BGU Physics Department
Radiation Physics and Thermoluminescence
Yigal Horowitz – leader of the group
Dr. Leonid Oster, Senior Lecturer, Negev Academic College;
Shlomo Biderman, Ph.D. Student;
Nail Issa, Ph.D. Student
Thermoluminesence and Thermoluminescent Dosimetry:
Supralinearity and efficiency of TL materials as a function of ionisation
density, the Unified Interaction Model for dose response in TL materials,
Heavy Charged Particle response, kinetics of thermoluminesnce, defect
studies via optical absorption, optical bleaching and spectral emission,
development of advanced TL materials. Application of computerised glow
curve deconvolution to TL mechanisms and radiation dosimetry, space dosimetry,
mixed-field dosimetry, solid-state nanodosimetry.
Radiation Detector Physics and Applications:
Photon general cavity theory, application of Monte Carlo calculations to
detector response, development of advanced Q-nanodosemeters, development
of advanced solid state beta ray spectrometers.
The scientific study of thermoluminescence has an extremely rich history
spanning many centuries and interacting with many other fields of endeavor:
archaeology, geology, medicine, solid-state physics, biology and organic
chemistry, to name just some of the mainstream areas of study. At Ben Gurion
University (BGU) we are interested in thermoluminescence application to
ionising radiation dosimetry as well as in the development of radiation
response theories for solid state systems. These areas of endeavor are
of major importance in fundamental questions of radiation ecology, which
in turn can have great impact on questions concerning the future
of nuclear energy and the effects of interaction of radiation, both
beneficial and harmful, with the human organism. Our efforts at BGU, spanning
three decades, have culminated recently in a major effort initiated at
BGU to develop a Q- nanodosimeter; a solid-state dosimeter,
of miniscule dimensions, capable of at least partially mimicking the double-strand
response of DNA to ionising radiation.
Graduate Students and Research Associates:
Research in these areas of interest was initiated by Prof. Horowitz in
the mid -1970s and has continued vigorously and unabated to the present
time. In these twenty five years, twenty three research students have studied
for graduate degrees in the Radiation Physics Laboratory; nine graduate
students were awarded a PhD degree and two PhD students are currently engaged
in research for their degrees. Three of the graduated PhD students
went on to highly successful academic careers and are currently tenured
Professors of Nuclear Engineering at Ben Gurion University (Dubi), and
Medical Physics (Moscovitch - Georgetown University Washington D.C.) and
the University of Ionnina (Kalef-Ezra-Greece); three are employed in research
and development in the Israeli Defense Industries (Elta and IRR-1) and
two as high school and college teachers. One of the recently graduated
PhD students (Y. Weizman) was recently awarded the Intel Prize for
excellence in his PhD research, the only student in 1999, from the Faculty
of Natural Sciences, so honoured.
Current International Collaborations are with: (i) Professor
M. Zaider on the development of a Q-dosemeter based on ionisation density
thermoluminescence (TL) phenomena in LiF;Mg,Ti, (ii) Professor M.E. Brandan
- UNAM-Mexico on the study of heavy charged particle efficiency in LiF:Mg,Ti
using the UNAM Pelletron accelerator and (iii) Dr. A. Semones, Houston,
NASA – on the study of the HCP response of the peak 5a nanodosimeter for
Research Funding: The various research projects and the Radiation
Physics Laboratory have been supported over the years by four contracts
with the International Atomic Energy Agency (60 K USD); three contracts
with the U.S.- Israel Binational Science Foundation (370 K USD); one contract
with the Israeli Cancer Association (15 K USD), four contracts with the
Canadian Owned Group of Nuclear Reactors- CANDU (475 K): The Rashi Foundation
(L. Oster) and various contracts in support of the UNAM collaboration:
total worth of awarded contracts approximately 1 M USD.
Description of Research Activity.
I. The Unified Interaction Model:
We have developed a theory of dose response, the Unified Interaction Model
(UNIM) which is capable of explaining all the important features of the
supralinearity and sensitisation of the various glow peaks in LiF:Mg,Ti
(TLD-100) and other TL materials (1-4). The model combines the physical
concepts of the Defect Interaction Model (DIM) for gamma rays (uniformly
ionising radiation) first proposed by Fain and Monnin and elaborated by
McKeever, with features of the Track Interaction Model (TIM) (developed
at BGU by Horowitz and collaborators) for densely ionising heavy charged
particles (HCPs), into a unified mathematical framework. The UNIM is the
only radiation effects model of solid state systems capable of explaining
the ionisation density dependence of peak 5 supralinearity (both gamma
ray energy and radiation type). The UNIM incorporates a localized trapping
entity (the track for HCPs, the spatially correlated TC/LC pairs for gamma
rays and electrons) which dominates the dose response at low dose. The
spatial features of the occupation density of the trapping centers and
luminescent centers sets the scene for the relative efficiencies of the
competitive mechanisms and leads to the linear /supralinear behaviour and
to the dependence of the supralinearity on ionisation density. The ability
of the UNIM to describe the supralinearity (TL efficiency) as a function
of dose (ionisation density) for both gamma rays and HCPs in a unified
mathematical and physical framework is a singular and unique achievement
among the many previous models proposed to explain TL supralinearity.
1. S. Mahajna and Y.S. Horowitz "The Unified Interaction Model applied
to the gamma induced supralinearity and sensitisation of peak 5 in LiF:Mg,Ti
(TLD-100) ", J. Phys. D. Appl. Phys., 30, 2603-2619 (1997).
2. Y.S. Horowitz et al, Invited Paper, "The Unified Interaction
Model applied to the gamma induced supralinearity and sensitisation of
peak 5 in LiF:Mg,Ti (TLD-100", Radiat. Prot. Dosim., 78, 169-193
3. Y.S. Horowitz: "Theory of thermoluminescence gamma dose response:
The unified interaction model", Nucl. Instrum. B.,184, 68-84 (2001).
II. The Track Interaction Model (TIM) and Modified Track Structure Theory
The study of the properties of thermoluminescent (TL) materials to HCPs
has been of particular interest in recent years due to their possible applications
to dose measurements during radiation therapy treatments with heavy ions.
The microscopic processes that lead to the emission of light are highly
complex due to the highly localised ionisation density in the HCP track.
During the last twenty years Horowitz and collaborators have performed
both theoretical and experimental studies of the HCP response of LiF:Mg,Ti
(TLD-100). The interpretation of the experimental results has led to a
continuing development of models based on the structure of the HCP track
to understand relative efficiencies (4) and the interaction between spatially
correlated entities along the HCP track to explain supralinearity (5-7).
More recently the BGU and UNAM groups have studied the TL response of LiF:Mg,Ti
to 3 and 7.5 MeV helium ions and have interpreted the results in terms
of a combined theory using both a modified Monte Carlo Track Interaction
Model (MCTIM) and modified track structure theory (MTSM) (8-9). These experiments
and their successful interpretation has led to a far deeper understanding
of the HCP relative TL efficiencies as a function of ionisation density,
energy and particle type.
4. Kalef-Ezra, J. and Horowitz, Y.S., "Heavy Charged Particle
thermoluminescence dosimetry:Track structure theory and experiments",
Int. J. Appl. Radiat. Isot.,33, 1085-1100 (1982).
5. Horowitz, Y.S., Moscovitch, M. and Dubi, A., "Response curves for
the thermoluminescence induced by alpha particles using track structure
theory", Phys. Med. Biol., 27, 1325-1338 (1982).
6. Moscovitch, Y.S. and Horowitz, Y.S. "Microdosimetric track interaction
model applied to alpha particle induced supralinearity and linearity in
LiF:Mg,T", J. Phys. D. Appl. Phys., 21, 804-814 (1988).
7. Horowitz, Y.S., et al., "The Track Interaction Model for alpha particle
induced supralinearity:Dependence of the supralinearity on the vector properties
of the alpha particle radiation field", J. Phys. D. Appl. Phys., 29, 205-217
8. Y.S. Horowitz et al and M.E. Brandan et al UNAM), "The Extended
Track Interaction Model: supralinearity and saturation He-ion TL fluence
response in sensitised TLD-100", Radiat. Meas., 33, 459-473 (2001).
9. Y.S. Horowitz, O. Avila and M. Rodriguez-Villafuerte, "Theory of
heavy charged particle response (efficiency and supralinearity in TL materials",
Nucl. Instrum. Meths., B184, 85-112 (2001).
III. Development and Characterization of Advanced TL Materials
In collaboration with the NRC-Negev and with funding from the IAEA and
the U. S.-Israel BSF, the BGU group was instrumental in the development
of super-sensitive LiF:Mg,Cu, P TL materials with superior dosimetric properties.
These included a material 30-50 times more sensitive than LiF:Mg,Ti as
well as an additional material 15-20 times more sensitive than LiF:Mg,Ti
with a negligible residual signal following conventional readout (10).
The BGU group was the first to characterize the exceptionally low neutron
sensitivity of LiF:
Mg,Cu, P (11) as well as the first to systematically study the properties
of the material at maximum glow curve heating temperatures between 240oC
and 280oC (12,13) These studies were instrumental in the acceptance of
LiF:Mg,Cu,P in environmental and personnel applications.
10. Y.S. Horowitz, Invited paper, "LiF:Mg,Ti versus LiF:Mg,Cu,P:The
competition heats up", Radiat. Prot. Dosim., 47, 135-141 (1993).
11. Y.S. Horowitz and B. Ben Shachar, "Thermoluminescent LiF:Mg, Cu,
P for gamma ray dosimetry in mixed fast neutron-gamma radiation fields",
Radiat. Prot. Dosim., 23,. 401-404 (1988).
12. L. Oster, Y.S. Horowitz et al., "Further studies of the stability
of LiF:Mg, Cu,P (GR-200) at maximum readout temperatures between 240oC
and 280oC", Radiat. Prot. Dosim., 65, 159-162 (1996).
13. G. Ben-Amar, Y.S. Horowitz et al "Investigation of the glow peak
parameters, reusability and dosmetric precision of LiF:Mg,Cu,P at high
heating rates up to 20 K s-1", Radiat. Prot. Dosim., 84, 235-238 (1999).
IV. Computerised Glow Curve Deconvolution (CGCD): Applications to TLD
The BGU group has pioneered the implementation and development of advanced
CGCD routines and their application to dosimetric problems (14). From the
early 1980s we have improved the "state-of-the-art" using computerised
analysis techniques: In increased precision and lowered minimum measurable
dose(15, 16); In high dose dosimetry (17);In the optimization of annealing
procedures (18, 19); In fading properties (20); In kinetic analysis (21,)
and in the retrieval of dosimetric information (22).
14. Y.S. Horowitz and D. Yossian, "Computerised Glow Curve deconvolution:
Application to thermoluminescence Dosimetry", Monograph, Radiat. Prot.
Dosim., 60, 1-115 (1995).
15. M.Moscovitch, Y.S. Horowitz et al "LiF thermoluminescence dosimetry
via computerized first order kinetics glow curve analysis", Radiat. Prot.
Dosim., 6, 1-4 (1984).
16. Y.S. Horowitz and M. Moscovitch "Computerized glow curve deconvolution
applied to ultra low dose LiF thermoluminescence dosimetry", Nucl. Instrum.
& Meths. A244, 556-564 (1986).
17. Y.S. Horowitz and M. Moscovitch, "Computerised glow curve deconvolution
applied to high dose (103 - 105) TL dosimetry", Nucl. Instrum. Meths.,
A243, 207-214 (1986).
18. Y.S. Horowitz, Invited Paper, "The annealng characteristics of
LiF:Mg,Ti", Radiat. Prot. Dosim., 30, 219-230 (1990).
19. B. Ben Shachar and Y.S. Horowitz, "Thermoluminescence in annealed
and unannealed LiF:Mg,Ti (TLD-100, Harshaw) as a function of glow curve
heating rate and using computerized glow curve deconvolution", J. Phys.
D. Appl. Phys., 25, 694-703 (1992).
20. Y.S. Horowitz et al "Study of the long-term stability of peaks
4 and 5 in TLD-100: correlation with isothermal decay measurements at elevated
temperatures", J. Phys. D. Appl. Phys., 26, 1475-1481 (1993).
21. D. Yossian and Y.S. Horowitz, "Computerized glow curve deconvolution
applied to the analysis of the kinetics of peak 5 in LiF:Mg,Ti (TLD-100)",
J. Phys. D. Appl. Phys., 28, 1495-1508 (1995).
22. D. Yossian and Y.S. Horowitz, "Retrieval of dosimetric information
from distorted glow curves using computerised glow curve deconvolution",
Radiat. Prot. Dosim., 66, 75-78 (1996).
V. The LiF:Mg,Ti System
We are carrying out a multi-pronged investigation of the LiF:Mg,Ti system
using a variety of experimental techniques including optical absorption,
spectral emission analysis using an advanced CCD spectrphotometer,
HCP studies, glow curve kinetic analysis as a function of dopant concentration
as well as optical bleaching. The studies are aimed at the investigation
of the nature of the spatially correlated TC/LC pair (23) responsible
for the unique/complex behaviour of the TL efficiency of LiF:Mg,Ti
as a function of ionisation density. We have recently established, using
Tm-Tstop techniques, that peak 5 is a composite of three peaks (peaks 5a,
5 and 5b) (24). The discovery of this "fine-structure" has led to an on-going
revolution in our understanding of the LiF:Mg,Ti system. Optical
bleaching at 310 nm has revealed that the conversion efficiency of peak
5a to peak 4 is unusually high at 30%, and that of peak 5 is much
lower, of the order of a few per-cent. We have proposed that the high conversion
efficiency of peak 5a is due to the doubly trapped e-h characteristics
of the TC/LC complex giving rise to peak 5a and the hole-only trapping
characteristics of peak 4. Ionisation of an electron from the e-h occupied
complex leaves behind the hole-only occupied complex, which gives rise
to peak 4 (25). The next stage in our research has established the geminate
nature of the recombination process of peak 5a-this in order to develop
a Q-nanodosemeter based on the two-hit trapping characteristics of the
TC/LC structure giving rise to peak 5a. (26). On-going research is
aimed at the characterization of the peak 5a nanodosimeter in order to
establish its use in space nanodosimetry and clinical applications (27).
23. Y.Weizman, Y.S. Horowitz et al "Mixed-order kinetic analysis of
the glow curve characteristics of single crystal LiF:Mg,Ti as a function
of Ti concentration", Radiat. Meas., 29, 517-525 (1998).
24. Y.S. Horowitz et al "Ionisation density effects in the thermoluminescence
of TLD-100:Computerised Tm-Tstop glow curve analysis", Radiat. Prot. Dosim.,
84, 239-242 (1999).
25. Y. Weizman, Y.S. Horowitz and L. Oster "Investigation of the composite
structure of peak 5 in the thermoluminescent glow curve of LiF:Mg,Ti (TLD-100)
using optical bleaching", J. Phys. D. Appl. Phys., 32, 2118-2127 (1999).
26. Y.S. Horowitz, L. Oster, D. Satinger, S. Biderman and Y. Einav,
"The composite structure of peak 5 in the glow curve of LiF:Mg,Ti (TLD-100):
Confirmation of peak 5a arising from a locally trapped electron-hole configuration",
Radiat. Prot. Dosimetry, (2002) in press
27. Y.S. Horowitz, "Thermoluminescence radiation dosimetry in space:A
critique of current practise and future perspectives" Abstract (D12, p.59),
2nd Int. Workshop on Space Radiation Research (IWSSRR-2) 2002, Nara, Japan.