No abstract available

[en] This note discusses the assumptions and results of synchrotron radiation shielding estimates for ALS bend magnet and wiggler beamlines. Estimates of gas bremsstrahlung production are not included and are dealt with elsewhere

[en] The Bevatron accelerated protons up to 6.2 GeV and heavy ions up to 2.1 GeV/amu. It operated from 1954 to 1993. Radioactivity was induced in some concrete radiation shielding blocks by prompt radiation. Prompt radiation is primarily neutrons and protons that were generated by the Bevatron's primary beam interactions with targets and other materials. The goal was to identify the gamma-ray emitting nuclides (t_1/2 > 0.5 yr) that could be present in the concrete blocks and estimate the depth at which the maximum radioactivity presently occurs. It is shown that the majority of radioactivity was produced via thermal neutron capture by trace elements present in concrete. The depth of maximum thermal neutron flux, in theory, corresponds with the depth of maximum induced activity. To estimate the depth at which maximum activity occurs in the concrete blocks, the LAHET Code System was used to calculate the depth of maximum thermal neutron flux. The primary beam interactions that generate the neutrons are also modeled by the LAHET Code System

[en] The reaction ⁷Li(p,n)⁷ Be has been proposed as an accelerator-based source of neutrons for Boron Neutron Capture Therapy (BNCT). This reaction has a large steep resonance for proton energies of about 2.3 MeV which ends at about 2.5 MeV. It has generally been accepted that one should use 2.5 MeV protons to get the highest yield of neutrons for BNCT. This paper suggests that for BNCT the optimum proton energy may be about 2.3 MeV and that a proton energy of about 2.2 MeV will provide the same useful neutron flux outside a thinner moderator as the neutron flux from a 2.5 MeV proton beam with a, thicker moderator. These results are based on optimization of the useful neutron spectrum in air at the point of irradiation, not on depth-dose profiles in tissue/tumor

[en] Estimates are made of the induced activity created during high-energy electron showers in tungsten, using the EGS4 code. Photon track lengths, neutron yields and spatial profiles of the induced activity are presented. 8 refs., 9 figs., 1 tab

[en] The reaction ⁷Li(p,n)⁷ Be has been proposed as an accelerator-based source of neutrons for Boron Neutron Capture Therapy (BNCT). This reaction has a large steep resonance for proton energies of about 2.3 MeV which ends at about 2.5 MeV. It has generally been accepted that one should use 2.5 MeV protons to get the highest yield of neutrons for BNCT. This paper suggests that for BNCT the optimum proton energy may be about 2.3 MeV and that a proton energy of about 2.2 MeV will provide the same useful neutron fluence outside a thinner moderator as the neutron fluence from a 2.5 MeV proton beam with a thicker moderator

[en] Offsite neutron fluences resulting from Bevatron operations reached a maximum in 1959, prior to the addition of a permanent concrete roof shield, which was constructed in 1962. From the first operation of the Bevatron measurements of neutron fluence were made at locations around the perimeter of the Lawrence Berkeley National Laboratory (LBNL) campus. Since the late 1950's measurements made at several locations, and particularly at the site of what is now called the Olympus Gate Environmental Monitoring Station, have been routinely reported and published. Early measurements were used to establish the shape of the neutron-energy spectrum from which an energy-averaged fluence-to-dose equivalent conversion coefficient could be derived. This conversion coefficient was then applied to a measured total neutron fluence to obtain the appropriate dose equivalent quantity required by regulation. Recent work by Thomas et al. (2000) have compared the early conversion coefficients used in the sixties with those accepted today and suggest suggested that ''the dose equivalents reported in the late fifties and early sixties were conservative by factors between two and four. In any current review of the historical data, therefore it would be prudent to reduce the reported dose equivalents by at least a factor of two.'' However, that analysis was based on the ''state of the art'' neutron energy-spectra of the '60s. This paper provides a detailed knowledge of the neutron energy spectrum at the site boundary paper thus removing any uncertainty in the analysis of Thomas et al., which might be caused by the use of the early neutron energy-spectra. Detailed Monte Carlo analyses of the interactions of 6.2 GeV protons in thick, medium-A targets are described. In the computer simulations, neutrons produced were allowed to scatter in the atmosphere. Detailed neutron energy spectra were calculated at a distance and elevation corresponding to the location of the Olympus Gate EMS. Both older and newer sets of conversion coefficients were applied to the calculated neutron energy spectra. It is concluded by this independent assessment that early dose equivalent estimates were conservative by at least a factor of 4. This reduction results from three factors: (1) a better understanding of the neutron energy spectrum at the laboratory site boundary (factor of ∼2); (2) revised conversion coefficients (factor of ∼2); and (3) the intrinsic conservatism of the reported dose equivalents (factor of ∼2). An investigation of the detector response to neutrons strongly suggests an additional systematic overestimation of the total neutron fluence by the routinely used environmental monitors. The influence of the ground on detector response has also been studied. Based on IAEA response functions, when calibrated with standard ²³⁹PuBe neutron sources, 6-inch dia. spherical polyethylene moderators would have overestimated the dose equivalents in the accelerator spectra by a factor of about 1.3. It was also possible to show that at locations near the Olympus Gate Environmental Monitoring Station radiation levels at places not in direct view of the Bevatron were further reduced by a factor of about 2 because skyshine contributed about half the total dose equivalent

[en] The Active Personnel Dosimeter (APD) provides a digital readout of events caused by neutrons interacting with superheated liquid droplets. The droplets are suspended in a gel held in a replaceable cartridge. Upon neutron interaction, the superheated droplet vaporizes, forming a bubble. The sound produced in this process is recorded by transducers that sense the accompanying pressure pulse. The APD electronically discriminates against spurious noise and vibration. Studies with the production prototype APDs indicate that the detector response is linear up to about 0.40 mSv, with large variations sometimes from predicted values and between cartridges at higher dose equivalents. The response to standard neutron sources (bare ²⁵²Cf, PuBe, PuB, PuF, PuLi) is reported and compared with the expected response. Unirradiated cartridges self-nucleate when heated to temperatures of 46 degree C. The APD is insensitive to low-energy photons but responds to high-energy photons and electrons. 9 refs., 2 figs., 3 tabs

[en] The Bevatron of the Lawrence Berkeley National Laboratory operated with no permanent shielding-roof from 1954 to 1962. Neutron fluences measured at the laboratory perimeter reached a maximum in 1959, and were reported as an annual dose equivalent of 8.1 mSv (54% of the then operative radiation limit). The addition of temporary local shielding and improved operational techniques subsequently led to a steady decline in dose equivalent at the laboratory perimeter. A permanent concrete shielding-roof was constructed in 1962. In those early years of operation the reported dose equivalent, H, was derived from a measured total neutron fluence, F, and an estimated spectrum-weighted fluence to dose equivalent conversion coefficient, (g), where H=(g)F. The uncertainty in H was almost entirely due to the uncertainty in (g). While the measurements of F were accurate the estimates of (g) were quite crude and depended upon measurements of average neutron energy, on assumptions about the shape of the neutron energy spectrum, and primitive values of fluence to dose equivalent conversion coefficients for monoenergetic neutrons. These early reported dose equivalents were known to be overestimated. This paper has reappraised the dose equivalents in the light of better information now available. Environmental neutron spectra have been calculated which more accurately correspond to the operational conditions of the Bevatron in the 1950s and early 1960s, than did those spectra available at that time. A new fluence to dose equivalent conversion function based on the latest data and for isotropic irradiation geometry was developed. From these two parameters better estimates of the coefficient (g) were determined and compared with the earlier values. From this reappraisal it is shown that the early reported dose equivalents were conservative by a factor of at least five. (author)

[en] The Active Personnel Dosimeter (APD) provides a digital readout of events caused by neutrons interacting with superheated liquid droplets. The droplets are suspended in a gel held in a replaceable cartridge. Upon neutron interaction, the superheated droplet vaporizes, forming a bubble. The sound produced in this process is recorded by transducers that sense the accompanying pressure pulse. The APD electronically discriminates against spurious noise and vibration. Studies with the production prototype APDs indicate that the detector response is linear up to about 0.40 mSv, with large variations sometimes from predicted values and between cartridges at higher dose equivalents. The response to standard neutron sources (bare ²⁵²Cf, PuBe, PuB, PuF, PuLi) is reported and compared with the expected response. Unirradiated cartridges self-nucleate when heated to temperatures of 46 degrees C. The APD is insensitive to low-energy photons but responds to high-energy photons and electrons. 8 refs., 2 figs., 3 tabs