Depths dose measurements in a human phantom
MATROSHKA is an ESA project that is realized under the direction of the DLR in collaboration with industrial partners DTM technologies (Modena) and Kayser-Italia (Livorno). MATROSHKA is a facility that simulates as exact as possible an astronaut while he leaves the 'protective' area of the spaceship in order to carry out work in free space. The task is to measure particle fluence and energy spectra, dose and dose rates outside and inside a human phantom over the period of a year. The data are needed to improve the determination of radiation exposure of an astronaut performing a space walk.
The MATROSHKA facility basically consists of a human phantom, a Base Structure and a Container. The container as well as the phantom will be mounted to the base structure which serves as a footprint for the human phantom. The container is a Carbon Fiber structure and forms with the Base Structure a closed volume that contains a dry oxygen atmosphere and protects the phantom against e.g. space vacuum, space debris, solar UV, and material off-gassing. It acts also as a simulation of the space suit. The container is pressed over the phantom at the head and the shoulders to stabilize the total structure. In the Base Structure the facility and experiment electronics are accommodated. The facility electronics provide the interface between MATROSHKA and the Russian Service module. Temperature, pressure and experiment data are collected during the mission and transferred to the onboard computer system. From there data are downlinked to ground.
The phantom body consists of commercial phantom parts, well introduced in the field of radiotherapy. It consists of several slices composed of natural bones, embedded in tissue equivalent plastic of different density for tissue and lung. Its upper part alone, trunk and head give access to most of the organs of interest. The Phantom slices are equipped with channels and cut-outs toll allow the accommodation of active experiment sensors and passive experiment sensors, temperature sensors and of the internal and external harness to scientific and hosekeeping (temperature, pressure) sensors.
Two types of experiment detectors will be integrated in the Phantom:
Passive experiment packages (e.g. solid state nuclear track detectors, thermoluminescence dosimeters (TLDs)) which will be returned to the ground after experiment execution for their further investigation.
Active experiment packages consisting of the sensor and an electronic board for sensor data processing during experiment execution.
The experiment packages will be integrated in the Phantom at the positions of the eye, lung, stomach, kidney and intestine. To measure a depths dose profile through the body TLDs are implemented in each single layer in a grid of 25 mm. In addition also the skin dose is measured. The phantom is clothed therefore with a jacket carrying stripes of TLDs embedded in Poly-ethylene foils and sewed in the jacket. In addition, the jacket itself serves to fix the cables for the active experiments.All types of dosimeters described under "Dosimetry in the space" will be used in this experiment.
One major design criteria of MATROSHKA is the easy exchange of the passive experiment sensors onboard SM (less than 8 hours crew time). Therefore each slice of the phantom has a center hole which allows to assemble the whole phantom over a rod which is fixed to the Base Structure.
In order to remove the experiments from the phantom after the one year exposition the container is removed. The central rod on the top of the head is extended by unscrewing an additional rod which allows to lift up each single layer by 15 cm. This is a comfortable way to exchange the passive experiments.
Matroshka: Virtual Control Room