In a typical nuclear physics experiment, an accelerated ion beam impinges onto a thin target foil to produce the nuclear species to be investigated. The target foil is a stable isotope, often of isotopically enriched material. Radioactive targets can also be manufactured, but not in our laboratory. Targets are produced from a wide range of elements throughout the periodic table. The target is crucial to the success of an experiment, and it has to meet tight specifications of purity, thickness, uniformity and robustness in transport and in-beam operation. A wide variety of techniques are employed in the target preparation laboratory to produce the targets, the main ones being mechanical rolling and thermal heating to evaporate the material onto a substrate.

Targets can be requested using our on-line form​ or by email.

For further information, please contact Marc Labiche or Paul Morrall.​

​Range of elements prepared as targets in the laboratory

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NPG targets have been used worldwide

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Target productio​n techniques

Electron Beam​​ Gun

The electron beam gun consists of a source of electrons (a hot filament) that are accelerated using a high-voltage power supply. The accelerated electrons are then focused using electromagnets and bent through an angle of 270^​o into a crucible where the isotopic material is mounted for evaporation. The electron beam gun has been incorporated into an Edwards 306 coating rig along with a Maxtec ASF 140 oscillating quartz sensor head that monitors the deposition rate and thickness, this in turn is connected to a Maxtec MDC 360 deposition controller.​

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Rolli​ng

The rolling technique is used to produce a wide variety of foil targets covering isotopes over most of the periodic chart. This is often the preferred method of producing target foils since there is very little wastage of the expensive isotope material. The apparatus employed is a Durston electric rolling mill. It consists of two hardened and polished rolls of 124 mm face width by 60 mm diameter, driven by a Fenner 2 horsepower D.C. Motor.

S​​puttering​

​The sputtering rig makes use of two beams of Argon ions (emitted from the ion sources) to bombard the target material. Atoms from the target are then released and form what is akin to a fine mist, which is then deposited onto a substrate. This substrate is supported, and positioned using a planetary motion drive to improve the uniformity of the thin film.

Thermal​​​ evaporation

The thermal evaporation rig is an Edwards 306 thermal resistance evaporation system. It is highly versatile allowing a wide variety of target foils, backings and chemical reductions to be performed. This system is used to produce self-supporting films by evaporation of samples onto glass slides or backing foils.
Evaporation or physical vapour deposition, involves heating the source material until it vaporises. The vapour escapes from the source and condenses onto whatever surfaces are in its path. The target laboratory has three thermal coating systems: one for gold, one for general evaporations and one for chemical reductions.​

Auxiliary equip​​​ment

The laboratory has a range of auxiliary equipment for target foil manufacture including:  a tube furnace, a vacuum furnace, a hydraulic press, fume cupboards, micro balances and vacuum storage facilities.​

Thickness Me​​asurement​

In addition to weighing the target, the laboratory has an alpha particle system to determine target thickness and uniformity.  This system comprises an alpha source and a Si detector that measures the energy loss as the alpha particles pass through the target foil.

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