| 0.55–0.9 | 315 | 241.3 | 105 | 0.25 | 1.1 | — |
| 0.9–1.25 | 261.5 | 238 | 107 | — | — | — |
The results obtained show that, if the dimensions of the incident-radiation field are comparable with the transverse dimensions of the barrier, the radiation flux through the side face cannot be neglected; in magnitude it is comparable with the reflected flux (when normalized to the incident flux, respectively, 0.089 and 0.115).
When calculating shielding against side radiation, one should take into account not only the presence of a hard component (absent in the reflected flux), but also the anisotropy with respect to the angles \(\Theta\) and \(\varphi\).
REFERENCES
- B. V. Bulatov et al. Albedo of \(\gamma\)-Radiation. Moscow, Atomizdat, 1968.