Magill J., Galy J. Radioactivity Radionuclides Radiation

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114 6. Archaeology and Dating

be reconstructed. From this information, rates of groundwater formation can be

established and used to estimate available water resources. For “older” groundwater,

the

C-method can be used for age determination.

Recently, water from the oasis Ballad Seet in Oman in the south east of the

Arabian peninsula has been analysed. How was it possible in a region consisting of

desert and sterile mountains that such a rich and powerful culture could develop in

this oasis? The analysis showed that the water age in the oasis was 5–6 years old.

This was the length of time required for the water from the plateau to seep through to

the groundwater almost 1000 meters below. The oasis inhabitants knew that a single

rainfall every ﬁve years would be sufﬁcient to guarantee their water supply from the

oasis.

Nuclear Forensic Science – Age of Plutonium Particles

At the Institute for Transuranium Elements, a range of analytical techniques is being

developed for veriﬁcation and detection purposes to check nation state compliance

with their non-proliferation commitments. As part of these activities, a technique is

being developed to determine the “age” of plutonium particles [12, 13]. The “age”

Sample F19A: Experimental isotope

ratios and the deduced particle “Age”

from decay correlation

Pu/U atom ratios vs. “Age”.

F19A Expt. “Age”

ratio (y)

238

Pu/

234

U: 109.4 1.18

238

Pu/

234

U: log(Age) = 2.0228 − 0.9563 log(Pu/U)

239

Pu/

235

U: 670.9 51.9 ⇐

239

Pu/

235

U: log(Age) = 4.541 − 0.9994 log(Pu/U)

240

Pu/

236

U: 476.3 19.9

240

Pu/

241

U: log(Age) = 3.9744 − 0.9563 log(Pu/U)

Fig. 6.9. “Age” determination of plutonium particles: since the uranium contamination is

signiﬁcant in sample F19A, the ages determined from the ratios disagree largely. The most

accurate value of 19.9 y is expected from the

240

Pu/

236

U ratio since there is no

236

U present in

natural uranium from the

240

Pu/

236

U ratio, i.e. 19.9 y, since there is no

236

U present in natural

uranium.

Nuclear Forensic Science – Age of Plutonium Particles 115

of a particle is deﬁned as the time elapsed since the last chemical separation of

daughter nuclides from the parent. The particles to be analysed can be obtained from

the environment or from “swipes” taken at nuclear installations where clandestine

activities are suspected. In view of the pending international agreement to stop the

production of weapon materials, the age of such “suspected” particles is of course

of great interest for veriﬁcation purposes.

For bulk samples, gamma spectroscopy can be used. However, for very small

particles, because of the low activity, this technique is not possible. Fresh plutonium

particles will in general contain the isotopes

238

Pu,

239

Pu,

240

Pu,

241

Pu, and

242

Pu in

different amounts, depending on the production route. With time, these nuclides de-

cay to

234

235

236

241

Am,

238

U respectively. By determining the ratios of parent

to daughter (

238

Pu/

234

239

Pu/

235

240

Pu/

236

241

Pu/

241

Am,

242

Pu/

238

U) one can

deduce the elapsed time and therefore the age of the particle. Because these ratios

are measured by secondary ion mass spectrometry (SIMS), one cannot obtain the

ratio

241

Pu/

241

Am. In addition, if the particle has some uranium contamination, one

cannot use the ratio

242

Pu/

238

U. This leaves the three ratios

238

Pu/

234

239

Pu/

235

240

Pu/

236

U which are suitable for age determination. The correlation between the

atom ratios and the age as calculated is shown in Fig. 6.9. The time scale of interest

is in the range 1–50 years. The correlation between the “age” of a particle and the

Pu/U atom ratio was obtained with Nuclides.net. Since the uranium contamination is

signiﬁcant, the ages determined from the ratios disagree largely. The most accurate

is expected from the

240

Pu/

236

U ratio, i.e. 19.9 y, since there is no

236

U present in

natural uranium.

7. Radioisotopes in Medicine

Radionuclides were ﬁrst used for therapeutic purposes almost 100 years following

the observation by Pierre Curie that radium sources brought into contact with the

skin produced burns. Already by 1915, sealed sources of radium-226 and radon-222

were in use. By the 1950s radiotherapy had become much more widespread due to

the development of remote source handling techniques and the availability of reactor

produced radionuclides such as cobalt-60.

Ionising radiation from radionuclides kills cells by damaging the DNA thereby

inhibiting cellular reproduction. The energy of the radiation (in the form of photons,

electrons, heavy particle, etc.) required to damage DNA should be greater than a few

electron volts (eV) corresponding to the binding energy of the outer electrons [1].

Fig. 7.1. A collection of normal chromosomes

with their single centres (indicated by a X shape).

An anomalous chromosome with a double centre

(XX) can be seen at the bottom right-hand corner.

Imaging

Nuclear diagnostic imaging techniques provide information about physiological and

biochemical processes and compliment other imaging methods such as conventional

radiology, nuclear magnetic resonance, and ultrasound. They have a very important

role to play in identiﬁcation of heart disease, brain disorder, lung and kidney function,

and a range of cancers.

Gamma Imaging

One of the main applications in medical applications is the use of gamma cameras

to detect diseases in the heart, brain, bone, lung, and the thyroid. More than 20,000

118 7. Radioisotopes in Medicine

Table 7.1. Main isotopes used for gamma imaging

Organ Nuclide

Lung

81m

Kr,

99m

Tc,

133

Bone

99m

Thyroid

99m

Tc,

123

131

Kidney

99m

Tc,

111

In,,

131

Brain

99m

Tc,

123

133

Liver, pancreas

99m

Tc,

111

Abdomen

Ga,

99m

Blood

99m

Tc,

111

Heart

Rb,

99m

Tc,

201

gamma cameras are in use throughout the world in some 8500 nuclear medicine

departments [2]. The main radionuclide in use is

99m

Tc, however other nuclides are

also in use as summarised in Table 7.1.

Positron Emission Tomography (PET)

There are some 250 PET cameras in use today mainly for the diagnosis of cancer. The

radio-pharmaceutical mostly used is the

F compound ﬂuoro-deoxy-glucose which

is similar to glucose in behaviour, ahough the development of alternatives based on

Cu,

Y, and

124

I is underway.

Fig. 7.2. Superposition of magnetic resonance imaging (which shows the morphology of the

brain) and positron emission tomography showing the active areas (coloured zones) in the

brain. Courtesy of the Montr´eal Neurological Institute, McGill University

Ion Beam Therapy 119

External Beam Radiotherapy

In external beam radiotherapy, where radiation is delivered from outside the body,

photon energies of millions of electron volts are required to penetrate the tissue and

reach the tumours inside the body. Radiotherapy is also being carried out with sealed

sources of

Co with some 1500 units in operation. A new process, known as the

Gamma Knife, is being introduced especially for brain tumour treatment.

Brachytherapy

Today, hundreds of thousand of patients are treated each year based on brachytherapy

(Brachys is the Greek word for near) in which sealed sources of radiation are brought

into the body and placed in or near the tumour to be treated leaving the surrounding

healthy tissue undamaged. Using these brachytherapy implants, radionuclides with

photons energies as low as 20 keV can be used. The radionuclide palladium-103,

for example, used for prostate implantation has an average energy of only 21 keV.

Some gamma ray emitters commonly used are

192

Ir,

137

Cs,

125

103

Pd and have an

effective range of a few centimetres. Beta emitters include

188

Re, and

P with

effective ranges of a few millimetres in tissue [3].

The technique is particularly successful for the treatment of prostate cancer at

an early stage. In the U.S. almost 57,000 patients were treated for prostate cancer in

1999 using brachytherapy seed implants based on

103

Pd,

125

137

Cs and

192

Ir.

Immunotherapy

In the last ten years, the technique known as radio-immunotherapy has been under

investigation. In this technique, a radionuclide is chemically attached to an antibody

which is then injected into the bloodstream. The antibodies go to the source of the

tumour and the attached radionuclides, for example

131

I, emit charged particles to kill

the tumour cells. The development of therapeutic substances for radiotherapy is be-

ing actively pursued by many companies and research organisations. Techniques are

being developed which combine the radioisotopes

131

153

Sm, and

213

Bi with

monoclonal antibodies and smaller molecules such as peptides. The three main appli-

cations of radionuclides for therapeutic purposes, however, remain a) sealed sources

for prostrate therapy, b) sources for intravascular therapy and c) radio-pharmaceutical

therapy. It is expected that these therapies will see rapid growth in the near future.

Ion Beam Therapy

In December 1997, the GSI heavy ion radiotherapy started with the irradiation of

the ﬁrst two patients. The distribution of biological effective dose (isodose contours

from carbon ion deposition) is shown in Fig. 7.3 superimposed on the image of the

brain. The tumour, situated in the centre of the brain, is treated directly by depositing

the ion beam energy in this region.

120 7. Radioisotopes in Medicine

Fig. 7.3. Distribution of biological effective dose (isodose contours from carbon ion deposition)

mbH

Boron Neutron Capture Therapy

In Boron Neutron Capture Therapy (BNCT), a boron containing compound is ad-

ministered intravenously to the patient. The boron accumulates preferentially in the

malignant tumour. The patient is then irradiated with a beam of intermediate en-

ergy neutrons of a few keV, directed towards the tumour bed. The neutrons lose

their energy through neutron scatter in the overlying tissue, whereby the thermalised

neutrons are then captured by the

B atoms. These immediately disintegrate into

two highly energetic particles: Li- and He-nuclei, which in principle can destroy the

cancer cells, whilst sparing the healthy cells.

The American biophysicist G. L. Locher ﬁrst came up with the idea of the NCT

treatment in 1936. Pioneering work in the development of BNCT was carried out in

the 1950s and 1960s at Brookhaven and MIT in the USA.

However, initial clinical results were disappointing. With hindsight, this was due

to the non-accumulation in the tumour of the boron compounds used at the time

and also the use of low energy neutrons, which in order to be able to give a high

enough dose at depth, produced very high doses at shallower depths in healthy tissue.

Nevertheless, in the late 1960s and early 1970s, improvements in both drug delivery

and construction of higher energy neutron beams, led to a major improvement in this

therapy [4].

Radioactive “Bullets” – Alpha-Immunotherapy 121

Fig. 7.4. BNCT: Clinical facility in Petten, showing the irradiation room, which has been built

to reﬂect as closely as possible, a hospital-type environment. The clinical facilities have been

installed at the High Flux Reactor (HFR) of the Joint Research Centre of the European Union

(EU) in Petten. Courtesy R. Moss

Since October 1997, the ﬁrst European clinical trial on BNCT is being performed

at the High Flux Reactor of the Joint Research Centre of the European Commission,

under the guidance of clinicians from the University of Essen and in collaboration

with NRG Petten and ﬁve other hospitals.A Phase I clinical trial for the post-operative

BNCT treatment of patients with glioblastoma multiforme, targets this highly ag-

gressive brain tumour, which affects around 15,000 people in Europe every year.

The trial is the ﬁrst of its type in Europe and is also the ﬁrst time that a clinical

application has been realised on a completely multi-national scale, whereby a unique

facility localised in one country (The Netherlands), is operated by radiotherapists

from another country (Germany), and treats patients coming from different countries

(France, Germany, Austria, Switzerland and The Netherlands).

Since the start of BNCT trials at Petten, four other centres are performing BNCT

in Europe (in Finland, Sweden, Czech Republic and Italy). Elsewhere in the world,

BNCT is also carried out in Japan, USA and Argentina.

Radioactive “Bullets” – Alpha-Immunotherapy

Form the early 1980s, a new form of treatment for cancer therapy based on the use

of radioactice isotope “bullets” in diseased cells began to attract increasing interest.

Previouly, treatment mainly involved the use of relatively low energy beta emitters.

More recently, isotopes emitting alpha particles have been recognised as more ef-

fective and selective against blood-borne cancers, widespread tumours, and residual

cells remaining after surgical intervention. Production of suitable alpha emitters,

122 7. Radioisotopes in Medicine

Fig. 7.5.

213

Bi is coupled to a

monoclinical antibody using a

chelation agent. The alpha

emitting radionuclide is then

close enough to the cancerous

cell to destroy it with little

damage to the surrounding

tissue.

their stable coupling to suitable carriers, and safe use of such tools in hospitals have

become the main goals.

Treatment of cancer by radio-immunotherapy involves injecting the patient with a

radioactive isotope “bullet” connected to a speciﬁc carrier such as a monoclonal anti-

body, with the aim of selectively destroying targeted tumour cells. During radioactive

decay, photons, electrons, or even heavier particles are emitted and damage or kill

cells along their trajectory.

Alpha-emitting radionuclides are amongst the most promising radionuclides for

the treatment of blood-borne cancers and micro-metastatic cancers cells. Because

of their short range (60 to 100 micrometer) and high linear energy transfer values,

alpha-emitters can deliver such a high radiation dose over the distance of a few cell

diameters that they will effectively kill the cells. When alpha-emitters are conjugated

to tumour-seeking monoclonal antibodies (a protein molecule that attaches to the

cell), the resulting product is expected to be an efﬁcient cancer drug. Other smaller

molecular weight carriers such as peptides and fragments of the antibodies are being

investigated because they can enter into larger sized tumours.

A number of alpha-emitting isotopes have been considered, but most gave rise

to various drawbacks that preclude large-scale implementation. The preferred option

today is the use of bismuth-213 (

213

Bi), which has a half-life of 45 minutes. Actually

213

Bi is mainly a beta emitter with half-life of 46 m. This nuclide decays however to

213

Po, a very short-lived (half-life 4.2 µs) nuclide, which decays by alpha emission.

So effectively

213

Bi is an alpha emitter with a half-life of 46 m.Actinium-225 (

225

Ac),

which has a half-life of 10 days and is the parent nuclide of

213

Bi, does not occur

Radioactive “Bullets” – Alpha-Immunotherapy 123

in nature. The actinium isotope can, however, be obtained in small quantities from

nuclear waste.

The ﬁrst European clinical trials of such alpha-immunotherapy started in April

2000 in Basel on patients with glioblastoma and, since early 2001, in Heidelberg

on patients with non-Hodgkin’s-lymphoma. The results vary from highly promising

indications to cautious optimism, depending on the type and status of the disease.

At the Memorial Sloan-Kettering Cancer Center in New York, clinical trilas are also

continuing on patients with acute myeloid leukaemia. Other aspects of pre-clinical

trials are being studied in Germany, Belgium and France. Clinical trial on leukaemia

patients showed that the alpha particles were 100–1000 times more cytotoxic than

beta particles, which have also been used, and caused much less damage to surround-

ing healthy tissue [5].