“Self-sacrifice is the real miracle out of which all the reported miracles grow” - Ralph Waldo Emerson
The word of the day today is sievert
|ˈsēvərt| (abbr: Sv) noun
The SI unit of dose equivalent (the biological effect of ionising radiation), defined as that which delivers a joule of energy per kilogram of recipient mass.
: named after Rolf M. Sievert
(1896–1966), Swedish radiologist.
1.0 Sv = 1.0 joule/kilogram or 100 rem.
has the same units as the gray
and is equal to the absorbed dose times the quality factor, which compares the health consequences of that type of radiation with those of x-rays. The rem
bears the same relationship to the rad
as the sievert does to the gray.
Just in case you got lost in that definition, let’s put it in a practical context. Firstly, one Sievert of radiation is a huge dose, which will do great harm to living things. That is why we generally speak of millisieverts when talking about daily or even yearly exposure under normal circumstances. A millisievert (mSv) is a thousandth of a sievert
. Contextualising it further: An average person would probably absorb six millisieverts per year
from natural and artificial (e.g. X-rays for diagnostic purposes) sources. A radiation worker would be expected to absorb about 20 millisieverts per year
, averaged over five years with a maximum of 50 millisieverts in any one year
. You can see now what I mean about the sievert being a huge dose of radiation…
The workers in Japan working to limit the effects of radiation leaks in the stricken nuclear reactors have to access areas where their exposure is 600 millisieverts, equal to several years of daily exposure limit
. These workers are putting their health and life at great risk as exposure to such levels of radiation can be highly destructive. These effects are divided into short-term and long-term:
Short term effects:
Exposure to high levels of radiation can harm exposed tissues of the human body. Such radiation effects can be clinically diagnosed in the exposed individual; they are called deterministic effects because once a radiation dose above the relevant threshold has been received, they will occur and the severity depends on the dose. They include the symptoms of radiation poisoning such as burns, tissue damage, blood cell damage, death of rapidly dividing cells (causing nausea, vomiting, diarrhoea, hair falling out, anaemia, immune deficiency, etc).
Studies of populations exposed to radiation, especially of the survivors of the atomic bombing of Hiroshima and Nagasaki, have shown that exposure to radiation can also lead to the delayed induction of cancer (thyroid, leukaemia, bone, skin, breast, lung, etc) and hereditary damage. Effects such as these cannot usually be confirmed in any particular individual exposed but can be inferred from statistical studies of large irradiated populations.
Let’s contextualise again: Exposure for a short time to a single 1 sievert (1,000 millisievert) dose
of radiation would cause (temporary) radiation sickness such as nausea and decreased white blood cell count, but not death. However, exposure to 1 sievert of radiation is estimated to increase the lifetime risk of fatal cancer by around 5%.
Above this, severity of illness increases with dose. For example, a single dose of 5 sieverts (5,000 millisievert)
would kill about half those receiving it within a month. Survivors would have chronic disease and a greatly increased risk of cancers.
There about 180 emergency workers at Japan’s damaged Fukushima Dai-ichi complex of nuclear power stations. They are already being lauded as heroes by the Japanese as they are putting themselves at a huge health risk and premature death through radiation exposure. Another word springs to mind immediately:
(in World War II) A Japanese aircraft loaded with explosives and making a deliberate suicidal crash on an enemy target.
• The pilot of such an aircraft.
adjective [ attrib.]
Of or relating to such an attack or pilot.
• Reckless or potentially self-destructive: He made a kamikaze run across three lanes of traffic.
Japanese, from kami
‘divinity’ + kaze
‘wind,’ originally referring to the gale that, in Japanese tradition, destroyed the fleet of invading Mongols in 1281.
The last definition of the word may be applied to these workers in that they act self-destructively in order to achieve their mission. Which makes me think of:
The belief in, or practice of, disinterested and selfless concern for the well-being of others: Some may choose to work with vulnerable elderly people out of altruism.
• Zoology Behaviour of an animal that benefits another at its own expense.
mid 19th century: From French altruisme
, from Italian altrui
‘somebody else,’ from Latin alteri huic
‘to this other.’
We are a strange species, we humans. A curious mixture of the angelic and the demonic; of the evil and benevolent, the bad and the good. We may choose to kill others of our kind with abandon, or go to great lengths to preserve the life of strangers, not caring about our own well-being or our own life… We destroy and then preserve, we demolish only to build up again. We exploit and then relent, in order to conserve. Oh, the glory and curse of being a human!