C. E. Klabunde

Low‐Temperature Reactor Irradiation Effects in Metals

The effects of structural and chemical defects on the low‐temperature (30–50°K) annealing peak in low‐temperature reactor‐irradiated aluminum and copper were studied. From the fact that the density of reactor‐induced defects did not affect the annealing kinetics, it was possible to conclude that the low‐temperature annealing process was of the first order without a unique activation energy. The fact fact that both oversized and undersized atoms could suppress this annealing peak led to the conclusion that the radiation‐induced defects were more complicated than simple point defects. The suggestion is made that a defect similar to a crowdion must be created by low‐temperature neutron irradiation. This data also supports to some degree the viewpoint that a radiation‐induced defect, possibly a crowdion, has sufficient knock‐on energy to migrate several hundred atomic distances. The experiments also contain evidence which rule out all forms of vacancy‐interstitial annihilation.

Reactor Damage in Pure Metals

By relocating the fuel in the vicinity of a liquid helium cryostat located in the Oak Ridge Graphite Reactor it has been possible to separate the thermal and fast components of the reactor neutron flux. Studies of the radiation damage effects arising from each type of flux have been made. It has been found that an appreciable fraction of the reactor damage in several metals arises from thermal neutrons. The effect results from the recoil of an atom from the (n,γ) reaction at the time of thermal neutron capture. The low temperature recovery of thermal neutron damage is greater and shows more annealing peak structure than the recovery of fast neutron damage. Thermal neutron damage concentration studies have been made on cadmium, and pronounced suppression of the annealing is found as the concentration is increased. The mean primary recoil energy from a thermal neutron capture event has been calculated for several elements. Values range from about 50 eV for the heavier elements to several hundred eV for the ...

Thermal Neutron damage in cadmium

Abstract The isochronal annealing of the damage produced by thermal neutron irradiation of cadmium at 3.6 °K has been studied for several initial doses which vary by a factor of 1000. The recovery results show a strong dependence upon initial dose. This effect, which is not seen to this extent in the fcc metals, cannot be accounted for by an irradiation annealing mechanism. In contrast to the observation of two processes involving long range defect migration for several fcc metals only one process, at high temperatures, is discernable from isochronal annealing of Cd. The presence of another process at low temperatures is clearly established by other means. Irradiation annealing effects observed during the production of damage at high defect concentrations indicate that the spontaneous annihilation volume between the defects of a new capture event and the defects from an earlier event is 80 atomic volumes. Other results suggest that damage production and recovery mechanisms may be associated with the aniso...

Damage recovery in vanadium between 3.8-6.0 K

Abstract The isochronal recovery of thermal neutron damage in V was recently studied1 from 6–320 K by means of resistivity changes. One interesting result was the observation of continuous recovery from 6–40 K in contrast to the spectra of discrete recovery processes seen at low temperatures for thermal neutron damage in nearly all other metals studied. The absence of recovery rate peaks in this low temperature range led to the speculation that the onset of recovery in V may occur by means of long-range interstitial migration rather than the collapse of close Frenkel pairs which is believed to initiate the recovery in most other metals. Another possibility is that close pair recovery in V occurs below 6 K. This speculation is not unreasonable, since recovery below 6 K has been observed in Au, Cd, In, and Zn.2 In the case of Cd, a large recovery rate peak occurs at 5.2 K with a subpeak at 3.6 K.3 In this report, we give results of an investigation which extends the recovery study of thermal neutron damage ...

The role of radioactive decay in irradiation damage in metals

Abstract The effects which may accompany radioactive decay in irradiated metals can be described in terms of five mechanisms. Two are responsible for the production of defects, and two can annihilate existing defects. The fifth mechanism is the formation of transmutations. The relative importance of each mechanism is dependent upon the nuclear properties and damage state of the metal. The experimental observation of the effects of some of these mechanisms is made by means of resistivity change measurements in thermal neutron-irradiated Cu, W, Re, and Au. The observation of those effects which produce compensating changes is accomplished through the use of post-irradiation annealing procedures and control of defect concentration.

LOW-TEMPERATURE RESISTIVITY OF SODIUM AND THE EFFECTS OF NUCLEAR IRRADIATION

Neutron irradiation effects on sodium electrical conductivity at low temperatures were measured using the hole 12 cryostat of the Oak Ridge graphite reactor, Data were compared with those for copper; it is suggested that the displacement threshold for sodium is less than that for copper. Results from pulse-annealing studies are presented in graphical form. The importance of the thermal history of sodium is stressed; sodium is far from an ideal simple metal. (L.N.N.)

A method of transferring irradiated samples in liquid helium

A large copper sample was neutron irradiated at liquid helium temperature and transferred into a neutron spectrometer cryostat without warming above liquid helium temperature. This paper describes the procedure and includes a method of constructing a small aluminium Dewar required in the process.

Miniature uranium fuel plates cooled by liquid helium for irradiation damage studies

The low-temperature irradiation facility (LTIF) located at the bulk shielding reactor in Oak Ridge National Laboratory was designed and has been operated for several years for the study of thermal neutron damage in metals at low temperatures. The highly thermalized neutron flux is obtained by interposing tanks of heavy water between a face of the reactor (swimming-pool type) and the irradiation cryostat. A schematic diagram of the irradiation portion of the cryostat is given in Fig. 1. This design is improved over earlier published versions [1,2].