click on "Literature" for further information about applications

On this web-page

1. Summary of applications

2. Deep space and the Human Mars Mission

"One click per second on Earth …. a hundred clicks per second in Deep Space … except in a large flare, when the click rate goes through the roof."

published on www.radfet.com COPYRIGHT REM 2005

please acknowledge as "private communication" or cite website

1. SUMMARY OF REM'S "DOT" DOSIMETER SYSTEM BASED ON THE RADFET: FUNCTIONALITY, STABILITY AND APPLICATIONS

Andrew Holmes-Siedle

RADFET n. An acronym for RADIATION-SENSING FIELD-EFFECT TRANSISTOR based on the metal-oxide-silicon p-channel structure. An integrating dosimeter which measures dose (rad or Gy(Si)) by virtue of the field effect caused by space charge trapped in an inorganic insulator (SiO₂).The RADFET was invented in 1970 .by Andrew Holmes-Siedle (now sole owner of REM) and his co-worker, the late Waldemar Poch. Details were published in 1974. The acronym was coined by Robert Hughes in 1986. Used for the last 20 years in aerospace industry, now has a future in medicine, nuclear industry and science.

"DOT" (Dosimetry by Oxide Trapping). The DOT sensor is designed to detect the field produced when space-charge is trapped in the gate oxide region of the FET. An electrical measurement [shift of threshold voltage] by the DOT reader then gives a relative value of dose in a silicon environment (rad or Gy(Si)). The charge remains for many years.

REM OXFORD Ltd.

64A ACRE END ST., EYNSHAM, OXFORD OX29 4PD, ENGLAND

phone +44 18 65 88 00 50 . fax +44 18 65 88 00 30

email: holmes.siedle@dial.pipex.com

Introduction

The RADIATION-SENSING FIELD-EFFECT TRANSISTOR (abbreviation: RADFET) is a microminiature type of integrating radiation dosimeter. The sensor has a microscopically small sensor volume, which offers opportunities for radical new designs of miniature radiation sensing system. The sensing principle is long-term charge storage. The p-MOSFET responds to the field produced when space-charge is trapped in the oxide region. An electrical measurement [shift of threshold voltage] then gives a relative value of dose in rad or Gy(Si). Compared to other detector systems, the RADFET system is compact and easily coupled with computer power.

APPLICATIONS

Dosimetric experts recognize that, due to the microminiature dimensions of the ionization-sensitive region [only 0.05 mm²] the dose resolution is not as good as for gas tubes, film badges and TLD dosimeters, which achieve “millirad resolution”. Thus, the main applications are in high-dose applications such as radiotherapy and space. The dosimetric information, trapped charge, is both generated and stored in an oxide film only a micrometre thick and a fraction of a square millimetre in area. Because the sensor die is minute and readout is convenient, radical new designs of dosimeter are possible. In radiotherapy, “Tactical dosimetry” for military personnel and in spacecraft dosimetry, these special properties have already created a commercial market.

A table of uses for the RADFET system matched to the dose range and size, is given below. Associated dosimeter types, already built, are quoted in brackets. A superscript “ ^R” indicates a device designed and built by REM.

Controller for radiotherapy (CA-1 catheter probe)^R

Personal dosimeter for civil accident and military battlefield (US Army "Tie-Clip" device) ^R

Monitor on robots in a nuclear power station environment (TELEMAN Tel-H dosimeter)^R

Nuclear waste cleanup (TELEMAN Tel-H dosimeter)^R

Space vehicle health monitor (ESA/PSI: Radiation Effects Monitor)

High-energy accelerator; dose mapper for crystals (BaBar RADFET Monitoring Board)^R

Response to radiation: The DOT sensor is designed to detect the field produced when space-charge is trapped in the gate oxide region of the FET. An electrical measurement [shift of threshold voltage] by the DOT reader then gives a relative value of dose in a silicon environment (rad or Gy(Si)). The charge remains for many years. The oxide dielectric responds to all forms of particle and photon radiation in proportion to the ionization produced. Response to neutrons is relatively small. Radiation responses [photons] are specified in individual REM data sheets for doses varying from 1 cGy to 1E8 cGy.

The net positive charge in the oxide trapped (ot) charge region is generated when electrons escape to the external circuit. The effects of other trapping phenomena in the structure are reduced as much as possible in the design of the dosimeter. Accurate calibrations in the radiation of choice are normally the responsibility of the user, comparing the voltage shift to the response of a standard detector such as an air ionization dosemeter. Co-60 gamma rays are commonly use by the suppliers to standardize a sensor lot. An eight-decade curve of these responses (“nominal growth curve”) is available for general reference.

Reading out the charge - the reader box

Readers for RADFET dosimeter systems consist of circuits for tracking the threshold voltage of the pMOS FET and applying electrical stress as required during exposure. The common electrical bias modes are shown in Table 1. REM designs of reader (DOT system for "Dosimetry by Oxide Trapping") range from simple, manually switched versions to systems controlled by PC and microprocessor. As Fig 1 suggests, this can be a slim-built device using battery power and can connect to the Internet.

Amongst other users, the European Space Agency has sponsored the development of several readers suitable for monitoring aboard unmanned spacecraft (e.g. the SREM, developed by PSI, Villigen). Thomson Associates has licensed an analogue reader, for use in medicine and sterilization, to several industrial firms. A student project at Harvard Medical School gave rise to a PC-controlled reader, for which Dr David Gladstone won the Young Investigator prize of the American Association of Physicists in Medicine of 1991. This was one of the first systems used in the clinical treatment of cancer. The BaBar project at Stanford Linear Accelerator, California, has developed a RADFET Monitoring Board. The Centre for Medical Radiation Physics (CMRP) at University of Wollongong, Australia have developed the Clinical Semiconductor Dosimetry System (CSDS) which is available for commercial development.

FUNCTIONALITY

In the production cycle RADFETs are tested for functionality and stability after assembly. Mechanical damage to a single FET, generated during handling, does not affect other FETs on the same die. On the other hand, “border states", which are sometimes produced during processing, affect stability and tend to affect a segment of a wafer uniformly. This and other stability issues are discussed below

STABILITY

1. Border (slow) states

The drift up (du) of threshold voltage signal with time due to border states is usually of significance only after irradiation. It is usually measured as a function of the time interval after the reader has been switched on (i.e. the "expose” mode has been switched to the “read” mode). The rate of border state drift decreases as the logarithm of time (Holmes-Siedle et al 1983). The value of “the drift up in any twofold time increase (dutti)” or in any decade of time will therefore be the same for both short and long periods. Before irradiation, the value of “dutti” is often less than 0.001V but the value becomes significant as integrated dose accumulates. For example, at 1E4 rads, the value is about 0.02 V.

2. Temperature: effects

All semiconductor devices are prone to strong effects of temperature on operation. In this respect, they are at a disadvantage versus other types such as air chambers and TLDs. Their other advantages such as size, simplicity and ruggedness have to overcome this disadvantage.

The measured electrical parameters of a diode [leakage current, responsivity to radiation etc] tend to rise with temperature and are also affected by radiation in complex ways. For example the temperature sensitivity of the response of a dosimeter diode to radiation, before irradiation is about 1 percent per deg C but after heavy irradiation it may be as high as 4 percent per de C. The electrical parameter which is changed by temperature is a dynamic one [ the conductivity, which can be compared to the static parameter changed in the MOSFET case]. Thus, radiotherapy under the control of a silicon diode requires good knowledge of the device temperature and an accurate correction which changes in value per deg C with "wear and tear" on the diode. In the MOSFET, the correction needed results from the high temperature coefficient of threshold voltage. At a current of 40 mA, the value is about 5 mV per ^oC. This is a DC effect [change in a static potential] which gives access to several correction strategies which are not possible with the diode. First of all, there is an operating point [one value of current] which gives a “zero temperature coefficient"called a "ZTC point”. For example, at I_D = 200 mA, the coefficient is less than 0.5mV per degree C. Corrections for temperature effects can be made by the "dual bias method" where a second MOSFET is irradiated. The threshold shift is corrected by analogue electronics in the reader (see e.g. Soubra et al 1994). The third strategy is to monitor the temperature, say by thermistor, and calculating the correction digitally in a microcontroller forming part of the reader. In all cases. there is a similar problem of responses changing with "wear and tear" but all the correction strategies will result in only small sensitivity to temperature near the end of life.

Grades of sensor.. A device of "Acceptable stability, in the “excellent” range" with one type R and one type K functional would receive the symbol A_e'' (RK). See Appendices and other REM technical data for details of availability of given wafer configurations, such as RK and RKKR, at a given time.

The sensor: The construction of the sensor is that of a conventional p-channel Metal-Oxide-Silicon (MOS) transistor with an Al gate. The silicon die, sawn from a single-crysta wafer after processing, measures 1 mm x 1 mm x 0.5mm and carries four MOSFETs. Of these, the two type K FETs are sensitive to "kilorad” levels of dose; and the two type R give access to “rad” levels or even lower dose values (1 rad = 0.01 Gy). The response, r, of the sensor is the “change in threshold voltage, DV_T ", a function of integrated radiation dose. We could also obtain this response by measuring the gate capacitance in a manner which gives us the "change in flatband voltage, DV_FB”. The value of responsivity, r is proportional to the square of the thickness, t_ox, of the gate oxide layer and varies in a complex way with dose. The amount of charge trapped also varies with the oxide field applied during exposure, often called “irradiation bias, V_I”, which can be positive " Vi+" or zero "Vi0" by choice. In the construction of the sensor, the values of t_oxare manipulated by the sensor designer. The oxide thickness is usually much larger than for commercial MOSFETs.

Electrical properties: RADFETs are enhancement pMOS transistors. I‑V characteristics resemble those of pMOS switching FETs. Dosimetry involves tracking threshold voltage, V(T), at 10 to 250 uA. For values of V(T) see Table. The shift of V(T) given by a given amount of charge trapping is dependent on the thickness of the gate oxide.

Typical RADFET sensor, a summary of the construction

Wafer - REM TOT601B Mask Set : Si Wafer, 4 inch diameter. Each die carries dual pMOSFETs in perfect symmetry, a p+n photodiode and a MOScapacitor.

Chip size: less than 1x1 mm

Gate Oxide thickness: 0.1 to 1.25 micrometres.

Typical radiation responses: Vi+; 2 mV/cGy Vi0; 0.5 mV/cGy

Chip carrier (header): 6-way polymeric substrate, width 1 to 9 mm, length - variable.

Encapsulation: Black epoxy

Cable and connections; 6-way commercial Flat Flexible Cables and sockets. Commercial FFC in various lengths, and sockets are available from catalogue stockists. The polymeric carriers fit the FFC sockets

Chip carriers and encapsulation: Sensor chips are mounted and wired to a chip carrier [a "header"] and covered with the minimum possible amount of opaque epoxy resin or a plane lid. Low atomic weights are used wherever possible. The geometries and connection schemes (“pinouts”) are shown in individual REM data sheets. REM's "CC" series of dosimeters is designed in "chip-on-board" technology, optimized for producing low-cost commercial devices. It is possible to trade dosimeter size against the number of FETS available per package. REM's polymeric chip carriers are engineered to fit into small orifices, the current target being a catheter with internal diameter less than 2mm. With small sensors, it is often possible to make the necessary buildup cap by drilling the appropriate hole in a block of tissue-equivalent plastic or aluminium. Using a REM chip, Gladstone and co-workers (1991) designed a special ultra-miniature probe to fit within a “flexineedle” and make dose measurements within a living tumour.

Conclusion

The concept of the RADIATION-SENSING FIELD-EFFECT TRANSISTOR, an integrating dosimeter based on the metal-oxide-silicon p-channel structure, was made in a practical form in 1970 and put in the public domain in 1974 by REM and the present author. The acronym RADFET was coined by Robert Hughes in 1986 and REM has specific permission to use this name. Used for the last 20 years in aerospace industry, now has a future in medicine, nuclear industry and science. This summary review of the device and its literature by the inventor indicates that REM is pursuing that future. There is a stimulating level of commercial competition from later comers who read the literature and saw the possibilities outlined by REM.

Literature and Application Notes

for other references, click on "Literature"

A.G. Holmes-Siedle, "The Space Charge Dosimeter ‑ General Principles of a New Method of Radiation Dosimetry", Nucl. Instrum. Methods 121, 169 (1974) (original literature reference, putting MOSFET dosimetr in the public domain and giving priority of invention of many variants to REM).

R.C. Hughes. “Theory of response of radiation sensing field-effect transistors in zero-bias operation”. J. Appl. Phys., 60 (3) 1216-7 (1986) (origin of name “RADFET”).

A. Holmes Siedle and L. Adams, "RADFETs: A Review of the Use of Metal‑Oxide‑Silicon Devices as Integrating Dosimeters" Radiation Physics and Chemistry, 28, (2) 235 ‑ 244 (1986) (first general review)

A. Holmes‑Siedle, L. Adams and G. Ensell. "MOS dosimeters ‑ improvement of responsivity (dosimetres MOS ‑ amelioration de reponsivite)". RADECS '91, Montpellier, France, 9-12 Sept 1991, IEEE Catalogue No. 91 THO400-2 (development of thick oxides).

D.J. Gladstone, L.M. Chin and A.G. Holmes ‑ Siedle, " MOSFET Radiation Detectors used as Patient Radiation Dose Monitors during Radiotherapy", Paper S3, 33rd Ann. Mtg. Am, Assoc. of Physicists in Medicine, San Francisco, July 21-25 1991, submitted to Medical Physics (use in testicular cancer).

A.B. Rosenfeld, M.L. Lerch, T. Kron, E. Brauer-Krisch, A. Bravin, A. Holmes-Siedle and B.J. Allen (2001). "Feasibility study of online high-spatial-resolution MOSFET dosimetry in static and pulsed X-ray radiation fields". IEEE Transactions on Nuclear Science, NS-48 (6) 2061-8 (December 2001) (the micron resolution of dose profiles and the use of new reader).

R.C. Hughes, D. Huffman, J.V. Snelling, T.E. Zipperian, A.J. Ricco and C.A. Kelsey, "Miniature Radiation Dosimeter for in vivo Radiation Measurements", Int. J. Radiation Oncology Biol. Phys, 14, 963-7 (1988) (First medical application).

S.J. Kronenberg and G.J. Brucker . "The use of hydrogenous material for sensitizing pMOS dosimeters to neutrons" IEEE Trans. Nucl. Sci. NS-42, 20-6 [also see pp33-40] (February 1995) (tactical dosimetry).

A bibliography of research on RADFETs: Appendix D of A. Holmes-Siedle and L. Adams, "Handbook of Radiation Effects" (Oxford University Press, 2nd Edition 2002). Book available by mail order from REM in the UK and Europe or (in USA) from mike@icsrad.com.

Application notes on RADFETs available from REM

1. rfi05genl.doc. Technical Note REM-05-01TR "REM'S INTEGRATING DOSIMETER SYSTEM BASED ON THE RADFET: AN INTRODUCTION (Jan 2005)

2. rfi05sum01.doc Technical Note No.REM-05-02SUMM,"SUMMARY OF REM'S "DOT" DOSIMETER SYSTEM BASED ON THE RADFET:FUNCTIONALITY, STABILITY AND APPLICATIONS" (January 2005)

3. tosp02-9-504xcc8resp.doc, Technical Note No. REM-02-9-504xCC8resp, "NOTES ON TOT500/CC8 RADFETs - RESPONSE TO GAMMA RAYS (December 12, 2002)

File rfi05sumWEB03.doc August 11, 2005 ahs

2. RADIATION MONITORS FOR THE MARS MISSION

Summary : The European Space Agency [ESA] and the authors, working in the ESA contract team, recently completed a one-year study on "Radiation Exposure and Mission Strategies for Interplanetary Manned Missions (REMSIM)". The Belgian Institute for Space Aeronomy was responsible for the work package "Radiation Hazard and Space Weather Warning System" that dealt with space science and warning issues. REM contributed the portion on monitoring and warning. The team also proposed measures required to manage solar flares, cosmic rays space weather and radiation detection in deep space missions. Some specific recommendations for warning systems in the Human Mars Mission were made [see reference BIRA05]. A UK authority is quoted recently as saying that human missions cannot go further than Mars because it is "impossible to protect against radiation". When going as far as Mars we can be more precise - it is possible to find ways of minimising serious damage on the way to Mars and on its surface.

1. General

The REMSIM programme in 2004 was a project of the European Space Agency aimed at assessing the radiation risks to humans in deep space, especially en route to the Moon or Mars. REM Oxford Ltd was a team member in the REMSIM project, a study having the objective of pushing forward the knowledge of radiation protection for humans on the Mars and Lunar missions. The radiation risk in the Human Mars Mission is much the greater of those two missions. REM's assignment was to develop a system concept for giving warning to deep space crew of space radiation hazards. These come fromtwo different sources - from the Sun in bursts and from the galaxy as a constant stream. The galactic part is of such high energy that some might call it "unstoppable". In deep space, the walls of the vehicle are always light [say half an inch of aluminium]- we cannot afford the weight for heavy shields. The environment is mixed. There are different concerns from steady galactic cosmic rays (GCR) and sudden solar flares. Working out warning strategies involved several types of instrumentation - sentinel detectors in solar orbit, modules bolted to the outside of the vehicle; modules sited inside and on suits. That meant that the shielding effect of the spacecraft or Martian building materials was also of crucial concern. Others dealt with those aspects [ environment and the transport of particles through materials] and REM took up their findings as they developed.

A UK authority is quoted recently as saying that human missions cannot go further than Mars because it is "impossible to protect against radiation". When going as far as Mars we can be more precise. The overall mission risk, quantified as the future risk of cancer, is several hundred times the risk of staying on Earth. Mission models by NASA suggest that a 3-year mission to Mars would exceed the levels considered safe for US astronauts in ISS [ click on … NCRP-132, Asso03, Atwe03b, Brit03].

However, careful engineering - shielding, warning bleeps and ergonomics - can combine to cut down those risks considerably. ". Thus, when going as far as Mars we can be more precise - there are ways of minimising serious damage on the way to Mars [and on its surface] and we will find them.

The history of some of REM's approaches to radiation monitors and warning methods is given in our references [click on "Literature"] and indeed REM sees new systems developing out of this process of engineering protecton for human missions in deep space [click on REMWARN]

History and background. In 1974, REM Oxford published the principle of using a Field-Effect Transistor (MOSFET) as a space-charge measuring dosimeter. The word REM came from the acronym for "Radiation Experiments and Monitors" but a "rem" is also a unit of human radiation dose. In 1985, R. Hughes supplied the name “RADFET” for the silicon integrating radiation detector invented by REM and demonstrated its use in breast cancer treatment. REM began selling the RADFET sensor commercially to groups making small satellites and then developed a reader system. The dosimetry system was adopted by the European Space Agency (METEOSAT). Next came several explorations of wider use – in personnel safety devices (accident dosimetry), tumour research (radioimmunotherapy), nuclear safety (ROBUG) and high-energy physics (CERN, SLAC). By 2004, a Canadian group had RADFETs on the Space Station, a French group had them in homeland-defence instruments, Japanese and Korean groups were experimenting in space and nuclear plants and several companies are launching “smart” systems for clinical radiotherapy. REM's version is called DOT for "Dosimetry by Oxide Trapping". [click on "about RADFETs"]. The REMSIM project opens a chapter of detailed study of man's problems on long space voyages.

The European Space Agency [ESA] and the authors, working in the ESA contract team, recently completed a one-year study on "Radiation Exposure and Mission Strategies for Interplanetary Manned Missions (REMSIM)". The Belgian Institute for Space Aeronomy was responsible for the work package "Radiation Hazard and Space Weather Warning System" that dealt with space science and warning issues. REM contributed the portion on monitoring and warning. The team also proposed measures required to manage solar flares, cosmic rays space weather and radiation detection in deep space missions. Some specific recommendations for warning systems in the Human Mars Mission were made [see reference BIRA05].

In radiotherapy, there is a growing interest in making smaller radiation beams and shaping them to the precise shape of tumours. A general name for this method is Intensity-Modulated Radiotherapy. In this field, the RADFET has several advantages over other detectors, starting with the fact that (a) the sensor volume is truly minute, being a film of dielectric [silicon dioxide] no more than 10 micrometres wide (b) silicon dioxide is such a good insulator that it retains charge for many years. In scientific jargon, it is a "high-spatial-resolution low-fade dosimeter". Research is needed to raise the other desirable feature of "high-dose resolution". With research, this should come.

REMSIM report. The approaches to space radiation protection are set to the carefully balanced risk policies adopted by space agencies - in particular that crew members should not incur more than 3 percent additional lifetime risk of cancer from the space mission. Given the difficulty in forecasting solar flares, a increase in our growing systematic network of detectors throughout the solar system is essential [see references on RxTec and BIRA work]. A deep-space crewed vehicle is a unique structure, unlike space shuttle or an orbiting space station. REM studies the existing instrumentation of space systems and how they should be built into this vehicle by the selection of absorbers, sensors, circuitry and software. The aim is to use the monitored information to lower the radiation doses for crew members by as large a factor as possible over the 1000-day length of the mission. Crew must be warned to shelter when approaching major solar flares are sensed - a passing life-or-death risk. Then there is the chronic risk of cancer in future, caused by the very energetic cosmic rays passing through the vehicle and the body. That must be minimsed by fitting together work patterns and the built-in shielding provided by the overall structure or the craft. WE have implied earlier that shielding will always be "rationed" - there can never be enough while on the flight. However, "hot spots" and "cool spots" will be found in the vehicle. Certain bays will be "cooler" and the crew must share out the profit from this. That situation changes once they are digging their shelters on Mars. Now we have as much regolith material as we can handle, to build shelter. Alenia, a team member noted that, on the Moon, there are probably caves in which we can park [click on ….].

Where to place the sensors

In the REMWARN instrumentation system there will be sensors both inside and outside. three equally important locations

1. on the outer surface of the vehicle, sensing photons or non-penetrating particles.

2. inside the bulkheads of the vehicle sensing penetrating particles and the "secondaries" , including showers of neutrons.

3. attached to the helmet or space suit, especially the ones used for space-walks.

Size, weight and power budgets will demand some radical re-thinking of sensor system design, ssensor placing, software and ergonomics . In the report, we give an overview of radiation warning monitors, concluding that the conventional approaches are barely adequate. The long, three-year task of radiation protection outside the shelter of the Earth, with such a limit on weight, needs more efficient sensors as well as superb shielding skill.

We then note that, given the Mars and Moon project dates, there is time to examine unconventional approaches. We show some of the possible advanced, unconventional approaches such as (a.) a MOS detector of variability in UV emission from the Sun (b.) a portable combination of a scintillator and an intensifier CCD that make the tracks visible to the crew member.. Other avenues for synergy in research are pointed out. For example, designers of fire prevention systems and radiation protection systems in the nuclear industry have an immmense base of developed skills for the terrestrial case and the whole object of the Aurora programme is to harness such skills to this demanding space project. More than usual, we have time in which to make important advances in sensor technology [launch date 2030? click on …]. Thus, the serious nature of the radiation hazards on a Mars mission and the responsive technology programmes now launched by national space agencies give a n unusual passport to extra safety of a small dedicated crew.

Development of systems

The case under study here is a long-duration exploratory mission in deep space, the variation with respect to time should be monitored differently from past cases. How should the philosophy of protection be different for this case? The following key points of philosophy can be reiterated.

There are …..

* “Acute” hazards of short-lived intense doses of protons, varying in severity from “mild” to “killer”;

* “Chronic” hazards - steady, very-slowly-varying environments, mainly due to galactic cosmic rays [GeV protons].

The overall risks are hundreds of times greater than the better-known hazards of the natural “gamma-photon background” on Earth received by humans from rocks, food and air. Let us compare the Mars mission via deep space with any manned mission carried out so far. At best, the dose rates inside the vehicle for the deep-space segment of the Mars mission (GCR component) are higher, the mass of shielding available is lower and hospital treatment facilities are beyond consideration. Thus, techolgy should strain to provide the most advanced possible hardware and software to warn crew and help them to avoid dangerous doses. The hazards of cosmic rays alone will be enough to make radiation health a key mission parameter. The solar-flare emergencies - an these are only possibilities and probabilities, not certainties - add to that background requirement.

Our ability to change the minimum crew GCR dose for the mission is quite low once the shielding weight budget is decided. The weight assignments made years before launch may determine this the minimum crew GCR dose. Logic says that we have to work to lower it further by a sensible management of dose rates during work and sleep. In the reposrt, we recommend that, as ESA's AURORA programme and NASA's Space Radiation Health programmes expand [click on …], the radiation protection procedures discussed here must be put in the "must have" category.

There is one immediate line which we are taking : the logical need to influence crew practices requires the making of qccurate dose map. In technical terms, this is a "Three-dimensional Virtual-Reality Radiation Isodose Map” of the spacecraft, derived from the basic built-in shielding of a given vehicle design. We hope to engage with developers of Virtual Reality tools in the terrestrial nuclear industry for work practice optimisation. [click on reference RADVIS04]. The on-board hardware systems have to be backed by extremely reliable and friendly software. REM studied total doses and dose rates and their relative weights as triggers of alarms and further considered how dose rates and total doses shift in importance as one moves through the 11-year solar-activity cycle. A set of "algorithms" for converting radiation information into well-timed warnings was developed with RxTec. Internal instruments are supplemented by extensive intelligence from an array of remote sensors and the forecasts based on them. "Sentinel" satellites and terrestrial observatories will supply these forecasts to the space agencies. In instrument technology, we expect the development and use of active monitors on the outside and inside of the spacecraft shells, smaller passive "badge" dosimeters on crew [with a few “pocket dosimeters” such as the “electronic personnel dosimeter” used for Health and Safety at Work here on Earth]. Finally, the [at present unconventional] "EVA MOSFET " technology flown by the Canadian Space Agency on space walks, may come into its own in some applications.

To crystallize the comparisons of radiation on Earth versus the galactic background versus the "solar flare" event, we made the summarising if "homely" comparison of various hazards on the road to Mars:

One click per second on Earth …. a hundred clicks per second in Deep Space … except in a large flare, when the click rate goes through the roof.

This is saying, in simple language, that the health risks from cosmic rays in deep space are much more severe than on Earth; that they are steady, predictable and that some element of the risk can be avoided by good monitoring. When a solar event happens, and the Geiger count goes through the roof, take shelter in special places. There is time to develop novel methods to handle this situation during the technology phase of AURORA of giving the crew the information which they need to stay alive and healthy. Some say that, in deep space, it is "impossible to protect against radiation". We are here being more precise - it is possible to find ways of minimising serious damage on the way to Mars but it will take time and work..

REFERENCES

ESA'S "AURORA" PROGRAMME. This programme has initiated a Dossier of Enabling Technologies for the Mars programme and this includes radiation detection. A period of further development of sensors offers itself in the form of the ten-year AURORA technology development period, including many unmanned sample-return and manned spacecraft technology proving flights in which radiation counters and dosimeters can be included.

BIRA'05.

The results of the BIRA-REM work on the Mars mission are available online and in several scientific papers :

http://space-env.esa.int/R_and_D/PN-Radiation.html [ Under "REMSIM" CLICK ON "Radiation hazard and Space Weather warning system": http://space-env.esa.int/R_and_D/TN5.pdf ]

for other references, click on "Literature"

please acknowledge as "private communication" or cite website