Slow-positron beamline temperature rise reduction at Kyoto University Research Reactor

Contribution of cadmium to the total amount of positron creation in a reactor-based slow positron beamline

“…Therefore, assuming that the positron moderation efficiency of the W-strip assembly is 5 × 10 −5 , the number of slow positrons is estimated to be ∼8 × 10 6 slow e + /s. The actual beam intensity of the slow positrons obtained during 5 MW KUR operation has been confirmed to be 6.2 × 10 6 slow e + /s at the end of the beamline [30]. The above-estimated value seems to be reasonable compared to the measured value.…”

“…The re-emitted slow positrons are extracted by an electric field, guided by a magnetic field excited by solenoid coils, and are then transported about 10 m downstream to a sample position. Details regarding the KUR slow positron beamline have been described elsewhere [28,29,30].…”

“…imum thermal power, the temperature of the Cd cap in its mounted position reaches nearly 300 • C due to nuclear heating, which is close to its melting point (321 • C). For this reason, an additional cooling system of the positron source has been installed to enable safe extraction of a slow positron beam during 5 MW operation [30], and special attention must be paid to its temperature to avoid melting. Using the Cd cap as the positron source is the same as the other reactor-based slow positron beam facilities.…”

“…Using the Cd cap as the positron source is the same as the other reactor-based slow positron beam facilities. However, removing heat from the Cd cap in the KUR positron source is difficult because of its structure [30], described above. Therefore, estimating how much the Cd cap contributes to positron creation becomes an interesting matter.…”

Effect of neutron–photon converter materials (Cd, Gd, and Sm) on the positron production in a reactor-based slow positron beamline

“…A reactor-based positron source containing a neutronphoton converter is exposed to an intense nuclear heating environment. As Cd has a relatively low melting point (321 • C), the positron source must be designed with sufficient consideration for its cooling [26].…”